JP7764232B2 - Inspection method, inspection device, inspection system, and program - Google Patents

Description

Embodiments of the present invention relate to an inspection method, an inspection device, an inspection system, and a program.

In general, electric power equipment is often constructed so that conductive parts (conductors) made of metal are covered with resin to maintain insulation.

However, during the process of covering the conductive parts with resin, foreign matter may become mixed into the resin. Such foreign matter can cause partial discharge or dielectric breakdown in the power equipment, potentially resulting in a malfunction of the power equipment.

For this reason, there is a need to inspect the inside of the resin covering the conductive parts to check for the presence of foreign matter. In this case, it is possible to inspect whether foreign matter has been mixed inside the resin by destroying the resin, for example, but this inspection method requires the destruction of the resin, which is undesirable from the perspective of the destruction costs and labor required for inspection. For this reason, it is desirable to inspect the inside of the resin without destroying it (i.e., non-destructively).

However, the resin covering the conductive parts is thick, and the structure (for example, the shape of the resin) varies depending on the power equipment (product), making it difficult to inspect the inside of the resin non-destructively. Furthermore, while it is useful to identify the type of foreign matter that has entered the resin in order to take measures to prevent the intrusion of foreign matter, it is also difficult to identify (inspect) the type of foreign matter non-destructively. Many of the foreign matter is particularly small, requiring precise inspection. For this reason, inspecting the inside of the resin non-destructively takes a long time.

Japanese Patent Application Laid-Open No. 2019-105649

The problem that this invention aims to solve is to provide an inspection method, inspection device, inspection system, and program that can shorten the time required to non-destructively inspect the inside of the resin that covers the conductive parts of electric power equipment.

According to an embodiment, an inspection method for inspecting the inside of a resin covering a conductive part in an electric power device is provided. The inspection method includes the steps of acquiring a reflected wave signal corresponding to a wave reflected from an interface of a foreign substance mixed inside the resin, the reflected wave signal being generated from a pulse wave irradiated based on a plurality of irradiation points set on the resin, and generating an image including the foreign substance based on the acquired reflected wave signal. The plurality of irradiation points are set sparsely with respect to a plurality of pixels constituting the generated image . The generating step generates the image by applying compressed sensing technology. The number of the plurality of irradiation points set varies depending on the type of foreign substance that may be mixed inside the resin.

FIG. 2 is a diagram showing an example of the functional configuration of an inspection apparatus according to an embodiment. FIG. 2 is a diagram showing an example of a hardware configuration of an inspection apparatus. FIG. 2 is a diagram schematically illustrating an electric power device. FIG. 10 is a diagram showing an example of the positional relationship between an oscillator and a receiver that employs a lens system. FIG. 1 is a diagram for explaining an oscillator and a receiver that employ a lensless system. FIG. 10 is a diagram showing another example of the positional relationship between the oscillator and the receiver. FIG. 10 is a diagram showing an example of a processing procedure of an inspection device. FIG. 1 is a diagram for explaining an overview of a simulation model. 5A and 5B are diagrams for explaining an example of a reflected wave reflected at an interface between a first material and a second material; 5A and 5B are diagrams for explaining an example of a reflected wave reflected at an interface between a first material and a second material; 5A and 5B are diagrams for explaining an example of a reflected wave reflected at an interface between a first material and a second material; FIG. 10 is a diagram showing an example of a reflected waveform based on an actual inspection result. FIG. 10 is a diagram showing an example of reflection intensity based on an actual inspection result. FIG. 1 is a diagram for explaining an example of an image generated by applying compressed sensing technology. 10A and 10B are diagrams for explaining the difference in characteristics of a reflected wave when a reflected wave from a foreign object is compared with a reflected wave from resin surrounding the foreign object; FIG. 10 is a diagram showing an example of an image generated when a lens system is adopted. FIG. 10 is a diagram showing an example of an image generated when a lensless system is adopted.

Hereinafter, embodiments will be described with reference to the drawings.
The inspection device of this embodiment is used to inspect the inside of resin without destroying it (i.e., to detect foreign matter mixed inside the resin) by irradiating pulse waves onto electric power equipment that is configured so that conductive parts (conductors) are covered with resin.

In this embodiment, types of foreign matter that may be mixed into the resin include, for example, metal, air bubbles, and resin burrs. Furthermore, types of foreign matter may also include abnormalities (defects) in the power equipment, such as peeling between the conductive part and the resin or cracks in the resin.

Electric power equipment includes, for example, circuit breakers, disconnecting switches, current transformers, and voltage transformers. Furthermore, electric power equipment may also be, for example, a power transformer, gas-insulated switchgear, generator, electric motor, or reactor, as long as it is equipment that may generate partial discharge. Because such electric power equipment carries high voltages and large currents from the outside via power cables, its conductive parts are covered with resin to maintain insulation.

Methods for non-destructively inspecting the interior of the resin mentioned above include methods that use electromagnetic waves such as X-rays or infrared rays, and methods that use ultrasonic waves. Below, we will briefly explain some of the methods used for such inspections.

First, X-rays have good penetration through resin, so they can be used to inspect the inside of resin. However, because X-rays have low penetration through metal, it may not be possible to properly inspect structures with embedded metal. For example, while it is possible to inspect (observe) the inside of resin even when metal is embedded using an X-ray CT scanner (X-ray CT inspection), large electric power equipment cannot be inspected using a general X-ray CT scanner. While there are X-ray CT scanners that can handle large electric power equipment, these X-ray CT scanners have special specifications, making inspection using them impractical. Furthermore, radiation management is also required when using X-rays.

Furthermore, in order to take measures against the contamination of foreign matter, it is useful to identify the type of foreign matter that has been mixed into the resin. From the perspective of identifying the type of foreign matter, when using X-rays, it is thought that it is possible to distinguish between metals and air bubbles that have been mixed into the resin due to differences in density. However, it is not possible to distinguish between and detect objects with similar densities, such as resin burrs.

Next, while infrared (thermography) can easily obtain information about the inside of resin, it becomes difficult to obtain this information when the resin is thick (for example, 3 mm or thicker). Furthermore, infrared has low resolution, making it difficult to detect small foreign objects. Furthermore, since the type of foreign object is determined by differences in thermal conductivity, it is difficult to distinguish the type of foreign object using infrared.

