Six-channel acoustic wave retroreflector based on acoustic grating

Abstract

The application provides a six-channel sound wave inverse reflector based on an acoustic grating, the upper surface and the lower surface of the six-channel sound wave inverse reflector are respectively provided with a plurality of periodically arranged grooves with the same rectangular cross section; all the grooves have the same width, depth and period, and the width, depth and period are set to meet the following conditions: when incident sound waves are incident at 0°, θ, 180°-θ, 180°, 180°+θ and 360°-θ as the incident angle, the incident sound waves are all completely reflected by the inverse reflector, and the reflected sound waves all propagate along the direction opposite to the original incident path. The six-channel sound wave inverse reflector based on the acoustic grating can make the incident sound waves in the six channels be completely reflected by the inverse reflector and make the reflected sound waves propagate along the direction opposite to the original incident path by adjusting the geometric parameters of the grooves in the acoustic grating, so that the problems of few channels and large sound loss existing in the prior art sound wave inverse reflector are solved, and the structure is simple and compact.

Description

Technical Field

[0001] The invention belongs to the field of acoustics, and in particular relates to a six-channel acoustic wave retroreflector based on an acoustic grating. Background Art

[0002] With the continuous development of acoustic technology, the precise control of sound field distribution and propagation paths in space has become an international research hotspot. An acoustic retroreflector is an acoustic device that completely reflects incident sound waves back to their original direction of incidence. It supports acoustic retroreflection in multiple acoustic channels, and the retroreflected sound waves can transmit the contained acoustic information back to the sound source. With its unique acoustic response characteristics, acoustic retroreflectors have attracted widespread attention from numerous scholars and have great application value in fields such as acoustic remote sensing, acoustic communications, target identification, and nondestructive testing.

[0003] At the current technological level, acoustic retroreflectors can be realized primarily using acoustic mirrors, acoustic Luneburg lenses, and acoustic metasurfaces. An acoustic mirror is the simplest acoustic retroreflector, but it can only fully retroreflect vertically incident sound waves, meaning it only supports single-channel acoustic retroreflection. Acoustic Luneburg lenses are also widely used in the design of acoustic retroreflectors. For example, an acoustic Luneburg lens with a gradient refractive index can be constructed from Archimedean spiral units. However, such Luneburg lens-based acoustic retroreflectors are too bulky, severely restricting the development of acoustic devices towards miniaturization and integration. Subwavelength-scale acoustic metasurfaces provide an effective method for designing simple, compact, and planar acoustic retroreflectors. Examples include an acoustic retroreflector constructed from two cascaded metasurfaces, a three-channel acoustic retroreflector based on acoustic surface impedance control, and a multifunctional acoustic retroreflector capable of mirror reflection, quasi-retroreflection, and three-channel retroreflection. An acoustic grating is an artificial acoustic structure composed of periodic subwavelength units. By adjusting the unit parameters, the amplitude and phase of the diffracted wave can be effectively controlled. Acoustic gratings can achieve a variety of unique acoustic functions, such as anomalous reflection or refraction, perfect sound absorption, acoustic focusing, acoustic cloaking, and unidirectional sound propagation. They also provide a potential approach for the design of acoustic retroreflectors.

[0004] According to research reports, the maximum number of channels supported by existing acoustic retroreflectors is three, and acoustic retroreflectors capable of achieving a higher number of channels have yet to be reported. A new generation of acoustic retroreflectors supporting a higher number of channels would be of great significance for improving the efficiency of acoustic communications. Furthermore, these acoustic retroreflectors contain multiple unit structures within a single cycle, resulting in a complex structural design. Furthermore, the unit structures are often spatially coiled. When sound waves propagate through narrow acoustic channels, the high viscous acoustic losses inevitably lead to low acoustic retroreflection efficiency.

