Optical fiber low-frequency acoustic sensor based on coupled cavity type mechanical filtering structure

Abstract

The invention relates to the technical field of acoustic sensors, and discloses an optical fiber low-frequency acoustic sensor based on a coupled cavity type mechanical filtering structure, which comprises a coupled cavity type mechanical filtering structure and an acoustic sensing unit, the coupled cavity type mechanical filtering structure comprises a sound guide tube, a sound resistance tube, and a front cavity and a rear cavity which are separated by a partition plate, and is used for realizing flat response of a low-frequency sound wave band, weakening high-frequency signal interference and controlling a detected low-frequency sound range; the acoustic sensing unit comprises a sensitive diaphragm, a single-mode optical fiber, a glass insertion core and a glass tube, wherein the single-mode optical fiber and the sensitive diaphragm form a Fabry-Perot cavity; an optical fiber flange of the coupled cavity type mechanical filtering structure is connected with a single-mode optical fiber of the acoustic sensing unit and a rear-end testing system, so that efficient and stable transmission of an optical signal is realized; the device has an excellent low-frequency detection function, can customize a low-frequency detection range and weaken high-frequency signal interference, and has the characteristics of small size, portability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of acoustic sensors, and in particular relates to an optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filtering structure. Background Art

[0002] In the atmosphere, many natural disasters and human activities, such as earthquakes, tsunamis, volcanic eruptions, nuclear explosions, and oil pipeline leaks, radiate low-frequency acoustic waves with characteristic signals. Therefore, the precise detection and perception of low-frequency acoustic signals has significant application value in the fields of public security, industrial safety, and national defense and military security. Although electrical low-frequency acoustic sensors are technologically mature and low-cost, they are susceptible to electromagnetic interference in the low-frequency band, have limited sensitivity, and are difficult to achieve long-distance transmission and multi-point distributed measurement, significantly limiting their application in complex environments. Fiber-optic acoustic sensors offer advantages such as immunity to electromagnetic interference, high sensitivity, compact size, and long-distance transmission. However, the detection frequency range of conventional fiber-optic low-frequency acoustic sensors is typically from a few hertz to several kilohertz, making them difficult to detect weak low-frequency acoustic signals. Therefore, the development of a fiber-optic low-frequency acoustic sensor with a simple structure, high sensitivity, strong noise immunity, and high frequency selectivity is of great significance. Summary of the Invention

[0003] (1) Purpose of the invention

[0004] The purpose of the present invention is to provide an optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filtering structure to solve the problems that the low-frequency band of acoustic wave signals is susceptible to electromagnetic interference, has limited sensitivity, has poor detection function for weak low-frequency acoustic waves, and has low selectivity in the low-frequency range of measurable acoustic waves.

[0005] (2) Technical solution

[0006] In order to solve the above technical problems, the present invention provides an optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure, comprising a coupled cavity mechanical filter structure 1 and an acoustic sensitive unit 2;

[0007] The coupled cavity mechanical filter structure 1 includes an acoustic conduit 14, an acoustic impedance tube 15, and a front cavity 13 and a rear cavity 17 separated by a partition. The front cavity 13 is provided with an air inlet pipe 11 and an optical fiber flange 12. The air inlet pipe 11 is connected to the atmosphere. The acoustic conduit 14 is mounted on the partition, with its front end exposed in the front cavity 13 and its rear end extending into the rear cavity 17 to connect to the acoustic impedance tube 15. The acoustic impedance tube 15 is located in the rear cavity 17. The inner end of the optical fiber flange 12 is located in the front cavity 13 and connected to the acoustic sensitive unit 2.

[0008] The acoustic sensitive unit 2 is installed on the partition and includes a sensitive diaphragm 21, a single-mode optical fiber 22, a glass ferrule 23, and a glass tube 24. The upper end of the glass tube 24 is located in the front cavity 13, and the lower end is located in the rear cavity 17. The sensitive diaphragm 21 is fixed to the upper end of the glass tube 24, and the single-mode optical fiber 22 is fixed to the lower end of the glass tube 24 through the glass ferrule 23. There is no contact between the sensitive diaphragm 21 and the single-mode optical fiber 22, forming a Fabry-Perot cavity; the single-mode optical fiber 22 passes through the partition and is connected to the optical fiber flange 12.

