Acoustic superstructure-based internal defect detection system and method of detecting the same

Abstract

The application relates to the field of ultrasonic nondestructive testing, in particular to an internal defect detection system based on an acoustic superstructure and a detection method thereof. The detection system comprises a host computer, a signal generating receiver, a pulse signal generating receiver, a scanning mechanism and an ultrasonic sensor. The ultrasonic sensor comprises a planar piezoelectric element and an acoustic superstructure array. The planar piezoelectric element is bonded with the acoustic superstructure array, and the acoustic superstructure array is closely attached to the surface of a measured piece through a coupling agent. The host computer is used for controlling the signal generating receiver and driving the pulse signal generating receiver to excite the planar piezoelectric element to generate planar ultrasonic waves. The host computer is also used for controlling the scanning mechanism to drive the ultrasonic sensor to perform ultrasonic scanning along the surface of the measured piece, so as to detect the internal defects of the measured piece. The application does not need to rely on a coupling wedge or a curved piezoelectric element, can simplify the structure and cost of the detection system, and significantly improves the defect detection efficiency and resolution.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic nondestructive testing technology, and particularly relates to an internal defect detection system and method based on acoustic superstructure. Background Technology

[0002] Ultrasonic nondestructive testing (NDT) technology, due to its advantages such as strong penetration, excellent directivity, and non-destructive testing process, has been widely used in industrial fields such as aerospace, rail transportation, pressure vessels, and petrochemicals. Traditional ultrasonic testing methods typically employ conventional single-probe or ultrasonic phased array sensors. In actual testing, especially when dealing with typical structural defects such as grooves, cracks, and welds, coupling wedges are often required to achieve good acoustic wave coupling. However, this approach not only increases the structural complexity of the testing system but also prolongs the ultrasonic wave propagation path, leading to increased signal loss and affecting testing efficiency and accuracy.

[0003] Furthermore, traditional single-probe sensors typically rely on curved piezoelectric elements or built-in acoustic lenses to achieve sound field focusing. These auxiliary structures not only increase the design complexity and manufacturing cost of ultrasonic sensors but also limit their adaptability in detecting complex structures. While ultrasonic phased array sensors possess beam deflection capabilities, their control systems are complex and costly.

[0004] In recent years, acoustic metamaterials, as artificial composite materials composed of subwavelength-scale unit structures arranged in a specific manner, have demonstrated a powerful ability to manipulate sound waves, including sound field focusing, deflection, and filtering. Acoustic superlenses based on acoustic metamaterials can achieve flexible manipulation of sound waves at the subwavelength scale, possessing properties not found in natural materials such as equivalent negative elastic modulus and equivalent negative mass density. Therefore, they show broad application prospects in fields such as ultrasonic imaging, non-destructive testing, and underwater acoustic detection.

[0005] Although acoustic metamaterials have significant advantages in sound field manipulation, how to organically integrate acoustic metamaterials with existing ultrasonic testing technologies to achieve efficient sound field manipulation and defect detection with low cost and simplified system structure remains an urgent technical problem to be solved. Summary of the Invention

[0006] In view of this, the present invention aims to provide an internal defect detection system and method based on acoustic superstructure, so as to solve the problems of existing ultrasonic detection technology, such as system complexity, large signal loss, insufficient sound field control capability and high cost.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: An internal defect detection system based on acoustic superstructure includes a host computer, a signal generator and receiver, a pulse signal generator and receiver, a scanning mechanism, and an ultrasonic sensor; wherein, The ultrasonic sensor is connected to the scanning mechanism, the host computer is connected to the signal generator and receiver and the scanning mechanism respectively, the signal generator and receiver is connected to the pulse signal generator and receiver and the pulse signal generator and receiver is connected to the planar piezoelectric element; The ultrasonic sensor includes a planar piezoelectric element and an acoustic metastructure array. The planar piezoelectric element is bonded to the acoustic metastructure array, and the acoustic metastructure array is tightly attached to the surface of the test object through a coupling agent. The host computer is used to control the signal generator receiver, drive the pulse signal generator receiver to excite the planar piezoelectric element to generate planar ultrasonic waves; the host computer is also used to control the scanning mechanism, drive the ultrasonic sensor to perform ultrasonic scanning along the surface of the workpiece to detect internal defects in the workpiece.