[0005] Therefore, it is of great significance to design a multi-channel, high-efficiency, simple and compact acoustic retroreflector (such as a six-channel acoustic retroreflector). Among them, the six-channel acoustic retroreflector can make the incident acoustic waves in the six channels propagate in the direction opposite to the original incident path.

[0006] References:

[0007] [1]YYFu,JFLi,YBXie,C.Shen,YDXu,HYChen,andS.A.Cummer.Compact acoustic retroreflector based on a mirrored Luneburglens.Physical Review Materials,2018,2(10):105202.

[0008] [2]GYSong,Q.Cheng,TJCui,and Y.Jing.Acoustic planar surfaceretroreflector.Physical Review Materials,2018,2(6):065201.

[0009] [3] C. Shen, A. Díaz-Rubio, JFLi, and SACummer. A surface impedance-based three-channel acoustic metasurface retroreflector. Applied Physics Letters, 2018, 112(18): 183503.

[0010] [4]YYFu,YYCao,and YDXu.Multifunctional reflection in acousticmetagratings with simplified design.Applied Physics Letters,2019,114(5):053502.

[0011] [5] ALSong, CYSun, YXXiang, and F.-Z.Xuan. Switchable acousticmetagrating for three-channel retroreflection and carpet cloaking. Applied Physics Express, 2022, 15(2):024002. Summary of the Invention

[0012] The purpose of the present invention is to provide a six-channel acoustic wave retroreflector based on an acoustic grating to solve the problems of the existing acoustic wave retroreflectors such as a small number of channels, large acoustic loss and complex structure.

[0013] In order to achieve the above-mentioned objectives, the present invention provides a six-channel acoustic wave retroreflector based on an acoustic grating, wherein the six-channel acoustic wave retroreflector based on the acoustic grating is a flat substrate, and the upper surface and lower surface of the substrate are each provided with a plurality of first grooves and second grooves with the same rectangular cross-section periodically arranged along a first direction; all the first grooves and second grooves have the same width, depth and period of periodic arrangement; the width, depth and period of periodic arrangement of the first grooves and second grooves are set so that the propagation directions of the incident sound wave and the reflected sound wave of the six-channel acoustic wave retroreflector based on the acoustic grating satisfy: when the incident sound wave is incident on the six-channel acoustic wave retroreflector based on the acoustic grating at incident angles of 0°, θ, 180°-θ, 180°, 180°+θ, and 360°-θ, respectively, and when 20°<θ<90°, the incident sound wave is completely reflected by the retroreflector, and the reflected sound wave propagates in a direction opposite to the original incident path.

[0014] The width, depth and period of the periodic arrangement of the first groove and the second groove are set so that the sound pressure field distribution of the reflected wave satisfies: when the incident sound wave is incident in each channel, the reflection coefficient of the diffraction wave of the order corresponding to the reflection direction opposite to the incident direction is the largest, and the reflection coefficients of the diffraction waves of the remaining orders are the smallest.

[0015] The period a of the periodic arrangement of the first groove and the second groove is determined by the formula of the x-direction wave number component of the n-th order diffraction wave. The period a of the periodic arrangement of the first groove and the second groove is: a=λ / (2sinθ), where λ is the wavelength of the sound wave in the air; the width w of the first groove and the second groove is taken as 0 <w<a范围中的任意值。

[0016] When θ=60°, the period a of the periodic arrangement of the first groove and the second groove is 57.735 mm, the width w of the first groove and the second groove is 28.8675 mm, the depth h of the first groove and the second groove is 16 mm, and the thickness of the acoustic grille is 36 mm.

[0017] The number of the first grooves and the number of the second grooves are both any integer greater than 2.

[0018] The number of the first grooves and the number of the second grooves are both 12.

[0019] The acoustic impedance of the material of the six-channel acoustic wave retroreflector based on the acoustic grating is greater than 41500 Pa·s / m.

[0020] The material of the six-channel acoustic wave retroreflector based on the acoustic grating includes one of 3D printing materials, metals and alloys.

