CN118010147A - Optical fiber microphone and microphone system based on microstructure cantilever beam - Google Patents

Abstract

The present invention discloses an optical fiber microphone and a sound transmission system based on a microstructure cantilever beam, comprising: a diaphragm, a rectangular through hole is opened at the middle position of the diaphragm; a microstructure cantilever beam, the microstructure cantilever beam is arranged in the rectangular through hole, connected to the wide side of the rectangular through hole, and is arranged to swing in a direction perpendicular to the surface of the diaphragm under the action of sound waves; wherein the microstructure cantilever beam comprises a first beam arm and a second beam arm connected to each other, the end of the first beam arm is arranged to be connected to the wide side of the rectangular through hole, and the second beam arm is a free end; the width of the second beam arm is greater than the width of the first beam arm, the length of the second beam arm is less than the length of the first beam arm, and the geometric center of the second beam arm overlaps with the geometric center of the diaphragm. The optical fiber microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention can maintain an effective reflective area while reducing the size of the cantilever beam, can improve sensitivity by reducing the equivalent spring coefficient of the cantilever beam, and can also improve the frequency response bandwidth by reducing the equivalent mass.

Description

Optical fiber microphone and sound transmission system based on microstructure cantilever beam

Technical Field

The invention belongs to the technical field of sound wave signal perception, and in particular relates to an optical fiber microphone and a sound transmission system based on a microstructure cantilever beam.

Background technique

A microphone is a transducer that can convert sound energy into electrical energy. It is widely used in mobile communications, hearing aids, ultrasonic medical treatment and other fields. Traditional electronic microphones such as condenser and electret microphones represent the latest technology, but they generally have limitations such as insufficient sensitivity, high electrical noise, and susceptibility to electromagnetic interference, making them difficult to apply to complex industrial sites. Therefore, it is urgent to develop a new microphone based on new principles and new structures.

Fiber optic microphones have attracted widespread attention due to their compact structure, high sensitivity, and easy processing. Fiber optic microphones use the Fabry-Perot (F-P) interference principle to establish an "acoustic signal-optical signal-electrical signal" energy conversion mechanism. Its main structure consists of a ceramic ferrule at the end of the optical fiber and a rigid diaphragm. When working, the incident light is injected by the optical fiber and is reflected multiple times on the end face of the ceramic ferrule and the inner side of the rigid diaphragm to form F-P interference; when the external sound wave signal acts on the rigid diaphragm, the surface of the rigid diaphragm undergoes elastic deformation, causing the phase of the interference light to change. The interference light with phase change is received by a highly sensitive photodetector and converted into a voltage signal output.

In the current F-P microphone diaphragm design, the introduction of a cantilever beam structure can further improve the sensitivity of the microphone. The bending deformation of the cantilever beam is 10 times greater than the tensile deformation of an ordinary circular diaphragm, and the response is more sensitive and linear. At present, ordinary rectangular cantilever beams usually adopt the method of increasing the length of the cantilever beam and reducing the width and thickness, so that it can produce a larger deformation under the same sound pressure, thereby improving its sensitivity. However, this optimization method faces two limitations: First, the cantilever beam needs to retain a certain reflective area so that it can reflect light and form F-P interference, so the size cannot be infinitely reduced to improve sensitivity; second, there is a performance trade-off when optimizing the sensitivity and frequency response of the cantilever beam. Although increasing the length and reducing the width and thickness improves the sensitivity, it will also significantly reduce the resonant frequency of the cantilever beam, thereby significantly reducing the frequency response bandwidth of the microphone.

Summary of the invention

In view of this, some embodiments disclose a fiber optic microphone based on a microstructure cantilever beam, comprising:

A diaphragm, wherein a rectangular through hole is provided in the middle of the diaphragm;

A microstructure cantilever beam, the microstructure cantilever beam is arranged in the rectangular through hole, connected to the wide side of the rectangular through hole, and is arranged to swing in a direction perpendicular to the diaphragm surface under the action of sound waves;

The microstructure cantilever beam comprises a first beam arm and a second beam arm connected to each other, the end of the first beam arm is connected to the wide side of the rectangular through hole, and the second beam arm is a free end;

The width of the second beam arm is greater than that of the first beam arm, the length of the second beam arm is less than that of the first beam arm, and the geometric center of the second beam arm overlaps with the geometric center of the diaphragm.

In the fiber optic microphone based on the microstructure cantilever beam disclosed in some embodiments, the ratio of the length of the first beam arm to the second beam arm is greater than or equal to 3:1; and the ratio of the width of the first beam arm to the second beam arm is less than or equal to 1:2.

Some embodiments disclose an optical fiber microphone based on a microstructure cantilever beam, wherein the microstructure cantilever beam is a symmetrical structure; wherein the first beam arm is a slender symmetrical structure, and the second beam arm is a short and wide symmetrical structure.

In some embodiments of the fiber optic microphone based on the microstructure cantilever beam disclosed, the resonant frequency _f0 of the microstructure cantilever beam is expressed as:

In the above formula, k _eff is the equivalent spring coefficient of the microstructure cantilever beam, and m _eff is the equivalent mass of the microstructure cantilever beam;

Among them, the equivalent spring coefficient k _eff of the microstructure cantilever beam is expressed as:

In the above formula, E is the Young's modulus of the microstructure cantilever beam, W is the equivalent width of the microstructure cantilever beam, and L is the equivalent length of the microstructure cantilever beam.

