Inspection of ultrasonic testing dead zones using signal integration.

Abstract

To provide a method of detecting an anomaly below a front face in non-destructive inspection of structures.SOLUTION: An ultrasonic inspection system 100 includes an ultrasonic probe 102 configured to direct ultrasound waves 130 into a structure 120 from a front face 122 thereof and receive reflected waves 132 to generate a response signal 108. The system further includes a processor 105 configured to rectify the response signal for generating a rectified signal, integrate a portion of the rectified signal included in a detection time window for calculating an energy sum, and generate output 150 based on the energy sum. The detection time window is restricted to a front face reflection and at least a portion of a near-surface dead zone following the front face reflection.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to the field of non-destructive testing or evaluation of structures. [Background technology]

[0002] Nondestructive testing (NDI) is a technique for inspecting structures without damaging or causing permanent physical changes to them. For example, NDI is used in the aviation industry to inspect aircraft structures for damage or defects during their construction and / or use. Ultrasonic testing is one type of NDI technique. In pulse-echo ultrasonic testing, a probe transmits ultrasonic waves into a structure and detects reflected waves, or echoes, from a reflecting source (e.g., anomalies or imperfections on the surface, bottom, or interior of the structure). The elapsed time between the probe transmitting the ultrasonic wave and receiving the reflected wave indicates the depth location of the reflecting source. A typical probe contains piezoelectric elements (i.e., transducers) that function as both transmitters and receivers. When functioning as a transmitter, the piezoelectric element vibrates in response to an excitation pulse to emit ultrasonic waves. When functioning as a receiver, the piezoelectric element vibrates in response to a reflected wave to generate a response signal. A reverberant vibration, known as ring-down, persists for a certain period of time after the initial vibration. The ring-down of the piezoelectric element creates a dead zone below the surface of the structure, referred to herein as the near-surface dead zone. Efficient detection of anomalies or imperfections located in the near-surface dead zone below the surface of a structure is a challenge in ultrasonic testing. Summary of the Invention

[0003] The present disclosure relates to an improved ultrasonic testing technique that enables inspection of near-surface dead zones. In summary, a probe transmits ultrasonic waves to a structure and receives reflected waves to generate a response signal. The response signal (after rectification) from the probe includes pulses representing reflections from the surface of the structure. The portion of the response signal that falls within a detection time window set to include the surface reflection is integrated to measure the energy of the response signal within the detection time window. Reflections from anomalies or imperfections located just below the surface may overlap with the surface reflection or may be determined as a pulse in the response signal following the surface reflection. By summing the energy of the response signals within the detection time window, anomalies or imperfections in the near-surface dead zone can be detected. As a technical effect, this improved ultrasonic testing technique enables the detection of anomalies or imperfections just below the surface of a structure that cannot be detected using conventional ultrasonic testing.

[0004] One embodiment relates to an ultrasonic inspection system including an ultrasonic probe configured to transmit ultrasonic waves from a surface of a structure to an interior of the structure and to receive reflected waves and generate a response signal. The ultrasonic inspection system further includes a processor configured to rectify the response signal to generate a rectified signal, integrate a portion of the rectified signal that falls within a detection time window to determine an energy sum, and generate an output based on the energy sum. The detection time window is limited to a surface reflection and at least a portion of a near-surface dead zone following the surface reflection.

[0005] In another embodiment, the processor is configured to generate the rectified signal by performing negative half-wave rectification and inversion on the response signal.

[0006] In another embodiment, the processor is configured to generate the rectified signal by performing positive half-wave rectification on the response signal.

[0007] In another embodiment, the processor is configured to generate the rectified signal by performing full-wave rectification on the response signal.

[0008] In another embodiment, the processor is configured to define a null gate preceding the surface reflection and to null the rectified signal within the null gate.

[0009] In another embodiment, the processor is configured to generate C-scan data of the structure based on the energy sum.

[0010] In another embodiment, the ultrasound inspection system further comprises a robotic arm configured to move the ultrasound probe over the structure and a position sensor configured to determine position data of the ultrasound probe.

[0011] In another embodiment, the processor is configured to issue an alert when the energy sum exceeds a threshold.

[0012] In another embodiment, the structure is a composite part.

[0013] In another embodiment, the surface of the composite part is provided with an opaque layer, and the detection time window is set based on the depth of a resin puddle below the surface.

[0014] In another embodiment, the structure is an aircraft part.

[0015] Another embodiment relates to a method for inspecting a structure, the method including: directing ultrasonic waves from a surface of the structure into the structure, receiving reflected waves to generate a response signal, rectifying the response signal to generate a rectified signal, integrating a portion of the rectified signal within a detection time window to determine an energy sum, and generating an output based on the energy sum, the detection time window being limited to a surface reflection and at least a portion of a near-surface dead zone following the surface reflection.

[0016] Yet another embodiment relates to a non-transitory computer-readable medium embodied with program instructions for execution by a processor, the instructions causing the processor to perform a method for inspecting a structure, the method including: directing ultrasonic waves from a surface of the structure into the structure, receiving reflected waves to generate a response signal, rectifying the response signal to generate a rectified signal, integrating a portion of the rectified signal within a detection time window to determine an energy sum, and generating an output based on the energy sum, the detection time window being limited to a surface reflection and at least a portion of a near-surface dead zone following the surface reflection.

