A rotationally symmetrical five-mode material low-frequency acoustic wave emission device and test method

Abstract

The present invention discloses a rotationally symmetrical five-mode material low-frequency sound wave emission device and test method, belonging to the technical fields of acoustic communication, acoustic detection and acoustic metamaterials. The device includes a metal truncated cone cylinder, a five-mode acoustic metamaterial, a non-directional transducer and a sound signal generating device; the five-mode acoustic metamaterial and the non-directional transducer are fixedly installed in the metal truncated cone cylinder, and the distance between the front end face of the transducer and the surface of the five-mode acoustic metamaterial is between one-third of the working wavelength and two times the working wavelength; the cable of the non-directional transducer passes through the back cover to connect the sound signal generating device; the non-directional transducer converts the sound signal generated by the sound signal generating device into a non-directional sound wave, the five-mode acoustic metamaterial gathers the energy of the non-directional sound wave, and the metal truncated cone cylinder plays a role in waveform control and wavefront guidance of the non-directional sound wave. The present invention can realize the directional emission of low-frequency sound waves with a wavelength equal to or greater than the outlet diameter.

Description

Technical Field

[0001] The present invention belongs to the technical fields of acoustic communication, acoustic detection and acoustic metamaterials, and specifically relates to a rotationally symmetric five-mode material low-frequency sound wave emission device and an experimental method. The device designs a sound wave focusing device based on a five-mode acoustic metamaterial, thereby realizing the emission of high-directivity low-frequency sound waves. Background Art

[0002] Sonar is an electronic device that uses the propagation characteristics of sound waves underwater to complete underwater detection, positioning and communication tasks through electroacoustic conversion and information processing. It not only plays a very important role in underwater communication, detection and navigation operations, but also has become an important means for humans to understand, develop and use the ocean in peacetime. Due to the limitations of system architecture and diffraction limit, the existing underwater acoustic sound source is subject to the "wavelength-length" limitation in basic principle, and there is an irreconcilable contradiction between size and working frequency. In order to obtain a highly directional sound source, it is often necessary to increase the size of the sound source or increase the frequency. Traditional underwater acoustic detection devices are limited in size and have poor low-frequency directivity, which seriously affects their detection distance and accuracy. How to subvert the traditional sonar design concept and design a highly directional low-frequency sound source based on a new principle has become a very challenging and significant research topic in the field of underwater acoustics, with important theoretical and practical value. Summary of the invention

[0003] In view of this, the present invention provides a rotationally symmetric five-mode material low-frequency sound wave emitting device and a test method. By arranging a rotationally symmetric five-mode acoustic metamaterial in a metal truncated cone cylinder, the low-frequency sound waves (within tens of kHz) emitted by a non-directional sound source can be focused and directed to improve their directivity, thereby achieving directional emission of low-frequency sound waves with a wavelength equal to or greater than the outlet diameter.

[0004] A rotationally symmetrical five-mode material low-frequency sound wave emission device, comprising a metal truncated cone cylinder, a five-mode acoustic metamaterial, a non-directional transducer and a sound signal generating device;

[0005] The metal truncated cone has an outer shape of a truncated cone, and the interior of the truncated cone has a through hole of equal diameter. The five-mode acoustic metamaterial and the omnidirectional transducer are fixedly installed in the through hole, and the distance between the front end face of the transducer and the surface of the five-mode acoustic metamaterial is between one-third of the working wavelength and two times the working wavelength; the through hole is located at the opening of the large end of the truncated cone and is closed by a back cover, and the cable of the omnidirectional transducer passes through the back cover to connect to the sound signal generating device; the omnidirectional transducer converts the sound signal generated by the sound signal generating device into an omnidirectional sound wave, and the five-mode acoustic metamaterial gathers the energy of the omnidirectional sound wave, and the metal truncated cone plays a role in waveform regulation and wavefront guidance of the omnidirectional sound wave.

[0006] Furthermore, annular holes and limiting holes are processed on the surface of the metal truncated cone, and bolts are passed through the annular holes and the limiting holes to radially fix and axially limit the five-mode acoustic metamaterial respectively, and the length of the bolts is as short as possible.