Ultrasound can also provide information about the interior of resin with high resolution and relatively easy access. However, ultrasound is significantly attenuated in resin, making it difficult to inspect thick resin (e.g., 10 mm or thicker) using standard methods. Ultrasound also significantly attenuates in air, making inspection cumbersome, requiring immersion in water or passing through gel. The type of foreign matter can be determined by taking advantage of the fact that the reflectivity and propagation speed of ultrasound vary depending on the material. Ultrasound-based inspection is particularly effective for foreign matter on the surface of power equipment (resin).

In addition to the above-mentioned X-rays, infrared rays, and ultrasound, it is also possible to use high-frequency electromagnetic waves (for example, terahertz waves). Terahertz waves are electromagnetic waves that have good resin penetration, and can detect foreign matter mixed inside even thick resin (for example, about 60 mm). Furthermore, if a scanning mechanism is installed, it can be used to detect large power equipment (i.e., inspect the inside of the resin in large power equipment). Furthermore, it may be possible to determine the type of foreign matter by taking advantage of the fact that the transmission characteristics of terahertz waves vary depending on the material.

In this embodiment, therefore, an inspection device is described that uses the above-mentioned terahertz waves to inspect the inside of the resin covering the conductive parts of electric power equipment. Note that the inspection of the inside of the resin in this embodiment includes detecting foreign matter (e.g., metal, air bubbles, resin burrs, etc.) that has become mixed in the inside of the resin, as well as detecting the occurrence of the above-mentioned peeling or cracks (i.e., defects in the electric power equipment). Furthermore, the inspection of the inside of the resin may also include identifying the type of foreign matter that has become mixed in the inside of the resin.

Figure 1 shows an example of the functional configuration of an inspection device according to this embodiment. The inspection device 10 shown in Figure 1 is an information processing device (electronic device) such as a personal computer, smartphone, tablet computer, or server device.

As shown in FIG. 1, the inspection device 10 is connected to an oscillator (oscillator) 20 and a receiver (receiver) 30. In this embodiment, the inspection device 10, oscillator 20, and receiver 30 constitute an inspection system.

The oscillator 20 functions as an irradiation device used to irradiate the power equipment (the resin covering the conductive parts) with a predetermined pulse wave (terahertz wave), and is configured to oscillate the terahertz wave in response to instructions from the inspection device 10, for example. The terahertz wave oscillated by the oscillator 20 is assumed to be an electromagnetic wave in a frequency band ranging from 0.05 to 10 THz, for example.

As described above, when terahertz waves emitted from the oscillator 20 are irradiated onto resin, the terahertz waves are reflected, for example, by (the interface of) foreign matter mixed inside the resin. The receiver (detector) 30 is configured to receive (detect) such reflected waves. The receiver 30 converts the received reflected waves into an electrical signal, thereby generating a reflected wave signal corresponding to the reflected waves. This reflected wave signal includes the intensity (signal intensity) of the reflected waves received by the receiver 30, the peak value of the intensity of the reflected waves, and the time at which the peak is reached (hereinafter referred to as the peak arrival time).

In this embodiment, the measured optical delay time of the terahertz waves irradiated to the power equipment (i.e., the terahertz waves emitted by the oscillator 20) is, for example, 160 seconds. When converted to an optical path length, this is equal to 48 mm. When using the reflective type, the measurable thickness is 24 mm (round trip 48 mm, refractive index 1.0). The terahertz waveform acquisition speed is 1000 waveforms/second. The acquisition speed during imaging is 1000 pixels/second. The sampling interval is 0.1 psec. The terahertz wave oscillation band is greater than 2.0 THz.

Note that there are various types of oscillator 20, such as high-output and broadband types, but the type of oscillator 20 used should be appropriate depending on the material of the resin to be irradiated with terahertz waves (i.e., the object to be inspected).

The inspection device 10 shown in Figure 1 includes a propagation behavior prediction unit 11, a reflected wave signal acquisition unit 12, a waveform data generation unit 13, an image generation unit 14, a depth calculation unit 15, a discrimination unit 16, and an output unit 17.

The propagation behavior prediction unit 11 predicts the propagation behavior of terahertz waves when inspecting the inside of the resin covering a conductive part in electric power equipment, based on, for example, at least one of the structure of the electric power equipment and the relative dielectric conductivity of the resin and any foreign matter that may be mixed inside the resin. The frequency of the terahertz waves emitted by the oscillator 20 during the above-mentioned inspection (i.e., the terahertz waves irradiated onto the resin), the position of the oscillator 20, and the position of the receiver 30 are set based on the prediction results by the propagation behavior prediction unit 11.

The reflected wave signal acquisition unit 12 acquires the reflected wave signal generated by the receiving device 30 from the receiving device 30.

The waveform data generation unit 13 generates waveform data indicating the waveform of the reflected wave (hereinafter referred to as the reflected waveform) based on the reflected wave signal acquired by the reflected wave signal acquisition unit 12. Specifically, the waveform data generation unit 13 generates waveform data that reflects the intensity of the reflected wave contained in the reflected wave signal, the peak value of the intensity of the reflected wave, the time to reach the peak, etc.

The image generation unit 14 generates an image (e.g., a planar image) based on the reflected wave signal acquired by the reflected wave signal acquisition unit 12. Specifically, the image generation unit 14 generates three-dimensional image data based on the reflected wave signal. The three-dimensional image data includes pixel values corresponding to the intensity of the reflected wave contained in the reflected wave signal for each coordinate value in a Cartesian coordinate system in three-dimensional space. The image generation unit 14 generates an image containing a foreign object based on this three-dimensional image data. Specifically, the image generation unit 14 generates a planar image in which the value of one of the coordinate axes (x, y, z) in three-dimensional space is fixed. For example, if the coordinate value of the Z axis is fixed, the image generation unit 14 can generate a planar image related to the XY plane at the fixed Z axis coordinate value.

The depth calculation unit 15 calculates the depth of any foreign matter mixed inside the resin based on the reflected wave signal acquired by the reflected wave signal acquisition unit 12. The depth of the foreign matter is the distance from the surface of the resin irradiated with the terahertz waves to the foreign matter, and is calculated based on the peak arrival time (delay time) included in the reflected wave signal and the refractive index of the resin. The refractive index of the resin is assumed to be measured in advance and stored inside the inspection device 10, for example.

The discrimination unit 16 discriminates the type of foreign matter contained in the resin based on an index whose value varies depending on the type of foreign matter obtained by analyzing the reflected wave signal acquired by the reflected wave signal acquisition unit 12. In this embodiment, the type of foreign matter is discriminated using, for example, an index (characteristic) that appears in the waveform data generated by the waveform data generation unit 13.

The output unit 17 outputs the waveform data generated by the waveform data generation unit 13, the image generated by the image generation unit 14, the depth of the foreign object calculated by the depth calculation unit 15, and the type of foreign object identified by the identification unit 16.