[0017] The above-described features, functions, and advantages may be achieved individually in various embodiments or may be combined in yet other embodiments, the details of which will become apparent with reference to the following description and drawings. [Brief explanation of the drawings]

[0018] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which the same reference numerals are used in all the drawings to indicate the same or similar elements, and in which:

[0019] [Figure 1] FIG. 1 is a block diagram of an ultrasound inspection system in an exemplary embodiment. [Figure 2] FIG. 2 is an enlarged view of the surface of the ultrasonic probe and the structure. [Figure 3] 10 is a graph showing a portion of a response signal. [Figure 4] 1 is a flowchart illustrating a method for inspecting a structure in an exemplary embodiment. [Figure 5] 10 is a graph illustrating a response signal in an exemplary embodiment. [Figure 6] 10 is a graph illustrating a rectified signal in an exemplary embodiment. [Figure 7] 10 is a graph illustrating a rectified signal in an exemplary embodiment. [Figure 8] 10 is a graph illustrating a rectified signal in an exemplary embodiment. [Figure 9] 10 is a graph illustrating a detection time window in an exemplary embodiment. [Figure 10] FIG. 2 is another block diagram of an ultrasound inspection system in an exemplary embodiment. [Figure 11] 1 is a cross-sectional view of a composite part in an exemplary embodiment; [Figure 12] 1 is a flowchart illustrating a method for inspecting a structure in an exemplary embodiment. [Figure 13] FIG. 1 illustrates an ultrasonic inspection system positioned adjacent a composite part in an exemplary embodiment. [Figure 14] 10 is a graph illustrating a response signal in an exemplary embodiment. [Figure 15] 10 is a graph illustrating a rectified signal in an exemplary embodiment. [Figure 16] 10 is a graph illustrating a null gate in an exemplary embodiment. [Figure 17] 10 is a graph illustrating a detection time window in an exemplary embodiment. [Figure 18] FIG. 1 illustrates a C-scan display of C-scan data in an exemplary embodiment. [Figure 19] 1 is a flowchart illustrating a method of manufacturing and using an aircraft in accordance with an illustrative embodiment. [Figure 20] 1 is a diagrammatical illustration of an aircraft in an illustrative embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0020] The accompanying drawings and the following description describe several exemplary embodiments. It should be noted that even if aspects are not explicitly described or shown in the present specification, those skilled in the art will be able to create various aspects that implement the principles described herein and are encompassed by the scope of the claims below. Furthermore, all examples described herein are intended to aid in understanding the principles of the present disclosure and should not be construed as limiting. Therefore, the present disclosure is not limited to the embodiments or examples described below, but is limited by the scope of the claims and their equivalents.

[0021] FIG. 1 is a block diagram of an ultrasonic inspection system 100 in an exemplary embodiment. The ultrasonic inspection system 100 includes a device, or a collection of equipment, machines, or subsystems, configured to perform ultrasonic testing (UT) of a structure or specimen. The ultrasonic inspection system 100 can be used to inspect various structures in various industries where it is desirable to detect defects or flaws in the structure, such as in the aircraft, automotive, or construction industries. In this embodiment, the ultrasonic inspection system 100 includes, as subsystems, an ultrasonic probe 102 and a controller 104. The ultrasonic probe 102 (also referred to as an ultrasonic sensor) is a device or component that transmits or emits ultrasonic waves and detects or receives reflected waves or echoes. The ultrasonic probe 102 includes a single piezoelectric element (PZT) 110 or transducer that functions as both a transmitter and a receiver. The controller 104 includes circuits, logic circuits, hardware, means, etc., and is configured to provide excitation signals (i.e., excitation pulses) to the ultrasonic probe 102, process response signals from the ultrasonic probe 102, and perform other functions for ultrasonic measurement. The controller 104 may be implemented on a hardware platform configured with analog and / or digital circuits. The controller 104 (shown in FIG. 1 ) may be implemented on a processor 105 that executes instructions 107 stored in a memory 106. The processor 105 includes a hardware integrated circuit configured to execute the instructions 107. The memory 106 is a non-transitory computer-readable storage medium for storing data, instructions 107, etc., and is accessible by the processor 105. The ultrasonic inspection system 100 may include various other components not shown in FIG. 1 . For example, the ultrasonic inspection system 100 may include a power supply, a network interface, a user interface, etc.

[0022] In this embodiment, the ultrasonic inspection system 100 is described as performing an inspection of a structure 120. The term "structure" is not intended to be limiting, as inspections with the ultrasonic inspection system 100 can be performed on any number of different shapes and sizes of parts or structures, such as, for example, machined forgings, castings, or composite panels. Additionally, inspections can be performed on newly manufactured structures or on existing structures for preventative maintenance purposes. Furthermore, the structure 120 can be made of any number of materials. For example, the structure 120 can be a metallic material (e.g., aluminum), a composite material, etc.