[0009] Furthermore, the front cavity 13 of the coupled cavity type mechanical filter structure 1 serves as a front acoustic volume cavity, and the rear cavity 17 serves as a rear acoustic volume cavity, and together with the acoustic resistance tube 15, they constitute an acoustic filter, and its frequency response function is as follows:

[0010]

[0011] Wherein, V1 and V2 are the volumes of the front cavity 13 and the rear cavity 17 respectively, l1 and l2 are the lengths of the intake pipe 11 and the acoustic resistance tube 15 respectively, r1 is the radius of the intake pipe 11, c is the speed of sound, ρ is the air density, μ is the air viscosity coefficient, and s is the Laplace variable.

[0012] Furthermore, the operating frequency range of the optical fiber low-frequency acoustic sensor covers 1 Hz to 500 Hz, and has high sensitivity in the range of 1 Hz to 500 Hz; at the same time, the lower limit of frequency detection can be extended to 0.002 Hz, and the upper limit of frequency detection can be extended to 1000 Hz.

[0013] Furthermore, the acoustic sensitive unit 2 is mounted on the partition through a sealing connection 16 .

[0014] Furthermore, the partition on the rear cavity 17 of the coupled cavity mechanical filtering structure 1 is provided with three corresponding mounting holes according to the sizes of the sound conduit 14 , the sealing connector 16 and the single-mode optical fiber 22 in the acoustic sensitive unit 2 .

[0015] Furthermore, the optical fiber flange 12 of the coupled cavity mechanical filtering structure 1 adopts a standard FC round head flange and is connected to a back-end testing system.

[0016] Furthermore, the air inlet pipe 11 of the coupled cavity type mechanical filtering structure 1 is made of aluminum alloy, with a pagoda head at the upper end and a lower end fixed to the front cavity 13 by a nut.

[0017] Furthermore, the sound conduit 14 is made of polypropylene material, and the sound conduit 14 and the rear cavity 17 are connected by epoxy resin glue; the acoustic resistance tube 15 is made of a transparent silicone capillary, and the sound conduit 14 and the acoustic resistance tube 15 are tightly connected by a heat shrink tube; the sensitive diaphragm 21 is made of polymer material, and the glass core 23 and the glass tube 24 are both made of quartz glass.

[0018] Furthermore, the front cavity 13 and the rear cavity 17 are both made of aluminum alloy, made into cylinders, and connected by screw locking.

[0019] (3) Beneficial effects

[0020] The above technical solution provides an optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filtering structure, which has excellent low-frequency detection function. The low-frequency detection range can be customized and high-frequency signal interference can be reduced according to the coupled cavity mechanical filtering structure. It also has the characteristics of small size and portability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a schematic diagram of the appearance of the present invention;

[0023] Figure 3 It is a three-dimensional structural diagram of the acoustic sensitive unit of the present invention.

[0024] Among them: 1. Coupled cavity mechanical filtering structure; 2. Acoustic sensitive unit; 11. Inlet pipe; 12. Fiber optic flange; 13. Front cavity; 14. Sound guide tube; 15. Acoustic resistance tube; 16. Sealing connector; 17. Back cavity; 21. Sensitive diaphragm; 22. Single-mode optical fiber; 23. Glass ferrule; 24. Glass tube. DETAILED DESCRIPTION

[0025] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings and examples.

[0026] like Figure 1 As shown, the present invention provides an optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure, comprising a coupled cavity mechanical filter structure 1 and an acoustic sensitive unit 2;

[0027] Among them, the coupled cavity mechanical filtering structure 1 includes a sound conduit 14, an acoustic impedance tube 15, a sealing connector 16, and a front cavity 13 and a rear cavity 17 separated by a partition. The front cavity 13 is provided with an air intake pipe 11 and an optical fiber flange 12. The air intake pipe 11 is connected to the atmosphere to ensure that the external sound pressure signal can enter the sensor unimpeded. The sound pressure signal is transmitted through the front cavity 13 and acts on the acoustic sensitive unit 2; the sound conduit 14 is installed on the partition, with the front end exposed in the front cavity 13 and the rear end extending to the rear cavity 17 to connect with the acoustic impedance tube 15. The acoustic impedance tube 15 is located in the rear cavity 17 and is connected to the rear cavity 17 as an acoustic impedance. The acoustic impedance tube 15 attenuates the sound wave energy through a slender pipe structure; the inner end of the optical fiber flange 12 is located in the front cavity 13 and is connected to the acoustic sensitive unit 2, and the outer end is connected to the rear test system.