[0007] Furthermore, the five-mode acoustic metamaterial includes a metametal matrix and sound-transmitting polyurethane. The metametal matrix is ​​a closed axisymmetric geometric configuration with a cavity inside, and the cross-section is arranged in a periodic honeycomb structure. The wall thickness at the thinnest point is 0.2mm, the wall thickness accuracy requirement is ±0.05mm, and the overall accuracy requirement of the metametal matrix is ​​±0.2mm. The sound-transmitting polyurethane is combined with the metametal matrix by an injection mold, and the overall outer diameter of the five-mode acoustic metamaterial is matched with the inner diameter of the metal truncated cone countersunk hole with a tolerance of -0.2mm.

[0008] Furthermore, the metal frustum cylinder is made of aluminum alloy or titanium alloy.

[0009] Furthermore, all sharp angles of the metal frustum tube are not chamfered, and the unmarked dimensions and hole tolerances are ±0.2 mm.

[0010] Furthermore, the material of the superstructure metal matrix is ​​aluminum alloy or titanium alloy.

[0011] Furthermore, the low-frequency sound wave emitting device is hoisted in a horizontal state by a clamp, a suspension rod and a suspension bracket.

[0012] Furthermore, the omnidirectional transducer is in a horizontal posture during use, the effective value of the transducer excitation voltage does not exceed 400V, and the sound source level in the low-frequency acoustic range of tens of kHz is 170dB.

[0013] A test method for a rotationally symmetrical five-mode material low-frequency sound wave emitting device, the method comprising the following steps:

[0014] S1: Rotationally symmetrical five-mode material and transducer installation;

[0015] S2: Metal round cone cylinder hoisting and fixing;

[0016] S3: Adjustment of the level and water permeability of the low-frequency sound wave emission device;

[0017] S4: Test and evaluation of the directivity and launch distance of the launch device.

[0018] Furthermore, the process of installing the five-mode acoustic metamaterial in step S1 includes: the five-mode acoustic metamaterial is pushed into the countersunk opening of the metal frustum until the axial limit is achieved at the bolt of the front end limit hole, and then the five-mode acoustic metamaterial is radially fixed by bolts through the annular holes on the metal frustum.

[0019] Furthermore, the process of installing the omnidirectional transducer in step S1 includes: the cable of the omnidirectional transducer is fastened to the back cover through a sleeve and marked, the center of the sphere is 50 mm away from the end face of the back cover boss, the inner diameter of the sleeve is matched with the diameter of the cable of the omnidirectional transducer with a tolerance of +0.2 mm, the outer diameter of the sleeve changes in a wedge shape along the axial direction, and the diameter on the boss side is small based on the back cover direction; the cable of the omnidirectional transducer is inserted from the boss side of the back cover and then passes through the sleeve, and then the sleeve and the cable of the omnidirectional transducer are knocked into the center hole of the plug together to fasten the omnidirectional transducer; the back cover is fixedly connected to the metal conical cylinder through circumferentially evenly distributed limit holes; the fixed vertical and horizontal positions between the omnidirectional transducer and the back cover and the metal conical cylinder are marked with a marker to ensure that the posture and position of the subsequent transducer can remain consistent after the plug is removed and replaced.

[0020] Furthermore, the process of hoisting and fixing the metal frustoconical cylinder in step S2 includes: first fixing the clamp to the metal frustoconical cylinder, then hoisting and fixing the metal frustoconical cylinder to the hanger using a hanging rod, and finally hoisting and fixing the hanger to the test platform.

[0021] Furthermore, the method for adjusting the level of the low-frequency sound wave emitting device in step S3 includes: adjusting the nut on the suspension rod to adjust the fixed position of the low-frequency sound wave emitting device; if it is inconvenient to adjust the level of the hanger by the length of the screw rod on site, by installing a sling nut on the two suspension rods at the rear end of the hanger, the length of the sling nut and the suspension rope connected to the platform fixing position are adjusted by a turnbuckle, and the level of the hanger is adjusted by adjusting the length of the turnbuckles on both sides respectively, and confirmed with a level meter on the top of the toggle plates on both sides of the tooling, so as to finally ensure the level of the low-frequency sound wave emitting device.

[0022] Furthermore, in the process of adjusting the water permeability of the transducer of the low-frequency sound wave emitting device in step S3, in order to ensure that the non-directional transducer inside the metal frustum tube is completely immersed in water after entering the water, M6 countersunk holes are opened above and below 65 mm from the bottom of the tube to effectively discharge the air.

