Acoustic sensing method and acoustic sensor based on photomechanical effect

Abstract

The present invention discloses an acoustic sensor based on the photoforce effect, comprising: an acoustic sensing module, in which spherical particles are captured by laser near the center of the inner cavity of a weighted housing. The weighted housing is in sync with the acoustic field medium, and the particles and the housing move relative to each other; a capture optical path module, in which the light beam emitted by the laser is coupled to an optical fiber to form a Gaussian beam that propagates in opposite directions and is precisely aligned, stably capturing the spherical particles in the center of the inner cavity; and a position detection module, in which the scattered light from the particles is received by an optical fiber to accurately detect the position of the particles in real time. The displacement information of the particles relative to the housing can be used to obtain the vibration information of the housing, and further obtain the vector information of the acoustic field. The single acoustic sensor based on the photoforce effect proposed by the present invention can simultaneously obtain complete scalar and vector information of the acoustic field. Theoretically calculated equivalent self-noise pressure of the corresponding acoustic sensor is far lower than the ambient noise spectrum level, which is of great significance in the field of low-noise acoustic field measurement.

Description

Technical Field

[0001] The present invention relates to the field of acoustic sensing technology, and in particular to an acoustic sensing method and an acoustic sensor based on a photomechanical effect. Background Art

[0002] Land-based acoustic detection technology has significant advantages in detecting low-altitude and ultra-low-altitude targets, forming a large-area early warning detection area. It uses multi-source data fusion technology and can be applied to long-range detection and positioning of targets such as stealth aircraft, and improve the reliability of regional reconnaissance and early warning.

[0003] The attenuation of sound waves in seawater is much smaller than that of electromagnetic waves. Therefore, sound waves are an effective tool for detecting targets and transmitting information in seawater. They play an important role in improving the modern navy's underwater communication, detection, target positioning, and tracking capabilities. They are also widely used in civilian applications such as navigation, marine environment monitoring, and the development of marine resources.

[0004] Acoustic transducers, which receive and convert acoustic signals into measurable signals, are called acoustic sensors. They play an indispensable role in studying the generation, radiation, propagation, reception, and measurement of sound waves, as well as issues related to target detection and information transmission. With the application of anechoic tiles, the continuous upgrading of power systems, and the rapid development of stealth technology for aircraft and spacecraft, the radiated noise source level of low-noise platforms has approached that of ambient noise, making highly sensitive sound field measurements increasingly urgent.

[0005] Quantum theory shows that a light beam is a stream of photons traveling at the speed of light, possessing both mass and momentum. When a light beam refracts and reflects off a particle's surface, the photons' momentum vector changes. According to the law of conservation of momentum, the particle's momentum vector also changes accordingly, indicating that the light beam exerts a force on the particle, known as the optical radiation force or optical force.

[0006] Optical tweezers utilize light radiation pressure to stably suspend optical medium particles in a gas-liquid environment. This optical suspension reduces interference from environmental factors such as clamping thermal noise, which is unavoidable with traditional oscillators. The optical interference method itself provides a means of detecting displacements with high spatial and temporal resolution. Therefore, optical tweezers have a wide range of applications in cell biology, weak force sensing, and quantum physics. In weak force sensing applications, optical tweezers in low-pressure gas can measure extremely weak accelerations, making them a critical requirement in areas such as non-Newtonian gravity verification and ultra-precision navigation. Currently, nanometer-level precision measurements have been achieved. Summary of the Invention

[0007] In order to overcome the shortcomings of the existing technology and meet the urgent needs of current acoustic detection technology for long-distance detection and positioning of stealth targets, the present invention provides an acoustic sensing method and acoustic sensor based on the photomechanical effect.

[0008] The technical solution of the present invention to achieve its technical purpose is as follows:

[0009] An acoustic sensing method based on the photomechanical effect couples the particle vibration velocity of the acoustic field medium into the relative displacement of the particles in the photomechanical system, and performs vector measurement of the ambient sound field through the photomechanical effect.

[0010] The environment is water, and the average density of the optical force system sensor module is the same as that of water, so that the optical tweezers counterweight shell and the water vibrate simultaneously, and the size of the optical tweezers sensor module does not affect the distribution and propagation of the sound field; the sound field drives the counterweight shell to vibrate, and the captured particles undergo relative displacement under the action of inertia; the relative vibration information of the particles reflects the vibration velocity information of the particles in the sound field, and the scalar and vector information of the sound field is obtained based on the real-time detection information of the particle displacement in three orthogonal directions.

