JP6430923B2 - Wave receiving method and receiving apparatus - Google Patents

Description

  The present invention relates to a wave receiving method and a receiving apparatus for detecting and evaluating a defect of a member by receiving a wave which is an elastic wave.

  The components of various machines may be placed deep in the machine. Moreover, long members, such as a building member and a construction member, may be embedded in a building or the ground. In such a case, even if changes in shape and material characteristics occur due to cracks, wear, corrosion, deformation, etc. due to aging, it is difficult to directly inspect the changes (defects) visually.

  Therefore, a wave traveling in the axial direction of the long member (generally an elastic wave that is solid vibration) is transmitted from a place where the long member can be directly accessed, and a wave reflected from a portion whose shape has changed is received. Has proposed an inspection method (for example, an elastic wave pulse reflection method) for detecting the presence of a defect, its position, the degree of the defect, and the like.

  In the reception of the wave in the inspection method, the distance to the defect is evaluated based on the time from the transmission of the inspection signal to the object to the reception of the reflected wave and the propagation speed of the wave. The degree of defect is evaluated by the amplitude of the wave. In general, a wave to be received is a wave packet having a spatially finite width. The reception of the wave packet is performed by a reception sensor installed at a predetermined location on the long member.

  Here, if a wave arriving from a direction (hereinafter referred to as “rearward”) opposite to the direction to be inspected (hereinafter referred to as “frontward”) is present, it causes noise. Therefore, by installing two sensors, the front sensor and the rear sensor, and setting the appropriate delay time to the received signals of both of them and taking a linear sum, the wave packet coming from behind (hereinafter referred to as “rear wave”) In some cases, the effect of canceling and suppressing the influence of This process is known as a reception (wave) directivity control method.

Shunpei Kameyama and five others, “Guided wave flaw detection system”, Japan Nondestructive Inspection Association, Nondestructive Inspection, Vol. 52, No. 12, pages 672-678, issued on December 1, 2003 Yoshiaki Nagashima and three others, “Pipe thinning inspection technology using guided waves, Nippon Kogyo Publishing Co., Ltd., Piping Technology, pp. 19-24, June 2008 issue

  In conventional directivity control of received waves, specifically, the interval between two sensors is set to 1/4 wavelength of the wave at the center frequency of the received wave packet, and the delay time is set to 4% of the wave at the center frequency. The backward wave is canceled and suppressed by setting one cycle of That is, the influence of the backward wave is offset and suppressed by subtracting a signal obtained by adding a delay time of a quarter period to the reception signal received by the rear sensor from the reception signal received by the front sensor. Similarly, the amplitude of the wave packet coming from the front (hereinafter referred to as “front wave”) is obtained by adding a delay time of a quarter period to the reception signal of the front sensor and adding it to the reception signal of the rear sensor. Can be doubled (in the case of a single sensor).

  However, in the above method, the group velocity, which is the speed at which the wave packet advances, and the phase velocity, which is the speed at which the phase advances (the speed at which a point of the same phase [for example, a peak or valley of amplitude] advances), In general, it can only be handled. Therefore, when the phase velocity and the group velocity are different, there is a problem that, for example, the backward wave cannot be completely eliminated, or the amplitude of the forward wave can be completely doubled to improve the SN ratio of the received signal. is there.

  The present invention has been made in view of this problem. Even when the phase velocity and the group velocity are different, the received signal SN ratio is reduced by eliminating the backward received signal or increasing the amplitude of the forward received signal. An object of the present invention is to provide a wave receiving method and receiving apparatus capable of improving the frequency.

  The wave receiving method of the present invention is for determining the arrangement of the first sensor and the second sensor based on the difference between the group velocity and the phase velocity of the wave packet and the wavelength of the wave at the center frequency of the wave packet. An arrangement determination time calculating step for calculating an arrangement determination time; a delay time calculating step for calculating a delay time for canceling or amplifying a received signal based on the difference and the wavelength; and the arrangement determination time. A receiving step of receiving the wave packet by the first sensor and the second sensor installed on the object to be inspected at a distance where the wave packet travels at the group velocity; and one of the first sensor and the second sensor. A delay signal generation step of generating a delay signal obtained by delaying the reception signal by the delay time; a signal obtained by linearly adding the delay signal and the other reception signal of the first sensor or the second sensor; Output signal And gist to carry out the force step.

  Further, the receiving apparatus of the present invention has an arrangement determination time determined to set the arrangement of the sensor based on the difference between the group velocity and the phase velocity of the wave packet and the wavelength of the wave at the center frequency of the wave packet. In the meantime, receiving the wave packet detected by the first sensor and the second sensor, and the first sensor and the second sensor installed on the object to be inspected at a distance that the wave packet travels at the group velocity. A reception unit that outputs a reception signal, and delays one reception signal of the first sensor or the second sensor by a delay time determined to cancel or amplify the reception signal based on the difference and the wavelength. A delay signal generation unit that generates a delayed signal, and a signal output unit that outputs a signal obtained by linearly summing the delay signal and the other reception signal of the first sensor or the second sensor. Is the gist.

  According to the present invention, even when the phase velocity and the group velocity are different from each other, it is possible to cancel the backward received signal and increase the amplitude of the forward received signal. A receiving device can be provided.

It is a figure which shows the relationship between a to-be-inspected object and the sensor of a receiver. It is a figure which shows the example of the relationship between the reception time of a backward wave, and a phase, (a) represents the received signal of the 2nd sensor 12, (b) represents the received signal of the 1st sensor 11. It is a figure which shows the function structural example of the receiver 100 of embodiment of this invention. 6 is a diagram illustrating an operation flow of the receiving device 100. FIG. It is a figure which shows the relationship of n, m, Vg, t0, and Vg / Vph about the case where Vg> Vph> 0 from the shorter one about the distance L represented by wavelength (lambda). It is a figure which shows the example of the relationship between the reception time of a backward wave, and a phase, (a) represents the received signal of the 2nd sensor 12, (b) represents the received signal of the 1st sensor 11. It is a figure which shows the relationship of n, m, Vg, t0, and Vg / Vph about the case where Vph> Vg and Vph> 0 from the smaller one of n and m. It is a figure which shows collectively the conditions, relational expression, etc. which delete a back wave about the case where arrangement | positioning decision time and delay time are equal (t0 = t0 ', n = n'). It is a figure which shows collectively the conditions, relational expression, etc. which increase the amplitude of a forward wave, when arrangement | positioning decision time and delay time are equal (t0 = t0 ', n = n'). It is a figure which shows the calculation result of the dispersion curve of the guide wave F (1, 1) mode in a steel cylindrical solid rod. It is a figure which shows the parameter used for the calculation of FIG. It is a figure which shows the calculation result of the dispersion curve of the guide wave F (0, 1) mode in a steel cylindrical solid rod. It is a figure which shows the calculation result of the dispersion curve of the guide wave L (0,2) mode in a steel cylindrical solid rod. 3 is a diagram illustrating a functional configuration example of a receiving device 200 obtained by modifying the receiving device 100. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated. Before describing specific embodiments of the present invention, an outline of a wave receiving method (hereinafter referred to as a receiving method) of the present invention will be described.

[Reception method]
FIG. 1 shows the relationship between an inspection object, which is an inspection object to be inspected using the receiving method of the present invention, and a sensor. In the receiving method of the present invention, the two objects of the first sensor 11 and the second sensor 12 are installed on the object to be inspected 10, and the wave of solid vibration that propagates in the interior or surface of the object 10 in the axial direction ( Elastic wave).

  The reception signal received by the first sensor 11 and the second sensor 12 is based on a wave packet that reaches the sensor from the front after the transmitted wave is reflected in front of the inspection object 10 or passes through the inspection target portion of the inspection object. Is. The transmission wave is a wave packet input to the inspection object 10 by a transmitter (not shown). The wave packet is a wave limited spatially (in a finite region) and is a wave bundle generated by superposing waves of a certain range of frequencies in the vicinity of the center frequency f. The transmitted wave (elastic wave wave packet) can be generated by, for example, a piezoelectric element probe.

  For example, the transmitter may be configured integrally with the first sensor 11 or the second sensor 12, or only the transmitter may be installed at any position of the inspection object 10. In the following description, it is assumed that the transmitter is disposed on the front side of the first sensor 11.

  The speed at which the wave packet of the elastic wave travels in the longitudinal direction of the object to be inspected 10 in the longitudinal direction is expressed as a group speed Vg. The speed at which the phase of the wave that constitutes the wave packet (more precisely, the wave of the center frequency f that constitutes the wave packet) advances (the speed at which the point of the same phase [for example, the peak / valley point] advances) is expressed as the phase velocity Vph. . The phase velocity Vph can be expressed by the following equation.

