JP2014134462A - Visualization method of structure defect, visualization device for structure defect, and visualization device for air bubbles or lesion region - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a visualization method of a structure defect and a visualization device for a structure defect by which discriminability between a closed crack and an open crack included in a structure can be improved and a defect such as a closed crack can be detected with high discriminability, and to provide a visualization device for air bubbles or a lesion region in which air bubbles or a lesion region included in a tissue can be detected with high discriminability.SOLUTION: Transmission/reception means 1: transmits a plurality of kinds of ultrasonic waves with a predetermined fundamental frequency and having amplitudes different from each other to a structure as transmission signals, respectively; receives ultrasonic waves reflected from the structure; and obtains a plurality of kinds of reception signals corresponding to the transmission signals. A signal processor 2: applies band-pass filtering for passing a component having the fundamental frequency, to the reception signals obtained in the transmission/reception means 1; obtains a plurality of kinds of video data corresponding to the reception signals; performs arithmetic operation based on magnitudes of the amplitudes of the corresponding transmission signals; and obtains a video image of a defect.

Description

  The present invention relates to a structure defect imaging method, a structure defect imaging apparatus, and a bubble or lesion imaging apparatus.

  In order to ensure the safety of important equipment such as nuclear reactors, aircraft, and railways, and to ensure the soundness of manufactured and joined materials, ultrasonic waves are reflected from cracks and imperfect joint surfaces that cause destruction. Safety management is carried out by detecting it by scattering and scattering and exchanging it if there is a risk while accurately evaluating its size. However, in a closed crack with a large crack closing stress or a closed crack with an oxide film formed on the crack surface, reflection and scattering of ultrasonic waves are small, and the measurement error of the crack length and depth is large. Is a problem. Such a “closed crack” includes a crack having an opening width of nanometer order or less.

  The process of obtaining an image of a crack by adding a signal with a different delay depending on the position of the element to the scattered wave obtained by the receiving array element is called a phased array method, and is known in the field of nondestructive inspection. (For example, see Non-Patent Document 1). However, there is a problem that it is difficult to accurately measure the closed crack even by the image by the phased array method.

  Against this background, a closed crack quantitative evaluation method and a closed crack quantitative evaluation device that uses high-amplitude ultrasonic waves and uses harmonics and subharmonic waves generated by a closed crack are available. It has been proposed (see, for example, Patent Document 1). In this evaluation method and apparatus, a closed crack can be visualized by applying the phased array method to the subharmonic wave. This method is named SPACE (subharmonic phased array for crack evaluation) (see, for example, Non-Patent Document 2). Here, “subharmonic” means subharmonic.

FIG. 8 shows the principle of SPACE. As shown in FIG. 8, in SPACE, as an elemental technology, a transmitter using a LiNbO ₃ single crystal resonator that can generate large-amplitude ultrasonic waves and has excellent pressure resistance, and an array receiver for performing imaging And a frequency pass filter (digital filter). By entering a large amplitude ultrasonic wave (frequency f) from the transmitter, in addition to the linear scattering of the fundamental wave (frequency f) at the crack opening, the closed crack surface of the closed wave is a large amplitude ultrasonic wave. A subharmonic wave (frequency f / 2) is generated by opening and closing vibration due to tensile stress. By receiving this with an array receiver and separating each component with a digital filter, a fundamental wave image and a subharmonic wave image can be observed. As shown in FIG. 8, when the crack tip is closed, the crack depth which is underestimated in the fundamental wave image can be accurately measured by the subharmonic image.

  In the field of medical ultrasound, in order to improve the discriminability of nonlinear scatterers such as bubbles, images are obtained by separating nonlinear components with filters from received waveforms with different incident wave amplitudes, then large amplitude images and small amplitudes. There has been proposed a method of performing a difference between an image obtained by multiplying an image obtained by multiplying the image by an amplitude ratio (see, for example, Patent Document 2). In defect inspection in a solid, SSM (scaling subtraction method) has been proposed as a method of performing a difference calculation without using a filter (see, for example, Non-Patent Document 3). Further, an amplitude difference (AD) method has been proposed in which a method similar to that of Patent Document 2 is introduced into SPACE, and a damped double node (DDN) simulation (see, for example, Non-Patent Document 4) and an experiment. Has been demonstrated to improve the selectivity of closed cracks (see Non-Patent Document 5, for example).

  On the other hand, in the open / close vibration of a closed crack, it is reported that not only a harmonic wave or a subharmonic wave but also a fundamental wave is generated and a threshold phenomenon is shown (for example, see Non-Patent Document 6).