[0023] The structure 120 includes a surface 122 (also referred to as a front wall or front surface) and a bottom surface 124 (also referred to as a rear wall or back surface). In pulse-echo mode, the ultrasonic probe 102 is positioned near the surface 122 and transmits ultrasonic waves 130 from the surface 122 to the interior of the structure 120. The ultrasonic probe 102 may be in contact with the surface 122 or separated from the surface 122 by a delay line. A couplant 112 (e.g., water or other fluid) may be interposed between the surface 122 and the ultrasonic probe 102. The couplant 112 is a substance that facilitates transmission of the ultrasonic waves 130 from the ultrasonic probe 102 to the structure 120. The ultrasonic probe 102 also receives reflected waves 132 (also referred to as reflections, echoes, or echo waves) of the ultrasonic waves 130 reflected by a reflecting source within the structure 120. The ultrasonic probe 102 converts the reflected waves 132 into a response signal 108. The converted response signal is recorded or stored in memory 106 .

[0024] FIG. 2 is an enlarged view of the ultrasonic probe 102 and the surface 122 of the structure 120. When ultrasonic waves 130 are emitted from the ultrasonic probe 102 toward the structure 120, a portion of the ultrasonic waves 130 is reflected by the surface 122 and received by the ultrasonic probe 102, generating a response signal 108. A dead zone detection gap 210 typically exists below the surface 122. This is an area where abnormalities or imperfections previously could not be detected due to ring-down of the ultrasonic probe 102. The depth 212 of the dead zone detection gap 210 varies depending on the frequency of the ultrasonic waves 130, the material of the object being inspected, and other factors. For example, if the signal is 5 MHz and the object being inspected is a composite material, the depth 212 would be less than 0.100 inches from the surface 122. The area below the dead zone detection gap 210 can be detected after ring-down of the ultrasonic probe 102 (i.e., ring-down due to reflection from the surface 122). Thus, the depth location directly below the deadband detection gap 210 is the next inspectable location on the surface 122 and is referred to as the nearest inspectable depth 214 .

[0025] FIG. 3 is a graph 300 illustrating a portion of the response signal 108. Note that the excitation pulse, or initial pulse, applied to the ultrasonic probe 102 is omitted from the graph 300. This portion of the response signal 108 (e.g., an A-scan) shows a surface reflection 302 (also called a front surface reflection) and the time interval following the surface reflection 302. The surface reflection 302 represents the ultrasonic wave 130 reflected from the surface 122 (see FIG. 2) of the structure 120. When the piezoelectric element 110 in the ultrasonic probe 102 receives the surface reflection 302, it vibrates to generate the response signal 108, as shown in FIG. 3. The reverberation of this vibration continues for a certain period of time (called ring-down) after the reception of the surface reflection 302. This results in a dead zone following the surface reflection 302. This dead zone is referred to herein as a near-surface dead zone 304. The near-surface dead zone 304 is the time period following a reflection (e.g., surface reflection 302) during which reverberation or vibration continues in the ultrasonic probe 102 that receives the reflection. For example, the near-surface dead zone 304 may correspond to one, two, three, etc. periods of the response signal 108, depending on the attenuation characteristics of the ultrasonic probe 102. A time point 306 after the near-surface dead zone 304 represents the nearest interrogable depth 214 (see FIG. 2 ) below the surface 122.

[0026] According to the embodiments described herein, the ultrasonic inspection system 100 can detect anomalies or imperfections that fall within the near-surface dead zone 304. Figure 4 is a flowchart illustrating an exemplary embodiment of a method 400 for inspecting a structure 120. The steps of the method 400 are described with reference to the ultrasonic inspection system 100 of Figure 1, but one skilled in the art will understand that the described method may be performed by other systems or equipment. Additionally, the described method steps are not all-inclusive and may include other steps not described. Additionally, the steps illustrated in the flowchart may be performed in a different order.

[0027] First, as shown in FIG. 1, the ultrasonic probe 102 is positioned near the surface 122 of the structure 120 and operated in pulse-echo mode to inspect the structure 120 at that location. In pulse-echo mode, the ultrasonic probe 102 converts electrical pulses into mechanical vibrations. Therefore, the controller 104 (e.g., via a pulser) supplies an excitation pulse to the ultrasonic probe 102. Upon receiving the excitation pulse, the ultrasonic probe 102 transmits, transmits, or transmits ultrasonic waves 130 from the surface 122 of the structure 120 toward the interior (step 402). The ultrasonic waves 130 reflected by the structure 120 return to the ultrasonic probe 102 and are converted into response signals 108. Thus, the ultrasonic probe 102 receives one or more reflected waves 132 and generates a response signal 108 (step 404). The amplitude of the response signal 108 is recorded over time and visually visualized as A-scan data, as shown in FIG. 3.