[0021] The operating frequency of the six-channel acoustic wave retroreflector based on the acoustic grating may be in the audible frequency range of 20 Hz to 20 kHz or in the ultrasonic frequency range above 20 kHz.

[0022] The six-channel acoustic wave retroreflector based on the acoustic grating proposed in the present invention adjusts the geometric parameters of the grooves in the acoustic grating so that the incident sound waves in the six channels can all be completely reflected by the retroreflector, and the reflected sound waves all propagate in the direction opposite to the original incident path. This solves the problems of the small number of channels and large sound loss in existing acoustic wave retroreflectors, and has a simple and compact structure. It can meet the important requirements of the new generation of acoustic wave retroreflectors for multi-channel, high efficiency, simplicity and compactness, and has broad application prospects in the fields of acoustic remote sensing, acoustic communication, target identification, non-destructive testing, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the geometric structure of a six-channel acoustic wave retroreflector based on an acoustic grating designed according to an embodiment of the present invention.

[0024] Figure 2 Yes Figure 1 Schematic diagram of the unit structure of the acoustic grating of the six-channel acoustic wave retroreflector shown.

[0025] Figure 3 It is a schematic diagram of the working principle of the six-channel acoustic wave retroreflector based on the acoustic grating of the present invention.

[0026] Figure 4A This is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 0° (channel 1). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 0°. Figure 4B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 0° (channel 1). The black arrow indicates the reverse reflection of the reflected sound wave at a reflection angle of 0°.

[0027] Figure 5AThis is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 60° (channel 2). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 60°. Figure 5B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 60° (channel 2). The black arrow indicates the reverse reflection of the reflected sound wave at a reflection angle of 60°.

[0028] Figure 6A This is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 120° (channel 3). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 120°. Figure 6B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 120° (channel 3). The black arrow indicates that the reflected sound wave is reversely reflected at a reflection angle of 120°.

[0029] Figure 7A This is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 180° (channel 4). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 180°. Figure 7B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 180° (channel 4). The black arrow indicates that the reflected sound wave is reversely reflected at a reflection angle of 180°.

[0030] Figure 8A This is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 240° (channel 5). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 240°. Figure 8B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 240° (channel 5). The black arrow indicates that the reflected sound wave is reversely reflected at a reflection angle of 240°.

[0031] Figure 9A This is the sound pressure field distribution diagram of the incident wave when a plane acoustic wave with a frequency of 3430 Hz is incident at an incident angle of 300° (channel 6). The white arrow indicates that the plane acoustic wave is incident at an incident angle of 300°. Figure 9B This is the sound pressure field distribution diagram of the reflected wave when a plane sound wave with a frequency of 3430 Hz is incident at an incident angle of 300° (channel 6). The black arrow indicates that the reflected sound wave is reversely reflected at a reflection angle of 300°.

[0032] Figure 10It is the far-field directivity diagram of the reflected sound waves in the six channels when a plane sound wave with a frequency of 3430 Hz is incident on the six-channel acoustic wave retroreflector at incident angles of 0°, 60°, 120°, 180°, 240°, and 300°. DETAILED DESCRIPTION

[0033] The six-channel acoustic wave retroreflector of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Figure 1 FIG. 1 is a schematic diagram of the geometric structure of a six-channel acoustic wave retroreflector based on an acoustic grating designed according to an embodiment of the present invention. Figure 1 As shown, the six-channel acoustic wave retroreflector based on the acoustic grating is a flat substrate 1, and the upper surface and lower surface of the substrate 1 are each provided with a plurality of first grooves 2 and second grooves 3 of the same rectangular cross-section periodically arranged along the first direction (i.e., the x direction in the figure). The first grooves 2 and the second grooves 3 correspond to each other one by one, and each pair of first grooves 2 and second grooves 3 are arranged back to back to each other. The length extension direction of the first grooves 2 and the second grooves 3 is both perpendicular to the first direction (i.e., the z direction in the figure). In this embodiment, the number of the first grooves 2 and the second grooves 3 is 12, however, in other embodiments, the number of the first grooves 2 and the second grooves 3 is any integer greater than 2, and the number of the first grooves 2 and the second grooves 3 is independent of the operating frequency and the incident angle. The acoustic wave retroreflection effect can be achieved for the sound waves incident at six incident angles in six channels.

