An acousto-optic device sound absorption device and method for converting body waves into surface waves

Abstract

A sound absorption device and method for an acousto-optic device that converts body waves into surface waves. The sound absorption device of the acousto-optic device mainly adopts a crystal similar to the acousto-optic crystal of the acousto-optic device, and the sound absorption crystal guides out and absorbs the sound energy in the acousto-optic crystal. The specific implementation method comprises the following steps: (1) calculating the sound velocity slowness curve of the acousto-optic interaction surface of the acousto-optic crystal and the sound absorption crystal; (2) using the Snell law of anisotropic crystals, calculating the phase velocity of the incident sound wave and the angle of the sound absorption surface when the reflected sound energy propagates along the interface at the sound absorption surface of the sound absorption crystal; (3) using the Snell law of anisotropic crystals, designing the angle of the connection surface between the sound absorption crystal and the acousto-optic crystal, so that the direction of the sound wave phase velocity in the sound absorption crystal is the design direction; (4) connecting the sound absorption crystal cut according to the design angle to the acousto-optic crystal, so that the ultrasonic energy is transmitted into the sound absorption crystal, and is converted from body waves to surface waves on the sound absorption surface and rapidly attenuated and absorbed, thereby improving the influence of the reflected sound field interference of the traditional sound absorption structure.

Description

Technical Field

[0001] The present invention designs an acousto-optic device sound absorption device and method for converting body waves into surface waves, which belongs to the design field of acousto-optic devices and is suitable for improving the absorption of sound field energy in the medium of the acousto-optic device, enhancing the uniformity of the optical properties of the medium of the acousto-optic device, thereby effectively controlling optical diffraction. Background Art

[0002] Acousto-optic devices are devices that utilize the elasto-optic effect in the acousto-optic medium, that is, the elastic strain in the sound field area causes the light to deflect, diffract, and change energy. They are widely used because of their advantages such as fast band switching, flexible switching, and no mechanical moving parts. In order to ensure that the sound field in the acousto-optic medium is relatively evenly distributed, the acousto-optic device mainly adopts the traveling wave working mode. To ensure that the sound wave in the acousto-optic device is a traveling wave, it is necessary to perform sound absorption operations at the acousto-optic medium interface in the direction of the sound wave to prevent the sound wave reflection from interfering with the incident sound wave.

[0003] At present, acousto-optic devices mainly use reflective sound absorption structures to reflect sound waves back to the interior of the acousto-optic medium in a manner that deviates from the main propagation direction. However, sound waves will diverge as the propagation distance increases, so it is inevitable to cause interference with the sound wave energy in the main propagation direction, thereby affecting the diffraction performance of the acousto-optic device. Therefore, in the design and processing of acousto-optic devices, it is necessary to consider optimizing the sound absorption structure of the sound reflection interface as much as possible.

[0004] To solve this problem, an acousto-optic device sound absorption device and method for converting body waves into surface waves are designed. The main body of the sound absorption device is a crystal with an acoustic impedance similar to that of the acousto-optic crystal of the acousto-optic device. The acoustic energy in the acousto-optic crystal is almost completely transmitted to the sound absorption crystal through the fixed surface. The method utilizes the characteristics of different incident angles and reflection angles at the interface of acoustic anisotropic crystals according to Snell's law. By changing the phase velocity angle and the angle of the sound absorption surface, the angle between the reflected sound wave group velocity direction and the normal line is greater than 90°, and the body wave is converted into a surface wave. The rapid dissipation characteristics of the surface wave are used to achieve the purpose of sound absorption of the acousto-optic device, thereby improving the influence of the reflected sound field interference on the acoustic wave body grating in the acousto-optic crystal of the traditional sound absorption structure. Summary of the invention

[0005] The purpose of the present invention is to provide an acousto-optic device sound absorption device and method for converting body waves into surface waves in order to solve the problem that the body grating distribution in the acousto-optic crystal is disturbed due to the reflection of sound waves in the acousto-optic device.