ここで、fは波の周波数（正確には、波束を構成する波の中心周波数）、λはその波長である。なお以下では、位相速度Vphが正（Vph>0）であるとして記述を行うが、群速度Vgの符号に制限はなく、これによって一般性が損なわれることはない。

Here, f is the frequency of the wave (more precisely, the center frequency of the wave constituting the wave packet), and λ is its wavelength. In the following description, the phase velocity Vph is described as being positive (Vph> 0). However, the sign of the group velocity Vg is not limited, and this does not impair generality.

(When group velocity Vg> phase velocity Vph)
First, a method of canceling and canceling backward wave signals received by the first sensor 11 and the second sensor 12 when the group velocity Vg is faster than the phase velocity Vph (Vg>Vph> 0) will be described. . The first sensor 11 and the second sensor 12 are installed with an interval of a distance L satisfying the following expression spaced in the axial direction of the inspection object 10.

式（２）より分かるように、センサ間の距離Lは、その時間t0の間に（対象としている波束が）群速度Vgで進行する距離である。従って、t0は、対象としている波束に対して第１センサ１１と第２センサ１２とで信号を受信する際の時間差にもなっている。

As can be seen from the equation (2), the distance L between the sensors is the distance that the target wave packet travels at the group velocity Vg during the time t0. Therefore, t0 is also a time difference when signals are received by the first sensor 11 and the second sensor 12 with respect to the target wave packet.

  Here, the time difference t0 is a time determined by the following equation, where the first integer n is an integer of 1 or more.

つまり、距離Lは、群速度Vgによる進行距離と位相速度Vphによる進行距離の差が波のの半波長の整数倍となるような時間差t0の間に、波束が群速度Vgで移動する距離のことである。以降、時間差t0は配置決定時間t0と称する。図１に示す様に、第１センサ１１と第２センサ１２とは、そのような距離Lの間隔を空けて設置される。

That is, the distance L is the distance that the wave packet travels at the group velocity Vg during the time difference t0 such that the difference between the traveling distance due to the group velocity Vg and the traveling distance due to the phase velocity Vph is an integral multiple of the half wavelength of the wave. That is. Hereinafter, the time difference t0 is referred to as an arrangement determination time t0. As shown in FIG. 1, the first sensor 11 and the second sensor 12 are installed with such a distance L therebetween.

  Here, the relationship between the position on the time axis and the phase of the received signal of the backward wave will be described with reference to FIG. FIGS. 2A and 2B are conceptual diagrams illustrating an example of a relationship between received signals (by wave packets) received by the second sensor 12 and the first sensor 11, respectively. 2A and 2B, the horizontal axis represents time t, and the vertical axis represents signal amplitude. FIGS. 2A and 2B are diagrams showing an example of the case where the group velocity Vg is faster than the phase velocity Vph (Vg> Vph) and the first integer n is n = 1.

  The backward wave received by the second sensor 12 is represented as a signal starting from the time t = 0. Therefore, a signal obtained by delaying the reception time of the backward wave received by the second sensor 12 by a time equal to the arrangement determination time t0 completely overlaps with the signal of the backward wave received by the first sensor 11 on the time axis ( The start time and the end time coincide with each other). Hereinafter, the time for delaying the received signal is referred to as delay time t0 ′. As will be described later, the arrangement determination time t0 and the delay time t0 ′ may be generally different times (t0 ≠ t0 ′), but here, for simplicity, the case where both are equal (t0 = t0 ′) will be described.

  Next, the relationship between the phase of the backward wave reception signal received by the first sensor 11 and the signal obtained by delaying the backward wave reception time received by the second sensor 12 by the delay time t0 will be described. An arbitrary point in the backward wave (wave packet) reception signal received by the second sensor 12, for example, the point P12, travels at the phase velocity Vph in the real space, and therefore the first sensor 11 has a time of t0 · Vg / Vph. Reach, late. Therefore, the point P12 of the reception signal of the second sensor 12 corresponds to the point P11 in the reception signal of the first sensor 11.

  Therefore, regarding the signal obtained by delaying the backward wave reception signal received by the second sensor 12 by the delay time t0 and the backward wave reception signal received by the first sensor 11, the time difference ΔT at any corresponding point is expressed by the following equation. It can be expressed as

式（４）に式（３）を代入して式（１）を用いると時間差ΔTは次式で表せる。

When equation (3) is substituted into equation (4) and equation (1) is used, time difference ΔT can be expressed by the following equation.

ここで、Tは波の周期（T=f^-1）である。この時間差ΔTは、両受信信号の全ての点について同一であるため、式（５）は、第２センサ１２の受信信号に遅延時間t0を付加した遅延信号と、第１センサ１１で受信した信号との位相差に対応する時間を表していると言うことができる。

Here, T is the wave period (T = f ⁻¹ ). Since this time difference ΔT is the same for all points of both reception signals, the equation (5) is obtained by adding a delay time t 0 to the reception signal of the second sensor 12 and the signal received by the first sensor 11. It can be said that it represents the time corresponding to the phase difference.

  Therefore, in the case of t0 = t0 ′, when the first integer n is an odd number, the delay signal obtained by adding the delay time t0 ′ to the reception signal of the second sensor 12 and the signal received by the first sensor 11 The phase difference is π. That is, both signals are inverted from each other as shown in FIG. Therefore, by delaying the backward reception signal received by the second sensor 12 by the delay time t0 and adding it to the reception signal of the first sensor 11, the backward reception signal can be canceled and eliminated.

  When the first integer n is an even number, the phase difference generated by the first sensor 11 is zero. That is, the wave packet obtained by delaying the wave packet received by the second sensor 12 by the time difference t0 is a wave packet that matches the backward wave received by the first sensor 11. In this case, the backward wave can be canceled and canceled by delaying the wave packet of the backward wave received by the second sensor 12 by the time difference t0 and subtracting it from the received signal of the first sensor 11. Since the received signal overlaps at the same time on the time axis by the process of delaying the time axis of the second sensor 12 relative to the first sensor 11 by the delay time t0 (adding the delay time t0), the wave packet If the shape (the envelope of the wave packet) is the same when it is received by the first sensor 11 and the second sensor 12 and is not deformed (approx.), The backward wave is completely canceled in principle. Can be erased.

  In the following, the method of canceling by overlapping the received signals of the backward waves from the two sensors completely on the time axis (matching the start time and the end time of the signals) and canceling will be referred to as subtraction priority. There is also.

  When the phase velocity Vph and the group velocity Vg are different, the backward wave cancellation and suppression described above can be performed regardless of the value of both. Furthermore, it is also possible to enhance the forward wave signal simultaneously with the cancellation and suppression of the backward wave.

  When the wave packet received by the second sensor 12 is delayed by a time difference t0 equal to the arrangement determination time, for the forward wave, the delayed signal of the second sensor 12 and the received signal of the first sensor 11 are t0 on the time axis. As a result, the wave for which the forward wave enhancement is performed at the same time is to select a wave whose double of t0 is a half integer multiple of the period 1 / f (Equation (6)). . Here, selecting a wave means that a transmission wave (wave packet) having a frequency satisfying the condition of Equation (6) as a center frequency f is input from the transmitter to the device under test 10, and reception and signal processing are performed by the method described here. It is to be.

ここで、ｍは0以上の任意の整数であり、fは波束の中心周波数信号の周波数である。この条件を満たす波を選択、利用することにより、第１の整数ｎの偶数/奇数によらず、後方波の消去、抑制と同時に第１センサ１１と第２センサ１２で受信される前方波の信号振幅増大を実現することができる。

Here, m is an arbitrary integer of 0 or more, and f is the frequency of the center frequency signal of the wave packet. By selecting and using a wave satisfying this condition, the forward wave received by the first sensor 11 and the second sensor 12 simultaneously with the elimination and suppression of the backward wave, regardless of the even / odd number of the first integer n. An increase in signal amplitude can be realized.

  Regarding the forward wave, the phase difference between the reception signal received by the first sensor 11 and the delay signal generated by adding the delay time t0 to the reception signal of the second sensor 12 is 0 (n is an odd number) / π ( Since n is an even number, if the sum of the two (n is an odd number) / difference (n is an even number) is taken, the signal amplitude can be increased in a region where both overlap in time after adding the delay time t0. .