In some embodiments of the fiber optic microphone based on the microstructure cantilever beam disclosed, the sensitivity S _m of the microstructure cantilever beam is expressed as:

S _m = Δz/ΔP

In the above formula, Δz is the displacement of the free end of the microstructure cantilever beam when the external sound pressure P acts uniformly on the surface of the microstructure cantilever beam;

Where Δz is expressed as:

In the above formula, I is the moment of inertia of the microstructure cantilever beam, I=h ³ W/12, and h is the thickness of the microstructure cantilever beam.

Some embodiments disclose a fiber optic microphone based on a microstructure cantilever beam, further comprising:

A base, wherein a first through cavity is formed in the middle of the base;

A bracket, which is arranged above the base and used to support the diaphragm; a second through cavity is opened in the middle of the bracket, and the first through cavity is connected to the second through cavity; when the diaphragm is adapted and arranged on the bracket, the microstructure cantilever beam corresponds to the second through cavity;

A fixing plate is arranged above the bracket and is used to cooperate with the bracket to fix the diaphragm; a third through cavity is opened in the middle of the fixing plate, and the third through cavity corresponds to the second through cavity;

The optical fiber and the ceramic ferrule are adapted to be arranged in the first through cavity; an F-P interference cavity is formed between the optical fiber and the ceramic ferrule and the microstructure cantilever beam.

In the optical fiber microphone based on the microstructure cantilever beam disclosed in some embodiments, a pressure balance hole is provided on the side wall of the base for connecting the first through cavity with the outside of the base.

In the optical fiber microphone based on the microstructure cantilever beam disclosed in some embodiments, the diameters of the first through cavity, the second through cavity and the third through cavity are the same.

In some embodiments, the optical fiber microphone based on the microstructure cantilever beam is disclosed, and the optical sensitivity Si of the optical fiber microphone _is expressed as:

In the above formula, _R1 is the reflectivity of the optical fiber and the ceramic ferrule, _R2 is the reflectivity of the microstructure cantilever beam; _Ii is the intensity of the incident light; λ is the wavelength of the incident light; Lc is the static cavity length of the FP interferometer cavity.

Some embodiments disclose a fiber optic acoustic transmission system based on a microstructure cantilever beam, comprising the above-mentioned fiber optic microphone.

The optical fiber microphone and sound transmission system based on the microstructure cantilever beam disclosed in the embodiment of the present invention, the first beam arm of the microstructure cantilever beam is set as a slender structure to reduce the equivalent spring coefficient of the cantilever beam, so that it is easy to deform under sound waves and has excellent sensitivity; the second beam arm of the microstructure cantilever beam is reduced in size on the basis of ensuring the reflective surface, reducing the equivalent mass of the microstructure cantilever beam, improving the problem of the reduction of the resonant frequency caused by the shape of the first beam arm, thereby improving the frequency response bandwidth of the optical fiber microphone. The optical fiber microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention can maintain the effective reflective area while reducing the size of the cantilever beam, can improve the sensitivity by reducing the equivalent spring coefficient of the cantilever beam, and can also improve the frequency response bandwidth by reducing the equivalent mass. The optical fiber microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention can be applied to the detection of weak sound wave signals, and can also be used in industrial environments with strong electromagnetic interference. The optical sound transmission system based on the microstructure cantilever beam disclosed in the embodiment of the present invention has a simple structure, low manufacturing cost, anti-electromagnetic interference, and long detection distance, and has good application prospects in the field of sound wave detection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a microstructure cantilever beam in Example 1;

FIG2 is a schematic diagram of the mechanical deformation principle of the microstructure cantilever beam of Example 1;

FIG3 is a schematic structural diagram of a microstructure cantilever beam according to Embodiment 2;

FIG4 is a schematic structural diagram of a microstructure cantilever beam according to Embodiment 3;

FIG5 is a schematic structural diagram of an optical fiber microphone based on a microstructure cantilever beam according to Embodiment 4;

FIG6 is a schematic diagram of the working principle of the optical fiber microphone based on the microstructure cantilever beam of Example 4;

FIG7 is a schematic structural diagram of an optical fiber sound transmission system based on a microstructure cantilever beam in Example 5;

FIG8 is a frequency response curve diagram of cantilever beams with different structures in Example 6;

FIG9 is a frequency response curve diagram of cantilever beams with different structures in Example 7;

FIG10 is a frequency response curve diagram of cantilever beams with different structures in Example 8;

FIG11 is a graph showing the real-time output voltage of the optical fiber microphone based on the microstructure cantilever beam under different sound pressures in Example 9;

FIG12 is a fitting curve of the output voltage of the optical fiber microphone based on the microstructure cantilever beam under different sound pressures in Example 10;

FIG13 is a frequency response diagram of the optical fiber microphone based on the microstructure cantilever beam of Example 11.

Reference numerals

1 Diaphragm 11 Rectangular through hole

2 Microstructure cantilever beam 21 First beam arm

22 Second beam arm 3 Fixing plate

31 Third through cavity 4 Bracket

41 Second cavity 5 Base

51 First cavity 6 Optical fiber and ceramic ferrule

7 Gasket

Detailed ways

The word "embodiment" used here as an "exemplary" does not necessarily mean that any embodiment described is superior to or better than other embodiments. Unless otherwise specified, the performance index tests in the embodiments of this application are performed using conventional test methods in the art. It should be understood that the terms described in this application are only used to describe specific implementation methods and are not used to limit the content disclosed in this application.

Unless otherwise specified, the technical and scientific terms used in this document have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

The terms "substantially" and "approximately" used herein are used to describe small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. The numerical data represented or presented in the range format herein are used only for convenience and brevity, and should therefore be flexibly interpreted as including not only the values clearly listed as the limits of the range, but also all independent values or sub-ranges contained in the range. For example, the numerical range of "1-5%" should be interpreted as including not only the clearly listed values of 1% to 5%, but also the independent values and sub-ranges within the range shown. Therefore, independent values such as 2%, 3.5% and 4% and sub-ranges such as 1%-3%, 2%-4% and 3%-5% are included in this numerical range. This principle also applies to the range of only one numerical value. In addition, such an interpretation applies regardless of the width of the range or the characteristics described.

