Ultrasound examination apparatus and ultrasound examination method

Abstract

We provide an ultrasonic inspection device that can detect even minute defects. [Solution] The transmitting probe 110 of the ultrasonic inspection apparatus Z has a plurality of wave packets, including a first wave packet with a wavenumber of 2 or more at the fundamental frequency which is the excitation frequency of the transmitting probe 110, and a second wave packet with a wavenumber of 2 or more. An ultrasonic beam is emitted by applying a voltage waveform that repeats a group of wave packets, the wave packet delay time between the first wave packet and the second wave packet being arbitrarily set. The signal processing unit 250 of the control device 2 includes a frequency conversion unit 230 that converts the received signal of the receiving probe into a first frequency component with a time including at least the first wave packet as the first conversion target period, and converts it into a second frequency component with a time including at least the second wave packet as the second conversion target period. One of the conversion target periods, the first or the second conversion target period, includes a plurality of wave packets.

Description

Technical Field

[0001] The present disclosure relates to an ultrasonic inspection apparatus and an ultrasonic inspection method.

Background Art

[0002] A method for inspecting a defective part of a subject using an ultrasonic beam is known. For example, when there is a defective part (such as a cavity) with a small acoustic impedance, such as air, inside the subject, an acoustic impedance gap occurs inside the subject, so the transmission amount of the ultrasonic beam becomes small. Therefore, by measuring the transmission amount of the ultrasonic beam, defective parts inside the subject can be detected.

[0003] The technique described in Patent Document 1 regarding an ultrasonic inspection apparatus is known. Patent Document 1 describes "an ultrasonic inspection apparatus that inspects a subject by irradiating an ultrasonic beam to the subject through a fluid, the ultrasonic inspection apparatus including a scanning measurement device that scans and measures the ultrasonic beam to the subject, and a control device that controls the driving of the scanning measurement device, the scanning measurement device including a transmission probe that emits the ultrasonic beam and a reception probe that receives the ultrasonic beam, the control device including a signal processing unit, the signal processing unit including a filter unit that reduces at least the maximum intensity frequency component among the reception signals of the reception probe, the filter unit detecting a skirt component other than the maximum intensity frequency component among the fundamental wavebands including the maximum intensity frequency component."

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology described in Patent Document 1, defects are detected using frequency components other than the frequency component with the highest intensity in the received signal (paragraph 0049). However, because frequency components other than the highest intensity are used, the signal intensity of the frequency component used for detection may be low. Therefore, if the signal intensity of the frequency component used for detection can be increased, the defect detection performance can be further improved. The problem that this disclosure aims to solve is to provide an ultrasonic inspection apparatus and ultrasonic inspection method that improve the detection performance of defects, for example, by reducing the detectable defect size and enabling the detection of even minute defects. [Means for solving the problem]

[0006] The ultrasonic inspection apparatus of this disclosure is an ultrasonic inspection apparatus that inspects an object to be inspected by injecting an ultrasonic beam into the object to be inspected via a fluid, comprising: a scanning and measuring apparatus that scans and measures the ultrasonic beam onto the object to be inspected; and a control device that controls the drive of the scanning and measuring apparatus, wherein the scanning and measuring apparatus comprises: a transmitting probe that emits the ultrasonic beam; and a receiving probe that receives the ultrasonic beam and is installed on the opposite side of the transmitting probe with respect to the object to be inspected, wherein the transmitting probe emits a first wave packet with a wavenumber of 2 or more at a fundamental frequency which is the excitation frequency of the transmitting probe; and a second wave packet with a wavenumber of 2 or more. An ultrasonic inspection device emits an ultrasonic beam by applying a voltage waveform that repeats a group of wave packets having multiple wave packets, with the wave packet delay time between the first wave packet and the second wave packet arbitrarily set. The control device includes a signal processing unit, which converts the received signal of the receiving probe into a first frequency component with a time including at least the first wave packet as the first conversion target period, and into a second frequency component with a time including at least the second wave packet as the second conversion target period, wherein at least one of the first or second conversion target periods includes multiple wave packets. Other solutions will be described later in the embodiments for carrying out the invention. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide an ultrasonic inspection apparatus and ultrasonic inspection method that can adjust the signal intensity caused by defects, thereby improving the detection performance of defects, for example, by reducing the detectable defect size and enabling the detection of even minute defects. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing the configuration of the ultrasound inspection apparatus according to the first embodiment. [Figure 2] This is a schematic cross-sectional view showing the structure of the transmitting probe. [Figure 3A] This diagram shows the propagation path of an ultrasonic beam in a conventional ultrasound examination method, specifically when the beam enters a healthy tissue area. [Figure 3B] This diagram shows the propagation path of an ultrasonic beam in a conventional ultrasonic inspection method, specifically the path when the beam is incident on a defective area. [Figure 4] This diagram illustrates the interaction between a defect within the body being inspected and an ultrasonic beam, specifically showing how the directly arriving ultrasonic beam is received. [Figure 5] This diagram schematically shows scattered waves, which are ultrasonic beams interacting with a defect. [Figure 6] This is a functional block diagram of the control unit. [Figure 7] This is the voltage waveform of a conventional burst wave applied to the transmitting probe. [Figure 8] This is the voltage waveform of the burst wave in this embodiment, applied to the transmitting probe. [Figure 9] This diagram schematically shows the distribution of frequency components of a received signal. [Figure 10] This figure shows the spectrum of the fundamental frequency band of the received signal of an ultrasonic beam that has passed through the object being inspected. [Figure 11] This diagram schematically shows the spectrum of the fundamental frequency band. [Figure 12] This is a diagram explaining the meaning of bandwidth. [Figure 13] This diagram shows the relationship between wavenumber and the bandwidth of the fundamental frequency band. [Figure 14]It is a diagram schematically showing the spectrum of a received signal when using a burst wave composed of a beam group having a plurality of beams. [Figure 15] It is the result of plotting the magnitude of the frequency component at the detection frequency when changing the inter-beam frequency. [Figure 16] It is a diagram showing a beam group composed of two beams [Figure 17A] It is the case where the beam delay amount αd = 5, and it is a diagram showing an example of a burst wave of a single beam which is a conventional example. [Figure 17B] It is the case where the beam delay amount αd = 5.5, and it is a diagram showing an example of a burst wave composed of a plurality of beams of the present embodiment. [Figure 18A] It is the spectrum and interference function in the case where the beam delay amount αd = 5.25. [Figure 18B] It is the spectrum and interference function in the case where the beam delay amount αd = 5.75. [Figure 19A] It is a graph plotting the magnitude of the frequency component at a detection frequency of 0.74 MHz with respect to the inter-beam frequency. [Figure 19B] It is a graph plotting the magnitude of the frequency component at a detection frequency of 0.76 MHz with respect to the inter-beam frequency. [Figure 19C] [[ID=XX]]It is a graph plotting the magnitude of the frequency component at a detection frequency of 0.82 MHz with respect to the inter-beam frequency. [Figure 19D] It is a graph plotting the magnitude of the frequency component at a detection frequency of 0.90 MHz with respect to the inter-beam frequency. [Figure 20A] In the second embodiment, it is a diagram showing the signal of a burst wave composed of two beams. [Figure 20B] It is a diagram showing the spectrum (solid line) and interference function K (dashed line) for the burst wave shown in Fig. 20A. [Figure 21A] In the third embodiment, it is a diagram showing the signal of a burst wave composed of two beams. [Figure 21B] It is a diagram showing the spectrum (solid line) and interference function K (dashed line) for the burst wave shown in Fig. 21A. [Figure 22A] This figure shows a burst wave signal composed of two wave packets in the fourth embodiment. [Figure 22B] Figure 22A shows the spectrum (solid line) and interference function K (dashed line) for the burst wave. [Figure 23A] This figure shows a burst wave signal composed of two wave packets in the fifth embodiment. [Figure 23B] This figure shows the spectrum for the burst wave shown in Figure 23A. [Figure 24] This is a block diagram showing the configuration of the ultrasound examination apparatus according to the sixth embodiment. [Figure 25] This is a two-dimensional map showing how the interference function changes with respect to two parameters: frequency and wave packet delay. [Figure 26] This figure schematically shows the waveform of the burst wave applied to the transmitting probe in the sixth embodiment. [Figure 27] This diagram shows a detailed view of a part of the signal processing unit. [Figure 28] This figure schematically shows the waveform of the burst wave applied to the transmitting probe in the seventh embodiment. [Figure 29] This is an example of an image synthesized by the image synthesis unit. [Figure 30A] This diagram shows the configuration of the image synthesis unit in this embodiment. [Figure 30B] This figure shows an example of a composite image obtained with the configuration shown in Figure 30A. [Figure 31] This diagram shows the configuration of the signal synthesis unit in this embodiment. [Figure 32A] This figure shows the frequency spectrum of the received signal of the ultrasonic beam after it has passed through the object being inspected. [Figure 32B] This is a two-dimensional map showing how the interference function changes with respect to two parameters: frequency and wave packet delay. [Figure 33] This is a block diagram showing the configuration of the ultrasound examination apparatus according to the ninth embodiment. [Figure 34] This figure shows an example of a display screen shown on a display device. [Figure 35A] This figure schematically shows the propagation path of an ultrasonic beam when the focal length of the transmitting probe and the focal length of the receiving probe are equal in the tenth embodiment. [Figure 35B] This figure schematically shows the propagation path of the ultrasonic beam when the focal length of the receiving probe is longer than the focal length of the transmitting probe in the tenth embodiment. [Figure 36] This diagram illustrates the relationship between the beam incidence area in the transmitting probe and the beam incidence area in the receiving probe. [Figure 37] This diagram schematically shows the arrangement of the transmitting probe, the object under test, and the receiving probe in the 11th embodiment. [Figure 38] This figure shows the configuration of the ultrasound examination apparatus in the twelfth embodiment. [Figure 39A] This diagram illustrates the transmitting and receiving sound axes and eccentricity distances, assuming that the transmitting and receiving sound axes extend vertically. [Figure 39B] This diagram illustrates the transmitting and receiving sound axes and eccentricity distance, specifically the case where the transmitting and receiving sound axes extend at an angle. [Figure 40] This figure shows the configuration of the ultrasound examination apparatus in the 13th embodiment. [Figure 41] This diagram explains the reason why the effects of the 13th embodiment occur. [Figure 42] This figure shows the configuration of the ultrasound examination apparatus in the 14th embodiment. [Figure 43] This diagram shows the hardware configuration of the control unit. [Figure 44] This is a flowchart showing the ultrasound examination method for each embodiment. [Modes for carrying out the invention]

[0009] The following describes embodiments for implementing this disclosure, with reference to the drawings. The following is merely an example of how to implement the invention related to this disclosure, and this disclosure is not limited to the following example. Within the description of one embodiment below, other embodiments applicable to that embodiment will also be described as appropriate. This disclosure is not limited to the following embodiment, and different embodiments can be combined or modified as appropriate without significantly impairing the effects of this disclosure. In addition, the same reference numerals will be used for the same components, and redundant explanations will be omitted. Furthermore, components having the same function will be given the same name. The illustrations are schematic, and for illustrative purposes, the actual configuration may be changed or some components may be omitted or modified between drawings without significantly impairing the effects of this disclosure. Also, the same embodiment does not necessarily need to have all the components.

[0010] (First Embodiment) Figure 1 shows the configuration of the ultrasonic inspection apparatus Z according to the first embodiment. In Figure 1, the scanning measurement device 1 is shown in a schematic cross-sectional view. Figure 1 shows a coordinate system with three orthogonal axes, including the x-axis as the left-right direction of the paper, the y-axis as the orthogonal direction of the paper, and the z-axis as the up-down direction of the paper.

[0011] The ultrasonic inspection device Z inspects an object to be inspected E by injecting an ultrasonic beam U (described later) into the object to be inspected E via a fluid F. The fluid F is, for example, a liquid W (described later) such as water, or a gas G such as air, and the object to be inspected E is contained within the fluid F. In the first embodiment, the fluid F is air (an example of gas G). Therefore, the inside of the housing 101 of the scanning measurement device 1 is a cavity filled with air. As shown in Figure 1, the ultrasonic inspection device Z comprises a scanning measurement device 1, a control device 2, and a display device 3. The display device 3 is connected to the control device 2.

[0012] The scanning measurement device 1 scans and measures an ultrasonic beam U onto the object to be inspected E, and is equipped with a sample stage 102 fixed to the housing 101, on which the object to be inspected E is placed. It is preferable that the object to be inspected E is fixed to the sample stage 102 with a fixing device (not shown) to prevent movement. If the object to be inspected E is sufficiently heavy and does not move unintentionally, a fixing device may not be necessary. The object to be inspected E is made of any material. The object to be inspected E is, for example, a solid material, more specifically, a metal, glass, resin material, or a composite material such as CFRP (carbon fiber reinforced plastics). In the example in Figure 1, the object to be inspected E has a defect D inside. The defect D (defect) is a cavity, etc. Examples of defect D are cavities, foreign materials different from the material that should be there, etc. In the object to be inspected E, the part other than the defect D is called the sound part N.

[0013] Because the defective area D and the healthy area N are composed of different materials, their acoustic impedances differ, causing a change in the propagation characteristics of the ultrasonic beam U. The ultrasonic inspection device Z observes this change and detects the defective area D.

[0014] The scanning measurement device 1 includes a transmitting probe 110 that emits an ultrasonic beam U and a receiving probe 121 that receives the ultrasonic beam U. The transmitting probe 110 is installed in the housing 101 via a transmitting probe scanning unit 103 and emits an ultrasonic beam U. The receiving probe 121 is installed on the opposite side of the transmitting probe 110 with respect to the object under inspection E and receives the ultrasonic beam U. It is a receiving probe 140 (coaxially arranged receiving probe) that is coaxially arranged with the transmitting probe 110 (the eccentricity distance L described later is zero). Therefore, in this disclosure, the eccentricity distance L (distance, described later) between the transmitting sound axis AX1 (sound axis) of the transmitting probe 110 and the receiving sound axis AX2 (sound axis) of the receiving probe 140 is zero. This allows the transmitting probe 110 and the receiving probe 140 to be easily installed.

[0015] Here, "opposite side of the transmitting probe 110" means the space opposite to the space where the transmitting probe 110 is located (opposite in the z-axis direction) among the two spaces separated by the object under inspection E, and does not mean that it is limited to opposite sides with the same x and y coordinates (i.e., a position symmetrical with respect to the xy-plane).

[0016] In the example of this disclosure, the transmitting probe 110 is positioned such that the transmitting sound axis AX1 of the transmitting probe 110 is perpendicular to the mounting surface 1021 of the sample stage 102. That is, the transmitting probe 110 is positioned so that the transmitting sound axis AX1 is in the direction normal to the mounting surface 1021 of the object under inspection E on the sample stage 102. In this way, for a plate-shaped object under inspection E, the transmitting sound axis AX1 is positioned perpendicular to the surface of the object under inspection E, which has the effect of making it easier to understand the correspondence between the scanning position and the position of the defect D.

[0017] However, this disclosure is not limited to positioning the transmitting probe 110 so that the transmitting sound axis AX1 is perpendicular to the mounting surface 1021 of the object under inspection E on the sample stage 102. The effects of this disclosure are still present even if the transmitting sound axis AX1 is not perpendicular to the mounting surface 1021 of the object under inspection E on the sample stage 102. In the latter case, to accurately determine the position of the defect D, the path of the transmitting sound axis AX1 can be calculated according to the inclination of the transmitting sound axis AX1 from the vertical direction.

[0018] Here, we will describe the positional relationship between the transmitting probe 110 and the receiving probe 121. The distance between the transmitting sound axis AX1 of the transmitting probe 110 and the receiving sound axis AX2 of the receiving probe 121 is defined as the eccentricity distance L, as described above. In this disclosure, the eccentricity distance L is set to zero, as described above. That is, the receiving probe 121 is positioned such that the transmitting sound axis AX1 and the receiving sound axis AX2 are coaxial. This is called a coaxial arrangement. Note that in this disclosure, the eccentricity distance L is not limited to 0.

[0019] In this disclosure, the arrangement of the receiving probe 121 is referred to as a coaxial arrangement when the transmitting sound axis AX1 and the receiving sound axis AX2 are arranged coaxially, and as an eccentric arrangement when the two sound axes (transmitting sound axis AX1 and receiving sound axis AX2) are offset (i.e., eccentric arrangement). This disclosure is effective in both cases, when the receiving probe 121 is in a coaxial arrangement and when it is in an eccentric arrangement. Therefore, this disclosure includes both coaxial and eccentric arrangements for the receiving probe 121. A specific illustration of the eccentric arrangement will be shown later.

[0020] In this disclosure, when specifying the receiving position, a coaxially positioned receiving probe 121 will be referred to as receiving probe 140 (coaxial receiving probe), and an eccentrically positioned receiving probe 121 will be referred to as receiving probe 120 (eccentrically positioned receiving probe; see below). When referred to as receiving probe 121, neither coaxial nor eccentric configuration is specifically specified.

[0021] The sound axis is defined as the central axis of the ultrasonic beam U. Here, the transmitted sound axis AX1 is defined as the sound axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. In other words, the transmitted sound axis AX1 is the central axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. The transmitted sound axis AX1 will include refraction at the interface of the object under inspection E, as described below. That is, if the ultrasonic beam U emitted from the transmitting probe 110 is refracted at the interface of the object under inspection E, the center (sound axis) of the propagation path of that ultrasonic beam U becomes the transmitted sound axis AX1.