  Specifically, with respect to the reception signal of the wave packet of the forward wave, if the reception signal of the first sensor 11 starts from the time t = 0, the reception signal of the second sensor 12 starts from t = t0, By adding a delay time t0 to the received signal of the sensor 12, the time difference between them (the time difference between the start time and the end time of the received signal) becomes 2 · t0. Here, when the sum (n is an odd number) / difference (n is an even number), when the time width of the forward wave received by the first sensor 11 exceeds 2 · t0, both received signals overlap on the time axis. In the region, the signal amplitude can be increased. On the other hand, when the time width of the forward wave received by the sensor is 2 · t0 or less, the two signals are separated on the time axis, but even in this case, the sum (n is an odd number) / difference (n The phase difference between the two signals is 0 in the processed signal.

  Here, the condition for simultaneously realizing complete cancellation of the backward wave and the coincidence of the phase of the forward wave (increase in signal amplitude due to addition if overlapping on the time axis after adding the delay time) will be described in more detail. To do. First, the cycle T (= 1 / f) can be expressed by the following equation from Equation (1).

そこで、上記の式（３）と式（７）を式（６）に代入して整理すると次式を得る。

Therefore, when the above formulas (3) and (7) are substituted into formula (6) and rearranged, the following formula is obtained.

つまり、nを1以上の整数、mを0以上の整数として、式（８）を満たすような位相速度Vph、群速度Vgの関係を満たす送信波（波束）を用いることにより、後方波の理論的には完全な相殺、消去と、前方波の強調（遅延時間付加後に時間軸上で重なっていれば足し合わせによる信号振幅の増大）とを同時に実現することができる。なお、このとき、センサ間隔Lは次式の様に表せる。

In other words, by using a transmission wave (wave packet) satisfying the relationship between the phase velocity Vph and the group velocity Vg satisfying Equation (8), where n is an integer of 1 or more and m is an integer of 0 or more, the theory of backward waves Specifically, complete cancellation and cancellation and enhancement of the forward wave (increase in signal amplitude due to addition if they overlap on the time axis after adding a delay time) can be realized simultaneously. At this time, the sensor interval L can be expressed by the following equation.

なお、加算優先とも称する前方波の受信信号を時間軸上で完全に重ね合わせて（信号の開始時刻と終了時刻を一致させて）足し合せて強調する手法については、実施形態の中で説明する。

A method for emphasizing the received signals of the forward waves, also called addition priority, by superimposing them completely on the time axis (by matching the start time and the end time of the signals) will be described in the embodiment. .

  As described above, in the wave receiving method of the present invention, first, the arrangement of the first sensor 11 and the second sensor 12 is based on the difference between the wave packet group velocity Vg and the phase velocity Vph and the half wavelength of the wave. An arrangement determination time t0 for determining is calculated. Next, the first sensor 11 and the second sensor 12 installed at an interval of the distance L obtained from the arrangement determination time t0 and the group velocity Vg receive a signal based on a wave packet of elastic waves propagating through the inspection object 10. To do. Next, a delay signal is generated by delaying one reception signal of the first sensor 11 or the second sensor 12 by a delay time t0 ′ (in the above description, the case of t0 ′ = t0). Finally, a signal obtained by linearly summing the delayed signal and the other received signal of the first sensor 11 or the second sensor 12 is output.

  According to the reception method of the present invention that operates as described above, even when the phase velocity Vph and the group velocity Vg are different, the reception signal of the backward wave is completely erased and the amplitude of the reception signal of the forward wave (the forward wave) The signal-to-noise ratio of the received signal can be improved by doubling (for the region where the two received signals overlap in time after adding the delay time t0 ′).

  Hereinafter, a specific embodiment of the present invention will be shown and the operation will be described in more detail.

Embodiment
FIG. 3 shows a functional configuration example of the receiving device 100 according to the embodiment of the present invention. The receiving device 100 includes a first sensor 11, a second sensor 12, a receiving unit 20, a delay signal generating unit 30, and a signal output unit 40. The receiving apparatus 100 excluding the first sensor 11 and the second sensor 12 is realized by reading a predetermined program into a computer composed of, for example, a ROM, a RAM, a CPU, and the like, and executing the program by the CPU. Is.

  The operation will be described with reference to the operation flow of the receiving apparatus 100 shown in FIG. The first sensor 11 and the second sensor 12 are installed on the inspection object 10 with the distance L described above therebetween. The first sensor 11 is installed, for example, on the front side with respect to the second sensor 12.

  The distance L is the distance that the wave packet travels at the group velocity Vg during the arrangement determination time t0 that is determined based on the difference between the group velocity Vg and the phase velocity Vph of the wave packet and the wavelength of the wave at the center frequency of the wave packet. It is. This arrangement determination time t0 is obtained by calculation based on the difference between the wave packet group velocity Vg and the phase velocity Vph and the wave wavelength before the reception apparatus 100 starts the reception operation (formula (3)) ( Step S1).

  Next, a delay time t0 ′ for canceling or amplifying the received signal is calculated based on the difference between the group velocity Vg and the phase velocity Vph of the wave packet and the wavelength of the wave at the center frequency of the wave packet (step S2). . The obtained delay time t0 ′ is input to the receiving apparatus 100 as information.

  The receiving unit 20 receives the wave packets detected by the first sensor 11 and the second sensor 12, converts each wave packet into a voltage signal having an amplitude that allows signal processing, and outputs the voltage signal (step S3). The receiving unit 20 may be provided as an independent configuration for each of the first sensor 11 and the second sensor 12.

  The delay signal generation unit 30 delays one of the reception signals received by the first sensor 11 or the second sensor 12 by a delay time t0 ′ to generate a delay signal (step S4).

  The signal output unit 40 outputs a signal obtained by linearly adding the delayed signal and the other received signal received by the first sensor 11 or the second sensor 12 (step S5). The operations in steps S3 to S5 are repeated until the receiving apparatus 100 stops the receiving operation.

  In order to completely cancel the signal due to the backward wave and to superimpose the forward wave as much as possible in time, the distance L (formula (2)) between the first sensor 11 and the second sensor 12 is: The shortest possible wave wavelength λ is desirable. According to the equation (9), the distance L is minimum with respect to the wavelength λ when (n, m) = (1, 0), and can be expressed as the following equation.

また、（ｎ,m）＝（1,0）の時の位相速度Vphと群速度Vgとの関係は、式（８）に基づき次式により表せる。

Further, the relationship between the phase velocity Vph and the group velocity Vg when (n, m) = (1,0) can be expressed by the following equation based on the equation (8).

つまり、この場合、後方波の相殺・消去と前方波の位相の一致とを同時に行う条件は、群速度Vgが位相速度Vphの3倍の波を選択して利用することであり、センサ間隔Lは波長λの3/4倍であることが分かる。図５に、波長λで規格化した距離L（=|Vg|・ｔ0）が、短い方からいくつかの場合についてn,m,Vg,t0,Vg/Vphの関係を示す。例えば（ｎ,m）＝（1,1）の場合、センサ間の距離Lは5λ/4であり、群速度Vgと位相速度Vphの比はVg/Vph=5/3である。又、（ｎ,m）=（3,0）の場合は、センサ間の距離Lは7λ/4であり、群速度Vgと位相速度Vphの比はVg/Vph=7である。

That is, in this case, the condition for simultaneously canceling and canceling the backward wave and matching the phase of the forward wave is to select and use a wave whose group velocity Vg is three times the phase velocity Vph, and the sensor interval L Is 3/4 times the wavelength λ. FIG. 5 shows the relationship among n, m, Vg, t0, and Vg / Vph for several cases where the distance L (= | Vg | · t0) normalized by the wavelength λ is shorter. For example, when (n, m) = (1,1), the distance L between the sensors is 5λ / 4, and the ratio of the group velocity Vg to the phase velocity Vph is Vg / Vph = 5/3. When (n, m) = (3,0), the distance L between the sensors is 7λ / 4, and the ratio of the group velocity Vg to the phase velocity Vph is Vg / Vph = 7.

  When a wave that satisfies the following equation is selected and used instead of the above equation (6), a delay time t0 is added to the reception signal of the second sensor 12 for the forward wave, and the first wave It is also possible to eliminate or suppress by taking a linear sum with the received signal of the sensor 11.

つまり、遅延時間t0の2倍が周期1/fの整数倍であるような波を選択することによって、遅延時間t0を付加し、線形和を実施することによって、時間軸上で両者の重なる時間領域に関して、両者の信号を互いに打ち消し合う関係とすることが可能である。なお、この条件式（１２）は、式（１）、式（３）等を用いて整理すると、位相速度Vphと群速度Vgとの関係として次式で表すことができる。

In other words, by selecting a wave whose delay time t0 is an integral multiple of the period 1 / f, by adding a delay time t0 and performing a linear sum, the time over which both overlap on the time axis Regarding the region, it is possible to have a relationship in which both signals cancel each other. The conditional expression (12) can be expressed by the following expression as a relationship between the phase velocity Vph and the group velocity Vg when arranged using the equations (1), (3), and the like.

