A sound wave induction device for reducible acoustic imaging based on transformation acoustics

Abstract

The present invention discloses a sound wave induction device based on transformation acoustics that can reduce acoustic imaging. The device comprises a plurality of acoustic metamaterial units arranged and evenly distributed on a two-dimensional plane. The acoustic metamaterial units are made of an acoustic metamaterial with a solid outer layer, and the equivalent mass density and bulk modulus of the acoustic metamaterial are anisotropically distributed. The plurality of acoustic metamaterial units are arranged in multiple layers and columns in a circular pattern, and the spacing between each acoustic metamaterial unit and its adjacent acoustic metamaterial units is equal. The acoustic metamaterial units adopt a crisscross unit structure with a length of d and a width of t, and the length d of each layer of the crisscross unit structure is different. The present invention changes the refractive index of each layer of the acoustic metamaterial unit by disposing a plurality of acoustic metamaterial units, thereby affecting the scattering field generated when the sound wave passes through the sound wave induction device, thereby achieving the purpose of reducing acoustic imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of sound wave induction, and in particular to a sound wave induction device capable of reducing sound imaging based on transformation acoustics. Background Art

[0002] Acoustic induction refers to the ability to manipulate sound waves through theoretical design, such as altering their propagation path or reducing their magnitude through partial cancellation. These capabilities enable the design of acoustic metamaterials to create acoustic induction devices, which have applications in a wide range of fields, including underwater detection, stealth cloaking, and noise reduction.

[0003] Transformation acoustics is a theory developed from transformation optics. Through transformation optics, we can accurately control the propagation direction of electromagnetic waves and change the shape of electromagnetic waves. Analogous to transformation optics, transformation acoustics refers to a method of manipulating the propagation mode of sound waves. Its main principle is to obtain the required material parameters based on a series of coordinate transformations of the sound field, such as compression and stretching, so as to obtain the relationship between the coordinate transformation and the medium parameters. Acoustic metamaterials are made into sound wave induction devices, that is, a layer of medium is wrapped on the surface of the target to be protected and hidden, which can achieve the effect of reduction or even stealth in acoustic imaging, thereby realizing the function of deceiving radar, sonar and other detectors.

[0004] With the development of metamaterials and the rise of transformation acoustics theory, a variety of novel and unique devices have emerged. For example, illusion devices that can be invisible to or deceive detection waves have been widely studied. However, functional devices designed based on transformation acoustics face the challenge of complex material parameters, such as inhomogeneity and anisotropy. Summary of the Invention

[0005] The present invention proposes a sound wave induction device based on transformation acoustics that can reduce acoustic imaging. The arrangement of acoustic metamaterial units can change the refractive index of the sound wave. By arranging metamaterial units with different refractive indices in layers, the sound wave can bend after entering the device, causing the sound wave to be induced by the device, bypass the device and propagate backward, scattering fewer sound waves, thereby achieving the purpose of reducing acoustic imaging. This can effectively solve the above-mentioned technical problems. The present invention is achieved through the following technical solutions:

[0006] A sound wave induction device with reducible acoustic imaging based on transformation acoustics includes multiple acoustic metamaterial units arranged and evenly distributed on a two-dimensional plane. The acoustic metamaterial units are made of an acoustic metamaterial with a solid outer layer, and the equivalent mass density and elastic modulus of the acoustic metamaterial are anisotropically distributed. The multiple acoustic metamaterial units are distributed in multiple layers and columns in a circular pattern, and the spacing between each acoustic metamaterial unit and its adjacent acoustic metamaterial units is equal. The acoustic metamaterial units adopt a crisscross unit structure with a length of d and a width of t. The length d of each layer of the crisscross unit structure is different. The position arrangement and equivalent acoustic parameters of the acoustic metamaterial units result in a smaller scattering cross section when sound waves pass through the device.

[0007] Furthermore, the acoustic metamaterial unit is provided with multiple layers, the length d of the multiple layers of acoustic metamaterial unit increases sequentially from the inside to the outside, and the width t of the multiple layers of acoustic metamaterial unit remains unchanged.