[0028] The controller 104 receives the response signal 108 from the ultrasonic probe 102 and records or stores the received response signal 108. FIG. 5 is a graph 500 illustrating the response signal 108 in an exemplary embodiment. The graph 500 shows a front wall reflection 302 and a back wall reflection 504, which represent the ultrasound waves 130 reflected from the front surface 122 and the back surface 124, respectively. In FIG. 4, the controller 104 then processes the response signal 108 as follows: The controller 104 rectifies the response signal 108 to generate a rectified or processed signal (step 406). The rectified signal may be a positive-going signal or a negative-going signal, as desired. In one embodiment, the controller 104 performs negative half-wave rectification and inversion on the response signal 108 to generate a positive rectified signal with the negative half-wave rectified and inverted (processing step 420). 6 is a graph 600 illustrating a rectified signal 602 in an exemplary embodiment. In this embodiment, the rectified signal 602 is generated by performing negative half-wave rectification and inversion on the response signal 108. The rectified signal 602 includes a series of pulses. The pulse having the first highest peak 610 in the rectified signal 602 represents the surface reflection 302 and is also referred to as a surface pulse 606.

[0029] In another embodiment, the controller 104 generates the rectified signal 602 by performing positive half-wave rectification on the response signal 108 (process step 422 of FIG. 4 ). FIG. 7 is a graph 700 illustrating the rectified signal 602 in an exemplary embodiment. In this embodiment, the rectified signal 602 is generated by performing positive half-wave rectification on the response signal 108. Again, the rectified signal 602 includes a series of pulses, with the first pulse with the highest peak 610 (i.e., the surface pulse 606) representing the surface reflection 302.

[0030] In another embodiment, the controller 104 performs full-wave rectification on the response signal 108 to generate the rectified signal 602 (process step 424 in FIG. 4 ). FIG. 8 is a graph 800 illustrating the rectified signal 602 in an exemplary embodiment. In this embodiment, the rectified signal 602 is generated by performing full-wave rectification on the response signal 108. In the rectified signal 602 obtained by full-wave rectification, the surface reflection 302 is represented by two pulses: a pulse having the first highest peak 610 in the rectified signal 602 (i.e., surface pulse 606) and a subsequent pulse 806.

[0031] In FIG. 4 , the controller 104 integrates 408 the portion of the rectified signal 602 that falls within a detection time window. The detection time window is limited to the surface reflection 302 and at least a portion of the near-surface dead zone 304 that follows the surface reflection 302. FIG. 9 is a graph 900 illustrating a detection time window 910 in an exemplary embodiment. The graph 900 shows the rectified signal 602 generated by negative half-wave rectification (and inversion) of the response signal 108. However, a similar process can be performed for a rectified signal 602 generated by positive half-wave or full-wave rectification. Different points on the rectified signal 602 along the time axis correspond to different depth locations within the structure 120. The detection time window 910 (also called a detection gate) is limited or restricted to the surface 122 and the detection gap 210 below the surface 122. In one embodiment, the controller 104 defines a detection time window 910 that begins with the surface reflection 302 (i.e., the surface pulse 606). For example, when operating in the positive region, the detection time window 910 begins with the rising edge 920 of the surface reflection 302 or when the rising edge 920 of the surface reflection 302 crosses a threshold voltage (e.g., 0.4 volts). The detection time window 910 ends a predetermined time after the rising edge 920. Thus, the detection time window 910 is set to capture only the surface reflection 302 and the signal in the near-surface dead zone 304 that follows the surface reflection 302. For example, the detection time window 910 is set or defined to end one cycle after the surface reflection 302, two cycles after the surface reflection 302, three cycles after the surface reflection 302, or some other time. The size (length of time) of the time window 910 may be set based on, for example, the frequency of the ultrasonic waves 130, the material of the structure 120, the ring-down time of the ultrasonic probe 102, the estimated depth of the anomaly or imperfection from the surface 122, etc. The detection time window 910 is set so that the integrated portion of the rectified signal 602 is limited to the surface 122 of the structure 120 and at least a portion of the detection gap 210 located below the surface 122 (e.g., from the surface 122 down to the nearest inspectable depth 214), but does not include other anomalies below the detection gap 210 or the bottom surface 124.

[0032] Such integration allows the controller 104 to determine the sum of the energy of the portion of the rectified signal 602 that falls within the detection time window 910. This sum can be used to indicate anomalies or imperfections in the detection gap 210 that are located below the surface 122. Anomalies or imperfections below the surface 122 may cause the surface pulse 606 to have a higher peak because their reflections are superimposed on the surface reflection 302. Additionally or alternatively, anomalies or imperfections below the surface 122 may cause one or more pulses to follow the surface pulse 606. Summing the energy of the signals within the detection time window 910 has the technical effect of detecting anomalies or imperfections by capturing reflections from anomalies or imperfections below the surface 122 in the near-surface dead-zone 304.

[0033] In FIG. 4, the controller 104 generates an output 150 based on the energy sum (step 410). This output is also shown in FIG. 1. In one embodiment, the controller 104 compares the energy sum to a threshold and issues an alert 152 if the energy sum exceeds the threshold (process step 426). The alert 152 may be an audible alert, a visual alert, or another type of alert. In another embodiment, the controller 104 generates C-scan data 154 of the structure 120 based on the energy sum (process step 428). A C-scan is an image in which data collected during an ultrasound inspection is plotted on a plan view of the structure 120. Thus, the C-scan data 154 generated by the controller 104 may include data points of a C-scan image of the structure 120. The ultrasound probe 102 is then moved to another position relative to the surface 122 of the structure 120 (step 412), and the method 400 is repeated at the new position.

