JP2016109536A - Wave transmission method and inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an SN ratio by the erasure of a backward transmission wave or an increase in the amplitude of a forward transmission wave even when a phase velocity and a group velocity are different.SOLUTION: A wave transmission method according to an embodiment includes a transmission step in which each of a first sensor 11 and a second sensor 12 transmits a wave packet in which a phase velocity and a group velocity are different. Assuming a phase velocity Vph, a group velocity Vg, a first integer n that is an integer greater than or equal to 1, and a wavelength λ of a transmitted wave, and that a distance L between the first sensor 11 and the second sensor 12 satisfies equation (1) below, one of the first sensor 11 and the second sensor 12 starts transmitting a wave in the transmission step with a timing and a phase difference that cancel or amplify the wave transmitted by the other sensor on the basis of the phase velocity, the group velocity, and the wavelength of the wave. L=Vg×0.5×n×λ/|Vg-Vph| (1)SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wave transmission method and an inspection apparatus.

  2. Description of the Related Art Conventionally, long members of various machine components, building members, construction members, and the like may be disposed deep in the machine, or may be embedded in a building or underground. In such cases, even if cracks, wear, corrosion, deformation, etc. occur due to changes over time, and changes in cross-sectional area, cross-sectional shape, and material properties occur, it is difficult to directly inspect the changes (defects) visually. It is. Therefore, an elastic wave traveling in the axial direction of the long member is transmitted from a place where the long member can be directly accessed, and an elastic wave (hereinafter referred to as an “echo wave”) reflected from a portion whose shape has changed is received. Thus, an elastic wave pulse reflection method for detecting the presence, position, degree, etc. of defects has been proposed.

  In the method described above, the distance to the defect is evaluated based on the time from transmission of the elastic wave to reception of the reflected echo wave and the propagation speed of the wave, and the defect amplitude is determined by the amplitude of the echo wave. Assessing the degree. In general, an elastic wave to be transmitted is a wave packet having a spatially finite width, but from a set of transmission sensors (for example, a probe, a probe, a transmitter, etc.) installed at a predetermined position of a long member, Elastic waves are transmitted to both sides of the long member in the axial direction. Therefore, an elastic wave transmitted in a direction opposite to the direction to be inspected (hereinafter referred to as “front”) (hereinafter referred to as “rear”) causes noise when it reaches the reception sensor by reflection or the like, for example. .

  For this reason, by installing two sets of transmission sensors and setting an appropriate transmission delay time for both, so-called elastic waves transmitted hereinafter (hereinafter referred to as “rear transmission waves”) are offset and suppressed. There is a case where direction control of a transmission wave is performed. Specifically, for example, the interval between two sensors is set to a quarter wavelength of the elastic wave to be transmitted, and the elastic wave transmitted backward is canceled by setting the transmission delay time to a quarter cycle. And suppress. In this case, in principle, the backward transmission wave is theoretically canceled out by giving a delay of a quarter cycle to the backward sensor and driving with a reverse polarity signal. Can do. Compared with the case of using one sensor, the rear sensor is driven by a signal of the same polarity by giving a delay of a quarter cycle to the front sensor. The amplitude of the elastic wave transmitted forward (hereinafter referred to as “forward transmission wave”) can be doubled.

Shunpei Kameyama, others, guided wave flaw detection system, Japan Nondestructive Inspection Association, Nondestructive Inspection, Vol. 52, No. 12, 672-678, issued on December 1, 2003 Nagashima Yoshiaki, etc., Pipe thinning inspection technology using guide waves, Nihon Kogyo Publishing Co., Ltd., Piping Technology, pages 19-24, June 2008 issue Masanari Shoji, others, Experimental study of ultrasonic guided wave flaw detection in cylindrical rods, 21st Symposium on Nondestructive Evaluation by Ultrasound, Japan Nondestructive Inspection Association, Ultrasound Division, Proceedings, 153-156 Page, issued on January 20, 2014 KWUN Hegeon, et al., The magnetostrictive sensor technology for long range guided wave testing and monitoring of structures, Materials Evaluation, vol. 61, no. 1, pp. 80-84, 2003

  However, in the above-described method, complete superposition of wave packets can be realized only when the phase velocity and the group velocity coincide. That is, in the general case where the phase velocity and the group velocity are different, the above-described method can eliminate the rear transmission wave completely, or increase the amplitude of the front transmission wave completely by a factor of 2, thereby increasing the SN ratio. (Signal-to-noise ratio) cannot be improved.

  Therefore, the present invention provides a wave transmission method and an inspection apparatus that can improve the S / N ratio by eliminating the backward transmission wave or increasing the amplitude of the forward transmission wave even when the phase velocity and the group velocity are different. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the wave transmission method includes a transmission step in which each of the first sensor and the second sensor transmits a wave having a phase velocity and a group velocity different from each other. When the phase velocity Vph, the group velocity Vg, a first integer n that is an integer equal to or greater than 1, and the wavelength λ of the transmitted wave, the distance L between the first sensor and the second sensor is A value satisfying the following formula (1) is set, and in the transmission step, one of the first sensor and the second sensor is based on the phase velocity, the group velocity, and the wave wavelength. The transmission of the wave is started at a timing and a phase difference that cancel or amplify the wave transmitted by the other sensor.

  L = Vg · 0.5 · n · λ / | Vg−Vph | (1)

  According to the present invention, even when the phase velocity and the group velocity are different, the SN ratio can be improved by eliminating the backward transmission wave or increasing the amplitude of the forward transmission wave.

FIG. 1 is a configuration diagram illustrating an overview of a transmission method according to an embodiment. FIG. 2 is a diagram illustrating a configuration example of the inspection apparatus in the transmission method according to the embodiment. FIG. 3 is a conceptual diagram illustrating an example of the relationship between the phase velocity and the group velocity in the transmission method according to the embodiment. FIG. 4 is a diagram illustrating an example of a processing procedure of the transmission method according to the embodiment. FIG. 5 is a diagram illustrating distances and the like that satisfy the conditions in the transmission method according to the embodiment. FIG. 6 is a conceptual diagram illustrating an example of the relationship between the phase velocity and the group velocity in the transmission method according to the embodiment. FIG. 7 is a diagram illustrating distances that satisfy the conditions in the transmission method according to the embodiment. FIG. 8 is a conceptual diagram illustrating a relationship based on the magnitude relationship between the phase velocity and the group velocity in the transmission method according to the embodiment. FIG. 9 is a diagram illustrating another example of the processing procedure of the transmission method according to the embodiment. FIG. 10 is a diagram illustrating a calculation result of the dispersion curve of the specific example 1 according to the embodiment. FIG. 11 is a diagram illustrating parameters of the long member according to the embodiment. FIG. 12 is a diagram illustrating a calculation result of the dispersion curve of the specific example 2 according to the embodiment. FIG. 13 is a diagram illustrating a calculation result of the dispersion curve of the specific example 3 according to the embodiment. FIG. 14 is a diagram illustrating an installation interval between two sensor pairs according to a modification. FIG. 15 is a diagram illustrating an example of a processing procedure of the transmission method according to the modification. FIG. 16 is a diagram illustrating a computer that executes a wave transmission program.

  Embodiments of a wave transmission method according to the present application will be described below in detail with reference to the drawings. The wave transmission method according to the present application is not limited by this embodiment.

[Overview]
First, an outline of a wave transmission method according to the present application will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, two sets of sensors 11 and 12 are installed on a long member 200 that is an object to be inspected at a predetermined interval in the axial direction. Hereinafter, the direction in which the long member 200 is inspected is assumed to be the front, and the direction not inspected is assumed to be the rear. Here, the sensor 11 is installed in front of the sensor 12 in the axial direction of the long member 200. Moreover, the sensors 11 and 12 use the sensor which can transmit an equivalent wave (the sensor 11 and 12 do not necessarily need to be the same sensor if an equivalent wave can be transmitted). For example, the sensors 11 and 12 are connected to the inspection apparatus 100 and driven by the inspection apparatus 100 as shown in FIG. In the present embodiment, the sensor 11 is used as a transmission sensor and a reception sensor.