In this document, including in the claims, transitional words such as "comprises," "includes," "with," "having," "containing," "involving," "accommodating," etc. are understood to be open-ended, i.e., meaning "including but not limited to." Only the transitional words "consisting of" and "composed of" are closed transitional words.

In order to better illustrate the content of the present application, numerous specific details are given in the specific examples below. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present application.

Under the premise of no conflict, the technical features disclosed in the embodiments of the present application can be arbitrarily combined, and the obtained technical solutions belong to the contents disclosed in the embodiments of the present application. It should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like mentioned in the present application indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the technical features and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention, unless it conflicts with the context. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance, unless it conflicts with the context.

In some embodiments, the fiber optic microphone based on a microstructured cantilever beam comprises:

The diaphragm has a rectangular through hole in the middle of the diaphragm. Usually, the diaphragm has a suitable thickness and size, and can generate vibrations perpendicular to its surface under the action of sound waves. Usually, the diaphragm has a symmetrical structure, such as a rectangle, a square, a polygon, a circle, etc. Generally, the diameter of the diaphragm is in the millimeter order, the thickness is in the micrometer order, and the width of the rectangular through hole is in the micrometer order. The rectangular through hole is arranged in the middle of the diaphragm, which can effectively prevent the swing of the microstructure cantilever beam arranged in the rectangular through hole from being hindered by the surrounding environment and affecting the detection result.

A microstructure cantilever beam, wherein the microstructure cantilever beam is arranged in a rectangular through hole, connected to the wide side of the rectangular through hole, and is arranged to swing in a direction perpendicular to the surface of the diaphragm under the action of sound waves; usually, the diaphragm is fixed on a bracket so that the microstructure cantilever beam is in a free state, an external sound field is applied to the microstructure cantilever beam, and the microstructure cantilever beam located in the middle of the diaphragm undergoes continuous deformation under the action of the sound wave pressure, and the microstructure cantilever beam swings in a direction perpendicular to the surface of the diaphragm, converting the sound wave signal into a mechanical vibration signal, thereby realizing the conversion of sound wave energy into mechanical vibration energy; in some embodiments, the microstructure cantilever beam has a suitable thickness, shape and size; in some embodiments, the length of the microstructure cantilever beam is 2 mm and the width is 0.5 mm;

The microstructure cantilever beam includes a first beam arm and a second beam arm connected to each other, the end of the first beam arm is connected to the wide side of the rectangular through hole, the second beam arm is a free end, and the center of the second beam arm coincides with the center of the diaphragm; in some embodiments, the first beam arm, the second beam arm and the diaphragm are an integrally formed structure;

The width of the second beam arm is greater than that of the first beam arm, the length of the second beam arm is less than that of the first beam arm, and the geometric center of the second beam arm overlaps with the geometric center of the diaphragm.

In some embodiments, the microstructure cantilever beam is a symmetrical structure; generally, the symmetrical structure is conducive to regular deformation under the action of sound waves, and then regular swinging, which is conducive to improving the response stability to the sound wave signal; wherein, the first beam arm is a slender symmetrical structure, and the second beam arm is a short and wide symmetrical structure. The first beam arm is set as a slender symmetrical structure, which can reduce the equivalent spring coefficient of the microstructure cantilever beam, thereby improving the sensitivity of the microstructure cantilever beam, and the second beam arm is set as a short and wide symmetrical structure, which can reduce the equivalent mass of the microstructure cantilever beam on the basis of ensuring the reflective area of the microstructure cantilever beam, thereby improving the resonant frequency of the microstructure cantilever beam.

In some embodiments, while ensuring the reflective area of the microstructure cantilever beam, the size of the second beam arm is gradually reduced, which can reduce the equivalent mass of the microstructure cantilever beam, increase the resonant frequency of the microstructure cantilever beam, and improve the bandwidth of the optical fiber microphone without affecting the sensitivity of the microstructure cantilever beam.

In some embodiments, the first beam arm is configured to be rectangular in shape.

In some embodiments, the second beam arm is shaped as a rectangle, a square, a circle, a trapezoid, a triangle, or an ellipse.

In some embodiments, the ratio of the length of the first beam arm to the second beam arm of the microstructure cantilever beam is greater than or equal to 3:1; the ratio of the width of the first beam arm to the second beam arm is less than or equal to 1:2. The length of the first beam arm is much greater than the length of the second beam arm, and the second beam arm can be equivalent to a counterweight added to the free end of the first beam arm. The size of the first beam arm mainly affects the equivalent spring coefficient of the microstructure cantilever beam, and the size of the second beam arm mainly affects the equivalent mass of the microstructure cantilever beam, and has little effect on the equivalent spring coefficient.

In some embodiments, the microstructure cantilever beam is made of a metal material, a polymer or a semiconductor material, such as stainless steel, gold, silver, aluminum, silicon, etc.