Figure 2 shows an example of the hardware configuration of the inspection device 10 shown in Figure 1. The inspection device 10 includes a CPU 101, non-volatile memory 102, RAM 103, and a communication device 104. The inspection device 10 also includes a bus 105 that interconnects the CPU 101, non-volatile memory 102, RAM 103, and communication device 104.

CPU 101 is a processor for controlling the operation of each component within inspection device 10. CPU 101 may be a single processor or may be composed of multiple processors. CPU 101 executes various programs loaded from non-volatile memory 102 to RAM 103. In this embodiment, the programs executed by CPU 101 include inspection program 103a.

Note that some or all of the propagation behavior prediction unit 11, reflected wave signal acquisition unit 12, waveform data generation unit 13, image generation unit 14, depth calculation unit 15, discrimination unit 16, and output unit 17 shown in FIG. 1 above are realized by software, for example, when the CPU 101 (i.e., the computer of the inspection device 10) executes the inspection program 103a. This inspection program 103a may be distributed by being stored on a computer-readable storage medium, or may be downloaded to the inspection device 10 via a network.

Here, we have described the above units 11 to 17 as being partly or entirely implemented by software, but these units 11 to 17 may also be partly or entirely implemented by hardware such as an integrated circuit (IC), or may be implemented by a combination of software and hardware.

Non-volatile memory 102 is a storage medium used as an auxiliary storage device. RAM 103 is a storage medium used as a main storage device. Although only non-volatile memory 102 and RAM 103 are shown in FIG. 2, the inspection device 10 may also be equipped with other storage devices, such as an HDD (Hard Disk Drive) and an SSD (Solid State Drive).

The communication device 104 is a device configured to perform wired or wireless communication with external devices.

Although omitted in FIG. 2, the inspection device 10 may further include an input device such as a mouse or keyboard and a display device such as a display.

Next, we will explain the principle of inspecting the inside of resin using the inspection device 10 according to this embodiment.

Figure 3 shows a schematic diagram of electric power equipment 40 arranged in a three-dimensional space defined by mutually orthogonal X, Y, and Z directions. As shown in Figure 3, electric power equipment 40 is composed of a conductive part 41 made of a metal material and a resin (insulator) 42 that covers the conductive part 41. For convenience, only a portion of the conductive part 41 and the resin 42 is shown in Figure 3.

Resin 42 is formed, for example, from an epoxy resin containing a filler. Bisphenol A epoxy resin, for example, may be used as the epoxy resin. An acid anhydride may be used as the curing agent for resin 42. Silica, for example, is used as the filler. Note that the resin 42 described here is just one example; for example, dicyclopentadiene or the like may be used instead of bisphenol A epoxy resin.

As mentioned above, foreign matter 43 may be mixed into the resin 42 in the electric power equipment 40, and this foreign matter 43 may include metal, air bubbles, resin burrs, etc.

Next, we will explain the oscillator 20 that emits terahertz waves that are irradiated onto the above-mentioned power equipment 40 (resin 42) and the receiver 30 that receives the terahertz waves reflected from the power equipment 40.

Figure 4 shows the positional relationship between the oscillator 20 and receiver 30 when terahertz waves are irradiated from a direction perpendicular to the interface between the power equipment 40 and air, for example.

In this case, a portion of the terahertz waves emitted from the oscillator 20 is reflected by the beam splitter 51, but the terahertz waves that are not reflected by the beam splitter 51 are transmitted through the beam splitter 51. The terahertz waves that have transmitted through the beam splitter 51 are converged by the lens 52. The converged terahertz waves reach the electric power equipment 40. A portion of the terahertz waves (reflected waves) reflected by the electric power equipment 40 (the interface of the foreign matter 43 mixed inside the resin 42) is refracted by the beam splitter 51 and received by the receiver 30.

In Figure 4, an oscillator device 20 and a receiver device 30 equipped with a lens 52 (i.e., an oscillator device 20 and a receiver device 30 employing a lens system) are described, but the oscillator device 20 and the receiver device 30 may also be configured without a lens 52 (i.e., employing a lensless system) as shown in Figure 5.

Furthermore, Figure 6 shows the positional relationship between the oscillator 20 and receiver 30 when terahertz waves are irradiated from an angle that is not perpendicular to the interface between the power equipment 40 and the air.

In this case, the oscillator 20 is positioned so that the terahertz waves emitted by the oscillator 20 are irradiated onto the power equipment 40 at a predetermined angle. The predetermined angle is, for example, an angle that is not perpendicular to the interface between the power equipment 40 and the air. In this way, the terahertz waves emitted from the oscillator 20 reach the power equipment 40. The terahertz waves (reflected waves) reflected by the power equipment 40 (the interface of the foreign matter 43 mixed inside the resin 42) are received by the receiver 30.

For example, if the oscillator 20 and receiver 30 are used in the positional relationship described in Figure 4, there is a theoretical loss of 75% of the terahertz waves due to the influence of the beam splitter 51.

On the other hand, when the oscillator 20 and receiver 30 are used in the positional relationship shown in Figure 6, the receiver 30 can receive the terahertz waves (or their reflected waves) without passing through the beam splitter 51, thereby reducing loss due to the beam splitter 51 and improving the reception (detection) capability of the reflected waves.

Furthermore, while Figure 6 assumes that the oscillator 20 and receiver 30 employ a lens system, the oscillator 20 and receiver 30 shown in Figure 6 may employ a lensless system.

Note that the intensity of the reflected waves during inspection by the inspection device 10 varies depending on the angle of the terahertz waves irradiated onto the electric power equipment 40, and also on whether the oscillator 20 and receiver 30 use a lens system or a lensless system. Therefore, the angle of the terahertz waves irradiated onto the electric power equipment 40 (normal incidence or oblique incidence) and the system used by the oscillator 20 and receiver 30 (lens system or lensless system) can be selected appropriately depending on the electric power equipment 40 (product).

Next, an example of the processing procedure of the inspection device 10 according to this embodiment will be described with reference to the flowchart in Figure 7.

In this embodiment, the inside of the resin 42 is inspected based on a reflected wave signal (a reflected wave signal generated by the receiving device 30) corresponding to the reflected wave received by the receiving device 30. The intensity of the reflected wave is thought to vary depending on, for example, the frequency band of the terahertz wave and the angle at which the terahertz wave is irradiated.