[0022] Furthermore, the received sound axis AX2 is defined as the sound axis of the propagation path of a virtual ultrasonic beam, assuming that the receiving probe 121 emits an ultrasonic beam U. In other words, the received sound axis AX2 is the central axis of the virtual ultrasonic beam, assuming that the receiving probe 121 emits an ultrasonic beam U.

[0023] As a concrete example, let's consider the case of a non-converging receiving probe with a planar transducer surface. In this case, the direction of the receiving sound axis AX2 is the direction of the normal to the transducer surface, and the axis passing through the center point of the transducer surface becomes the receiving sound axis AX2. If the transducer surface is rectangular, its center point is defined as the intersection of the diagonals of the rectangle.

[0024] A control device 2 is connected to the scanning measurement device 1. The control device 2 controls the drive of the scanning measurement device 1 and controls the movement (scanning) of the transmitting probe 110 and the receiving probe 121 by issuing instructions to the transmitting probe scanning unit 103 and the receiving probe scanning unit 104. As the transmitting probe scanning unit 103 and the receiving probe scanning unit 104 move synchronously in the x and y directions, the transmitting probe 110 and the receiving probe 121 scan the object under inspection E in the x and y directions. Furthermore, the control device 2 emits an ultrasonic beam U from the transmitting probe 110 and performs waveform analysis based on the signal acquired from the receiving probe 121. The plane formed by the two axes, the x and y directions, which are the scanning directions of the transmitting probe 110, will be called the scanning plane.

[0025] In this disclosure, an example is shown in which the object to be inspected E is fixed to the housing 101 via the sample stage 102, that is, the object to be inspected E is fixed to the housing 101, and the transmitting probe 110 and the receiving probe 121 are scanned. Conversely, the transmitting probe 110 and the receiving probe 121 may be fixed to the housing 101, and the position of the sample stage 102 may be scanned in the x-axis and y-axis directions. In this configuration, the object to be inspected E placed on the sample stage 102 also moves, so its relative position to the transmitting probe 110 is scanned in the x-axis and y-axis directions.

[0026] In the illustrated example, a gas G (an example of a fluid F; a liquid W (described later) may also be used) is interposed between the transmitting probe 110 and the object under inspection E, and between the receiving probe 121 and the object under inspection E. Therefore, the transmitting probe 110 and the receiving probe 121 can inspect the object under inspection E without contact, making it possible to smoothly and quickly change their relative positions in the xy-plane. In other words, by interposing a fluid F (gas G) between the transmitting probe 110 and the receiving probe 121 and the object under inspection E, smooth scanning becomes possible.

[0027] When a localized ultrasonic beam U is emitted from the transmitting probe 110, the emitted ultrasonic beam U irradiates the object under inspection E locally. The position where the localized ultrasonic beam U irradiates is changed by scanning. As described above, the ultrasonic beam U that reaches the receiving probe 121 changes between the defective area D and the healthy area N of the object under inspection E, so this configuration makes it possible to detect the defective area D.

[0028] In this embodiment, a focusing type transmitting probe 110 was used to generate a localized ultrasonic beam U. The specific configuration of the focusing type transmitting probe 110 will be described later. As a configuration for generating a localized ultrasonic beam U, a configuration that reduces the beam diameter by reducing the area of ​​the piezoelectric element that generates the ultrasonic beam U (the transducer 111 described later; the same applies hereinafter) may also be used. The focusing type transmitting probe 110 is more preferable because it can reduce the beam diameter while increasing the area of ​​the piezoelectric element, thus generating a localized ultrasonic beam U with high beam intensity and a small beam diameter.

[0029] The transmitting probe 110 is a converging transmitting probe 110. On the other hand, the receiving probe 121 is a probe with less convergence than the transmitting probe 110. In this disclosure, the receiving probe 121 is a non-converging probe with a flat transducer surface. Therefore, the receiving probe 121 is a non-converging receiving probe. By using such a non-converging receiving probe 121, information on the defect D can be collected over a wide range.

[0030] Figure 2 is a schematic cross-sectional view showing the structure of the transmitting probe 110. In Figure 2, for simplification, only the outer outline of the emitted ultrasonic beam U is shown, but in reality, numerous ultrasonic beams U are emitted across the entire surface of the transducer surface 114 in the direction of the normal vector of the transducer surface 114.

[0031] The transmitting probe 110 is configured to focus an ultrasonic beam U. This allows for high-precision detection of minute defects D in the object E under inspection. The reason why minute defects D can be detected will be explained later. The transmitting probe 110 comprises a transmitting probe housing 115, and inside the transmitting probe housing 115 are a backing 112, a transducer 111, and a matching layer 113. An electrode (not shown) is attached to the transducer 111, and the electrode is connected to a connector 116 by lead wires 118. Furthermore, the connector 116 is connected to a power supply (not shown) and a control device 2 by lead wires 117.

[0032] In this disclosure, the transducer surface 114 of the transmitting probe 110 or the receiving probe 121 is defined as the surface of the matching layer 113 if a matching layer 113 is provided, and as the surface of the transducer 111 if a matching layer 113 is not provided. That is, in the case of the transmitting probe 110, the transducer surface 114 is the surface that emits the ultrasonic beam U, and in the case of the receiving probe 121, the surface that receives the ultrasonic beam U.

[0033] Here, as a comparative example, we will explain the conventional ultrasound examination method.

[0034] Figure 3A shows the propagation path of an ultrasonic beam U in a conventional ultrasonic inspection method, specifically when it is incident on a healthy area N. Figure 3B shows the propagation path of an ultrasonic beam U in a conventional ultrasonic inspection method, specifically when it is incident on a defective area D. In a conventional ultrasonic inspection method, for example, as described in Patent Document 1, a transmitting probe 110 and a receiving probe 140 (as a receiving probe 121) are arranged so that the transmitting sound axis AX1 and the receiving sound axis AX2 coincide.

[0035] As shown in Figure 3A, when an ultrasonic beam U is incident on a healthy portion N of the object under inspection E, the ultrasonic beam U passes through the object under inspection E and reaches the receiving probe 140. Therefore, the received signal becomes larger. On the other hand, as shown in Figure 3B, when an ultrasonic beam U is incident on a defective portion D, the transmission of the ultrasonic beam U is blocked by the defective portion D, so the received signal decreases. The defective portion D is detected by this decrease in the received signal. This is as described in Patent Document 1.

[0036] Here, as shown in Figures 3A and 3B, the method of detecting the defect D by reducing the received signal due to the blocking of the transmission of the ultrasonic beam U at the defect D will be referred to here as the "blocking method".

[0037] Here, detection becomes difficult when the size of the defect D becomes smaller than the beam size. This point will be explained with reference to Figure 4.

[0038] Figure 4 shows the interaction between the defect D and the ultrasonic beam U within the object under inspection E, illustrating the reception of the direct-reaching ultrasonic beam U (hereinafter referred to as "direct wave U3"). The direct wave U3 will be described later. Here, we consider the case where the size of the defect D is smaller than the width of the ultrasonic beam U (hereinafter referred to as beam width BW). Here, beam width BW is the width of the ultrasonic beam U when it reaches the defect D.

[0039] Furthermore, Figure 4 schematically shows the shape of the ultrasonic beam U in a minute region near the defect D, and therefore the ultrasonic beam U is depicted as parallel; however, in reality, it is a focused ultrasonic beam U. Moreover, the position of the receiving probe 121 in Figure 4 is a conceptual position indicated for illustrative purposes, and the position and shape of the receiving probe 121 are not accurately scaled. That is, considering the enlarged scale of the shape of the defect D and the ultrasonic beam U, the receiving probe 121 is located at a position further away in the vertical direction of the drawing than the position shown in Figure 4.

[0040] Figure 4 shows the case of a blocking method where the transmitting sound axis AX1 and the receiving sound axis AX2 are aligned. When the defect D is smaller than the beam width BW, some of the ultrasonic beam U is blocked, so the received signal decreases, but it does not become zero. For example, if the cross-sectional area of ​​the defect D is 5% of the beam cross-sectional area defined by the beam width BW, the received signal will only decrease by approximately 5%, making it difficult to detect the defect D. In other words, in the case shown in Figure 4, the received signal will only decrease by 5% where the defect D is present. Thus, when the defect D is smaller than the beam width BW, a large amount of beam passes through without interacting with the defect D, so the detection accuracy of the defect D decreases.

[0041] Figure 5 schematically shows scattered waves U1, which are ultrasonic beams U that interact with a defect D. In this disclosure, the ultrasonic beam U that interacts with a defect D is called scattered waves U1. Therefore, in this disclosure, "scattered waves U1" refers to ultrasonic waves that interact with a defect D. Some scattered waves U1 change direction, as shown in Figure 5. In addition, some scattered waves U1 change at least one of the phase or frequency of the wave due to interaction with the defect D, but the direction of propagation does not change. Ultrasonic waves that pass through without interacting with the defect D are called direct waves U3. If scattered waves U1 can be detected separately from direct waves U3, it will be easier to detect small defect D. In this disclosure, scattered waves U1 can be efficiently detected by focusing on differences in frequency.

[0042] In this embodiment, a gas G such as air is used as the fluid F between the transmitting probe 110 and the object under inspection E. In this case, for the reasons described below, the detection of minute defects D becomes particularly difficult with the above blocking method. Therefore, the effect of detecting scattered waves U1 in this disclosure is significant.

[0043] Compared to liquid W, the attenuation of ultrasound is greater in gas G. It is known that the attenuation of ultrasound in gas G is proportional to the square of the frequency. For this reason, the upper limit for ultrasound propagation in gas G is around 1 MHz. In the case of liquid W, ultrasound can propagate even at frequencies of 5 MHz to several tens of MHz, so the usable frequency range in gas G is smaller than that in liquid W.

[0044] Generally, as the frequency of the ultrasonic beam U decreases, it becomes more difficult to focus the ultrasonic beam U. Therefore, a 1 MHz ultrasonic beam U propagating through a gas G has a larger focusing diameter compared to an ultrasonic beam U in a liquid W. On the other hand, as shown in Figure 4 above, it is difficult to detect defects D smaller than the beam size with the above blocking method. However, according to this disclosure, as shown in Figure 5 above, by increasing the proportion of the scattered wave U1 component during detection, it is possible to detect defects D smaller than the beam size.

[0045] Figure 6 is a functional block diagram of the control device 2. The control device 2 controls the drive of the scanning measurement device 1. The control device 2 comprises a transmission system 210, a reception system 220, a data processing unit 201, a scan controller 204, a drive unit 202, a position measurement unit 203, and a signal processing unit 250. The drive unit 202 changes the relative positions of the transmitting probe 110 and the receiving probe 121 with respect to the object under inspection E by driving the transmitting probe 110 and the receiving probe 121, for example. The position measurement unit 203 measures the scanning position. The scan controller 204 drives the transmitting probe 110 and the receiving probe 121 through the drive unit 202. The scanning position by the transmitting probe 110 and the receiving probe 121 is input to the scan controller 204 through the position measurement unit 203.

[0046] The receiving system 220 and the data processing unit 201 together are referred to as the signal processing unit 250. In other words, the signal processing unit 250 comprises the receiving system 220 and the data processing unit 201, and performs signal processing to extract meaningful information from the signal from the receiving probe 121 through amplification processing, filtering processing, etc.

[0047] (Natural frequency fres and excitation frequency fex of the transmitting probe 110) The transmission system 210 is a system that generates the voltage applied to the transmission probe 110. The transmission system 210 includes a waveform generator 211, a signal amplifier 212, and a delay time setting unit 213. The waveform generator 211 generates a burst wave signal. The generated burst wave signal is then amplified by the signal amplifier 212. The voltage output from the signal amplifier 212 is applied to the transmission probe 110. Therefore, the transmission probe 110 is driven by the burst wave.

[0048] Here, we will discuss the burst wave signal. The configuration of the burst wave signal is a distinctive feature of this disclosure. Figure 7 shows a conventional burst wave signal, and Figure 8 shows the burst wave signal in this embodiment.

[0049] Figure 7 shows the voltage waveform of a conventional burst wave applied to the transmitting probe 110. A conventional burst wave consists only of one type of wave packet. The horizontal axis represents time, and the vertical axis represents voltage. In the example in Figure 7, 10 sine waves with a fundamental frequency f0 of 0.78 MHz are applied. These 10 waves are called a wave packet. The fundamental frequency f0 is the excitation frequency fex of the transmitting probe 110 (the frequency that excites the transmitting probe 110). The reciprocal of the fundamental frequency f0 is called the fundamental period T0. As shown in the figure, the fundamental period T0 is the period of the waves that make up one wave packet. The number of waves with fundamental frequency f0 that make up one wave packet is called the wave number N0. The wave packet is applied with a repetition period Tr = 5 ms. Therefore, the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform of a repetition wave packet, which consists of wave packets with a wave number N0 of 2 or more, is applied to it.

[0050] Figure 8 shows the voltage waveform of the burst wave in this embodiment applied to the transmitting probe 110. A characteristic of this burst wave is that each wave with a repetition period Tr is composed of multiple (multiple types) wave packets (wave packet 10, wave packet 11). That is, a group of wave packets composed of multiple (two or more) wave packets is repeated with a repetition period Tr.

[0051] Figure 8 shows an example consisting of two wave packets, namely wave packet 10 and wave packet 11. The time from the start time of wave packet 10 to the start time of wave packet 11 is called the wave packet delay time Δtd. The wave packet delay time Δtd indicates how much the start time of wave packet 11 is delayed from the start time of wave packet 10. The time from the end time of wave packet 10 to the start time of wave packet 11 is called the inter-wave packet time ΔtI. The inter-wave packet time ΔtI is the time between adjacent wave packets 10 and wave packet 11.

[0052] Although Figure 8 shows an example where the wave packet group consists of two wave packets, it may also consist of three or more wave packets. Furthermore, the wavenumber N0 of wave packet 10 and the wavenumber N0 of wave packet 11 may be different. The voltage amplitude of wave packet 10 and the voltage amplitude of wave packet 11 may also be different. Furthermore, in the example of this disclosure, the fundamental frequencies f0 of each of the multiple wave packets 10 and 11 are different. That is, the fundamental frequency f0 of wave packet 11 is different from the fundamental frequency f0 of wave packet 10. This improves the detection performance of the defect D.

[0053] As shown in Figure 8, a key feature of this disclosure is the use of a burst wave that repeats with a period Tr in the wave packet group. As described above, the wave packet group has multiple wave packets, including a wave packet 10 (first wave packet) with a fundamental frequency f0, which is the excitation frequency of the transmitting probe 110, and a wave packet 11 (second wave packet) with a wave number of 2 or more. The effects brought about by this feature will be described later.

[0054] Figure 7 above shows a typical example of the wave packet's time width and repetition period Tr. The fundamental period T0 of the wave packet is 1.2 μs, and the wave number N0 = 10, so the wave packet's time width is 12 μs, while the repetition period Tr is 5 ms.

[0055] On the other hand, Figure 8 shows a typical example of the time width of a wave packet group. The fundamental period T0 of the wave packet is 1.2 μs, and the wave number N0 = 5, so when the inter-packet time ΔtI is 10 μs, the time width of the wave packet group is 22 μs. Meanwhile, the repetition period Tr is 5 ms. The time width of the wave packet group is small, about 0.4% of Tr.

[0056] Thus, the time width of the wave packet group is typically 30% or less of the repetition period Tr, and more preferably 20% or less. In this way, a wave packet group composed of multiple wave packets can be clearly distinguished even in terms of its time waveform.

[0057] It should be noted that the time examples presented here are typical examples, and this disclosure is not limited to them.

[0058] Returning to the configuration diagram in Figure 6, the burst wave signal, composed of multiple wave packets as shown in Figure 8, is input to the signal amplifier 212, amplified, and applied to the transmitting probe 110. As a result, the transmitting probe 110 emits an ultrasonic beam U of burst waves composed of multiple wave packets. That is, the transmitting probe 110 emits an ultrasonic beam U by applying a voltage waveform that repeats a group of wave packets having the following multiple wave packets, with an arbitrarily set wave packet delay time Δtd between the first wave packet and the second wave packet.

[0059] In another embodiment, the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform is applied that has a wave packet delay time Δtd whose frequency component is larger than the frequency component when the inter-wave packet time ΔtI, which is the time between multiple wave packets, is zero. Furthermore, in yet another embodiment, the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform is applied that repeats a group of wave packets having multiple wave packets. These multiple wave packets include a first wave packet (e.g., wave packet 10) with a fundamental frequency f0, which is the excitation frequency fex of the transmitting probe 110, and a wave number of 2 or more, and a second wave packet (e.g., wave packet 11) with a wave number of 2 or more. However, as described above, the multiple wave packets may further include a third wave packet (e.g., wave packet 12 described below) with a wave number of 2 or more.

[0060] The transmission system 210 includes a delay time setting unit 213 as described above. The delay time setting unit 213 is provided in the scanning measurement device 1 and sets the wave packet delay time Δtd of multiple wave packets. The delay time setting unit 213 can set the wave packet delay time Δtd between multiple wave packets to an appropriate value. An appropriate value here is a value that can generate a tail component W3 (described later) with an intensity sufficient to detect the defect D using the tail component W3.

[0061] The delay time setting unit 213 sets the wave packet delay time Δtd such that the magnitude of frequency components different from the fundamental frequency f0 is greater than the magnitude of frequency components when the wave packet delay time ΔtI is zero, by making the inter-wave packet time ΔtI of multiple wave packets greater than zero. This makes it possible to detect defects D using frequency components different from the fundamental frequency f0.