In some embodiments, the resonant frequency _f0 of the microstructure cantilever beam is expressed as:

In the above formula, k _eff is the equivalent spring coefficient of the microstructure cantilever beam, and m _eff is the equivalent mass of the microstructure cantilever beam;

Among them, the equivalent spring coefficient k _eff of the microstructure cantilever beam is expressed as:

In the above formula, E is the Young's modulus of the microstructure cantilever beam, W is the equivalent width of the microstructure cantilever beam, and L is the equivalent length of the microstructure cantilever beam. Generally, the equivalent width of the microstructure cantilever beam is the width of the second beam arm, and the equivalent length of the microstructure cantilever beam is the sum of the lengths of the first beam arm and the second beam arm. It can be seen from the above formula that increasing the length of the microstructure cantilever beam and reducing the width of the microstructure cantilever beam can reduce the equivalent spring coefficient of the microstructure cantilever beam, making the microstructure cantilever beam easier to deform under the action of external sound waves. When optimizing the structure of the cantilever beam, the cantilever beam should be made as slender as possible. However, reducing the equivalent spring coefficient of the cantilever beam will lead to a decrease in the resonant frequency, thereby reducing the frequency response bandwidth of the optical fiber microphone.

In some embodiments, the sensitivity S _m of the microstructured cantilever beam is expressed as:

S _m = Δz/ΔP

In the above formula, Δz is the displacement of the free end of the microstructure cantilever beam when the external sound pressure P acts uniformly on the surface of the microstructure cantilever beam;

Where Δz is expressed as:

In the above formula, I is the moment of inertia of the microstructure cantilever beam, I=h ³ W/12, and h is the thickness of the microstructure cantilever beam. It can be seen from the above formula that the longer the length of the microstructure cantilever beam, the smaller the thickness and the smaller the width, the greater the deformation under the same sound pressure, and the higher the sensitivity.

In order to improve the sensitivity of the microstructure cantilever beam, the first beam arm should be made as slender as possible, and the size of the second beam arm should be reduced while ensuring the reflective surface, thereby reducing the mass of the microstructure cantilever beam, increasing the resonant frequency of the microstructure cantilever beam, and compensating for the problem of decreased frequency response bandwidth due to increased sensitivity.

In some embodiments, the optical fiber microphone based on the microstructure cantilever beam further comprises:

A base, wherein a first through cavity is formed in the middle of the base;

A bracket, the bracket is arranged above the base and is used to support the diaphragm; a second through cavity is opened in the middle of the bracket, and the first through cavity is connected to the second through cavity; when the diaphragm is adapted and arranged on the bracket, the microstructure cantilever beam corresponds to the second through cavity;

A fixing plate is arranged above the bracket and is used to cooperate with the bracket to fix the diaphragm; a third through cavity is opened in the middle position of the fixing plate, and the third through cavity corresponds to the second through cavity; when the optical fiber microphone is working, external sound waves act on the microstructure cantilever beam through the third through cavity, so that the microstructure cantilever beam vibrates between the second through cavity and the third through cavity;

The optical fiber and the ceramic ferrule are adapted to be arranged in the first through cavity; the end faces of the optical fiber and the ceramic ferrule are parallel to the microstructure cantilever beam, forming an F-P interference cavity. In the F-P interference cavity, a light parallel to the axis of the resonant cavity, after being reflected by the parallel microstructure cantilever beam and the end faces of the optical fiber and the ceramic ferrule, still propagates in the direction parallel to the axis and never escapes from the cavity. Generally, the optical fiber is made of glass and the ceramic ferrule is made of ceramic.

Usually, the diaphragm is fixed on the bracket so that the microstructure cantilever beam is in a free state, and then an external sound field is applied. The microstructure cantilever beam located in the middle area of the diaphragm will deform under the action of the sound wave pressure, and produce a swing perpendicular to the surface of the diaphragm, changing the cavity length of the F-P interference cavity, thereby changing the phase of the interference light and realizing the conversion of sound energy into light energy.

In some embodiments, the base, the bracket and the fixing plate can be made of polyester fiber as raw material through 3D printing, and the sizes of the base, the bracket and the fixing plate can be adjusted according to the size of the microstructure cantilever beam.

In some embodiments, a pressure balance hole is provided on the side wall of the base, which is used to connect the first through cavity with the outside of the base to maintain the internal and external air pressure balance and avoid the obstruction of the movement of the microstructure cantilever beam caused by the gas compression in the F-P interference cavity.

In some embodiments, the components of the microstructure cantilever optical fiber microphone are fixed by screws or light-curing adhesive.

In some embodiments, the diameters of the first through lumen, the second through lumen, and the third through lumen are the same.

In some embodiments, the optical sensitivity _Si of the fiber optic microphone is expressed as:

In the above formula, _R1 is the reflectivity of the optical fiber and the ceramic ferrule, _R2 is the reflectivity of the microstructure cantilever beam, _Ii is the incident light intensity, λ is the incident light wavelength, and Lc is the static cavity length of the FP interferometer. When the cavity length of the FP interferometer and the wavelength of the incident light satisfy _Lc = (2n+1)λ/8, the optical sensitivity of the fiber microphone is the maximum, where n is a natural number.

In some embodiments, the optical fiber acoustic transmission system based on the microstructure cantilever beam includes the above optical fiber microphone. The optical fiber microphone based on the microstructure cantilever beam acts as an acoustic wave sensing device, responds to acoustic waves, and converts acoustic wave signals into mechanical vibration signals.

In some embodiments, the optical acoustic transmission system of the microstructure cantilever beam further comprises:

A laser is used to provide a detection laser. Usually, the laser includes a temperature controller and a current controller. The temperature controller and the current controller are used to control the wavelength of the laser. Generally, the laser is a DFB laser.

Photodetectors for detecting interfering light;

An optical fiber circulator, used to transmit the detection laser emitted by the laser to the optical fiber microphone, and transmit the interference light emitted by the optical fiber microphone to the photodetector;

The data acquisition and processing component is used to collect and process the photoelectric detector signal, generally including a data acquisition card and a computer, wherein the data acquisition card is used to receive the photoelectric detector signal and input it into the computer, and the computer demodulates the voltage signal into an acoustic wave signal.

