A dual-diaphragm composite optical microphone

Abstract

The present invention relates to a double diaphragm composite optical microphone, which includes a packaging sleeve, a reflective diaphragm, a waveguide structure, and a single-mode optical fiber. One end of the packaging sleeve is open, and the interior of the packaging sleeve has a cavity extending horizontally. A through hole is provided at the other end of the packaging sleeve for the cavity; the reflective diaphragm is arranged at the open end of the packaging sleeve; the waveguide structure is accommodated in the cavity of the packaging sleeve, and the waveguide structure is connected to the reflective diaphragm; the single-mode optical fiber is accommodated in the cavity of the packaging sleeve through the through hole, and one end of the single-mode optical fiber is connected to the waveguide structure. The present invention adopts a double diaphragm structure composed of a single-mode optical fiber, a waveguide structure, and a reflective diaphragm. When there is an acoustic pressure effect, the reflective diaphragm and the waveguide structure deform simultaneously and the refractive index of the waveguide structure changes, so as to improve the acoustic pressure sensitivity and frequency response range of the sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of optical acoustic detection, and in particular to a double diaphragm composite optical microphone. Background Art

[0002] Acoustic detectors such as microphones and hydrophones are important information acquisition tools, which are widely used in many fields such as voice communication, environmental noise monitoring, detection and tracking of aircraft and underwater vehicles, bearing fault diagnosis, wind turbine measurement, oil and gas pipeline leakage monitoring, photoacoustic spectroscopy, etc. At present, the most common acoustic detector is the electret condenser microphone, which is relatively common in the market. However, the traditional electret condenser microphone has low sensitivity, weak anti-electromagnetic interference ability, and the metal diaphragm is prone to slow corrosion in the air, so it imposes certain limitations on the application of the electret condenser microphone. The fiber optical acoustic sensor (FOAS) has the advantages of being immune to electromagnetic interference, low transmission loss, and adapting to harsh environments, and has become an ideal substitute for electroacoustic sensors.

[0003] Common structures of FOAS include Michelson interferometer (MI), Mach–Zehnder interferometer (MZI), and Fabry–Pérot (FP) interferometer. Compared with sensors based on MI and MZI structures, the FOAS with FP interference structure has a more compact sensing structure and higher sensitivity, and can effectively detect weak sound signals.

[0004] Generally, the FP-type ultrasonic sensor structure based on the fiber end uses a single-mode fiber to fuse a capillary glass tube or a hollow fiber, and a reflective film is prepared on the end face of the capillary glass tube or the hollow fiber to form an FP resonant cavity. When the ultrasonic sound pressure acts on the film, the film will vibrate with the sound pressure, and the length of the FP cavity changes with the acoustic wave frequency. By demodulating the reflected light intensity, the corresponding acoustic wave information can be restored. Due to the excellent performance of the FP interferometer in the field of acoustic detection, FP optical microphones with different structures have received wide attention. For example, in 2017, Wu et al. developed a high-sensitivity fiber microphone based on graphene oxide film, which maintained a linear sound pressure response and a flat frequency response in the range of 100 Hz to 20 kHz; in 2018, Liu et al. designed an FP-type microphone based on a corrugated silver film, with a pressure sensitivity of 52 nm / Pa and a minimum detectable stress of 86.97 μPa / Hz 1 / 2 ; in the same year, Chen et al. designed an optical microphone with a diaphragm integrated cantilever beam structure, with a pressure sensitivity of up to 211.2 nm / Pa and a minimum detectable pressure of 5 μPa / Hz 1 / 2; In 2022, Wu et al. designed an FP-type microphone based on a tire-shaped glass diaphragm structure, which can effectively reduce air damping and improve sensitivity. Its pressure sensitivity is 755 mV / Pa@500 Hz, and the minimum detectable pressure is 251 μPa / Hz1 / 2.

[0005] The above various structures all detect sound waves by changing different diaphragm structures and materials. Although using thin films such as metals, polymers, and graphene to prepare the reflective film can effectively reduce the diaphragm thickness, the preparation process is relatively complex, with poor stability and high cost. Moreover, the structure only changes the phase information of the interference spectrum by changing the cavity length, and the sound pressure sensitivity cannot be further improved.

[0006] Therefore, there is an urgent need to propose a double-diaphragm composite optical microphone to solve the problems of low microphone response frequency, poor sensitivity, and narrow frequency bandwidth existing above. Summary of the Invention

[0007] To this end, the technical problem to be solved by the present invention is to overcome the problems existing in the prior art and propose a double-diaphragm composite optical microphone, which adopts a single-mode optical fiber, a waveguide structure, and a reflective diaphragm to form a double-film structure. When there is a sound pressure effect, the reflective diaphragm and the waveguide structure deform simultaneously and the refractive index of the waveguide structure changes to improve the sound pressure sensitivity and frequency response range of the sensor.