[0062] As will be described later, the performance of the ultrasound inspection device Z in this embodiment can be improved by setting the excitation frequency fex to an appropriate value.

[0063] Generally, when the transmitting probe 110 is operated at a specific frequency determined for each probe, the amplitude intensity (sound pressure) of the generated ultrasonic beam U is maximized. This frequency at which the sound pressure is maximized is called the resonance frequency (fres) of the transmitting probe 110. The reason why the sound pressure is maximized at the resonance frequency (fres) is that the vibration of the built-in piezoelectric element (resonator 111) resonates at the resonance frequency (fres). For this reason, the transmitting probe 100 is usually used with the excitation frequency (fex) set to be equal to the resonance frequency (fres).

[0064] The excitation frequency fex corresponds to the fundamental frequency f0 in Figure 8.

[0065] In this embodiment, the excitation frequency fex may be equal to the intrinsic frequency fres of the transmitting probe 110, or it may be shifted. Setting the excitation frequency fex to be shifted from the natural frequency fres is preferable because it makes it easier to receive the scattered wave U1 at the defect D described later. The natural frequency fres of the transmitting probe 110 used in this embodiment was 0.82 MHz. The excitation frequency fex may also be set to 0.82 MHz, which is equal to the natural frequency fres. Alternatively, the excitation frequency fres can be shifted by about 5% from the natural frequency fres, to 0.78 MHz or 0.86 MHz. Shifting the excitation frequency fres from the natural frequency fres in this way makes it easier to detect the defect D.

[0066] The ultrasonic beam U of the burst wave emitted from the transmitting probe 110 passes through the object under inspection E and is received by the receiving probe 140. The receiving probe 140 converts the ultrasonic beam U into an electrical signal. The converted electrical signal is input to the receiving system 220. The receiving system 220 amplifies the electrical signal output by the receiving probe 140 using a signal amplifier 222.

[0067] The electrical signal output by the signal amplifier 222 is a time-domain waveform. In a time-domain waveform, the horizontal axis represents time and the vertical axis represents the signal voltage. The output of the signal amplifier 222 is input to the frequency conversion unit 230.

[0068] The frequency conversion unit 230 is provided in the signal processing unit 250 and converts the received signal from the receiving probe 140 into frequency components. Specifically, the frequency conversion unit 230 converts a time-domain waveform into a frequency-domain signal. A frequency-domain signal is a signal that represents the magnitude of signal components for each frequency, and typically the horizontal axis is frequency and the vertical axis is the magnitude of the frequency component. The frequency-domain signal includes the spectrum. The frequency components of a frequency-domain signal may possess phase information in addition to magnitude information. Furthermore, the frequency components may be complex numbers. The fact that the frequency components are complex numbers is equivalent to the frequency components possessing both magnitude and phase information. When the frequency components of a frequency domain signal are complex numbers, the phase information of the frequency components can also be used to detect the defect D, which makes it easier to detect the defect D and is therefore preferable. The frequency conversion unit 230 may be located within the signal processing unit 250, or it may be located within the data processing unit 201, which will be described later. The frequency conversion unit 230 may also be called a frequency component conversion unit. In this specification, the terms frequency conversion unit and frequency component conversion unit are synonymous, and they are as defined above.

[0069] The conversion in the frequency conversion unit 230 can be performed, for example, by a Fourier transform. Alternatively, the conversion may be performed along with the extraction of only frequency components within a pre-specified frequency range (frequency parameter). The signal converted into frequency components by the frequency conversion unit 230 is input to the data processing unit 201. The frequency conversion unit 230 may be located inside the data processing unit 201; that is, the conversion to frequency components may be performed within the data processing unit.

[0070] The frequency conversion unit 230 converts the received signal within a time range containing at least two wave packets from among a plurality of wave packets into frequency components. This improves the defect detection performance, which is an effect of this disclosure obtained by using two wave packets.

[0071] However, as will be described in detail later, in the example of this disclosure, the frequency conversion unit 230 converts a received signal in a time range containing at least two wave packets into multiple (e.g., two) frequency components. Specifically, the frequency conversion unit 230 converts the received signal from the receiving probe 121 into a first frequency component, with the time containing at least a first wave packet (e.g., wave packet 10) as the first conversion target period. At the same time, the frequency conversion unit 230 converts it into a second frequency component, with the time containing at least a second wave packet (e.g., wave packet 12) as the second conversion target period. In this case, at least one of the first or second conversion target periods (synonymous with frequency conversion period) contains multiple wave packets.

[0072] As will be described in detail later, in the example of this disclosure, the first conversion period is integration period 1 shown in Figure 26 below, and includes wave packets 10 and 11. The second conversion period is integration period 2 shown in Figure 26 below, and includes wave packet 10. Therefore, the first conversion period and the second conversion period do not need to be exactly the same, and may partially overlap. In other words, the wave packets included in the first conversion period and the wave packets included in the second conversion period may partially overlap, as long as they do not completely overlap. By frequency-converting the first and second conversion periods, the detection performance of the defect D can be further improved.

[0073] Furthermore, the wave packets included in the first conversion period and the wave packets included in the second conversion period may partially overlap, but they do not have to overlap at all.

[0074] (Accumulation of frequency component data) The data processing unit 201 includes a storage unit 261, a frequency selection unit 242, an imaging unit 262, and a display unit 263. Accordingly, the signal processing unit 250 includes a frequency conversion unit 230, an imaging unit 262, a frequency selection unit 242, and a display unit 263.

[0075] In the example of this disclosure, the frequency conversion unit 230 converts the time-domain waveform into frequency component data and stores it in the storage unit 261 along with position information. The imaging unit 262 then generates an image 273 (described later) indicating the defect location using the portion of the converted frequency components specified by the frequency parameter, as will be described in detail later. That is, the imaging unit 262 images the signal features based on the input frequency parameter. In other words, when the object under inspection E is measured once, the conversion to frequency component data is only required once for each conversion target period (e.g., the first conversion target period and the second conversion target period), and the extraction of signal features from the frequency component data is performed multiple times.

[0076] This configuration is preferable in the following two respects: The first consideration is the computation time. The conversion process to frequency component data in the frequency conversion unit 230 takes time. Typically, the Fourier transform is used as described above, but even using the Fast Fourier Transform (FFT), which is known as a fast algorithm, the processing time for this conversion is long. On the other hand, the calculation of signal features is performed using equation (1) described later, and the computation time for this is short. As a typical example, even for measurement points of 100 rows x 100 columns, the processing is completed in less than 0.2 seconds.

[0077] Therefore, according to the example of this disclosure, although the details will be described later, by "updating" the frequency parameters, it is possible to instantly obtain the updated image 273 (described later). In this way, by storing the frequency component data in the storage unit 261, it is possible to quickly select a frequency set suitable for improving the detection performance of the defective part D.

[0078] Secondly, there is a reduction in the amount of data. The signal waveform from the receiving probe 140 has about 100,000 points in the time domain for one measurement position, whereas for frequency component data, only complex numbers for 20 to 100 different frequencies are needed. In other words, the amount of data for the object under test E can be reduced to about 1 / 1000. Thus, there is also the advantage of being able to significantly reduce the amount of data stored in the memory unit 261.

[0079] The data processing unit 201 also receives scanning position information from the scan controller 204. In this way, data relating to the frequency components of the received signal at the current two-dimensional scanning position (x, y) (hereinafter referred to as frequency component data) is obtained. The data processing unit 201 associates the scanning position (x, y) with the frequency component data at that position and stores it in the storage unit 261. Furthermore, by determining the signal features determined from the frequency component data for each scanning position, an image 273 relating to the defective area D is created.

[0080] Frequency component data consists of frequency components corresponding to multiple frequencies. In a typical example, frequency component data is the frequency spectrum obtained by the Fourier transform of a received signal. As mentioned above, it is preferable for frequency components to include phase information in addition to amplitude (absolute value). This is equivalent to treating frequency components as complex numbers. As will be discussed later, including phase information allows for the calculation of higher-performance signal features.

[0081] In Figure 6, the data processing unit 201 includes an imaging unit 262. The imaging unit 262 is provided in the signal processing unit 250 and generates an image 273 (described later) showing the location of the defect D (defect location) using the portion of the frequency components specified by the frequency parameter from the converted frequency components. Specifically, the imaging unit 262 creates the image 273 based on the signal change (amount of change) caused by the defect D of the object under inspection, in the frequency spectrum of the portion of the frequency spectrum corresponding to the appropriate frequency parameter from the frequency spectrum corresponding to the frequency components converted by the frequency conversion unit 230. In this way, the image 273 can be generated.

[0082] In this example, the signal change (change in the received signal) refers to the signal feature. Therefore, the imaging unit 262 first calculates the signal feature from the portion of the frequency spectrum corresponding to the converted frequency components that contains the input frequency parameters. The signal feature is a value that represents the signal change, as described above, and is calculated from the frequency component data so as to appropriately include defect information (e.g., the location of the defect D). An example of a specific method for calculating the signal feature will be described later. By plotting the signal feature obtained in this way against the scanning position (x, y), a two-dimensional image (defect image) of the defect D located inside the object E under inspection is generated.

[0083] By performing the above procedure while changing the scanning position (x,y), the desired range is scanned. Upon completion of the scan, frequency component data and signal features corresponding to the scanning position (x,y) are stored in the storage unit 261 within the data processing unit 201. In this disclosure, signal features are calculated each time a signal is acquired at a scanning position. However, the frequency component data may be stored in the storage unit 261 during measurement, and the signal features may be calculated collectively after measurement to generate a defective image.

[0084] (Calculation of signal features) This document describes the method for calculating signal features from frequency component data, as used in the example provided. To make the formulas easier to read, we represent frequency f as angular frequency ω. Angular frequency ω is obtained by multiplying frequency f by 2π. Also, j represents the imaginary unit.

[0085] This shows the process of calculating the frequency component H(ω) from the measured time-domain signal waveform h1(t). This is an example of how the output signal of the signal amplifier 222 in Figure 6 is processed by the frequency conversion unit 230.

[0086]

number

[0087] Here, tk is a time sequence arranged at appropriate sampling frequency time intervals. k is zero or a finite number of positive integers (k=0,1,2,...). Equation (1) performs an operation roughly equivalent to integration over the time range over which the sum is taken. Equation (1) yields the frequency component H(ω).

[0088] An appropriate sampling frequency is one that satisfies the generally known sampling theorem. That is, the sampling frequency should be at least twice the frequency bandwidth of the signal being observed. Furthermore, setting the sampling frequency to at least 10 times the fundamental frequency f0 of the transmitted ultrasonic beam U is preferable because it allows for the reproduction of signal waveform distortions, etc. In this embodiment, the sampling frequency was set to 50 MHz for a signal waveform with a fundamental frequency f0 = 0.86 MHz.

[0089] The frequency component H(ω) obtained from equation (1) is a complex number. That is, the frequency component H(ω) has phase in addition to its absolute value. The frequency spectrum shown in Figure 12 above is a plot of the absolute value |H(ω)| of the complex number H(ω) against the frequency ω.

[0090] Next, we will show a method for calculating signal features from the frequency component H(ω) expressed as a complex number. First, h2(t) is calculated according to the following equation (2).

[0091]

number

[0092]

number

[0093] Here, in equation (2), j is the imaginary unit, and in equation (3), Re[ ] is the process of extracting the real part of the complex number. In equation (2), the subscript ω in the Σ symbol indicates the frequency set of the angular frequency components to be integrated. In equation (2), the angular frequency components to be integrated are set to an appropriately defined frequency set {ω}, as described below.

[0094] In equation (2), the set of frequencies {ω} to be included in the integration is called the frequency parameter. The frequency parameter may be specified in the form of a frequency set {ω} or in the form of a frequency range. The frequency parameter may also be set in advance or entered by the user.

[0095] The h(t) obtained by equation (3) is a time-domain signal waveform synthesized from a frequency set defined by the frequency parameter. In this disclosure, the difference between the maximum and minimum values ​​of h(t) (Peak-to-Peak value) is used as the signal feature. In this disclosure, the difference between the maximum and minimum values ​​(Peak-to-Peak value) is abbreviated as the PP value.

[0096] In equation (2), both H(ω) and exp(jωt) are complex numbers and are calculated as complex numbers. That is, the phase information of the frequency component H(ω) is also taken into consideration when calculating the signal features. This is preferable because it allows us to obtain signal features that accurately reflect the positional information of the defect D.

[0097] The selection of frequency parameters, i.e., the set of frequencies {ω} to be included in the integration in equation (2), is crucial. The fundamental frequency f0 is excluded from the set of frequencies {ω} included in the integration. In this way, a filter section (not shown) that reduces the maximum intensity frequency component can be constructed. In addition, the frequencies included in the integration include the frequency of the tail component W3 of the fundamental wave band W1. This improves the detection performance of the defect D in the object under inspection E. Furthermore, excluding frequency components near the fundamental frequency f0 is even more effective.

[0098] The angular frequency ω can be converted to frequency f using the relationship ω = 2πf, so we will interpret it by converting it as appropriate. For example, when it is written as "exclude the fundamental frequency f0 from the set of frequencies {ω}", it means "exclude ω0 = 2πf0".

[0099] The fundamental frequency f0 is the frequency of the wave constituting the wave packet 10, as shown in Figure 8. Since Figure 8 shows the voltage applied to the transmitting probe 110, the fundamental frequency f0 is equal to the excitation frequency fex.

[0100] Furthermore, in equation (2), the set of frequencies {ω} to be included in the integration may be configured to include only frequencies lower than the fundamental frequency f0. This allows for the construction of a filter section (not shown) having the characteristics of a low-pass filter. Similarly, it may be configured to include only frequencies lower than the fundamental frequency f0.

[0101] The frequency parameters are properly set in the frequency selection unit 242. In this way, the frequency conversion unit 230 and the frequency selection unit 242 constitute a filter unit (not shown).

[0102] The frequency parameters may be set to appropriate values ​​in advance of the test, or they may be changed after the measurement. Alternatively, the user may set them.

[0103] The signal features are not limited to the above calculation method and can be any value calculated from frequency component data so as to appropriately include the location information of the defect D. In the above example, the PP value of the time-domain signal waveform h(t) was used as the signal features, but the absolute value of h(t) and the area of ​​h(t) may also be calculated and used as the signal features. Here, the procedure for calculating the area is to sample h(t) at appropriate time intervals and calculate the sum of h(t) at the sampling points. Alternatively, the squared value of h(t) may be used instead of the absolute value of h(t). Furthermore, instead of using equations (2) and (3), the absolute value of the frequency component H(ω) may be summed over the input frequency set {ω} and used as the signal features.

[0104] Figure 9 schematically shows the frequency distribution (frequency spectrum) of the frequency components of a received signal. In Figure 9, the horizontal axis represents frequency, and the vertical axis represents component intensity (intensity). The vertical axis is shown on a logarithmic scale, schematically illustrating a wide range of intensity levels.

[0105] A strong frequency component appears near the fundamental frequency f0 of the wave packet 10 that constitutes the burst wave. The frequency components of the signal have a spread before and after the fundamental frequency f0, and this is called the fundamental band W1. Therefore, the fundamental band W1 is the range of frequency components that have a spread before and after the fundamental frequency f0. Note that the fundamental frequency f0 is equal to the excitation frequency fex.

[0106] The component with a frequency N times the fundamental frequency f0 (N × f0) is a harmonic. The component with a frequency 1 / N times the maximum component frequency f0 (f0 / N) is a subharmonic. Here, N is an integer N ≥ 2. Both harmonics and subharmonics have a spread. In this disclosure, when we particularly emphasize that harmonics and subharmonics have a frequency spread, we refer to them as the harmonic band and subharmonic band, respectively. Therefore, even when simply written as "harmonics," they have a frequency spread. The harmonic band and subharmonic band are generated by nonlinear phenomena and occur when the sound pressure of the ultrasonic beam U input to the object under test E is extremely strong.

[0107] As in the first embodiment, when a gas G is interposed between the transmitting probe 110 and the object under inspection E, it is generally difficult to introduce a high-sound-pressure ultrasonic beam U into the interior of the object under inspection E, and therefore, at least one of the harmonic band or subharmonic band is often not observed. Even under the conditions of the first embodiment, the harmonic band and subharmonic band were below the detection limit.

[0108] As shown in Figure 9, the fundamental frequency band W1 has a frequency spread. The frequency components of the fundamental frequency band W1 other than the fundamental frequency f0 will be called the "footline components W3". Although not shown in Figure 9, side lobes (peaks) of the fundamental frequency band W1 may appear at frequencies slightly shifted from the fundamental frequency f0. Since the side lobes are included in the fundamental frequency band W1 and are frequency components shifted from the fundamental frequency f0, the footline components W3 also include the side lobes of the fundamental frequency band W1.

[0109] In Figure 9, the horizontal axis shows a wide frequency range from 0 Hz to 2 × f0 or more. Looking at this wide frequency range, it can be seen that the fundamental frequency band W1 of the signal in this embodiment is contained within a relatively narrow range centered around the fundamental frequency f0. This is because burst waves with wavenumber N0 of 2 or more are used. In contrast, when a pulse voltage consisting of a single wavenumber N0 is applied, a high-bandwidth signal spreads across a wide frequency range.

[0110] Figure 10 shows the spectrum of the fundamental frequency band W1 of the received signal of the ultrasonic beam U that has passed through the object E under inspection. The fundamental frequency f0 is 0.82 MHz, and the horizontal axis represents a relatively narrow range of 0.70 to 0.90 MHz.