When the system is working, the laser emits a detection laser, which enters the fiber microphone through the fiber circulator. The detection laser is reflected between the microstructure cantilever beam and the end face of the optical fiber and the ceramic ferrule to form interference light. The interference light enters the photoelectric detector through the fiber circulator and is converted into a voltage signal. The voltage signal is output to the data acquisition and processing component, and the data acquisition and processing component demodulates the voltage signal into an acoustic wave signal. When the external sound field acts on the fiber microphone, the microstructure cantilever beam at the middle position of the diaphragm deforms under the action of sound pressure, causing the phase of the interference light to change, thereby causing the voltage signal output by the microphone to change.

The technical details are further illustrated below in conjunction with embodiments.

Example 1

FIG1 is a schematic diagram of the structure of the microstructure cantilever beam disclosed in Example 1; FIG2 is a schematic diagram of the mechanical deformation principle of the microstructure cantilever beam disclosed in Example 1.

As shown in Figure 1, the microstructure cantilever beam 2 is arranged in a rectangular through hole 11 opened in the middle part of the diaphragm 1, wherein the microstructure cantilever beam 2 includes a first beam arm 21 in the form of an elongated strip and a second beam arm 22 in the form of a square that are connected to each other, the end of the first beam arm 21 is connected to the wide side of the lower side of the rectangular through hole 11, the second beam arm 22 is a free end, and the geometric center of the second beam arm 22 overlaps with the geometric center of the diaphragm 1. The microstructure cantilever beam 2 swings in a direction perpendicular to the surface of the diaphragm 1 under the action of sound waves.

As shown in Figure 2, the microstructure cantilever beam 2 connected to the diaphragm 1 includes a first beam arm 21 and a second beam arm 22, wherein the length of the first beam arm 21 is 3/4L, the width of the first beam arm 21 is 1/2W, the length of the second beam arm 22 is 1/4L, and the width of the second beam arm 22 is W. The microstructure cantilever beam 2 can be equivalent to adding a counterweight to the free end of a rectangular cantilever beam with a length of L, a width of W, and a thickness of h.

Since the length of the first beam arm 21 is greater than the length of the second beam arm 22, and the width of the first beam arm 21 is less than the width of the second beam arm 22, under the action of external sound pressure P, elastic deformation is generated by the first beam arm 21 to provide sensitivity, and the equivalent mass of the microstructure cantilever beam is changed through the second beam arm 22, thereby changing the resonant frequency.

When the external sound pressure P acts uniformly on the surface of the microstructure cantilever beam, the displacement Δz generated at the free end of the microstructure cantilever beam is expressed as formula (1):

In formula (1), E is the Young's modulus of the micro cantilever beam, and I is the moment of inertia of the microstructure cantilever beam, where the moment of inertia I=h ³ W/12; the sensitivity of the microstructure cantilever beam S _m =Δz/ΔP, so thinner, longer, and finer microstructure cantilever beams are easier to deform under the same sound pressure and have higher sensitivity.

The resonant frequency _f0 of the microstructure cantilever beam is expressed as formula (2):

In formula (2), k _eff is the equivalent spring coefficient, and m _eff is the equivalent mass; the expression of k _eff is formula (3):

According to formula (3), the first arm 21 of the microstructure cantilever beam is optimized to be longer and thinner, which can reduce the equivalent spring coefficient of the cantilever beam and effectively improve the sensitivity; however, this optimization will also cause the resonant frequency in formula (2) to drop significantly, reducing the frequency response bandwidth of the fiber optic microphone. In order to compensate for the problem of decreased resonant frequency caused by increased sensitivity, the second arm 12 of the microcantilever beam can be optimized from square to circular or triangular, and the size of the second arm can be reduced while ensuring the reflective area. The shape optimization of the second arm has little effect on the equivalent spring coefficient of the microstructure cantilever beam, and can reduce the equivalent mass of the microstructure cantilever beam, thereby increasing the resonant frequency in formula (2) and improving the frequency response bandwidth of the fiber optic microphone.

Example 2

FIG3 is a schematic diagram of the structure of the microstructure cantilever beam disclosed in Example 2.

As shown in Figure 3, the microstructure cantilever beam 2 is arranged in a rectangular through hole 11 opened in the middle part of the diaphragm 1, wherein the microstructure cantilever beam 2 includes a first beam arm 21 in the form of an elongated strip and a second beam arm 22 in the form of a circle which are connected to each other, the end of the first beam arm 21 is connected to the wide side of the lower side of the rectangular through hole 11, the second beam arm 22 is a free end, and the geometric center of the second beam arm 22 overlaps with the geometric center of the diaphragm 1. The microstructure cantilever beam 2 swings in a direction perpendicular to the surface of the diaphragm 1 under the action of sound waves.

Example 3

FIG. 4 is a schematic diagram of the structure of the microstructure cantilever beam disclosed in Example 3.

As shown in Figure 1, the microstructure cantilever beam 2 is arranged in a rectangular through hole 11 opened in the middle part of the diaphragm 1, wherein the microstructure cantilever beam 2 includes a first beam arm 21 in the form of an elongated strip and a second beam arm 22 in the shape of a triangle which are connected to each other, the end of the first beam arm 21 is connected to the wide side of the lower side of the rectangular through hole 11, the second beam arm 22 is a free end, and the geometric center of the second beam arm 22 overlaps with the geometric center of the diaphragm 1. The microstructure cantilever beam 2 swings in a direction perpendicular to the surface of the diaphragm 1 under the action of sound waves.

