An acoustic lens for acoustic focusing and a method of manufacturing an acoustic lens

Abstract

The application relates to an acoustic lens for acoustic focusing and a preparation method of the acoustic lens, and the acoustic lens comprises a plurality of wave bands, wherein the wave band at the center of the lens is a circular acoustic transparent band, the rest of the wave bands are circular ring-shaped acoustic transparent bands and acoustic opaque bands, all the wave bands are coaxial, the acoustic transparent bands and the acoustic opaque bands are alternately distributed, the width of the wave band decreases from the center of the lens to the outside, compared with the prior art, according to the set acoustic emission distance and the expected focal length, the wave band size of the lens is changed, the material of the acoustic opaque band is high acoustic impedance material, that is, the acoustic component with the opposite phase of the acoustic transparent band can be reflected, thereby causing constructive interference, the acoustic focusing function under the condition of high frequency in water is realized, the focal length can be accurately adjusted according to the frequency size, and the designed acoustic lens has the characteristics of small lens size, flat geometric shape and high focusing efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of underwater acoustic focusing in engineering applications, and in particular to an acoustic lens for acoustic focusing suitable for underwater high-frequency acoustic focusing and having adjustable focal length and a preparation method of the acoustic lens. BACKGROUND

[0002] Acoustic focusing is one of the important research directions in the field of acoustics, and is usually achieved using an acoustic lens, which can be applied to diagnosis and treatment in the medical field, as well as non-destructive testing and food industry. For example, in the medical field, using ultrasonic focusing means, small tissue structures can be accurately located, and under the condition of ensuring treatment effect, no great damage is caused to the target tissue outside. For example, the acoustic detection function of a submarine or other underwater vehicle, one of the key points is to improve the signal-to-noise ratio of the sonar system, which can be achieved by laying an acoustic barrier on the surface of the submarine, which has a characteristic impedance much greater than that of seawater. Its main function is to improve the surface acoustic focusing / reflection capability, thereby improving the sensitivity of the sonar hydrophone.

[0003] Chinese utility model patent CN202120678557.6 discloses a metasurface device for realizing underwater broadband ultrasonic focusing, which can form concentrated reflection of sound waves, so that the reflected sound waves converge at the same point, thereby efficiently realizing underwater three-dimensional broadband focusing. However, in many scenarios, a nutritional acoustic lens is needed for transmission to achieve ultrasonic focusing. Therefore, it is necessary to develop an acoustic functional lens suitable for high frequency, underwater and having good focusing performance in various practical applications. SUMMARY

[0004] The purpose of the present application is to overcome the defects of the prior art and provide an acoustic lens for acoustic focusing and a preparation method of the acoustic lens. According to the set acoustic emission distance and the expected focal length, the lens waveband size is changed, and the material of the sound opaque band is a high acoustic impedance material, which can reflect the sound components opposite in phase to the sound transparent band, thereby causing constructive interference, achieving acoustic focusing function under underwater high frequency conditions, and the focal length can be accurately adjusted according to the frequency size. The designed acoustic lens has the characteristics of small lens size, flat geometric shape and high focusing efficiency.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] An acoustic lens for acoustic focusing, comprising a plurality of wavebands, wherein the waveband at the center of the lens is a circular sound transparent band, and the remaining wavebands are circular ring-shaped sound transparent bands and sound opaque bands, all the wavebands are coaxial and the sound transparent bands and the sound opaque bands are alternately distributed, and the width of the wavebands decreases outward from the center of the lens.

[0007] Preferably, the lens comprises a plurality of annular rings and a plurality of necks, the annular rings are made of high acoustic impedance material, the plurality of annular rings are arranged concentrically and connected by the necks, the center of the innermost annular ring forms a circular acoustic transparent zone, the remaining annular rings form acoustic opaque zones, the gap between adjacent annular rings forms an acoustic transparent zone, the width of each annular ring decreases from inside to outside, and the gap between adjacent annular rings decreases.