[0111] In Figure 10, the solid line represents the spectrum when observing the healthy portion N of the object under inspection E, and the dashed line represents the spectrum when observing the defective portion D. The spectra of the healthy portion N and the defective portion D are compared. It is found that the difference between the spectra is greater in the frequency range shifted from the fundamental frequency f0, for example, 0.75 to 0.80 MHz, than in the frequency range shifted from the fundamental frequency f0 = 0.82 MHz. In this embodiment, the defective portion D in the object under inspection E is detected by detecting changes in the signal intensity of the healthy portion N and the defective portion D. Therefore, a larger difference between the two (difference between spectra) makes it easier to detect the defect. In other words, detecting frequency components at frequencies shifted from the fundamental frequency f0 improves the detection performance of the defective portion D. As mentioned above, the frequency components of the fundamental band W1 other than the fundamental frequency f0 are the tail components W3.

[0112] Thus, shifting the detection frequency fdet from the excitation frequency fex (fundamental frequency f0) is effective in improving the detection performance of the defect D. However, since the component intensity (signal intensity) is not maximum at the frequency shifted from the excitation frequency fex, there is a problem that the frequency components may become smaller, as described above.

[0113] Figure 11 schematically shows the spectrum of the fundamental frequency band W1. The vertical axis represents the intensity of the frequency components (component intensity), and the horizontal axis represents the frequency. The solid line represents the case where wavenumber N0 is 10, and the dashed line represents the case where wavenumber N0 is 30. In both the solid and dashed cases, the spectrum of the fundamental frequency band W1 is maximum at the fundamental frequency f0, as shown in Figure 11. Therefore, as described above, at frequencies shifted from the fundamental frequency f0 (detection frequency fdet in Figure 11), the frequency components become relatively smaller.

[0114] Furthermore, increasing the wavenumber N0 of the burst wave increases the frequency component of the excitation frequency fex. However, because the bandwidth of the fundamental band W1 narrows, the frequency components of frequencies shifted from the excitation frequency fex do not increase, or may even decrease.

[0115] Figure 12 illustrates the meaning of bandwidth. The vertical axis represents spectral intensity (component intensity), and the horizontal axis represents frequency. Bandwidth (FWHM) refers to the full width at half maximum, which is the frequency range where the peak intensity is half at the frequency fm where the spectral intensity is maximum. Note that the frequency fm where the spectral intensity is maximum is equal to the fundamental frequency f0 in the case of a single burst wave. Furthermore, the full width at half maximum (FWHM) is defined as the FWHM ratio, which is the value normalized by the fundamental frequency f0. That is, the FWHM ratio is expressed by the following formula. FWHM ratio = Full width at half maximum / f0 The FWHM ratio is an indicator of bandwidth.

[0116] Figure 13 shows the relationship between wavenumber N0 and the bandwidth (FWHM) of the fundamental frequency band W1. The horizontal axis represents wavenumber N0, and the vertical axis represents the FWHM ratio. As shown in Figure 13, as wavenumber N0 increases, the FWHM ratio decreases. Therefore, as schematically shown in Figure 11 above, increasing wavenumber N0 makes the peak steeper, and the signal component at the detection frequency fdet actually decreases.

[0117] Thus, when using a conventional burst waveform as shown in Figure 7 above, it is difficult to increase the frequency component at a frequency shifted from the excitation frequency fex. Therefore, in this embodiment, this problem is solved by using a burst wave composed of a group of wave packets having multiple wave packets, as shown in Figure 8 above.

[0118] The frequency detected by the signal processing unit 250 (Figure 6) preferably includes frequencies in the range of (f0 ± 0.25f0), where f0 is the fundamental frequency of the wave packet (for example, wave packet 10 (first wave packet)). This is because the signal component containing information about the defect D appears in the frequency range of f0 ± 0.25f0. Therefore, including frequencies in this range can improve the detection accuracy of the defect D.

[0119] Furthermore, the full width at half maximum (FWHM) of the frequency spectrum of the fundamental wave band W1 is preferably 50% or less of the fundamental frequency f0 of the wave packet. In other words, the FWHM ratio is preferably 50% or less. This improves the detection accuracy of the defect D. As mentioned above, the fundamental wave band W1 is the range of frequency components that spreads before and after the fundamental frequency f0.

[0120] Furthermore, it is preferable that the wave number of the wave packet (for example, wave packet 10 (first wave packet)) be 30 or less. This allows for a wider full width at half maximum.

[0121] Figure 14 schematically shows the spectrum of a received signal when using a burst wave composed of a group of wave packets containing multiple wave packets. Figure 14 shows the case where the wave number N0 of wave packets 10 and 11 each have 5 waves. When the inter-package time ΔtI is zero (ΔtI=0, i.e., αI=0), the two wave packets are connected continuously, so it is the same as the configuration of a single wave packet with wave number N0=10 (see Figure 13 above; however, the shape in Figure 14 is slightly different from that in Figure 13). Here, αI is the inter-package wave number, and its definition will be explained later. In this case, the spectrum has a shape with the fundamental frequency f0 as the peak, as shown by the dashed line in Figure 14. In contrast, when the inter-package time ΔtI is 0.5 waves (ΔtI=0.5 waves, i.e., αI=0.5), the spectrum includes two peaks flanking the fundamental frequency f0, as shown by the solid line in Figure 14. Therefore, at the detection frequency fdet, which is a frequency that deviates from the fundamental frequency f0, the frequency component becomes stronger.

[0122] As will be explained in detail later, the inter-split time ΔtI is theoretically easier to handle using the inter-split wave number αI. The inter-split wave number αI is a value normalized by the fundamental period T0 of wave packet 10. That is, αI = ΔtI / T0. Therefore, the above "ΔtI = 0.5 waves" is equivalent to "αI = 0.5" as described above.

[0123] Figure 15 plots the magnitude of the frequency component at the detection frequency fdet when the wave number αI is varied. The horizontal axis represents the wave number αI, and the vertical axis represents the magnitude of the frequency component at the detection frequency fdet. Figure 15 shows an example where the fundamental frequency f0 = 0.82 MHz and the detection frequency fdet = 0.74 MHz. Therefore, the fundamental frequency f0 is different from the detection frequency fdet of the ultrasonic beam U by the receiving probe 140. In other words, the detection frequency fdet of the ultrasonic beam U by the receiving probe 140 is different from the fundamental frequency f0. αI = 0 is a burst wave of a single wave packet, i.e., a conventional configuration. If the magnitude of the frequency component when αI = 0 is 1, then when αI = 0.5 waves, the magnitude of the frequency component at the detection frequency fdet increases 22 times.

[0124] In this way, by making the burst wave signal applied to the transmitting probe 110 a signal that repeats a group of wave packets having multiple wave packets, it is possible to increase the frequency components at frequencies shifted from the fundamental frequency f0. As mentioned above, the components of the scattered wave U1 at the defect D in the object under inspection are largely contained in the tail component W3 of the fundamental wave band W1, which is shifted from the fundamental frequency f0. Therefore, with this embodiment, by appropriately setting the inter-packet time tI (inter-packet wave number αI), the effect of making the defect D easier to detect can be obtained.

[0125] The signal processing unit 250 (Figure 6) detects a tail component W3 that differs from the fundamental frequency f0 of the wave packet within the range of the fundamental band W1 from the frequency domain signal output from the frequency conversion unit 230. This improves the detection performance of the defect D. The fundamental band W1 is the range of frequency components that have a spread before and after the fundamental frequency f0, as described above.

[0126] (Frequency components of burst waves from multiple wave packets) The operation of this embodiment is described below. The spectrum of a burst wave composed of multiple wave packets is theoretically determined.

[0127] Figure 16 shows a wave packet group composed of two (or more; three or more are also possible) wave packets. The vertical axis represents signal intensity, and the horizontal axis represents time. The emitted ultrasonic beam U becomes a burst wave in which this wave packet group repeats with a repeating period Tr. The waveform of wave packet 10 is generally represented by f1(t). The waveform of wave packet 11 is f1(t-Δtd). Therefore, the waveform of the wave packet group is given by the following equation (4).

[0128]

number

[0129] Using the Fourier transform shift theorem, we can find the Fourier transform F1(ω) of f(t),

[0130]

number

[0131] Equation (5) is a complex number. Since the magnitude of the frequency component is the absolute value of F(t) in (Equation 5), it is the square root of the product of F(t) and its complex conjugate. Calculating this,

[0132]

number

[0133] Here, the wave packet delay αd is a quantity obtained by expressing the wave packet delay time Δtd in units of the fundamental period T0, as shown in equation (7).

[0134]

number

[0135] Furthermore, in equation (6) above, the frequency is expressed as frequency f, not angular frequency ω. Equation (6) can be expressed using the interference function K(f,f0,αd), as shown in equation (8).

[0136]

number

[0137] The functional form of the interference function K(f,f0,αd) is given by equation (9).

[0138]

number

[0139] In equation (8) above, |F1(f)| on the right-hand side represents the spectrum of wave packet 10 alone. That is, the spectrum of the burst wave composed of multiple wave packets shown in Figure 16 is obtained by multiplying the spectrum of wave packet 10 alone by the interference function K(f,f0,αd).

[0140] (Frequency characteristics of the interference function) Next, we will show the spectrum of equation (8) and the interference function of equation (9) using a specific example.

[0141] Figure 17A shows the case where the wave packet delay αd = 5 (wave number between wave packets αI = 0), illustrating an example of a burst wave of a single wave packet, which is a conventional example. Figure 17B shows the case where the wave packet delay αd = 5.5 (wave number between wave packets αI = 0.5), illustrating an example of a burst wave composed of multiple wave packets in this embodiment. In Figures 17A and 17B, the fundamental frequency f0 of wave packet 10 is 0.82 MHz, and the wave number N0 is 5.

[0142] Here, we summarize the relationship between the wave packet delay time Δtd, that is, the delay time between the beginning times of wave packet 10 and wave packet 11, and the inter-wave packet time ΔtI. As can be seen from Figure 8 above, the following relationship holds between the wave packet delay time Δtd and the inter-wave packet time ΔtI, given by equation (10). Here, N0 is the wave number of wave packet 10, and T0 is the fundamental period of wave packet 10.

[0143]

number

[0144] Therefore, the following equation (11) holds between the wave packet delay αd and the wave number αI.

[0145]

number

[0146] (Definitions and clarification of terms for wave packet delay time Δtd and wave packet inter-split time ΔtI) Here, we organize the quantities that represent the delay time between wave packet 10 and wave packet 11. The wave packet delay time Δtd is, as described above, the time from the beginning of wave packet 10 to the beginning of wave packet 11. In contrast, the inter-wave packet time ΔtI is, as described above, the time from the end of wave packet 10 to the beginning of wave packet 11.

[0147] Comparing the wave packet delay time Δtd and the wave packet inter-split time ΔtI, the wave packet delay time Δtd is a quantity that more easily represents the interference function K. On the other hand, using the wave packet inter-split time tI has the advantage of clearly distinguishing it from conventional single-wave packet burst waves. That is, ΔtI=0 corresponds to the conventional single-wave packet burst wave. For this reason, both the wave packet delay time Δtd and the wave packet inter-split time ΔtI are used in this specification.

[0148] As can be seen from equations (6) and (9) above, the wave packet delay time Δtd is easier to understand when expressed as the wave packet delay amount αd, which is obtained by dividing the wave packet delay time Δtd by the fundamental period T0 of wave packet 10. For this reason, the wave packet delay amount αd is also used. Similarly, the wave number αI, which is obtained by dividing the inter-wave packet time ΔtI by the fundamental period T0 of wave packet 10, is also used.

[0149] In Figures 17A and 17B, the solid line represents the spectrum expressed by equation (8), and the dashed line represents the interference function K(f,f0,αd) expressed by equation (9). In both cases, it can be seen that the spectrum shown by the solid line is strongly influenced by the frequency characteristics of the interference function K(f,f0,αd) shown by the dashed line. Hereafter, the interference function K(f,f0,αd) will be abbreviated as interference function K, etc.

[0150] The interference function K is a periodic function of frequency f and acts like a comb filter. The frequency positions where the value of the interference function K (the value of the frequency component) takes a minimum are called "nodes," and the frequency positions where the value of the interference function K takes a maximum are called "antinodes." Since the interference function K is a periodic function, nodes and antinodes alternate.

[0151] In Figure 17A, the interference function K is at its maximum position, i.e., its antinode, at the fundamental frequency f0. Therefore, the frequency component is largest at the fundamental frequency f0 = 0.82 MHz. On the other hand, at the detection frequency fdet = 0.74 MHz, the frequency component is smaller because it is close to a node of the interference function K.

[0152] In Figure 17B, which is an example of this embodiment, the value of the interference function K, shown by the dashed line, reaches a maximum value at 0.77 MHz, which is near the detection frequency fdet. That is, the frequency position near the detection frequency fdet is at the antinode. As a result, the frequency components of the burst wave also become larger. Therefore, the signal at the detection frequency can be acquired efficiently.

[0153] Similarly, by setting the wave packet delay αd to an appropriate value and determining the position of the antinode of the interference function K, it is possible to amplify the desired frequency components.

[0154] Figure 18A shows the spectrum (solid line) and interference function (dashed line) for a wave packet delay of αd = 5.25 (wave number αI = 0.25). The frequency components around 0.7MHz to 0.8MHz (especially around 0.77MHz), which are shifted from the fundamental frequency f0 = 0.82MHz, are large. Therefore, the wave packet delay of αd = 5.25 used in the calculation of Figure 18A is an αd value suitable when using a detection frequency fdet of around 0.77MHz.

[0155] Figure 18B shows the spectrum (solid line) and interference function (dashed line) for a wave packet delay of αd = 5.75 (wave number αI = 0.75). A frequency component of approximately 0.86 MHz, which is shifted from the fundamental frequency f0 = 0.82 MHz, is large. Therefore, a wave packet delay of αd = 5.75 is a suitable αd value when using a detection frequency fdet of approximately 0.86 MHz.

[0156] As shown in Figures 18A and 18B, the way the peak shown by the solid line deviates from the fundamental frequency f0 differs depending on the magnitude of the wave packet delay αd. Specifically, it deviates either to a frequency smaller than f0 or to a frequency larger than f0. Therefore, it is preferable to compare the magnitude of the peak occurring at a frequency smaller than f0 with the magnitude of the peak occurring at a frequency larger than f0 and use the relatively larger peak for detection. Specifically, it is preferable to set the detection frequency fdet to the side where the relatively larger peak exists.

[0157] (Reasons why it becomes periodic with respect to the wave packet wave number αI) We will explain why the relationship between the magnitude of the frequency component and the wave packet wave number αI exhibits the dependence shown in Figure 15.

[0158] Figure 19A is a graph plotting the magnitude of the frequency components against the wave number when the detection frequency fdet is 0.74 MHz. Figure 19B is a graph plotting the magnitude of the frequency components against the wave number when the detection frequency fdet is 0.76 MHz. Figure 19C is a graph plotting the magnitude of the frequency components against the wave number when the detection frequency fdet is 0.82 MHz. Figure 19D is a graph plotting the magnitude of the frequency components against the wave number when the detection frequency fdet is 0.90 MHz. In all cases, the fundamental frequency f0 of wave packet 10 is 0.82 MHz, and the wave number of wave packet 10 is 5.

[0159] In each figure, the solid line represents the magnitude of the frequency components calculated from the waveform composed of two wave packets. The dashed line plots the interference function K from equation (9). The dashed line represents a conventional example (a conventional example in which a burst wave consisting of only one wave packet is applied). Therefore, the value of the detected frequency component (vertical axis) is large for inter-wave packets where the difference between this embodiment shown by the solid line and the graph (straight line) shown by the dashed line is large.

[0160] Comparing the solid and dashed lines, their shapes correspond well, and it can be seen that the dependence of the frequency component shown by the solid line on αI mainly corresponds to the interference function K. In equation (9), when the frequency f is fixed, it becomes a periodic function of the wave packet delay αd, and this periodicity is shown in Figures 19A to 19D.

[0161] In Figure 19A, under the condition of detection frequency fdet = 0.74 MHz, the value of the interference function K becomes small at αI = 0, which corresponds to a single wave packet burst wave (dashed line). The frequency component is maximized around αI = 0.5. The frequency component becomes zero around αI = 1.1. Therefore, in Figure 19A, if αI is set so that the magnitude of the frequency component (solid line) is greater than the value at αI = 0 (dashed line), the detected frequency component can be increased, and the detection performance of the defect D can be improved. In other words, αI should be set to a range where the solid line is above the dashed line in Figure 19A. To put it another way, it is preferable that the inter-split wave number αI is a wave packet wave number αI that has a larger frequency component than the frequency component when the inter-split wave number αI, which is the wave number between multiple wave packets, is zero (αI = 0). In other words, it is preferable that the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform with an intersequence wavenumber αI having a frequency component that is larger than the frequency component when the intersequence wavenumber αI is zero is applied. This improves the detection performance of the defect D.

[0162] In the case shown in Figure 19B, the magnitude of the frequency component at αI=0 is large. Specifically, the magnitude of the frequency component is at the position of the dashed line in Figure 19B. Even in this case, if the interspinning wavenumber αI is set to a range where the magnitude of the frequency component (solid line) is larger than the value at αI=0 (dashed line), the detection performance of the defect D can be improved.

[0163] In the case shown in Figure 19C, the fundamental frequency f0 is the detection frequency fdet, and detection is performed by making the fundamental frequency f0 (=excitation frequency fex) and the detection frequency fdet equal. In this case, the frequency component is maximized at αI=0. In other words, it is best to use a burst wave of a single wave packet as usual.