[0035] The material of the six-channel acoustic wave retroreflector based on the acoustic grating is a 3D printing material, metal, alloy, or other material having an acoustic impedance greater than 100 times the acoustic impedance of air. Therefore, the acoustic impedance of the material of the six-channel acoustic wave retroreflector based on the acoustic grating must be greater than 41500 Pa·s / m.

[0036] Figure 2 Yes Figure 1 The schematic diagram of the unit structure of the acoustic grating of the six-channel acoustic wave retroreflector is shown. Since the upper and lower surfaces of the substrate 1 are each provided with a plurality of first grooves 2 and second grooves 3 of the same rectangular cross-section arranged periodically along the first direction, each periodic structure having one first groove 2 and one second groove 3 on the upper and lower surfaces, respectively, is an acoustic grating. Figure 2 As shown, the structure of each acoustic grating is the same, and all the first grooves 2 and second grooves 3 have the same width, depth and period of periodic arrangement, wherein the width of the first groove 2 and the second groove 3 is w, the depth of the first groove 2 and the second groove 3 is h, the period of periodic arrangement of the first groove 2 and the second groove 3 is a, and the thickness of the acoustic grating is t.

[0037] The width, depth and period of periodic arrangement of the first groove 2 and the second groove 3 are set so that the propagation directions of the incident sound wave and the reflected sound wave of the six-channel acoustic wave retroreflector based on the acoustic grating meet specific conditions. That is to say, by adjusting the width, depth and period of periodic arrangement of the first groove 2 and the second groove 3, the sound pressure field distribution of the reflected wave can be controlled (the sound pressure field distribution of the reflected wave is obtained by conducting finite element numerical simulation experiments in the multi-physics field coupling analysis software Comsol), wherein changing the depth of the first groove 2 and the second groove 3 can regulate the amplitude and phase of the reflected sound wave, thereby obtaining the propagation directions of the incident sound wave and the reflected sound wave of the six-channel acoustic wave retroreflector based on the acoustic grating. Because the acoustic grating provided by the present invention does not include a narrow channel and a resonant cavity, the viscous acoustic loss in the six-channel acoustic wave retroreflector is very low, and ultimately a very high acoustic wave retroreflection efficiency can be achieved.

[0038] like Figure 3 The figure shows the working principle of the six-channel acoustic wave retroreflector based on the acoustic grating of the present invention, which shows the conditions that the propagation directions of the incident sound wave and the reflected sound wave of the six-channel acoustic wave retroreflector based on the acoustic grating need to meet. The solid arrows indicate that the incident angle is θ i The direction of propagation of the incident sound wave, the dotted arrow indicates the reflection angle θ r The propagation direction of the reflected sound wave.

[0039] like Figure 3 As shown, when the plane sound waves in the six channels are incident on the six-channel sound wave retroreflector based on the acoustic grating at incident angles of 0° (channel 1), 60° (channel 2), 120° (channel 3), 180° (channel 4), 240° (channel 5), and 300° (channel 6), respectively, the incident sound waves can all be completely reflected by the retroreflector, and the reflected sound waves all propagate in a direction opposite to the original incident path, thereby achieving a sound wave retroreflection effect in the six channels.

[0040] In this embodiment, the six-channel acoustic wave retroreflector is described in detail by taking the acoustic wave frequency f = 3430 Hz and the incident angles 0°, 60°, 120°, 180°, 240°, and 300° (corresponding to six acoustic channels, respectively). The density of air is ρ = 1.21 kg / m 3 , the speed of sound in air is c = 343m / s, the corresponding sound wave number in air is k = 2πf / c, and the wavelength of sound wave in air is λ = 100mm.