  From here, a wave transmission method using the sensors 11 and 12 will be described. In the following description, sensors 11 and 12 are sensors having a phase velocity of transmitted waves of Vph, a wavelength of λ, and a frequency of f (Vph = λ · f). When the sensors 11 and 12 transmit a wave having a spatially finite width, the sensors 11 and 12 may superimpose waves having various frequencies including a wave having a frequency f (usually, a wave having a certain range of frequencies in the vicinity of f). The wave packet that is formed will be transmitted. Here, the group velocity of the wave packet transmitted by the sensors 11 and 12 is defined as Vg. Hereinafter, a wave transmitted forward from the sensors 11 and 12 may be referred to as a forward transmission wave, and a wave transmitted backward from the sensors 11 and 12 may be referred to as a backward transmission wave. The wave packets transmitted forward from the sensors 11 and 12 are also referred to as the forward wave packets, respectively, and the wave packets transmitted backward from the sensors 11 and 12 are combined together or the respective backward wave packets. Sometimes called. Also, t is a variable representing time, and the driving start time of the sensor that is driven first among the sensors 11 and 12 is the origin of time (t = 0). Further, the time t0 that has elapsed from the time when either one of the sensors 11 and 12 is driven (t = 0) until the other sensor is driven may be referred to as a delay time t0.

  First, a method for canceling and canceling backward transmission waves transmitted from the sensors 11 and 12 will be described. When the group velocity is faster than the phase velocity (Vph <Vg), the sensors 11 and 12 are installed with the distance L satisfying the following equation (2) opened in the axial direction of the long member 200.

  L = Vg · t0 (2)

  Here, the time t0 is a time determined by the wavelength, the group velocity, and the phase velocity, where the first integer n is an integer of 1 or more, and is represented by the following equation (3).

  t0 = 0.5 · n · λ / (Vg−Vph) (3)

  That is, the distance L indicates the distance that the wave packet travels (the distance that travels at the group velocity) during the time t0 such that the difference between the distance traveled by the group velocity and the phase velocity is an integral multiple of a half wavelength. In the example shown in FIG. 1, the sensors 11 and 12 are set apart by such a distance.

  Next, timing and polarity for driving the sensors 11 and 12 will be described. Hereinafter, a case will be described in which the sensor 12 is driven after the delay time t0 has elapsed from the origin (t = 0) of the time when the sensor 11 is driven.

  First, when the first integer n is an odd number, the sensor 11 is driven first, and after the delay time t0 has elapsed (t = t0), the sensor 12 is driven with a signal having the same polarity as the sensor 11. Here, the tip of the wave packet transmitted backward from the sensor 11 reaches the sensor 12 after t0. At this time, the phase of the backward transmission wave transmitted from the sensor 11 is inverted from the transmission time point. In other words, in the backward transmission wave transmitted from the sensor 11, the phase at the tip of the wave packet at the time t = t 0 is inverted by π with respect to the phase at the tip of the wave packet at the time t = 0. . Therefore, when the sensor 12 is driven at t = t0 with the same polarity (same phase, ie, phase difference 0) as the sensor 11 is driven, the sensor 12 is opposite to the wave packet transmitted from the sensor 11 and reaching the sensor 12. A wave packet having a phase (phase difference π) can be transmitted backward. Further, when the approximation that the shape of the wave packet is not deformed compared to the time of transmission from the sensor 11 is established, the wave packets transmitted backward from the sensor 11 and the sensor 12 are spatially completely superimposed. Therefore, in principle, wave packets transmitted backward from the sensor 11 and the sensor 12 can be completely canceled and eliminated.

  Here, an example of the phase shift in the wave packet will be described with reference to FIG. In FIG. 3, the horizontal axis represents the distance (spatial position) in the traveling direction (axial direction) of the wave packet, and the shape of the wave packet at an arbitrary time t1 (upper figure) and after t0 (n = 1, lower figure). Is a conceptual diagram showing an example of the relationship between the phase velocity and the group velocity. In the example shown in FIG. 3, the group velocity Vg is faster than the phase velocity Vph. First, in FIG. 3, the wave packet at time t = t1 is expressed as a wave packet including the point P11. Here, in the example shown in FIG. 3, the point P11 is located at the approximate center of the wave packet at the time t = t1 and is located at the point L11.

  Next, in FIG. 3, the wave packet at time t = t1 + t0 is represented as a wave packet including points P12 and P13. Here, in the example shown in FIG. 3, when time elapses from time t = t1 to time t = t1 + t0, the entire wave packet advances by the group velocity Vg · t0. That is, at the time t = t1 + t0, the wave packet point corresponding to the point P11 at the time t = 0 reaches the point L12. On the other hand, when time elapses from time t = t1 to time t = t1 + t0, the phase velocity is Vph, and the peak apex corresponding to the point P11 advances by the phase velocity Vph · t0. In the example shown in FIG. 3, since the phase velocity Vph is slower than the group velocity Vg, the peak apex of the point P11 at time t = t1 is shifted backward λ / 2 in the wave packet. Here, the phase of the point P13 at time t = t1 + t0 is shifted by π from the phase of the point P11 at time t = t1. In the above description, the point P11 at time t = t1 is described as a reference, but the same applies to any point of the wave packet at any time.

  Therefore, in the wave transmission method according to the present application, the distance traveled at the group velocity in the time interval in which the phase of the backward transmission wave from the sensor 11 is inverted (n: odd) or matched (n: even) (in FIG. The distance between the point L11 and the point L12 is an example of a reversal distance) The sensor 11 and the sensor 12 are installed at intervals, that is, the time point at the time t = t0 with respect to the phase of the tip of the wave packet at the time point t = 0. The sensor 12 is installed at a position where the phase at the tip of the wave packet is inverted by π shift or the phase difference is zero.

  When the first integer n is an even number, the sensor 11 is driven first, and after the delay time t0 has elapsed (t = t0), the sensor 12 is driven with a signal having a polarity opposite to that of the sensor 11. Here, the tip of the wave packet transmitted backward from the sensor 11 reaches the sensor 12 after t0. The waveform of the backward transmission wave packet from the sensor 11 is the same as the wave packet before or after the time t0 at an arbitrary time. In the backward transmission wave from the sensor 11, the waveform of the tip of the wave packet at the time t = 0 is obtained. With respect to the phase, the phase of the tip of the wave packet at time t = t0 is the same. Therefore, when the sensor 12 is driven at t = t0 with a signal (phase difference π) having a polarity opposite to the polarity that has driven the sensor 11, the sensor 12 transmits a wave packet having a phase opposite to that of the wave packet reached from the sensor 11 to the rear. be able to. When the approximation that the shape of the wave packet is not deformed as compared with the time of transmission from the sensor 11 holds, the wave packets from the sensor 11 and the sensor 12 to the rear are completely overlapped spatially. Therefore, in principle, wave packets transmitted backward from the sensor 11 and the sensor 12 can be completely canceled and eliminated.

[Processing procedure]
Here, the processing procedure of the wave transmission method for eliminating the backward wave packet described above will be described. FIG. 4 is a diagram illustrating an example of a processing procedure of the transmission method according to the embodiment.

  As shown in FIG. 4, first, the front sensor 11 is driven (step S11). After the sensor 11 is driven, the process waits until the delay time t0 has elapsed (step S12: No).

  When the delay time t0 has elapsed after driving the sensor 11 (step S12: Yes), the process is divided depending on the even / odd number of the first integer n. After the delay time t0 has elapsed (step S12: Yes), if the first integer n is an odd number (step S13: Yes), the rear sensor 12 is driven with the same polarity as the sensor 11 (step S14).

  On the other hand, after the delay time t0 has elapsed (step S12: Yes), when the first integer n is an even number (step S13: No), the rear sensor 12 is driven with a polarity opposite to that of the sensor 11 (step S15). . In this way, by changing the polarity of the wave transmitted from the sensor 12 according to the even number of the first integer n, the wave packet transmitted backward from the sensor 11 and the sensor 12 is canceled and eliminated.

  The backward transmission wave canceling control described above can be performed regardless of the value of both when the phase velocity Vph and the group velocity Vg are different. Furthermore, when the backward transmission wave is canceled as described above, the phases of the forward transmission waves from the sensors 11 and 12 can be matched simultaneously. For this purpose, a wave having twice the delay time t0 as a half integer multiple of the period 1 / f may be selected. That is, a wave that satisfies the following formula (4) is selected with the variable m set to an integer of 0 or more.