[0164] The results in Figure 19C show that setting the intersegmental wavenumber αI to something other than zero, as in this disclosure, is effective when the detection frequency fdet is shifted from the fundamental frequency f0. Therefore, an intersegmental wavenumber αI that has a larger frequency component than the frequency component when the intersegmental wavenumber αI is zero (αI=0) can be set by making the fundamental frequency f0 and the detection frequency fdet different (i.e., they are different).

[0165] In the case of Figure 19D, similar to Figures 19A and 19B above, the magnitude of the detected frequency component can be increased by making the wave packet wavenumber αI non-zero, thereby improving the detection performance of the defect D.

[0166] As described above, by setting the interspit wavenumber αI to a range where the magnitude of the frequency component at the detection frequency fdet is greater than the value at αI=0, the frequency component can be increased, and the detection performance of the defect D can be improved.

[0167] Furthermore, as shown in Figures 19A to 19D, the intensity of the frequency component at the detection frequency fdet corresponds to the magnitude of the interference function K. Therefore, by setting the inter-steam wavenumber αI to a range where the value of the interference function K is greater than that when αI=0, the detection performance of the defect D can be improved.

[0168] More preferably, in the relationship between the interference function K and the wave packet delay αd, the wave packet delay αd is set within a range such that the value of the interference function K is greater than half of the maximum value of the interference function K. This is even more preferable because the frequency component at the detection frequency fdet becomes larger, improving the detection performance of the defect D.

[0169] Accordingly, in the example of this disclosure, the signal processing unit 250 (Figure 6) detects frequency components at frequencies where the value of the interference function K is 1 / 2 or greater than the maximum value of the interference function K. This improves the detection performance of the defect D. The interference function K is a function whose parameters are the wave packet delay time Δtd between wave packet 10 (first wave packet) and wave packet 11 (second wave packet) among the multiple wave packets, and the fundamental frequency f0 of wave packet 10.

[0170] Furthermore, the wave packet delay αd and the wave number αI are related by equation (11) above. Therefore, it goes without saying that setting the wave packet delay αd is equivalent to setting the optimal range for the wave number αI.

[0171] The wave packet delay amount αd is expressed in equation (7) above as the wave packet delay time Δtd expressed in wavenumber units. Therefore, it goes without saying that setting the wave packet delay amount αd to an appropriate value is equivalent to setting the wave packet delay time Δtd to a corresponding appropriate value. Similarly, it is clear that setting the inter-wave packet wavenumber αI to an appropriate value is equivalent to setting the wave packet delay time Δtd to an appropriate value.

[0172] (Second Embodiment) A second embodiment of this disclosure will be described with reference to Figures 20A and 20B. This embodiment is an example in which the wave packet delay time Δtd is made longer compared to the first embodiment.

[0173] Figure 20A shows a signal of a burst wave composed of two wave packets in a second embodiment. This wave packet group, including the two wave packets, is repeated with a repetition period Tr = 5 ms. The horizontal axis represents time, and the vertical axis represents the signal voltage. The conditions are that the fundamental frequency of the wave packet is f0 = 0.82 MHz, the wavenumbers of wave packets 10 and 11 are N0 = 5, and the wave packet delay αd = 10.5. The frequency conversion period (synonymous with the integration period in this disclosure) will be described later.

[0174] Figure 20B shows the spectrum (solid line) and interference function K (dashed line) for the burst wave shown in Figure 20A. The horizontal axis represents frequency, and the vertical axis represents the magnitude of the frequency component. In this case as well, due to the influence of the interference function K, the frequency component at the fundamental frequency (center frequency) f0 = 0.82 MHz is reduced, and the signal components at 0.78 MHz and 0.86 MHz, which are shifted from the fundamental frequency f0, are increased. In this way, the tail component W3, which is the component shifted from the fundamental frequency f0 within the fundamental wave band W1 around the fundamental frequency f0, is increased. This has the effect of making it easier to detect the defect D.

[0175] One of the important points in this disclosure is the selection of the frequency conversion period (Figure 20A) when the frequency conversion unit 230 (Figure 6) converts a time-domain waveform into a frequency-domain signal (spectrum). The frequency conversion period (conversion target period) can be set to a range that includes wave packet 10 and wave packet 11, as shown in Figure 20A.

[0176] The frequency conversion period corresponds to the range over which the sum of equation (1) above is taken. By converting to frequency components over a frequency conversion period that spans, for example, two wave packets (i.e., a range that includes, for example, at least two wave packets), the two wave packets interfere in the frequency domain, generating an interference function K. As previously described, the effects of this disclosure are obtained through the action of this interference function K.

[0177] Therefore, even if methods such as inverting the phase of the wave packet at each repetition period Tr of the burst wave are used, the effects of this disclosure cannot be obtained by frequency conversion for each wave packet. The effects of this disclosure can be obtained by applying multiple wave packets at each repetition period Tr.

[0178] Next, if the wave packet delay αd is made larger than the wave number N0, the inter-wave packet wave number αI increases. This has the effect of reducing the impact on the wave packet 11 even when damped oscillations occur in the oscillator 111 (piezoelectric oscillator) of the transmitting probe 110. In other words, this effect can be obtained by setting the inter-wave packet wave number αI to be larger than the wave number of the damped oscillations of the transmitting probe 110. Typically, the wave number of the damped oscillations of the transmitting probe 110 is around 2 to 3 waves.

[0179] Damped oscillation of the transducer 111 of the transmitting probe 110 refers to the phenomenon in which the oscillation of the transducer 111 does not stop immediately after the voltage applied to the transmitting probe 110 is reduced, but rather the oscillation amplitude gradually decreases and stops.

[0180] (Third embodiment) A third embodiment of this disclosure will be described with reference to Figures 21A and 21B. This embodiment is an example in which the wave packet delay time Δtd is made longer compared to the first embodiment.

[0181] Figure 21A shows a signal of a burst wave composed of two wave packets in the third embodiment. This wave packet group, including the two wave packets, is repeated with a repetition period Tr = 5 ms. The horizontal axis represents time, and the vertical axis represents the signal voltage. The conditions are that the fundamental frequency of the wave packet is f0 = 0.82 MHz, the wavenumbers of wave packets 10 and 11 are N0 = 5, and the wave packet delay αd = 20.5.

[0182] Figure 21B shows the spectrum (solid line) and interference function K (dashed line) for the burst wave shown in Figure 21A. As the wave packet delay αd increases, the period of the interference function K shortens. This can be seen from the formula for the interference function K in equation (9) above. As a result, the spectrum (solid line) becomes fragmented, but the frequency components at frequencies shifted from the fundamental frequency f0 become larger. In the case of Figure 21B, the frequencies of the second largest frequency components are 0.76 MHz and 0.88 MHz. In this way, frequency components shifted by approximately ±5% from the fundamental frequency f0 can be efficiently acquired.

[0183] In this embodiment as well, the frequency conversion period of the frequency conversion unit 230 is set to include two wave packets (wave packet 10 and wave packet 11). By setting it in this way, the two wave packets interfere in the frequency domain, and an interference function K is generated.

[0184] (Fourth Embodiment) A fourth embodiment of this disclosure will be described with reference to Figures 22A and 22B. In this embodiment, wave packets 10 and 11 are set to have different amplitudes.

[0185] Figure 22A shows a burst wave signal composed of two wave packets in the fourth embodiment. This wave packet group, including the two wave packets, is repeated with a repetition period Tr = 5 ms. The horizontal axis represents time, and the vertical axis represents voltage (signal voltage). The conditions are that the fundamental frequency of the wave packet is f0 = 0.82 MHz, the wavenumbers of wave packets 10 and 11 are N0 = 5, and the wave packet delay αd = 5.5. The amplitude of wave packet 11 is half the amplitude of wave packet 10.

[0186] Figure 22B shows the spectrum (solid line) and interference function K (dashed line) for the burst wave shown in Figure 22A. As shown in Figure 22B, even if the amplitudes of wave packets 10 and 11 are set to be different, the frequency components at frequencies deviating from the fundamental frequency f0 become larger, and the effects of this disclosure are obtained. In this case, the functional form of the interference function K is different from that of equation (9) above, but the functional form of the interference function K is the same as in the first embodiment in that it is a periodic function with antinodes and nodes periodically. For this reason, the effects of this disclosure are obtained.

[0187] If the amplitudes of wave packets 10 and 11 are b1 and b2, respectively, the functional form of the interference function K(f,f0,αd) is given by the following equation.

[0188]

number

[0189] When b1=b2=1, the interference function K is the same as that of equation (9) above. Thus, even if the function form is different from that of equation (9), the interference function K is a function that has a maximum (antinode) with respect to frequency f, and the effects of this disclosure can be obtained. Specifically, the wave packet delay αd should be determined so that the frequency to be detected is near the maximum value of the interference function K. The dashed line in Figure 22B shows the interference function K of equation (12).

[0190] (Fifth embodiment) A fifth embodiment of the present disclosure will be described with reference to Figures 23A and 23B. In this embodiment, wave packets 10 and 11 are set to have different fundamental frequencies f0. That is, the fundamental frequencies f0 of each of the multiple wave packets are different.

[0191] Figure 23A shows a burst wave signal composed of two wave packets in the fifth embodiment. This wave packet group, including the two wave packets, is repeated with a repetition period Tr = 5 ms. The horizontal axis represents time, and the vertical axis represents voltage (signal voltage). The conditions are that the fundamental frequency f0 of wave packet 10 is 0.82 MHz, the wavenumber N0 of wave packets 10 and 11 is 5, and the wave packet delay αd is 5.5. The fundamental frequency f0 of the wave packets was set to f0 = 0.82 MHz for wave packet 10 and f0 (fundamental frequency f02) = 0.86 MHz (period T02) for wave packet 11.

[0192] Figure 23B shows the spectrum for the burst wave shown in Figure 23A. The spectrum has a maximum value at a frequency of 0.78 MHz, which is 40 kHz away from the fundamental frequency f0, and the frequency component that is shifted from the fundamental frequency f0 (the tail component W3 of the fundamental wave band W1) is large. As a result, the detection of the defect D is improved. Thus, the effects of this disclosure can be obtained even if the fundamental frequencies f0 of wave packet 10 and wave packet 11 are different (the fundamental frequencies f0 of each of the multiple wave packets are different).

[0193] (Sixth Embodiment) Figure 24 is a block diagram showing the configuration of the ultrasound inspection apparatus Z of the sixth embodiment. The ultrasound inspection apparatus Z of the sixth embodiment includes a signal processing unit 250, an integration period setting unit 280, and a database 281. The integration period setting unit 280 sets a plurality of integration periods (for example, integration period 1, integration period 2, integration period 3, etc.). The database 281 is a database that associates information about the detection frequency fdet by the receiving probe 121 (for example, frequency ratio f / f0) and information about the wave packet delay time Δtd (for example, wave packet delay amount αd).

[0194] (Characteristics of the interference function K) This embodiment is based on the following characteristics of the interference function K. These characteristics are described below. Figure 25 is a two-dimensional map showing the change in the interference function K due to two parameters: frequency and wave packet delay αd. Figure 25 is an example of a database 281 provided in the signal processing unit 250. However, the database 281 is not limited to graphs like Figure 25, but may also be maps, tables, functions, etc. The horizontal axis represents the frequency ratio (f / f0) between frequency f and center frequency f0. The vertical axis represents information about the wave packet delay time Δtd, which is the wave packet delay αd uniquely determined from the wave packet delay time Δtd.

[0195] Figure 25 shows the plot of equation (9) for the interference function K. In Figure 25, the solid line represents the location where the interference function K takes its maximum value, and the dashed line represents the location where it takes its minimum value. As can be seen from equation (9), the interference function K is uniquely determined by specifying two parameters: the frequency ratio (f / f0) and the wave packet delay αd.

[0196] Figures 17A, 17B, 18A, and 18B demonstrate that the interference function K is a periodic function with respect to frequency. As shown in the two-dimensional map in Figure 25, the interference function K is also a periodic function with respect to the wave packet delay αd.

[0197] We will now describe the conditions under which the interference function K, represented by equation (9), exhibits a maximum or minimum. The relationship between the combination of frequency ratio (f / f0) and wave packet delay αd that results in a maximum or minimum of the interference function K can be obtained as follows. The interference function K exhibits a maximum when the cosine function in equation (9) is +1, and a minimum when it is -1. Therefore, the condition under which the interference function exhibits a maximum is given by the following equation.

[0198]

number

[0199] Here, n is any integer. The condition for the interference function K to give a local minimum is given by the following equation.

[0200]

number

[0201] Here, n is any integer. The solid lines (local maximums) and dashed lines (local minimums) in Figure 25 are represented by these equations.

[0202] As shown in equation (8), the spectrum observed is obtained by multiplying the interference function K by the spectrum |F1(f)| of wave packet 1 alone. Therefore, for example, when detecting a signal at a frequency with a frequency ratio f / f0 = 0.95, the wave packet delay αd should be set so that the interference function K is maximized at this frequency. In this way, the intensity of the detected signal increases, making it easier to detect signals caused by defects D, and improving the detectability of minute defects D. Therefore, it is particularly preferable to set the wave packet delay αd in combination with the frequency ratio at which the interference function K is maximized (located on the solid line in Figure 25). However, the effects of this disclosure can also be obtained by setting the wave packet delay αd in combination with a frequency ratio that exists between the maximum and minimum in Figure 25, i.e., between the dashed line and the solid line (excluding those on the dashed line and the solid line), even if the interference function K is not maximized.

[0203] (Selection of detection frequency fdet) The detectability of the defect D changes depending on the selection of the detection frequency fdet, that is, the frequency at which detection is performed. The inventors have found that the components of the scattered wave U1 that are advantageous for detecting minute defect parts D are abundant in frequency components shifted from the center frequency f0. For example, the frequency ranges of frequency ratio 0.90 to 0.95 and 1.05 to 1.10. On the other hand, when detecting a defect D that is significantly larger than the width (size, diameter) of the converging beam, it may be easier to detect it using the conventional blocking method. In Figure 4, if the defect D is 10 times the beam width BW, the ultrasonic beam U is reliably blocked, so the defect D can be detected using the blocking method.

[0204] Thus, by selecting multiple detection frequencies fdet depending on the characteristics of the defect D to be observed, the defect D can be detected effectively. It is even more preferable if the defect D can be imaged at multiple detection frequencies fdet in a single measurement.

[0205] As an example, consider a case where a measurement is performed at a frequency ratio f / f0 = 0.90 to detect a minute defect D using scattered wave U1. Let's call this measurement condition A. In this case, as can be seen from Figure 25, if the wave packet delay αd is set to 5.5 on the solid line, the signal strength can be maximized, and the received signal can be detected efficiently. On the other hand, under this measurement condition A, the interference function K with a frequency ratio f / f0 = 1 gives a minimum value because the wave packet delay αd is on the dashed line at 5.5, making it unfavorable to detect the received signal at the center frequency f0. Thus, when attempting to measure at multiple detection frequencies fdet, two measurements are often required.

[0206] In this embodiment, to address this problem, multiple conversion target periods (e.g., integration period 1, integration period 2) are set, enabling measurement under measurement conditions suitable for two detection frequencies fdet in a single measurement. In integration period 1 and integration period 2, at least one wave packet among the wave packets included in each integration period is different. This allows the presence of the defect D to be detected from different perspectives, thereby improving the detection performance of the defect D. In the example shown in Figure 26 below, wave packet 10 is common to integration period 1 and integration period 2, while wave packet 11 is included in integration period 1 but not in integration period 2.

[0207] (Configuration of this embodiment) This embodiment will be explained using Figures 24 and 26. Figure 26 is a schematic diagram showing the waveform of the burst wave applied to the transmitting probe 110 in the sixth embodiment. As shown in Figure 26, in this embodiment, a burst wave having a wave packet group composed of multiple wave packets (wave packet 10 and wave packet 11) is applied to the transmitting probe 110. The wave packet delay time Δtd between wave packet 10 and wave packet 11 can be set to an appropriate value by the delay time setting unit 213 of the control device 2.

[0208] The signal processing unit 250 of the control device 2 includes an integration period setting unit 280. The integration period setting unit 280 sets the integration period for converting the received signal into frequency components in the frequency conversion unit 230. Note that the integration period is an example of the conversion target period, and when the signal of the conversion target period is frequency converted using the above equations (1) and (2), the conversion target period is synonymous with the integration period. Specifically, the integration period is, for example, the time range of tk to be integrated when converting to frequency components using the method of equation (1).

[0209] A key feature of this embodiment is that the integration period setting unit 280 sets multiple integration periods. Each integration period contains different types of wave packets. In the example shown in Figure 26, integration period 1 includes both wave packets 10 and 11. Integration period 2 includes only wave packet 10.

[0210] One of the key points of the invention in this embodiment is the discovery that the change in the received spectrum due to the interference function K occurs because different wave packets among the multiple wave packets included in the integration period interfere with each other in frequency space. In other words, by appropriately selecting the wave packets to be included in the integration period, the obtained received spectrum can be changed. This makes it possible to more easily detect the frequency component of the desired detection frequency fdet.

[0211] In this embodiment, the wave packet delay αd was set to 5.5 in order to detect the frequency at a frequency ratio f / f0 = 0.90. Therefore, when the frequency component is calculated with an integration period of 1, the signal component at the detected frequency fdet of 0.74 MHz can be efficiently detected. In other words, although it is within the fundamental band W1, this measurement condition allows for the efficient detection of the tail component W3, which is a component shifted from the center frequency f0. On the other hand, when the frequency component is calculated over an integration period of 2, interference effects from the wave packet 11 do not occur, allowing for efficient detection of the component at the center frequency f0. Therefore, this is a suitable measurement condition for detecting the defect D using the blocking method.