For this reason, before inspecting the inside of the resin 42 in the power equipment 40, the propagation behavior prediction unit 11 predicts (simulates) the propagation behavior (or reflection behavior) of terahertz waves in the resin 42 in advance (step S1).

The following describes the prediction (processing) of the propagation behavior of terahertz waves by the propagation behavior prediction unit 11. To predict the propagation behavior of terahertz waves, for example, the Finite-Difference Time-Domain method (FDTD) can be used in electromagnetic field analysis, which analyzes the interaction between an object and an electromagnetic field. In this case, for example, a simulation model that takes into account the presence of foreign matter is constructed in the electromagnetic field analysis, and the oscillation point (oscillation position) of the terahertz waves and the reception point (reception position) of the reflected waves of the terahertz waves are set in the simulation model.

Now, with reference to Figure 8, an overview of the above-mentioned simulation model will be described. According to the simulation model shown in Figure 8, a first material 61 corresponding to, for example, resin 42 and a second material 62 corresponding to foreign matter 43 are defined. Furthermore, in first material 61, an oscillation point 63 that oscillates terahertz waves (spherical waves) of an arbitrary frequency band and a reception point 64 that receives the terahertz waves reflected from the interface between first material 61 and second material 62 are set.

Note that the example shown in Figure 8 shows a case where the propagation behavior of terahertz waves is predicted in the case of perpendicular incidence, where the terahertz waves are irradiated perpendicularly onto the first material 61 and the second material 62, as described above in Figure 4. However, by changing the positions (settings) of the oscillation point 63 and the reception point 64, it is also possible to predict the propagation behavior of terahertz waves in the case of oblique incidence, where the terahertz waves are irradiated from an angle that is not perpendicular to the first material 61 and the second material 62.

This simulation model allows the propagation behavior of terahertz waves to be predicted by changing the frequency band, oscillation point, and reception point of the terahertz waves and predicting the intensity of the reflected wave (the electric field value corresponding to the reflected wave) of the terahertz waves received at the reception point. This makes it possible to select terahertz wave irradiation conditions that will produce useful (i.e., maximum) reflected wave intensity, even if, for example, the power equipment 40 (resin 42) has a complex structure (shape).

Furthermore, with reference to Figures 9 to 11, we will explain the reflected waves from the interface between the first material 61 and the second material 62 in the above-mentioned simulation model.

Figure 9 shows the incident and reflected waves received at reception point 64 when, for example, terahertz waves in the 0.1 THz band are transmitted from oscillation point 63. That is, Figure 9 shows that, based on the positional relationship between oscillation point 63 and reception point 64 set in the simulation model described above, the terahertz waves transmitted at oscillation point 63 are directly received at reception point 64 as incident waves, and then the reflected waves from the interface between first material 61 and second material 62 are received at reception point 64.

Figure 10 also shows an enlarged version of the reflected waveform shown in Figure 9. Specifically, Figure 10 shows reflected waveforms 71 to 74 predicted by the simulation model by changing the relative dielectric constant of the second material 62. The relative dielectric constants of the first material 61 and the second material 62 are shown in Figure 11.

Reflected waveform 71 shown in Figure 10 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 1. Reflected waveform 72 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 2. Reflected waveform 73 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 4. Reflected waveform 74 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 5. As shown in Figure 11, the relative dielectric constant of first material 61 is assumed to be 3.

In this case, the amplitude of the reflected waveforms 71 to 74 shown in Figure 10 corresponds to the intensity of the reflected waves, and when the magnitude of the intensity of the reflected waves is expressed using the relative dielectric constant of the second material 62, it becomes 1 > 5 > 2 > 4.

The reflection coefficient R of the terahertz wave at the interface between the first material 61 and the second material 62 (hereinafter simply referred to as the reflection coefficient of the second material 62) can be calculated using the following formula (1).

In equation (1), _Z1 is the characteristic impedance of the first material 61, and _Z2 is the characteristic impedance of the second material 62. In addition, in equation (1), ε is the relative permittivity, and μ is the magnetic permeability. For convenience, in equation (1), the magnetic permeability μ is set to 1.

According to formula (1), for example, by applying the relative dielectric constant of the first material 61 and the relative dielectric constant of the second material 62, the reflection coefficient of the second material 62 can be calculated.

The reflection coefficient of each of the second materials 62 having different relative dielectric constants calculated using the above-mentioned formula (1) is as shown in the following formula (2).

In addition, in equation (2), _R1 is the reflection coefficient of the second material 62 having a relative dielectric constant of 1, _R2 is the reflection coefficient of the second material 62 having a relative dielectric constant of 2, _R4 is the reflection coefficient of the second material 62 having a relative dielectric constant of 4, and _R5 is the reflection coefficient of the second material 62 having a relative dielectric constant of 5.

Equation (2) shows that the magnitude relationship of the amplitudes (i.e., the intensity of the reflected waves) of the reflected waveforms 71 to 74 corresponding to each of the above-mentioned relative dielectric constants roughly matches the magnitude relationship of the absolute values of the reflection coefficients of the second material 62. Furthermore, as shown in Figure 10, if the magnitude relationship between the relative dielectric constants of the first material 61 and the second material 62 differs, the reflected wave will be inverted.

While the simulation results described above show differences in the intensity and waveform of the reflected wave depending on the dielectric constant, similar trends have been confirmed in actual inspections (measurements). Specifically, Figure 12 shows an example of a reflected waveform based on actual inspection results. Figure 12 shows the reflected waveform obtained by placing various materials (metal, air bubbles, and resin burrs) corresponding to foreign matter 43 under a resin plate and irradiating the resin plate with terahertz waves from the top surface (i.e., performing an inspection). Figure 13 shows the intensity of the reflected wave (reflection intensity) based on the inspection results shown in Figure 12. The ratios in Figure 13 indicate the ratio of the intensity of the reflected wave from other materials when the intensity of the reflected wave from metal (Al plate) is set to 100%. Figure 13 shows that the intensity of the reflected wave decreases in the order of metal, air bubbles, and resin burrs.

As described above, the intensity of the reflected wave varies depending on the relative dielectric constant of the resin 42 (first material 61) and the foreign matter 43 (second material 62). Therefore, by knowing in advance the material (relative dielectric constant) of the resin 42 and the foreign matter 43 that may be mixed inside the resin 42, it is possible to more accurately predict the propagation behavior of the terahertz wave. In other words, in this embodiment, the irradiation conditions for the terahertz wave may be selected taking into account the material of the resin 42 and the foreign matter 43.