[0008] Preferably, the lens is integrally formed by metal etching technology.

[0009] Preferably, the thickness of the lens is sub-wavelength thickness.

[0010] Preferably, the width of each waveband is as follows:

[0011]

[0012] Wherein, n = 1, 2, …, N, N is the number of wavebands in the lens, d represents the incident distance, F is the designed focal length, λ is the designed wavelength, r0 is set to 0, the radius of the circular acoustic transparent zone is r1-r0, and the width of the nth waveband is r n -r n-1 .

[0013] A method for preparing an acoustic lens for acoustic focusing, comprising the following steps:

[0014] A lens model is constructed, the lens comprises a plurality of wavebands, wherein the waveband at the center of the lens is a circular acoustic transparent zone, the remaining wavebands are annular acoustic transparent zones and acoustic opaque zones, all the wavebands are coaxial and the acoustic transparent zones and the acoustic opaque zones are alternately distributed, and the width of the waveband decreases from the center of the lens to the outside;

[0015] The width of each waveband is determined so that the acoustic transparent zone can pass through the same phase acoustic wave, and the acoustic opaque zone filters out the acoustic wave with opposite phase.

[0016] Preferably, the annular rings are made of high acoustic impedance material, the inner and outer diameters of each annular ring are determined according to the width of each waveband, a plurality of annular rings are arranged concentrically and connected by the necks, the center of the innermost annular ring forms a circular acoustic transparent zone, the remaining annular rings form acoustic opaque zones, the gap between adjacent annular rings forms an acoustic transparent zone, the width of each annular ring decreases from inside to outside, and the gap between adjacent annular rings decreases.

[0017] Preferably, the preparation process is as follows: on a bottom plate made of high acoustic impedance material, a blank area is etched as an acoustic transparent zone by metal etching technology, a circular ring is reserved as an acoustic opaque zone, and a neck is reserved to connect the circular ring.

[0018] Preferably, the thickness of the lens is sub-wavelength thickness.

[0019] Preferably, the width of each wave band is determined as follows:

[0020] The working frequency f, the focal length F and the number of wave bands N are pre-designed, the radius a of the transmitter is determined, the underwater acoustic wavelength λ at the working frequency f is determined, the incident distance d is calculated, d=a 2 / λ, and the width of each wave band is determined according to the following formula:

[0021]

[0022] wherein n=1, 2, …, N, r0=0 is assumed, the radius of the acoustically transparent band is r1-r0, and the width of the nth wave band is r n -r n-1 .

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The lens has good focusing performance, the focal length is relatively accurate, and the focusing efficiency is relatively high.

[0025] (2) The focusing performance of the lens has high robustness, and when the lens size and the working frequency are changed within a certain range, the full width at half maximum (FWHM) at the focal point changes little.

[0026] (3) An acoustic lens preparation and design method is provided, and the lens with a determined size designed according to the method has a linear change between the actual focal length and the working frequency when the working frequency is changed within a certain range, and the focal length can be accurately controlled.

[0027] (4) The acoustic lens structure is designed in an integrated manner, and the actual processing can be realized in an integrated manner, the geometric shape is flat, and the structure size is small and light. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structural schematic view of an acoustic lens;

[0029] Figure 2 is a simulation and experimental comparison diagram of the field intensity near the focal point of an acoustic lens;

[0030] Figure 3 is a simulation and experimental comparison diagram of the lens performance of an acoustic lens;

[0031] The drawings show that: 1, acoustically opaque band, 2, acoustically transparent band, 3, narrow neck. DETAILED DESCRIPTION

[0032] The present application will be described in detail below in combination with the drawings and specific embodiments. The present embodiment is implemented on the basis of the technical solution of the present application, and detailed implementation and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0033] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, some components are appropriately exaggerated in the drawings.