Japanese Patent No. 4538629 JP 2002-301072 A

T. L. Szabo, “Diagnostic Ultrasound Imaging: Inside Out”, Academic Pr., September 7, 2004, p.171 Y. Ohara, S. Yamamoto, T. Mihara, and K. Yamanaka, “Ultrasonic Evaluation of Closed Cracks Using Subharmonic Phased Array”, Japanese Journal of Applied Physics, 2008, 47, pp. 3908-3915 M. Scalerandi, A. S. Gliozzi, C. L. E. Bruno, D. Masera, and P. Bocca, “A scalingmethod to enhance detection of a nonlinear elastic response”, Applied PhysicsLetters, 2008, 92, pp.101912-1-3 K. Yamanaka, Y. Ohara, M. Oguma, Y. Shintaku, “Two-Dimensional Analyzes of Subharmonic Generation at Closed Cracks in Nonlinear Ultrasonics”, AppliedPhysics Express, 2011, 4, pp.076601-1-3 Y. Ohara, Y. Shintaku, S. Horinouchi, M. Ikeuchi, and K. Yamanaka, “Enhancement of Selectivity in Nonlinear Ultrasonic Imaging of Closed Cracks Using AmplitudeDifference Phased Array”, Japanese Journal of Applied Physics, 2012, 51, pp.07GB18 -1-6 Yoshikazu Ohara, Satoshi Yamamoto, Atsushi Mihara, Kazushi Yamanaka, “Optimization of incident wave amplitude for closed crack imaging by nonlinear response of ultrasound”, Proceedingsof Ultrasonics Electronics Symposium, 2006, 27, 423-424

  In the SPACE shown in FIG. 8, when high distance resolution is required, a burst wave having a cycle number of 3 or less is used as an incident wave. At this time, since the frequency resolution is low, the nonlinear scatter source (crack closed portion) and the linear scatter source (bottom surface, crack opening, coarse crystal grain, weld defect) are close to each other and linear compared to the nonlinear scatter source. When the response from the scattering source is strong, not only the crack closed portion but also the fundamental wave component that cannot be removed by the filter appears in the subharmonic image. As a result, there is a problem that it becomes difficult to distinguish between a closed crack and an open crack, and the distinguishability is lowered. The burst wave is a wave composed of a sine wave having a plurality of cycles.

  In addition, in the methods described in Non-Patent Documents 3 to 5, the subharmonic wave generated by the closed crack is reflected by the bottom surface and received by the probe, so that a ghost response appears on the bottom surface. There is a problem that it cannot be completely removed. Patent Document 2 is a technique in the medical field, and as an example, only a method of performing analysis using subharmonic waves and harmonics is described, and a method of performing analysis using only the fundamental wave component is described. Not listed. For this reason, when applied to a defect such as a closed crack, as in Non-Patent Documents 3 to 5, the subharmonic wave generated by the closed crack is reflected by the bottom surface and received by the probe. For this reason, a ghost response appears on the bottom surface and cannot be completely removed.

  The present invention has been made paying attention to such a problem, and can improve the discrimination between a closed crack and an open crack contained in a structure, and can detect defects such as a closed crack with high discrimination. Structure defect imaging method, structure defect imaging device, and bubble and lesion imaging device capable of detecting bubbles and lesions contained in tissue with high discrimination The purpose is to provide.

  In order to achieve the above object, a structure defect imaging method according to the present invention is a structure defect imaging method for detecting a defect such as a closed crack included in a structure. A plurality of types of ultrasonic waves having different amplitudes at the fundamental frequency are transmitted to the structure as transmission signals, and an ultrasonic wave reflected from the structure is received, and a plurality of types of reception corresponding to the transmission signals are received. A transmission / reception step for obtaining a signal, a filtering step for applying a band-pass filter that passes the component having the fundamental frequency to each reception signal obtained in the transmission / reception step, and each reception signal after the filtering step An imaging process for obtaining a plurality of types of video data corresponding to each received signal, and an operation based on the magnitude of the amplitude of each corresponding transmission signal using each video data obtained in the imaging process. It was carried out, and a calculating step of obtaining an image of the defect, characterized in that it has.

In particular, in the imaging method of a structure defect according to the present invention, the transmission / reception step transmits two types of ultrasonic waves having an amplitude u ₁ and an amplitude u ₂ (u ₂ > u ₁ ) as each transmission signal. The imaging step obtains video data of response strength F ₁ corresponding to the transmission signal of amplitude u ₁ and video data of response strength F ₂ corresponding to the transmission signal of amplitude u ₂ , and the calculation step includes ΔF It is preferable to obtain a video of the defect by calculating a differential response intensity ΔF of each video data by = F ₂ − (u ₂ / u ₁ ) × F ₁ and selecting a positive part of the differential response intensity ΔF. .