[0008] Furthermore, the acoustic metastructure array can be a focusing array structure, a deflection array structure, or an oblique focusing array structure.

[0009] Furthermore, the acoustic superstructure array is a one-dimensional or two-dimensional array composed of two-layer superstructure units.

[0010] Furthermore, the dual-layer superstructure unit includes a vertically stacked rigid layer and a flexible layer. The flexible layer is bonded to a planar piezoelectric element, and the rigid layer is tightly bonded to the surface of the test piece via a coupling agent.

[0011] Furthermore, the rigid layer and the flexible layer are integrally formed using multi-material additive manufacturing technology, or the rigid layer and the flexible layer are formed separately and then bonded together.

[0012] Furthermore, the scanning mechanism can be a multi-degree-of-freedom robotic arm, a mobile platform, or a multi-degree-of-freedom motion mechanism.

[0013] An internal defect detection method, implemented using the aforementioned internal defect detection system, includes the following steps: S1: The host computer controls the signal generator and receiver to drive the pulse signal generator and receiver to excite the planar piezoelectric element to generate planar ultrasonic waves; S2: The planar ultrasonic wave is modulated by the acoustic superstructure array to form an ultrasonic wave with a preset sound field distribution, and then propagates into the interior of the test piece. S3: Ultrasonic waves with a preset sound field distribution are reflected by internal defects in the test piece to form defect reflection signals. The defect reflection signals are captured by the ultrasonic sensor, then modulated by the gain of the pulse signal generator receiver, and fed back to the signal generator receiver. The signal generator receiver then uploads the signals to the host computer. S4: The upper computer controls the scanning mechanism to drive the ultrasonic sensor to move along the surface of the test piece and collect defect reflection signals at different positions of the internal defects of the test piece; S5: Determine the size of the internal defects in the test piece based on all the defect reflection signals collected.

[0014] Furthermore, for each scanning position, multiple sets of defect reflection signals are acquired and averaged.

[0015] Furthermore, the maximum amplitude of the reflection signal of each defect is extracted, and the size of the internal defects in the test piece is calibrated by the half-wave height method.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) Simplify the structure of the detection system and reduce signal loss: The present invention utilizes an acoustic superstructure array to directly achieve sound field focusing or beam deflection without the need for additional coupling wedges, shortening the propagation path of ultrasonic waves, reducing the attenuation of ultrasonic energy, and reducing the structural complexity and assembly difficulty of the detection system.

[0017] (2) Reduce the cost of sensor development and manufacturing: The present invention adopts a planar piezoelectric element combined with an acoustic superstructure array to replace the traditional curved piezoelectric element or built-in acoustic lens scheme. The piezoelectric element can use a standard planar wafer, which greatly reduces the processing difficulty and manufacturing cost of ultrasonic sensors.

[0018] (3) Possesses multi-dimensional sound field control capability: By designing acoustic superstructure arrays of different configurations (focusing type, deflection type, oblique focusing type, etc.) and adopting one-dimensional or two-dimensional arrangement, the present invention can flexibly adapt to the sound field control requirements of a single plane or spatial domain, realize precise control of the sound beam focusing position, deflection angle and energy distribution, thereby adapting to the detection of internal defects of different types and depths.