[0034] Example 1:

[0035] On one hand, this application provides an acoustic lens for acoustic focusing, comprising multiple wavebands, wherein the waveband at the center of the lens is a circular acoustically transparent band 2, and the remaining wavebands are annular acoustically transparent bands 2 and acoustically opaque bands 1. The acoustically transparent band 2 allows sound waves of the same phase to pass through, while the acoustically opaque band 1 filters out sound waves with opposite phases. All wavebands are coaxial and the acoustically transparent band 2 and acoustically opaque band 1 are alternately distributed. From the center of the lens outwards, the width of the wavebands decreases. The width of the circular acoustically transparent band 2 is its radius, and the width of the annular waveband is the difference between its inner and outer radii.

[0036] The thickness of the lens is a subwavelength thickness.

[0037] like Figure 1 As shown, in this embodiment, the lens includes multiple rings and multiple thin necks 3. The rings are made of a high acoustic impedance material, such as brass. The rings are arranged concentrically and connected by the thin necks 3. The center of the innermost ring forms a circular acoustic transparency band 2, and the remaining rings form an acoustic opacity band 1. The gaps between adjacent rings form the acoustic transparency bands 2. From the inside out, the width of each ring decreases, and the gaps between adjacent rings also decrease. The thin necks 3, used for connection, are not considered in the design. Their function is only to connect the various wavebands, and since they are very small relative to the overall size, they have almost no impact on the focusing effect. Their material is the same as the lens body material, which is a high acoustic impedance material such as brass.

[0038] Specifically, during fabrication, the lens can be integrally formed using metal etching technology. On a base plate made of a high acoustic impedance material, a blank area is etched out using metal etching technology as the acoustically transparent band 2, while a circular ring is retained as the acoustically opaque band 1, and a thin neck 3 is retained to connect the circular ring.

[0039] In other embodiments, a material with high acoustic impedance can be selected as the acoustically opaque band 1, and a material with low acoustic impedance can be selected as the acoustically transparent band 2, and then connected in sequence.

[0040] To ensure that sound waves with the same phase converge to the focal point through the transparent region, while using the opaque region to filter out sound waves with opposite phase, the widths of each waveband are designed as follows:

[0041]

[0042] wherein n = 1, 2, …, N, N is the number of wave bands in the lens, d represents the incident distance, F is the designed focal length, λ is the designed wavelength, and r0=0, the radius of the circular acoustic transparent zone 2 is r1-r0, and the width of the nth wave band is r n -r n-1 .

[0043] In another aspect, the application provides a preparation method of an acoustic lens for acoustic focusing, comprising the following steps:

[0044] A lens model is constructed, the lens comprising a plurality of wave bands, wherein the wave band at the center of the lens is a circular acoustic transparent zone, and the remaining wave bands are circular ring-shaped acoustic transparent zones and acoustic opaque zones, all the wave bands are coaxial and the acoustic transparent zones and the acoustic opaque zones are alternately distributed, and the width of the wave band decreases from the center of the lens outward;

[0045] The width of each wave band is determined so that the acoustic transparent zone can pass through the acoustic wave with the same phase, and the acoustic opaque zone filters out the acoustic wave with the opposite phase.

[0046] Specifically, the background medium is water, and an acoustic wave transducer is arranged at a position with a distance d from the lens. Wherein d = a 2 / λ, wherein a is the radius of the radiation surface of the transducer, and λ is the underwater acoustic wavelength under the designed working frequency f. At this time, when a piston transducer is used as a transmitter, in the far field, the piston can be described as a point source transmitter with a given directivity.

[0047] The expected focal length F is designed, so that the acoustic wave with the same phase is converged to the focal point through the transparent region, and the acoustic wave with the opposite phase is filtered out by using the opaque region, and then the constructive interference can be realized at the other side F. Considering the λ / 2 increase between the pressure propagation paths of two consecutive regions, the design equation of the lens radius can be obtained, and the radius can be calculated using the following expression:

[0048] The working frequency f, the focal length F and the number of wave bands N are pre-designed, the radius a of the transmitter is determined, the underwater acoustic wavelength λ under the working frequency f is determined, the incident distance d is calculated, d = a 2 / λ;

[0049] After the size of the N wave bands is determined according to the pre-set working frequency f, the focal length F and the number of wave bands N, the actual focal length change relationship when the working frequency f is changed can be inversely deduced, as follows:

[0050]

[0051] wherein, Δ2=Nv,v is the underwater sound speed. It can be seen that when the working frequency is higher (about 5MHz), the last two terms of the equation are approximately 0, and thus the first term of the actual focal length F is approximately linearly related to the working frequency f.