  The structure defect imaging apparatus according to the present invention is a structure defect imaging apparatus for detecting a defect such as a closed crack included in a structure, and is different from each other at a predetermined fundamental frequency. A plurality of types of ultrasonic waves having amplitude are transmitted to the structure as transmission signals, respectively, and an ultrasonic wave reflected from the structure is received to obtain a plurality of types of reception signals corresponding to the transmission signals. Transmitting / receiving means, filter means configured to apply a band-pass filter that passes the component having the fundamental frequency to each received signal obtained by the transmitting / receiving means, and each reception after processing by the filter means A plurality of types of video data corresponding to each received signal based on the signal, and each transmission signal corresponding to each of the video data obtained by the video unit using the video data Performs calculation based of the magnitude of the amplitude, and a calculating unit configured to obtain an image of the defect, characterized in that it has.

In particular, in the imaging device of a structure defect according to the present invention, the transmission / reception means transmits two types of ultrasonic waves having amplitude u ₁ and amplitude u ₂ (u ₂ > u ₁ ) as transmission signals. The imaging means is configured to obtain video data of response intensity F ₁ corresponding to a transmission signal of amplitude u ₁ and video data of response intensity F ₂ corresponding to a transmission signal of amplitude u ₂ ; The calculation means calculates a differential response intensity ΔF of each video data by ΔF = F ₂ − (u ₂ / u ₁ ) × F ₁ and selects a positive part of the differential response intensity ΔF to thereby determine the defect. It is preferably configured to obtain an image.

  A structure defect imaging method and a structure defect imaging apparatus according to the present invention use a fundamental wave including a fundamental frequency of ultrasonic waves to be transmitted as a main component, and are included in the structure based on the following principle. Defects such as closed cracks can be detected.

That is, as shown in FIG. 1, the position vector of the closed crack is r _C , the position vector of the bottom surface in front of the closed crack which is a linear scattering source (left side in FIG. 1) is r _F , and the position vector behind the closed crack ( in Figure 1 the position vector of the bottom of the right side) and r _R. When the incident wave amplitude of the ultrasonic wave to be transmitted is small, since the ultrasonic wave passes through the closed crack, the response from the closed crack is very small. On the other hand, when the incident wave amplitude of the transmitted ultrasonic wave exceeds the threshold value, the closed crack is opened and closed by the stress of the ultrasonic wave, and the response of the fundamental wave as well as the subharmonic wave and the harmonic wave is remarkably increased. At this time, since the closed crack shows a nonlinear response to the incident wave amplitude of the ultrasonic wave, the nonlinear response is assumed to be a quadratic function which is the simplest nonlinear function shown in FIG.

Thus, the response strength F _C of the fundamental wave image in closed crack is as (1).
Here, c ₁ is the scattering coefficient of the fundamental wave at the closed crack, and u ₀ (r _C ) is the incident wave amplitude at the closed crack.

Next, consider the bottom response in the fundamental image. Response intensity of the fundamental wave image at the bottom of the front of the crack r _F and the rear of the bottom r _R F _F and F _R are the linear to the incident wave amplitude, respectively (2) and (3) Become.
Here, b ₁ is the scattering coefficient of the fundamental wave at the linear scattering source (bottom surface), and T is the reciprocal transmittance of the fundamental wave component at the closed crack r _T. Here, in the case of small amplitude, almost all of the fundamental wave is transmitted, so that T≈1, and in the case of large amplitude, energy of the fundamental wave is lost due to the opening / closing vibration of the crack, so that T <1.

From the equations (1) to (3), when the incident wave amplitude shown in FIG. 1 (a) is small, the incident wave amplitude u ₁ = u ₀ and the response intensity F ₁ of the fundamental wave image at the position r is (4) It becomes an expression.
Here, since the fundamental wave is almost completely transmitted at a small amplitude, T≈1, and δ (r) is a delta function having a large value near r = 0.

Further, from the equations (1) to (3), when the incident wave amplitude shown in FIG. 1B is large, the incident wave amplitude u ₂ = au ₀ (a = u ₂ / u ₁ > 1) is set at the position r. response intensity _{F 2} of the fundamental wave image is (5).

For comparison of intensity and sign, FIG. 3 shows a schematic diagram in which r _F , r _C and r _R are projected in one dimension and the response intensity at each position is expressed by a Gaussian function. FIG. 3A shows a response intensity F ₁ obtained by multiplying the response intensity F ₁ in the case of the small amplitude expressed by the expression (4) by the amplitude ratio a, and a response intensity F _{2 in} the case of the large amplitude expressed by the expression (5). Is shown in FIG. Here, when the difference of F ₁ obtained by multiplying F ₂ by the amplitude ratio a is taken, the bottom surface r _F is removed, and the difference response intensity ΔF at the position r is expressed by equation (6).