[0028] like Figure 1 and Figure 3 As shown, the acoustic sensitive unit 2 is installed on the partition, including a sensitive diaphragm 21, a single-mode optical fiber 22, a glass ferrule 23, and a glass tube 24. The upper end of the glass tube 24 is located in the front cavity 13, and the lower end is located in the rear cavity 17. The sensitive diaphragm 21 is fixed to the upper end of the glass tube 24, and the single-mode optical fiber 22 is fixed to the lower end of the glass tube 24 through the glass ferrule 23. There is no contact between the sensitive diaphragm 21 and the single-mode optical fiber 22, forming a Fabry-Perot cavity; the single-mode optical fiber 22 passes through the partition and is connected to the optical fiber flange 12; the sensitive diaphragm 21 serves as a sound pressure sensing module, and its structure and size play a decisive role in the sensitivity of the sensor.

[0029] The front cavity 13 of the coupled cavity mechanical filtering structure 1 serves as a front acoustic capacity cavity, and the rear cavity 17 serves as a rear acoustic capacity cavity, which together with the acoustic resistance tube 15 constitute an acoustic resonance system; the partition on the rear cavity 17 is provided with three corresponding mounting holes according to the size of the sound conduit 14, the sealing connector 16 and the single-mode optical fiber 22 in the acoustic sensitive unit 2.

[0030] The sealing connector 16 in the coupled cavity mechanical filtering structure 1 connects the rear cavity 17 and the acoustic sensitive unit 2 to ensure the airtightness and mechanical stability of the sensor.

[0031] The optical fiber flange 12 in the coupled cavity mechanical filtering structure 1 connects the single-mode optical fiber 22 in the acoustic sensitive unit 2 and the back-end test system, thereby realizing efficient and stable transmission of optical signals between the optical fiber and the back-end test system.

[0032] like Figure 2 As shown, in a specific embodiment, the optical fiber flange 12 in the coupled cavity mechanical filtering structure 1 adopts a standard FC round head flange, a part of which is embedded in the front cavity 13 and the other part is exposed to the outside for connection with the back-end test system.

[0033] In a specific embodiment, the upper end of the air intake pipe 11 in the coupled cavity mechanical filter structure 1 is designed and processed into a pagoda head to facilitate connection with the back-end test system; the air intake pipe 11 is made of aluminum alloy, and the lower end is threaded, and is locked with the front cavity 13 by a nut; the sound conduit 14 is made of polypropylene material, and epoxy resin glue is used to fix the sound conduit 14 to the back cavity 17 to ensure good air tightness; the acoustic resistance tube 15 is made of a transparent silicone capillary, and the sound conduit 14 and the acoustic resistance tube 15 are tightly connected with a heat shrink tube.

[0034] like Figure 2 As shown, in a specific embodiment, the front cavity 13 and the rear cavity 17 of the coupled cavity type mechanical filtering structure 1 are both made of aluminum alloy, made into cylinders, and connected by screw locking.

[0035] In a specific embodiment, the sealing connector 16 of the coupled cavity mechanical filtering structure 1 is made of aluminum alloy, the outer diameter of which is precisely matched with the hole position of the rear cavity 17, and the inner diameter is closely matched with the acoustic sensitive unit 2; after the components of the rear cavity 17 are connected, in order to further enhance the sealing performance and prevent the sound pressure signal from leaking during transmission, epoxy resin glue is used to reinforce the periphery of the connection to ensure efficient transmission and stability of the sensor.

[0036] The working principle of the present invention is as follows: In an acoustic system, a closed cavity with pores acts as an acoustic capacitor, which acts as an impedance to changes in air pressure, thereby storing acoustic energy; a slender tube is called an acoustic resistor, which dissipates acoustic energy through the viscous effect, achieving energy attenuation. In the present invention, the front cavity 13 of the coupled cavity-type mechanical filter structure 1 acts as the acoustic capacitor front cavity, and the rear cavity 17 acts as the acoustic capacitor rear cavity, together with the acoustic capacitor front cavity to form an acoustic resonant structure. The cavity and the acoustic resistor tube work together to form a frequency-selective structure, that is, an acoustic filter, whose frequency response function is as follows:

[0037]

[0038] Wherein, V1 and V2 are the volumes of the front cavity 13 and the rear cavity 17 respectively, l1 and l2 are the lengths of the intake pipe 11 and the acoustic resistance tube 15 respectively, r1 is the radius of the intake pipe 11, c is the speed of sound, ρ is the air density, μ is the air viscosity coefficient, and s is the Laplace variable;