[0019] (4) Improve detection efficiency and defect identification resolution: The subwavelength modulation characteristics of the acoustic superstructure array enable ultrasonic energy to be highly focused in the defect area, which significantly improves the signal-to-noise ratio and amplitude of the defect reflection signal; combined with the automated scanning mechanism, it can realize large-scale and efficient detection of the test piece. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the internal defect detection system described in the embodiments of the present invention; Figure 2This is a schematic diagram of the one-dimensional arrangement of the double-layer superstructure unit described in the embodiment of the present invention; Figure 3 A schematic diagram of the two-dimensional arrangement of the double-layer superstructure unit described in the embodiment of the present invention; Figure 4 A schematic diagram of the structure of the double-layer superstructure unit described in the embodiment of the present invention; Figure 5 A schematic diagram of the focused acoustic superstructure array described in the embodiment of the present invention; Figure 6 A schematic diagram of the focused acoustic field of the focused acoustic superstructure array described in the embodiment of the present invention; Figure 7 A schematic diagram of the deflection-type acoustic superstructure array described in the embodiment of the present invention; Figure 8 A schematic diagram of the deflection acoustic field of the deflection acoustic superstructure array described in the embodiment of the present invention; Figure 9 A schematic diagram of the oblique focusing acoustic superstructure array described in the embodiment of the present invention; Figure 10 A schematic diagram of the oblique focusing acoustic field of the oblique focusing acoustic superstructure array described in the embodiment of the present invention; Figure 11 This is a schematic diagram showing the height of the flexible layer at various positions in the acoustic superstructure array with different configurations when using a one-dimensional arrangement, as described in the embodiments of the present invention; wherein, the center of the length L of the acoustic superstructure array is taken as the zero point, the position of the double-layer superstructure unit to the left of the zero point is negative, and the position of the double-layer superstructure unit to the right of the zero point is positive. Figure 12 A schematic diagram showing the relationship between the time delay of the double-layer superstructure unit and the height ratio r of the flexible layer in an embodiment of the present invention; Figure 13 This is a schematic diagram of the time delay distribution of the focusing acoustic superstructure array described in the embodiment of the present invention; wherein, the relative distance refers to the distance between the two-layer superstructure units on both sides of the center of the length of the focusing acoustic superstructure array as the zero point. Figure 14 A schematic diagram showing the comparison results of defect reflection signals acquired by the ultrasonic sensor based on acoustic metastructure described in the embodiment of the present invention and a conventional single-probe sensor; Figure 15 This is a schematic diagram showing the comparison between the amplitude of the defect reflection signal and the length of the test piece obtained by the ultrasonic sensor based on acoustic metastructure and the conventional single-probe sensor described in the embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Host computer; 2. Signal generator and receiver; 3. Pulse signal generator and receiver; 4. Scanning mechanism; 5. Ultrasonic sensor; 51. Planar piezoelectric element; 52. Acoustic superstructure array; 521. Double-layer superstructure unit; 522. Hard layer; 523. Flexible layer; 6. Test piece; 61. Internal defect. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] like Figure 1As shown, this invention provides an internal defect detection system based on acoustic superstructure, including a host computer 1, a signal generator receiver 2, a pulse signal generator receiver 3, a scanning mechanism 4, and an ultrasonic sensor 5. The host computer 1 is connected to the signal generator receiver 2 via a USB data cable, providing power and an excitation signal to the signal generator receiver 2. The signal generator receiver 2 is connected to the pulse signal generator receiver 3 via a BNC data cable, transmitting the excitation signal generated by the host computer 1 to the pulse signal generator receiver 3. The pulse signal generator receiver 3 is connected to the ultrasonic sensor 5 via a BNC data cable, transmitting the excitation signal to the ultrasonic sensor 5, causing the ultrasonic sensor 5 to generate ultrasonic waves with a preset sound field distribution that propagate into the interior of the test piece 6. After reflection by the internal defect 61 of the test piece 6, a defect reflection signal is formed. The pulse signal generator receiver 3 also receives the defect reflection signal collected by the ultrasonic sensor 5, performs gain modulation on the defect reflection signal, and feeds back the gain-modulated defect reflection signal to the signal generator receiver 2, which then uploads it to the host computer 1. The host computer 1 is also connected to the scanning mechanism 4 via a USB data cable to send motion control commands to the scanning mechanism 4. The scanning mechanism 4 drives the ultrasonic sensor 5 to move on the surface of the workpiece 6 to achieve ultrasonic scanning.