[0006] The technical solution of the present invention is as follows: the sound absorption device of the acousto-optic device adopts a crystal with similar acoustic impedance to the acousto-optic crystal of the acousto-optic device, and the acoustic energy in the acousto-optic crystal of the acousto-optic device is extracted through the fixed surface, and the acoustic energy is absorbed on the sound absorption surface; the sound velocity slowness curve of the sound wave on the acousto-optic crystal and the sound-optic interaction surface in the sound-absorbing crystal is calculated according to the material parameters of the acousto-optic crystal of the acousto-optic device, and the Snell law of the sound wave at the anisotropic crystal interface is used to calculate the phase velocity direction of the incident sound wave and the angle of the sound absorption surface when the angle between the group velocity direction of the reflected sound wave at the sound absorption surface of the sound absorption crystal and the normal line of the interface exceeds 90°; and the sound absorption surface angle is calculated according to the ultrasonic volume in the acousto-optic crystal of the acousto-optic device. The phase velocity direction of the wave is determined by Snell's law of sound waves at the interface of anisotropic crystals. The angle of the fixed surface of the sound-absorbing crystal and the acousto-optic crystal is calculated to make the phase velocity direction of the sound wave in the sound-absorbing crystal meet the design direction. The sound-absorbing crystal is cut according to the design angles of the fixed surface and the sound-absorbing surface, and fixedly connected with the acousto-optic crystal. The ultrasonic body wave is transmitted through the acousto-optic crystal to the sound-absorbing crystal, and propagates to the boundary of the sound-absorbing crystal with a specific phase velocity direction. At the boundary of the sound-absorbing crystal, the body wave is converted into a surface wave and rapidly attenuated and absorbed, thereby achieving the purpose of sound wave absorption. This improves the influence of the reflected sound field interference on the acoustic wave body grating in the acousto-optic crystal of the traditional sound-absorbing structure.

[0007] The present invention is an acousto-optic device sound absorption device and method for converting body waves into surface waves. The sound absorption device body of the acousto-optic device adopts a crystal with similar acoustic impedance to the acousto-optic crystal of the acousto-optic device, and the sound energy in the acousto-optic crystal of the acousto-optic device is guided out through a fixed surface, and the sound energy is absorbed on the sound absorption surface. The design steps of the sound absorption method are as follows:

[0008] (1) Calculate the sound velocity slowness curve of the sound wave on the sound-optic interaction surface in the sound-optic crystal and the sound-absorbing crystal according to the material parameters of the sound-optic crystal of the sound-optic device;

[0009] (2) Using the sound velocity slowness curve in step (1) and the Snell's law of sound waves at the anisotropic crystal interface, calculate the phase velocity direction of the incident sound wave and the angle of the sound absorbing surface when the angle between the group velocity direction of the reflected sound wave at the sound absorbing surface of the sound absorbing crystal and the normal line of the interface exceeds 90°;

[0010] (3) Using the sound velocity slowness curve in step (1), combined with the phase velocity direction of the ultrasonic body wave in the acousto-optic crystal of the acousto-optic device and the Snell law of the acoustic wave at the anisotropic crystal interface, calculate the angle between the sound absorbing crystal and the acousto-optic crystal fixed surface, so that the phase velocity direction of the acoustic wave in the sound absorbing crystal satisfies the direction calculated in step (2);

[0011] (4) Using the sound absorbing surface angle calculated in step (2) and the fixed surface angle calculated in step (3), the sound absorbing crystal is cut and fixedly connected with the acousto-optic crystal, so that the ultrasonic body wave is transmitted through the acousto-optic crystal into the sound absorbing crystal, propagates to the boundary of the sound absorbing crystal in a specific phase velocity direction, and is converted from a body wave to a surface wave at the boundary of the sound absorbing crystal and rapidly attenuates and absorbs, thereby achieving the purpose of sound wave absorption, thereby improving the influence of the reflected sound field interference on the acoustic wave body grating in the acousto-optic crystal of the traditional sound absorbing structure.

[0012] Wherein step (1) calculates the sound velocity slowness curve of the sound wave on the sound-optic interaction surface in the acousto-optic crystal and the sound-absorbing crystal according to the acousto-optic crystal material parameters of the acousto-optic device: the acousto-optic crystal and the sound-absorbing crystal have acoustic anisotropy, and the material parameters required for calculating the sound velocity slowness curve are the crystal density and the crystal elastic stiffness coefficient.

[0013] Wherein step (2) uses the sound velocity slowness curve in step (1) and the Snell's law of sound waves at the interface of anisotropic crystals to calculate the phase velocity direction of the incident sound wave and the angle of the sound absorbing surface when the angle between the group velocity direction of the reflected sound wave at the sound absorbing surface of the sound absorbing crystal and the normal line of the interface exceeds 90°: the ultrasonic body wave in the acousto-optic device is a horizontal shear wave mode, and the reflection at the interface will not generate shear waves and longitudinal waves of other modes; the sound absorbing crystal is an acoustic anisotropic crystal, the phase velocity changes with the direction, and there is a difference between the incident angle and the reflection angle of the sound wave; the phase velocity direction and the group velocity direction in the acousto-optic crystal have a walk-off angle due to acoustic anisotropy; the Snell's law of sound waves at the interface of anisotropic crystals is expressed as:

[0014]

[0015] in, , , are the incident phase velocity, reflected phase velocity and transmitted phase velocity at the interface, respectively. , , are the incident angle, reflection angle and transmission angle of the phase velocity at the interface respectively; the sound wave group velocity is the normal direction of the tangent line of the phase velocity corresponding to the sound velocity slowness curve position. The calculation makes the angle between the reflected sound wave group velocity direction and the interface normal exceed 90°. Since the sound absorbing surface of the sound absorbing crystal is in contact with the air and the shear wave cannot propagate in the air, it is converted into surface acoustic wave at the sound absorbing surface and rapidly attenuated and absorbed, thus achieving the purpose of sound wave absorption.