As described above, in step S1, the propagation behavior of the terahertz waves is predicted based on at least one of the structure of the power equipment 40 (e.g., the shape of the conductive part 41 and resin 42) and the relative dielectric constant (material) of the resin 42 and any foreign matter 43 that may be mixed inside the resin 42.

Returning to FIG. 7 , irradiation conditions selected based on the propagation behavior of the terahertz waves predicted in step S1 are set (step S2). Note that the irradiation conditions set in step S2 include, for example, the frequency band of the terahertz waves and the positions of the oscillator 20 and receiver 30 (the angle at which the terahertz waves are irradiated) based on the oscillation point 63 and reception point 64 in the prediction of the propagation behavior of the terahertz waves described above, but may also include only at least one of the frequency band of the terahertz waves and the positions of the oscillator 20 and receiver 30.

When the processing of step S2 is executed, the inspection device 10 instructs the oscillator device 20 to emit terahertz waves in a frequency band included in the irradiation conditions set in step S2. Furthermore, if a mechanism for automatically adjusting the positions of the oscillator device 20 and the receiver device 30 (hereinafter referred to as a position adjustment mechanism) is provided, the positions of the oscillator device 20 and the receiver device 30 may be automatically adjusted (moved) based on the positions of the oscillator device 20 and the receiver device 30 included in the irradiation conditions set in step S2. If a position adjustment mechanism is not provided, the administrator of the inspection device 10 (inspection system) may confirm the positions of the oscillator device 20 and the receiver device 30 included in the irradiation conditions set in step S2, and manually adjust the positions of the oscillator device 20 and the receiver device 30.

In this embodiment, the oscillator 20 and receiver 30 (terahertz device) are equipped with a scanning mechanism that can scan, for example, the top surface (XY plane) of the electric power equipment 40 when inspecting the inside of the resin 42 covering the conductive portion 41 in the electric power equipment 40. With this configuration, terahertz waves are sequentially irradiated based on multiple irradiation points set on the top surface of the electric power equipment 40 (resin 42), allowing reflected waves from the interface of foreign matter 43 mixed inside the resin 42 to be received over a wide range of the resin 42. If the oscillator 20 uses a lens system, it is also possible to irradiate terahertz waves while sequentially changing the focus in the depth direction (Z-axis direction) of the electric power equipment 40 (resin 42).

Once the irradiation conditions are set in step S2, the oscillator 20 emits terahertz waves in accordance with the irradiation conditions while scanning the top surface of the power equipment 40 using the scanning mechanism. As a result, the receiver 30 receives reflected waves from the entire power equipment 40 (resin 42).

In this case, the reflected wave signal acquisition unit 12 acquires from the receiving device 30 a reflected wave signal corresponding to the reflected wave received by the receiving device 30 (step S3). The reflected wave signal acquired in step S3 includes the intensity of the reflected wave corresponding to the internal state of the resin 42, the peak value of the intensity of the reflected wave, and the time to reach the peak. Note that since the reflected wave signal may contain noise, the reflected wave signal acquisition unit 12 may perform signal processing such as averaging on the reflected wave signal to reduce the noise level.

The waveform data generator 13 generates waveform data based on the intensity of the reflected wave contained in the reflected wave signal acquired in step S3, the peak value of the intensity of the reflected wave, the time to reach the peak, etc. (step S4).

The image generation unit 14 can generate three-dimensional image data of the resin 42 covering the conductive portion 41 in the power equipment 40 based on the reflected wave signal acquired in step S3. The image generation unit 14 generates an image of the resin 42 based on the generated three-dimensional image data (step S5).

Here, the image (e.g., a planar image) of the resin 42 is composed of a plurality of pixels, each of which is assigned a pixel value corresponding to a reflected wave signal corresponding to the reflected waves of the terahertz waves irradiated based on a plurality of irradiation points set on the resin 42 (electric power equipment 40) by the oscillator 20 and receiver 30 scanning the top surface of the electric power equipment 40 as described above. In other words, to generate an image (three-dimensional image data) of the resin 42 that is clear enough to visually recognize the foreign matter 43, it is necessary to set a large number of irradiation points densely (i.e., at close intervals) on the plurality of pixels that make up the image.

However, it takes time to sequentially irradiate each of the numerous irradiation points set as described above with terahertz waves to inspect the inside of the resin 42.

For this reason, in this embodiment, image processing is incorporated when generating the image in step S5, thereby reducing the number of irradiation points (i.e., observation points for reflected waves). Here, it is assumed that image processing is performed based on compressed sensing technology (i.e., an image is generated by applying compressed sensing technology). Compressed sensing technology is a technology that restores target data from a smaller number of pieces of data than required. When compressed sensing technology is applied in this embodiment, unknown reflected wave signals can be derived from a small number of reflected wave signals (an image generated based on) obtained by irradiating terahertz waves to irradiation points that are sparsely set for multiple pixels that make up the image, and the image can be restored (generated) using the derived reflected wave signals. For restoration, coefficients (called an observation matrix) for converting an image acquired at dense irradiation points to an image acquired at sparse irradiation points must be set in advance. By correctly setting this matrix, it is possible to convert a sparse image into a dense image.

Here, with reference to Figure 13, we will explain an example of an image generated by applying compressed sensing technology in this embodiment.

First, the original image 81 shown in FIG. 13 is an image generated based on reflected wave signals obtained by irradiating terahertz waves onto irradiation points that are densely set on multiple pixels that make up the image generated by the image generation unit 14 (i.e., the image output by the output unit 17). The original image 81 is a clear image, and foreign matter 43 in the original image 81 can be easily seen. Note that it is assumed that the irradiation points are set at a pitch of, for example, 0.5 mm x 0.5 mm in the original image 81.

Next, the first thinned image 82 is an image generated based on reflected wave signals obtained by reducing the number of irradiation points by 75% compared to the original image 81 and irradiating the remaining 25% of irradiation points with terahertz waves. In other words, the pitch of the irradiation points in the first thinned image 82 is 1 mm x 1 mm. Because the number of irradiation points (i.e., reflected wave signals) in the first thinned image 82 is reduced compared to the original image 81, the clarity of the first thinned image 82 is lower than that of the original image 81. However, when compressed sensing technology is applied to the first thinned image 82 (the reflected wave signals used to generate it), a first restored image 83 can be obtained. The clarity of the first restored image 83 is improved compared to the first thinned image 82.