  2 · t0 = (0.5 + m) / f (4)

  Thereby, since the phases of the forward transmission wave packets from the sensors 11 and 12 coincide with each other regardless of whether the first integer n is even or not, the amplitude can be increased at a portion where they spatially overlap each other. Specifically, at the time t = 2 · t0, the tip of the wave packet transmitted forward from the sensor 12 reaches the position of the sensor 11. At this time, the phase of the tip of the wave packet transmitted forward from the sensor 12 matches the phase of the wave packet transmitted forward from the sensor 11 if the sensor 11 continues to be driven. Increase. On the other hand, when the transmission of the sensor 11 is completed when the wave packet transmitted forward from the sensor 12 reaches the sensor 11, the two wave packets transmitted forward from the sensors 11 and 12 are spatially overlapped. Without moving a certain distance, proceed forward.

  Here, specific conditions for realizing the complete cancellation of the backward wave packet and the coincidence of the phase of the forward wave packet will be described. First, the period 1 / f is expressed by the following equation (5).

  1 / f = λ / Vph (5)

  Accordingly, when the above formulas (3) and (5) are substituted into the above formula (4) and rearranged, the following formula (6) is obtained.

  (Vg / Vph) = 1 + n / (m + 0.5) (6)

  That is, by selecting and using a wave satisfying the relationship between the phase velocity and the group velocity satisfying the above equation (6), theoretically complete cancellation of the backward wave packet and the phase of the forward wave packet are obtained. Can be achieved. Equation (6) can also be expressed as the following equation (7).

  Vg · t0 = (n + m + 0.5) · λ / 2 (7)

  The distance L (= Vg · t0) between the sensors 11 and 12 should be as short as possible in order to completely cancel out the backward wave packet and overlap the forward wave packet as spatially as possible. Although it is desirable, the minimum value of the distance L (= Vg · t0) is when (n, m) = (1, 0) from Expression (7), and is expressed as the following Expression (8). .

  Vg · t0 = 3 · λ / 4 (8)

  Further, the relationship between the phase velocity and the group velocity when (n, m) = (1, 0) is expressed by the following equation (9) based on the above equation (6).

  (Vg / Vph) = 3 (9)

  That is, it can be seen that the group velocity is three times the phase velocity. FIG. 5 shows the relationship among n, m, Vg · t0, and Vg / Vph for several examples where the distance L is short with respect to the wavelength λ.

  When the following equation (10) is satisfied instead of the above equation (4), the polarity of the forward transmission wave from the sensors 11 and 12 can be reversed, that is, the phase can be shifted by π.

  2 · t0 = m / f (10)

  That is, by selecting a wave whose delay time t0 is an integral multiple of the period 1 / f, the polarities of wave packets transmitted forward from the sensors 11 and 12 are reversed, and spatially superimposed. The regions can be overlapped in a phase relationship that cancels each other.

  From here, the case where the phase velocity is faster than the group velocity (Vph> Vg> 0) will be described. When the phase velocity is faster than the group velocity, the distance L (= Vg · t0) at which the wave packet travels when the delay time t0 satisfies the following expression (11) is spaced apart in the axial direction of the long member 200 and the sensor 11 and 12 are installed.

  t0 = 0.5 · n · λ / (Vph−Vg) (11)

  Thereby, theoretically complete erasure of the rear transmission wave and phase matching of the front transmission wave can be realized by the same control as in the case where the group velocity is faster than the phase velocity (Vph <Vg). Therefore, when the above formulas (11) and (5) are substituted into the formula (4) and rearranged, the following formula (12) is obtained.

  (Vg / Vph) = 1-n / (m + 0.5) (12)

  Here, an example of the phase shift in the wave packet will be described with reference to FIG. In FIG. 6, the horizontal axis represents the distance (spatial position) in the traveling direction (axial direction) of the wave packet, and the shape of the wave packet at an arbitrary time t1 (upper figure) and after t0 (n = 1, lower figure). Is a conceptual diagram showing an example of the relationship between the phase velocity and the group velocity. In the example shown in FIG. 6, the phase velocity Vph is faster than the group velocity Vg. First, in FIG. 6, the wave packet at time t = t1 is represented as a wave packet including the point P21. Here, in the example shown in FIG. 6, the point P21 is located substantially at the center of the wave packet at the time t = t1 and is located at the point L21.

  Next, in FIG. 6, the wave packet at time t = t1 + t0 is represented as a wave packet including points P22 and P23. Here, in the example shown in FIG. 6, when time elapses from time t = t1 to time t = t1 + t0, the entire wave packet advances by the group velocity Vg · t0. That is, at the time t = t1 + t0, the wave packet point corresponding to the point P21 at the time t = 0 reaches the point L22. On the other hand, when time elapses from time t = t1 to time t = t1 + t0, the phase velocity is Vph, and the peak apex corresponding to the point P21 advances by the phase velocity Vph · t0. In the example shown in FIG. 6, since the phase velocity Vph is faster than the group velocity Vg, the peak apex of the point P21 at time t = t1 is shifted forward λ / 2 in the wave packet. Here, the phase of the point P23 at time t = t1 + t0 is shifted by π from the phase of the point P21 at time t = t1. In the above description, the point P21 at time t = t1 has been described as a reference, but the same applies to any point of the wave packet at any time.

  Therefore, in the wave transmission method according to the present application, the distance traveled by the group velocity at a time interval in which the phase of the backward transmission wave from the sensor 11 is inverted (n: odd) or coincident (n: even) (in FIG. The distance between the point L21 and the point L22 is an example of a reversal distance) The sensor 11 and the sensor 12 are installed at intervals, that is, the wave packet at time t = t0 with respect to the phase at the tip of the wave packet at time t = 0. The sensor 12 is placed at a position where the phase of the tip of the sensor is reversed by π or reversed or the phase difference coincides with zero.

  That is, by selecting and using a wave satisfying the relationship between the phase velocity and the group velocity satisfying the above equation (12), it is possible to substantially completely cancel the backward wave packet and match the phase of the forward wave packet. Can be realized. Note that the distance L (= Vg · t0) between the sensors 11 and 12 is as long as possible in order to cancel the backward wave packet almost completely and overlap the forward wave packet as spatially as possible. Short ones are desirable. FIG. 7 shows the relationship among n, m, Vg · t0, and Vg / Vph for several examples where the distance L is short with respect to the wavelength λ. FIG. 8 shows a list of the conditions and relational expressions described above.

  Note that the distance L (= Vg · t0) between the sensors 11 and 12, the delay time t0, and the like described above are not necessarily strict values. For example, the distance L between the sensors 11 and 12 is changed within a small range with respect to the wavelength of the wave to be transmitted within a range that does not significantly affect the elimination of the backward transmission wave and the superposition of the forward transmission wave, T0 may be changed within a small range with respect to / f.

  In the above description, the case where the delay time t0 is the same as t0 for determining the distance L (= Vg · t0) between the sensors 11 and 12 has been described. However, the delay time is the second integer n ′. Where t0 ′ satisfying the following expression (13) may be used.

  t0 ′ = 0.5 · n ′ · λ / (Vg−Vph) (13)

  That is, the sensor 12 is driven after the delay time t0 ′ has elapsed from the time (t = 0) when the sensor 11 is driven. In this case, when the second integer n ′ is an odd number, the polarity of the sensor 12 is the same as the polarity of the sensor 11, and when the second integer n ′ is an even number, the polarity of the sensor 12 is a polarity opposite to the polarity of the sensor 11. By driving, the phase of the wave transmitted backward from the sensors 11 and 12 can be inverted, that is, the phase difference can be set to π. When n and n ′ are different, waves transmitted backward from the sensors 11 and 12 are spatially shifted and cannot be completely superimposed.

  Next, a method for doubling the amplitude by ideally superimposing the forward transmission waves transmitted from the sensors 11 and 12 will be described. When the group velocity is faster than the phase velocity (Vph <Vg), the sensors 11 and 12 are installed with an interval of a distance L that is a distance satisfying the following equation (14) being opened in the axial direction of the long member 200. Hereinafter, a case will be described in which the sensor 11 is driven after the delay time t0 has elapsed from the origin (t = 0) of the time when the sensor 12 is driven.