[0039] The acoustic filter can cut off high-frequency sound waves and only allow low-frequency sound waves within a specified frequency band to pass through and cause vibration of the sensitive diaphragm 21; by optimizing the design of the volume of the front cavity and the rear cavity of the acoustic volume and the length of the acoustic resistance tube 15, the frequency selection and detection of low-frequency sound signals can be achieved.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure, characterized in that: It includes a coupled cavity-type mechanical filtering structure (1) and an acoustic sensitive unit (2); The coupled cavity mechanical filter structure (1) comprises a sound conduit (14), an acoustic impedance tube (15), and a front cavity (13) and a rear cavity (17) separated by a partition. The front cavity (13) is provided with an air intake pipe (11) and an optical fiber flange (12), and the air intake pipe (11) is connected to the atmosphere. The sound conduit (14) is mounted on the partition, with its front end exposed in the front cavity (13) and its rear end extending into the rear cavity (17) to connect to the acoustic impedance tube (15), and the acoustic impedance tube (15) is located in the rear cavity (17). The inner end of the optical fiber flange (12) is located in the front cavity (13) and connected to the acoustic sensitive unit (2). The acoustic sensitive unit (2) is mounted on a partition and comprises a sensitive diaphragm (21), a single-mode optical fiber (22), a glass ferrule (23), and a glass tube (24). The upper end of the glass tube (24) is located in the front cavity (13), and the lower end is located in the rear cavity (17). The sensitive diaphragm (21) is fixed to the upper end of the glass tube (24), and the single-mode optical fiber (22) is fixed to the lower end of the glass tube (24) through the glass ferrule (23). The sensitive diaphragm (21) and the single-mode optical fiber (22) are not in contact, forming a Fabry-Perot cavity. The single-mode optical fiber (22) passes through the partition and is connected to the optical fiber flange (12).

2. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The front cavity (13) of the coupled cavity type mechanical filter structure (1) serves as a front acoustic volume cavity, and the rear cavity (17) serves as a rear acoustic volume cavity, and together with the acoustic impedance tube (15) form an acoustic filter, the frequency response function of which is as follows: Wherein, V1 and V2 are the volumes of the front cavity (13) and the rear cavity (17), l1 and l2 are the lengths of the intake pipe (11) and the acoustic resistance tube (15), r1 is the radius of the intake pipe (11), c is the speed of sound, ρ is the air density, μ is the air viscosity coefficient, and s is the Laplace variable.

3. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filtering structure according to claim 2, characterized in that: The optical fiber low-frequency acoustic sensor has an operating frequency range of 1 Hz to 500 Hz and has high sensitivity within the range of 1 Hz to 500 Hz. At the same time, the lower limit of frequency detection can be extended to 0.002 Hz, and the upper limit of frequency detection can be extended to 1000 Hz.

4. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The acoustic sensitive unit (2) is mounted on the partition through a sealing connection (16).

5. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 4, characterized in that: The partition plate on the rear cavity (17) of the coupled cavity mechanical filtering structure (1) is provided with three corresponding mounting holes according to the sizes of the sound conduit (14), the sealing connector (16) and the single-mode optical fiber (22) in the acoustic sensitive unit (2).

6. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The optical fiber flange (12) of the coupled cavity type mechanical filtering structure (1) adopts a standard FC round head flange and is connected to a back-end test system.

7. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The air inlet pipe (11) of the coupled cavity type mechanical filter structure (1) is made of aluminum alloy, has a pagoda head at the upper end, and is fixed to the front cavity (13) at the lower end via a nut.

8. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The sound conduit (14) is made of polypropylene material, and the sound conduit (14) and the rear cavity (17) are connected by epoxy resin glue; the acoustic impedance tube (15) is made of transparent silicone capillary, and the sound conduit (14) and the acoustic impedance tube (15) are tightly connected by a heat shrink tube; the sensitive diaphragm (21) is made of polymer material, and the glass ferrule (23) and the glass tube (24) are both made of quartz glass.

9. The optical fiber low-frequency acoustic sensor based on a coupled cavity mechanical filter structure according to claim 1, characterized in that: The front cavity (13) and the rear cavity (17) are both made of aluminum alloy, are made into cylindrical bodies, and are connected by screw locking.

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