[0023] Furthermore, in step S2, the equipment preparation and test environment arrangement before the test:

[0024] S41: Check whether the transmitting transducer, power amplifier, signal generator, data acquisition and analysis instrument, B&K hydrophone, and computer are working properly. Adjust the non-directional transducer to a horizontal position and mark its top position to ensure that the transducer's posture and angle are consistent with those in the metal truncated cone. Arrange two groups of hydrophones, with No. 1 hydrophone 10m away from the front end of the rotationally symmetrical five-mode material low-frequency sound wave transmitting device, and No. 2 hydrophone 15m away.

[0025] S42: Test and evaluation of the directivity of the transmitting device; the frequency sampling points can be determined according to the actual measurement frequency range, and the number of sampling points is greater than 10 to ensure the resolution of data analysis; the directivity test is carried out at a distance of 15 meters using No. 2 hydrophone, and the test angle (with the exit end direction as 0°) is 360° in the circumferential range. The test angle step size and the decibel angle value required for evaluation are selected according to the actual situation;

[0026] S43: Test and evaluation of the launch distance of the launch device. The frequency sampling points are determined according to the actual measurement frequency range. The number of sampling points is greater than 10 to ensure the resolution of data analysis. The sound pressure at the front outlet of the rotationally symmetrical five-mode material low-frequency sound wave launch device at a distance of 10 meters and 15 meters is tested. The ratio of the effective launch distance to the non-directional transducer 13 alone is measured and evaluated.

[0027] Beneficial effects:

[0028] 1. The present invention installs the five-mode acoustic metamaterial inside the metal truncated cone, which is similar to the acoustic structure of the head of the white-fin dolphin. The five-mode acoustic metamaterial can gather the energy of the sound wave, enhance the propagation distance, and focus the propagation direction. The metal truncated cone acts as an acoustic hard boundary, which can regulate the waveform and guide the wavefront of the sound waves passing through the rotationally symmetric five-mode material inside it. Its function is similar to that of the dolphin mandible. The distance between the front end face of the transducer and the surface of the five-mode acoustic metamaterial is between one-third of the working wavelength and two times the working wavelength, which can ensure the sound wave regulation efficiency of the overall device. By combining the rotationally symmetric five-mode material and the metal truncated cone, the structural functions of the two main components can be fully utilized to achieve better acoustic directivity, thereby having a stronger directional emission function.

[0029] 2. The five-mode acoustic metamaterial of the present invention includes a metametal matrix and sound-transmitting polyurethane. The metametal matrix is ​​a closed axisymmetric geometric configuration with a cavity inside, and the cross section is arranged in a periodic honeycomb structure. The wall thickness at the thinnest point is 0.2mm, and the wall thickness accuracy requirement is ±0.05mm. The overall accuracy requirement of the metametal matrix is ​​±0.2mm. The sound-transmitting polyurethane is combined with the metametal matrix using an injection mold. The overall outer diameter of the five-mode acoustic metamaterial and the inner diameter of the metal truncated cone counterbore are matched with a tolerance of -0.2mm. The side length and wall thickness will directly affect the effects of sound wave energy convergence, enhanced propagation distance, and focused propagation direction. Therefore, it is necessary to strictly control the wall thickness and side length accuracy during processing. The metametal matrix is ​​coated with sound-transmitting polyurethane, and is precisely matched with the metal truncated cone to minimize the adverse effects of gaps and water on sound wave transmission.

[0030] 3. The test method of the present invention is finely designed around the installation of the transducer, hoisting and fixing, adjustment of the level and water permeability of the low-frequency sound wave transmitting device, testing and evaluation of the directivity and transmitting distance of the transmitting device, etc. It can effectively ensure the smooth implementation of the performance tests such as the acoustic directivity and transmitting distance of the rotationally symmetrical five-mode material low-frequency sound wave transmitting device, and can also provide a useful reference for the experimental testing of similar acoustic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a five-mode metamaterial with artificially designed microstructure;

[0032] Figure 2 It is a five-mode metamaterial with focusing ability;

[0033] Figure 3 It is a schematic diagram of the structure of the low-frequency sound wave emitting device after hoisting of the present invention;

[0034] Figure 4 The structure diagram of the low-frequency sound wave emitting device of the present invention;

[0035] Figure 5 It is a three-dimensional structural diagram of a metal truncated cone cylinder;

[0036] Figure 6 It is a two-dimensional structural diagram of a metal truncated cone cylinder;

[0037] Figure 7 This is a three-dimensional image of the metal skeleton of the five-mode acoustic metamaterial;

[0038] Figure 8 It is a two-dimensional picture of the metal skeleton encapsulation effect of the five-mode acoustic metamaterial;

[0039] Fig. 9 It is a schematic diagram of the hoop structure;

[0040] Fig.10 is a schematic diagram of the hanger structure;

[0041] Fig.11 This is the performance simulation result diagram of the low-frequency acoustic wave emission device of five-mode materials;

[0042] Fig.12 The figure is a flow chart of the test method for the low-frequency acoustic wave emission device of five-mode materials. DETAILED DESCRIPTION

[0043] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0044] Five-mode metamaterials can achieve specific macroscopic physical parameters based on microstructures, and it is possible to achieve good low-frequency acoustic directivity in a small size with the help of their special structural design. A typical five-mode material microstructure is shown in the figure below. Figure 1shown.