  L = Vg · t0 (14)

  Here, the time t0 is a time determined by the wavelength, the group velocity, and the phase velocity, where the first integer n is an integer of 1 or more, and is represented by the following formula (15).

  t0 = 0.5 · n · λ / (Vg−Vph) (15)

  That is, the distance L indicates the distance traveled by the wave packet during the time t0 such that the difference in travel distance between the group velocity and the phase velocity is an integral multiple of a half wavelength. In the example shown in FIG. The sensors 11 and 12 are set apart by this distance.

  First, when the first integer n is an odd number, the sensor 12 is driven first, and after the delay time t0 has elapsed (t = t0), the sensor 11 is driven with a signal having a polarity opposite to that of the sensor 12. Here, the tip of the wave packet transmitted forward from the sensor 12 reaches the sensor 11 after t0. At this time, the phase of the forward transmission wave from the sensor 12 is reversed from the transmission time. In other words, in the forward transmission wave from the sensor 12, the phase at the tip of the wave packet at the time t = t 0 is inverted by π with respect to the phase at the tip of the wave packet at the time t = 0. For this reason, when the sensor 11 is driven at t = t0 with a signal having a polarity opposite to the polarity at which the sensor 12 is driven, the sensor 11 can transmit a wave packet having the same phase as the wave packet reached from the sensor 12 to the front. In addition, since the forward wave packets from the sensor 11 and the sensor 12 are almost completely superimposed spatially, in principle, the forward wave packets can be almost completely overlapped so that the amplitude can be approximately doubled. .

  When the first integer n is an even number, the sensor 12 is driven first, and after the delay time t0 has elapsed (t = t0), the sensor 11 is driven with a signal having the same polarity (same as) the sensor 12. Here, the tip of the wave packet transmitted forward from the sensor 12 reaches the sensor 11 after t0. At this time, the phase of the forward transmission wave from the sensor 12 is the same as the transmission time point. In other words, in the forward transmission wave from the sensor 12, the phase of the tip of the wave packet at the time t = t0 is the same as the phase of the wave packet at the time t = 0. Therefore, when the sensor 11 is driven at t = t0 with a signal having the same polarity as the polarity that driven the sensor 12, the sensor 11 can transmit a wave packet having the same phase as that of the wave packet reached from the sensor 12. In addition, since the forward wave packets from the sensor 11 and the sensor 12 are spatially almost completely superimposed, in principle, the forward wave packets can be almost completely overlapped to double the amplitude.

[Processing procedure]
Here, the processing procedure of the wave transmission method that theoretically completely superimposes the forward wave packet will be described. FIG. 9 is a diagram illustrating an example of a processing procedure of the transmission method according to the embodiment.

  As shown in FIG. 9, first, the rear sensor 12 is driven (step S21). After the sensor 12 is driven, the process waits until the delay time t0 has elapsed (step S22: No).

  When the delay time t0 has elapsed after driving the sensor 12 (step S22: Yes), the process is divided depending on the even / odd number of the first integer n. After the delay time t0 has elapsed (step S22: Yes), when the first integer n is an odd number (step S23: Yes), the front sensor 11 is driven with a polarity opposite to that of the sensor 12 (step S24).

  On the other hand, after the delay time t0 has elapsed (step S22: Yes), when the first integer n is an even number (step S23: No), the front sensor 11 is driven with the same polarity as the sensor 12 (step S25). . In this way, by changing the polarity of the wave transmitted from the sensor 11 according to the even number of the first integer n, the wave bundles forward from the sensor 11 and the sensor 12 can be ideally perfectly superimposed. it can.

  It should be noted that the control for superimposing the forward transmission wave described above can be performed when the phase velocity Vph and the group velocity Vg are different from each other. Furthermore, when the forward transmission waves are superimposed as described above, the phases of the backward transmission waves from the sensors 11 and 12 can be shifted by π so as to cancel each other out at the same time. For this purpose, a wave having twice the delay time t0 as a half integer multiple of the period 1 / f may be selected. That is, a wave that satisfies the following formula (16) is selected, where m is an integer of 0 or more. It should be noted that the wave packets transmitted backward from the sensors 11 and 12 are spatially shifted by a certain distance and cannot theoretically be completely canceled out.

  2 · t0 = (0.5 + m) / f (16)

  By using a wave that satisfies this conditional expression, the phase of the wave packet transmitted backward from the sensors 11 and 12 is shifted by π regardless of the even or odd number of the first integer n. The wave can be overlapped by the phase relationship that cancels the amplitude. Specifically, at the time of t = 2 · t0, the tip of the wave packet transmitted backward from the sensor 11 reaches the position of the sensor 12. At this time, the phase of the tip of the wave packet transmitted backward from the sensor 11 is shifted by π from the phase of the wave transmitted backward from the sensor 12 if the sensor 12 continues to be driven. The phase relationship cancels each other out. On the other hand, when the transmission of the sensor 12 is completed when the wave packet transmitted backward from the sensor 11 reaches the sensor 12, the two wave packets transmitted backward from the sensors 11 and 12 are spatially overlapped. Without moving a certain distance, proceed backwards.

  Here, ideally, a description will be given of a condition for realizing a complete superposition of the forward wave packet and a superposition of the backward wave packet with a phase difference π, that is, a reduction in the amplitude of the spatially overlapping part. . First, the period 1 / f is expressed by the above equation (5). Therefore, when the above formulas (15) and (5) are substituted into the formula (16) and rearranged, the following formula (17) is obtained.

  (Vg / Vph) = 1 + n / (m + 0.5) (17)

  That is, by selecting and using a wave satisfying the relationship between the phase velocity and the group velocity that satisfies the above equation (17), the superposition of the phase difference 0 of the complete forward wave packet and the backward wave packet Superposition with a phase difference π can be realized. Expression (17) can also be expressed as the following expression (18).

  Vg · t0 = (n + m + 0.5) · λ / 2 (18)

  Theoretically, the distance L (= Vg · t0) between the sensors 11 and 12 is used in order to cancel the superposition of the forward wave packets completely and the superposition of the backward wave packets as much as possible. Is preferably as short as possible. However, from equation (18), the minimum value of the distance L (= Vg · t0) is when (n, m) = (1,0), and the following equation (19 ).

  Vg · t0 = 3 · λ / 4 (19)

  Further, the relationship between the phase velocity and the group velocity when (n, m) = (1, 0) is expressed by the following equation (20) from the above equation (17).

  (Vg / Vph) = 3 (20)

  That is, it can be seen that the group velocity is three times the phase velocity. As described above, some examples of the relationship among n, m, Vg · t0, and Vg / Vph are as shown in FIG.

  When the following equation (21) is satisfied instead of the above equation (16), the phases of the backward transmission waves from the sensors 11 and 12 can be matched.

  2 · t0 = m / f (21)

  That is, by selecting a wave whose delay time t0 is an integral multiple of the period 1 / f, the phases of wave packets transmitted backward from the sensors 11 and 12 are matched and spatially superimposed. It is also possible to increase the amplitude by overlapping the regions in phase with each other.

  From here, the case where the phase velocity is faster than the group velocity (Vph> Vg> 0) will be described. When the phase velocity is faster than the group velocity, the distance L (= Vg · t0) at which the wave packet travels when the delay time t0 satisfies the following equation (22) is opened in the axial direction of the long member 200 and the sensor 11 and 12 are installed.

  t0 = 0.5 · n · λ / (Vph−Vg) (22)

  Thus, by the same control as in the case where the group velocity is higher than the phase velocity (Vph <Vg), complete superposition of the forward wave packet and superposition of the backward wave packet with the phase difference π, that is, spatial A decrease in amplitude can be realized for the portion overlapping with. Therefore, when the above formulas (22) and (5) are substituted into the formula (4) and rearranged, the following formula (23) is obtained.

  (Vg / Vph) = 1-n / (m + 0.5) (23)

  That is, by selecting and using a wave satisfying the relationship between the phase velocity and the group velocity that satisfies the above equation (23), theoretically, a complete wave packet superimposition and a wave packet backward Can be realized with a phase difference of π. Note that some cases of the relationship of n, m, Vg · t0, and Vg / Vph are as shown in FIG.