[0008] To solve the above technical problems, the present invention provides a double-diaphragm composite optical microphone, including:

[0009] A packaging sleeve with one end open, and the interior of the packaging sleeve has a laterally extending cavity, and a through hole is provided at the other end of the cavity of the packaging sleeve;

[0010] A reflective diaphragm, which is arranged at the open end of the packaging sleeve;

[0011] A waveguide structure, which is accommodated in the cavity of the packaging sleeve, and the waveguide structure is connected to the reflective diaphragm;

[0012] A single-mode optical fiber, which is accommodated in the cavity of the packaging sleeve through the through hole, and one end of the single-mode optical fiber is connected to the waveguide structure;

[0013] Wherein, the single-mode optical fiber, the reflective diaphragm, and the waveguide structure form a double Fabry-Perot resonator structure. When there is a sound pressure effect, the reflective diaphragm and the waveguide structure deform simultaneously and the refractive index of the waveguide structure changes to improve the sound pressure sensitivity and frequency response range of the sensor.

[0014] In an embodiment of the present invention, the reflective diaphragm, the waveguide structure, and the single-mode optical fiber are coaxially arranged.

[0015] In one embodiment of the present invention, the waveguide structure is connected to the single-mode optical fiber by means of curing fusion splicing or 3D printing.

[0016] In one embodiment of the present invention, the waveguide structure is cylindrical, the diameter of the cylindrical waveguide structure is set to be 10 μm to 100 μm, and the height is set to be 10 to 100 μm.

[0017] In one embodiment of the present invention, the end face of the single-mode optical fiber is parallel to the reflective diaphragm.

[0018] In one embodiment of the present invention, the reflective diaphragm is circular, and the diameter of the circular reflective diaphragm is set to be 80 to 120 μm.

[0019] In one embodiment of the present invention, the thickness of the circular reflective diaphragm is set to be 3 to 10 μm.

[0020] In one embodiment of the present invention, one end of the cavity is set to be horn-shaped, and the diameter of the horn-shaped port increases in the direction extending towards the reflective diaphragm.

[0021] In one embodiment of the present invention, the encapsulation sleeve is a glass sleeve.

[0022] In one embodiment of the present invention, the height of the encapsulation sleeve is set to be 20 to 30 mm.

[0023] The above technical solutions of the present invention have the following advantages compared with the prior art:

[0024] The present invention provides a double-diaphragm composite optical microphone, which adopts a single-mode optical fiber, a waveguide structure and a reflective diaphragm to form a double-film structure. When there is an acoustic pressure effect, the reflective diaphragm and the waveguide structure deform simultaneously and the refractive index of the waveguide structure changes, so as to improve the acoustic pressure sensitivity and frequency response range of the sensor. The overall size of this optical microphone is small, the size of the external encapsulation sleeve can be adjusted flexibly, it is immune to electromagnetic interference, has a wide detection frequency, and can meet the use in various harsh environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the content of the present invention be more clearly understood, the following further describes the present invention in detail according to the specific embodiments of the present invention and in conjunction with the accompanying drawings.

[0026] Figure 1 FIG. is a schematic structural diagram of a double-diaphragm composite optical microphone in an embodiment of the present invention.

[0027] Figure 2 FIG. is a simulation comparison diagram of a double-diaphragm composite optical microphone of the present invention and a traditional optical microphone with a diaphragm fixed around.

[0028] Among them, the reference numerals are explained as follows: 1. Single-mode optical fiber; 2. Reflective diaphragm; 3. Waveguide structure; 4. Encapsulation sleeve. Specific embodiments

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited are not intended to limit the present invention.

[0030] Please refer to Figure 1 As shown, an embodiment of the present invention provides a dual-diaphragm composite optical microphone, which includes an encapsulation sleeve 4, a reflective diaphragm 5, a waveguide structure 3, and a single-mode optical fiber 1. One end of the encapsulation sleeve 4 is open, and the interior of the encapsulation sleeve 4 has a cavity extending horizontally. A through hole is provided at the other end of the cavity in the encapsulation sleeve 4; the reflective diaphragm 2 is disposed at the open end of the encapsulation sleeve 4; the waveguide structure 3 is accommodated in the cavity of the encapsulation sleeve 4, and the waveguide structure 3 is connected to the reflective diaphragm 2; the single-mode optical fiber 1 is accommodated in the cavity of the encapsulation sleeve 4 through the through hole, and one end of the single-mode optical fiber 1 is connected to the waveguide structure 3.