[0028] The scanning mechanism 4 of this invention can be a multi-degree-of-freedom robotic arm, a multi-degree-of-freedom motion platform, or other device capable of carrying an ultrasonic sensor 5 for mobile scanning. Taking a multi-degree-of-freedom robotic arm as an example, the end effector of the multi-degree-of-freedom robotic arm can be equipped with a clamp to hold and fix the ultrasonic sensor 5. Of course, this invention is not limited to this fixing method, and other methods can also be used to fix the ultrasonic sensor 5.

[0029] The ultrasonic sensor 5 is based on an acoustic metastructure. The ultrasonic sensor 5 includes a planar piezoelectric element 51 and an acoustic metastructure array 52. ​​The planar piezoelectric element 51 generates planar ultrasonic waves under excitation by an excitation signal, and the acoustic metastructure array 52 modulates the sound field of the planar ultrasonic waves to form ultrasonic waves with a preset sound field distribution. The planar piezoelectric element 51 is tightly connected to the acoustic metastructure array 52 by adhesive bonding to ensure stable propagation of the ultrasonic waves. The acoustic metastructure array 52 is tightly attached to the surface of the test piece 6 using a coupling agent, thereby propagating the ultrasonic waves with the preset sound field distribution formed after sound field modulation into the interior of the test piece 6.

[0030] The internal defect 61 of the test piece 6 can be a regular shape (such as a rectangle, circle, square, triangle or polygon) or an irregular shape (such as corrosion pit or processing damage). The length of the test piece 6 along the scanning direction is d, where d is any positive number. In this embodiment, for ease of explanation, d = 16 mm is taken.

[0031] like Figure 5 As shown, the acoustic superstructure array 52 is composed of a double-layer superstructure unit 521. The double-layer superstructure unit 521 can be arranged in one-dimensional or two-dimensional manner. Figure 2 As shown, when a one-dimensional arrangement is used, it is composed of N double-layer superstructure units 521 arranged along a straight line. N is a positive integer, the spacing between two adjacent double-layer superstructure units 521 is p, and the width of each double-layer superstructure unit 521 is s. In this embodiment, N=100, p=0.2mm, and s=0.5mm. It should be noted that the value of N can be any positive integer, and the values ​​of p and s can be any values. The above values ​​are only illustrative and do not constitute a limitation on the present invention. Figure 3 As shown, when arranged in two dimensions, it consists of M rows and N columns of double-layer superstructure units 521, with a spacing of m between each row of double-layer superstructure units 521. In this embodiment, M=N=100, W=5mm, m=0.3mm, and p=0.2mm. It should be noted that the values ​​of M and N can be any positive integers, the value of W can be any positive number, and the value of m can be any value. The above values ​​are merely illustrative and do not constitute a limitation on the present invention.

[0032] like Figure 4 As shown, the double-layer superstructure unit 521 includes a vertically stacked rigid layer 522 and a flexible layer 523. The flexible layer 523 is bonded to the planar piezoelectric element 51, and the rigid layer 522 is tightly bonded to the surface of the test piece 6 via a coupling agent. The rigid layer 522 and the flexible layer 523 are integrally formed using multi-material additive manufacturing (MMAM) technology, or the rigid layer 522 and the flexible layer 523 are formed independently and then bonded together.

[0033] The rigid layer 522 is made of a rigid material, which can be a non-metallic material, an alloy material, or a pure metallic material. Non-metallic materials include, but are not limited to, resin, ceramics, and glass. Pure metallic materials include, but are not limited to, steel, aluminum, gold, silver, and copper. Alloy materials include, but are not limited to, aluminum alloys, copper alloys, zinc alloys, magnesium alloys, and titanium alloys. In this embodiment, resin material is preferably used as the rigid layer 522, and it is processed using 3D printing technology, which has the advantages of high processing precision, low cost, and ease of forming complex structures. The flexible layer 523 is made of a rubber material, which includes, but is not limited to, silicone, nitrile rubber, neoprene rubber, or a combination of two or more components. The rubber material can also be a composite material with elastic deformation capabilities. In this embodiment, silicone material is preferably used as the flexible layer 523, utilizing its excellent elastic deformation capabilities and low sound propagation speed to achieve precise control of sound wave propagation time.