  Note that the distance L (= Vg · t0) between the sensors 11 and 12, the delay time t0, and the like described above are not necessarily strict values. For example, the sensor 11 has a small range with respect to the wavelength of the wave to be transmitted in a range that does not significantly affect the superposition of the forward transmission waves and the decrease in the amplitude in the spatially overlapping region of the backward transmission waves. , 12 may be changed, or t0 may be changed within a small range with respect to the period 1 / f.

  In the above description, the case where the delay time t0 and t0 for determining the distance L (= Vg · t0) between the sensors 11 and 12 are the same is described. However, the second integer n ′ is an integer greater than or equal to zero. Alternatively, a delay time t0 ′ that satisfies the following equation (24) may be used.

  t0 ′ = 0.5 · n ′ · λ / (Vg−Vph) (24)

  That is, the sensor 12 is driven after the delay time t0 ′ has elapsed from the time (t = 0) when the sensor 11 is driven. In this case, when the second integer n ′ is an odd number, the polarity of the sensor 12 is opposite to the polarity of the sensor 11, and when the second integer n ′ is an even number, the polarity of the sensor 12 is the same as the polarity of the sensor 11. By driving with polarity, the phases of the waves transmitted forward from the sensors 11 and 12 can be made the same, that is, the phase difference can be set to zero. When n and n ′ are different, the waves transmitted forward from the sensors 11 and 12 are spatially shifted, and cannot be completely superimposed over the entire wave packet.

  Here, as illustrated in FIG. 2, the inspection apparatus 100 includes a transmission / reception unit 110, a signal processing unit 120, a storage unit 130, a determination unit 140, and an output unit 150.

  As shown in FIG. 2, the transmission / reception unit 110 drives the sensors 11 and 12 installed on the long member 200 to be inspected. In addition, the transmission / reception unit 110 outputs, for example, a signal detected by the sensor 11 to the signal processing unit 120. In the inspection apparatus 100 shown in FIG. 2, the transmission unit and the reception unit are integrated into the transmission / reception unit 110. However, the components are functionally conceptual, and the transmission unit and the reception unit may be separated. Good.

  The signal processing unit 120, the storage unit 130, the determination unit 140, and the output unit 150 include, for example, an arithmetic device such as a CPU (Central Processing Unit), a storage device such as a memory and an HDD (Hard Disc Drive), a keyboard, a mouse, An input device that detects the input of information from outside, such as a pointing device, buttons, and touch panel, an I / F (Interface) device that sends and receives information from the outside, an LCD (Liquid Crystal Display), and an organic EL (Electro Luminescence) And a computer equipped with a display device such as the above. Specifically, the hardware resources as described above are controlled by a program installed in the computer, and the hardware device and the software cooperate to generate the signal processing unit 120, the storage unit 130, the determination unit 140, and the output. The unit 150 is realized.

  The signal processing unit 120 gives data of a predetermined waveform to the transmission / reception unit 110 and sends a wave to the long member 200. The signal processing unit 120 processes the signal received by the sensor 11 and detects the frequency characteristics of the average group velocity of the waves propagated through the long member 200. For example, the signal processing unit 120 measures the time from sending a wave to receiving it, and repeatedly calculating the average group velocity of the wave over a predetermined frequency range from the distance traveled by the wave, Obtain a frequency distribution profile.

  The storage unit 130 stores in advance the frequency dependence of the average group velocity of the waves propagating through the comparison target member such as the long member 200. For example, the storage unit 130 stores a frequency profile as the frequency characteristics of the average group velocity. Here, as described above, the comparison target member is a comparison target for detecting whether or not the inspection target member is deformed. For example, the inspection target member before use or the inspection target member before use is used. It consists of a member etc. which have the same shape. The frequency profile of the comparison target member can be obtained by a method equivalent to the method in which the signal processing unit 120 detects the frequency profile of the long member 200.

  The determination unit 140 compares the frequency characteristic of the average group velocity of the waves propagating through the inspection target member detected by the signal processing unit 120 with the frequency characteristic of the average group velocity of the comparison target member stored in the storage unit 130. Then, it is determined whether or not the shape of the inspection target member is the same as the shape of the comparison target member. In the present embodiment, the frequency profile of the inspection target member is compared with the frequency profile of the comparison target member, and it is determined whether or not there is a defect in the inspection target member based on whether or not they are the same. The determination result is output to the output unit 150.

  The output unit 150 outputs the determination result by the determination unit 140 to a monitor or the like. The above-described inspection apparatus 100 is an example, and any configuration can be used as long as the inspection of the long member 200 can be realized by the wave transmission method using the sensors 11 and 12 that are installed at a distance L apart. Also good.

  As a method of transmitting a wave to the long member 200 using the sensors 11 and 12, a method using a piezoelectric element probe (array) as the sensors 11 and 12, a method using a magnetostrictive sensor as the sensors 11 and 12, In principle, any combination of sensors 11 and 12 such as a method using an electromagnetic ultrasonic transducer (EMAT) or a laser ultrasonic method may be used as the sensors 11 and 12. Moreover, although the case where the sensor 11 was used as a transmission sensor and a reception sensor was shown in a present Example, you may use a sensor different from a transmission sensor as a reception sensor.

[Specific Example 1]
From here, some specific examples of the wave transmission method according to the present embodiment will be described. First, FIG. 10 shows a calculation result of a dispersion curve of a guide wave F (1,1) mode in a steel solid rod having a diameter of 10 mm in a vacuum. Here, the F mode means a mode in which the cylindrical long member 200 vibrates asymmetrically with respect to the axis. In the example shown in FIG. 10, the horizontal axis represents frequency, the vertical axis represents sound velocity, the broken line represents phase velocity, and the solid line represents group velocity. FIG. 11 shows parameters used in the calculation shown in FIG. In this mode, the group velocity is faster than the phase velocity in the range shown in FIG.

  As shown in FIG. 10, in the F (1,1) mode, at 110 kHz, the phase velocity Vph and the group velocity Vg are values shown in the following equations (25) and (26), respectively.

Vph = 2.3 × 10 ³ (m / s) (25)

Vg = 3.2 × 10 ³ (m / s) (26)

  Therefore, the ratio between the two is 1.4, which corresponds to the condition (n, m) = (1, 2) shown in FIG. Further, according to the above formulas (25) and (5), the wavelength λ is 21 mm. Therefore, the distance L (= Vg · t0) and the delay time t0 are values shown in the following expressions (27) and (28), respectively, according to the expressions (2) and (3).

  L = 7 · λ / 4 = 37 (mm) (27)

t0 = 0.5 · λ / (Vg−Vph) = 1.2 × 10 ⁻⁵ (s) (28)

  That is, in this specific example, it can be seen that the distance L between the sensors 11 and 12 is set to 37 mm and the delay time t0 is set to 12 μs. The sensor 11 is first driven to transmit a wave packet of 110 kHz F (1,1) mode guide wave, and after 12 μs, the sensor 12 is driven with the same polarity as the sensor 11, so that the theory is completely The backward wave packet can be canceled and canceled, and the wave packet in the forward direction can be matched and transmitted. In this case, the wave packet transmitted forward from the sensor 11 and the sensor 12 advances spatially with an interval of 2 · Vg · t0 shown in the following equation (29).

  2 · Vg · t0 = 2 · 7 · λ / 4 = 74 (mm) (29)

  When the width of the wave packet is sufficiently larger than 74 mm obtained by the above equation (29), for example, if the width is 420 mm (= 20 · λ), the wave packets transmitted from the sensor 11 and the sensor 12 are substantially overlapped. Thus, it is possible to transmit one wave packet having a substantially doubled amplitude compared to the case where waves are transmitted from one sensor. In general, in order to transmit a wave packet having a width of 20 · λ, in principle, the sensor may be driven over a period of 20 cycles (20 / f).

  As described above, a guide wave having a specific mode and a specific frequency is selected, the sensors 11 and 12 are set apart by a distance L (= Vg · t0), and the delay time t0 is set. It is possible to cancel the wave packet and increase the amplitude by matching the phase of the wave packet forward. Thereby, compared with the case where one sensor is used, SN ratio can be increased. In the same sensor arrangement, the sensor 12 is first driven to transmit a 110 kHz F (1,1) mode guide wave packet, and the sensor 11 is driven with a polarity opposite to that of the sensor 12 after 12 μs. The wave packets transmitted forward from the sensor 11 and the sensor 12 are theoretically completely overlapped to form a wave having an amplitude of about twice, and the phase of the wave transmitted backward from the sensor 11 and the sensor 12 is shifted by π. It is also possible to reduce the amplitude of the overlapping portion.