Here, A> 0 from a> 1. Further, B> 0 from a> 1, b ₁ > 0, and T <1. Therefore, the differential response intensity ΔF is as shown in FIG. As shown in FIG. 3 (c), by the sign of A and B, and the response intensity in closed crack r _C, it is possible distinguish between responses strength at the bottom r _R. That is, by determining that only a positive response intensity is a closed crack with 0 as a threshold value, all the bottom surface responses are removed as shown in FIG. Is obtained as equation (9).

Next, for comparison, the same processing was performed on the existing technology described in Patent Document 2 and Non-Patent Document 5 using the amplitude difference of the subharmonic image. In this case, leakage of the fundamental wave components are generated by the band-pass filter, closed Taki for subharmonics as it passes through the cleft r _T is generated, FIG. 1 of the incident wave amplitude u _{1 =} u ₀ shown in (d) of The response intensity of the subharmonic image S _{1 and} the response intensity of the subharmonic image S _{2 with} the incident wave amplitude u ₂ = au ₀ shown in FIG. 1 (e) are shown in FIGS. 3 (d) and 3 (e), respectively. )become that way. Taking the difference of S ₁ multiplied by the amplitude ratio a from S ₂ , the bottom surface r _F is removed, and the differential response intensity ΔS at the position r is given by equation (10).

Here, c ₂ is the scattering coefficient of the subharmonic waves in closed crack r _C. Β is a leak coefficient of the band-pass filter, and βB is a leak of the fundamental wave component B in the band-pass filter that occurs when a burst wave with a large amplitude is used. Further, c ₃ A is a subharmonic wave generated when passing through the closed crack r _T. As shown in FIG. 1 (e), this is proportional to u ₀ (r _T ) ² , but here it is assumed that it is proportional to c ₃ u ₀ (r _C ) ² for simplicity. Here, c ₃ is the generation factor of the subharmonic waves in transmission.

The response of the closed crack is c ₂ A> 0, as in the case of equation (6). On the other hand, since βB <0 but c ₃ A> 0, there may be βB + c ₃ A> 0. In this case, as shown in FIG. 3 (f), the differential response strength ΔS cannot be discriminated by the signs of c ₂ A and βB + c ₃ A because the response of the bottom surface is positive. For this reason, as shown in FIG. 1F, the closed crack and the bottom surface remain as positive responses, and the closed crack and the bottom surface response cannot be identified.

Next, the same process was performed for the existing technology described in Non-Patent Document 3 that does not use a band-pass filter for further comparison. In this case, the response intensity is expressed as the sum of the fundamental wave image and the subharmonic image. Therefore, the response intensity of the image U ₁ = F ₁ + S _{1 with} the incident wave amplitude u ₁ = u ₀ and the response intensity of the image U ₂ = F ₂ + S _{2 with} the incident wave amplitude u ₂ = au ₀ are respectively shown in FIG. 3 (g) and FIG. 3 (h). Taking the difference between U ₁ multiplied by the amplitude ratio a of U _2, bottom r _F is removed, the difference in response strength ΔU at position r is (11).

In the expression (11), it is obvious that (c ₁ + c ₂ ) A> 0 as in the expressions (6) and (10). Further, the leakage of the basic component in the band pass filter is (β + 1) B <0, but the subharmonic generated when passing through the crack is c ₃ A> 0, so (β + 1) B + c ₃ A> 0. It may become. In this case, as shown in FIG. 3 (i), the difference response intensity ΔU has a positive bottom response, and cannot be discriminated by the signs of (c ₁ + c ₂ ) A and (β + 1) B + c ₃ A. For this reason, the closed crack and the bottom surface remain as positive responses, and the closed crack and the bottom surface response cannot be distinguished.

  As described above, the structure defect imaging method and the structure defect imaging apparatus according to the present invention use only the fundamental wave, so that existing structures such as Patent Document 2, Non-Patent Document 3, and Non-Patent Document 5 are used. It can be said that closed cracks are more distinguishable than technology. The structure defect imaging method and the structure defect imaging apparatus according to the present invention can enhance the distinction between a closed crack and an open crack included in the structure, and can be a defect such as a closed crack. Can be detected with high discrimination.

  The structure defect imaging method and the structure defect imaging apparatus according to the present invention change the amplitude of a transmission signal in a process of obtaining a reception signal by scanning an ultrasonic wave having a predetermined amplitude as a transmission signal. However, it may be configured to obtain a plurality of types of received signals by repeating a plurality of times. Further, a plurality of types of reception signals may be obtained while changing the amplitude of the transmission signal at a predetermined period. The ultrasonic wave to be transmitted may be formed of a burst wave or a pulse wave composed of a sine wave having a plurality of cycles. Further, the ultrasonic wave to be transmitted may be a chirp wave whose frequency changes continuously, and the received signal may be configured by performing pulse compression processing on the received signal.