[0016] In step (3), the sound velocity slowness curve in step (1) is used to calculate the angle between the sound absorbing crystal and the acousto-optic crystal fixed surface by combining the phase velocity direction of the ultrasonic body wave in the acousto-optic crystal of the acousto-optic device and the Snell's law of the sound wave at the anisotropic crystal interface, so that the phase velocity direction of the sound wave in the sound absorbing crystal satisfies the direction calculated in step (2). In order to achieve the purpose of converting the body wave into the surface wave, the phase velocity direction usually needs to have a large angle with the

[110] axis of the crystal, and the angle between the normal line of the sound absorbing surface and the

[110] axis is also large, which affects the normal use of the acousto-optic device. In order not to affect the normal use of the acousto-optic device, it is necessary to transfer the sound energy to another anisotropic crystal of the same or similar material, as a sound absorbing crystal, to achieve the purpose of sound absorption by using angle cutting. In the fixed surface angle determines the phase velocity direction in the sound absorbing crystal, and the sound absorbing surface angle ensures that the body wave in the sound absorbing crystal is converted into a surface wave at the sound absorbing surface.

[0017] In step (4), the sound absorbing crystal is cut by using the sound absorbing surface angle calculated in step (2) and the fixing surface angle calculated in step (3), and the sound absorbing crystal is fixedly connected with the acousto-optic crystal, so that the ultrasonic body wave is transmitted through the acousto-optic crystal to the sound absorbing crystal, propagates to the boundary of the sound absorbing crystal in a specific phase velocity direction, and is converted from a body wave to a surface wave at the boundary of the sound absorbing crystal and rapidly attenuates and absorbs, thereby achieving the purpose of sound wave absorption, thereby improving the influence of the reflected sound field interference on the acoustic wave body grating in the acousto-optic crystal of the traditional sound absorbing structure: the sound absorbing crystal and the acousto-optic crystal are bonded by epoxy resin glue and fully cured to ensure that the two are rigidly fixed, and the thickness of the epoxy resin layer is much smaller than the wavelength of the sound. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of sound energy propagation in the sound-absorbing structure of the acousto-optic device. DETAILED DESCRIPTION

[0019] In order to better illustrate the purpose, technical solution and advantages of the present invention, the following is a clear and complete description of the implementation of the present invention in conjunction with the accompanying drawings, taking the mercurous bromide acousto-optic device bonded with mercurous chloride sound-absorbing crystal as an example, and the described embodiment is only a part of the embodiment of the present invention, rather than all the embodiments. The mercurous chloride crystal is the main body of the sound-absorbing device, and the sound energy in the mercurous bromide crystal is transmitted into the sound-absorbing device through the fixed surface, and is absorbed and dissipated on the mercurous chloride sound-absorbing surface. The specific sound absorption design method is as follows:

[0020] (1) The acousto-optic crystals used in acousto-optic devices are mostly acoustic anisotropic crystals. The density and elastic stiffness coefficient parameters of mercurous bromide and mercurous chloride are used to calculate the following: Figure 1 The slowness curve of the acousto-optic crystal interaction surface is shown.

[0021] (2) Using the sound velocity slowness curve in step (1) and Snell's law of sound waves at the anisotropic crystal interface, determine Figure 1 The angle between the phase velocity and the

[110] axis that enables the mercurous chloride sound absorbing surface to transform the body wave into the surface wave is , the angle between the sound absorbing surface and the

[001] axis is , where clockwise is positive and counterclockwise is negative: The ultrasonic wave in the acousto-optic device is a horizontal shear wave mode relative to the acousto-optic interaction surface, and the reflection at the interface will not generate other modes of shear waves and longitudinal waves, such as Figure 1 The phase velocity direction and the group velocity direction in the crystal shown have an angle due to acoustic anisotropy. The Snell law of acoustic waves at the anisotropic crystal interface can be expressed as:

[0022]

[0023] in, , , are the incident phase velocity, reflected phase velocity and transmitted phase velocity at the interface, respectively. , , are the incident angle, reflection angle and transmission angle of the phase velocity at the interface respectively; the acoustic group velocity is the normal direction of the tangent line of the phase velocity corresponding to the acoustic slowness curve position. The calculation makes the angle between the direction of the acoustic group velocity reflected by the mercurous chloride sound-absorbing surface and the interface normal exceed 90°. Since the sound-absorbing surface of the mercurous chloride crystal is in contact with the air and the shear wave cannot propagate in the air, it is converted into an acoustic surface wave at the sound-absorbing surface and rapidly attenuates and absorbs, achieving the purpose of acoustic wave absorption and improving the influence of the reflected sound field interference on the acoustic wave volume grating in the acousto-optic crystal.