[0034] The ultrasonic probe 102 may be moved manually by an operator to perform the above-described inspection of the structure 120. In other embodiments, the ultrasonic probe 102 may be moved automatically by the ultrasonic inspection system 100 to perform the inspection. FIG. 10 is another block diagram of an exemplary embodiment of the ultrasonic inspection system 100. In this embodiment, the ultrasonic inspection system 100 further includes a positioning system 1002 configured to move the ultrasonic probe 102 to different positions along the surface 122 of the structure 120. In this embodiment, the positioning system 1002 includes a robotic arm 1004 and a position sensor 1006 (or multiple position sensors). The ultrasonic probe 102 is mounted or attached to the robotic arm 1004, such as an end effector. The robotic arm 1004 moves the ultrasonic probe 102 on or along the structure 120 and sends measurement data to the controller 104. The robotic arm 1004 is automatically controlled based on commands from the controller 104 to move the ultrasonic probe 102 near the structure 120. The robotic arm 1004 is generally configured to be movable in multiple axes and, with software support, generates a three-dimensional profile that is used to measure and inspect the structure 120. The position sensor 1006 is configured to determine position data 1010 of the ultrasound probe 102 in the coordinate system of the structure 120 (e.g., X, Y, Z three-dimensional space). The robotic arm 1004 and position sensor 1006 can communicate with the controller 104 via wired or wireless connections.

[0035] In operation, the robotic arm 1004 moves the ultrasonic probe 102 to a first position relative to the surface 122 of the structure 120. At this first position, the ultrasonic probe 102 and controller 104 perform the tests described in method 400 to determine the energy sum of the rectified signal 602 at the first position. When generating the C-scan data 154, for example, the controller 104 converts the energy sum at the first position into a display value, such as a shade of gray or a color value. The controller 104 also receives position data 1010 for the first position from the position sensor 1006 and associates the received position data 1010 for the first position with the display value. The controller 104 stores this information as the C-scan data 154. The robotic arm 1004 then moves the ultrasonic probe 102 to a second position relative to the surface 122 of the structure 120. At this second location, the ultrasound probe 102 and controller 104 perform the tests described in method 400 to determine the energy sum of the rectified signal 602 at the second location. The controller 104 converts the energy sum at the second location to a display value, receives position data 1010 for the second location from the position sensor 1006, and associates the received position data 1010 for the second location with the display value. This process may be repeated for multiple locations, for example, to generate C-scan data 154 of the structure 120.

[0036] In another embodiment, the ultrasound inspection system 100 further includes a network interface 1020 and / or a user interface 1022. The network interface 1020 is hardware capable of communicating with a remote device over a network using a wired or wireless connection. The controller 104 uses the network interface 1020 to transmit the C-scan data 154 to the remote device over the network. The user interface 1022 is a hardware component for interacting with an end user or operator. For example, the user interface 1022 may include a screen or touch screen (e.g., a liquid crystal display (LCD), a light-emitting diode (LED) display, etc.), a keyboard or keypad, a tracking device (e.g., a trackball or trackpad), a speaker, and a microphone. The controller 104 can display the C-scan data 154 to the operator via the user interface 1022.

[0037] 11-18 show examples of ultrasonic testing in other embodiments. FIG. 11 is a cross-sectional view of a composite part 1100 in an exemplary embodiment. This part is an example of the structure 120 described above. The composite part 1100 is a laminate formed by sandwiching together multiple layers of material (e.g., carbon fiber reinforced polymer (CFRP)). The fibers in the laminate may be oriented parallel to each other in each layer and may be oriented differently in different layers. This can increase the strength along each dimension of the final composite part. The laminate further includes a resin (e.g., thermoplastic or thermosetting), which solidifies and hardens the layers of the laminate, completing the composite part 1100. Similar to the structure 120, the composite part 1100 has a front surface 122 and a bottom surface 124. In this example, an opaque layer 1102 is applied or disposed on the front surface 122. The opaque layer 1102 can be, for example, an opaque primer layer, a coating, a film, a surface film, or the like. The opaque layer 1102 can be co-cured with the composite part 1100. FIG. 11 also shows a puddle 1104 below the surface 122. This puddle is hidden beneath the opaque layer 1102 and therefore cannot be seen by visual inspection. The puddle 1104 is an example of an anomaly or imperfection located below the surface 122 that can potentially initiate cracks and thus adversely affect the integrity of the composite part 1100. As shown, the puddle 1104 has a depth 1112 below the surface 122. Because the puddle 1104 is located very close to the surface 122, it falls within the near-surface dead zone 304 and cannot be detected using conventional inspection techniques. However, the inspection method of the present disclosure can detect the puddle 1104.

[0038] 12 is a flowchart illustrating a method 1200 for inspecting a structure, such as composite part 1100, according to an exemplary embodiment. It will be appreciated that method 1200 may be used to inspect other types of structures. Method 1200 includes steps similar to those of method 400 described above, and such steps are indicated using the same reference numerals.