[0212] Figure 27 is a detailed diagram of a part of the signal processing unit 250. Data 1 stored in the memory unit 261 is the frequency component calculated from the received signal waveform based on the integration period 1. Data 1 is a collection of frequency component data for each measurement coordinate. Similarly, Data 2 stored in the memory unit 261 is the frequency component calculated from the received signal waveform based on the integration period 2. The memory unit 261 stores both Data 1 and Data 2.

[0213] The frequency selection unit 242 selects a frequency suitable for data 1 and calculates signal features. The definition of "suitable frequency" will be described later. One example of how to calculate signal features is the method shown in equation (2). For the frequency set {ω} selected by the frequency selection unit 242, a time waveform h2(t) is calculated based on equation (2), and the peak-to-peak value of h2(t) is taken as the signal feature. Using this signal feature, the imaging unit 262 generates image 1 showing the location and size of the defect D. Similarly, the frequency selection unit 242 selects a frequency suitable for data 2 and calculates signal features. The imaging unit 262 generates image 2 showing the location and size of defect D using the same method as described above. The generated image 1 and image 2 are combined by the image synthesis unit 282, as will be described in detail later.

[0214] The "suitable frequency" mentioned above is, as stated above, the detection frequency fdet that has been predetermined to match the defect D that is to be observed. In this embodiment, the "suitable frequency" is, for example, 0.74 MHz for data 1, where the frequency ratio f / f0 = 0.90, and 0.82 MHz for data 2, where f / f0 = 1.

[0215] Furthermore, it is preferable to set the detection frequency to a frequency range with an appropriate width that includes the frequencies mentioned above, as this further improves defect detection. This corresponds to the set of frequencies {ω} (frequency parameters) included in the integration in equation (2). By integrating terms of multiple frequency components, the signal-to-noise ratio (SNR) is improved, thus improving defect detection. In this example, the range was set to 0.72 to 0.76 MHz for data 1. The range was set to 0.80 to 0.84 MHz for data 2.

[0216] In this way, it becomes possible to acquire images 1 and 2 corresponding to multiple measurement conditions in a single measurement (ultrasound examination). In this embodiment, images 1 and 2 can be superimposed with different colors and displayed as defect images on the display device 3.

[0217] In this embodiment, Image 1 is a defect image under measurement conditions centered on a detection frequency fdet of 0.74 MHz, and in the frequency spectrum, it visualizes the tail component W3 of the fundamental wave band W1. On the other hand, Image 2 is a defect image under measurement conditions centered on a detection frequency fdet of 0.82 MHz, and mainly visualizes the direct wave component U3. In this way, it becomes possible to visualize both the scattered wave U1 component, which is excellent in detecting minute defect areas D, and the defect area D using a blocking method, which can visualize large defect areas D, in a single measurement.

[0218] In this embodiment, we have shown an example where Image 1 and Image 2 are combined and superimposed by the image synthesis unit 282. However, the method of using the two images to display the defective area image is not limited to superimposed display. For example, Image 1 and Image 2 may be displayed side by side on the display device 3 instead of being superimposed.

[0219] (Seventh Embodiment) A seventh embodiment will be described using Figure 28. In this embodiment, a burst wave is used, which repeats a group of wave packets consisting of three or more wave packets.

[0220] The problems that this embodiment aims to solve are described below. In this embodiment, a case of detecting frequency components in two types of frequency regions among the skirt components W3 of the fundamental waveband W1 with the center frequency f0 is shown. That is, it is a case of measuring in two types of frequency regions among the frequencies shifted from the center frequency f0. More specifically, the skirt component W3 of the fundamental waveband W1 with the center frequency f0 contains many scattered wave U1 components due to the defect portion D, and has the feature that the detectability of minute defect portions D is good. However, when examined in more detail, the inventors have found that there are differences in detectability depending on the frequency even among the skirt components W3 of the fundamental waveband W1.

[0221] For example, the frequency components with the frequency ratios f / f0 of 0.95 and 1.05 are respectively the skirt components W3 of the fundamental waveband W1. Among these, when detecting a frequency component lower than the center frequency f0 (for example, f = fdet = f0 × 0.95), it has the feature that the margin of the measurement conditions is wide. That is, the allowances such as the selection of the detection frequency fdet and the selection of the wave number N0 of the beam are wide. For this reason, the measurement is relatively easy. On the other hand, when detecting a frequency component higher than the center frequency f0 (for example, f = fdet = f0 × 1.05), it has the feature that the detectability of smaller defect portions D is high. These findings are newly discovered by the inventors this time. Therefore, there may be a case where it is necessary to measure at a plurality of detection frequencies fdet.

[0222] Next, consider the experimental conditions for efficiently performing defect detection at these two detection frequencies fdet. Referring to the two-dimensional map of the interference function K in FIG. 25, at the frequency ratio f / f0 = 0.95, the beam delay amount αd = 5.3 becomes maximum. However, when αd1 = 5.3 is set, it can be seen that at the frequency ratio f / f0 = 1.05, the interference function K is at a minimum value and the measurement is difficult. Conversely, at the frequency f / f0 = 1.05, the preferable beam delay amount is αd = 5.75, but under this condition, it becomes minimum at f / f0 = 0.95. Thus, it can be understood from the map of the interference function K in FIG. 25 that depending on the combination of frequencies to be detected, appropriate measurement conditions cannot be set simultaneously.

[0223] Thus, when measuring with two different detection frequencies, two measurements are required, which increases the time required for measurement. In this embodiment, even in such cases, the configuration allows measurement at two different detection frequencies in a single measurement. Therefore, according to this embodiment, there is an effect of shortening the measurement time required for measurement at multiple detection frequencies fdet.

[0224] Figure 28 schematically shows the waveform of the burst wave applied to the transmitting probe 110 in the seventh embodiment. The configuration of the ultrasonic inspection apparatus Z in this embodiment is the same as that shown in Figure 24.

[0225] The burst wave used in this embodiment is a burst wave that repeats a wave packet group composed of three or more wave packets. Figure 28 shows an example in which the wave packet group consists of three wave packets, namely wave packet 10, wave packet 11, and wave packet 12. The repetition period of the wave packet group is Tr.

[0226] The wave packet delay time Δtd1 between wave packet 10 and wave packet 11 can be set to an appropriate value by the delay time setting unit 213 of the control device 2. Similarly, the wave packet delay time Δtd2 between wave packet 11 and the third wave packet, wave packet 12, can also be set by the delay time setting unit 213. As described above, the wave packet delay amount αd1 is defined as the value obtained by dividing the wave packet delay time Δtd1 by the fundamental period T0 of wave packet 10. The wave packet delay amount αd2 is defined as the value obtained by dividing the wave packet delay time Δtd2 by the fundamental period T01 of wave packet 11. That is, αd1 = Δtd1 / T0 αd2 = Δtd2 / T01 Here, T01 is the fundamental period of wave packet 11. Therefore, the transmitting probe 110 emits an ultrasonic beam U by applying a voltage waveform that repeats a group of wave packets, each having a wave packet 10 with a wave number of 2 or more at a fundamental frequency f0 which is the excitation frequency fex of the transmitting probe 110, a wave packet 11 with a wave number of 2 or more, and a wave packet 12 (third wave packet) with a wave number of 2 or more. The wave packet delay time Δtd1 between wave packet 10 and wave packet 11 and the wave packet delay time Δtd2 between wave packet 11 and wave packet 12 are arbitrarily set.

[0227] The integration period setting unit 280 in Figure 24 sets multiple integration periods. In this embodiment, integration period 1 is set to include wave packet 10 and wave packet 11. Integration period 2 is set to include wave packet 11 and wave packet 12. The detection frequencies fdet are denoted as f1 and f2.

[0228] In this embodiment, the center frequency f0 is set to 0.82 MHz. The center frequency f0 is equal to the fundamental frequency of the wave packet 10. The detected frequencies fdet are f1 = 0.78 MHz (frequency ratio f1 / f0 = 0.95) and f2 = 0.86 MHz (frequency ratio f1 / f0 = 1.05).

[0229] Referring to the two-dimensional map of the interference function K in Figure 25, the interference function K reaches a maximum at a wave packet delay of αd = 5.25 for detection frequency f1. For detection frequency f2, the interference function reaches a maximum at a wave packet delay of αd = 5.75. Therefore, the delay time setting unit 213 sets the two wave packet delay amounts in Figure 28 to αd1 = 5.25 and αd2 = 5.75. In this way, the integration period 1 (first transformation period) includes wave packet 10 and wave packet 11, so the interference function K becomes maximum at detection frequency f1, making it easier to measure the frequency component (first frequency component) at detection frequency f1. On the other hand, the integration period 2 (second transformation period) includes wave packet 11 and wave packet 12, so the interference function K becomes maximum at detection frequency f2, making it easier to measure the frequency component (second frequency component) at detection frequency f2.

[0230] Therefore, by using the signal processing unit 250 configured in Figure 27, data 1 can be obtained under measurement conditions suitable for detection frequency f1. Simultaneously, data 2 can be obtained under measurement conditions suitable for detection frequency f2. Here, data 1 and data 2 are the frequency components of the received waveform at each measurement point. It is even more preferable that the frequency components are complex numbers. As is known, the fact that the frequency components are complex numbers is equivalent to a combination of the absolute value and phase of the frequency components.

[0231] The frequency conversion unit 230 converts the received signal from the receiving probe 121 into frequency components (first frequency components) using an integration period 1 (an example of a first conversion period) that includes at least one wave packet from wave packet 10, wave packet 11, or wave packet 12. At the same time, the frequency conversion unit 230 converts the received signal into frequency components (second frequency components) using an integration period 2 (an example of a second conversion period) that includes at least one wave packet from wave packet 10, wave packet 11, or wave packet 12, and a wave packet different from the wave packets included in integration period 1. In other words, the combination of wave packets included in integration period 1 is different from the combination of wave packets included in integration period 2. In the example of this disclosure, the frequency conversion unit 230 converts the received signals into frequency components using an integration period consisting of wave packets 10 and 11 as integration period 1, and an integration period consisting of wave packets 11 and 12 as integration period 2.

[0232] Next, as in the sixth embodiment, the frequency selection unit 240 sets an appropriate detection frequency fdet range for data 1 and data 2, respectively. The image synthesis unit 282 calculates the signal features corresponding to each data. In this way, two images, image 1 corresponding to data 1 and image 2 corresponding to data 2, can be obtained in a single measurement. The image synthesis unit 282 combines image 1 and image 2 into an appropriate display image, and then displays it on the display device 3.

[0233] As described above, the image synthesis unit 282 is provided in the ultrasound inspection device Z and generates multiple signal features corresponding to the frequency components of detection frequency f1 (first frequency component) and detection frequency f2 (second frequency component), and synthesizes image 1 and image 2 generated from the multiple signal features. This makes it possible to suppress the oversight of minute defects D and large defects D, and improves the detection performance of defects D.

[0234] In this embodiment, an example is shown in which the wave packet group constituting the burst wave is composed of three wave packets. A wave packet group may consist of four or more wave packets. Using four wave packets allows for setting three different wave packet delay values ​​αd, and as can be seen from the interference function K in Figure 25, it is possible to simultaneously measure measurement conditions suitable for three different detection frequencies fdet. In this way, by increasing the number of wave packets in the wave packet group that constitutes the burst wave, images of the defect D can be obtained under multiple measurement conditions in a single measurement. This reduces the measurement time. Furthermore, since multiple conditions can be measured in a single measurement, the operator can set multiple measurement conditions suitable for the object E under inspection to detect the defect D. This allows for more reliable detection of the defect D.

[0235] Furthermore, the case where the wave packet group contains only two wave packets (Figure 26) and the case where the wave packet group contains three or more wave packets (for example, only three) (Figure 28) can be used interchangeably depending on the size of the defect D. For example, the configuration in Figure 26 is suitable when a relatively large defect D is expected to be included. On the other hand, the configuration in Figure 28 is suitable when a relatively small defect D is expected to be included. Note that the size of the defect D can often be predicted to some extent depending on the type of object E under inspection, the object itself, etc.

[0236] When a wave packet group contains three or more wave packets, the operator may, for example, be allowed to select how many wave packets to use to detect the defect D. For example, although the specifications of the ultrasonic inspection device Z allow for the detection of the defect D using a wave packet group consisting of three wave packets, the settings of the ultrasonic inspection device Z may be changed so that the defect D is detected using a wave packet group consisting of only two of those three wave packets. In this way, the number of wave packets used can be arbitrarily selected depending on the expected size of the defect D.

[0237] (Example of an image compositing section) An example of the image synthesis unit 282 in Figure 27 is described below. Figure 29 shows an example of the image (synthetic image 290) synthesized by the image synthesis unit 282. This is a synthetic image 290 obtained by synthesizing and superimposing the two images (image 1 and image 2) shown in Figure 27. In the figure, the image shown by the dashed line is image 1, and the image shown by the solid line is image 2. The two images are displayed superimposed in different colors. Only the large defect D1 is shown in image 1. However, both the large defect D2a and the small defect D2b are shown in image 2. The defect D1 and the defect D2a are the same defect D in the inspection object E.

[0238] The image example in Figure 29 corresponds to two defects D of different sizes. The larger defect D is detected in both image 1 and image 2, like defects D1 and D2a. The smaller defect D is detected only in image 2, which has higher detection sensitivity like defect D2b. By displaying images under two types of measurement conditions in this way, the measurer can efficiently detect the defect D in the inspection object E.

[0239] (Eighth Embodiment) The eighth embodiment will be described using Figures 30A and 30B. Figure 30A is a diagram showing the configuration of the image synthesis unit 282 in this embodiment. The two images (image 1 and image 2) generated by the imaging unit 262 are sent to the image synthesis unit 282, and a logical sum (OR) is obtained. Here, the logical sum (OR) is an image processing in which a part where a defect D is detected in at least one of image 1 and image 2 indicates a defect image. In this way, the synthetic image 290 is obtained.

[0240] Figure 30B is a diagram showing an example of the synthetic image 290 obtained with the configuration of Figure 30A. Figure 30B corresponds to Figure 29. In this embodiment, in order to display the synthetic image 290 of the logical sum, if a defect D is detected under either of the two measurement conditions, the defect D is displayed in the synthetic image 290. Therefore, the synthetic image 290 is as shown in Figure 30B. In this way, the defect D can be efficiently detected.

[0241] A third embodiment of an ultrasound examination apparatus Z, which is equipped with a signal synthesis unit 283 instead of an image synthesis unit 282, is described below. Figure 31 shows the configuration of the signal synthesis unit 283 in this embodiment. The signal synthesis unit 283 generates a plurality of signal features corresponding to the frequency components of integration period 1 that generates image 1 and the frequency components of integration period 2 that generates image 2, and synthesizes the plurality of signal features. The signal synthesis unit 283 is provided in the ultrasound examination apparatus Z. The frequency component of integration period 1 that generates image 1 is the first frequency component. The frequency component of integration period 2 that generates image 2 is the second frequency component. Specifically, in the example of this disclosure, the signal synthesis unit 283 generates a new signal feature C from the respective signals A and B that generate the two images (image 1 and image 2). For example, the signal synthesis unit 283 generates the signal feature C by a temporary combination of the two signals A and B according to the following formula. C = aA + bB Here, signals A, B, and C are signals obtained at each measured coordinate, respectively. a and b are appropriate coefficients. The image synthesis unit 282 generates an image showing the defect D by plotting this new signal feature C against the coordinates. In this way, an image showing the defect D can also be generated.

[0242] The coefficients a and b may be input by the operator, for example, or determined by the control device 2 itself. If the control device 2 determines them, the coefficients a and b should be adjusted so that the defect D becomes easier to identify in the image by changing, for example, the contrast or contour of the image showing the defect D.

[0243] (Ninth Embodiment) The ninth embodiment shows a configuration in which multiple accumulation periods are set. Figures 32A and 32B illustrate a method for setting multiple integration periods. Figure 32A shows the frequency spectrum of the received signal of the ultrasonic beam U after passing through the object under inspection E. In the figure, the solid line represents the frequency spectrum in the healthy area N, and the dashed line represents the frequency spectrum in the defective area D. The figure shown in Figure 32A is displayed, for example, on the display device 3. The operator then looks at this frequency spectrum and selects and inputs the appropriate detection frequencies f1 and f2 for detecting the defective area D. For example, the operator can select and input the detection frequencies f1 and f2 that make the difference between the solid line and the dashed line larger. "Making the difference larger" here means, for example, that the difference becomes greater than or equal to a predetermined threshold value when compared with a predetermined threshold value.

[0244] Figure 32B is a two-dimensional map showing the change in the interference function K due to two parameters: frequency and wave packet delay αd. The vertical and horizontal axes are the same as in Figure 25 above. The control device 2 has an internal map of the interference function K as shown in Figure 32B. The frequency selection unit 242 finds the wave packet delay αd1 at the detection frequency f1 where the interference function K is maximized, and the wave packet delay αd2 at the detection frequency f2 where the interference function K is maximized. These wave packet delays αd1 and αd2 are transmitted to the delay time setting unit 213 in the transmission system 210, and the delay time setting unit 213 sets the wave packet delay αd between wave packets constituting the wave packet group. Then, the control device 2 sets integration period 1 to include wave packet 1 and wave packet 2, and sets integration period 2 to include wave packet 2 and wave packet 3, using the integration period setting unit 280 provided in the signal processing unit 250.