[Specific Example 2]
FIG. 12 shows the calculation result of the dispersion curve of the guide wave L (0, 1) mode of a steel solid rod having a diameter of 10 mm in vacuum. Here, the L mode means a mode in which the cylindrical long member 200 vibrates in an axial symmetry. In the example shown in FIG. 12, the horizontal axis represents frequency, the vertical axis represents sound velocity, the broken line represents phase velocity, and the solid line represents group velocity. In addition, the parameters shown in FIG. 11 were used for the calculation shown in FIG. In this mode, the phase velocity is faster than the group velocity in the range shown in FIG.

  As shown in FIG. 12, in the L (0, 1) mode, when the frequency is 275 kHz, the phase velocity Vph and the group velocity Vg are values shown in the following equations (30) and (31), respectively.

Vph = 4.4 × 10 ³ (m / s) (30)

Vg = 2.7 × 10 ³ (m / s) (31)

  Therefore, the ratio between the two is 0.6, which corresponds to the condition (n, m) = (1, 2) shown in FIG. Further, according to the above equations (30) and (5), the wavelength λ is 16 mm. Therefore, the distance L (= Vg · t0) and the delay time t0 are values shown in the following formulas (32) and (33), respectively, according to the formulas (2) and (11).

  L = 3 · λ / 4 = 12 (mm) (32)

t0 = 0.5 · λ / (Vph−Vg) = 4.7 × 10 ⁻⁶ (s) (33)

  That is, in this specific example, it can be understood that the distance L between the sensors 11 and 12 is set to 12 mm, and the delay time t0 is set to 4.7 μs. Then, the sensor 11 is first driven to transmit a 275 kHz L (0, 1) mode guide wave wave packet, and after 4.7 μs, the sensor 12 is driven with the same polarity as that of the sensor 11 so that the backward wave packet is obtained. Theoretically, it is possible to cancel and cancel completely, and to transmit the phase of the wave packet forward. In this case, the wave packet transmitted forward from the sensor 11 and the sensor 12 advances spatially with an interval of 2 · Vg · t0 shown in the following equation (34).

  2 · Vg · t0 = 2 · 3 · λ / 4 = 24 (mm) (34)

  When the width of the wave packet is sufficiently larger than 24 mm obtained by the above equation (34), for example, if the width is 320 mm (= 20 · λ), most of the wave packets transmitted from the sensor 11 and the sensor 12 are It is possible to transmit one wave packet having substantially doubled amplitude compared to the case where waves are transmitted from one sensor overlapping in the region. In general, in order to transmit a wave packet having a width of 20 · λ, in principle, the sensor may be driven over a period of 20 cycles.

  As described above, a guide wave having a specific mode and a specific frequency is selected, the sensors 11 and 12 are set apart by a distance L (= Vg · t0), and the delay time t0 is set. It is possible to cancel the wave packet and increase the amplitude by matching the phase of the wave packet forward. Thereby, compared with the case where one sensor is used, SN ratio can be increased. In the same sensor arrangement, the sensor 12 is first driven to transmit a 275 kHz L (0,1) mode guide wave packet, and the sensor 11 is driven with the opposite polarity to the sensor 12 after 4.7 μs. The wave packets transmitted forward from the sensors 11 and 12 are theoretically completely overlapped to form a wave having an amplitude of about twice, and the phase of the wave transmitted backward from the sensors 11 and 12 is π It is also possible to reduce the amplitude of the overlapping portions.

[Specific Example 3]
FIG. 13 shows a calculation result of a dispersion curve of a guide wave L (0, 2) mode of a steel solid rod having a diameter of 10 mm in a vacuum. In the example shown in FIG. 13, the horizontal axis represents frequency, the vertical axis represents sound velocity, the broken line represents phase velocity, and the solid line represents group velocity. Further, the parameters shown in FIG. 11 were used for the calculation shown in FIG. In this mode, the phase velocity is faster than the group velocity in the range shown in FIG.

  As shown in FIG. 13, in the L (0,2) mode, at 460 kHz, the phase velocity Vph and the group velocity Vg are values shown in the following equations (35) and (36), respectively.

Vph = 5.9 × 10 ³ (m / s) (35)

Vg = 4.2 × 10 ³ (m / s) (36)

  Therefore, the ratio between the two is 0.71, which corresponds to the condition (n, m) = (1, 3) shown in FIG. Further, according to the above formulas (35) and (5), the wavelength λ is 13 mm. Therefore, the distance L (= Vg · t0) and the delay time t0 are values shown in the following expressions (37) and (38), respectively, according to the expressions (2) and (11).

  L = 5 · λ / 4 = 16 (mm) (37)

t0 = 0.5 · λ / (Vph−Vg) = 4.4 × 10 ⁻⁶ (s) (38)

  That is, in this specific example, it is understood that the distance L between the sensors 11 and 12 is set to 16 mm and the delay time t0 is set to 4.4 μs. Then, the sensor 11 is first driven to transmit a 460 kHz L (0, 2) mode guide wave wave packet, and after 4.4 μs, the sensor 12 is driven with the same polarity as the sensor 11 so that the backward wave packet is obtained. Theoretically, it is possible to cancel and cancel completely, and to transmit the phase of the wave packet forward. In this case, the wave packet transmitted forward from the sensor 11 and the sensor 12 advances spatially with an interval of 2 · Vg · t0 shown in the following equation (39).

  2 · Vg · t0 = 2 · 5 · λ / 4 = 32 (mm) (39)

  If the width of the wave packet is sufficiently larger than 32 mm obtained by the above equation (39), for example, if the width is 260 mm (= 20λ), the wave packets transmitted from the sensor 11 and the sensor 12 are almost all regions. Overlapping, it is possible to transmit one wave packet having a substantially doubled amplitude compared to the case where waves are transmitted from one sensor.

  As described above, a guide wave having a specific mode and a specific frequency is selected, the sensors 11 and 12 are set apart by a distance L (= Vg · t0), and the delay time t0 is set. It is possible to cancel the wave packet and increase the amplitude by superimposing the phase of the wave packet forward. Thereby, compared with the case where one sensor is used, SN ratio can be increased.

[Specific Example 4]
In this specific example, a case where a wave of a guide wave L (0, 2) mode is transmitted into an aluminum cylindrical pipe having an outer diameter of 30 mm and an inner diameter of 10 mm in a vacuum is shown. In this case, according to the sound velocity calculation (bulk longitudinal wave sound velocity in aluminum 6400 m / s, bulk shear wave sound velocity 3040 m / s), at 150 kHz, the phase velocity Vph and the group velocity Vg are expressed by the following equations (40) and ( 41).

Vph = 5.55 × 10 ³ (m / s) (40)

Vg = 4.36 × 10 ³ (m / s) (41)

  Therefore, the ratio between the two is 0.78, and it can be seen that the L (0,2) mode of 150 kHz corresponds to the condition (n, m) = (1,4) shown in FIG. Further, according to the above formulas (40) and (5), the wavelength λ is 37 mm. Therefore, the distance L (= Vg · t0) and the delay time t0 are values shown in the following formulas (42) and (43), respectively, according to the formulas (2) and (11).

  L = 7 · λ / 4 = 65 (mm) (42)

t0 = 0.5 · λ / (Vph−Vg) = 1.6 × 10 ⁻⁵ (s) (43)

  That is, in this specific example, it can be understood that the distance L between the sensors 11 and 12 is set to 65 mm and the delay time t0 is set to 16 μs. Then, the sensor 11 is first driven to transmit a 150 kHz L (0, 2) mode guide wave packet, and after 16 μs, the sensor 12 is driven with the same polarity as the sensor 11 to theoretically calculate the backward wave packet. In other words, it is possible to completely cancel and cancel, and to transmit the wave packet in phase with the forward wave. In this case, the wave packet transmitted forward from the sensor 11 and the sensor 12 advances spatially with an interval of 2 · Vg · t0 shown in the following equation (44).

