JP4795092B2 - Acoustic waveguide device - Google Patents

Description

  The present invention relates to an acoustic wave waveguide device in general, and more particularly to an acoustic waveguide device that controls the propagation direction of an acoustic wave by frequency. Note that the term “acoustic wave” used herein refers to a sound wave propagating in a gas or liquid, an elastic wave propagating in a solid, or the like.

  A conventional waveguide device relating to electromagnetic waves will be described below with reference to FIG. 12 (for example, see Non-Patent Document 1). FIG. 12 is a diagram illustrating a simulation result of a waveguide device related to a conventional electromagnetic wave. In FIG. 12, (a) and (b) are shown in FIG. 4 and FIG. 3 is a simulation result shown in FIG.

  It is known that when a material different from the surrounding material is periodically arranged, the propagation direction of the electromagnetic wave propagating through this portion differs depending on the frequency when the boundary surface is inclined. Non-Patent Document 1 examines such a waveguide device. The device configuration is simple, and only a material different from the material through which electromagnetic waves propagate is periodically arranged. FIG. 12 shows a state in which materials different from the material through which electromagnetic waves propagate are periodically arranged, and circles are periodically arranged in a triangle. This portion will be referred to herein as a “periodic structure” for simplicity.

  Next, the operation of the conventional waveguide device relating to electromagnetic waves will be described. Electromagnetic waves are incident from the left side of FIGS. 12A and 12B, propagate through the periodic structure, and reach the right slope of the periodic structure. Thereafter, the light propagates through the right slope of the periodic structure, but the propagation direction differs depending on the frequency. FIG. 12 shows a state of propagation in the upper right direction of (a) when the frequency is 7.6 GHz and to the lower right direction of (b) when the frequency is 6.8 GHz. Thus, when passing through the right slope of the periodic structure, the propagation direction varies depending on the frequency. Note that Non-Patent Document 1 shows that not only simulations but also experiments were performed, and similar results were obtained.

S. Sudhakaran, Y. Hai, J. Dupuy and C. G. Parini, "Mesurement Verification of Negative Refraction in Generalized Electromagnetic Periodic Structures," 27th ESA Antenna Workshop, Session 11: Application of Electromagnetic Band Gap Structures and LHM

  As described above, there is a waveguide device in which the propagation direction differs depending on the frequency when the electromagnetic wave propagates through the periodic structure and passes through the inclined boundary surface. Since this apparatus can control the propagation direction according to the frequency, various applications can be considered. However, there is a problem that there is no such waveguide device for sound waves propagating in gas or liquid and elastic waves propagating in solid.

  The present invention has been made to solve the above-described problems, and its purpose is to control the direction of propagation of sound waves propagating in a gas or liquid, or elastic waves propagating in a solid by frequency. An acoustic waveguide device capable of satisfying the requirements is obtained.

The acoustic waveguide device according to the present invention includes a first material capable of propagating an acoustic wave, and a second material that is in the first material and has different acoustic wave propagation characteristics from the first material. The second material has a predetermined shape and is arranged in the first material at equal intervals in the vertical direction and the horizontal direction, and the first material and the plurality of second materials are arranged The periodic structure in which the boundary surface with the formed region is inclined, the shape of the periodic structure is a structure in which the incident surface on which the acoustic wave is incident and the transmission surface through which the acoustic wave is transmitted are not parallel, and the periodic structure is The acoustic wave is guided, and when the acoustic wave passes through the periodic structure, the propagation direction of the acoustic wave radiated from the transmission surface differs depending on the frequency.

  The acoustic waveguide device according to the present invention has an effect that the direction of propagation of sound waves propagating in gas or liquid and elastic waves propagating in a solid can be controlled by frequency.

Embodiment 1 FIG.
An acoustic waveguide device according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a diagram showing a configuration of an acoustic waveguide device according to Embodiment 1 of the present invention. In addition, in each figure, the same code | symbol shows the same or equivalent part.

  In FIG. 1, the acoustic waveguide device according to the first embodiment has a medium 1 capable of propagating acoustic waves, and a substance of a material that is acoustically different from the medium 1 (herein referred to as a different substance for simplicity). 2) is provided.

  The foreign substance 2 is periodically arranged in the vertical direction and the horizontal direction as shown in FIG. 1 to form a periodic structure. The periodic structure of the foreign substance 2 is parallel to the vibrator 3 on the left side of FIG. 1, and is not parallel to the vibrator 3 on the right side of FIG. The apparatus configuration in the present invention is only the periodic structure of the medium 1 and the foreign substance 2, and does not include the vibrator 3. The vibrator 3 is provided to explain the operation of the waveguide device.