[0045] The microstructure design of the five-mode material can be completed through the homogenization theory. The basic calculation formula of the homogenization theory is as follows

[0046]

[0047]

[0048] Where Y is the area where the unit cell is located, E ijkl is the substrate modulus, is the equivalent modulus of the substrate, v i is any virtual displacement function, Displacement field.

[0049] The five-mode material can achieve many unique acoustic properties, such as Figure 2 As shown in the figure, the five-mode material adopts the static wave control mechanism, so theoretically it has good control over the full-band sound waves. In practice, due to the existence of the microstructure, the effective frequency band of the five-mode material is only limited by the microstructure processing accuracy. The higher the accuracy, the higher the upper limit of the controllable sound wave frequency. In the wide low-frequency region on the effective frequency band, the five-mode material has good wave control ability, which can be applied to underwater acoustic devices to improve the acoustic pointing performance of low-frequency underwater acoustic detection devices.

[0050] The present invention provides a rotationally symmetrical five-mode material low-frequency sound wave emitting device, as shown in the attached Figure 3 and 4 As shown, the device includes a metal truncated cone tube 11, a five-mode acoustic metamaterial 12, a non-directional transducer 13 and an acoustic signal generating device 14. The low-frequency sound wave transmitting device 1 is hoisted by a suspension rod 2, a clamp 3 and a hanger 4.

[0051] As attached Figure 5 and 6As shown, the shape of the metal frustum cylinder 11 is a truncated cone, and the interior of the truncated cone has a through hole of equal diameter, which axially penetrates the front and rear end surfaces of the truncated cone. The material of the metal frustum cylinder 11 can be aluminum alloy, titanium alloy and other metals, and is made of rods through rotary cutting on a lathe. The inner diameter of the metal frustum cylinder 11 is the same, and there are annular grooves 111 in the middle and rear parts respectively, so as to facilitate the axial limitation of the clamp 2. The metal frustum cylinder 11 has annular grooves 111 in the middle and rear parts respectively, so as to facilitate the axial limitation of the clamp. Four positioning holes 112 are evenly distributed circumferentially in the two annular grooves 111, and the clamp is positioned circumferentially by bolts. Through the limiting hole 113, the five-mode acoustic metamaterial 12 is axially positioned by bolts. By using the annular hole 114, the five-mode acoustic metamaterial 12 is radially fixed by bolts. The back cover 116 is made of the same material as the metal frustum cone 11, and is fixedly connected to the metal frustum cone 11 through six circumferentially evenly distributed limiting holes 115. The metal frustum cone 11 acts as an acoustic hard boundary, which can play a role in waveform control and wavefront guidance for the five-mode acoustic metamaterial 12 inside it, and its role is similar to that of the dolphin mandible. Its material is not limited to aluminum alloy, titanium alloy and other metals, but can also be other metals or other materials with equivalent acoustic boundary performance.

[0052] As attached Figure 7 and 8 As shown, the five-mode acoustic metamaterial 12 includes: a metametallic matrix 121 and a sound-transmitting polyurethane 122. The metametallic matrix 121 may be made of metals such as aluminum alloy and titanium alloy, and may be made of a different material from the metal truncated cone 11. It is a closed axisymmetric geometric configuration with a cavity inside, which can be realized by 3D printing. The wall thickness at the thinnest part can reach 0.2 mm, the wall thickness accuracy requirement is ±0.05 mm, and the overall accuracy requirement is ±0.2 mm. The sound-transmitting polyurethane 122 is combined with the metametallic matrix 121 by injection molding. The overall outer diameter of the five-mode acoustic metamaterial 12 is matched with the inner diameter of the metal truncated cone 11 with a tolerance of -0.2 mm. The five-mode acoustic metamaterial 12 has good acoustic directivity, and can play the role of converging sound wave energy, enhancing the propagation distance, and focusing the propagation direction through special design.