[0041] In other embodiments, the structure of the six-channel acoustic wave retroreflector based on the acoustic grating of the present invention can also be used to design working conditions other than the above-mentioned working frequencies and incident angles. Among them, the conditions that the propagation directions of the incident sound waves and reflected sound waves of the six-channel acoustic wave retroreflector based on the acoustic grating need to meet include: when the incident sound waves are incident on the six-channel acoustic wave retroreflector based on the acoustic grating at incident angles of 0°, θ, 180°-θ, 180°, 180°+θ, and 360°-θ, respectively, and 20°<θ<90°, the incident sound waves are completely reflected by the retroreflector, and the reflected sound waves are propagated in the direction opposite to the original incident path. The working frequency can be the audible sound frequency range of 20Hz to 20kHz or the ultrasonic frequency range above 20kHz.

[0042] In this embodiment, the period a of the periodic arrangement of the first groove 2 and the second groove 3 is determined by the formula of the x-direction wave number component of the n-th order diffraction wave, and the width w of the first groove 2 and the second groove 3 can be taken as 0. <w<a范围中的任意值,第一凹槽2和第二凹槽3的深度h是通过计算反射系数的大小后确定的,其中反射系数为衍射波声压幅值与入射波声压幅值的比值。在多物理场耦合分析软件Comsol中利用几何参数扫描方法分别计算不同深度h下对应的反射系数,得到与入射方向相反的反射方向所对应阶次的衍射波的反射系数最大,且其余阶次的衍射波的反射系数最小时,对应的深度值即为本发明的声学栅的深度值h。

[0043] The design method and working principle of the six-channel acoustic wave retroreflector of the present invention are described in detail below.

[0044] When the incident angle is θ i When a plane acoustic wave is incident on a six-channel acoustic retroreflector, the incident wave will be reflected as multiple reflected waves of different diffraction orders.

[0045] Among them, the x-direction wave number component k of the n-th order diffraction wave is rx for:

[0046] k rx =ksinθ i +2πn / a,

[0047] Where k is the wave number of sound waves in air, θ i is the incident angle of the incident sound wave, a is the period of the periodic arrangement of the first groove 2 and the second groove 3, and n is the order of the diffraction wave.

[0048] When the diffraction wave is a propagable diffraction wave, it must satisfy |k rx | <k,得到衍射波的阶次n的范围是:-(1+sinθ i ) / |2sinθi | <n < (1 - sin θ i ) / |2 sin θ i

[0049] Since -1 < sin θ i < 1, the order n of the diffracted wave can only take three values: -1, 0 and +1.

[0050] For the propagating diffracted wave, its propagation direction can be represented by the reflection angle θ r , and the reflection angle θ r satisfies: θ r = sin -1 (sin θ i + nλ / a), where θ i is the incident angle of the incident sound wave, a is the period of the periodic arrangement of the first groove 2 and the second groove 3, n is the order of the diffracted wave, and λ is the wavelength of the sound wave in the air.

[0051] For the non-propagating diffracted wave (i.e. the evanescent wave), it propagates along the surface of the retroreflector and the sound energy rapidly decays along the normal direction, and will not propagate into the far field region.

[0052] In the present application, the width, depth and period of the periodic arrangement of the first groove 2 and the second groove 3 are set so that the sound pressure field distribution of the reflected wave (i.e. the amplitude and phase of the reflected wave) satisfies: when the incident sound wave is incident in each channel, the reflection coefficient of the diffracted wave corresponding to the reflection direction opposite to the incident direction is the largest, and the reflection coefficients of the diffracted waves of the remaining orders are the smallest. Thus, the propagating diffracted wave other than the retroreflected wave can be perfectly suppressed, and a high-efficiency sound wave retroreflecting effect can be achieved in the six channels.