[0011] An acoustic sensor based on photomechanical effect, comprising: an acoustic sensing module, a capture optical path module, and a position detection module;

[0012] The acoustic sensing module comprises a weighted housing and spherical particles, which are captured in the center of the inner cavity of the weighted housing. Density matching ensures that the average density of the weighted housing and its internal component assembly is the same as that of the measured acoustic field medium. The weighted housing and the acoustic field medium are in resonance, and inertia causes the particles in the cavity to move relative to the housing.

[0013] The capture optical path module includes a laser, a coupling optical fiber, and a beam adjustment lens. The light beam emitted by the laser enters the counterweight housing through the coupling optical fiber and forms a Gaussian beam that propagates in opposite directions and is aligned after passing through the beam adjustment lens, stably capturing the spherical particles in the center of the inner cavity.

[0014] The position detection module includes an imaging lens, a receiving optical fiber, and a detector. The scattered light of the spherical particles is coupled into the receiving optical fiber through the imaging lens, passes through the counterweight shell, and is received by the detector, which plays the role of real-time detection of the particle position. The displacement information of the spherical particles relative to the counterweight shell can be used to obtain the vibration information of the counterweight shell, and then the vector information of the sound field in which they are located can be obtained.

[0015] The counterweight shell is a spherical or cylindrical sealing structure with an optical fiber sealing interface, which allows the optical fiber to pass through the shell wall while preventing the measured sound field medium from entering the inner cavity of the counterweight shell.

[0016] The counterweight shell material is a single material, or a composite multi-layer material with matching average density.

[0017] The diameter of the spherical particles is greater than or equal to 1 micron, and the material of the spherical particles includes silicon and silicon dioxide.

[0018] The capture center formed by the Gaussian beam coincides with the center of the inner cavity of the counterweight housing.

[0019] The detector includes a CCD or QPD high-sensitivity photodetector.

[0020] The axis of the detection beam is perpendicular to the axis of the capture beam.

[0021] The present invention has at least the following beneficial effects:

[0022] The acoustic sensor based on the photomechanical effect proposed in this invention uses optical suspension to reduce the interference of environmental factors such as clamping thermal noise that is difficult to avoid with traditional oscillators. The optical interference method itself provides a displacement detection method with high spatial and temporal resolution. Therefore, optical tweezers technology can measure extremely weak accelerations, and the corresponding acoustic sensor equivalent self-noise pressure is far lower than the ambient noise spectrum level, which is of great significance in the field of low-noise measurement.

[0023] The acoustic sensor based on the photoforce effect proposed in the present invention is essentially a vector acoustic sensor. A single sensing unit can simultaneously obtain complete scalar and vector information of the sound field. Through the cross-correlation processing of this information, it can greatly suppress interference, improve the signal-to-noise ratio, extend the signal processing space, and be more conducive to the recognition of multiple targets in the far field. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 1 is a schematic diagram of a dual-beam light trap proposed in an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the force acting on particles in a Gaussian beam according to an embodiment of the present invention.

[0026] Figure 3 FIG. 4 is a schematic diagram of a module of a photomechanical effect acoustic sensor proposed in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] The optical force on the particle is divided into two parts: gradient force and scattering force. The gradient force is proportional to the light field gradient. In a focused light beam, a gradient force field pointing to the beam focus center can be obtained. The scattering force is proportional to the light intensity and is along the light beam propagation direction. In a focused light beam, its effect is to push the particle along the laser direction. Therefore, in a single light beam field, it is possible to capture the particle only if the gradient force in the light propagation direction is designed to be greater than the scattering force. Figure 1 In the dual-beam optical field shown, the scattering forces of the two counter-propagating beams on the trapped particles cancel each other out, significantly expanding the diameter of the captured particles, allowing them to capture particles with radii ranging from tens of nanometers to tens of microns, further improving acceleration sensitivity. Due to the radiation force of light, the counter-propagating beams can capture particles within a certain area, stabilizing them in a specific position. This area is called a light trap.

[0028] For the large-sized microspheres described in the present invention, the geometric optics method can be used to calculate the light momentum transferred by each refraction and reflection by ray tracing, and the scattering force along the propagation direction of the light beam can be approximately solved. F s and the gradient force pointing in the direction of stronger light intensity F g , as shown in formulas (1) and (2).

[0029]

[0030] In the formula P To capture optical power, n 1 P / c is the incident light momentum per second in the medium, α is the angle of incidence, γ is the refraction angle, R and T are the Fresnel reflection and refraction coefficients of the granular medium surface, respectively.

[0031] By integrating the optical force generated by each refraction and reflection, the optical field force on the particles can be calculated.