[0034] By designing the height of the flexible layer 523 at different locations, the time delay of each double-layer superstructure unit 521 can be adjusted to obtain the time delay distribution of the entire ultrathin acoustic superstructure array, thereby achieving different target sound field control functions. The target sound field control functions include sound field focusing, sound field deflection, and sound field oblique focusing.

[0035] When the time delay distribution of an ultrathin acoustic metastructure array corresponds to the sound field focusing function, the ultrathin acoustic metastructure array is a focusing array structure, such as... Figure 5 As shown, the focusing acoustic metastructure array acts like an optical convex lens, causing planar ultrasonic waves to converge during propagation, forming a focused sound field, such as... Figure 6 As shown, this can improve the detection sensitivity of minute defects.

[0036] When the time delay distribution of an ultrathin acoustic metastructure array corresponds to the sound field deflection function, the ultrathin acoustic metastructure array is a deflection array structure, such as... Figure 7 As shown, the deflection acoustic superstructure array 52 acts like an optical prism, causing the overall deflection of the planar ultrasonic wave propagation direction, forming a deflection sound field, such as... Figure 8 As shown, it is suitable for detecting tilted defects (such as sloping grooves and sloping cracks) or non-perpendicular incident scenarios, without the need for physical probe rotation.

[0037] When the time delay distribution of an ultrathin acoustic metastructure array corresponds to the oblique focusing function of the sound field, the ultrathin acoustic metastructure array is an oblique focusing array structure, such as... Figure 9 As shown. The oblique-focusing acoustic superstructure array is a combination of a focusing acoustic superstructure array and a deflection acoustic superstructure array. Planar ultrasonic waves not only deflect in direction but also converge along their deflected path, forming an oblique-focusing sound field, such as... Figure 10 As shown, this is suitable for detecting deep defects in complex structures, such as when incident at a non-perpendicular angle and focused on the defect location in a confined space. The specific configuration of the acoustic superstructure array 52 is determined based on the sound field control requirements.

[0038] like Figure 11 As shown, in a one-dimensional arrangement, the height t1 of the flexible layer 523 at different positions corresponding to the acoustic superstructure array realizing the sound field focusing function, sound field deflection function and sound field oblique focusing function is shown.

[0039] Existing acoustic metastructures employ frequency-domain phase design methods, the core idea of ​​which is to generate the desired phase delay in each unit at a specific frequency. Since the phase delay of each unit depends on resonance effects, it exhibits strong frequency dispersion characteristics. When the incident sound wave frequency deviates from the design frequency, the phase deviation of each unit is different, disrupting the pre-designed spatial phase distribution and causing the sound field control function to fail. Therefore, this type of acoustic metastructure can only operate within a single frequency or an extremely narrow bandwidth.

[0040] This invention differs from others by employing a time-domain time delay design method. Its physical essence lies in not directly controlling the phase of the sound wave at a specific frequency, but rather controlling the time delay required for the sound wave to pass through different double-layer superstructure units 521. The time delay for a sound wave to pass through a double-layer superstructure unit 521 is defined as the time taken for the sound wave to sequentially pass through the rigid layer 522 and the flexible layer 523. For a double-layer superstructure unit 521 composed of a rigid layer 522 and a flexible layer 523, the propagation speed of the sound wave in the flexible layer 523 is lower than that in the rigid layer 522. Therefore, by adjusting the height ratio of the flexible layer 523, r = t1 / t (where t is the total height of the double-layer superstructure unit 521 and t1 is the height of the flexible layer 523), the time delay for the sound wave to pass through the double-layer superstructure unit 521 can be continuously changed.