[0008] Furthermore, the length d of the acoustic metamaterial unit can be adjusted within a range of 2.02 mm to 9.02 mm, the width t is 1 mm, and the center distance between the acoustic metamaterial units in each layer is 1 cm.

[0009] Furthermore, the refractive index of the acoustic metamaterial unit is:

[0010]

[0011] Among them, if the sound wave is emitted from medium a into medium b, B0 and ρ0 represent the equivalent mass density and elastic modulus of medium a, and B and ρ represent the equivalent mass density and elastic modulus of medium b.

[0012] Furthermore, the solid structure of the acoustic metamaterial unit is made of ABS or photosensitive resin.

[0013] Furthermore, the solid structure of the acoustic metamaterial unit is processed using 3D printing technology.

[0014] Beneficial effects

[0015] The present invention proposes a sound wave induction device for reducible acoustic imaging based on transformation acoustics. Compared with the conventional prior art, it has the following advantages:

[0016] (1) This technical solution is based on the application of transformation acoustics theory and utilizes metasurface technology to design the unit structure. By controlling the refractive index of the outer unit structure, the sound wave is bent after entering the device, causing the sound wave to be induced by the device and propagate backward around the device, scattering fewer sound waves and producing a smaller scattering cross section, thereby achieving the purpose of reducing acoustic imaging. It can be used to cover the target object detected by the sound wave, reducing the target acoustic imaging, and achieving the purpose of avoiding detection.

[0017] (2) This technical solution reduces the acoustic imaging of the target object by a factor of three within the frequency range of 3.5kHz to 5.5kHz. Furthermore, the acoustic metamaterial units only need to be dispersedly covered on the outside of the target object, without affecting the contact between the object and the background medium. This makes the acoustic wave induction device have no rigid requirements on the shape of the target object, making it easy to use and allowing for customized design of the target object.

[0018] (3) This technical solution takes into account the characteristics of a wide working bandwidth and is made by 3D printing rapid prototyping technology, which is convenient for application in acoustic engineering fields such as sonar detection and induced stealth. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is an illustration of the principle of the present invention.

[0020] Figure (a) shows a radius of r h Sound wave distribution diagram of a hard sphere under the action of far-field sound waves;

[0021] Figure (b) shows a radius of 1 / 3r h Figure (c) shows the sound wave distribution of a hard sphere under the action of far-field sound waves. Figure (c) shows the sound wave distribution of a hard sphere covered with an acoustic wave inducing medium under the action of far-field sound waves.

[0022] Figure (d) shows the extracted refractive index distribution in two different directions of the material that can achieve reduced acoustic imaging.

[0023] Figure 2 It is a structural schematic diagram of the present invention.

[0024] Figure 3 Schematic diagram of the solid structure of the acoustic metamaterial unit in the present invention.

[0025] Figure 4 The theoretical medium at 4kHz and with a radius of 1 / 3r h A hard sphere with a radius of r h Comparison of the total sound pressure field and local amplification of a hard sphere without covering medium.

[0026] Figure 5 for Figure 4 Radiation intensity curves for the three cases described in .

[0027] Figure 6 The d value and refractive index curves of the unit structure at different frequencies.

[0028] Figure 7 The refractive index curve corresponding to different d values at different frequencies.

[0029] Figure 8The present invention is at 4kHz and the radius is 1 / 3r h Full-wave simulation and local magnification comparison of a hard sphere.

[0030] Figure 9 for Figure 8 Radiation intensity curves for the two cases.

[0031] Figure 10 The radius of the present invention is 1 / 3r at 3.5kHz h A comparison chart of full-wave simulation of a hard sphere.

[0032] Figure 11 for Figure 10 Radiation intensity curves for the two cases.

[0033] Figure 12 The radius of the present invention is 1 / 3r at 5.5kHz h A comparison chart of full-wave simulation of a hard sphere.

[0034] Figure 13 for Figure 12 Radiation intensity curves for the two cases. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Example 1:

[0037] A sound wave induction device based on transformation acoustics that can reduce acoustic imaging, its working principle is as follows Figure 1 As shown, Figure 1 (a) represents the radius r h The sound wave distribution diagram of a hard sphere under the action of far-field sound waves, Figure 1 (b) indicates a radius of 1 / 3r h The sound wave distribution diagram of a hard sphere under the action of far-field sound waves, Figure 1 (c) represents the radius r h Sound wave distribution diagram of a hard sphere covered with the designed metamaterial medium under the action of far-field sound waves.