  In the structure defect imaging method and the structure defect imaging apparatus according to the present invention, the defect exhibits a response in which the reflection intensity of the received signal is nonlinear with respect to the amplitude of the transmitted signal to be transmitted. It may consist of things. Examples of non-linear responses include closed cracks in structures, bubbles in tissues, and lesions. If the defect consists of bubbles or lesions in the tissue, replace “structure” with “tissue” and “defect” with “bubbles or lesion” to visualize the bubble or lesion imaging method. An imaging apparatus for a lesion can be configured. In this case, it is possible to improve the distinguishability of contrast medium bubbles and lesions in living tissue, and to detect bubbles and lesions contained in tissues by identifying the bubbles and lesions and other tissues. .

  According to the present invention, it is possible to improve the discrimination between a closed crack and an open crack included in a structure, and it is possible to detect a defect such as a closed crack with high discrimination. It is possible to provide an imaging method, a structure defect imaging apparatus, and a bubble and lesion imaging apparatus capable of detecting bubbles and lesions contained in a tissue with high discrimination.

1 is a principle diagram showing a structure defect imaging method and a structure defect imaging apparatus according to an embodiment of the present invention; The fundamental wave image intensity (I _C ) of the closed crack and the fundamental wave image intensity (I _S ) of the linear scattering source of the structure defect imaging method and structure defect imaging apparatus according to the embodiment of the present invention It is a graph showing incident wave amplitude dependence. (A) embodiment of a structure defect imaging device of the imaging method and a structure defect of the present invention, those in response F ₁ of the fundamental wave image in the small amplitude enters multiplied by the amplitude ratio a, (b) The response F ₂ of the fundamental wave image at the large amplitude incidence, (c) the response ΔF of the difference image of the fundamental wave, and (d) the subharmonic image at the small amplitude incidence of the existing technology using the amplitude difference of the subharmonic image. that the response S ₁ multiplied by the amplitude ratio a, not using (e) the subharmonic response S ₂ of the wave image at a large amplitude _incident, (f) content harmonic of the difference image of the response [Delta] S, (g) bandpass filter existing techniques, multiplied by the amplitude ratio a response U ₁ of the video in a small amplitude enters, is a graph illustrating the (e) response U ₂ video in large amplitude _incident, (f) response ΔU of these difference image . It is the longitudinal cross-sectional view which shows the imaging method of the structure defect of embodiment of this invention, and the imaging device of a structure defect, and the image | video obtained. It is the longitudinal cross-sectional view which shows the experiment arrangement | positioning of the imaging method of a structure defect, and the imaging apparatus of a structure defect of the comparative experiment using the amplitude difference of a subharmonic image, and the image | video obtained. It is a graph which shows the shift addition waveform in the closed crack of the image | video obtained by the comparative experiment shown in FIG. 5, and its wavelet transformation result. It is the longitudinal cross-sectional view which shows experiment arrangement | positioning, and the image | video obtained by the imaging method of the structure defect of embodiment of this invention and the imaging apparatus of a structure defect. It is the principle figure of the conventional SPACE which uses the phased array method with respect to a subharmonic wave.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
4 to 7 show a structure defect imaging method and a structure defect imaging apparatus according to an embodiment of the present invention. The structure defect imaging method of the embodiment of the present invention is preferably implemented by the structure defect imaging apparatus of the embodiment of the present invention.
As shown in FIG. 4, the structure defect imaging apparatus according to the embodiment of the present invention includes transmission / reception means 1 and a signal processor 2.

  The transmission / reception means 1 integrally has an ultrasonic transmitter capable of irradiating ultrasonic waves having an arbitrary incident wave amplitude and an array receiver composed of a plurality of sensor elements. The transmission / reception means 1 is configured to be capable of transmitting a plurality of types of ultrasonic waves having different amplitudes at a predetermined fundamental frequency to the closed crack C in the sample S of the structure by means of an ultrasonic transmitter. Yes. In addition, the transmission / reception means 1 receives ultrasonic waves reflected from the sample S including nonlinear scattered waves generated by the crack C closed by the ultrasonic waves transmitted from the ultrasonic transmitter by the array receiver, A plurality of types of reception signals corresponding to each transmission signal are obtained.