  2 · Vg · t0 = 2 · 7 · λ / 4 = 130 (mm) (44)

  If the width of the wave packet is sufficiently larger than 130 mm obtained by the above equation (44), for example, if the width is 740 mm (= 20 · λ), the wave packets transmitted from the sensor 11 and the sensor 12 are substantially overlapped. Thus, it is possible to transmit one wave packet having a substantially doubled amplitude compared to the case where waves are transmitted from one sensor. In general, in order to transmit a wave packet having a width of 20 · λ, in principle, the sensor may be driven over a period of 20 cycles.

  As described above, a guide wave having a specific mode and a specific frequency is selected, the sensors 11 and 12 are set apart by a distance L (= Vg · t0), and the delay time t0 is set. It is possible to cancel the wave packet and increase the amplitude by matching the phase of the wave packet forward. Thereby, compared with the case where one sensor is used, SN ratio can be increased. Further, in the same sensor arrangement, the sensor 12 is first driven to transmit a wave packet of a 150 kHz L (0, 2) mode guide wave, and after 16 μs, the sensor 11 is driven with the opposite polarity to the sensor 12. The wave packets transmitted forward from the sensor 11 and the sensor 12 are theoretically completely overlapped to form a wave having an amplitude of about twice, and the phase of the wave transmitted backward from the sensor 11 and the sensor 12 is shifted by π. It is also possible to reduce the amplitude of the overlapping portion.

[Modification]
In the above-described embodiment, the example using two sensors 11 and 12, that is, one sensor pair is shown, but two pairs of sensors 20 and 30 may be used as shown in FIG. In the example illustrated in FIG. 14, the sensor pair 20 includes a sensor 21 installed on the front side and a sensor 22 installed on the rear side. The sensor pair 30 includes a sensor 31 installed on the front side and a sensor 32 installed on the rear side.

  Here, in this modified example, the guide wave F (1, 1) mode in the steel cylindrical solid rod having a diameter of 10 mm in vacuum, which shows the dispersion curve shown in FIG. Use. In other words, the phase velocity Vph, the group velocity Vg, the distance L (= Vg · t0), and the delay time t0 in the present modification are the values shown in the above formulas (25) to (28) as in the first specific example. Become.

  That is, the sensor 21 and the sensor 22 are arranged with a distance L = 37 mm. Further, the sensor 31 and the sensor 32 are arranged with a distance L = 37 mm. The interval Lp between the sensor pair 20 and the sensor pair 30 will be described later. The drive start times of the sensors 21, 22, 31, and 32 will be described as t21, t22, t31, and t32, respectively.

[Processing procedure]
Here, the processing procedure of the wave transmission method in the present modification will be described. FIG. 15 is a diagram illustrating an example of a processing procedure of the transmission method according to the modification.

  As shown in FIG. 15, first, the sensor 31 of the sensor pair 30 is driven (step S31). After the sensor 31 is driven, the process waits until the delay time t0 has elapsed (step S32: No). If the delay time t0 has elapsed after driving the sensor 31 (step S32: Yes), the sensor 32 of the sensor pair 30 is driven with the same polarity as the sensor 31 (step S33).

  Further, the sensor 21 of the sensor pair 20 is driven with the same polarity as the sensor 31 (step S34). After the sensor 21 is driven, the process waits until the delay time t0 has elapsed (step S35: No). If the delay time t0 has elapsed after driving the sensor 21 (step S35: Yes), the sensor 22 of the sensor pair 20 is driven with the same polarity as the sensor 21 (step S36). In addition, the timing which drives the sensor 21 of the sensor pair 20 in step S34 may be before driving the sensor 32 as long as it is after driving the sensor 31 of the sensor pair 30 in step S31.

  Specifically, the sensor 32 is driven after a delay time t0 = 12 μs (that is, t32−t31) has elapsed since the sensor 31 was first driven. The sensor 21 is driven after the sensor 31 (that is, t21> t31), and the delay time of the sensor 22 with respect to the sensor 21 (that is, t22−t21) is set to 12 μs.

  As described above, in each of the sensor pairs 20 and 30, the backward transmission wave is canceled and the forward transmission wave is transmitted in phase. That is, this modification corresponds to using two pairs of the sensors 11 and 12 of the first specific example. Here, the delay time t2 (= t21−t31) of the sensor 21 with respect to the sensor 31 is represented by the following expression (45), where n2 is an even number of 2 or more.

  t2 = 0.5 · n2 · λ / (Vg−Vph) (45)

  For example, when n2 is 2, the value shown in the following formula (46) is obtained.

t2 = λ / (Vg−Vph) = 2.4 × 10 ⁻⁵ (s) (46)

  Further, an interval Lp between the sensor pair 20 and the sensor pair 30 is defined by the following expression (47).

  Lp = Vg · t2 (47)

  For example, when n2 is 2, the value shown in the following formula (48) is obtained.

  Lp = 77 (mm) (48)

  By using such an arrangement (distance Lp) and delay time (t2), the forward transmission wave transmitted from the sensor pair 30 and the forward transmission wave transmitted from the sensor pair 20 are spatially matched in phase. And the amplitude can be doubled. That is, it is possible to substantially increase the amplitude of the forward transmission wave by using the four sensors while erasing the backward transmission wave. Thereby, a dramatic increase in the SN ratio can be realized.

  The sensors 21, 22, 31, and 32 are similar to the sensors 11 and 12, a method using a piezoelectric element probe (array), a method using a magnetostrictive sensor, a method using an electromagnetic ultrasonic probe, In principle, any combination of sensors 21, 22, 31, 32 may be used, such as a sonic method.

  As described above, in the embodiment and the modification, the example in which the wave is transmitted with respect to the long member has been shown. However, the shape is not limited to the long member, and the shape may be two-dimensional or three-dimensional. For example, when transmitting a guide wave (for example, a Lamb wave) to a flat plate, or when transmitting a surface wave to the surface of a bulk member, it can be used when transmitting waves for various shapes. In addition, although a solid is taken as an example of a target for transmitting waves, the target may be a structure in which solids, liquids, and gases are combined regardless of whether they are solids, liquids, or gases. The wave to be transmitted is not limited to an elastic wave, and can be applied to waves having various phase velocities and group velocities, for example, electromagnetic waves such as light and radio waves.

[effect]
As described above, the wave transmission method according to the embodiment includes a transmission step in which each of the first sensor 11 and the second sensor 12 transmits a wave having a different phase velocity and group velocity, and the phase velocity. The distance L between the first sensor 11 and the second sensor 12 in the case where Vph, the group velocity Vg, the first integer n that is an integer equal to or greater than 1, and the wavelength λ of the transmitted wave is expressed by the above equation. The value is set to satisfy (1). In the transmission process, one of the first sensor 11 and the second sensor 12 transmits based on the phase velocity, group velocity, and wave wavelength. Wave transmission starts at the timing and phase difference at which the waves cancel or amplify.

  Thereby, the wave transmission method according to the embodiment can improve the SN ratio by erasing the backward transmission wave or increasing the amplitude of the forward transmission wave. Specifically, the wave transmission method can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude.

  Also, in the wave transmission method according to the embodiment, when m is an integer of 0 or more and the group velocity Vg is faster than the phase velocity Vph, the above equation (6) is satisfied, and the phase velocity Vph is faster than the group velocity Vg. Then, a wave satisfying the above equation (12) is transmitted.

  As a result, the phase of the forward transmission wave is matched while canceling the backward transmission wave almost completely, or the phase of the backward transmission wave is offset by π while the amplitude is doubled by superimposing the forward transmission waves almost completely. Can be sent. As described above, with respect to waves having different phase velocities and group velocities, the SN ratio is dramatically increased by reducing the noise caused by the backward transmission wave or increasing the signal intensity obtained by the forward transmission wave. Can do.

  In addition, the wave transmission method according to the embodiment is a time between the time when one sensor starts wave transmission and the time when the other sensor starts wave transmission in the two sensors 11 and 12. A certain delay time td (in the embodiment, t0 ′) is set to a value satisfying the following formula (49) when the second integer n ′ is an integer equal to or larger than 0.

  td = 0.5 · n ′ · λ / | Vg−Vph | (49)

  Thereby, the wave transmission method according to the embodiment can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude. Thereby, SN ratio can be improved.