[0031] This optical microphone has a dual-film composite structure. Among them, the waveguide structure 3 not only plays a role in connecting the single-mode optical fiber 1 and the reflective diaphragm 2. When an incident pressure wave acts on the reflective diaphragm 2, the reflective diaphragm 2 will deform. And due to the existence of the waveguide structure 3, the stiffness of the reflective diaphragm 2 will be improved. However, due to the deformation of the waveguide structure 3, and when the waveguide structure 3 transmits signal light, the effective refractive index will change, which further enhances the phase modulation and improves the sound pressure sensitivity in the response frequency range (low-frequency range) of the reflective diaphragm 2.

[0032] In a dual-diaphragm composite optical microphone proposed in an embodiment of the present invention, the reflective diaphragm 2, the waveguide structure 3 and the single-mode optical fiber 1 are coaxially arranged to jointly form a dual Fabry-Perot resonator structure. The signal light is guided by the single-mode optical fiber 1 and the waveguide structure 3. The reflective diaphragm 2 and the waveguide structure 3 are used as the acoustic wave sensing part. When there is an acoustic pressure, the reflective diaphragm 2 and the waveguide structure 3 deform simultaneously and the refractive index of the waveguide structure changes to improve the sound pressure sensitivity and frequency response range of the sensor.

[0033] The present invention provides a dual-diaphragm composite optical microphone, which consists of a single-mode optical fiber 1, a waveguide structure 3 and a reflective diaphragm 2 as sensitive elements. The waveguide structure 3 is located at the end face of the single-mode optical fiber 1. Its structure is compact, and the resonant frequency difference between the reflective diaphragm 2 and the cylindrical waveguide structure 3 is used to broaden the detected acoustic wave frequency range. Since the cylindrical waveguide structure 3 can increase the phase change, the sound pressure sensitivity of the microphone is greatly improved.

[0034] In a dual-diaphragm composite optical microphone proposed in an embodiment of the present invention, the frequency response range of the optical microphone is jointly determined by the reflective diaphragm 2 and the cylindrical waveguide structure 3. Among them, by adjusting the diameter and thickness of the reflective diaphragm 2, the low-frequency natural resonance frequency of the microphone can be directly controlled. Generally, the thicker the thickness of the reflective diaphragm 2 and the smaller the diameter, the larger the corresponding natural resonance frequency. At the same time, the larger the diameter and the smaller the height of the waveguide structure 3, the larger the corresponding natural resonance frequency. Since the natural resonance frequency of the cylindrical waveguide structure 3 is in the high-frequency range, which is much larger than the natural resonance frequency of the reflective diaphragm 2, compared with the diaphragm-type optical microphone, its frequency response range can be broadened.

[0035] Preferably, the material of the reflective diaphragm 2 can be materials such as silicon film, polymer film, metal film, etc., and the material of the waveguide structure 3 can be materials such as quartz, polymer, etc. The connection between the waveguide structure 3 and the single-mode optical fiber 1 is realized by methods such as fusion splicing or 3D printing. The diameter of the single-mode optical fiber 1 is 125 μm, the thickness of the reflective diaphragm 2 is 3 - 10 μm, and the diameter is 80 - 120 μm; the diameter of the cylindrical waveguide structure 3 is 10 - 100 μm, the height is 10 - 100 μm, and the length of the encapsulation sleeve 4 is 20 - 30 mm. The above geometric parameters and material properties can be appropriately adjusted according to the required detection frequency range.

[0036] The working principle of the present invention is based on the multi-beam interference principle. Among them, the single-mode optical fiber 1, the waveguide structure 3, and the reflective diaphragm 2 form a Fabry-Perot resonator. When the input signal light is input into the single-mode optical fiber 1, part of the light will be reflected back into the single-mode optical fiber 1 at the fiber end face, which is called the first reflected light; the reflectivity of the interface between the single-mode optical fiber 1 and the waveguide structure 3 is R 1 , so part of the light passes through the cylindrical waveguide structure 3, and reflection will also occur at the interface between the cylindrical waveguide structure 3 and the reflective diaphragm 2, which is called the second reflected light. The reflectivity of the interface between the cylindrical waveguide structure 3 and the reflective diaphragm 2 is R 2 , and when the forward transmitted light propagates, it will be reflected at the interface between the reflective diaphragm 2 and the external air and enter the cylindrical waveguide structure 3, which is called the third reflected light. The reflectivity of the interface between the reflective diaphragm 2 and the external air is R 3 . The intensity I R of the interference reflected light is expressed as follows:

[0037]