  The signal processor 2 is composed of a computer connected to the transmission / reception means 1, and has a filter means, an imaging means, and a calculation means. The filter unit is configured to apply a band-pass filter that passes a component having a fundamental frequency to each reception signal obtained by the array receiver of the transmission / reception unit 1. The imaging means is configured to obtain a plurality of types of video data corresponding to each received signal using a phased array method for each received signal processed by the filter means. That is, the imaging means shifts each received signal that has passed through the band-pass filter by a different time depending on the position of each sensor element of the array receiver, and then adds them to obtain a processed signal. Each video data is obtained based on the processed signal.

  The computing means is configured to obtain an image of the closed crack C by performing computation based on the amplitude of each corresponding transmission signal using each video data obtained by the imaging means.

In a specific example shown in FIG. 4, the structure defect imaging method and the structure defect imaging apparatus according to the embodiment of the present invention are represented by Equations (1) to (9) and FIGS. 1 to 3. Based on the principle shown, an image of a closed crack C is obtained. That is, the transmission / reception means 1 transmits two types of ultrasonic waves having amplitude u ₁ = u ₀ and amplitude u ₂ = au ₀ (a = u ₂ / u ₁ > 1) to the sample S as transmission signals, respectively. The ultrasonic waves reflected from the bottom surface B of the sample S, the closed crack C, and the like are received. After applying the band-pass filter of the filter means to each received signal, the imaging means for the imaging area D has a fundamental wave image (video data) of response intensity F ₁ corresponding to the transmission signal of small amplitude u ₁ = u _0. ) and I1, to obtain a large amplitude _u 2 = fundamental wave image of the response intensity _{F 2} corresponding to the transmission signal of au ₀ (image data) I2.

  At this time, in the fundamental wave image I1 having a small amplitude, since the ultrasonic wave passes through the closed crack C, the closed crack C at the position of the broken line 3 is not visualized, and only the bottom surface 4 and the bottom surface 5 appear. However, in the fundamental wave image I2 having a large amplitude, not only the subharmonic wave and the harmonic wave but also the fundamental wave is generated by the opening / closing vibration of the closed crack C, so that the response 6 of the closed crack C also appears. On the other hand, since the transmittance is reduced by the opening and closing vibration of the crack, the amplitude of the bottom surface 8 is reduced.

Next, the arithmetic means multiplies the small-amplitude fundamental wave image I1 by the amplitude ratio a to obtain a difference from the large-amplitude fundamental wave image I2, that is, each fundamental wave image by ΔF = F ₂ −a × F _1. The differential response intensity ΔF is calculated. Thereby, in the difference image I3, the closed crack C appears as an increment, the bottom 10 becomes 0, and the bottom 11 appears as a decrement. Therefore, by displaying only the incremental difference image I3, that is, by selecting a positive portion of the differential response intensity ΔF, the bottom surface 11 is removed, and only the response 9 of the closed crack C can be visualized.

  As described above, the structure defect imaging method and the structure defect imaging apparatus according to the embodiment of the present invention use only the fundamental wave to obtain a closed defect and an open crack included in the structure. The discriminability can be improved, and a defect such as a closed crack can be detected with high discriminability. In addition, since the fundamental wave has a frequency twice that of the subharmonic wave, the spatial resolution can be improved as compared with that obtained from the amplitude difference of the conventional subharmonic image.

  In the structure defect imaging method and the structure defect imaging apparatus according to the embodiment of the present invention, the defect to be detected is not limited to a closed crack, but the magnitude of the amplitude of a transmitted signal to be transmitted. As long as the reflection intensity of the received signal exhibits a non-linear response, any signal may be used. Examples of the nonlinear response include air bubbles and lesions in the tissue in addition to the closed crack in the structure. If the defect consists of bubbles or lesions in the tissue, replace “structure” with “tissue” and “defect” with “bubbles or lesion” to visualize the bubble or lesion imaging method. An imaging apparatus for a lesion can be configured. In this case, it is possible to improve the distinguishability of contrast medium bubbles and lesions in living tissue, and to detect bubbles and lesions contained in tissues by identifying the bubbles and lesions and other tissues. .

  Note that the structure defect imaging method and the structure defect imaging apparatus according to the embodiment of the present invention include a step of obtaining a reception signal by scanning an ultrasonic wave having a predetermined amplitude as a transmission signal. It may be configured to obtain a plurality of types of received signals by repeating a plurality of times while changing the amplitude. Further, a plurality of types of reception signals may be obtained while changing the amplitude of the transmission signal at a predetermined period. The ultrasonic wave to be transmitted may be formed of a burst wave or a pulse wave composed of a sine wave having a plurality of cycles. Further, the ultrasonic wave to be transmitted may be a chirp wave whose frequency changes continuously, and the received signal may be configured by performing pulse compression processing on the received signal.