[0038] from Figure 1 It can be seen that the radius after covering the medium is r h The sound field radiation generated by the hard sphere is the same as that of the hard sphere with a radius of 1 / 3r hThe acoustic field radiation generated by the hard sphere is similar to that of the hard sphere. From the detection results, the acoustic imaging of the hard sphere is reduced by 3 times. The acoustic wave induction device converts the modulus and density of the material into the refractive index through the transformation acoustic theory. The refractive index can be divided into the refractive index distribution in the radial and polar directions, such as Figure 1 (d) shown.

[0039] The refractive index of the metamaterial medium used to make the acoustic metamaterial unit is determined through theoretical calculation, which facilitates the subsequent design of the metamaterial unit structure.

[0040] like Figure 2 As shown, the acoustic wave induction device for reducible acoustic imaging based on transformation acoustics includes multiple acoustic metamaterial units arranged on a two-dimensional plane and evenly distributed; the multiple acoustic metamaterial units are distributed in multiple layers and columns in a circular pattern, and the spacing between each acoustic metamaterial unit and its adjacent acoustic metamaterial units is equal. Figure 3 As shown, the acoustic metamaterial unit is a crisscross solid structure with a length of d, a thickness of t, and an angle of 45°; and the length d of each layer of the crisscross unit structure is different.

[0041] The acoustic metamaterial unit is made of an acoustic metamaterial with a solid outer layer. The equivalent mass density and elastic modulus of the acoustic metamaterial are anisotropically distributed. The position arrangement and equivalent acoustic parameters of the acoustic metamaterial unit result in a smaller scattering cross-section when sound waves pass through the device.

[0042] The key to detecting the target's transformation lies in the reduction of acoustic imaging, that is, generating smaller scattered sound waves. The position of each acoustic metamaterial unit in the layer arrangement corresponds to the different refractive index distribution of the sound wave induction device. All the acoustic metamaterial units that radiate outward are arranged in sequence to form the parameter distribution required to reduce the acoustic imaging, thereby reducing the acoustic imaging of the target object by 3 times. Figure 4 The figure shows that the total sound pressure field of the theoretical medium is similar to that of the actual object reduced by 3 times. However, objects not covering the theoretical medium will block the sound waves. After entering the acoustic wave induction device, the sound waves are bent, causing them to be induced by the gaps between the multiple acoustic metamaterial units, bypassing the acoustic metamaterial units and propagating backward, scattering fewer sound waves and producing a smaller scattering cross section, thereby achieving the purpose of reducing acoustic imaging.

[0043] In order to quantitatively measure the degree of reduction, the radiation intensity curve is used for illustration, such as Figure 5 The solid line represents an object with a size reduced by 3 times, and the dotted line represents an object with a radius of r. hThe short-dashed line represents the theoretical device. Comparing the three curves at 4 kHz, the sound pressure curve for the theoretical device is similar to that for an object 3 times smaller, indicating that the device can be used to image an object 3 times smaller at 4 kHz.

[0044] In order to confirm the wide working bandwidth of the device, the refractive index distribution of different d values at different frequencies was verified, such as Figure 6 、 7 shown. Figure 6 It shows that the refractive index of the unit structure has a similar distribution trend with the change of d value at 3.5kHz, 4kHz, and 5.5kHz. Figure 7 It shows that between 2kHz and 6kHz, the refractive index of the unit structure with different d values changes relatively smoothly, indicating that the device has a wide operating bandwidth.

[0045] Specifically, the acoustic metamaterial units have different refractive indices. These units are made of a weakly anisotropic acoustic metamaterial, comprising a solid structure and a background medium. The equivalent mass density and bulk modulus of the acoustic metamaterial are anisotropically distributed. Specifically, the acoustic wave induction device is made of multiple acoustic metamaterials with different refractive indices. These metamaterials have varying lengths d, and these varying d values cause the refractive index of the acoustic metamaterials to vary. Arranging these metamaterials in layers creates the induction device.