[0041] The time delay is approximately constant over a wide frequency range, depending only on the geometry of the bilayer superstructure unit 521 and the sound velocity of the material, unlike the phase which is linearly related to frequency. Although the phase value changes with frequency, the time delay itself remains constant. Therefore, once the spatial time delay distribution of an acoustic superstructure array designed based on time delay is determined, it can maintain the same wavefront timing relationship at all frequencies, thereby achieving broadband sound field manipulation.

[0042] Specifically, the present invention achieves wideband operation through the following steps: i. Pre-calibrate the relationship between the time delay of the double-layer superstructure unit 521 and the height ratio r of the flexible layer 523.

[0043] For the selected rigid and flexible materials, the relationship curve between the height ratio r of the flexible layer 523 and the time delay is established through simulation or experiment, such as... Figure 12 As shown in the figure, this relationship curve remains constant over a wide frequency range and does not change with the frequency of the incident sound wave.

[0044] ii. Design the time delay distribution of the ultrathin acoustic superstructure array based on the target sound field control function.

[0045] Based on the required acoustic field control functions (such as focusing, deflection, and oblique focusing), the time delay required for each double-layer superstructure unit 521 on the array is designed, resulting in the time delay distribution of the acoustic superstructure array. Taking a focusing acoustic superstructure array as an example, its time delay distribution is as follows: Figure 13 As shown, this time delay distribution is independent of frequency.

[0046] iii. Inversely determine the height t1 of the flexible layer 523 of each double-layer superstructure unit 521.

[0047] Substituting the time delay of each double-layer superstructure unit 521 into the relationship curve between the height proportion r of the flexible layer 523 and the time delay, the height proportion r of the flexible layer 523 in each double-layer superstructure unit 521 is determined in reverse. Then, the height t1 of the flexible layer 523 in each double-layer superstructure unit 521 is calculated using the formula r = t1 / t. Since the total height t of the double-layer superstructure unit 521 is a known quantity, the height t2 of the rigid layer 522 is also determined after calculating the height t1 of the flexible layer 523.

[0048] Through the above design, when the frequency of the incident sound wave changes, although the phase delay of each double-layer superstructure unit 521 changes linearly, the relative time delay relationship between different double-layer superstructure units 521 remains unchanged. Therefore, the wavefront shape (i.e., the equiphase surface shape) of the sound wave remains the same at all frequencies, thereby enabling stable sound field control function over a wide frequency range.

[0049] In existing ultrasonic testing, when using conventional single-probe sensors or phased array sensors to detect defects such as grooves, cracks, and welds, a coupling wedge is usually required to change the incident direction of the sound beam or achieve focusing. This invention directly integrates an acoustic superstructure array 52 (focusing, deflection, or oblique focusing type) into the ultrasonic sensor 5. The acoustic superstructure array 52 controls the propagation behavior of the planar ultrasonic waves (such as focusing and deflection), fundamentally eliminating the need for a coupling wedge. This shortens the ultrasonic wave propagation path, reduces ultrasonic energy loss, and simplifies the structural complexity and assembly difficulty of the detection system.

[0050] Furthermore, achieving sound field focusing using conventional single-probe sensors relies on curved piezoelectric elements or built-in acoustic lenses, which are difficult and costly to manufacture. While ultrasonic phased array sensors can deflect and focus ultrasonic waves, their control systems are complex and the equipment is expensive. This invention achieves deflection and focusing control of ultrasonic waves through an acoustic superstructure array 52, transferring the sound field control function from piezoelectric elements or acoustic lenses to the acoustic superstructure array 52. ​​This allows the use of standard planar piezoelectric elements 51 to generate ordinary planar ultrasonic waves. Compared to curved piezoelectric elements, planar piezoelectric elements 51 do not require curved surface processing, offering advantages such as simple manufacturing and extremely low cost.

[0051] The foregoing details the structure and working principle of the internal defect detection system provided by this invention. This invention also provides an internal defect detection method based on the internal defect detection system, comprising the following steps: S1: The host computer 1 controls the signal generator receiver 2, which drives the pulse signal generator receiver 3 to excite the planar piezoelectric element 51 to generate planar ultrasonic waves.