[0053] The sound wave propagation when the plane sound wave is incident from the upper side of the six-channel sound wave retroreflector will be discussed below, and the corresponding incident angles are 60° (channel 2), 0° (channel 1) and 300° (channel 6), respectively.

[0054] When the plane sound wave with an incident angle of 60° (channel 2) is incident on the six-channel sound wave retroreflector (i.e. θ = 60°), the order of the propagating diffracted wave that requires the reflected wave to propagate in the reflection direction with a reflection angle of 60° is n = -1, and the propagating diffracted waves of the remaining orders are suppressed from being excited. The horizontal component of the wave number of the -1 order diffracted wave is k sin 60°, and since this horizontal component is in the negative direction of the x axis, the x direction wave number component of the -1 order diffracted wave is -k sin 60°, and thus the period a of the periodic arrangement of the first groove 2 and the second groove 3 is:

[0055] a = λ / (2 sin 60°) = 57.735 mm,

[0056] ​The width w of the first groove 2 and the second groove 3 is set to: w=0.5a=28.8675 mm.

[0057] It should be noted that, in other embodiments, when the six channels of the six-channel acoustic wave retroreflector correspond to incident acoustic waves with incident angles of 0°, θ, 180°-θ, 180°, 180°+θ, and 360°-θ, respectively, the period a of the periodic arrangement of the first groove 2 and the second groove 3 is a=λ / (2sinθ), and the width of the first groove 2 and the second groove 3 is w(0 <w<a)。

[0058] When the groove depth h varies from 0 to 0.5λ, the reflection coefficients of the -1st, 0th, and +1st order diffracted waves are calculated in sequence. When the -1st order reflection coefficient is the maximum and the reflection coefficients of the remaining orders are the minimum, the corresponding groove depth is the required value. For each propagating order of diffracted waves, the reflection coefficient is the ratio of the diffracted wave sound pressure amplitude to the incident wave sound pressure amplitude. For each non-propagating order of diffracted waves (i.e., evanescent waves), their acoustic energy decays rapidly along the normal direction and does not propagate into the far field, so there is no need to calculate their reflection coefficient.

[0059] In this embodiment, according to the reflection coefficient of each order of diffraction wave, the depth of the first groove 2 and the second groove 3 is set to h = 16 mm, the corresponding reflection wave phase is 0.64π, and the thickness of the acoustic grating is set to t = 36 mm.

[0060] When a plane acoustic wave with an incident angle of 0° (channel 1) is incident on the six-channel acoustic retroreflector, according to the range of diffraction wave orders, only the 0th-order diffraction wave (specular reflection wave) is excited, so acoustic retroreflection can occur in this channel.

[0061] When a plane acoustic wave with an incident angle of 300° (channel 6) is incident on the six-channel acoustic retroreflector, according to the range of diffraction wave orders and the geometric symmetry of the acoustic grating, only the +1-order diffraction wave (retroreflection wave) is excited, so acoustic retroreflection can occur in this channel.

[0062] Regarding the propagation of plane sound waves when they are incident from the bottom side of the six-channel acoustic retroreflector, the corresponding incident angles are 120° (channel 3), 180° (channel 4), and 240° (channel 5). Since the grooves on the upper and lower surfaces of the acoustic grating are identical and symmetrical, acoustic retroreflection can also occur in the three channels on the bottom side.

[0063] Based on the above analysis, the six-channel acoustic wave retroreflector based on the acoustic grating proposed in the present invention can achieve a retroreflective effect on incident sound waves in six channels.

[0064] The above embodiment is a preferred example of the present invention. In actual applications, the geometric parameters of the groove can be determined using the above method introduced in the present invention for specific operating frequencies and incident angles.

[0065] Simulation Results

[0066] A specific finite element numerical simulation experiment was carried out in the multi-physics field coupling analysis software Comsol to verify the effect of the six-channel acoustic wave retroreflector. In the simulation experiment, the six-channel acoustic wave retroreflector was placed in an air background medium with a density of ρ = 1.21 kg / m 3 , the speed of sound in air is c = 343 m / s, all boundaries of the retroreflector are set to hard acoustic boundary conditions, and the frequency of the incident sound wave is 3430 Hz.