[0039] First, the ultrasonic probe 102 is positioned near the surface 122 of the composite part 1100 (see FIG. 13 ) and operated in pulse-echo mode to inspect the composite part 1100 at this position. The ultrasonic probe 102 emits ultrasonic waves 130 from the surface 122 of the composite part 1100 to the interior (see step 402 in FIG. 12 ). Reflected waves of the ultrasonic waves 130 return to the ultrasonic probe 102 and are converted into response signals 108. Thus, the ultrasonic probe 102 receives one or more reflected waves 132 and generates the response signals 108 (step 404). The controller 104 receives the response signals 108 from the ultrasonic probe 102 and records or stores the received response signals 108. FIG. 14 is a graph 1400 illustrating the response signals 108 in an exemplary embodiment. The graph 1400 shows the surface reflection 302 and the bottom reflection 504. These reflections are ultrasound waves 130 reflected from the front surface 122 and the bottom surface 124. The response signal 108 is a signal representing the raw A-scan data at this location on the composite part 1100.

[0040] 12, the controller 104 processes the response signal 108 as follows. The controller 104 rectifies the response signal 108 by performing negative half-wave rectification and inversion on the response signal 108 to generate a rectified signal (step 420). FIG. 15 is a graph 1500 illustrating a rectified signal 602 in an exemplary embodiment. The rectified signal 602 includes a series of pulses. The first pulse of the rectified signal 602 having the highest peak 610 (i.e., the surface pulse 606) represents the surface reflection 302. Note that although negative half-wave rectification is used in this embodiment, other types of rectification as described above may also be used.

[0041] In FIG. 12 , the controller 104 defines a null gate (step 1202) for the portion of the rectified signal 602 preceding the surface reflection 302 and nulls the rectified signal 602 within the null gate (step 1204). FIG. 16 is a graph 1600 illustrating a null gate 1602 in an exemplary embodiment. The null gate 1602 is used to "zero out" the entire portion of the rectified signal corresponding to a predetermined time period preceding the surface reflection 302. Thus, the null gate 1602 begins at a point preceding the surface reflection 302 and ends at the beginning of the surface reflection 302. For example, the controller 104 may define the end point of the null gate 1602 at the rising edge 920 of the surface reflection 302 (i.e., the surface pulse 606) or when the rising edge 920 of the surface reflection 302 exceeds a threshold voltage (e.g., 0.4 volts). The controller 104 may further define the beginning of the null gate 1602 to be a predetermined number of samples (e.g., 150 samples) preceding the rising edge 920. The portion of the rectified signal 602 included in the null gate 1602 is treated as a reference voltage (e.g., 0 volts), so that a pulse in the rectified signal 602 preceding the surface reflection 302 is not erroneously detected as the surface reflection 302.

[0042] In FIG. 12 , the controller 104 defines a detection time window 910 or detection gate (step 1206). FIG. 17 is a graph 1700 illustrating the detection time window 910 in an exemplary embodiment. As described above, the detection time window 910 is limited or restricted to the surface 122 and the detection gap 210 below the surface 122. In this embodiment, the controller 104 defines the detection time window 910 starting from the surface reflection 302 (i.e., the surface pulse 606). For example, the detection time window 910 begins at the rising edge 920 of the surface reflection 302 or when the rising edge 920 of the surface reflection 302 crosses a threshold voltage (e.g., 0.4 volts). The detection time window 910 ends a predetermined time after the rising edge 920. Thus, the detection time window 910 is set to capture only the signal from the surface reflection 302 and the near-surface dead zone 304 that follows the surface reflection 302. The size of the detection time window 910 in this embodiment may be set based on the estimated depth 1112 of the resin puddle 1104 below the surface 122. Note that the detection time window 910 may be set to start before the surface reflection 302 if the portion of the rectified signal 602 preceding the surface reflection 302 is nulled using a process similar to step 1204. Regardless of where the detection time window 910 begins, the detection time window 910 ends at or prior to the nearest inspectable depth 214 so that only the surface 122 and the detection gap 210 directly below the surface 122 are considered.

[0043] 12 , the controller 104 integrates the portion of the rectified signal 602 that falls within the detection time window 910 (step 408). By integrating the portion that falls within the detection time window 910, the controller 104 calculates the energy sum of the rectified signal 602 for the portion that falls within the detection time window 910. The controller 104 then generates C-scan data 154 based on the energy sum (step 428). For example, the controller 104 converts the energy sum at the current measurement position to a display value and associates the converted display value with the position data 1010. The ultrasonic probe 102 is then moved to another position relative to the surface 122 of the composite part 1100 (step 412), and the method 1200 is repeated at the new position.

[0044] After scanning composite part 1100, or at least a portion of composite part 1100, is completed, controller 104 transmits C-scan data 154 to a remote device via network interface 1020 for display on the remote device (step 414) or displays C-scan data 154 via user interface 1022 (step 414). FIG. 18 illustrates a C-scan display 1800 that depicts C-scan data 154 in an exemplary embodiment. C-scan display 1800 is a point cloud representation of a top view of composite part 1100. For each measurement point on composite part 1100, controller 104 integrates rectified signal 602 for the portion of detection time window 910. This allows anomalies or imperfections located directly below surface 122 and within near-surface dead zone 304 to be displayed in C-scan display 1800. In FIG. 18, the darker areas represent resin puddles 1104 below surface 122. One technical advantage is that an operator can determine where puddle 1104 is located on composite part 1100, even though puddle 1104 is obscured by opaque layer 1102 applied to surface 122. Another advantage is that because puddle 1104 is detectable, opaque layer 1102 can be co-cured with composite part 1100, saving time.