[0052] The host computer 1 controls the signal generator receiver 2 to send a drive command, which in turn triggers the pulse signal generator receiver 3 to generate a high-voltage pulse. This high-voltage pulse excites the planar piezoelectric element 51, causing it to generate planar ultrasonic waves.

[0053] S2: The planar ultrasonic wave is modulated by the acoustic superstructure array 52 to form an ultrasonic wave with a preset sound field distribution, and then propagates into the interior of the test piece 6.

[0054] The planar ultrasonic wave generated by the planar piezoelectric element 51 propagates to the acoustic metastructure array 52 tightly bonded to it. The acoustic metastructure array 52 utilizes a specific arrangement of its subwavelength-scale double-layer metastructure units 521 to modulate the sound field of the incident planar ultrasonic wave, forming an ultrasonic wave with a preset sound field distribution. For example, if using… Figure 5 The focused acoustic superstructure array 52 shown demonstrates that planar ultrasonic waves are modulated into a focused sound field; if using Figure 7 The deflection-type acoustic superstructure array 52 shown in the diagram modulates planar ultrasonic waves into a sound field with a specific deflection angle. The modulated ultrasonic waves then enter the interior of the test object 6 through a coupling agent.

[0055] S3: Ultrasonic waves with a preset sound field distribution are reflected by the internal defect 61 of the test piece to form a defect reflection signal. The defect reflection signal is captured by the ultrasonic sensor 5, and then modulated by the gain of the pulse signal generator receiver 3, and fed back to the signal generator receiver 2, and then uploaded to the host computer 1 by the signal generator receiver 2.

[0056] When an ultrasonic wave with a preset sound field distribution encounters an internal defect 61 in the test piece 6, it will be reflected to form a defect reflection signal. The defect reflection signal is then received by the ultrasonic sensor 5 via a coupling agent. The defect reflection signal received by the ultrasonic sensor 5 is amplified by the pulse signal generator receiver 3 and fed back to the signal generator receiver 2. The signal generator receiver 2 then uploads the signal to the host computer 1, where it is recorded and stored.

[0057] S4: The upper computer 1 controls the scanning mechanism 4 to drive the ultrasonic sensor 5 to move along the surface of the test piece 6 and collect defect reflection signals at different positions of the internal defect 61 of the test piece 6.

[0058] During the above-mentioned ultrasonic wave transmission and reception process, the host computer 1 synchronously controls the scanning mechanism 4, which moves along a preset path to drive the ultrasonic sensor 5 to perform step-by-step scanning along the surface of the test piece 6, covering the entire length range of the test piece 6.

[0059] To reduce the impact of background noise on the defect reflection signal, R sets of defect reflection signals are continuously acquired at each scanning position and averaged. R is a positive integer, and in this embodiment, R=50.

[0060] S5: Calibrate the size of the internal defect 61 of the tested part 6 based on all the defect reflection signals collected.

[0061] This invention employs a method that relies on defect reflection signals to calibrate the size of the internal defect 61. For example, the half-wave height method (also known as the 6dB method) is used. Specifically, the method involves extracting the location point corresponding to the maximum amplitude of the defect reflection signal at all scanning positions, using the location point corresponding to a 6dB decrease in amplitude at that location point as the defect boundary, and the distance between the two location points as the size parameter of the defect.

[0062] like Figure 14 The image shows a comparison of signals acquired using a conventional single-probe sensor and the ultrasonic sensor 5 of this invention. It can be seen that the ultrasonic sensor 5 acquires a higher amplitude reflected signal and a better signal-to-noise ratio.

[0063] like Figure 15 The figure shows a comparison between the amplitude of the reflected signal and the detection position when using different sensors. The amplitude distribution of the conventional single-probe sensor is wider and the resolution is lower; while the amplitude distribution of the ultrasonic sensor 5 is more concentrated and the peak is sharper.