[0067] Figure 4A , Figure 5A , Figure 6A , Figure 7A , Figure 8A , Figure 9A The following is the sound pressure field distribution diagram of the incident wave when the six-channel acoustic wave retroreflector is irradiated by sound waves with incident angles of 0°, 60°, 120°, 180°, 240°, and 300° (the white arrow indicates the propagation direction of the incident sound wave). Figure 4B , Figure 5B , Figure 6B , Figure 7B , Figure 8B , Figure 9B Figure 2 shows the acoustic pressure distribution of the reflected waves at the corresponding incident angles (black arrows indicate the propagation direction of the reflected sound waves). These reflected wave acoustic pressure distribution diagrams clearly demonstrate that when plane sound waves in the six channels are incident on the six-channel acoustic retroreflector, they are completely reflected back to the initial direction of incidence. The reflected sound waves propagate in a direction opposite to the original incident path, thus achieving acoustic retroreflection in all six channels. Because the acoustic grating consists only of periodically arranged grooves, its viscous acoustic loss is very low, and the acoustic retroreflection efficiency in all six channels is close to 100%.

[0068] When the propagation direction of the incident sound wave is perpendicular to the six-channel acoustic retroreflector, Figure 4B , Figure 7B The distribution diagrams of the reflected wave sound pressure field at incident angles of 0° and 180° are shown. There are some excited surface waves in the surface area of ​​the six-channel acoustic retroreflector, but the energy of these surface waves decays rapidly along the normal direction and does not propagate to the far field area.

[0069] Figure 10The far-field directivity diagrams of the reflected sound waves in the six channels are shown when a plane sound wave with a frequency of 3430 Hz is incident on a six-channel acoustic retroreflector at angles of 0°, 60°, 120°, 180°, 240°, and 300°. Based on the sound pressure field distribution of the reflected wave, the acoustic energy values ​​at different angles in the far field are extracted in a cylindrical coordinate system. A distribution diagram of the relationship between the acoustic energy value and angle is plotted, which is the far-field directivity diagram of the reflected sound wave. The far-field directivity diagram of the reflected sound wave shows that the incident sound waves in the six channels are completely reflected back to the original incident direction by retroreflector 1, with reflection angles of 0°, 60°, 120°, 180°, 240°, and 300°, respectively.

[0070] The sound pressure field distribution diagrams and far-field directivity diagrams of the reflected waves in the above six channels both confirm that the six-channel acoustic wave retroreflector based on the acoustic grating proposed in the present invention can achieve efficient acoustic wave retroreflection effects in the six channels.

[0071] The six-channel acoustic wave retroreflector based on the acoustic grating proposed in the present invention adjusts the geometric parameters of the grooves in the acoustic grating so that the incident sound waves in the six channels can all be completely reflected by the retroreflector, and the reflected sound waves all propagate in the direction opposite to the original incident path. This solves the problems of the small number of channels and large sound loss in existing acoustic wave retroreflectors, and has a simple and compact structure. It can meet the important requirements of the new generation of acoustic wave retroreflectors for multi-channel, high efficiency, simplicity and compactness, and has broad application prospects in the fields of acoustic remote sensing, acoustic communication, target identification, non-destructive testing, etc.