  Further, the wave transmission method according to the embodiment makes the polarities of the waves transmitted by the two sensors 11 and 12 the same or reverse.

  Thereby, the wave transmission method according to the embodiment can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude. Thereby, SN ratio can be improved.

  In the wave transmission method according to the embodiment, the first integer n and the second integer n ′ are set to the same value.

  Thereby, the wave transmission method according to the embodiment can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude. Thereby, SN ratio can be improved.

  Moreover, the wave transmission method according to the embodiment sends an elastic wave to a pipe or solid rod inspection object for inspection.

  Thereby, the wave transmission method according to the embodiment can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude in the inspection object of the pipe or the solid rod. . Thereby, SN ratio can be improved.

  In addition, the inspection apparatus 100 according to the embodiment includes a transmission / reception unit 110 that transmits and receives signals to and from the first sensor 11 and the second sensor 12 that transmit waves having different phase velocities and group velocities to the inspection target, and a transmission / reception unit. And a determination unit 140 that determines the presence of a defect in the inspection object based on the signal received by 110, and the first sensor 11 and the second sensor 12 have a distance and a phase velocity that travel at a group velocity. The transmission / reception unit 110 is separated from the traveling distance by a distance traveling at a group velocity at a time when the difference from the traveling distance is an integer multiple of 1 or more of a half wavelength of the transmitted wave. Based on the phase velocity, the group velocity, and the wave wavelength, one of the sensors 12 starts wave transmission at the timing and phase difference that cancels or amplifies the wave transmitted by the other sensor.

  Thereby, the inspection apparatus 100 according to the embodiment can improve the S / N ratio by erasing the backward transmission wave or increasing the amplitude of the forward transmission wave. Specifically, the wave transmission method can substantially cancel the backward transmission wave or superimpose the forward transmission wave to double the amplitude. Furthermore, by selecting a wave that has a specific relationship (ratio) between the phase velocity and the group velocity, the phase of the forward transmission wave is matched while the backward transmission wave is substantially canceled, or the forward transmission wave is superimposed. Thus, the phase of the backward transmission wave can be shifted by π while the amplitude is approximately doubled. As described above, with respect to waves having different phase velocities and group velocities, the SN ratio is dramatically increased by reducing the noise caused by the backward transmission wave or increasing the signal intensity obtained by the forward transmission wave. And the presence of a defect in the inspection object can be detected.

(Configuration etc.)
Note that each component of each illustrated apparatus is functionally conceptual and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to that shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. Further, all or any part of each processing function performed in each device may be realized by a CPU and a program analyzed and executed by the CPU, or may be realized as hardware by wired logic.

  In addition, among the processes described in the present embodiment, all or part of the processes described as being automatically performed can be manually performed, or the processes described as being manually performed can be performed. All or a part can be automatically performed by a known method. In addition, the processing procedure, control procedure, specific name, and information including various data and parameters shown in the above-described document and drawings can be arbitrarily changed unless otherwise specified.

(program)
It is also possible to create a program in which the wave transmission method according to the above embodiment is described in a language that can be executed by a computer. In this case, the same effect as the above-described embodiment can be obtained by the computer executing the program. Further, such a program may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by the computer and executed to execute the same processing as in the above embodiment. An example of a computer that executes a wave transmission program will be described below.

  FIG. 16 is a diagram illustrating a computer that executes a wave transmission program. As shown in FIG. 16, for example, the computer 1000 includes a memory 1010, a CPU (Central Processing Unit) 1020, a hard disk drive interface 1030, a disk drive interface 1040, a serial port interface 1050, a video adapter 1060, a network, and the like. Interface 1070. These units are connected by a bus 1080.

  The memory 1010 includes a ROM (Read Only Memory) 1011 and a RAM (Random Access Memory) 1012. The ROM 1011 stores a boot program such as BIOS (Basic Input Output System). The hard disk drive interface 1030 is connected to the hard disk drive 1090. The disk drive interface 1040 is connected to the disk drive 1100. A removable storage medium such as a magnetic disk or an optical disk is inserted into the disk drive 1100, for example. For example, a mouse 1110 and a keyboard 1120 are connected to the serial port interface 1050. For example, a display 1130 is connected to the video adapter 1060.

  Here, as shown in FIG. 16, the hard disk drive 1090 stores, for example, an OS 1091, an application program 1092, a program module 1093, and program data 1094. Each piece of information described in the above embodiment is stored in, for example, the hard disk drive 1090 or the memory 1010.

  The wave transmission program is stored in the hard disk drive 1090 as a program module in which a command to be executed by the computer 1000 is described, for example. Specifically, the program module describing the wave transmission method described in the above embodiment is stored in the hard disk drive 1090.

  Data used for information processing by the wave transmission program is stored as program data in, for example, the hard disk drive 1090. Then, the CPU 1020 reads out the program module 1093 and the program data 1094 stored in the hard disk drive 1090 to the RAM 1012 as necessary, and executes the above-described procedures.

  Note that the program module 1093 and the program data 1094 related to the wave transmission program are not limited to being stored in the hard disk drive 1090. For example, the program module 1093 and the program data 1094 are stored in a removable storage medium and are stored in the removable storage medium by the CPU 1020 via the disk drive 1100 or the like. It may be read out. Alternatively, the program module 1093 and the program data 1094 related to the detection program are stored in another computer connected via a network such as a LAN (Local Area Network) or a WAN (Wide Area Network), and are transmitted via the network interface 1070. It may be read by the CPU 1020.

DESCRIPTION OF SYMBOLS 11,12 Sensor 100 Inspection apparatus 110 Transmission / reception part 120 Signal processing part 130 Storage part 140 Judgment part 150 Output part

Claims (7)

A transmitting step in which each of the first sensor and the second sensor transmits a wave having a different phase velocity and group velocity;
Including
When the phase velocity Vph, the group velocity Vg, a first integer n that is an integer equal to or greater than 1, and the wavelength λ of the transmitted wave, the distance L between the first sensor and the second sensor is A value that satisfies the following equation (1):
In the transmitting step, one of the first sensor and the second sensor cancels the wave transmitted by the other sensor based on the phase velocity, the group velocity, and the wave wavelength. A wave transmission method, wherein transmission of the wave is started at a timing and a phase difference to be amplified.
L = Vg · 0.5 · n · λ / | Vg−Vph | (1) When m is an integer greater than or equal to 0 and the group velocity Vg is faster than the phase velocity Vph, the following equation (2) is satisfied, and when the phase velocity Vph is faster than the group velocity Vg, the following equation (3) is satisfied. The wave transmission method according to claim 1, wherein a wave that satisfies the condition is transmitted.
(Vg / Vph) = 1 + n / (m + 0.5) (2)
(Vg / Vph) = 1-n / (m + 0.5) (3) In the first sensor and the second sensor, a delay time td, which is a time between the time when one sensor starts transmitting the wave and the time when the other sensor starts transmitting the wave, 3. The wave transmission method according to claim 1, wherein when the second integer n ′ is an integer greater than or equal to 0, the value satisfies the following expression (4): 4.
td = 0.5 · n ′ · λ / | Vg−Vph | (4)   The polarity of the wave transmitted by each of the first sensor and the second sensor is the same (phase difference 0) or inverted (phase difference π). Wave transmission method described in one.   The wave transmission method according to claim 3, wherein the first integer n and the second integer n ′ have the same value.   6. The wave transmission method according to claim 1, wherein an elastic wave is transmitted to a pipe or a solid rod inspection object for inspection. A first sensor that transmits waves with different phase velocities and group velocities to the object to be inspected, and a transceiver that transmits and receives signals to and from the second sensor;
A determination unit for determining the presence of a defect in the inspection object based on a signal received by the transmission / reception unit;
With
The first sensor and the second sensor have a group velocity at a time when the difference between the distance traveling at the group velocity and the distance traveling at the phase velocity is an integer multiple of 1 or more of a half wavelength of the transmitted wave. Placed at a distance of travel,
The transmission / reception unit cancels or cancels the wave transmitted by the other sensor based on the phase velocity, the group velocity, and the wave wavelength of one of the first sensor and the second sensor. Start transmission of the wave at the timing and phase difference to be amplified,
Inspection apparatus characterized by that.

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