以上の説明は、群速度Vgが位相速度Vphよりも速い場合についてである。次に、位相速度Vphが群速度Vgよりも速い（Vph>Vg）について説明する。

The above description is for the case where the group velocity Vg is faster than the phase velocity Vph. Next, the case where the phase velocity Vph is faster than the group velocity Vg (Vph> Vg) will be described.

(When phase velocity Vph> group velocity Vg)
When the phase velocity Vph is faster than the group velocity Vg, the distance to which the wave packet travels L (= | Vg | · t0) is set to the inspection object 10 (for example, a long member) during the arrangement determination time t0 determined by the following equation. The first sensor 11 and the second sensor 12 are installed in the axial direction.

この配置で受信した信号に関して、位相速度Vphよりも群速度Vgが速い場合と同様の信号処理により、後方波の理論的には完全な消去を実施することができる。更に、同時に前方波の位相の一致による増幅、強調とを実施するためには、式（６）を満たすような波を選択し、利用することが条件となる。式（１４）と式（７）を式（６）に代入して整理すると、次式を得る。

With respect to the signal received with this arrangement, the backward wave can be theoretically completely erased by the same signal processing as when the group velocity Vg is faster than the phase velocity Vph. Furthermore, in order to simultaneously perform amplification and enhancement by matching the phase of the forward wave, it is necessary to select and use a wave that satisfies Equation (6). Substituting Equation (14) and Equation (7) into Equation (6) and rearranging results in the following equation.

ここでmは0以上の任意の整数である。

Here, m is an arbitrary integer of 0 or more.

  The position and phase on the time axis of the backward wave reception signal will be described with reference to FIG. FIGS. 6A and 6B are diagrams illustrating an example of the relationship between the reception signals of the two sensors, the first sensor 11 and the second sensor 12. In FIG. 6, the horizontal axis represents time, and the vertical axis represents signal amplitude. FIG. 6 shows an example where Vph> Vg and the first integer n = 1.

  In FIG. 6, the backward wave received by the second sensor 12 is represented as a signal starting from time t = 0 (FIG. 6A). At this time, the backward wave received by the first sensor 11 can be expressed as a signal starting from time t = t0. Therefore, when the time axis is delayed by t0 with respect to the backward wave reception signal received by the second sensor 12, the backward wave reception signal received by the first sensor 11 completely overlaps on the time axis (start time and end time). The time matches).

  Next, the phase relationship will be described. An arbitrary point in the received signal of the backward wave received by the second sensor 12, for example, the point P 12, travels at the phase velocity Vph in the real space, so that the received signal of the first sensor 11 receives the second sensor 12. This is delayed by t0 · Vg / Vph from the time, and corresponds to the signal at point P11 shown in FIG. 6 (b). Therefore, the point P12 of the reception signal of the second sensor 12 corresponds to the point P11 in the reception signal of the first sensor 11.

  Therefore, the time difference ΔT at an arbitrary point between the signal obtained by delaying the backward wave reception signal received by the second sensor 12 by the delay time t0 and the backward wave reception signal received by the first sensor 11 is expressed by the following equation: It can be expressed as

式（１６）に式（１４）を代入して式（１）を用いると時間差ΔTは次式で表せる。

When equation (14) is substituted into equation (16) and equation (1) is used, time difference ΔT can be expressed by the following equation.

この時間差ΔTは、受信信号の全ての点について同一であるため、式（１７）は、遅延時間t0付加後の2つの受信信号の位相差に対応する時間を表しているということができる。

Since this time difference ΔT is the same for all points of the received signal, it can be said that Expression (17) represents a time corresponding to the phase difference between the two received signals after the addition of the delay time t0.

  When the first integer n is an odd number, the phase difference of the received signal is π. Therefore, by adding a delay time t0 to the received signal of the second sensor 12 and adding the received signal of the first sensor 11, The backward wave can be canceled and eliminated.

  When the first integer n is an even number, the phase difference of the received signal is 0 (the phase is the same), so that the delay signal obtained by adding the delay time t0 to the received signal of the second sensor 12 and the first sensor By taking the difference from the 11 received signals, the backward wave can be canceled and eliminated. Since the received signal overlaps at the same time on the time axis by the process of delaying the time axis of the second sensor 12 relative to the first sensor 11 by the delay time t0 (adding the delay time t0), the wave packet If the shape (the envelope of the wave packet) is the same when it is received by the first sensor 11 and the second sensor 12 and is not deformed (approx.), The backward wave is completely canceled in principle. Can be erased.

  Further, when receiving a wave satisfying the relationship between the phase velocity Vph and the group velocity Vg determined by the equation (15), by performing the signal processing for canceling and erasing the received signal of the backward wave, the forward wave is simultaneously obtained. With respect to the received signals, the amplitude can be amplified and emphasized (for time domains overlapping on the time axis).

  In other words, by using the wave packet satisfying the above equation (15), the received signal is canceled and canceled by the wave packet coming from behind, and the received signal is emphasized by the wave packet coming from the front (phase difference 0 is added [n odd number ) Or [n even number] by subtracting by the phase difference π, it is possible to simultaneously realize an increase in amplitude in the region overlapping in time), for example, even if the backward wave and the forward wave reach the sensor at the same time Since the signal for amplifying and enhancing the reception signal of the forward wave can be obtained while eliminating and suppressing the reception signal of the backward wave, the SN ratio can be dramatically improved.

  In order to cancel the backward wave and to superimpose the forward wave as much as possible to enhance the signal, the distance L (= | Vg | · t0) between the first sensor 11 and the second sensor 12 is used. Is preferably as short as possible with respect to the wavelength λ.

  FIG. 7 shows the relationship between n, m, Vg, t0, and Vg / Vph for some cases where n and m are relatively small with respect to the distance L (= | Vg | · t0) expressed by the wavelength λ. For example, when (n, m) = (1,2), the distance L between the sensors is 3λ / 4, and the ratio of the phase velocity Vph to the group velocity Vg is Vg / Vph = 3/5. When (n, m) = (1,4), the distance L is 7λ / 4, and the speed ratio is Vg / Vph = 7/9. FIG. 8 collectively shows conditions, relational expressions, and the like for eliminating the backward wave when the arrangement determination time and the delay time are equal (t0 = t0 ′).

  Note that the delay time and the distance L are not necessarily set to strict values. For example, the distance L is changed in a range of a small distance with respect to the wavelength λ of the received wave in a range that does not significantly affect the elimination of the backward wave and the superposition of the phase of the forward wave. Alternatively, substantially the same effect can be obtained by changing the delay time within a small range with respect to the period 1 / f.

  In the above description, the delay time t0 ′ and the arrangement determination time t0 for determining the distance L (= | Vg | · t0) between the first sensor 11 and the second sensor 12 are the same. As described above, as the delay time, t0 ′ satisfying the following equation may be used with the second integer n ′ as an arbitrary integer.

つまり、第２センサ１２の受信信号に対して、遅延時間t0′を付加し、第１センサ１１の受信信号と線形和をとる。この場合、第２の整数n′が奇数のとき両者の和をとり、第２の整数n′が偶数のとき両者の差をとることにより、時間軸上で重なり合う時間領域については、後方波受信信号を抑制することができる。

That is, the delay time t0 ′ is added to the reception signal of the second sensor 12 and a linear sum is obtained with the reception signal of the first sensor 11. In this case, when the second integer n ′ is an odd number, the sum of the two is taken, and when the second integer n ′ is an even number, the difference between the two is taken. The signal can be suppressed.

  When the delay time t0 ′ different from t0 is employed using the second integer n ′, the condition for simultaneously enhancing the forward wave is expressed by equation (19) when Vg> Vph. Further, when Vph> Vg, Expression (20) is obtained. These are expressions corresponding to Expression (8) and Expression (15) in the case of t0 = t0 ′.