  Next, the operation of the acoustic waveguide device according to the first embodiment will be described with reference to the drawings. FIG. 2 is a diagram showing simulation conditions for the acoustic waveguide device according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing a transmission signal having a center frequency of 2 MHz used in the acoustic waveguide device according to Embodiment 1 of the present invention. FIG. 4 is a diagram showing a sound field simulation result when the acoustic waveguide device according to Embodiment 1 of the present invention is excited through a vibrator with a transmission signal having a center frequency of 2 MHz. FIG. 5 is a diagram showing a transmission signal having a center frequency of 3.3 MHz used in the acoustic waveguide device according to Embodiment 1 of the present invention. FIG. 6 is a diagram showing a sound field simulation result when the acoustic waveguide device according to Embodiment 1 of the present invention is excited through a vibrator with a transmission signal having a center frequency of 3.3 MHz.

  In FIG. 1, an acoustic wave is generated in the medium 1 by the vibrator 3 and propagates in the medium 1.

  The acoustic wave generated by the vibrator 3 propagates through the periodic structure of the foreign substance 2 and passes through the right slope of the periodic structure. The transmitted acoustic wave propagates through the medium 1 again. At this time, the propagation direction differs depending on the frequency. In FIG. 1, the propagation directions of the frequency f1 and the frequency f2 are indicated by arrows.

  An acoustic waveguide device having different propagation directions depending on the frequency will be specifically described. A simulation was conducted to visualize the sound field and the propagation direction of the elastic wave propagating in the solid was determined depending on the frequency. A two-dimensional FDTD method was used for the simulation model. FIG. 2 shows the simulation conditions. As shown in (a), a waveguide device was assumed in which air holes having a diameter of 0.18 mm were formed in acrylic having a length of 10 mm and a width of 9.8 mm, and the air holes were periodically arranged in a triangle. That is, acrylic corresponds to the medium 1, air holes correspond to the foreign substance 2, and a periodic arrangement of the air holes corresponds to a periodic structure. As shown in (b), the arrangement interval of the periodic structures was 0.24 mm in the vertical and horizontal directions. Further, the vibrator 3 having a size of 3.3 mm is bonded to the left side of the acrylic. In the periodic structure, the left side is parallel to the vibrator 3 and the right side is inclined with respect to the vibrator 3.

  FIG. 3 shows a signal having a center frequency of 2 MHz, where (a) is a frequency spectrum and (b) is a time response waveform.

  FIG. 4 shows a sound field simulation result when the vibrator 3 is subjected to thickness vibration using the signal shown in FIG. 3 as a transmission signal. FIGS. 4A and 4B show sound field snapshots of 2.5 μs and 4.0 μs after the vibrator 3 is vibrated in thickness. In FIG. 4, the interval between two striped patterns corresponds to one wavelength. Since the vibrator 3 is vibrated in thickness, a longitudinal wave propagates through the acrylic as an elastic wave. The elastic wave propagating through the periodic structure starts to be emitted from the right slope of the periodic structure in the vicinity of 2.0 μs. From the subsequent sound field simulation results of 2.5 μs and 4.0 μs, it can be seen that an elastic wave having a center frequency of 2 MHz propagates obliquely downward in FIG.

  On the other hand, FIG. 5 shows a signal having a center frequency of 3.3 MHz, where (a) is a frequency spectrum and (b) is a time response waveform.

  FIG. 6 shows a sound field simulation result when the vibrator 3 is subjected to thickness vibration using the signal shown in FIG. 5 as a transmission signal. Similar to FIG. 4, FIGS. 6A and 6B show sound field snapshots of 2.5 μs and 4.0 μs after the vibrator 3 is vibrated in thickness, and longitudinal waves are generated as elastic waves. It shows how it propagates. In order to make the state of propagation easier to understand, the display sensitivity of elastic waves is made higher than that in FIG. As can be seen from FIG. 6, the elastic wave propagated through the periodic structure starts to be emitted from the right slope of the periodic structure in the vicinity of 2.5 μs. From the acoustic field simulation result of 4.0 μs, it can be seen that the elastic wave transmitted through the periodic structure propagates obliquely upward in FIG. In the case of a transmission signal having a center frequency of 3.3 Mhz, a transverse wave generated by mode conversion is also emitted from the periodic structure of the air hole. In FIG. 6B, 4.0 μs shows a state in which a transverse wave is radiated.