[0245] Thus, in this embodiment, the control device 2 is equipped with a map of interference function K (an example of database 281), which allows for the automatic setting of measurement conditions suitable for measurement at desired detection frequencies f1 and f2. Here, the measurement conditions include setting the wave packet delay amount αd between multiple wave packets constituting the wave packet group of burst waves, and multiple integration periods.

[0246] Figure 33 is a block diagram showing the configuration of the ultrasound examination apparatus Z according to the ninth embodiment. The spectrum calculation unit 223 provided in the data processing unit 201 of the control device 2 displays the frequency spectrum shown in Figure 32A on the display device 3.

[0247] Figure 34 shows an example of the display screen 270 displayed on the display device 3. The spectrum display unit 271 of the display device 3 displays the frequency spectrum shown in Figure 32A. The operator refers to this and inputs the appropriate detection frequency fdet using the input device 4. The input device 4 consists of a keyboard or the like. The input information is entered into the reception unit 224 in the data processing unit 201. Here, the delay time setting unit 213 calculates appropriate wave packet delay amounts αd1 and αd2 by referring to the database 281 which contains a map of the interference function K, etc.

[0248] In other words, the control device 2 includes a reception unit 224 that receives input of a detection frequency fdet. From the multiple detection frequencies fdet received, the control device 2 refers to the database 281 to determine the wave packet delay amounts αd1 and αd2, which are information about the wave packet delay times Δtd1 and Δtd2 of multiple wave packets. As described above, the database 281 is a database that associates information about the detection frequency fdet from the receiving probe 121 with information about the wave packet delay times Δtd1 and Δtd2 (for example, wave packet delay amounts αd1 and αd2; wave packet delay times Δtd1 and Δtd2). These multiple wave packet delay amounts αd1 and αd2 are input to the delay time setting unit 213, and a burst wave is generated that repeats the wave packet group composed of multiple wave packets.

[0249] As described above, the data processing unit 201 calculates multiple integration periods (integration period 1 and integration period 2) and outputs them to the integration period setting unit 280. The frequency conversion unit 230 converts the received signal over the set integration period into frequency components based on the integration period set by the integration period setting unit 280.

[0250] (Tenth embodiment. Focal length of the receiving probe 121) In the tenth embodiment, the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. This is even more preferable because, as described below, it becomes possible to detect more components of the scattered wave U1. As mentioned above, the scattered wave U1 is an ultrasonic beam U that has interacted with the defect D, so the more the proportion of the scattered wave U1 component increases, the easier it becomes to detect the defect D.

[0251] Figure 35A schematically shows the propagation path of the ultrasonic beam U in the tenth embodiment when the focal length R1 of the transmitting probe 110 and the focal length R2 of the receiving probe 121 are equal. The receiving probe 121 can detect the ultrasonic beam U within the range of the cone (shape) C2 of the virtual beam virtually emitted from the receiving probe 121. In the example shown in Figure 35A, the convergence point of the ultrasonic beam U transmitted from the transmitting probe 110 and the convergence point of the virtual beam virtually emitted from the receiving probe 121 are the same. Therefore, ultrasonic beam U whose propagation direction does not change at the defect D can be efficiently received. On the other hand, ultrasonic beam U whose propagation direction changes at the defect D becomes difficult to detect.

[0252] Figure 35B schematically shows the propagation path of the ultrasonic beam U in the tenth embodiment when the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. The receiving probe 121 can detect the ultrasonic beam U within the range of the cone (shape) C3 of the virtual beam virtually emitted from the receiving probe 121. Therefore, even scattered waves U1 (not shown in Figure 35B) whose propagation direction has changed slightly at the defect D can be detected if they are within the range of the cone C3. In this way, by making the focal length R2 of the receiving probe 121 longer than the focal length R1 of the transmitting probe 110, the number of detectable scattered waves U1 can be increased. As mentioned above, scattered waves U1 are waves that have interacted with the defect D, so this can further improve the detection performance of the defect D.

[0253] The relative magnitudes of convergence are also defined by the relative magnitudes of the beam incidence areas T1 and T2 on the surface of the object E under inspection. The beam incidence areas T1 and T2 are explained below.

[0254] Figure 36 illustrates the relationship between the beam incidence area T1 at the transmitting probe 110 and the beam incidence area T2 at the receiving probe 121. The beam incidence area T1 at the object under inspection E of the transmitting probe 110 is the intersection area of ​​the ultrasonic beam U emitted from the transmitting probe 110 with the surface of the object under inspection E. The beam incidence area T2 at the receiving probe 121 is the intersection area of ​​a hypothetical ultrasonic beam U2, assuming that ultrasonic beam U is emitted from the receiving probe 121, with the surface of the object under inspection E.

[0255] Note that in Figure 36, the path of the ultrasonic beam U is shown when there is no object under inspection E. When there is an object under inspection E, the ultrasonic beam U is refracted at the surface of the object under inspection E, so the ultrasonic beam U propagates along a different path than the one shown by the dashed line. Here, as shown in Figure 36, the beam incidence area T2 of the receiving probe 121 at the object under inspection E is larger than the beam incidence area T1 of the transmitting probe 110 at the object under inspection E. By doing so, the focusing ability of the receiving probe 121 can be made looser than that of the transmitting probe 110.

[0256] Furthermore, the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. Even in this way, the convergence of the receiving probe 121 can be made looser than that of the transmitting probe 110. In this case, the distance from the object under inspection E to the transmitting probe 110 and the receiving probe 121 is, for example, the same for both, but it does not have to be the same.

[0257] In the example of this disclosure, the convergence of the receiving probe 121 is made looser than that of the transmitting probe 110. That is, the focal length R2 of the receiving probe 121 is set to be longer than the focal length R1 of the transmitting probe 110. As a result, the beam incidence area T2 of the receiving probe 121 is widened, so that a wide range of scattered waves U1 can be detected. This makes it possible for the receiving probe 121 to detect scattered waves U1 even if the propagation path of scattered waves U1 changes somewhat. As a result, a wide range of defects D can be detected.

[0258] Furthermore, the focal point P1 of the receiving probe 121 is located on the side of the transmitting probe 110 (above in the illustrated example) than the focal point P2 of the transmitting probe 110. By shifting the focal points P1 and P2 in this way, the receiving probe 121 can more easily receive the scattered wave U1, and the scattered wave U1 can be more easily detected.

[0259] Furthermore, to configure the receiver probe 121 to have a focal length R2 that is longer than the focal length R1 of the transmitter probe 110, a non-converging probe (not shown) may be used as the receiver probe 121. Since the focal length R2 of a non-converging probe is infinite, it will be longer than the focal length R1 of the transmitter probe 110. In other words, even with a non-converging receiver probe 121, the convergence of the receiver probe 121 will be looser than that of the transmitter probe 110.

[0260] (11th embodiment) In the 11th embodiment, similar to the embodiments shown in Figures 35A, 35B, 36, etc., the beam incidence area T2 of the receiving probe 121 is larger than the beam incidence area T1 of the transmitting probe. This is even more preferable because, as described below, it becomes possible to detect more components of the scattered wave U1. As mentioned above, the scattered wave U1 is an ultrasonic beam U that has interacted with the defect D, so the more the proportion of the scattered wave U1 component increases, the easier it becomes to detect the defect D.

[0261] Figure 37 schematically shows the arrangement of the transmitting probe 110, the object under inspection E, and the receiving probe 121 in the 11th embodiment. In this embodiment, the transmitting probe 110 and the receiving probe 121 have the same focal length. However, the transmitting probe 110, the object under inspection E, and the receiving probe 121 are arranged such that the distance d2 between the receiving probe 121 and the surface of the object under inspection E is shorter than the distance d1 between the transmitting probe 110 and the surface of the object under inspection E. Therefore, the beam incidence area T2 of the receiving probe 121 is larger than the beam incidence area T1 of the transmitting probe 110. As a result, a wide range of scattered waves U1 can be detected. This makes it possible to detect scattered waves U1 with the receiving probe 121 even if the propagation path of the scattered waves U1 changes somewhat. As a result, a wide range of defects D can be detected.

[0262] In this embodiment, the configuration is shown where the focal lengths of the transmitting probe 110 and the receiving probe 121 are the same, but the focal lengths do not need to be equal. By appropriately setting the distance d2 between the receiving probe 121 and the surface of the object E under inspection, the effects of this embodiment can be obtained if the beam incidence area T2 of the receiving probe 121 is wider than the beam incidence area T1 of the transmitting probe 110.

[0263] Thus, if the beam incidence area T2 of the receiving probe 121 is wider than the beam incidence area T1 of the transmitting probe 110, the receiving probe 121 can detect scattered waves U1 over a wide area. As a result, the defect D can be detected efficiently. In this case, the focal lengths of the transmitting probe 110 and the receiving probe 121 may be equal or different.

[0264] (12th embodiment) Figure 38 shows the configuration of the ultrasound inspection apparatus Z in the 12th embodiment. In the 12th embodiment, the transmitting sound axis AX1 of the transmitting probe 110 and the receiving sound axis AX2 of the receiving probe 121 are offset from each other. That is, the receiving probe 121 in the 12th embodiment is a receiving probe 120 (eccentrically positioned receiving probe) having a receiving sound axis AX2 positioned differently from the transmitting sound axis AX1 of the transmitting probe 110. Therefore, the eccentric distance L (distance) between the transmitting sound axis AX1 (sound axis) of the transmitting probe 110 and the receiving sound axis AX (sound axis) of the receiving probe 120 is greater than zero.

[0265] This arrangement allows for the detection of scattered waves U1 whose spatial direction has changed. By combining the principle of extracting frequency-based scattered waves U1 based on the frequency spectrum of the received signal (Figure 10) with the principle of extracting spatial scattered waves U1 based on the eccentric arrangement, the detection performance of the defect D can be further improved.

[0266] In the twelfth embodiment, the receiving probe 120 is positioned offset from the transmitting probe 110 by an eccentric distance L in the x-axis direction of Figure 38, but the receiving probe 120 may be positioned offset in the y-axis direction of Figure 38. Alternatively, the receiving probe 120 may be positioned at L1 in the x-axis direction and L2 in the y-axis direction (i.e., with the position of the transmitting probe 110 in the xy-plane as the origin, the position is (L1, L2)).

[0267] Figure 39A illustrates the transmitting sound axis AX1, the receiving sound axis AX2, and the eccentricity distance L, where the transmitting and receiving sound axes AX1 and AX2 extend vertically. Figure 39B also illustrates the transmitting and receiving sound axes AX1 and AX2 and the eccentricity distance L, where the transmitting and receiving sound axes AX1 and AX2 extend at an angle. For reference, the receiving probe 140 (coaxial receiving probe) is also shown by a dashed line in Figures 39A and 39B.

[0268] The direction of the receiving sound axis AX2 is normal to the transducer surface 114 (Figure 2). This is because the virtual ultrasonic beam U emitted from the receiving probe 121 is emitted in the direction normal to the transducer surface 114. When receiving the ultrasonic beam U, the ultrasonic beam U incident in the direction normal to the transducer surface 114 can be received with high sensitivity.

[0269] The eccentricity distance L is defined as the distance of the deviation between the transmitting sound axis AX1 and the receiving sound axis AX2. Therefore, as shown in Figure 39B, when the ultrasonic beam U emitted from the transmitting probe 110 is refracted, the eccentricity distance L is defined as the distance of the deviation between the refracting transmitting sound axis AX1 and the receiving sound axis AX2. In the ultrasonic inspection apparatus Z of the tenth embodiment, the transmitting probe 110 and the receiving probe 120 are adjusted by an eccentricity distance adjustment unit 105 (Figure 38) which adjusts the eccentricity distance L so that the eccentricity distance L defined in this way is greater than zero.

[0270] Figure 39A shows the case where the transmitting probe 110 is positioned in the direction normal to the surface of the object E under inspection. In Figures 39A and 39B, the transmitting sound axis AX1 is shown by a solid line. The receiving sound axis AX2 is shown by a dashed line. Note that in Figures 39A and 39B, the position of the receiving probe 121 shown by the dashed line is the position where the eccentricity distance L is zero, and the receiving probe 121 where the transmitting sound axis AX1 and the receiving sound axis AX2 coincide is the receiving probe 140 as a coaxial receiving probe. Also, the receiving probe 121 shown by the solid line is the receiving probe 120 (eccentric receiving probe) positioned at an eccentricity distance L greater than zero. When the transmitting probe 110 is installed so that the transmitting sound axis AX1 is perpendicular to the horizontal plane (the xy plane in Figure 38), the propagation path of the ultrasonic beam U does not refract. In other words, the transmitting sound axis AX1 does not refract. This corresponds to the case where the transmitting probe 110 is positioned so that the transmitting sound axis AX1 of the transmitting probe 110 is perpendicular to the mounting surface 1021 of the sample stage 102.

[0271] In this embodiment, the transmitting probe 110 is positioned so that the transmitting sound axis AX1 is normal to the mounting surface 1021 of the object under inspection E on the sample stage 102. As mentioned above, in this case, the transmitting sound axis AX1 is positioned perpendicular to the surface of the object under inspection E in the case of a plate-shaped object under inspection E, which has the effect of making it easier to understand the correspondence between the scanning position and the position of the defect D.

[0272] Figure 39B shows the case where the transmitting probe 110 is positioned at an angle α from the normal direction to the surface of the object under inspection E. In Figure 39B, as in Figure 39A, the transmitting sound axis AX1 is shown as a solid line and the receiving sound axis AX2 is shown as a dashed line. In the example shown in Figure 39B, the propagation path of the ultrasonic beam U is refracted at the refraction angle β at the interface between the object under inspection E and the fluid F. Therefore, the transmitting sound axis AX1 bends (refracts) as shown by the solid arrow in Figure 39B. In this case, the position of the receiving probe 140, shown as a dashed line, is on the transmitting sound axis AX1, so the eccentricity distance L is zero. As mentioned above, even when the ultrasonic beam U is refracted, the receiving probe 120 is positioned so that the distance between the transmitting sound axis AX1 and the receiving sound axis AX2 is L. Note that in the example shown in Figure 38, the transmitting probe 110 is installed in the direction normal to the surface of the object under inspection E, so the eccentricity distance L is as shown in Figure 39A.

[0273] It is even more preferable to set the eccentricity distance L to a position such that the signal strength at the defective part D of the inspected object E is greater than the signal strength at the healthy part N.

[0274] (13th Embodiment) Figure 40 shows the configuration of the ultrasonic inspection apparatus Z in the 13th embodiment. In the 13th embodiment, the scanning measurement device 1 includes an installation angle adjustment unit 106 that adjusts the tilt of the receiving probe 120. This increases the strength of the received signal and improves the signal-to-noise ratio (SNR) of the signal. The installation angle adjustment unit 106 is composed of, for example, an actuator, a motor, etc., although these are not shown in the figures.

[0275] Here, the angle θ between the transmitting sound axis AX1 and the receiving sound axis AX2 is defined as the receiving probe installation angle. In the case of Figure 40, since the transmitting probe 110 is installed vertically, the transmitting sound axis AX1 is vertical, and therefore the angle θ, which is the receiving probe installation angle, is the angle between the transmitting sound axis AX1 (i.e., vertical) and the normal to the transducer surface of the receiving probe 120. Then, the installation angle adjustment unit 106 tilts the angle θ toward the side where the transmitting sound axis AX1 exists, setting the angle θ to a value greater than zero. That is, the receiving probe 120 is positioned at an angle. Specifically, the receiving probe 120 is positioned at an angle such that 0° < θ < 90°, and the angle θ is, for example, 10°, but is not limited to this.

[0276] When the inventors actually performed defect detection on the defective part D with the receiving probe 120 positioned at an angle in this manner, the signal strength of the received signal increased threefold compared to the case where θ=0.

[0277] Furthermore, the eccentricity distance L when the receiving probe 120 is positioned at an angle is defined as follows: Define the intersection point P12 between the receiving sound axis AX2 and the transducer surface of the receiving probe 120. Also define the intersection point P11 between the transmitting sound axis AX1 and the transducer surface of the transmitting probe 110. The eccentricity distance L is defined as the distance between the coordinate position (x4, y4) (not shown) obtained by projecting the position of intersection point P11 onto the xy plane and the coordinate position (x5, y5) (not shown) obtained by projecting the position of intersection point P12 onto the xy plane.

[0278] Figure 41 illustrates the reason for the effect of the 13th embodiment. The scattered wave U1 propagates in a direction away from the transmitting sound axis AX1. Therefore, as shown in Figure 41, when the scattered wave U1 reaches the outside of the object under inspection E, it is incident on the interface between the object under inspection E and the outside at a non-zero angle α2 with respect to the normal vector of the surface of the object under inspection E. The angle of the scattered wave U1 exiting from the surface of the object under inspection E has an angle β2, which is a non-zero exit angle with respect to the normal direction of the surface of the object under inspection E. The scattered wave U1 can be received most efficiently when the normal vector of the transducer surface of the receiving probe 120 is aligned with the direction of propagation of the scattered wave U1. In other words, the received signal strength can be increased by tilting the receiving probe 120.

[0279] Furthermore, the reception effect is highest when the angle β2 of the ultrasonic beam U emitted from the object under inspection E matches the angle θ between the transmitting sound axis AX1 and the receiving sound axis AX2. However, even if angles β2 and θ do not perfectly match, the effect of increasing the received signal can still be obtained, so as shown in Figure 41, angles β2 and θ do not need to perfectly match.