なお、第１の整数nと第２の整数n′とが異なる場合は、例えばn′をnから減じて行くに従って、前方波の受信信号に関して、線形和をとる際に時間軸上で、両者が重なり合う時間をより長くすることができるようになり、その結果、前方波の受信信号の振幅を増幅、強調する時間を増やすことができる。しかしながら、n′をnから減じて行くに従って、後方波の受信信号に関しては、線形和をとる際に時間軸上で両者が重なり合う時間が短くなって行くため、後方波の受信信号を消去、抑制できる時間領域は短くなって行くことになる。即ち、第１の整数nと第２の整数n′とが異なる場合は、後方波消去と前方波増大の両方が完全ではない。しかし、第２の整数n′の選択によって後方波消去と前方波増大の軽重を任意に選択することができる。つまり、受信信号のSN比の改善方法の選択肢の幅を広げる効果を奏する。

When the first integer n and the second integer n ′ are different, for example, as n ′ is subtracted from n, both are obtained on the time axis when taking a linear sum with respect to the received signal of the forward wave. As a result, it is possible to increase the time for amplifying and enhancing the amplitude of the reception signal of the forward wave. However, as n ′ is subtracted from n, the backward wave received signal is erased and suppressed for the backward wave received signal because the time over which the two overlap on the time axis becomes shorter when taking the linear sum. The possible time domain will become shorter. That is, when the first integer n and the second integer n ′ are different, both backward wave cancellation and forward wave increase are not perfect. However, the weight of backward wave cancellation and forward wave increase can be arbitrarily selected by selecting the second integer n ′. That is, there is an effect of widening the range of options for the method for improving the SN ratio of the received signal.

[Additional priority]
Next, a method of ideally superimposing the forward waves received by the first sensor 11 and the second sensor 12 and doubling the amplitude (in the case of one sensor) will be described. Also in the case of addition priority, the first sensor 11 and the second sensor 2 are installed with an interval of the distance L in Expression (2), as in the case of the above-described subtraction priority.

  First, the forward wave first reaches the first sensor 11 (the arrival time of the wave packet tip is t = 0) and is received, and then reaches the second sensor 12 (arrival time t = t0 of the wave packet tip). And received. Therefore, when the delay time is the same as the arrangement determination time (t0 = t0 ′), a delay signal obtained by delaying the reception signal of the first sensor 11 by the delay time t0 by the delay time addition process, The reception signal of the sensor 12 overlaps at the same time on the time axis.

  First, the case where the group velocity Vg is faster than the phase velocity Vph will be described. In this case, the first sensor 11 and the second sensor 12 are installed at a distance L determined by the equations (2) and (3). When the first integer n is an odd number, the phases of the forward waves received by the first sensor 11 and the second sensor 12 are inverted from each other. That is, the phase difference between the delayed signal obtained by adding the delay time t0 to the received signal received by the first sensor 11 and the received signal of the second sensor 12 is π.

  Therefore, the received signal can be amplified and emphasized by taking the difference between these signals.

  If the approximation that the shape of the received signal of the wave packet (the shape of the envelope of the wave packet) is the same between the first sensor 11 and the second sensor 12 and is not deformed is sufficient, in principle, one sensor A received signal having twice the amplitude compared to the case can be obtained.

  When the first integer n is an even number, the forward wave is obtained by taking the sum of the delay signal obtained by adding the delay time t0 to the reception signal of the first sensor 11 and the reception signal received by the second sensor 12. Can be emphasized. That is, when the first integer n is an even number, the phase of the delayed signal of the first sensor 11 and the signal received by the second sensor 12 match (phase difference 0). For forward waves, the amplitude of the received signal can be increased and enhanced.

  When the phase velocity Vph and the group velocity Vg are different from each other, the enhancement of the reception signal of the forward wave described above can be performed regardless of the value of both. Furthermore, when the forward wave is emphasized as described above, it is possible to cancel and suppress the backward wave reception signal at the same time.

  For this purpose, a wave packet in which twice the delay time t0 is a half integer multiple of the period 1 / f may be used. That is, a wave satisfying the equation (6) or the equation (8) is selected with m being an integer of 0 or more. In this case, since the backward wave reception signals received by the first sensor 11 and the second sensor 12 do not completely overlap on the time axis when taking the linear sum, the backward wave is completely erased over the entire time. It is not possible.

  The above contents will be described in detail. With respect to reception of a wave that satisfies Equation (6) or Equation (8), the first integer n is obtained by delaying the reception signal of the first sensor 11 by t0 using the arrangement determination time t0 of Equation (3) as a delay time. Regardless of the even number / odd number, a linear sum (sum when n is an even number / difference when n is an odd number) is used to obtain the delayed signal of the first sensor 11 and the second sensor 12 for the backward received signal. The received signal can be canceled, suppressed, and erased in a region where they both overlap in time.

  With respect to the received signal of the backward wave, when the duration exceeds 2 · t0, there is a time region in which both overlap on the time axis after adding the delay time t0. On the other hand, when the duration of the received signal is 2 · t0 or less, there is no time region where both received signals overlap after the addition of the delay time t0.

  Here, ideally the superposition of the forward wave (summing with a phase difference of 0 over the entire duration of the signal) and the superposition of the backward wave with the phase difference π, that is, the region overlapping in time The specific conditions for simultaneously realizing the amplitude cancellation and suppression will be summarized again. Substituting the above formulas (3) and (7) into formula (6) and rearranging them gives the following formula.

つまり、式（２１）を満たすような位相速度Vphと群速度Vgとの関係を満たす波を選択して利用することにより、受信に際して、前方波の受信信号の継続時間を時間軸上で一致させて、且つ線形和によって強調し、更に同時に後方波の受信信号については、時間軸上で重なる領域について、信号（振幅）を抑制することができる。なお、このとき、センサ間隔Lは次式となる。

That is, by selecting and using a wave satisfying the relationship between the phase velocity Vph and the group velocity Vg that satisfies the equation (21), the duration of the reception signal of the forward wave is matched on the time axis upon reception. In addition, it is possible to suppress the signal (amplitude) in the region overlapping on the time axis with respect to the received signal of the backward wave at the same time with emphasis by the linear sum. At this time, the sensor interval L is as follows.

理論的には後方波を完全に重ね合わせて、且つ後方波を可能な限り空間的に重ね合わせて相殺するためには、第１センサ１１と第２センサ１２との間の距離L（=|Vg|・t0）は、波長λに対して可能な限り短いものが望ましい。式（２２）より、距離L（=|Vg|・t0）の最小値は（n,m）=（1,0）の時であり、次式のように表せる。

Theoretically, the distance L (= |) between the first sensor 11 and the second sensor 12 is used to completely overlap the backward waves and cancel the backward waves by overlapping them as spatially as possible. Vg | · t0) is preferably as short as possible with respect to the wavelength λ. From Equation (22), the minimum value of the distance L (= | Vg | · t0) is when (n, m) = (1,0), and can be expressed as the following equation.

また、（n,m）=（1,0）の時の位相速度Vphと群速度Vgとの関係は、上記の式（２１）より次式により表せる。

Further, the relationship between the phase velocity Vph and the group velocity Vg when (n, m) = (1,0) can be expressed by the following equation from the above equation (21).

つまり、群速度Vgが位相速度Vphの3倍の場合であることが分かる。波長λで表した距離L（=|Vg|・ｔ0）について、短い方からいくつかの場合についてn,m,Vg,t0,Vg/Vphの関係は、図５に示すようになる。

That is, it can be seen that the group velocity Vg is three times the phase velocity Vph. With respect to the distance L (= | Vg | · t0) represented by the wavelength λ, the relationship among n, m, Vg, t0, and Vg / Vph is as shown in FIG.

  In addition, by imposing the condition of Expression (12) instead of the condition of Expression (6), the phase of the backward wave reception signal in the delayed signal of the first sensor 11 and the reception signal of the second sensor 12 is matched, and the time It is also possible to emphasize the region that overlaps (summing with a phase difference of 0 or taking a difference with a phase difference of π).

  From here, the case where the phase velocity Vph is faster than the group velocity Vg (Vph> Vg) will be described. Even when the phase velocity Vph is faster than the group velocity Vg, the inspection object 10 (long) is spaced by a distance L (= | Vg | · t0) at which the wave packet travels when the delay time t0 satisfies the equation (14). The first sensor 11 and the second sensor 12 are installed in the axial direction of the scale member).

  As a result, the same control as when the group velocity Vg is faster than the phase velocity Vph (Vph <Vg), that is, the delay time t0 is added to the received signal of the first sensor 11 and the received signal of the second sensor 12 is compared. By performing the linear sum operation, it is possible to realize complete superposition of the reception signals of the forward waves (matching the signal durations and summing them with a phase difference of 0 or taking a difference with a phase difference of π). This sensor arrangement and signal processing can be performed when the phase velocity Vph and the group velocity Vg are different from each other. Furthermore, when such forward wave enhancement is performed, sensitivity to the backward wave (reduction and suppression of received signals) can be simultaneously performed.

  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 formula (6) is selected with m being an integer of 0 or more. In this case, the backward waves of the first sensor 11 and the second sensor 12 do not completely overlap with each other in time, and thus cannot be completely canceled or deleted.

  When the above conditional expressions are arranged, the following expression is obtained by substituting Expression (7) and Expression (14) into Expression (6).