[0046] According to the theory of transformation acoustics, the refractive index of the acoustic metamaterial unit is:

[0047]

[0048] Among them, if the sound wave is emitted from medium a into medium b, B0 and ρ0 represent the equivalent mass density and elastic modulus of medium a, and B and ρ represent the equivalent mass density and elastic modulus of medium b.

[0049] like Figure 2 As shown, the acoustic metamaterial unit is provided with multiple layers, the length d of the multiple layers of acoustic metamaterial unit increases sequentially from the inside to the outside, and the width t of the multiple layers of acoustic metamaterial unit remains unchanged.

[0050] The length d of the acoustic metamaterial unit can be adjusted within a range of 2.02 mm to 9.02 mm, the width t is 1 mm, and the center distance between the acoustic metamaterial units in each layer is 1 cm.

[0051] According to the refractive index of the acoustic metamaterial unit, the metamaterial unit structures with different d values are arranged in layers, with the center distance between layers being 1 cm. That is, the radius distance between adjacent acoustic metamaterial units in each layer of the circle surrounded by multiple layers of acoustic metamaterial units is 1 cm.

[0052] In this embodiment, the acoustic metamaterial units are arranged in 7 layers; the arrangement of the acoustic metamaterial units is distributed according to the refractive index. In order to obtain the acoustic wave induction device with a wide working bandwidth and capable of reducing acoustic imaging, the acoustic metamaterial units are arranged in layers, and the arrangement order is carried out according to the refractive index distribution of the unit structure, and the refractive index is determined by the d value of the unit structure, such as Figure 2 As shown, the overall radius of the induction device is 14.5 cm. The length d of the acoustic metamaterial unit can be adjusted from 2.02 mm to 9.02 mm, and the width t is 1 mm. There are 7 layers in total, and the difference in radius between adjacent layers is 1 cm. The radius of the circle formed by each layer of acoustic metamaterial units is shown in the following table:

[0053] Layer sequence number Radius (cm) Refractive index Acoustic metamaterial unit length d (mm) 1 8.5 1.05 2.02 2 9.5 1.15 4.51 3 10.5 1.30 5.62 4 11.5 1.35 6.01 5 12.5 1.41 7.82 6 13.5 1.51 8.20 7 14.5 1.61 9.02

[0054] The refractive index and arrangement of the acoustic metamaterial unit structure will directly affect the scattering cross section size generated when the sound wave passes through the induction device. The change in refractive index is related to the length d of the unit structure. The arrangement has been determined. The unit structure is arranged in layers, with a total of 7 layers, and the center distance between layers is 1 cm. Figures 8 to 13 As shown, this solution can achieve the effect of reducing acoustic imaging from 3.5kHz to 5.5kHz.

[0055] The method in this solution can be used to achieve the purpose of reducing the acoustic imaging of the designed frequency band. Figure 8 As shown, the induction devices are arranged in layers on the outer layer of the hard sphere. When the sound wave passes through the induction device, the refractive index changes, causing the sound wave to be induced by the device, bypassing the device and propagating backward, scattering fewer sound waves and producing a smaller scattering cross section, thereby achieving the purpose of reducing acoustic imaging.

[0056] like Figure 2 The following figure illustrates the design process of a reduced acoustic imaging device. First, it is clear that the functional effect of the acoustic wave induction device for reduced acoustic imaging must be to reduce the acoustic imaging of the detected object by a factor of three while maintaining a good operating bandwidth. To achieve this, the principle of transformation acoustics is applied to bend the sound wave after entering the acoustic wave induction device. After being induced by the acoustic wave induction device, the sound wave generates a smaller scattered sound pressure and scattering cross section as it continues to propagate backward. By designing metamaterial units with different refractive indices and arranging them in layers on the outside of the object, a device that reduces the acoustic imaging of the object by a factor of three at frequencies between 3.5kHz and 5.5kHz can be obtained.