Closed cracks were detected using the structure defect imaging method and structure defect imaging apparatus according to the embodiment of the present invention. An austenitic stainless steel SUS316L produced by a three-point bending fatigue test was used as a test piece structure, and a closed fatigue crack introduced into the austenitic stainless steel was detected. Incidentally, fatigue conditions used here, the maximum stress intensity factor _K max = 18.6MPa ^{· m 1/2,} which is the minimum stress intensity factor _K min = 0.6MPa ^{· m 1/2.} For comparison, the same crack was also detected using the amplitude difference of the subharmonic image described in Non-Patent Document 5.

  The structure defect imaging apparatus uses a PZT array probe (5 MHz, 32 elements, 0.5 mm pitch) as the transmission / reception means 1. As the incident wave, a burst wave having a frequency of 7 MHz and 3 cycles was used. For the incident wave, a displacement of 8.9 nm (stress 2.4 MPa) and a displacement of 26.7 nm (stress 7.3 MPa) were used as a small amplitude and a large amplitude, respectively.

  FIG. 5 shows a subharmonic image when the amplitude difference of the subharmonic image of the comparative experiment is used. As shown in FIG. 5, the response of the closed crack C appeared in the small-amplitude subharmonic image I11 and the large-amplitude subharmonic image I12. However, as a response other than the closed crack C, the bottom surface B and the notch N also appeared as ghosts due to leakage in the band pass filter. Therefore, the signal processor 2 multiplies the small-amplitude subharmonic image I11 by the amplification factor a = 26.7 nm / 8.9 nm≈3 of the incident wave displacement amplitude to obtain a large-amplitude subharmonic image I12. To obtain a differential image I13. In the difference image I13, the discriminability, which is the intensity ratio of the closed crack C to the bottom surface B and the notch N, is improved by 7.6 dB compared to the large amplitude subharmonic image I12. However, the bottom surface B and the notch N could not be completely removed. This is presumably because the bottom surface B appeared as an increment in the subharmonic image as well as the closed crack C.

  Here, the shift addition waveform W1 before applying the band pass filter and the wavelet transform (time frequency analysis) result W2 at the position of the closed crack C of the large amplitude subharmonic image I12 are shown in FIG. As shown in FIG. 6, in the wavelet transformation result W2, it can be seen that not only the subharmonic wave having the frequency of 3.5 MHz but also the scattered wave of the fundamental wave having the frequency of 7 MHz is generated. This is considered to be a fundamental wave generated accompanying the generation of subharmonic waves due to crack opening and closing vibrations.

  Next, FIG. 7 shows the amplitude difference of the fundamental wave image obtained by the structure defect imaging method of the embodiment of the present invention. A closed crack C response appeared in the small-amplitude fundamental wave image I14 and the large-amplitude fundamental wave image I15. However, as a response other than the closed crack C, the bottom surface B also appeared. Accordingly, the signal processor 2 subtracts the incident wave displacement amplitude amplification factor a = 26.7 nm / 8.9 nm≈3 from the small amplitude fundamental wave image I14 from the large amplitude fundamental wave image I15. Only the increment was displayed to obtain a differential image I16. In the difference image I16, the bottom surface B and the notch N are removed, and only the closed crack C can be extracted. In the difference image I16, the discriminability, which is the intensity ratio of the closed crack C to the bottom surface B, was improved by 34 dB compared to the large-amplitude fundamental wave image I17. Also, the spatial resolution was improved about twice compared with I13. This is because the frequency of the fundamental wave is twice the frequency of the subharmonic wave.

  As described above, the structure defect imaging method and the structure defect imaging apparatus according to the embodiment of the present invention are closed with respect to the existing technology such as Non-Patent Document 5 by using only the fundamental wave. It can be said that it is excellent in crack discrimination.

  The structure defect imaging method and the structure defect imaging apparatus according to the present invention are used in non-destructive evaluation of important equipment such as nuclear reactors, aircrafts, railways, and manufactured materials and bonded materials. It can be used to detect defects such as closed cracks with high discrimination.

DESCRIPTION OF SYMBOLS 1 Transmission / reception means 2 Signal processor 3, 6, 9 Closed crack (response)
4, 5, 7, 8, 10, 11 Bottom (response)
S Sample B Bottom C Closed crack D Imaging region N Notch I1, I14 Fundamental wave image with small amplitude (incident) I2, I15 Fundamental wave image with large amplitude (incident) I3, I16 Difference image I11 Small amplitude (incident) Subharmonic image I12 Large amplitude (incident) subharmonic image I13 Difference image W1 Shift addition waveform W2 Wavelet analysis result

Claims (8)