[0032] Taking the particles on the optical axis of a Gaussian beam as an example, the size of the sensing particles in the present invention is larger than the wavelength of light, so the Mie particle ray optical model is used to analyze the force on them, as shown in the following example: Figure 2 As shown in Figure 2, the radial optical force of the fundamental mode Gaussian beam on the particle in the homogeneous medium is 0, and the axial optical force is expressed as Equation (3).

[0033] (3)

[0034] coefficient q s and q g They are calculated by formula (4) and formula (5) respectively.

[0035] (4)

[0036] (5)

[0037] in F z is the axial optical force in the light emission direction, n 1 is the refractive index of the medium, P is the optical power, c is the speed of light in vacuum, r 0 is the particle radius, φ for Figure 2 Microelement B Deviation in the vertical planex The angle of the axis, θ is a microelement B The angle between the radius and the optical axis, r is a microelement B The distance to the optical axis, ω is a microelement B The spot radius at R z The intersection of the incident light and the optical axis along the optical axis to the infinitesimal element B The distance to the vertical axis plane, α is the angle of incidence, γ is the refraction angle, R and T are the Fresnel reflection and refraction coefficients of the granular medium surface, R c is the curvature radius of the beam surface, and the distance from the beam waist on the optical axis is z of microelement R c Calculated by equations (6) and (7), the radius of curvature of the wavefront of the infinitesimal element not on the optical axis is obtained by the iterative method, where ω 0 is the spot radius of the beam waist, λ 0 is the wavelength of vacuum light.

[0038] (6)

[0039] (7)

[0040] It can be seen from formula (3) that two precisely aligned opposing Gaussian beams can capture the particles. Compared with traditional oscillators, optical suspension reduces the interference of environmental factors such as clamping thermal noise.

[0041] For the above-mentioned light trap to capture particles, if the ambient sound field is coupled to the acceleration of the particles in the light trap, the ambient sound field can be measured through the light trap. Figure 1 By density-matching the light trap housing and its internal components, the average density is made equal to that of the acoustic field medium being measured. The counterweighted light trap housing resonates with the acoustic field medium. According to general relativity, ambient vibrations cause the captured particles to move relative to the housing. By measuring this position, the ambient vibration can be sensed.

[0042] by Figure 1Taking a pair of precisely aligned, counter-propagating Gaussian beams as an example, the particle achieves force equilibrium in the trap, with all three orthogonal directions oscillating around the center. When the measured acoustic field causes the relative position between the particle and the beam to change, the relative displacement of the particle can be measured to calculate the acceleration of the particle in that direction in the inertial coordinate system caused by the measured physical quantity.

[0043] On the other hand, under free-field conditions, the sound pressure P 0 Acceleration of the medium in which the sound propagates a 0 The following relationship is satisfied:

[0044] (8)

[0045] in ω a is the angular frequency of the sound wave, ρ 0 is the density of the liquid being measured, c 0 is the sound velocity in the measured liquid. From formula (8), we can know that the sound pressure can be calculated by measuring the vector vibration acceleration of the sound propagation medium.

[0046] The simulation results of the acoustic pressure sensitivity of a hydrophone based on the optical force effect provide the foundation for other acoustic performance simulations and designs. Therefore, when selecting an optical force calculation model, it is important to consider its applicability. If the designed particle size is smaller than the wavelength of light, the optical force calculation should be performed using the Rayleigh scattering model. If the designed particle size is comparable to the wavelength of light, the electromagnetic scattering model should be used instead.

[0047] like Figure 3 As shown, the present invention provides an acoustic sensor based on the photomechanical effect, comprising:

[0048] The acoustic sensing module is mainly composed of a counterweight shell and spherical particles. The spherical particles are located near the center of the inner cavity of the counterweight shell. Through density matching, the average density of the counterweight shell and its internal component assembly is made the same as the measured sound field medium. The counterweight shell and the sound field medium are in resonance, and inertia causes the particles in the cavity and the shell to have relative motion; the capture optical path module is mainly composed of a laser, a coupling optical fiber, and a beam adjustment lens. The light beam emitted by the laser enters the counterweight shell through the coupling optical fiber, and after passing through the beam adjustment lens, it forms a Gaussian beam that propagates in opposite directions and is precisely aligned, stably capturing the spherical particles near the center of the inner cavity; the position detection module is mainly composed of an imaging lens, a receiving optical fiber, and a detector. The scattered light of the ball is coupled into the receiving optical fiber through the imaging lens, and is received by the detector after passing through the counterweight shell, which plays the role of real-time and accurate detection of the particle position. The vibration information of the shell can be obtained through the displacement information of the particle relative to the shell, and then the vector information of the sound field can be obtained.