The second thinned image 84 is an image generated based on reflected wave signals obtained by reducing the number of irradiation points by 96% compared to the original image 81 and irradiating the remaining 4% of irradiation points with terahertz waves. That is, the pitch of the irradiation points in the second thinned image 84 is 2 mm x 2 mm. Because the number of irradiation points in the second thinned image 84 is further reduced compared to the first thinned image 82, the clarity of the second thinned image 84 is even lower than that of the first thinned image 82. However, when compressed sensing technology is applied to the second thinned image 84 (the reflected wave signals used to generate it), a second restored image 85 can be obtained. The clarity of the second restored image 85 is improved compared to the second thinned image 84.

Furthermore, the third thinned image 86 is an image generated based on the reflected wave signals obtained by reducing the number of irradiation points by 99% compared to the original image 81 and irradiating the remaining 1% of irradiation points with terahertz waves. In other words, the pitch of the irradiation points in the third thinned image 86 is 5 mm x 5 mm. Because the number of irradiation points in the third thinned image 86 is further reduced compared to the second thinned image 84, the clarity of the third thinned image 86 is even lower than that of the second thinned image 84. However, when compressed sensing technology is applied to the third thinned image 86 (or the reflected wave signals used to generate it), a third restored image 87 can be obtained. The clarity of the third restored image 87 is improved compared to the third thinned image 86.

In the first restored image 83 and the second restored image 85 shown in Figure 13 above, the foreign object 43 is easily visible, just like in the original image 81. Therefore, when compressed sensing technology is applied in this embodiment, it is thought that the number of illumination points can be reduced by up to 96% compared to the original image 81 (i.e., illumination points densely set for multiple pixels that make up the image).

In other words, in this embodiment, by applying compressed sensing technology, it is possible to obtain an image that is useful for recognizing (understanding) foreign matter 43, even if, for example, irradiation points are set sparsely for multiple pixels that make up the image (i.e., the number of irradiation points is reduced). Note that setting irradiation points sparsely for multiple pixels that make up the image means, for example, setting fewer irradiation points than the number of irradiation points set to obtain original image 81 (i.e., setting irradiation points at wider intervals than the irradiation points set to obtain original image 81).

Note that although the third restored image 87 has lower clarity (is unclear) compared to the original image 81, it is possible to visually identify the foreign matter 43 depending on the type of foreign matter 43. Therefore, if it is expected that the foreign matter 43 mixed inside the resin 42 can be relatively easily visually identified, it is acceptable to reduce 99% of the illumination points set to obtain the original image 81.

Step S5 in Figure 7 assumes that a planar image (an image in the XY plane) is generated, but a tomographic image (an image in the XZ plane or YZ plane) may also be generated in step S5.

Next, the depth calculation unit 15 calculates the depth of the foreign matter 43 mixed in the resin 42 based on the reflected wave signal acquired in step S3 (step S6). In this case, the depth of the foreign matter 43 is calculated based on the peak arrival time (measured light delay time of the terahertz wave) included in the reflected wave signal and the refractive index of the resin 42.

Note that in FIG. 7, the processes of steps S5 and S6 are described as being performed based on the reflected wave signal acquired in step S3, but these processes may also be performed based on the waveform data generated in step S4. Furthermore, the process of step S6 may also be performed taking into account the image (e.g., a tomographic image) generated in step S5.

Next, the discrimination unit 16 discriminates the type of foreign matter 43 contained in the resin 42 based on the waveform data generated in step S4 (step S7).

The processing of step S7 will be described below. As mentioned above, the propagation and reflection behavior of terahertz waves differs depending on the dielectric constant of the material; for example, metal causes total reflection. In this embodiment, this characteristic (property) is utilized to non-destructively determine (estimate) the type (material) of foreign matter 43 mixed inside resin 42.

Figure 15 is a diagram illustrating the difference in characteristics between a reflected wave from a foreign object (or defect) (hereinafter referred to as a first reflected wave) and a reflected wave from the resin surrounding the foreign object (surrounding resin without foreign objects) (hereinafter referred to as a second reflected wave) when comparing the first and second reflected waves. Note that the first and second reflected waves shown in Figure 15 are reflected waves obtained as a result of actually inspecting the resin (inside).

Figure 15 shows the differences between the first and second reflected waves in terms of the reflected waveform characteristics, time delay characteristics, and frequency characteristics, with a circle, triangle, or cross indicating the degree of difference. Note that a circle indicates a difference in the characteristics, a cross indicates no difference (or an extremely small difference) in the characteristics, and a triangle indicates a difference between a circle and a cross.

First, let's explain the differences in the reflected waveform characteristics shown in Figure 15. The diagram shown here shows the reflected terahertz waveform, with the horizontal axis representing time and the vertical axis representing reflected wave intensity. If the foreign object is metal, the terahertz wave is totally reflected, and the amplitude of the first reflected wave is larger than that of the second reflected wave. Furthermore, the difference in amplitude between the first and second reflected waves occurs widely (within a range of several picoseconds) around the depth of the foreign object. Therefore, if the foreign object is metal, it can be said that there is a difference in the reflected waveform characteristics between the first and second reflected waves.

If the foreign object is an air bubble, the reflectivity is small, but a slight difference in amplitude occurs due to the difference in dielectric constant with the surrounding resin. Therefore, if the foreign object is an air bubble, there will be a difference in the reflected waveform characteristics between the first and second reflected waves.

When the foreign object is a resin burr, the difference in dielectric constant with the surrounding resin is small, but because the surrounding resin is uniform and flat, while an interface exists at the location of the resin burr, a slight amplitude difference occurs. It is also thought that this amplitude difference is influenced by the wrinkled shape of the resin burr within the resin. However, because this amplitude difference is smaller than when the foreign object is metal or when the foreign object is an air bubble, the difference between the first and second reflected waves in the reflected waveform characteristics when the foreign object is a resin burr is rated as fair.

Next, we will explain the differences in the time delay characteristics shown in Figure 15. The diagram shown here shows the correlation of the time difference between the first reflected wave and the second reflected wave, with the horizontal axis representing time and the vertical axis representing correlation. When the foreign object is metal or an air bubble, the time delay difference is 0 and the correlation between the foreign object and the surrounding resin is at its maximum, so there is almost no time delay difference (i.e., there is no difference between the first and second reflected waves in the time delay characteristics). On the other hand, when the foreign object is a resin burr, there is a clear time delay difference (i.e., there is a difference between the first and second reflected waves in the time delay characteristics).