[0045] Again, while method 1200 has been described as being used to inspect composite part 1100, the method may also be used to inspect other types of structures. For example, method 1200 may be used to detect inclusions or voids that exist below the surface of a metal part.

[0046] Embodiments of the disclosure may be described in relation to aircraft manufacturing and service method 1900 shown in Figure 19 and aircraft 2000 shown in Figure 20. As a pre-production step, exemplary method 1900 includes specification and design 1904 of aircraft 2000 and material procurement 1906. During production, component and subassembly manufacturing 1908 and system integration 1910 of aircraft 2000 occurs. Aircraft 2000 then undergoes certification and delivery 1912 and enters service 1914. While in service, aircraft 2000 undergoes a routine maintenance and service schedule 1916, which may include modification, reconfiguration, retrofit, etc.

[0047] Each step of method 1900 may be performed or implemented by a system integrator, a third party, and / or an operator (e.g., a customer). Note that a system integrator may include, but is not limited to, any number of aircraft manufacturers and major system subcontractors. A third party may include, but is not limited to, any number of vendors, subcontractors, and suppliers. An operator may be an airline, a leasing company, a military entity, a service organization, etc.

[0048] 20 , aircraft 2000 produced by exemplary method 1900 includes an airframe 2002 having a plurality of systems 2004 and an interior 2006. Examples of the plurality of systems 2004 include one or more of a propulsion system 2008, an electrical system 2010, a hydraulic system 2012, and an environmental system 2014, as well as any number of other systems. Note that while embodiments are described with respect to aircraft, the principles disclosed herein are applicable to other industries, such as the automotive industry.

[0049] The described apparatus and methods may be employed at any one or more stages in method of manufacture and use 1900. For example, the components or subassemblies at operation 1908 may be made or manufactured in a manner similar to components or subassemblies made or manufactured during the in-service life of aircraft 2000. Also, one or more of the apparatus embodiments, method embodiments, or a combination thereof may be employed, for example, during manufacturing operations 1908 and 1910. This may significantly expedite or reduce the cost of, for example, assembly of aircraft 2000. Similarly, one or more of the apparatus embodiments, method embodiments, or a combination thereof may be employed during the in-service life of aircraft 2000, such as, but not limited to, maintenance and service 1916.

[0050] Supplementary Note 1: An ultrasonic probe (102) configured to emit ultrasonic waves (130) from a surface (122) of a structure (120) to the interior thereof and receive reflected waves (132) to generate a response signal (108); a processor (105) configured to rectify the response signal to generate a rectified signal (602), integrate a portion of the rectified signal that falls within a detection time window (910) to determine an energy sum, and generate an output (150) based on the energy sum; The ultrasound inspection system (100), wherein the detection time window is limited to a surface reflection (302) and at least a portion of a near-surface dead zone (304) following the surface reflection.

[0051] Appendix 2. The ultrasonic inspection system of Appendix 1, wherein the processor is configured to generate the rectified signal by performing negative half-wave rectification and inversion on the response signal.

[0052] Appendix 3. An ultrasonic inspection system as described in Appendix 1 or 2, wherein the processor is configured to generate the rectified signal by performing positive half-wave rectification on the response signal.

[0053] Appendix 4. An ultrasonic inspection system according to any one of appendices 1 to 3, wherein the processor is configured to generate the rectified signal by performing full-wave rectification on the response signal.

[0054] Appendix 5. An ultrasound inspection system as described in any of Appendixes 1 to 4, wherein the processor is configured to define a null gate (1602) preceding the surface reflection and to null the rectified signal within the null gate.

[0055] Appendix 6. An ultrasonic inspection system according to any one of appendices 1 to 5, wherein the processor is configured to generate C-scan data (154) of the structure based on the energy sum.

[0056] Appendix 7. A robotic arm (1004) configured to move the ultrasonic probe over the structure; 7. The ultrasound inspection system of claim 6, further comprising: a position sensor configured to determine position data of the ultrasound probe.

[0057] Appendix 8. An ultrasound inspection system according to any one of appendices 1 to 7, wherein the processor is configured to issue an alert (152) when the energy sum exceeds a threshold.

[0058] Appendix 9: The ultrasonic inspection system according to any one of appendices 1 to 8, wherein the structure is a composite part (1100).

[0059] Addendum 10. The surface of the composite part is provided with an opaque layer (1102); 10. The ultrasonic inspection system of claim 9, wherein the detection time window is set based on the depth (1112) of the resin reservoir (1104) below the surface.

[0060] Appendix 11. An ultrasonic inspection system according to any one of appendices 1 to 10, wherein the structure is a part of an aircraft (2000).

[0061] Appendix 12. A method (400) for inspecting a structure, comprising: Incidentally, ultrasonic waves are applied from the surface of the structure to the interior thereof (402); receiving the reflected wave and generating a response signal (404); rectifying (406) the response signal to generate a rectified signal; integrating the portion of the rectified signal that falls within the detection time window to calculate a sum of the energies (408); generating an output based on the energy sum (410); The method, wherein the detection time window is limited to a surface reflection and at least a portion of a near-surface dead zone following the surface reflection.