つまり、式（２５）を満たすような位相速度Vphと群速度Vgとの関係を満たす波（送信波としての波束）を選択して利用することにより、受信に際して、理論的には完全な前方波の重ね合わせと後方波については、感度の抑制（位相差0での差、又は位相差πでの和）を実現することができる。波長λで表した距離L（=|Vg|・ｔ0）について、n,ｍの小さい方からいくつかの場合についてn,m,Vg,t0,Vg/Vphの関係は、図７に示すようになる。

That is, by selecting and using a wave (wave packet as a transmission wave) satisfying the relationship between the phase velocity Vph and the group velocity Vg that satisfies the equation (25), a theoretically complete forward wave can be received. As for the superposition and backward wave, suppression of sensitivity (difference at phase difference 0 or sum at phase difference π) can be realized. As shown in FIG. 7, the relationship between n, m, Vg, t0, and Vg / Vph in some cases from the smaller n and m with respect to the distance L (= | Vg | · t0) represented by the wavelength λ. Become.

  In addition, by imposing the condition of the expression (12) instead of the condition of the expression (6), the phase of the received signal of the backward wave in the delayed signal of the first sensor 11 and the signal of the second sensor 12 is matched. It is also possible to perform processing for emphasizing the overlapping region (summation with phase difference 0 or difference with phase difference π). FIG. 9 shows the conditions and relational expressions for the method of emphasizing the forward wave described above ideally by completely superimposing them (addition priority).

  Note that the distance L and the delay time are not necessarily set to strict values. For example, the distance L is changed in a range of a small distance with respect to the wavelength of the wave to be received in a range that does not significantly affect the elimination of the backward wave and the superposition of the phase of the forward wave. Alternatively, the delay time may be changed within a small range with respect to the period 1 / f, which is the same as described in the subtraction priority above.

  Similarly, the delay time t0 ′ (formula (18)) in which the second integer n ′ is an arbitrary integer may be used. That is, when the first integer n and the second integer n ′ are different, both forward wave amplification and backward wave cancellation are not perfect. However, the weight of forward wave amplification and backward wave cancellation can be selected by selecting the second integer n ′. That is, there is an effect of widening the range of options for the method for improving the SN ratio of the received signal.

[Specific Example 1]
Specific examples of delay time t0 ′, distance L, linear sum processing, and the like of the reception method of this embodiment will be described. In all the following specific examples, the delay time t0 ′ is equal to the arrangement determination time t0 in order to explain by taking subtraction priority or addition priority as an example. FIG. 10 shows a calculation result of the dispersion curve of the guide wave F (1,1) mode in a steel solid cylindrical rod having a diameter of 10 mm in a vacuum.

Guide waves are elastic waves that propagate along waveguides (rods, pipes, flat plates, solid surfaces, solid surface protrusions, etc.) formed by physical boundaries, and are generally multimode and distributed. It has the characteristic of having a characteristic (there is a frequency dependence of the phase velocity). The guide wave F mode is a kind of elastic wave propagating in the direction of the central axis in the cylindrical inspection object 10 (long member), and means a mode that vibrates asymmetrically with respect to the axis. In FIG. 10, the horizontal axis represents frequency, the vertical axis represents sound velocity, the broken line represents phase velocity Vph, and the solid line represents group velocity Vg. In the range shown in FIG. 10, the group velocity Vg is faster than the phase velocity Vph. FIG. 11 shows the parameters used to calculate the dispersion curve shown in FIG. The density of the steel material was 7860 kg / m ³ , the longitudinal wave velocity was 5900 m / s, and the transverse wave velocity was 3200 m / s. Hereinafter, an example of receiving the wave packet of the guide wave will be described.

  The phase velocity Vph at the frequency f = 110 kHz is the value shown in the equation (26) and the group velocity Vg is the value shown in the equation (27).

したがって、両者の比は約1.4となり、図５に示す（n,m）=（1,2）の条件に対応することが分かる。また、式（１）に位相速度Vphと周波数fとを代入することにより、波長λはλ=21mmとなる。そのため、距離L（=|Vg|・t0）と遅延時間は、それぞれ次式に示す値になる。

Therefore, the ratio between the two is about 1.4, which corresponds to the condition (n, m) = (1,2) shown in FIG. Further, by substituting the phase velocity Vph and the frequency f into the equation (1), the wavelength λ becomes λ = 21 mm. Therefore, the distance L (= | Vg | · t0) and the delay time are values shown in the following equations, respectively.

本具体例においては、第１センサ１１と第２センサ１２との距離Lを37mmに設置し、遅延時間を12μsとすれば良いことが分かる。第１センサ１１と第２センサ１２とに、前方よりF（1,1）モード110kHzの波束が到来した場合、同時に後方より同じモード、同じ中心周波数の波束が到来したとしても、第２センサ１２の受信信号に12μsの遅延時間を付加し、第１センサ１１の受信信号と和を取る信号処理を行うことで、後方波の受信信号を消去、抑制し、同時に前方波の受信信号を増幅、強調することができる。

In this specific example, it is understood that the distance L between the first sensor 11 and the second sensor 12 is set to 37 mm and the delay time is set to 12 μs. When a wave packet of F (1, 1) mode 110 kHz arrives at the first sensor 11 and the second sensor 12 from the front, even if a wave packet of the same mode and the same center frequency arrives at the same time, the second sensor 12 By adding a 12 μs delay time to the received signal and performing signal processing that sums it with the received signal of the first sensor 11, the backward received signal is eliminated and suppressed, and at the same time the forward received signal is amplified, Can be emphasized.

  In this case, the forward wave is shifted by 2 · t0 = 24 μm in time between the reception signal of the second sensor 12 and the reception signal of the first sensor after adding the delay time. Therefore, if the duration of the received signal exceeds 24 μs, there is a region where both overlap in time, and the signal strength is emphasized in that region.

  The condition where the duration exceeds 24 μs corresponds to the spatial width of the forward wave (wave packet) exceeding the width of 2 · Vg · t0 shown in the following equation.

前方波の幅が74mmより十分大きい場合、例えば幅が420mm（=20・λ）であれば、この波による受信信号の継続時間tcは130μsとなる。

When the width of the forward wave is sufficiently larger than 74 mm, for example, if the width is 420 mm (= 20 · λ), the duration tc of the reception signal by this wave is 130 μs.

したがって、上記の信号処理によって継続時間tcから24μsを差し引いた106μsの時間にわたって前方波が位相差0で足し合されることとなり、この領域では前方波が強調されることとなる。一方、後方波は、上記の信号処理によって（継続時間tcの全体にわたって位相差πで足し合されるため）相殺、消失する。

Therefore, the forward wave is added with a phase difference of 0 over a period of 106 μs obtained by subtracting 24 μs from the duration time tc by the signal processing described above, and the forward wave is emphasized in this region. On the other hand, the backward wave cancels out and disappears by the above signal processing (because the phase difference π is added over the entire duration tc).

  As described above, a transmission wave having a specific mode and a specific frequency is selected, the first sensor 11 and the second sensor 12 are set apart by a distance L (= | Vg | · t0), and the delay time t0 ′ is set. By setting (t0 ′ = t0 in this example), it becomes possible to eliminate the influence of the backward wave and increase the signal intensity of the forward wave. This reception method can improve the SN ratio of the received signal even when the phase velocity Vph and the group velocity Vg are different (subtraction priority).

  When receiving the same 110 kHz F (1,1) mode transmission wave packet in the same sensor arrangement, a delay time of 12 μs is added to the reception signal of the first sensor 11 and the reception signal of the second sensor 12 is received. By taking the difference from the above, it is possible to theoretically completely overlap the forward wave to make the amplitude about twice the amplitude, and to erase and reduce the backward wave amplitude in the temporally overlapping region (addition priority) ).

[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 a vacuum. The L mode is a type of elastic wave propagating in the direction of the central axis in the cylindrical object to be inspected 10 (long member), and is a mode that vibrates axisymmetrically. This means vibration that has only the radial direction (the vibration component in the circumferential direction of the rod is 0). The relationship between the horizontal axis and the vertical axis in FIG. 12 is the same as that in FIG. The parameters used for calculating the dispersion curve are also the same as the values shown in FIG.

  For the L mode, the phase velocity Vph when the frequency f = 275 kHz is a value represented by the equation (32), and the group velocity Vg is a value represented by the equation (33).