[0072] The six-channel acoustic wave retroreflector based on the acoustic grating of the present invention includes periodically arranged grooves of the same rectangular cross section on its upper and lower surfaces. By adjusting the width, depth, and period of the periodic arrangement of the grooves in the acoustic grating, the excitation of propagable diffracted waves other than the retroreflected waves is perfectly suppressed, so that the incident sound waves in the six channels can all be completely reflected by the retroreflector, and the reflected sound waves all propagate in the direction opposite to the original incident path, achieving the purpose of six-channel acoustic wave retroreflection. Plane sound waves incident in the six channels at angles of incidence of 0° (channel 1), 60° (channel 2), 120° (channel 3), 180° (channel 4), 240° (channel 5), and 300° (channel 6) are completely reflected back to the original incident direction by the six-channel acoustic wave retroreflector, and the reflected sound waves all propagate in the direction opposite to the original incident path. The design scheme based on the acoustic grating makes the six-channel acoustic wave retroreflector flat, simple and compact in structure, and can achieve very high acoustic wave retroreflection efficiency due to low viscous acoustic loss. The present invention has the advantages of multi-channel, high efficiency, simplicity and compactness. Simulation experiments have proved that the six-channel acoustic wave retroreflector of the present invention can achieve efficient acoustic wave retroreflection effect in six channels.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that: without departing from the principles and functions of the present invention, several improvements and modifications (such as the contour shape of the groove) can be made, and these improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A six-channel acoustic wave retroreflector based on an acoustic grating, characterized in that: The six-channel acoustic wave retroreflector based on the acoustic grating is a flat substrate, wherein the upper surface and the lower surface of the substrate are respectively provided with a plurality of first grooves and second grooves of the same rectangular cross-section periodically arranged along a first direction; all the first grooves and the second grooves have the same width, depth and period of periodic arrangement; the width, depth and period of periodic arrangement of the first grooves and the second grooves are set so that the propagation directions of the incident sound wave and the reflected sound wave of the six-channel acoustic wave retroreflector based on the acoustic grating meet the following requirements: when the incident sound wave is at 0°, θ , 180°- θ , 180°, 180°+ θ , 360°- θ is the incident angle incident on the six-channel acoustic wave retroreflector based on the acoustic grating, and 20°< θ When the angle is less than 90°, the incident sound waves are completely reflected by the retroreflector, and the reflected sound waves propagate in the direction opposite to the original incident path.

2. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 1, characterized in that: The width, depth and period of the periodic arrangement of the first groove and the second groove are set so that the sound pressure field distribution of the reflected wave satisfies: when the incident sound wave is incident in each channel, the reflection coefficient of the diffraction wave of the order corresponding to the reflection direction opposite to the incident direction is the largest, and the reflection coefficients of the diffraction waves of the remaining orders are the smallest.

3. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 2, characterized in that: The period of the periodic arrangement of the first groove and the second groove is a Is to use the n order diffraction waves x The period of the periodic arrangement of the first groove and the second groove is determined by the formula of the directional wave number component. a for: a = λ / (2sin θ ), λ is the wavelength of sound waves in air; the width of the first groove and the second groove w Set to 0 <w<a Any value in the range.

4. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 3, characterized in that: when θ =60°, the period of the periodic arrangement of the first groove and the second groove is a The width of the first groove and the second groove is 57.735 mm. w The depth of the first groove and the second groove is 28.8675 mm. h The thickness of the acoustic grille is 36 mm.

5. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 1, characterized in that: The number of the first grooves and the number of the second grooves are both any integer greater than 2.

6. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 5, characterized in that: The number of the first grooves and the number of the second grooves are both 12.

7. The six-channel acoustic wave retroreflector based on an acoustic grating according to claim 1, characterized in that: The acoustic impedance of the material of the six-channel acoustic wave retroreflector based on the acoustic grating is greater than 41500 Pa·s / m.

8. The six-channel acoustic wave retroreflector based on the acoustic grating according to claim 7, characterized in that: The material of the six-channel acoustic wave retroreflector based on the acoustic grating includes one of a 3D printing material and a metal.

9. The six-channel acoustic wave retroreflector based on an acoustic grating according to claim 1, characterized in that: The operating frequency of the six-channel acoustic wave retroreflector based on the acoustic grating is an audible sound frequency range of 20 Hz to 20 kHz or an ultrasonic frequency range above 20 kHz.

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