[0024] (3) Using the sound velocity slowness curve in step (1), combined with the mercuric bromide acousto-optic device to transduce the ultrasonic cutting angle , the angle between the fixed surface of mercurous bromide and the

[001] axis According to Snell's law of acoustic waves on anisotropic crystal interfaces, the angle between the solid surface of mercurous chloride and the

[001] axis is calculated to be , so that the phase velocity in the sound-absorbing crystal satisfies the direction calculated in step (2): In order to achieve the purpose of converting body waves into surface waves, a larger phase velocity direction angle and sound-absorbing surface angle are required. In order not to affect the normal use of the acousto-optic device, the sound energy needs to be transferred from the mercurous bromide crystal to another acoustic anisotropic crystal of the same or similar material. Among them, mercurous chloride has excellent performance in terms of sound transmission coefficient and transmission angle. Therefore, mercurous chloride is selected as the sound-absorbing crystal, and the angle design of the sound-absorbing structure is carried out.

[0025] (4) The mercurous chloride crystal is cut according to the sound absorption surface angle calculated in step (2) and the bonding surface angle calculated in step (3), and the mercurous chloride crystal is bonded to the fixed surface of the mercurous bromide crystal using epoxy resin. The thickness of the epoxy resin layer is much smaller than the wavelength of the sound and is fully cured to ensure that the two are in a rigid connection condition, so that the body wave energy is converted into surface waves on the sound absorption surface of the sound absorption crystal. The purpose of sound wave absorption is achieved through the rapid attenuation absorption of the surface wave, thereby improving the influence of the reflected sound field of the traditional sound absorption structure on the sound wave body grating interference in the acousto-optic crystal.

Claims

1. A method for designing an acousto-optic device for converting bulk waves into surface waves, characterized in that: The main body of the sound absorbing device adopts a crystal with similar acoustic impedance to the acousto-optic crystal of the acousto-optic device, and the acoustic energy in the acousto-optic crystal of the acousto-optic device is exported to the sound absorbing crystal through the fixed surface, and the sound energy is absorbed and propagated to the boundary of the sound absorbing crystal in a specific phase velocity direction on the sound absorbing surface, and is converted from body waves to surface waves at the boundary of the sound absorbing crystal and rapidly attenuated and absorbed. The design method of the sound absorbing device includes the following steps: (1) Calculate the sound velocity slowness curve of the sound wave on the sound-optic interaction surface in the sound-optic crystal and the sound-absorbing crystal according to the material parameters of the sound-optic crystal of the sound-optic device; (2) Using the sound velocity slowness curve in step (1) and the Snell's law of sound waves at the anisotropic crystal interface, calculate the phase velocity direction of the incident sound wave and the angle of the sound absorbing surface when the angle between the group velocity direction of the reflected sound wave at the sound absorbing surface of the sound absorbing crystal and the normal line of the interface exceeds 90°; (3) Using the sound velocity slowness curve in step (1), combined with the phase velocity direction of the ultrasonic body wave in the acousto-optic crystal of the acousto-optic device and the Snell law of the acoustic wave at the anisotropic crystal interface, calculate the angle between the sound absorbing crystal and the acousto-optic crystal fixed surface, so that the phase velocity direction of the acoustic wave in the sound absorbing crystal satisfies the direction calculated in step (2); (4) Using the sound absorbing surface angle calculated in step (2) and the fixed surface angle calculated in step (3), the sound absorbing crystal is cut and fixedly connected with the acousto-optic crystal, so that the ultrasonic body wave is transmitted through the acousto-optic crystal to the sound absorbing crystal, propagates to the boundary of the sound absorbing crystal in a specific phase velocity direction, and is converted from a body wave to a surface wave at the boundary of the sound absorbing crystal and rapidly attenuated and absorbed, thereby achieving the purpose of sound wave absorption.

2. The method for designing an acousto-optic device for converting bulk waves into surface waves according to claim 1, wherein in step (1): the acousto-optic crystal and the sound-absorbing crystal have acoustic anisotropy, and the material parameters required for calculating the sound velocity slowness curve are the crystal density and the crystal elastic stiffness coefficient.

3. The method for designing a sound absorbing device for an acousto-optic device that converts bulk waves into surface waves according to claim 1, wherein in step (4): the sound absorbing crystal and the acousto-optic crystal are bonded by epoxy resin glue and fully cured to ensure that the two are rigidly connected and the thickness of the epoxy resin layer is much smaller than the wavelength of the sound.

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