Example 4

FIG. 5 is a schematic diagram of the structure of the optical fiber microphone based on the microstructure cantilever beam disclosed in Example 4; FIG. 6 is a schematic diagram of the working principle of the optical fiber microphone based on the microstructure cantilever beam disclosed in Example 4.

As shown in FIG5 , the optical fiber microphone based on the microstructure cantilever beam includes a fixing plate 3, a bracket 4, and a base 5 which are arranged in sequence from left to right, wherein a first through cavity 51 is opened at the middle position of the base 5, a second through cavity 41 which is connected to the first through cavity 51 is opened at the middle position of the bracket 4, and a third through cavity 31 which is connected to the second through cavity 41 is opened at the middle position of the fixing plate 3; wherein the diaphragm 1 is arranged in the third through cavity 31, the microstructure cantilever beam 2 is arranged at the middle position of the diaphragm 1, and the optical fiber and the ceramic ferrule 6 are adapted to be arranged in the first through cavity 51 through a gasket 7, so that an F-P interference cavity is formed between the left end surface of the optical fiber and the ceramic ferrule 6 and the right side surface of the microstructure cantilever beam 2.

As shown in FIG6 , when the fiber optic microphone is working, the incident light enters from the optical fiber and the ceramic ferrule 6, is transmitted through the ceramic ferrule, passes through the air medium, is reflected by the lower surface of the microstructure cantilever beam 2, returns to the air medium, and emits reflected light from the ceramic ferrule. When the reflectivity of the lower surface of the microstructure cantilever beam 2 and the upper surface of the optical fiber and the ceramic ferrule is low, it can be simplified to a double-beam interference model, and the reflected light forms interference light with the incident light.

When there is no external sound field, the interference light intensity _Ir in the above fiber optic microphone is expressed as formula (4):

In formula (4), _Ii is the incident light intensity; _R1 is the reflectivity of the optical fiber and the ceramic ferrule, and _R2 is the reflectivity of the microstructure cantilever beam. is the phase difference between the incident light and the reflected light;

In this embodiment, when stable interference is formed, φ＝4πL _c /λ, where λ is the wavelength of the incident light and Lc is the static cavity length of the FP; the optical sensitivity _Si of the fiber microphone is expressed as formula (5):

In formula (5), when the wavelength of the incident light and the cavity length of the FP interferometer cavity satisfy L _c =(2n+1)λ/8, the optical sensitivity of the FP interferometer cavity is maximum, where n is a natural number.

From the expression of the optical sensitivity _Si of the fiber optic microphone, it can be seen that under the same fiber optic microphone structure, the optical sensitivity can be optimized by adjusting the FP cavity length of the assembled fiber optic microphone to a specific corresponding relationship with the wavelength of the detection light.

Example 5

FIG. 7 is a schematic structural diagram of the optical fiber sound transmission system based on the microstructure cantilever beam disclosed in Example 5.

As shown in FIG7 , the optical fiber sound transmission system based on the microstructure cantilever beam includes:

An optical fiber microphone, which is an optical fiber microphone based on a microstructure cantilever beam;

A laser, used for providing a detection laser; the laser includes a temperature controller and a current controller; the temperature controller and the current controller are used for controlling the wavelength of the laser;

An optical fiber circulator is connected to the laser and is used to transmit the detection laser emitted by the laser to the optical fiber microphone, and transmit the interference light emitted by the optical fiber microphone to the photoelectric detector;

A photodetector is connected to the optical fiber circulator and is used to detect interference light. The photodiode in the photodetector converts the optical signal into an electrical signal for output;

The data acquisition and processing component is used to collect and process the photoelectric detector signal. The data acquisition and processing component includes a data acquisition card and a computer, wherein the data acquisition card is connected to the photoelectric detector and is used to receive the photoelectric detector signal. The computer is connected to the data acquisition card and is used to process the information collected by the data acquisition card and demodulate the voltage signal into an acoustic wave signal.

When the system is working, the laser emits a detection laser, which enters the fiber optic microphone through the fiber optic circulator. The detection laser is reflected between the microstructure cantilever beam and the end faces of the optical fiber and the ceramic ferrule to form interference light. The interference light enters the photoelectric detector through the fiber optic circulator and is converted into a voltage signal. The voltage signal is output to the data acquisition card, and the data acquisition card transmits the collected voltage signal to the computer, which demodulates the voltage signal into an acoustic wave signal.

When the external sound field acts on the fiber optic microphone, the microstructure cantilever beam in the middle of the diaphragm deforms under the action of sound pressure, causing the phase of the interference light to change, thereby causing the voltage signal output by the microphone to change.

Example 6

FIG8 is a frequency response graph of cantilever beams with different structures disclosed in Example 6.

Example 6 studies the sensitivity of an ordinary rectangular cantilever beam with a length of L, the sensitivity of a microstructured cantilever beam with a first beam arm length of 1/2L, and the sensitivity of a microstructured cantilever beam with a first beam arm length of 3/4L. As shown in Figure 8, compared with the ordinary rectangular cantilever beam, the sensitivity of the microstructured cantilever beam with a first beam arm length of 1/2L increases, and the resonant frequency does not change much; the sensitivity of the microstructured cantilever beam with a first beam arm length of 3/4L increases, and the resonant frequency decreases; compared with the microstructured cantilever beam with a first beam arm length of 1/2L, the sensitivity of the microstructured cantilever beam with a first beam arm length of 3/4L increases, and the resonant frequency decreases.

Example 7

FIG. 9 is a frequency response graph of cantilever beams with different structures disclosed in Example 7.