  As described above, the acoustic waves transmitted through the acoustic waveguide device shown in the first embodiment have been specifically described in the manner in which the propagation direction differs depending on the frequency. That is, the acoustic waveguide device shown here has an effect that the propagation direction can be controlled by the frequency.

  Further, in the specific description by simulation, the foreign substance 2 is an air hole, but it may not be an air hole. It may be in a state like a puddle or a solid. In short, any material that is acoustically different may be used.

  Furthermore, the shape of the foreign substance 2 may not be round. In the specific description by FIG. 1 and simulation, the shape of the foreign substance 2 is described as a circle, but it may be an ellipse or a square, and the shape is not limited.

  Although the case where the periodic structures are two-dimensionally arranged as shown in FIG. 1 has been described here, the arrangement may be three-dimensional.

  Moreover, although the case where the acoustic wave is an elastic wave has been described in the specific description by the simulation, the acoustic wave may not be an elastic wave. Even with sound waves propagating in gas or liquid, similar effects can be obtained with the same configuration. Further, the same effect can be obtained with a similar configuration even in a high-frequency sound wave or elastic wave, so-called ultrasonic wave.

  Until now, the operation of the periodic structure was explained by simulation, but an experiment was conducted to confirm the simulation result. The experiment was carried out by making a test specimen having a through hole in acrylic. In addition, since it was difficult in terms of manufacturing technology to provide a through hole with a diameter of 0.18 mm and an array period of 0.24 mm as shown in FIG. 2, an array period of 1 mm with a diameter of 1 mm. A test specimen of 5 mm was made. FIG. 7 is a diagram showing a prototype test body. FIG. 8 is a block diagram showing a configuration of an experimental system of the test body of FIG. As shown in FIG. 8, a burst signal having carrier frequencies of 0.39 MHz and 0.84 MHz is generated by the waveform generator 21 of the experimental system 20, amplified by the power amplifier 22, and the transmission probe 23 is excited. The ultrasonic wave that has propagated through and passed through the test body (periodic structure) 1A is received by the receiving probe 24 provided on the opposite surface side. An experiment was conducted in which the propagation direction of the transmitted ultrasonic wave was obtained by scanning the receiving probe 24. The signal received by the receiving probe 24 was amplified by the receiving amplifier 25 and measured by the digital oscilloscope 26. The received signal was stored in a PC (personal computer) 27.

  FIG. 9 is a diagram showing experimental results of the experimental system of FIG. FIGS. 9A and 9B show experimental results with carrier frequencies of 0.39 MHz and 0.84 MHz, respectively. In the figure, the experimental results using an acrylic test specimen without a periodic structure are also shown for comparison. A white circle mark is a signal transmitted through an acrylic test specimen without a periodic structure, and a black square mark is transmitted through the periodic structure. Is the signal voltage. As can be seen from the figure, when the carrier frequency is 0.39 MHz, the voltage of the received signal is higher on the right side than the center. On the other hand, when the carrier frequency is 0.84 MHz, the voltage of the received signal is higher on the left side than the center. This is experimental data supporting the simulation result that the propagation direction of the ultrasonic wave propagating through the periodic structure differs depending on the frequency.

  In addition, the simulation by the two-dimensional elastic wave FDTD method was performed on the same conditions as experiment, and the received signal was calculated | required. FIGS. 10A and 10B are diagrams showing simulation results by the two-dimensional elastic wave FDTD method. Comparing FIG. 10 and FIG. 9, the two are almost the same. That is, since the validity of the simulation has been confirmed, the simulation results shown in FIGS. 4 and 6 are also considered to be valid.

  Finally, an example of a specific application of the acoustic waveguide device that can control the propagation direction according to the frequency will be described. FIG. 11 is a diagram in which an acoustic waveguide device is applied to a wedge of an oblique probe used in an ultrasonic flaw detection test.

  As shown in FIG. 11, the acoustic waveguide device is arranged so that the frequency f1 and the frequency f2 are propagated from the probe wedge 1A in different directions and the frequency f2 is perpendicularly incident on the test body 4. If designed, the frequency f1 can be used for normal oblique flaw detection, and the frequency f2 can be used for vertical flaw detection. The echo received by the transducer 3 is a signal containing frequency components of f1 and f2, but can be identified by providing a filter 14 in the flaw detector 10. Note that the flaw detector 10 is provided with a transmission unit 11, a reception unit 12, a changeover switch 13, a filter 14, and a display unit 15.