[0064] Figure 14 The results show a comparison of defect reflection signals acquired under the same detection conditions using a conventional single-probe sensor and the ultrasonic sensor 5 based on an acoustic metastructure array 52 of this invention. It can be seen that using the ultrasonic sensor 5 of this invention significantly improves both the signal-to-noise ratio and amplitude of the defect reflection signal. Figure 15 The comparison curves of the maximum amplitude of the defect reflection signal collected by the two sensors at different positions along the length of the test piece 6 are further shown. By extracting the maximum amplitude of the defect reflection signal at all scanning positions and using the 6dB method, the position and lateral dimension parameters of the internal defect 61 can be accurately determined.

[0065] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0066] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An internal defect detection system based on acoustic metastructures, characterized in that, It includes a host computer, a signal generator and receiver, a pulse signal generator and receiver, a scanning mechanism, and an ultrasonic sensor; among which, The ultrasonic sensor is connected to the scanning mechanism, the host computer is connected to the signal generator and receiver and the scanning mechanism respectively, the signal generator and receiver is connected to the pulse signal generator and receiver and the pulse signal generator and receiver is connected to the planar piezoelectric element; The ultrasonic sensor includes a planar piezoelectric element and an acoustic metastructure array. The planar piezoelectric element is bonded to the acoustic metastructure array, and the acoustic metastructure array is tightly attached to the surface of the test object through a coupling agent. The host computer is used to control the signal generator receiver, drive the pulse signal generator receiver to excite the planar piezoelectric element to generate planar ultrasonic waves; the host computer is also used to control the scanning mechanism, drive the ultrasonic sensor to perform ultrasonic scanning along the surface of the workpiece to detect internal defects in the workpiece.

2. The internal defect detection system according to claim 1, characterized in that, Acoustic superstructure arrays can be focused array structures, deflection array structures, or oblique focused array structures.

3. The internal defect detection system according to claim 1 or 2, characterized in that, Acoustic superstructure arrays are one-dimensional or two-dimensional arrays composed of two-layer superstructure units.

4. The internal defect detection system according to claim 3, characterized in that, The dual-layer superstructure unit consists of a vertically stacked rigid layer and a flexible layer. The flexible layer is bonded to a planar piezoelectric element, while the rigid layer is tightly bonded to the surface of the test piece via a coupling agent.

5. The internal defect detection system according to claim 4, characterized in that, The rigid layer and the flexible layer are integrally formed using multi-material additive manufacturing technology, or the rigid layer and the flexible layer are formed separately and then bonded together.

6. The internal defect detection system according to claim 1, characterized in that, The scanning mechanism is a multi-degree-of-freedom robotic arm, a mobile platform, or a multi-degree-of-freedom motion mechanism.

7. An internal defect detection method, implemented using the internal defect detection system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: The host computer controls the signal generator and receiver to drive the pulse signal generator and receiver to excite the planar piezoelectric element to generate planar ultrasonic waves; S2: The planar ultrasonic wave is modulated by the acoustic superstructure array to form an ultrasonic wave with a preset sound field distribution, and then propagates into the interior of the test piece. S3: Ultrasonic waves with a preset sound field distribution are reflected by internal defects in the test piece to form defect reflection signals. The defect reflection signals are captured by the ultrasonic sensor, then modulated by the gain of the pulse signal generator receiver, and fed back to the signal generator receiver. The signal generator receiver then uploads the signals to the host computer. S4: The upper computer controls the scanning mechanism to drive the ultrasonic sensor to move along the surface of the test piece and collect defect reflection signals at different positions of the internal defects of the test piece. S5: Calibrate the size of the internal defects in the test piece based on all the defect reflection signals collected.

8. The internal defect detection method according to claim 7, characterized in that, In step S4, for each scanning position, multiple sets of defect reflection signals are acquired and averaged.

9. The internal defect detection method according to claim 7, characterized in that, In step S5, the maximum amplitude of the reflection signal of each defect is extracted, and the size of the internal defect of the test piece is calibrated by the half-wave height method.

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