したがって、両者の比は約0.6となり、図７に示す（n,m）=（1,2）の条件に対応することが分かる。また、式（１）に位相速度Vphと周波数fとを代入することにより、波長λはλ=21mmとなる。そのため、距離L（=|Vg|・t0）と遅延時間は、それぞれ次式に示す値になる。

Therefore, the ratio between the two is about 0.6, which corresponds to the condition (n, m) = (1,2) shown in FIG. Further, by substituting the phase velocity Vph and the frequency f into the equation (1), the wavelength λ becomes λ = 21 mm. Therefore, the distance L (= | Vg | · t0) and the delay time are values shown in the following equations, respectively.

本具体例においては、第１センサ１１と第２センサ１２との距離Lを12mmに設置し、遅延時間を4.7μsとすれば良いことが分かる。第１センサ１１と第２センサ１２とに、前方よりL（0,1）モード275kHzの波束が到来した場合、同時に後方より同じモード、同じ周波数の波束が到来したとしても、第２センサ１２の受信信号に4.7μsの遅延時間を付加し、第１センサ１１の受信信号と和を取る信号処理を行うことで、後方波の受信信号の消去、抑制と同時に、前方波の受信信号の増幅、強調により、SN比を向上することができる。

In this specific example, it can be seen that the distance L between the first sensor 11 and the second sensor 12 is set to 12 mm and the delay time is set to 4.7 μs. When a wave packet of L (0, 1) mode 275 kHz arrives at the first sensor 11 and the second sensor 12 from the front, even if a wave packet of the same mode and the same frequency arrives from the rear at the same time, By adding a delay time of 4.7 μs to the received signal and performing signal processing that sums it with the received signal of the first sensor 11, the received signal of the forward wave is amplified simultaneously with the elimination and suppression of the received signal of the backward wave, The SN ratio can be improved by emphasis.

  In this case, the forward wave is shifted by 2 · t0 = 9.4 μs in time between the reception signal of the second sensor 12 and the reception signal of the first sensor after the delay time is added. Therefore, if the duration of the received signal exceeds 9.4 μs, there is a region where both overlap in time, and the signal strength is emphasized (added by a phase difference of 0) in that region.

  The condition that the duration exceeds 9.4 μs corresponds to the spatial width of the forward wave (wave packet) exceeding the width of 2 · Vg · t0 shown in the following equation.

前方波の幅が24mmより十分大きい場合、例えば幅が320mm（=20・λ）であれば、この波による受信信号の継続時間tcは120μsとなる。

If the width of the forward wave is sufficiently larger than 24 mm, for example, if the width is 320 mm (= 20 · λ), the duration tc of the received signal by this wave is 120 μs.

したがって、上記の信号処理によって継続時間tcから9.4μsを差し引いた110μsの時間にわたって前方波が位相差0で足し合されることとなり、この領域では前方波が強調されることとなる。一方、後方波は、上記の信号処理によって（継続時間tcの全体にわたって位相差πで足し合されるため）相殺、消失する(減算優先)。

Therefore, the forward wave is added with a phase difference of 0 over a period of 110 μs obtained by subtracting 9.4 μs from the duration time tc by the above signal processing, and the forward wave is emphasized in this region. On the other hand, the backward wave is canceled and disappears (subtraction priority) by the above signal processing (because the phase difference π is added over the entire duration tc).

  In addition, when receiving the same f = 275 kHz L (0,1) mode guide wave packet in the same sensor arrangement, a delay time of 9.4 μs is added to the received signal of the first sensor 11 and the received signal of the second sensor 12 is received. By taking the difference, the forward wave packet reception signal can be theoretically completely overlapped to double the amplitude of the signal, and the signal amplitude of the backward arriving wave can be eliminated or reduced in the temporally overlapping region. (Addition priority).

[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. The relationship between the horizontal axis and the vertical axis in FIG. 13 is the same as in FIG. The parameters used for calculating the dispersion curve are also the same as the values shown in FIG.

  For the L (0,2) mode, the phase velocity Vph at the frequency f = 460 kHz is the value shown in Equation (38), and the group velocity Vg is the value shown in Equation (39).

したがって、両者の比は約0.71となり、図７に示す（n,m）=（1,3）の条件に対応することが分かる。また、式（１）に位相速度Vphと周波数fとを代入することにより、波長λはλ=13mmとなる。そのため、距離L（=|Vg|・t0）と遅延時間は、それぞれ次式に示す値になる。

Therefore, the ratio between the two is about 0.71, which corresponds to the condition (n, m) = (1,3) shown in FIG. Further, by substituting the phase velocity Vph and the frequency f into the equation (1), the wavelength λ becomes λ = 13 mm. Therefore, the distance L (= | Vg | · t0) and the delay time are values shown in the following equations, respectively.

本具体例においては、第１センサ１１と第２センサ１２との距離Lを16mmに設置し、遅延時間を4.4μsとすれば良いことが分かる。第１センサ１１と第２センサ１２とに、前方よりL（0,2）モード460kHzの波束が到来した場合、同時に後方より同じモード、同じ周波数の波束が到来したとしても、第２センサ１２の受信信号に4.4μsの遅延時間を付加し、第１センサ１１の受信信号と和を取る信号処理を行うことで、後方波の受信信号については消去、抑制し、前方波の受信信号については増幅、強調することでSN比を向上することができる。

In this specific example, it can be seen that the distance L between the first sensor 11 and the second sensor 12 is set to 16 mm and the delay time is set to 4.4 μs. When a wave packet of L (0, 2) mode 460 kHz arrives at the first sensor 11 and the second sensor 12 from the front, even if a wave packet of the same mode and the same frequency arrives from the rear at the same time, By adding a delay time of 4.4 μs to the received signal and performing signal processing that sums the received signal of the first sensor 11, the backward received signal is erased and suppressed, and the forward received signal is amplified. The signal-to-noise ratio can be improved by emphasizing.

  In this case, the forward wave is shifted by 2 · t0 = 8.8 μ in time between the reception signal of the second sensor 12 and the reception signal of the first sensor after adding the delay time. Therefore, if the duration of the received signal exceeds 8.8 μs, there is a region where both overlap in time, and the signal strength is emphasized in that region.

  The condition that the duration exceeds 8.8 μs corresponds to the spatial width of the forward wave (wave packet) exceeding the width of 2 · Vg · t0 shown in the following equation.

前方波の幅が33mmより十分大きい場合、例えば幅が260mm（=20・λ）であれば、この波による受信信号の継続時間tcは62μsとなる。

When the width of the forward wave is sufficiently larger than 33 mm, for example, if the width is 260 mm (= 20 · λ), the duration tc of the reception signal by this wave is 62 μs.

したがって、上記の信号処理によって継続時間tcから8.8μsを差し引いた53μsの時間にわたって前方波の受信信号が位相差0で足し合されることとなり、この領域では前方波の受信信号が強調されることとなる。一方、後方波の受信信号は、上記の信号処理によって（継続時間tcの全体にわたって位相差πで足し合されるため）相殺、消失する。

Therefore, the reception signal of the forward wave is added by the phase difference 0 over the time of 53 μs obtained by subtracting 8.8 μs from the duration time tc by the above signal processing, and the reception signal of the forward wave is emphasized in this region. It becomes. On the other hand, the received signal of the backward wave cancels and disappears by the above signal processing (because it is added with the phase difference π over the entire duration tc).

[Specific Example 4]
This specific example shows a case where a guide wave L (0, 2) mode wave packet is received in an aluminum cylindrical pipe having an outer diameter of 30 mm and an inner diameter of 10 mm in a vacuum. 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), the phase velocity Vph at the frequency f = 150 kHz is expressed by the equation (44), and the group velocity Vg is expressed by the equation ( 45).

したがって、両者の比は約0.78となり、周波数f=150kHzのL（0,2）モードは、図７に示す（n,m）=（1,4）の条件に対応することが分かる。また、式（１）に位相速度Vphと周波数fとを代入することにより、波長λはλ=37mmとなる。そのため、距離L（=|Vg|・t0）と遅延時間は、それぞれ次式に示す値になる。

Therefore, the ratio between the two is about 0.78, and it can be seen that the L (0,2) mode with the frequency f = 150 kHz corresponds to the condition (n, m) = (1,4) shown in FIG. Further, by substituting the phase velocity Vph and the frequency f into the equation (1), the wavelength λ becomes λ = 37 mm. Therefore, the distance L (= | Vg | · t0) and the delay time are values shown in the following equations, respectively.