[0062] Clause 13. The method of clause 12, wherein rectifying the response signal includes generating the rectified signal by performing negative half-wave rectification and inversion (420) on the response signal.

[0063] Addendum 14. The method of Addendum 12 or 13, wherein generating the output based on the energy sum includes generating (428) C-scan data of the structure based on the energy sum.

[0064] Addendum 15. The method of any of Addendums 12-14, wherein generating the output based on the energy sum includes issuing an alert (426) when the energy sum exceeds a threshold.

[0065] Addendum 16. The structure is a composite part; an opaque layer is provided on the surface of the composite part; 16. The method of any of claims 12 to 15, wherein the detection time window is set based on the depth of a resin pool below the surface.

[0066] Clause 17. A non-transitory computer-readable medium (106) embodying program instructions (107) for execution by a processor (105), the instructions causing the processor to perform a method for inspecting a structure (120), the method comprising: Incidentally, ultrasonic waves (130) are incident on the surface (122) of the structure from the inside. receiving the reflected wave (132) and generating a response signal (108); rectifying the response signal to generate a rectified signal (602); calculating a sum of energies by integrating the portion of the rectified signal that falls within a detection time window (910); generating an output (150) based on the energy sum; The computer-readable medium, wherein the detection time window is limited to a surface reflection (302) and at least a portion of a near-surface dead zone (304) following the surface reflection.

[0067] Clause 18. The computer-readable medium of Clause 17, wherein rectifying the response signal includes generating the rectified signal by performing negative half-wave rectification and inversion on the response signal.

[0068] Appendix 19. The computer-readable medium of Appendix 17 or 18, wherein generating the output based on the energy sum includes generating C-scan data (154) of the structure based on the energy sum.

[0069] Clause 20. The computer-readable medium of Clause 17, 18, or 19, wherein generating the output based on the energy sum includes issuing an alert (152) when the energy sum exceeds a threshold.

[0070] Any of the various elements shown or described herein may be implemented by hardware, software, firmware, or a combination thereof. For example, any element may be implemented as dedicated hardware. Dedicated hardware elements may be referred to as a “processor,” “controller,” or similar terms. When a certain function is implemented by a processor, such function may be implemented by a single dedicated processor, a single shared processor, or multiple individual processors, some of which may be shared. Furthermore, although the terms “processor” or “controller” are explicitly used, these terms should not be construed to refer solely to hardware capable of executing software. These terms may implicitly include, but are not limited to, digital signal processor (DSP) hardware, network processors, application-specific integrated circuits (ASICs) or other circuitry, field-programmable gate arrays (FPGAs), read-only memory (ROM) for storing software, random-access memory (RAM), non-volatile storage, logic circuitry, or other physical hardware components or modules.

[0071] Additionally, any element may be embodied as instructions executable by a processor or computer that cause the element to perform its function. Examples of such instructions include software, program code, and firmware. When executed by a processor, these instructions control the processor to perform the function of the element. These instructions may be stored in a processor-readable storage device. Examples of storage devices include digital or solid-state memories, magnetic storage media such as magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media.

[0072] Although descriptions of specific embodiments are presented, the scope of the disclosure is not limited to these specific embodiments, and is instead defined by the following claims and their equivalents.

Claims

1. an ultrasonic probe configured to emit ultrasonic waves from a surface of a structure to an interior thereof, receive reflected waves, and generate a response signal; a processor configured to rectify the response signal to generate a rectified signal, integrate a portion of the rectified signal that falls within a detection time window to determine an energy sum, and generate an output based on the energy sum; The ultrasonic inspection system, wherein the detection time window is limited to a surface reflection and at least a portion of a near-surface dead zone following the surface reflection.

2. The ultrasound inspection system of claim 1 , wherein the processor is configured to generate the rectified signal by performing negative half-wave rectification and inversion on the response signal.

3. The ultrasound inspection system of claim 1 or 2, wherein the processor is configured to generate the rectified signal by performing positive half-wave rectification on the response signal.

4. 4. The ultrasonic inspection system according to claim 1, wherein the processor is configured to generate the rectified signal by performing full-wave rectification on the response signal.

5. 5. The ultrasound inspection system of claim 1, wherein the processor is configured to define a null gate preceding the surface reflection and to null the rectified signal within the null gate.

6. The ultrasonic inspection system of any one of claims 1 to 5, wherein the processor is configured to generate C-scan data of the structure based on the energy sum.

7. a robotic arm configured to move the ultrasonic probe over the structure; The ultrasound inspection system of claim 6 , further comprising: a position sensor configured to determine position data of the ultrasound probe.

8. The ultrasound inspection system of any preceding claim, wherein the processor is configured to issue an alarm when the energy sum exceeds a threshold.

9. The ultrasonic inspection system according to any one of claims 1 to 8, wherein the structure is a composite part.

10. an opaque layer is provided on the surface of the composite part; The ultrasonic inspection system of claim 9 , wherein the detection time window is set based on a depth of a resin puddle below the surface.

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