[0053] The omnidirectional transducer 13 converts the acoustic signal into omnidirectional sound waves, and should have certain sound source level and power requirements, and should be in a horizontal position during use. The effective value of the transducer excitation voltage does not exceed 400V, and the sound source level in the low-frequency acoustic range of tens of kHz is about 170dB.

[0054] The acoustic signal generating device 14 includes conventional acoustic devices such as a signal generator and a power amplifier, and is used to generate an acoustic wave signal and control the signal frequency, pulse length, and the like.

[0055] The material of the clamp 2 is aluminum alloy. The upper and lower clamps are connected to the metal truncated cone tube 11 through the annular limit hole 21 and fastened with bolts 22. A polyurethane gasket 23 is sandwiched in the middle to compensate for the clearance error with the metal truncated cone tube 11. The outer side of the clamp 2 has a hole 24, which is connected to the suspension rod 3. Fig. 9 shown.

[0056] The material of the suspension rod 3 is aluminum alloy, and the upper and lower ends are respectively provided with threads of a certain length, and the fixing position of the low-frequency sound wave transmitting device 1 is adjusted by adjusting the nut. The upper part of the suspension rod 3 is connected to the hanger 4.

[0057] The material of the hanger 4 is aluminum alloy. The thickness of the upper mounting plate 41 connected to the test or use platform is greater than 30mm to ensure the installation strength. Two sets of installation interfaces M20*6 and M12.5*6 are reserved on it. A positioning hole 42 is reserved in the center of the upper mounting plate 41, and the center of the hole is aligned with the front end of the metal round cone tube 11. Multiple horizontal support plates 43 are used to enhance the lateral rigidity and stability of the hanger 4. The positioning hole 44 is connected to the metal round cone tube 11 through the suspension rod 3, as shown in the attached figure. Fig.10 shown.

[0058] The front end of the metal truncated cone tube 11 is 3mm thick to avoid being too sharp. In order to ensure the acoustic emission effect of the low-frequency sound wave emitting device, all sharp angles of the metal truncated cone tube 11 are not chamfered, and the unnoted dimensions and hole tolerances are ±0.2mm. The process must ensure a smooth surface, blunt edges, and deburred edges. In order to ensure the anti-corrosion effect under long-term underwater use, anti-rust paint is sprayed on the outside of the metal truncated cone tube 11, and the inside is not treated to ensure the acoustic emission effect. In order to ensure that the non-directional transducer 13 inside the metal truncated cone tube 11 is completely immersed in water after entering the water, M6 countersunk holes are opened above and below 65mm from the bottom of the tube to effectively discharge the air.

[0059] The five-mode acoustic metamaterial 12 is pushed in from the bottom of the metal truncated cone cylinder 11 until it reaches the bolt of the front limiting hole 113. The axial opening position of the limiting hole 113 is determined according to the axial length of different five-mode acoustic metamaterials 12 and the relative position with the non-directional transducer 13. Then, the five-mode acoustic metamaterial 12 is radially fixed by bolts through the annular hole 114.

[0060] The cable of the omnidirectional transducer 13 is fastened to the back cover 116 through a sleeve and marked, and the center of the sphere is 50 mm away from the end face of the boss of the back cover 116. The inner diameter of the sleeve is matched with a tolerance of +0.2 mm compared to the diameter of the cable of the omnidirectional transducer 13, and the outer diameter of the sleeve changes in a wedge shape along the axial direction, with the back cover direction as the reference, and the diameter on the boss side is small. The cable of the omnidirectional transducer 13 is inserted from the boss side of the back cover, and then passes through the sleeve, and then the sleeve and the cable of the omnidirectional transducer 13 are knocked into the center hole of the plug together to well fasten the omnidirectional transducer 13. The back cover 116 is fixedly connected to the metal conical cylinder 11 through six circumferentially evenly distributed limiting holes 115.

[0061] The process of hanger 4 needs to ensure smooth surface, blunt edges, deburring, firm and reliable welding, no cracks, slag inclusions and other defects, no flaws, sharp angles blunt 1×45°, unfilled size and hole tolerance is ±0.1mm, unfilled shape and position tolerance is in accordance with GB / T1184-H grade. All holes are processed after welding to ensure the relative position size requirements.

[0062] The performance simulation results of the five-mode material low-frequency acoustic wave emission device are shown in the attached figure. Fig.11 As shown, in certain specific frequency ranges, the device can emit highly directional sound waves. Compared with directional sound wave emitting devices of the same size without the five-mode acoustic metamaterial of the present invention, the present device has significantly better directivity.