[0052] Therefore, the width of each wave band can be determined according to the following formula:

[0053]

[0054] wherein n=1, 2, …, N, r0 is set to 0, the radius of the circular sound-transparent band is r1-r0, and the width of the nth wave band is r n -r n-1 At this time, the phase distribution of the sound wave passing through each region is [(n-1)π, nπ].

[0055] The approximate linear correlation between the actual focal length and the working frequency is verified theoretically, simulated and experimentally. The acoustic lens designed according to the present application has a linear change in the actual focal length and the working frequency within a certain range when the working frequency is changed, and can accurately control the focal length.

[0056] Based on the above determined geometric parameters, a high-frequency acoustic focusing lens with a flat cross-section, i.e. with the same thickness, is prepared. The thickness of the lens is sub-wavelength, as follows: a high acoustic impedance material is used to make a circular ring and a neck. The inner and outer diameters of each circular ring are determined according to the width of each wave band. A plurality of circular rings are arranged concentrically and connected by the neck. The center of the innermost circular ring forms a circular sound-transparent band, and the remaining circular rings form sound-opaque bands. The gap between adjacent circular rings forms a sound-transparent band. From the inside to the outside, the width of each circular ring decreases, and the gap between adjacent circular rings decreases.

[0057] The preparation process is as follows: on a bottom plate made of a high acoustic impedance material, a blank area is etched as a sound-transparent band using a metal etching technique, and a circular ring is reserved as a sound-opaque band, and a neck is reserved to connect the circular ring.

[0058] In this embodiment, the transducer radius a is 12.7mm, and the incident distance d is 134.4mm. The number of wave bands N is 16. When the designed focal length F is 10, 20, and 30mm, the lens radii are 10.363, 12.078, and 13.491mm, respectively. The lens radius here is the overall size of the lens radius.

[0059] The present application verifies the focusing effect of the designed acoustic lens suitable for underwater high-frequency acoustic focusing and adjustable focal length through experiments, as shown in FIG. 4. Figure 2 FIG. 4 is a comparison chart of simulation and experiment, wherein, Figure 2The (a) and (c) in the figure are simulation results of the cross-section and longitudinal cross-section field pattern of sound intensity at the focal point, and the (b) and (d) are experimental results of the cross-section and longitudinal cross-section field pattern of sound intensity at the focal point, it can be seen from the figure that the simulation and experimental results are close, and the full width at half maximum is about one wavelength. Figure 3 As shown in the figure, the simulation and experimental comparison of the robustness and focal length of the structure, Figure 3 The (a) and (b) in the figure are simulation and experimental comparison of the influence of F / D and working frequency f on the full width at half maximum, and the (3) is simulation and experimental comparison of the relationship between the working frequency and the actual focal length (10S, 15S and 20S represent simulation results of the designed focal length F of 10mm, 15mm and 20mm respectively, and 10E, 15E and 20E represent experimental results of the designed focal length F of 10mm, 15mm and 20mm respectively), wherein the overall diameter of the lens is changed by changing the number of wave bands, it can be seen that when the lens size and working frequency are changed within a certain range, the focusing effect is relatively stable, which indicates that the focusing effect of the structure has a certain robustness; at the same time, when the working frequency is changed, it can be seen that the actual focal length and the working frequency have a linear change relationship, which provides a condition for precise control of the actual focal length, and realizes the initial design purpose.

[0060] The above describes the preferred embodiments of the application in detail. It should be understood that those skilled in the art can make many modifications and changes without creative labor according to the concept of the application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment on the basis of the prior art according to the concept of the application should be within the protection scope determined by the claims.