Finally, we will explain the differences in frequency characteristics shown in Figure 15. Here, the correlation between the foreign matter (first reflected wave) and the surrounding resin (second reflected wave) in the 0.05 to 2.5 THz band is shown as a frequency characteristic. If the foreign matter is metal, no difference can be detected between the first and second reflected waves, and it can be said that there is no difference in the frequency characteristics between the first and second reflected waves. If the foreign matter is an air bubble, a difference between the first and second reflected waves can be detected in some low-frequency components, and the difference in frequency characteristics between the first and second reflected waves is evaluated as fair. Furthermore, if the foreign matter is a resin burr, a clear difference can be detected between the first and second reflected waves, especially in low-frequency components up to the 1 THz band, and it can be said that there is a difference in the frequency characteristics between the first and second reflected waves.

In this embodiment, the type of foreign matter is identified by understanding the characteristics (properties) described above and then using a specified foreign matter identification algorithm.

In the above-mentioned foreign matter discrimination algorithm, for example, multiple waveform data are extracted by random sampling of the results (waveform data) of actual resin inspections, and a correlation filter (a filter containing information about the surrounding resin without any foreign matter) is created. The correlation filter is then shifted while performing a convolution process to ensure consistency of amplitude and phase differences within each region. This allows the region furthest from the correlation filter to be detected as a location where a foreign matter has been mixed in (or a defective location). In this case, by inputting waveform data indicating the reflected waves from the location where the foreign matter has been mixed in (i.e., the amplitude, phase difference, frequency characteristics, etc. related to the foreign matter) into an identifier, the type of the foreign matter can be determined based on the correlation with the surrounding resin (waveform data indicating the reflected waves from the surrounding resin). The identifier to which this waveform data is input can use a trained model that has previously learned the correlation (and thus the type of foreign matter) between the waveform data indicating the reflected waves from the interfaces of each of the above-mentioned foreign matters and the waveform data indicating the reflected waves from the surrounding area of the foreign matter.

When the processing of step S7 is executed, the output unit 17 outputs, for example, the waveform data generated in step S4, the image generated in step S5, the depth of the foreign object 43 calculated in step S6, and the type of foreign object 43 determined in step S7 as inspection results for the inside of the resin 42 covering the conductive part 41 in the electric power equipment 40 (step S8).

Specifically, in step S8, the waveform data, image, depth of the foreign matter 43, and type of foreign matter 43 are output to, for example, a display device provided in the inspection device 10 and displayed on the display device. This allows an inspector using the inspection device 10 to easily identify foreign matter 43 that has become mixed in the resin 42 by visually checking the waveform data, image, depth of the foreign matter 43, and type of foreign matter 43.

The waveform data, image, depth of foreign matter 43, and type of foreign matter 43 may be displayed in a variety of ways. Specifically, for example, the waveform data and image may be displayed side by side on the same screen, or the depth of foreign matter 43 and type of foreign matter 43 may be displayed superimposed on the image. Furthermore, the waveform data, image, depth of foreign matter 43, and type of foreign matter 43 may be processed as appropriate before being displayed. In this case, for example, the position of foreign matter 43 (brightness value, area value, etc.) may be extracted from the image, and the image may be displayed in a manner that allows the foreign matter 43 (or type of foreign matter 43) to be easily visually identified.

Here, the waveform data, image, depth of the foreign object 43, and type of foreign object 43 are described as being displayed on the display device, but the waveform data, image, depth of the foreign object 43, and type of foreign object 43 may also be output (transmitted) to an external server device for further analysis processing, etc.

Furthermore, the inspection results output in step S8 may include at least one of waveform data, an image, the depth of the foreign matter 43, and the type of the foreign matter 43.

Although omitted from Figure 7, it is conceivable that the reflected waves from the interface of foreign matter 43 mixed in resin 42 covering conductive portion 41 in the above-described power device 40 will differ depending on the frequency band of the terahertz waves, and therefore steps S3 to S7 may be performed for each specific frequency band. Specifically, steps S3 to S7 may be performed for each frequency band subdivided (divided) into, for example, a range of 0.05 to 1 THz.

Alternatively, for example, a configuration may be adopted in which it is determined whether or not foreign matter has been mixed into the resin 42 based on the waveform data generated in step S4 and the image generated in step S5, and if it is determined that foreign matter has been mixed into the resin 42, the processes of steps S6 and S7 are executed.

As described above, in this embodiment, terahertz waves (pulse waves) are irradiated based on multiple irradiation points set on the resin 42, and reflected wave signals corresponding to waves reflected from the interface of foreign matter 43 mixed inside the resin 42 are acquired. An image including the foreign matter 43 is generated based on the reflected wave signals, and the multiple irradiation points are set sparsely relative to the multiple pixels that make up the generated image.

In this embodiment, this configuration makes it possible to reduce the number of irradiation points (i.e., the number of times terahertz waves are irradiated during inspection), thereby shortening the time (hereinafter simply referred to as inspection time) required to non-destructively inspect the interior of the resin 42 covering the conductive portion 41 of the power device 40.

Note that when multiple illumination points are set sparsely as described above, applying compressed sensing technology can generate a restored image in which foreign objects are visible to the same extent as the original image described above. However, as long as it is possible to generate an image in which foreign objects are visible even when illumination points are set sparsely, technology similar to compressed sensing technology or technology other than compressed sensing technology may also be applied.

In addition, in this embodiment, the propagation behavior of terahertz waves (pulse waves) is predicted based on at least one of the structure of the electric power equipment 40 and the relative dielectric constant of the resin 42 and foreign matter 43 that may be mixed inside the resin 42, and the irradiation conditions for the terahertz waves are set based on the predicted propagation behavior of the terahertz waves. In this embodiment, this configuration makes it possible to set appropriate irradiation conditions for the electric power equipment 40 and inspect the inside of the resin 42, thereby reducing the possibility of obtaining low-accuracy reflected wave signals, for example. In other words, in this embodiment, efficient inspections can be performed, and as a result, the inspection time can be shortened.

The above-mentioned terahertz wave irradiation conditions include, for example, at least one of the frequency band of the terahertz waves, the position of the oscillator device 20 configured to emit the terahertz waves, and the position of the receiver device 30 configured to receive the reflected terahertz waves, but may also include other conditions (for example, the intensity of the terahertz waves).

In addition, in this embodiment, waveform data indicating a reflected waveform is generated based on the reflected wave signal obtained from the receiving device 30, and the type of foreign matter 43 mixed in the resin 42 is determined based on the generated waveform data. However, the type of the foreign matter 43 may also be determined using a trained model that has previously learned the correlation between the waveform data and waveform data indicating the reflected waveform from the resin surrounding the foreign matter. In this embodiment, this configuration makes it possible to non-destructively determine the type of foreign matter 43 mixed in the resin 42, and the determination result (type of foreign matter 43) can be used for checking the quality of the resin 42, analyzing the cause of the foreign matter being mixed in the resin 42, and taking measures to prevent the foreign matter 43 from being mixed in.