Example 7 studies the sensitivity of an ordinary rectangular cantilever beam with a width of W, the sensitivity of a microstructured cantilever beam with a first beam arm width of 1/2W, and the sensitivity of a microstructured cantilever beam with a first beam arm width of 1/4W. As shown in Figure 9, compared with the ordinary rectangular cantilever beam, the sensitivity of the microstructured cantilever beam with a first beam arm width of 1/2W increases, and the resonant frequency decreases; the sensitivity of the microstructured cantilever beam with a first beam arm width of 1/4W increases, and the resonant frequency decreases; compared with the microstructured cantilever beam with a first beam arm width of 1/2W, the sensitivity of the microstructured cantilever beam with a first beam arm width of 1/4W increases, and the resonant frequency decreases.

Example 8

FIG. 10 is a frequency response graph of cantilever beams with different structures disclosed in Example 8.

Example 8 studies the sensitivity of an ordinary rectangular cantilever beam, a microstructure cantilever beam with a square second arm, a microstructure cantilever beam with a circular second arm, and a microstructure cantilever beam with a triangular second arm, wherein the length of the first arm of the microstructure cantilever beam with a square second arm, the microstructure cantilever beam with a circular second arm, and the microstructure cantilever beam with a triangular second arm are all 3/4L and 1/2W respectively.

In FIG10 , the curve with a square pattern is the curve of the microstructure cantilever beam whose second beam arm is a square, the curve with a circular pattern is the curve of the microstructure cantilever beam whose second beam arm is a circular, and the curve with a triangular pattern is the curve of the microstructure cantilever beam whose second beam arm is a triangle.

As shown in Figure 10, the sensitivities of the microstructured cantilever beam with a square second arm, the microstructured cantilever beam with a circular second arm, and the microstructured cantilever beam with a triangular second arm are all higher than those of the ordinary rectangular cantilever beam, and the resonant frequencies of the microstructured cantilever beam with a square second arm, the microstructured cantilever beam with a circular second arm, and the microstructured cantilever beam with a triangular second arm gradually increase, and the resonant frequency of the microstructured cantilever beam with a triangular second arm exceeds the resonant frequency of the ordinary rectangular cantilever beam.

Example 9

FIG. 11 is a graph showing the real-time output voltage of the optical fiber microphone based on the microstructure cantilever beam disclosed in Example 9 under different sound pressures.

In Example 9, under a sound wave signal of 1 kHz, sound pressures of 5 mPa, 10 mPa and 20 mPa were applied to the optical fiber microphone with a square second beam arm, a circular second beam arm and a triangular second beam arm, respectively, for testing.

In FIG11 , the curve with a square pattern is the curve of the optical fiber microphone with a square second beam arm, the curve with a circular pattern is the curve of the optical fiber microphone with a circular second beam arm, and the curve with a triangular pattern is the curve of the optical fiber microphone with a triangular second beam arm.

As shown in FIG11 , as the sound pressure increases, the output voltages of the optical fiber microphones whose second beam arms are square, circular, and triangular all increase synchronously, indicating that the optical fiber microphone based on the microstructure cantilever beam disclosed in this embodiment has good energy conversion efficiency.

Example 10

FIG. 12 is a fitting curve of the output voltage of the optical fiber microphone based on the microstructure cantilever beam disclosed in Example 10 under different sound pressures.

In Figure 12, the curve with a square pattern is the curve of the optical fiber microphone with a square second beam arm, the curve with a circular pattern is the curve of the optical fiber microphone with a circular second beam arm, and the curve with a triangular pattern is the curve of the optical fiber microphone with a triangular second beam arm. The shaded area of the curve represents the standard deviation of multiple measurements, indicating that the output signal of the optical fiber microphone is stable.

As shown in Figure 12, under a 1kHz sound wave signal, the output voltage of the fiber microphone based on the microstructure cantilever beam increases with the increase of sound pressure, and the fitting curve of the output voltage has good linearity. The sensitivity of the fiber microphones with square, circular and triangular second beam arms is higher than that of the fiber microphone with ordinary rectangular cantilever beams. Among them, the sensitivity of the fiber microphone with a circular second beam arm is the highest, which is 302.8mV/Pa, which is much higher than the sensitivity of the fiber microphone with ordinary rectangular cantilever beams.

In this embodiment, the sensitivity of the fiber optic microphone with a circular second arm is 302.8 mV/Pa, the sensitivity of the fiber optic microphone with a triangular second arm is 144.3 mV/Pa, and the sensitivity of the fiber optic microphone with a square second arm is 71.7 mV/Pa, all of which are higher than the electronic commercial microphone produced by Denmark's B&K company, whose sensitivity is 50 mV/Pa.

Embodiment 11

FIG. 13 is a frequency response diagram of the optical fiber microphone based on the microstructure cantilever beam disclosed in Example 11.

In this embodiment 11, sound wave signals of 100 Hz to 3 kHz are applied to the optical fiber microphones having three different shapes of the second beam arm of the microstructure cantilever beam, respectively, and the sensitivity of the optical fiber microphones at different sound wave frequencies is tested and plotted as frequency response curves.

In FIG13 , the curve with a square pattern is the curve of the optical fiber microphone with a square second beam arm, the curve with a circular pattern is the curve of the optical fiber microphone with a circular second beam arm, and the curve with a triangular pattern is the curve of the optical fiber microphone with a triangular second beam arm.

As shown in Figure 13, the frequency response curves of the fiber optic microphones with three different shapes of the second beam arm of the microstructure cantilever beam are much higher than those of the ordinary cantilever beam. The resonant frequencies of the fiber optic microphones with square second beam arms, circular second beam arms, and triangular second beam arms gradually increase from 1478 Hz to 1507 Hz and 2028 Hz, respectively, indicating that the fiber optic microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention not only optimizes the sensitivity, but also improves the frequency response bandwidth of the fiber optic microphone.