[0063] The rotationally symmetrical five-mode material low-frequency sound wave emitting device of the present invention can focus and direct low-frequency sound waves (within the range of tens of kHz) emitted by a non-directional sound source, improve its directivity, and realize the directional emission of low-frequency sound waves with a wavelength equal to or greater than the outlet diameter. In certain specific frequency ranges, the device can emit highly directional sound waves. The rotationally symmetrical five-mode material is the core component of the present low-frequency sound wave emitting device. The present invention can be used as a sound wave transducer component of an underwater acoustic communication device, and can also be used as a highly directional sound source of an underwater detection device.

[0064] Embodiment 2, the present invention also provides a method for testing a rotationally symmetrical five-mode material low-frequency sound wave emitting device, as shown in the attached Fig.12 As shown, the implementation steps of the method include:

[0065] S1: Rotationally symmetrical five-mode material and transducer installation;

[0066] S2: Metal round cone cylinder hoisting and fixing;

[0067] S3: Adjustment of the level and water permeability of the low-frequency sound wave emission device;

[0068] S4: Test and evaluation of the directivity and launch distance of the launch device.

[0069] In a preferred embodiment of the present invention, the above step S1 includes:

[0070] S11, installation of rotationally symmetric five-mode acoustic metamaterial. The rotationally symmetric five-mode acoustic metamaterial 12 is installed inside the metal frustum cylinder 11, and the five-mode acoustic metamaterial 12 is pushed in from the bottom of the metal frustum cylinder 11 until it reaches the bolt of the limiting hole 113 at the front end. The axial opening position of the limiting hole 113 is determined according to the axial length of different rotationally symmetric five-mode acoustic metamaterials 12 and the relative position with the non-directional transducer 13. Subsequently, the five-mode acoustic metamaterial 12 is radially fixed by bolts by using the annular hole 114.

[0071] S12, installation of omnidirectional transducer. The omnidirectional transducer 13 converts the acoustic signal into omnidirectional sound waves, and should have certain sound source level and power requirements, and be in a horizontal posture during use. The cable of the omnidirectional transducer 13 is fastened to the back cover 116 through a sleeve and marked, and its sphere center is 50mm away from the end face of the boss of the back cover 116. The inner diameter of the sleeve is matched with the cable diameter of the omnidirectional transducer 13 with a tolerance of +0.2mm, and the outer diameter of the sleeve changes in a wedge shape along the axial direction, with the back cover direction as the reference, and the boss side has a small diameter. The cable of the omnidirectional transducer 13 is inserted from the back cover boss side, and then passes through the sleeve, and then the sleeve and the cable of the omnidirectional transducer 13 are knocked into the center hole of the plug together to well fasten the omnidirectional transducer 13. Since there is a deviation in the outer diameter of the transducer and the sleeve fixing point in actual use, it can be appropriately wrapped with electrical tape to thicken it to enhance the fixing effect. It is confirmed by actual observation inside the cylinder that the fixing of the sleeve can ensure the centering effect of the transducer. The rear cover 116 is fixedly connected to the metal truncated cone cylinder 11 through six circumferentially evenly distributed limiting holes 115. The fixed vertical and horizontal positions between the non-directional transducer 13 and the rear cover 116 and the metal truncated cone cylinder 11 are marked with a marker to ensure that the subsequent transducer posture and position can remain consistent after the plug is removed and replaced.

[0072] In a preferred embodiment of the present invention, the above step S2 includes:

[0073] S21, the clamp is fixed to the metal truncated cone tube. The clamp 2 is made of aluminum alloy. The upper and lower clamps are connected to the metal truncated cone tube 11 through the annular limiting holes 21 and fastened with bolts 22. A polyurethane gasket 23 is sandwiched in the middle to compensate for the matching clearance error with the metal truncated cone tube 11. The metal truncated cone tube 11 has annular grooves 111 in the middle and rear to facilitate axial limiting of the clamp. Four positioning holes 112 are evenly distributed in the circumference of the two annular grooves 111, and the clamp is positioned annularly by bolts.