While this embodiment has been described as using terahertz waves in a frequency band ranging from 0.05 to 10 THz, it is preferable to use terahertz waves in the 0.075 to 0.125 THz band. Furthermore, if the foreign matter 43 or defect mixed in the resin 42 is, for example, at least one of metal, air bubbles, resin burrs, peeling, and cracks, terahertz waves in the 0.1 THz band can effectively visualize the foreign matter 43 in an image generated based on the reflected wave signal. Therefore, this embodiment preferably uses terahertz waves in the 0.1 THz band, particularly in the 0.075 to 0.125 THz band. In other words, the 0.1 THz band is preferentially selected as the frequency band of terahertz waves included in the terahertz wave irradiation conditions in this embodiment, compared to other frequency bands. However, depending on the results of the prediction of the propagation behavior of terahertz waves described above, frequency bands other than the 0.1 THz band may also be included in the terahertz wave irradiation conditions.

Furthermore, the oscillator 20 and receiver 30 in this embodiment may employ a lens system (a configuration including a lens that converges the terahertz waves and their reflected waves) or a lensless system (a configuration that does not include a lens that converges the terahertz waves and their reflected waves). However, if the oscillator 20 and receiver 30 employ a lens system, they can receive reflected waves with high intensity, thereby generating an image in which foreign matter 43, for example, as shown in FIG. 16, can be easily identified. In other words, the lens system can improve the accuracy of inspection based on reflected wave signals corresponding to reflected waves.

On the other hand, if the oscillator 20 and receiver 30 use a lensless system, the intensity of the reflected wave decreases, reducing the visibility of the foreign object 43 in the image, as shown in Figure 17. However, the lensless system eliminates the need for focusing and other tasks, which can contribute to shortening the inspection time.

As described above, the lens-based and lensless-based methods used in the oscillator 20 and receiver 30 each have different advantages, so the appropriate method should be selected depending on the object to be inspected (electric power equipment 40).

In this embodiment, multiple averaging processes may be performed on the reflected wave signal to reduce the noise level of the reflected wave signal, but the number of averaging processes may be reduced to shorten the inspection time.

In this embodiment, the electric power equipment 40 is mainly described as being irradiated with terahertz waves, but ultrasound can also be used as the pulse waves in this embodiment.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are within the scope of the invention and its equivalents as defined in the claims, as well as the scope and spirit of the invention.

10...Inspection device, 11...Propagation behavior prediction unit, 12...Reflected wave signal acquisition unit, 13...Waveform data generation unit, 14...Image generation unit, 15...Depth calculation unit, 16...Discrimination unit, 17...Output unit, 20...Oscillator, 30...Receiver, 40...Power equipment, 41...Conductive part, 42...Resin, 43...Foreign matter, 51...Beam splitter, 52...Lens, 101...CPU, 102...Non-volatile memory, 103...RAM, 103a...Inspection program, 104...Communication device.

Claims (10)

An inspection method for inspecting the inside of a resin covering a conductive part in an electric power device, comprising:
acquiring a reflected wave signal corresponding to a wave reflected from an interface of a foreign substance mixed inside the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin;
and generating an image including the foreign object based on the acquired reflected wave signal,
the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image ;
the generating step generates the image by applying a compressed sensing technique;
The number of the plurality of irradiation points that are set varies depending on the type of foreign matter that may be mixed inside the resin . and predicting a propagation behavior of the pulse wave based on at least one of a structure of the electric power device and a relative dielectric constant of the resin and a foreign matter that may be mixed in the resin,
The inspection method according to claim 1 , wherein the pulse wave irradiation conditions are set based on the predicted propagation behavior of the pulse wave. 3. The inspection method according to claim 2, wherein the pulse wave irradiation conditions include at least one of the frequency of the pulse wave, the position of an oscillator configured to oscillate the pulse wave, and the position of a receiver configured to receive the reflected wave. generating waveform data representing a reflected waveform based on the acquired reflected wave signal;
and determining the type of the foreign matter based on the generated waveform data,
The inspection method according to any one of claims 1 to 3, wherein the type of the foreign matter is determined using a trained model that has previously trained the correlation between waveform data showing the waveform reflected from the interface of the foreign matter and waveform data showing the waveform reflected from the resin surrounding the foreign matter. the foreign matter includes at least one of metal, air bubbles, resin burrs, peeling, and cracks;
The inspection method according to any one of claims 1 to 4 , wherein the pulsed wave includes terahertz waves in at least a 0.1 terahertz band. The inspection method according to any one of claims 1 to 5, wherein an oscillator configured to oscillate the pulse wave and a receiver configured to receive the reflected wave are configured to include lenses that converge the pulse wave and the reflected wave . The inspection method according to any one of claims 1 to 5, wherein an oscillator configured to oscillate the pulse wave and a receiver configured to receive the reflected wave are configured not to include a lens that converges the pulse wave and the reflected wave . An inspection device for inspecting the inside of a resin covering a conductive part in an electric power device,
an acquisition means for acquiring a reflected wave signal corresponding to a reflected wave from an interface of a foreign substance mixed in the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin;
generating means for generating an image including the foreign matter based on the acquired reflected wave signal;
the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image ;
the generating means generates the image by applying a compressed sensing technique;
The number of the plurality of irradiation points that are set varies depending on the type of foreign matter that may be mixed inside the resin . An inspection system for inspecting the inside of a resin covering a conductive part in an electric power device,
an oscillator configured to generate pulse waves to be irradiated based on a plurality of irradiation points set on the resin;
a receiving device configured to receive a reflected wave of the pulse wave from an interface of a foreign substance mixed inside the resin;
an inspection device including: an acquisition means for acquiring a reflected wave signal corresponding to the reflected wave received by the receiving device; and a generation means for generating an image including the foreign matter based on the acquired reflected wave signal;
the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image ;
the generating means generates the image by applying a compressed sensing technique;
The number of the plurality of irradiation points that are set varies depending on the type of foreign matter that may be mixed inside the resin . A program executed by a computer of an inspection device that inspects the inside of a resin that covers a conductive part in an electric power device,
The computer,
acquiring a reflected wave signal corresponding to a wave reflected from an interface of a foreign substance mixed inside the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin;
generating an image including the foreign matter based on the acquired reflected wave signal;
the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image ;
the generating step generates the image by applying a compressed sensing technique;
The number of the plurality of irradiation points that are set varies depending on the type of foreign matter that may be mixed inside the resin .