[0049] The counterweight housing is a spherical or cylindrical sealing structure with an optical fiber sealing interface, which allows the optical fiber to pass through the housing wall while preventing the measured sound field medium from entering the counterweight housing cavity. The counterweight housing material can be a single material or a composite multi-layer material with matching average density.

[0050] The spherical particles have a diameter greater than or equal to 1 micron, are made of silicon or silicon dioxide, and have properties that meet the capture requirements of a light trap. The center of the light trap formed by the Gaussian beam coincides with the center of the inner cavity of the counterweight housing. The detector comprises a CCD or QPD high-sensitivity photodetector. The axis of the detection beam is perpendicular to the axis of the capture beam.

[0051] During actual production, it is necessary to combine the photomechanical effect and sealing requirements to carry out the process design of the photomechanical effect acoustic sensor. Based on the properties of the selected counterweight shell material, the micromachining method is optimized to process the complex structure inside the counterweight shell, while ensuring the microstructure machining accuracy and avoiding the influence of machining stress on the structural accuracy. Design the alignment assembly equipment of the counterweight shell, transmission optical fiber, and lens to ensure that the transmission optical fiber, lens, and the internal cavity of the shell are coaxial. Encapsulate the sensing particles inside the shell, and constrain the movement range of the particles through the internal structure size to improve the particle capture efficiency. In order to meet the needs of the acoustic sensing environment, the encapsulation glue is optimized to ensure the pressure resistance and sealing requirements while ensuring the bonding strength, and at the same time increase the sealing performance of the structural joints through the sealing structure.

[0052] The acoustic sensor based on the photomechanical effect proposed in this invention uses optical suspension to reduce the interference of environmental factors such as clamping thermal noise that is difficult to avoid with traditional oscillators. The optical interference method itself provides a displacement detection method with high spatial and temporal resolution. Therefore, optical tweezers technology can measure extremely weak accelerations, and the corresponding acoustic sensor equivalent self-noise pressure is far lower than the ambient noise spectrum level, which is of great significance in the field of low-noise measurement.

[0053] The acoustic sensor based on the photoforce effect proposed in the present invention is essentially a vector acoustic sensor. A single sensing unit can simultaneously obtain complete scalar and vector information of the sound field. Through the cross-correlation processing of this information, it can greatly suppress interference, improve the signal-to-noise ratio, extend the signal processing space, and be more conducive to the recognition of multiple targets in the far field.

Claims

1. An acoustic sensor based on photomechanical effect, characterized in that: include: Acoustic sensing module, capture optical path module, position detection module; The acoustic sensing module comprises a weighted housing and spherical particles, which are captured in the center of the inner cavity of the weighted housing. Density matching ensures that the average density of the weighted housing and its internal component assembly is the same as that of the measured acoustic field medium. The weighted housing and the acoustic field medium are in resonance, and inertia causes the particles in the cavity to move relative to the housing. The capture optical path module includes a laser, a coupling optical fiber, and a beam adjustment lens. The light beam emitted by the laser enters the counterweight housing through the coupling optical fiber and forms a Gaussian beam that propagates in opposite directions and is aligned after passing through the beam adjustment lens, stably capturing the spherical particles in the center of the inner cavity. The position detection module includes an imaging lens, a receiving optical fiber, and a detector. The scattered light of the spherical particles is coupled into the receiving optical fiber through the imaging lens, passes through the counterweight shell, and is received by the detector, which plays the role of real-time detection of the particle position. The displacement information of the spherical particles relative to the counterweight shell can be used to obtain the vibration information of the counterweight shell, and then the vector information of the sound field in which they are located can be obtained.

2. The acoustic sensor based on the photomechanical effect according to claim 1, wherein: The counterweight shell is a spherical or cylindrical sealing structure with an optical fiber sealing interface, which allows the optical fiber to pass through the shell wall while preventing the measured sound field medium from entering the inner cavity of the counterweight shell.

3. The acoustic sensor based on photomechanical effect according to claim 1, wherein: The counterweight shell material is a single material, or a composite multi-layer material with matching average density.

4. The acoustic sensor based on photomechanical effect according to claim 1, wherein: The diameter of the spherical particles is greater than or equal to 1 micron, and the material of the spherical particles includes silicon and silicon dioxide.

5. The acoustic sensor based on photomechanical effect according to claim 1, wherein: The capture center formed by the Gaussian beam coincides with the center of the inner cavity of the counterweight housing.

6. The acoustic sensor based on photomechanical effect according to claim 1, wherein: The detector includes a CCD or QPD high-sensitivity photodetector.

7. The acoustic sensor based on photomechanical effect according to claim 1, wherein: The axial direction of the detection light beam of the receiving optical fiber is perpendicular to the axial direction of the capture light beam.

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