[0280] (14th Embodiment) Figure 42 shows the configuration of the ultrasonic inspection apparatus Z according to the 14th embodiment. In the 14th embodiment, the fluid F is liquid W, which in the illustrated example is water. The ultrasonic inspection apparatus Z inspects the object to be inspected E by injecting an ultrasonic beam U into the object to be inspected E through the liquid W, which is the fluid F. The object to be inspected E is placed below the liquid surface L0 of the liquid W and is immersed in the liquid W.

[0281] Similar to the first embodiment, in this embodiment, the excitation frequency fex is set to a frequency shifted from the natural frequency fres of the transmitting probe 110. Therefore, the scanning measurement device 1 drives the transmitting probe 110 with an excitation frequency fex that is shifted from the natural frequency fres (synonymous with the resonant frequency) of the transmitting probe 110. By setting the excitation frequency fex to an appropriate value, the performance of the ultrasonic inspection device Z in this embodiment can be improved.

[0282] The fluid F may be a gas G (Figure 1) as described above, or a liquid W (Figure 42) as in this embodiment. However, when a gas G such as air is used as the fluid F, it provides even more favorable effects as described above.

[0283] Furthermore, as described above, when a gas G is used as the fluid F, it becomes more difficult to reduce the beam size of the ultrasonic beam U, thus achieving an even greater effect from this disclosure. In this way, this disclosure can obtain more favorable effects when a gas G is used as the fluid F.

[0284] (15th Embodiment) In the above explanation, a sine wave has been used as an example of the wave constituting the wave packet. However, this disclosure is not limited to sine waves. In the burst wave configuration shown in Figure 8 above, wave packets 10 and 11 may be composed of rectangular waves. The effects of this disclosure can be obtained in this case as well. It is clear from equations (4) to (9) above that this disclosure is not limited to sine waves. This is because these equations hold for any waveform, not just sine waves, of the wave packet 10. In other words, the interference function K shown in equation (9) holds true even if each wave packet is not a sine wave.

[0285] Figure 43 shows the hardware configuration of the control device 2. Each of the above-mentioned configurations, functions, and parts constituting the block diagram may be implemented in hardware, or in whole, for example, by designing them as integrated circuits. Alternatively, as shown in Figure 43, each of the above-mentioned configurations, functions, etc., may be implemented in software by having a processor such as the CPU 252 interpret and execute programs that realize each function. The control device 2 includes, for example, a memory 251, a CPU 252, a storage device 253 (SSD, HDD, etc.), a communication device 254, and an I / F 255. Information such as programs, tables, and files that realize each function can be stored in memory, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC (Integrated Circuit) card, an SD (Secure Digital) card, or a DVD (Digital Versatile Disc), in addition to being stored in the HDD.

[0286] Figure 44 is a flowchart showing the ultrasonic inspection method for each of the embodiments described above. The ultrasonic inspection method of this disclosure can be executed by the control device 2 of the ultrasonic inspection apparatus Z described above, and will be explained with reference to Figure 24, etc., as an example. The ultrasonic inspection method of this disclosure inspects the object to be inspected (Figure 1) by injecting an ultrasonic beam U into the object to be inspected (Figure 1) through a gas G (Figure 1; an example of fluid F). Although the embodiment in which this ultrasonic inspection method uses gas G as fluid F will be described, it goes without saying that this ultrasonic inspection method is also effective in embodiments in which liquid W is used as fluid F.

[0287] The ultrasound examination method of this disclosure includes steps S100 to S104, S111, and S22. Here, an example is shown in which a burst wave of a wave packet group composed of multiple wave packets is used and multiple integration periods are used.

[0288] First, the user (measurer) inputs the wave packet delay time Δtd between wave packet 1 and wave packet 2 to the delay time setting unit 213, for example, through the input device 4. The delay time setting unit 213 then sets the wave packet delay time Δtd (step S100, delay time setting step). Next, the integration period setting unit 280 sets multiple integration periods (step S101, integration period setting step). Integration period 1 includes wave packet 1 and wave packet 2. Integration period 2 includes wave packet 1 only.

[0289] Next, at the command of the control device 2, the transmitting probe 110 performs step S102 (emission step) in which it emits an ultrasonic beam U from the transmitting probe 110. In step S102, the transmitting probe 110 emits an ultrasonic beam U by applying a voltage waveform that repeats a group of wave packets, each having a wave packet 10 and a wave packet 11, and the wave packet delay time Δtd between wave packet 10 (first wave packet) and wave packet 11 (second wave packet) is arbitrarily set. Wave packet 10 (first wave packet) is a wave packet with a fundamental frequency f0, which is the excitation frequency fex of the transmitting probe 110 emitting the ultrasonic beam U, and a wave number of 2 or more. Wave packet 11 (second wave packet) is a wave packet with a wave number of 2 or more.

[0290] Next, in step S103 (receiving step), the receiving probe 121 receives the ultrasonic beam U.

[0291] Subsequently, the frequency conversion unit 230 converts the signal of the ultrasonic beam U received by the receiving probe 121 (e.g., waveform signal) into frequency components (frequency conversion) based on the signal of the ultrasonic beam U received by the receiving probe 121 (step S104, frequency component conversion step).

[0292] In step S104, the ultrasonic beam U signal received in step S103 is converted into frequency component 1 (an example of a first conversion period) with the time including at least wave packet 10 as integration period 1 (an example of a first conversion period). At the same time, the ultrasonic beam U signal received in step S103 is converted into frequency component 2 (an example of a second conversion period) with the time including at least wave packet 11 as integration period 2 (an example of a second conversion period). As a result, multiple types of frequency components are obtained corresponding to multiple integration periods. In other words, two types of frequency components are obtained: frequency component 1 obtained from integration period 1 and frequency component 2 obtained from integration period 2. Note that at least one of integration periods (an example of a conversion period) among integration period 1 or integration period 2 includes multiple wave packets. In the example of this disclosure, integration period 1 includes multiple wave packets 10, 11.

[0293] The scanning position information of the transmitting probe 110 and the receiving probe 121 is transmitted from the position measurement unit 203 to the scan controller 204. The data processing unit 201 associates the scanning position information of the transmitting probe 110 obtained from the scan controller 204 with the above-mentioned multiple frequency components (frequency component 1 and frequency component 2) and stores them in the storage unit 261.

[0294] The data processing unit 201 determines whether the scan is complete or not (step S111). If the scan is complete (Yes), the control device 2 proceeds to step S22. If the scan is not complete (No), the data processing unit 201 outputs a command to the drive unit 202 to move the transmitting probe 110 and the receiving probe 121 to the next scan position (step S112), and returns to step S102.

[0295] Next, we will describe step S22 (image processing step). Step S22 includes steps S120 to S122. Immediately after step S111 and immediately before step S120, the storage unit 261 stores multiple types of frequency components (frequency component 1 and frequency component 2) corresponding to multiple integration periods.

[0296] Then, the data processing unit 201 performs step S120 (signal intensity calculation step) to detect the tail component W3 of the fundamental band W1 from the converted frequency components and generate signal intensity data. Therefore, in step S120, the tail component W3 of the fundamental band W1 in the signal of the ultrasonic beam U is detected. As a method for generating signal intensity data, in this embodiment, a time-domain waveform h(t) is reconstructed from the converted frequency components using the above equations (2) and (3) for an appropriate frequency range, and the peak-to-peak signal of this h(t) is used. This is the difference between the maximum and minimum values ​​of the signal. In step S120, signal strength data is generated from each of the multiple types of frequency components (frequency component 1 and frequency component 2). That is, two types of signal strength data are generated: signal strength data 1 and signal strength data 2.

[0297] Next, in step S121 (signal synthesis step), these two types of signal intensity data are appropriately combined to generate synthesized signal intensity data. Next, step S122 (shape display step) is performed. The combined signal intensity data at each scanning position is plotted against the scanning position information stored in the memory unit 261. In this way, the combined signal intensity data is visualized, and the shape of the defective part D is displayed.

[0298] Steps S121 and S122 may be treated as a single step. For example, using the two types of signal intensity data (signal intensity data 1 and signal intensity data 2) generated in step S120, image 1 may be generated from signal intensity data 1 and image 2 from signal intensity data 2. These two images may then be displayed superimposed. When displaying them superimposed, it is even preferable to display images 1 and 2 in different colors from each other, as this improves visibility.

[0299] According to the ultrasonic inspection apparatus Z and ultrasonic inspection method described above, the detection performance of defective parts D, such as the ability to detect minute defects, can be improved.

[0300] In the embodiments described above, the defective part D is described as a cavity, but the defective part D may also be a foreign substance made of a different material from the material of the object E under inspection. In this case as well, since there is a difference in acoustic impedance (Gap) at the interface where different materials come into contact, scattered waves U1 are generated, and the configurations of the embodiments described above are effective. The ultrasonic inspection apparatus Z according to the embodiments described above is based on an ultrasonic defect imaging apparatus, but it may also be applied to a non-contact in-line internal defect inspection apparatus.

[0301] This disclosure is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail for the purpose of explaining this disclosure, and are not necessarily limited to having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0302] Furthermore, in each embodiment, only those control lines and information lines deemed necessary for explanation are shown, and not all control lines and information lines are necessarily shown in the actual product. In practice, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0303] 1. Scanning measurement device 10 wave packet (1st wave packet) 100 Transmitting Probes 101 cabinets 102 Sample stage 1021 Mounting surface 103 Transmitting probe scanning unit 104 Receiving probe scanning unit 105 Eccentric distance adjustment section 106 Installation angle adjustment section 11 Wave packet (second wave packet) 110 Transmitting Probe 111 Oscillator 112 Backing 113 Matching layer 114 Probe surface 115 Transmitter Probe Housing 116 Connector 117 Lead wire 118 Lead wires 12 wave packet 120 Receiving probe 121 Receiving probe 140 receiving probes 2 Control device 201 Data Processing Unit 202 Drive Unit 203 Position Measurement Unit 204 Scan Controller 210 Transmission System 211 Waveform Generator 212 Signal Amplifier 213 Delay time setting section 220 Receiving System 222 Signal Amplifier 223 Spectrum Calculation Unit 224 Reception Department 230 Frequency conversion section 240 Frequency Selection Section 242 Frequency Selection Section 250 Signal Processing Unit 261 Storage section 262 Image Processing Unit 263 Display section 270 display screen 271 Spectrum display section 272 Detection frequency specification section 273 images 274 Update button 275 Wave packet delay input section 276 Defective Image Display Unit 277 Interference Function Display Section 280 Accumulation Period Setting Section 281 Databases 282 Image Synthesis Unit 283 Signal Synthesis Unit 290 Composite Images 3 Display device 4 Input devices S100 Step (Delay Time Setting Step) S101 Step (Accumulation Period Setting Step) S102 Step (Release Step) S103 Step (Receiving Step) S104 Step (Frequency Component Conversion Step) S111 Step S112 Step S120 Step (Signal strength calculation step) S121 Step (Signal Synthesis Step) S122 Step (Shape Indication Step) S22 Step (Image Processing Step)

Claims

1. An ultrasonic inspection apparatus that inspects an object to be inspected by injecting an ultrasonic beam into the object to be inspected via a fluid, The system comprises a scanning and measuring device that scans and measures the ultrasonic beam on the object to be inspected, and a control device that controls the operation of the scanning and measuring device, The scanning measurement device is The system comprises a transmitting probe that emits the ultrasonic beam, and a receiving probe that is installed on the opposite side of the object to be inspected from the transmitting probe and receives the ultrasonic beam. The transmitting probe has a plurality of wave packets, including a first wave packet with a wavenumber of 2 or more at a fundamental frequency which is the excitation frequency of the transmitting probe, and a second wave packet with a wavenumber of 2 or more. An ultrasonic beam is emitted when a voltage waveform is applied to repeat a group of wave packets, the wave packet delay time between the first wave packet and the second wave packet is arbitrarily set. The control device includes a signal processing unit, The signal processing unit includes a frequency conversion unit that converts the received signal from the receiving probe into a first frequency component, with a time including at least the first wave packet being the first conversion target period, and converts it into a second frequency component, with a time including at least the second wave packet being the second conversion target period. At least one of the first or second conversion target period includes a plurality of wave packets. Ultrasound examination device.

2. The ultrasonic inspection apparatus according to claim 1, characterized in that at least one wave packet among the wave packets included in each of the first and second conversion target periods is different.

3. The ultrasonic inspection apparatus according to claim 1, further comprising a signal synthesis unit that generates a plurality of signal feature quantities corresponding to each from the first frequency component and the second frequency component, and synthesizes the plurality of signal feature quantities.

4. The ultrasound inspection apparatus according to claim 1, further comprising an image synthesis unit that generates a plurality of signal feature quantities corresponding to the first frequency component and the second frequency component, and synthesizes an image generated from the plurality of signal feature quantities.

5. An ultrasonic inspection apparatus that inspects an object to be inspected by injecting an ultrasonic beam into the object to be inspected via a fluid, The system comprises a scanning and measuring device that scans and measures the ultrasonic beam on the object to be inspected, and a control device that controls the operation of the scanning and measuring device, The scanning measurement device is The system comprises a transmitting probe that emits the ultrasonic beam, and a receiving probe that is installed on the opposite side of the object to be inspected from the transmitting probe and receives the ultrasonic beam. The transmitting probe has a plurality of wave packets, including a first wave packet with a wavenumber of 2 or more at the fundamental frequency which is the excitation frequency of the transmitting probe, a second wave packet with a wavenumber of 2 or more, and a third wave packet with a wavenumber of 2 or more. An ultrasonic beam is emitted when a voltage waveform is applied to repeat a group of wave packets, the wave packet delay time between the first wave packet and the second wave packet and the wave packet delay time between the second wave packet and the third wave packet is arbitrarily set. The control device includes a signal processing unit, The signal processing unit includes a frequency conversion unit that converts the received signal from the receiving probe into frequency components. Ultrasound examination device.

6. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the scanning measurement device includes a delay time setting unit for setting the wave packet delay time of the plurality of wave packets.

7. The ultrasonic inspection apparatus according to claim 6, characterized in that the signal processing unit includes a database relating information on the detection frequency by the receiving probe to information on the wave packet delay time.

8. The ultrasonic inspection apparatus according to claim 5, characterized in that the frequency conversion unit converts the received signal of the receiving probe into a first frequency component with a time period including at least one of the first wave packet, the second wave packet, or the third wave packet as the first conversion target period, and converts it into a second frequency component with a time period including at least one of the first wave packet, the second wave packet, or the third wave packet, and a wave packet different from the wave packet included in the first conversion target period as the second conversion target period.

9. The frequency conversion unit converts the received signal from the receiving probe into a first frequency component, with the time period including at least one of the first wave packet, the second wave packet, or the third wave packet being the first conversion period, and converts the time period including at least one of the first wave packet, the second wave packet, or the third wave packet, and a wave packet different from the wave packet included in the first conversion period, into a second frequency component, with the time period including the second conversion period. The ultrasonic inspection apparatus according to claim 5, further comprising a signal synthesis unit that generates a plurality of signal feature quantities corresponding to each from the first frequency component and the second frequency component, and synthesizes the plurality of signal feature quantities.

10. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the signal processing unit detects a tail component different from the fundamental frequency of the wave packet from the frequency domain signal output from the frequency conversion unit, within the range of the fundamental wave band, which is the range of frequency components that extend before and after the fundamental frequency.

11. The ultrasonic inspection apparatus according to claim 1 or 5, wherein the control device includes a receiving unit for receiving input of detection frequencies, and determines information regarding the wave packet delay times of the plurality of wave packets by referring to a database that associates information regarding the detection frequencies from the receiving probe with information regarding the wave packet delay times from the plurality of detection frequencies received.

12. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the beam incidence area of ​​the receiving probe is larger than the beam incidence area of ​​the transmitting probe.

13. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the receiving probe is a non-converging type receiving probe.

14. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the full width at half maximum of the frequency spectrum of the fundamental wave band, which is the range of frequency components that extend before and after the fundamental frequency, is 50% or less of the fundamental frequency of the wave packet.

15. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the wave number of the first wave packet is 30 or less.

16. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the frequency detected by the signal processing unit includes frequencies in the range of (f0 ± 0.25f0), where f0 is the fundamental frequency of the first wave packet.

17. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that each of the plurality of wave packets has a different fundamental frequency.

18. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the distance between the sound axis of the transmitting probe and the sound axis of the receiving probe is greater than zero.

19. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the fluid is a gas.

20. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the transmitting probe emits the ultrasonic beam when the voltage waveform having the wave packet delay time, which is the time between the plurality of wave packets, is applied to it, and the frequency component is greater than the frequency component when the wave packet delay time is zero.

21. The ultrasonic inspection apparatus according to claim 1 or 5, characterized in that the detection frequency of the ultrasonic beam by the receiving probe is different from the fundamental frequency.

22. An ultrasonic inspection method for inspecting an object to be inspected by injecting an ultrasonic beam into the object to be inspected via a fluid, An emission step in which an ultrasonic beam is emitted by applying a voltage waveform that repeats a group of wave packets, each having a first wave packet with a wavenumber of 2 or more at a fundamental frequency which is the excitation frequency of a transmitting probe that emits an ultrasonic beam, and a second wave packet with a wavenumber of 2 or more, wherein the wave packet delay time between the first wave packet and the second wave packet is arbitrarily set. The receiving step of receiving the ultrasonic beam, The frequency component conversion step includes converting the signal of the ultrasonic beam received in the receiving step into a first frequency component with a time including at least the first wave packet as the first conversion target period, and converting it into a second frequency component with a time including at least the second wave packet as the second conversion target period, At least one of the first or second conversion target period includes a plurality of wave packets. An ultrasound examination method characterized by the following features.

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