A structure defect imaging method for detecting a defect such as a closed crack contained in a structure,
A plurality of types of ultrasonic waves having mutually different amplitudes at a predetermined fundamental frequency are transmitted to the structure as transmission signals, and ultrasonic waves reflected from the structure are received, and a plurality of types of ultrasonic waves corresponding to the transmission signals are received. A transmission / reception step for obtaining a received signal;
A filter step of applying a band pass filter that passes the component having the fundamental frequency to each received signal obtained in the transmission / reception step;
An imaging step for obtaining a plurality of types of video data corresponding to each received signal based on each received signal after the filtering step;
Using each video data obtained in the imaging step, performing a calculation based on the magnitude of the amplitude of each corresponding transmission signal, and obtaining a video of the defect,
A method of imaging a structure defect, comprising: The transmission / reception step transmits two types of ultrasonic waves having amplitude u ₁ and amplitude u ₂ (u ₂ > u ₁ ) as transmission signals,
The imaging step obtains video data of response intensity F ₁ corresponding to a transmission signal of amplitude u ₁ and video data of response intensity F ₂ corresponding to a transmission signal of amplitude u ₂ ,
The calculation step calculates a differential response intensity ΔF of each video data by ΔF = F ₂ − (u ₂ / u ₁ ) × F ₁ and selects a positive part of the differential response intensity ΔF to thereby determine the defect. The method of imaging a structure defect according to claim 1, wherein an image is obtained.   3. The imaging of a structure defect according to claim 1, wherein the defect comprises a reflection response of the received signal that exhibits a non-linear response with respect to the amplitude of the transmitted signal to be transmitted. Method. A structure defect imaging device for detecting a defect such as a closed crack contained in a structure,
A plurality of types of ultrasonic waves having mutually different amplitudes at a predetermined fundamental frequency are transmitted to the structure as transmission signals, and ultrasonic waves reflected from the structure are received, and a plurality of types of ultrasonic waves corresponding to the transmission signals are received. Transmitting and receiving means configured to obtain a received signal;
Filter means configured to apply a band-pass filter that passes the component having the fundamental frequency to each received signal obtained by the transmission / reception means;
Based on each received signal processed by the filter means, an imaging means configured to obtain a plurality of types of video data corresponding to each received signal;
Using each video data obtained by the imaging means, calculation based on the magnitude of the amplitude of each corresponding transmission signal, and calculation means configured to obtain the image of the defect,
A structure defect imaging apparatus characterized by comprising: The transmitting / receiving means is configured to transmit two types of ultrasonic waves having amplitude u ₁ and amplitude u ₂ (u ₂ > u ₁ ), respectively, as each transmission signal,
The imaging means is configured to obtain video data of response intensity F ₁ corresponding to a transmission signal of amplitude u ₁ and video data of response intensity F ₂ corresponding to a transmission signal of amplitude u ₂ ;
The calculation means calculates a differential response intensity ΔF of each video data by ΔF = F ₂ − (u ₂ / u ₁ ) × F ₁ and selects a positive part of the differential response intensity ΔF to thereby determine the defect. 5. The structure defect imaging apparatus according to claim 4, wherein the structure defect imaging apparatus is configured to obtain an image.   6. The imaging of a structure defect according to claim 4 or 5, wherein the defect comprises a non-linear response of the reflection intensity of the received signal with respect to the amplitude of the transmitted signal to be transmitted. apparatus. A bubble and lesion imaging device for detecting bubbles and lesions contained in tissue,
A plurality of types of received signals corresponding to each transmission signal by transmitting a plurality of types of ultrasonic waves having different amplitudes at a predetermined fundamental frequency to the tissue as transmission signals, receiving ultrasonic waves reflected from the tissue, Transmitting and receiving means configured to obtain
Filter means configured to apply a band-pass filter that passes the component having the fundamental frequency to each received signal obtained by the transmission / reception means;
Based on each received signal processed by the filter means, an imaging means configured to obtain a plurality of types of video data corresponding to each received signal;
Using each video data obtained by the imaging means, performing a calculation based on the magnitude of the amplitude of each corresponding transmission signal, and a calculation means configured to obtain an image of the bubble or lesion,
A bubble or lesion imaging apparatus characterized by having a bubble or a lesion. The transmitting / receiving means is configured to transmit two types of ultrasonic waves having amplitude u ₁ and amplitude u ₂ (u ₂ > u ₁ ), respectively, as each transmission signal,
The imaging means is configured to obtain video data of response intensity F ₁ corresponding to a transmission signal of amplitude u ₁ and video data of response intensity F ₂ corresponding to a transmission signal of amplitude u ₂ ;
The calculation means calculates a differential response intensity ΔF of each video data by ΔF = F ₂ − (u ₂ / u ₁ ) × F _1, and selects the positive part of the differential response intensity ΔF to thereby calculate the bubbles and 8. The bubble or lesion imaging device according to claim 7, wherein the imaging device is configured to obtain an image of a lesion.