[0074] S22, the metal truncated cone tube is hoisted and fixed to the hanger. There is a hole 24 on the outside of the clamp 2, which is connected to the hanger 3. The hanger 3 is made of aluminum alloy, and has a certain length of thread at the upper and lower ends. The fixed position of the low-frequency sound wave emitting device 1 is adjusted by adjusting the nut. The hanger 4 is made of aluminum alloy. The thickness of the upper mounting plate 41 connected to the test or use platform is greater than 30mm to ensure the installation strength. Two sets of mounting interfaces M20*6 and M12.5*6 are reserved on it. A positioning hole 42 is reserved in the center of the upper mounting plate 41, and the center of the hole is aligned with the front end surface of the metal truncated cone tube 11. A plurality of lateral support plates 43 are used to enhance the lateral rigidity and stability of the hanger 4, and the positioning hole 44 is connected to the metal truncated cone tube 11 through the hanger 3.

[0075] S23, the hanger 4 is fixed to the test platform. The interface M20*6, M12.5*6 for connecting the hanger 4 to the test or use platform can be modified according to the actual situation.

[0076] In a preferred embodiment of the present invention, the above step S3 includes:

[0077] S31, horizontal adjustment of the low-frequency sound wave emitting device. The material of the suspension rod 3 is aluminum alloy, and the upper and lower ends each have a certain length of thread. The fixing position of the low-frequency sound wave emitting device 1 is adjusted by adjusting the nut. If it is inconvenient to adjust the level of the hanger by the length of the screw rod on site, a hanging nut can be installed on the two suspension rods at the rear end of the hanger 4, and the length of the hanging nut and the hanging rope connected to the platform fixing point can be adjusted by a basket screw. The level of the hanger can be adjusted by adjusting the length of the basket screws on both sides respectively, and confirmed with the spirit level on the top of the toggle plates on both sides of the tooling to ultimately ensure the level of the low-frequency sound wave emitting device. It is recommended to use a stainless steel rope for the hanging rope, and fix the ends with a stainless steel U-shaped clamp to ensure the connection strength.

[0078] S32, adjust the water permeability at the transducer of the low-frequency sound wave transmitting device. In order to ensure that the non-directional transducer 13 inside the metal truncated cone cylinder 11 is completely immersed in water after entering the water, M6 countersunk holes are opened at 65mm above and below the bottom of the cylinder to effectively discharge the air. It is confirmed through actual operation that when the rotationally symmetric five-mode acoustic metamaterial 12 is not installed, the metal truncated cone cylinder 11 is fixed with the cover 116 with the non-directional transducer 13 in the air and then placed in water. After the cover 116 is opened and fixed in the water, no obvious bubbles are found to overflow; after the rotationally symmetric five-mode acoustic metamaterial 12 is installed, the metal truncated cone cylinder 11 is fixed with the cover 116 with the non-directional transducer 13 in the air and then placed in water. After the cover 116 is opened and fixed in the water, obvious bubbles are found to overflow. It is necessary to use a 500ml syringe and a catheter to extract air and water from the M6 ​​countersunk hole reserved at the tail of the metal truncated cone cylinder 11 to effectively ensure the discharge of the gas around the non-directional transducer 13. It has been verified through actual operation that the above method can ensure that the non-directional transducer 13 is completely immersed in water, so as to effectively guarantee the final acoustic measurement effect.

[0079] In a preferred embodiment of the present invention, the above step S4 includes:

[0080] S41, equipment preparation and test environment layout before the test. Check whether the transmitting transducer, power amplifier, signal generator, data acquisition and analyzer, B&K hydrophone, computer and other equipment and instruments are working properly. Test the sound source level of the non-directional transducer 13. Since the spherical transducer also has a certain directionality, when testing the transducer alone, a special tool will be used to adjust its posture to a horizontal level, and its top position will be marked to ensure that the transducer posture and angle are consistent with the posture placed in the metal truncated cone tube 11. Arrange two groups of hydrophones, hydrophone No. 1 is 10m away from the front end of the rotationally symmetrical five-mode material low-frequency sound wave transmitting device, and hydrophone No. 2 is 15m away.

[0081] S42, test and evaluation of the directivity of the transmitting device. The frequency sampling points can be determined according to the actual measurement frequency range. It is recommended that the number of sampling points be greater than 10 to ensure the resolution of data analysis. Use No. 2 hydrophone to conduct a directivity test at a distance of 15 meters. The test angle (with the exit direction as 0°) is 360° circumferential range. The test angle step size and the decibel angle value required for evaluation can be selected according to the actual situation.