[0057] In order to verify the effect of the acoustic wave induction device for reduced acoustic imaging of the present invention, we used COMSOL MUTIPHYSICS multi-physics simulation software to perform full-wave simulation on the case and obtained the following results: Figure 8 、 10, 12 shows the full-wave simulation comparison of the induction device and the hard ball with the size reduced by three times at 4kHz, 3.5kHz, and 5.5kHz. Figure 9 、 11 The similarity between the sound pressure field shown in the simulation and the radiation intensity curves shown in Figure 13 and the degree of overlap between the radiation intensity curves indicate that the designed induction device has a good reduction effect in the 3.5kHz to 5.5kHz range and also demonstrates that the prototype has the advantage of a wide operating bandwidth. The actual calculation results are nearly consistent with the theoretical calculation results, verifying the correctness of this implementation case.

[0058] The specific processing and preparation process of the acoustic wave induction device is as follows:

[0059] (1) Based on the transformation acoustics theory, the refractive index of the acoustic metamaterial unit is deduced and calculated to obtain the acoustic parameters required for the reduced image generation. The unit structure is arranged in layers according to the regional distribution requirements to obtain the device parameters, structural parameters and geometric model distribution for the target area.

[0060] (2) The obtained structural parameters and geometric model are used to create a three-dimensional solid model in SOLIDWORKS software, and the file type that can be used for a 3D printer is exported and then processed into a finished product by a 3D printer.

[0061] (3) Subsequent processing of the printed induction device mainly includes static placement, curing, polishing, and arrangement.

[0062] (4) In order to verify the correctness of the function of the device of the present invention, samples can be taken for numerical simulation and experimental verification comparison to verify the distribution characteristics of the total sound pressure field and scattered sound pressure field, etc. When the experimental data are consistent with the theoretical data, the preparation is completed.

Claims

1. An acoustic wave induction device for reducible acoustic imaging based on transformation acoustics, characterized by: The invention comprises a plurality of acoustic metamaterial units arranged on a two-dimensional plane and uniformly distributed. The acoustic metamaterial units are made of an acoustic metamaterial with a solid outer layer. The equivalent mass density and elastic modulus of the acoustic metamaterial are anisotropically distributed. The position arrangement and equivalent acoustic parameters of the acoustic metamaterial units result in a smaller scattering cross-section when sound waves pass through the device. The plurality of acoustic metamaterial units are arranged in multiple layers and columns in a circular pattern, and the spacing between each acoustic metamaterial unit and its adjacent acoustic metamaterial units is equal. The acoustic metamaterial units are crisscross-shaped solid structures with a length of d, a thickness of t, and an angle of 45 degrees. The length d of each crisscross-shaped unit structure is different. The position of each acoustic metamaterial unit according to the layer arrangement corresponds to a different refractive index distribution of the sound wave induction device. All acoustic metamaterial units that are distributed outwardly are arranged in sequence to form a parameter distribution required to reduce acoustic imaging, thereby reducing the acoustic imaging of the target object by 3 times.

2. The acoustic wave induction device for reducible acoustic imaging based on transformation acoustics according to claim 1, characterized in that: The acoustic metamaterial unit is provided with multiple layers, the length d of the multiple layers of acoustic metamaterial unit increases sequentially from the inside to the outside, and the width t of the multiple layers of acoustic metamaterial unit remains unchanged.

3. The acoustic wave induction device for reducible acoustic imaging based on transformation acoustics according to claim 1 or 2, characterized in that: The length d of the acoustic metamaterial unit can be adjusted within a range of 2.02 mm to 9.02 mm, the width t is 1 mm, and the center distance between the acoustic metamaterial units in each layer is 1 cm.

4. The acoustic wave induction device for reducible acoustic imaging based on transformation acoustics according to claim 3, characterized in that: The refractive index of the acoustic metamaterial unit is: Among them, if the sound wave is emitted from medium a into medium b, B0 and ρ0 represent the equivalent mass density and elastic modulus of medium a, and B and ρ represent the equivalent mass density and elastic modulus of medium b.

5. The acoustic wave induction device for reducible acoustic imaging based on transformation acoustics according to claim 1, 2 or 4, characterized in that: The solid structure of the acoustic metamaterial unit is made of ABS or photosensitive resin.

6. The acoustic wave induction device for reducible acoustic imaging based on transformation acoustics according to claim 1, 2 or 4, characterized in that: The solid structure of the acoustic metamaterial unit is processed using 3D printing technology.

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