The optical fiber microphone and sound transmission system based on the microstructure cantilever beam disclosed in the embodiment of the present invention, the first beam arm of the microstructure cantilever beam is set as a slender structure to reduce the equivalent spring coefficient of the cantilever beam, so that it is easy to deform under sound waves and has excellent sensitivity; the second beam arm of the microstructure cantilever beam is reduced in size on the basis of ensuring the reflective surface, reducing the equivalent mass of the microstructure cantilever beam, improving the problem of the reduction of the resonant frequency caused by the shape of the first beam arm, thereby improving the frequency response bandwidth of the optical fiber microphone. The optical fiber microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention can maintain the effective reflective area while reducing the size of the cantilever beam, can improve the sensitivity by reducing the equivalent spring coefficient of the cantilever beam, and can also improve the frequency response bandwidth by reducing the equivalent mass. The optical fiber microphone based on the microstructure cantilever beam disclosed in the embodiment of the present invention can be applied to the detection of weak sound wave signals, and can also be used in industrial environments with strong electromagnetic interference. The optical sound transmission system based on the microstructure cantilever beam disclosed in the embodiment of the present invention has a simple structure, low manufacturing cost, anti-electromagnetic interference, and long detection distance, and has good application prospects in the field of sound wave detection.

The technical solutions disclosed in the present invention and the technical details disclosed in the embodiments are merely illustrative of the inventive concept of the present invention and do not constitute a limitation on the technical solutions of the present invention. Any conventional changes, substitutions or combinations of the technical details disclosed in the embodiments of the present invention have the same inventive concept as the present invention and are within the protection scope of the claims of the present invention.

Claims (10)

1. Optical fiber microphone based on micro-structure cantilever beam, characterized by comprising:

A rectangular through hole is formed in the middle of the vibrating diaphragm;

the micro-structure cantilever beam is arranged in the rectangular through hole, is connected with the wide edge of the rectangular through hole and is arranged to swing along the direction perpendicular to the surface of the vibrating diaphragm under the action of sound waves;

The micro-structure cantilever comprises a first beam arm and a second beam arm which are connected with each other, wherein the end part of the first beam arm is connected with the broadside of the rectangular through hole, and the second beam arm is a free end;

The width of the second beam arm is larger than that of the first beam arm, the length of the second beam arm is smaller than that of the first beam arm, and the geometric center of the second beam arm is overlapped with the geometric center of the vibrating diaphragm.

2. The micro-structured cantilever-based fiber optic microphone according to claim 1, wherein the ratio of the lengths of the first and second beam arms is greater than or equal to 3:1, a step of; the ratio of the widths of the first beam arm to the second beam arm is less than or equal to 1:2.

3. The micro-structured cantilever-based fiber microphone of claim 1, wherein the micro-structured cantilever is a symmetrical structure; the first beam arm is of an elongated symmetrical structure, and the second beam arm is of a short-wide symmetrical structure.

4. The micro-cantilever based fiber microphone according to claim 1, wherein the resonance frequency f ₀ of the micro-cantilever is expressed as:

In the formula, k _eff is the equivalent spring coefficient of the micro-structure cantilever beam, and m _eff is the equivalent mass of the micro-structure cantilever beam;

Wherein, the equivalent spring coefficient k _eff of the micro-structure cantilever beam is expressed as:

In the above formula, E is the Young's modulus of the micro-structure cantilever, W is the equivalent width of the micro-structure cantilever, and L is the equivalent length of the micro-structure cantilever.

5. The micro-cantilever based fiber microphone according to claim 4, wherein the sensitivity S _m of the micro-cantilever is expressed as:

S_m＝Δz/ΔP

In the above description, Δz is the displacement generated by the free end of the micro-structure cantilever when the external sound pressure P uniformly acts on the surface of the micro-structure cantilever;

Wherein Δz is expressed as:

In the above formula, I is the moment of inertia of the micro-structure cantilever, i=h ³ W/12, and h is the thickness of the micro-structure cantilever.

6. The micro-structured cantilever-based fiber optic microphone of claim 1, further comprising:

the base is provided with a first through cavity at the middle position;

The bracket is arranged above the base and is used for supporting the vibrating diaphragm; a second through cavity is formed in the middle of the bracket, and the first through cavity is communicated with the second through cavity; when the vibrating diaphragm is arranged on the support in an adapting mode, the micro-structure cantilever beam corresponds to the second through cavity;

The fixing piece is arranged above the bracket and is used for fixing the vibrating diaphragm in a matched manner with the bracket; a third through cavity is formed in the middle of the fixing piece, and the third through cavity corresponds to the second through cavity;

the optical fiber and the ceramic ferrule are adaptively arranged in the first through cavity; and an F-P interference cavity is formed between the optical fiber and the ceramic ferrule and the microstructure cantilever beam.

7. The micro-cantilever based fiber microphone according to claim 6, wherein an air pressure balance hole is provided on a sidewall of the base for communicating the first through cavity with the outside of the base.

8. The micro-cantilever based fiber microphone according to claim 6, wherein the first, second and third through cavities have the same diameter.

9. The micro-structured cantilever-based fiber microphone according to claim 6, wherein the optical sensitivity S _i of the fiber microphone is expressed as:

In the formula, R ₁ is the reflectivity of the optical fiber and the ceramic ferrule, and R ₂ is the reflectivity of the microstructure cantilever beam; i _i is the intensity of the incident light; lambda is the wavelength of incident light; lc is the static cavity length of the F-P interferometric cavity.

10. A micro-structured cantilever based fiber optic microphone system comprising the fiber optic microphone of any of claims 1-9.