[0082] S43, test and evaluation of the launch distance of the launch device. The frequency sampling points can be determined according to the actual measurement frequency range. It is recommended that the number of sampling points is greater than 10 to ensure the resolution of data analysis. Test the sound pressure at 10 meters and 15 meters from the front end outlet of the rotationally symmetrical five-mode material low-frequency sound wave launch device. Measure and evaluate the ratio of the effective launch distance to the case when there is only a non-directional transducer 13.

[0083] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A rotationally symmetrical five-mode material low-frequency sound wave emitting device, characterized in that: The device includes a metal truncated cone cylinder, a five-mode acoustic metamaterial, a non-directional transducer and an acoustic signal generating device; The metal truncated cone has an outer shape of a truncated cone, and the interior of the truncated cone has a through hole of equal diameter. The five-mode acoustic metamaterial and the omnidirectional transducer are fixedly installed in the through hole, and the distance between the front end face of the transducer and the surface of the five-mode acoustic metamaterial is between one-third of the working wavelength and two times the working wavelength; the through hole is located at the opening of the large end of the truncated cone and is closed by a back cover, and the cable of the omnidirectional transducer passes through the back cover to connect to the sound signal generating device; the omnidirectional transducer converts the sound signal generated by the sound signal generating device into an omnidirectional sound wave, and the five-mode acoustic metamaterial gathers the energy of the omnidirectional sound wave, and the metal truncated cone plays a role in waveform regulation and wavefront guidance of the omnidirectional sound wave.

2. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: Annular holes and limiting holes are processed on the surface of the metal truncated cone cylinder, and bolts are passed through the annular holes and the limiting holes to radially fix and axially limit the five-mode acoustic metamaterial respectively, and the length of the bolts is as short as possible.

3. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: The five-mode acoustic metamaterial includes a metametal matrix and sound-transmitting polyurethane. The metametal matrix is ​​a closed axisymmetric geometric configuration with a cavity inside, and the cross-section is arranged in a periodic honeycomb structure. The thinnest wall thickness is 0.2 mm, the wall thickness accuracy requirement is ±0.05 mm, and the overall accuracy requirement of the metametal matrix is ​​±0.2 mm. The sound-transmitting polyurethane is combined with the metametal matrix by using an injection mold, and the overall outer diameter of the five-mode acoustic metamaterial is matched with the inner diameter of the metal truncated cone countersunk hole with a tolerance of -0.2 mm.

4. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: The metal frustum cylinder is made of aluminum alloy or titanium alloy.

5. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: All sharp angles of the metal frustum cylinder are not chamfered, and the unmarked dimensions and hole tolerances are ±0.2mm.

6. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 3, characterized in that: The material of the superstructure metal matrix is ​​aluminum alloy or titanium alloy.

7. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: The low-frequency sound wave emitting device is hoisted in a horizontal state by a hoop, a suspension rod and a suspension bracket.

8. The rotationally symmetrical five-mode material low-frequency sound wave emitting device according to claim 1, characterized in that: The non-directional transducer is in a horizontal posture during use, the effective value of the transducer excitation voltage does not exceed 400V, and the sound source level in the low-frequency acoustic range of tens of kHz is 170dB.

9. A test method for the rotationally symmetrical five-mode material low-frequency acoustic wave emitting device according to any one of claims 1 to 8, characterized in that: The steps to implement this method include: S1: Rotationally symmetrical five-mode material and transducer installation; S2: Metal round cone cylinder hoisting and fixing; S3: Adjustment of the level and water permeability of the low-frequency sound wave emission device; S4: Test and evaluation of the directivity and launch distance of the launch device.

10. The test method of the rotationally symmetric five-mode material low-frequency sound wave emitting device according to claim 9, characterized in that: The process of installing the omnidirectional transducer in step S1 includes: the cable of the omnidirectional transducer is fastened to the back cover through a sleeve and marked, the center of the sphere is 50mm away from the end face of the back cover boss, the inner diameter of the sleeve is matched with the diameter of the cable of the omnidirectional transducer with a tolerance of +0.2mm, the outer diameter of the sleeve changes in a wedge shape along the axial direction, and the diameter on the boss side is small based on the back cover direction; the cable of the omnidirectional transducer is inserted from the boss side of the back cover and then passes through the sleeve, and then the sleeve and the cable of the omnidirectional transducer are knocked into the center hole of the plug together to fasten the omnidirectional transducer; the back cover is fixedly connected to the metal conical cylinder through circumferentially evenly distributed limiting holes; the fixed vertical and horizontal positions between the omnidirectional transducer, the back cover and the metal conical cylinder are marked with a marker.

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