  That is, if the filter 14 is configured to pass the frequency f1 and cut off the frequency f2 by the changeover switch 13, a normal oblique flaw detection is performed. On the other hand, if the filter 14 is configured such that the frequency f1 is cut off by the changeover switch 13 and the frequency f2 is passed, normal vertical flaw detection is performed. In this way, only by operating the changeover switch 13 connected to the filter 14, there is an effect that the oblique flaw detection and the vertical flaw detection can be combined.

  Instead of using the frequency f2 for vertical flaw detection, it can also be used for measuring the thickness lt of the test body 4. The thickness lt of the test body 4 is an important parameter used when obtaining the depth of flaws in oblique flaw detection with 1.5 skip or more. Normally, the thickness lt of the test body 4 is separately measured with a caliper or the like, and then the flaw detection is performed. However, the measurement using the caliper or the like can be omitted by using the frequency f2 for measuring the thickness lt of the test body 4. effective.

  Furthermore, the frequency f2 can be used for the coupling check. When echoes are not received by oblique flaw detection, it is impossible to determine whether there is a flaw or whether the contact state between the probe and the specimen 4 is bad. Therefore, an operation of adding a coupling check function to the oblique angle probe and confirming a contact state between the probe and the test body 4 is performed. On the other hand, the frequency f2 is received as a bottom echo if the contact state between the probe and the specimen 4 is good, but no echo is received if the contact state is bad. That is, the echo of the frequency f2 can be used as a coupling check signal. As described above, if the echo of the frequency f2 is used as a coupling check signal, there is no need to newly add a coupling check function, so that the configuration of the oblique probe can be simplified.

It is a figure which shows the structure of the acoustic waveguide apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the simulation conditions of the acoustic waveguide device concerning Embodiment 1 of this invention. It is a figure which shows the transmission signal of center frequency 2MHz used for the acoustic waveguide device concerning Embodiment 1 of this invention. It is a figure which shows the sound field simulation result at the time of exciting the acoustic waveguide device based on Embodiment 1 of this invention through a vibrator | oscillator with the transmission signal of center frequency 2MHz. It is a figure which shows the transmission signal of the center frequency of 3.3 MHz used for the acoustic waveguide device concerning Embodiment 1 of this invention. It is a figure which shows the sound field simulation result at the time of exciting the acoustic waveguide device based on Embodiment 1 of this invention through the vibrator | oscillator with the transmission signal of center frequency 3.3MHz. It is a figure which shows the test body made as a trial. It is a block diagram which shows the structure of the experimental system of the test body of FIG. It is a figure which shows the experimental result by the experimental system of FIG. It is a figure which shows the simulation result by the two-dimensional elastic wave FDTD method. It is the figure which applied the acoustic waveguide device concerning Embodiment 1 of this invention to the wedge of the oblique probe used in an ultrasonic flaw detection test. It is a figure which shows the simulation result of the waveguide apparatus regarding the conventional electromagnetic wave.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Medium, 1A Wedge, 2 Different substance, 3 Vibrator, 4 Test body, 10 Flaw detector, 11 Transmission part, 12 Reception part, 13 Changeover switch, 14 Filter, 15 Display part.

Claims (7)

A first material capable of propagating acoustic waves;
A second material in the first material and having a different acoustic wave propagation characteristic from the first material;
The second material has a predetermined shape, is arranged in the first material at equal intervals in the vertical and horizontal directions, and the first material and a plurality of second materials are arranged in the region. Constitutes a periodic structure with a sloping interface with
The shape of the periodic structure is a structure in which an incident surface on which the acoustic wave is incident and a transmission surface on which the acoustic wave is transmitted are not parallel.
The periodic structure controls waveguide of the acoustic wave, and when the acoustic wave passes through the periodic structure, the propagation direction of the acoustic wave radiated from the transmission surface varies depending on the frequency. An acoustic waveguide device. The acoustic waveguide device according to claim 1, wherein the periodic structure includes the second material arranged two-dimensionally. The acoustic waveguide device according to claim 1, wherein the periodic structure includes the second material arranged three-dimensionally. The acoustic waveguide device according to claim 1, wherein the acoustic wave is a sound wave propagating in a gas or a liquid. The acoustic waveguide device according to claim 1, wherein the acoustic wave is an elastic wave propagating in a solid. The acoustic waveguide device according to claim 1, wherein the acoustic wave is an ultrasonic wave. The first material is acrylic;
The acoustic waveguide device according to claim 1, wherein the second material is air.

Images