本具体例においては、第１センサ１１と第２センサ１２との距離Lを65mmに設置し、遅延時間を16μsとすれば良いことが分かる。第１センサ１１と第２センサ１２とに、前方よりL（0,2）モード150kHzの波束が到来した場合、同時に後方より同じモード、同じ周波数の波束が到来したとしても、第２センサ１２の受信信号に16μsの遅延時間を付加し、第１センサ１１の受信信号と和を取る信号処理を行うことで、後方波の受信信号を消去、抑制し、前方波の受信信号を増幅、強調することにより、SN比を向上することができる。

In this specific example, it can be seen that the distance L between the first sensor 11 and the second sensor 12 is set to 65 mm and the delay time is set to 16 μs. When a wave packet of L (0, 2) mode 150 kHz arrives at the first sensor 11 and the second sensor 12 from the front, even if a wave packet of the same mode and the same frequency arrives from the rear at the same time, By adding a delay time of 16 μs to the received signal and performing signal processing that sums it with the received signal of the first sensor 11, the backward received signal is eliminated and suppressed, and the forward received signal is amplified and emphasized. As a result, the SN ratio can be improved.

  In this case, with respect to the forward wave, the reception signal of the second sensor 12 and the reception signal of the first sensor after adding the delay time t0 are shifted by 2 · t0 = 32 μ in time. Therefore, if the duration of the received signal exceeds 32 μs, there is a region where both overlap in time, and the signal strength is emphasized in that region.

  The condition that the duration exceeds 32 μs corresponds to the spatial width of the forward wave (wave packet) exceeding the width of 2 · Vg · t0 shown in the following equation.

前方波の幅が130mmより十分大きい場合、例えば幅が740mm（=20・λ）であれば、この波による受信信号の継続時間tcは170μsとなる。

If the width of the forward wave is sufficiently larger than 130 mm, for example, if the width is 740 mm (= 20 · λ), the duration tc of the received signal by this wave is 170 μs.

したがって、上記の信号処理によって継続時間tcから32μsを差し引いた約140μsの時間にわたって前方波の受信信号が位相差0で足し合されることとなり、この領域では前方波の受信信号が強調されることとなる。一方、後方波の受信信号は、上記の信号処理によって（継続時間tcの全体にわたって位相差πで足し合されるため）相殺、消失する（減算優先）。

Therefore, the reception signal of the forward wave is added by the phase difference 0 over the time of about 140 μs obtained by subtracting 32 μs from the duration time tc by the above signal processing, and the reception signal of the forward wave is emphasized in this region. It becomes. On the other hand, the received signal of the backward wave cancels out and disappears (subtraction priority) by the above signal processing (because the phase difference π is added over the entire duration tc).

  As described above, according to the receiving apparatus 100 of this embodiment, even when the phase velocity Vph and the group velocity Vg are different, the backward wave can be canceled and the amplitude of the forward wave can be increased at the same time. Can be improved. In the embodiment, the transmitter is described as being disposed on the front side of the first sensor 11, but the position of the transmitter is not limited to this example. For example, the transmitter may be installed at the rear part of the inspection object 10 on the second sensor 12 side.

  Further, although specific examples of the first sensor 11 and the second sensor 12 have not been mentioned, a piezoelectric element probe can be used for these sensors as in the transmitter. When a piezoelectric element probe is used, it is usual to use a plurality of probes as a set of sensors as described in the prior art documents. In addition, various methods such as a method using a magnetostrictive sensor, a method using an electromagnetic acoustic transducer (EMAT), and a laser ultrasonic method are known. A sensor may be used.

  In the embodiment, the example of the long member is described as the shape of the object to be inspected 10, but the shape may be anything. For example, it may have a two-dimensional or three-dimensional spread. For example, when transmitting a transmission wave such as a Lamb wave or SH wave, or a transmission wave of a Rayleigh wave or a surface SH wave to the surface of the bulk member, the reception method described in the above embodiment can be applied.

  Moreover, although the individual | organism | solid was taken as an example as the to-be-inspected object 10, an object may be any of solid, liquid, and gas. Moreover, it may be a combination of them. In addition, the waves transmitted and received are not limited to elastic waves, and various waves having different phase velocities Vph and group velocities Vg can be used.

  Further, although the receiving apparatus 100 has been described as an example in which the operation starts with the delay time t0 ′ known, the receiving apparatus 100 may calculate the delay time t0 ′ by itself. FIG. 14 shows a functional configuration example of the receiving apparatus 200 in which the arrangement determining time t0 is determined from the received signal and the delay time t0 ′ is calculated.

  The receiving apparatus 200 is different from the receiving apparatus 100 in that the receiving apparatus 200 includes a receiving unit 50, an arrangement determination time calculating unit 60, and a delay time calculating unit 70. The receiving unit 50 measures information on the group velocity Vg and the phase velocity Vph from the received wave packet and outputs the information to the arrangement determination time calculating unit 60. The arrangement determination time calculation unit 60 is an arrangement for determining the arrangement of the first sensor 11 and the second sensor 12 based on the difference between the group velocity Vg of the wave packet and the phase velocity Vph and the half wavelength of the center frequency signal of the wave packet. Calculate decision time t0 and output to outside.

  The user using the receiving device 200 calculates the distance L from the arrangement determination time t0 (formula (2)), and installs the first sensor 11 and the second sensor 12 with an interval of the distance L. The delay time calculator 70 calculates the delay time t0 ′ based on the difference between the group velocity Vg and the phase velocity Vph of the wave packet received by the receiver 50 and the half wavelength of the wave at the center frequency of the wave packet. The operation after calculating the delay time t0 ′ is the same as that of the receiving apparatus 100.

  Information on the group velocity Vg and the phase velocity Vph may be given to the delay time calculation unit 70 from the outside. Further, the second integer n ′ necessary for the calculation of the delay time t0 ′ may be set as a constant in the delay time calculation unit 70, or may be input from the outside like the group velocity Vg and the like. Also good.

  Further, it is possible to omit the step of installing the first sensor 11 and the second sensor 12 with an interval of the distance L after calculating the arrangement determination time t0. If the step is omitted, measurement may be performed by changing the wave mode and frequency in various ways, and a wave (mode or frequency) that matches | Vg | · t0 with a preset distance L may be selected.

  The above-described embodiment is not limited to elastic waves in principle, and can be generally applied to reception of waves having different phase velocities Vph and group velocities Vg. As described above, the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the gist.

10: Inspected object 11: First sensor 12: Second sensor 20: Receiver 30: Delay signal generator 40: Signal output unit 50: Receiver 60: Arrangement determination time calculator 70: Delay time calculator

Claims (6)

An arrangement determination time for calculating an arrangement determination time for determining the arrangement of the first sensor and the second sensor based on the difference between the group velocity and the phase velocity of the wave packet and the wavelength of the wave at the center frequency of the wave packet. A calculation step;
A delay time calculating step of calculating a delay time for canceling or amplifying the received signal based on the difference and the wavelength;
A receiving step of receiving the wave packet by the first sensor and the second sensor installed on the object to be inspected at a distance that the wave packet travels at the group velocity during the arrangement determination time;
A delay signal generation step of generating a delay signal obtained by delaying one reception signal of the first sensor or the second sensor by the delay time;
And a signal output step of outputting a signal obtained by linearly summing the delayed signal and the other received signal of the first sensor or the second sensor. The wave receiving method according to claim 1,
The arrangement determination time is t0, the distance between the first sensor and the second sensor is L, the phase velocity is Vph, the group velocity is Vg, a first integer that is an integer of 1 or more is n, and the center frequency is When the wavelength of the wave is λ, Vph may be positive, Vg may be positive or negative, and the arrangement determination time and the distance are calculated by the following equations:

A wave receiving method characterized by the above. The wave receiving method according to claim 2,
When the group velocity is faster than the phase velocity and when the phase velocity is faster than the group velocity, the wave packets represented by the following equations are received, where m is an integer of 0 or more, respectively.

A wave receiving method characterized by the above. The wave receiving method according to claim 2 or 3,
When the delay time for delaying one received signal of the first sensor or the second sensor is t0 ′ and the second integer which is an arbitrary integer is n ′, the value satisfies the following equation:

A wave receiving method characterized by the above. The wave receiving method according to claim 4,
A wave receiving method, wherein a first integer n which is a decision variable for the arrangement determination time and a second integer n ′ for determining the delay time are set to the same value. Based on the difference between the group velocity and the phase velocity of the wave packet, and the wavelength of the wave at the center frequency of the wave packet,
A first sensor and a second sensor installed on an object to be inspected at a distance that the wave packet travels at the group velocity during an arrangement determination time determined to set an arrangement of sensors;
A receiver that receives the wave packet detected by the first sensor and the second sensor and outputs a received signal;
Delay signal generation for generating a delay signal obtained by delaying one received signal of the first sensor or the second sensor by a delay time determined to cancel or amplify the received signal based on the difference and the wavelength And
And a signal output unit that outputs a signal obtained by linearly summing the delayed signal and the other received signal of the first sensor or the second sensor.

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