Claims

1. An acoustic lens for acoustic focusing, characterized by, The lens comprises a plurality of wave bands, wherein the wave band at the center of the lens is a circular acoustic transparent band, and the rest of the wave bands are circular ring-shaped acoustic transparent bands and acoustic opaque bands, all the wave bands are coaxial, and the acoustic transparent bands and the acoustic opaque bands are alternately distributed, and the width of the wave bands decreases from the center of the lens to the outside; the lens comprises a plurality of circular rings and a plurality of necks, the circular rings are made of high acoustic impedance material, the plurality of circular rings are arranged concentrically and connected by the necks, the center of the circular ring located at the innermost side forms a circular acoustic transparent band, the rest of the circular rings form acoustic opaque bands, and the gap between adjacent circular rings forms an acoustic transparent band, and the width of each circular ring decreases from the inside to the outside, and the gap between adjacent circular rings decreases. The width of each wave band is as follows: wherein, 1, 2,..., , is the number of wave bands in the lens, denotes the incident distance, is the designed focal length, is the designed wavelength, let 0, the radius of the circular acoustic transparent band is , the width of the first wave band is ; According to the preset working frequency , focal length and the number of wave bands , the radius of the transmitter and the incident distance are determined N After the size of the wave band is determined , the actual focal length change relationship when the working frequency is changed can be inversely deduced as follows: wherein , , is the underwater sound velocity, whereby the first term actual focal length is approximately linearly dependent on the operating frequency .

2. An acoustic lens for acoustic focusing according to claim 1, wherein, The lens is integrally formed by a metal etching technology.

3. An acoustic lens for acoustic focusing according to claim 1, wherein, The thickness of the lens is a sub-wavelength thickness.

4. A method for producing an acoustic lens for acoustic focusing, for producing an acoustic lens for acoustic focusing according to any one of claims 1 to 3, characterized in that The method comprises the following steps: A lens model is constructed, the lens comprises a plurality of wave bands, wherein the wave band at the center of the lens is a circular acoustic transparent band, and the rest of the wave bands are circular ring-shaped acoustic transparent bands and acoustic opaque bands, all the wave bands are coaxial, and the acoustic transparent bands and the acoustic opaque bands are alternately distributed, and the width of the wave bands decreases from the center of the lens to the outside; The width of each wave band is determined so that the acoustic transparent band can pass through acoustic waves of the same phase, and the acoustic opaque band filters out acoustic waves having an opposite phase.

5. A method of fabricating an acoustic lens for acoustic focusing according to claim 4, wherein, The circular rings are made of high acoustic impedance material, the inner and outer diameters of each circular ring are determined according to the width of each wave band, a plurality of circular rings are arranged concentrically and connected by the necks, the center of the circular ring located at the innermost side forms a circular acoustic transparent band, the rest of the circular rings form acoustic opaque bands, and the gap between adjacent circular rings forms an acoustic transparent band, and the width of each circular ring decreases from the inside to the outside, and the gap between adjacent circular rings decreases.

6. A method of fabricating an acoustic lens for acoustic focusing according to claim 5, wherein, The preparation process is specifically as follows: on a bottom plate made of high acoustic impedance material, a blank area is etched as an acoustic transparent band by a metal etching technology, and a circular ring is reserved as an acoustic opaque band, and a neck connecting the circular ring is reserved.

7. The method of claim 4, wherein the acoustic lens is formed by, The thickness of the lens is a sub-wavelength thickness.

8. The method of claim 4, wherein the acoustic lens is used for acoustic focusing. The width of each wave band is determined as follows: Pre-design operating frequency focal length and number of wave bands determining the radius of the emitter determining the underwater acoustic wavelength at the operating frequency calculating the distance of incidence , , determining the width of each wave band according to the formula: wherein 1, 2,... , let 0, the radius of the circular acoustically transparent band is , the width of the th band is .

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