[0038] Among them, E 0 (λ) represents the intensity of the incident signal light, λ represents the wavelength of the signal light, A 1 and A 2 are the transmission coefficients between the interface of the single-mode optical fiber 1 and the cylindrical waveguide structure 3 and between the cylindrical waveguide structure 3 and the reflective diaphragm 2, and their expressions are respectively (1 - α 1 )(1 - R1 )(1 - α 1 )(1 - R 1 )(1 - α 2 )(1 - R 2 ), where α 1 and α 2 respectively represent the transmission loss factors, and respectively represent the phase difference between two adjacent reflected light beams, and their expressions are respectively and where n w and n m respectively represent the refractive indices of the cylindrical waveguide structure 3 and the reflective diaphragm 2, L w and L m respectively represent the height of the cylindrical waveguide structure 3 and the thickness of the reflective diaphragm 2. When the acoustic wave acts on the reflective diaphragm 2, the reflective diaphragm 2 will vibrate, and the corresponding thickness of the reflective diaphragm 2 is squeezed, and both L w and L m will change. At the same time, due to the change of the refractive index inside the Fabry - Perot cavity and the effective refractive index of the waveguide n w after extrusion, the phase of the reflected light changes, and the corresponding acoustic wave information is demodulated by demodulating the magnitude of the phase change.

[0039] In this embodiment, as Figure 2 the simulation comparison sets the diameter of the reflective diaphragm 2 to be 3 mm, the thickness to be 10 μm, and the height of the waveguide structure 3 to be 50 μm. After that, the displacement changes of the corresponding reflective diaphragm 2 and waveguide structure 3 are studied under different diameters of the waveguide structure 3. The simulation results show that for the diaphragm, the resonance frequency is much lower than 1 MHz, the waveguide resonance frequency is about 33 MHz. For the double - diaphragm compound optical microphone corresponding to different diameters of the waveguide structure 3, in the frequency range below 1 MHz, the corresponding displacement is significantly improved compared with the diaphragm - type optical microphone, and its response bandwidth in the high - frequency region is expanded.

[0040] The present invention proposes a double - diaphragm compound optical microphone, which adopts a double - film structure composed of a single - mode optical fiber 1, a waveguide structure 3, and a reflective diaphragm 2. When there is an acoustic pressure, the reflective diaphragm 2 and the waveguide structure 3 deform simultaneously and the refractive index of the waveguide structure 3 changes, so as to improve the acoustic pressure sensitivity and frequency response range of the sensor. The overall size of this optical microphone is small, the size of the external encapsulation sleeve 4 can be flexibly adjusted, immune to electromagnetic interference, with a wide detection frequency, and can meet the use in various harsh environments.

[0041] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A double-diaphragm composite optical microphone, characterized in that, it includes: A packaging sleeve with one end open. There is a cavity extending horizontally inside the packaging sleeve, and a through hole is provided at the other end of the cavity of the packaging sleeve; A reflective diaphragm, which is arranged at the open end of the packaging sleeve; A waveguide structure, which is accommodated in the cavity of the packaging sleeve, and the waveguide structure is connected to the reflective diaphragm; A single-mode optical fiber, which is accommodated in the cavity of the packaging sleeve through the through hole, and one end of the single-mode optical fiber is connected to the waveguide structure; Wherein, the single-mode optical fiber, the reflective diaphragm and the waveguide structure form a double Fabry-Perot resonant cavity structure. When there is an acoustic pressure effect, the reflective diaphragm and the waveguide structure deform simultaneously and the refractive index of the waveguide structure changes to improve the acoustic pressure sensitivity and frequency response range of the sensor; the reflective diaphragm, the waveguide structure and the single-mode optical fiber are coaxially arranged; one end of the cavity is set to be trumpet-shaped, and the diameter of the trumpet-shaped port increases in the direction extending towards the reflective diaphragm.

2. A double-diaphragm composite optical microphone according to claim 1, characterized in that: The waveguide structure and the single-mode optical fiber are connected by a curing fusion or 3D printing method.

3. A double-diaphragm composite optical microphone according to claim 1, characterized in that: The waveguide structure is cylindrical, the diameter of the cylindrical waveguide structure is set to be 10 μm to 100 μm, and the height is set to be 10 to 100 μm.

4. A double-diaphragm composite optical microphone according to claim 1, characterized in that: The end face of the single-mode optical fiber is parallel to the reflective diaphragm.

5. A double-diaphragm composite optical microphone according to claim 1 or 4, characterized in that: The reflective diaphragm is circular, and the diameter of the circular reflective diaphragm is set to be 80 to 120 μm.

6. A double-diaphragm composite optical microphone according to claim 5, characterized in that: The thickness of the circular reflective diaphragm is set to be 3 to 10 μm.

7. A double-diaphragm composite optical microphone according to claim 1, characterized in that: The packaging sleeve is a glass sleeve.

8. A double-diaphragm composite optical microphone according to claim 1, characterized in that: The height of the packaging sleeve is set to be 20 to 30 mm.

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