A polyimide (PI) film-based optical fiber cantilever beam acoustic sensor

Abstract

The application belongs to the technical field of optical fiber sensing, and discloses a kind of optical fiber cantilever beam acoustic sensor based on polyimide (PI) film, comprising the following components: gold-plated polyimide (PI) cantilever beam film, two pieces of stainless steel ring substrate, 3D printing shell and optical fiber ceramic core, wherein the thickness of polyimide (PI) film is 25 µm, 200 nm gold film is plated by magnetron sputtering, and the reflectivity reaches 85%; the cantilever beam adopts a triangular-rectangular composite structure, with a total size of 1.5 mm x 0.8 mm, an isosceles triangle with a base of 0.8 mm and a height of 0.5 mm at the top, and a rectangular arm with a size of 1 mm x 0.5 mm at the bottom. Based on the Fabry-Perot interference principle, the application achieves the purpose of high-precision acoustic signal detection, significantly improves the sensitivity and dynamic response range, and is suitable for acoustic signal detection in extreme environments, with low cost and easy mass production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, and particularly relates to an optical fiber cantilever beam acoustic sensor based on a polyimide (PI) film. The sensor is suitable for detecting weak acoustic signals in the fields of geological exploration, pipeline leakage monitoring, underwater acoustic detection and photoacoustic spectroscopy, and particularly exhibits excellent performance in extreme environments such as high temperature and high noise. By combining the unique material properties of the polyimide (PI) film and the optical fiber Fabry-Perot interference (FPI) technology, the present application provides a high-sensitivity and wide-frequency-response acoustic detection solution. BACKGROUND

[0002] Acoustic sensing technology has important application value in the fields of industrial monitoring, medical diagnosis and environmental detection. Traditional acoustic sensors (such as capacitive and piezoelectric sensors) can meet the basic needs under normal conditions, but they have significant limitations: low sensitivity, insufficient anti-electromagnetic interference ability, difficulty in realizing long-distance signal transmission, and particularly in extreme environments such as high temperature, high noise or strong electromagnetic field, the performance is significantly reduced. In recent years, optical fiber acoustic sensors have gradually become a powerful alternative to traditional sensors due to their advantages of anti-electromagnetic interference, small size and low transmission loss. Among them, optical fiber acoustic sensors based on the Fabry-Perot interference (FPI) principle have attracted widespread attention due to their compact structure and high sensitivity.

[0003] In the prior art, an optical fiber FPI acoustic sensor is usually composed of an optical fiber end face and an acoustic sensitive element (such as a film or a cantilever beam), which together form an interference cavity. When an acoustic wave acts on the sensitive element, its vibration causes a change in the length of the interference cavity, thereby modulating the interference spectrum and realizing the detection of acoustic signals. However, the current optical fiber cantilever beam acoustic sensor still has deficiencies in material selection and structure design. Metal films represented by stainless steel have a high Young's modulus (about 200 GPa), which results in a large rigidity of the cantilever beam, and the vibration amplitude is limited, so the sensitivity is low. For example, a certain commercial stainless steel cantilever beam acoustic sensor has a sensitivity of only 787.6 mV / Pa near 4 kHz, which is difficult to meet the needs of high-precision weak acoustic signal detection.

[0004] In order to overcome the limitations of metal materials, researchers have tried to use polymer materials (such as polystyrene, PS) to make cantilever beams. The Young's modulus of polymer materials is relatively low (about 3-4 GPa), which can theoretically enhance the vibration response of the cantilever beam and thus improve the sensitivity. However, the reflectivity of polymer films is generally low (usually less than 10%), which results in insufficient interference signal strength and limits the detection accuracy. In addition, polymer materials are prone to softening or degradation in high-temperature environments, which cannot meet the application requirements in extreme conditions.

[0005] Polyimide (PI) as a high-performance engineering plastic, has excellent high-temperature resistance (can withstand more than 400 ℃), low Young's modulus (about 2-3 GPa) and good mechanical stability, has been widely used in aerospace, electronic packaging and other fields. Compared with stainless steel, the Young's modulus of polyimide (PI) film is only about 1 / 50 of that of stainless steel, which can theoretically significantly improve the vibration sensitivity of the cantilever beam. However, the natural reflectivity of polyimide (PI) film is low (about 5%), and if it is directly used for FPI acoustic sensor, the interference signal strength is insufficient, and it is difficult to achieve high-precision detection.

[0006] In view of the above problems, the present application provides a kind of based on gold-plated polyimide (PI) film optical fiber cantilever beam acoustic sensor. By plating nanoscale gold film on the surface of polyimide (PI) film, the reflectivity is increased to 85%, which significantly enhances the interference signal intensity, while retaining the advantage of low Young's modulus of polyimide (PI) film. In addition, the present application adopts innovative triangular-rectangular composite cantilever beam structure, optimizes stress distribution, further improves sensitivity and frequency response range. This design not only overcomes the defect of low sensitivity of traditional metal cantilever beam, but also solves the problems of low reflectivity and poor high-temperature resistance of polymer film, and has significant creativity and practical value. SUMMARY

[0007] The purpose of the present application is to provide a kind of based on polyimide (PI) film optical fiber cantilever beam acoustic sensor, to solve the technical problems of insufficient sensitivity, low reflectivity and poor high-temperature adaptability of existing optical fiber acoustic sensor, and realize high-precision, wide frequency response acoustic signal detection.

[0008] The technical scheme of the present application is as follows:

[0009] A kind of based on polyimide (PI) film optical fiber cantilever beam acoustic sensor, comprising the following components:

[0010] Gold-plated polyimide (PI) cantilever beam film: select the thickness of 25 µm polyimide (PI) film as cantilever beam substrate, 200 nm thick gold film is plated on the surface of the film by magnetron sputtering process, to form the high reflection surface of F-P interference cavity, and the reflectivity reaches 85%.

[0011] Stainless steel ring substrate: two pieces of stainless steel ring substrate with a thickness of 100 µm are used to fix the gold-plated polyimide (PI) cantilever beam film and provide stable structural support.

[0012] 3D printing shell: the shell size is 15 mm in diameter and 10 mm in length, which is used to package the sensor components and protect the internal structure from external interference.

[0013] Optical fiber ceramic core: connected with single-mode optical fiber (Corning SMF-28), the optical fiber ceramic core forms the light incident channel of the F-P interference cavity, and ensures efficient transmission of the optical signal.

[0014] Cantilever beam geometry design: the overall size of the cantilever beam is 1.5 mm (length) x 0.8 mm (width), the top is an isosceles triangle with a base of 0.8 mm and a height of 0.5 mm, and the bottom is a rectangular arm with a length of 1 mm and a width of 0.5 mm. This composite structure optimizes the vibration mode, improves the sensitivity and frequency response.

[0015] Further, the Young's modulus of the polyimide (PI) cantilever beam film is 1 / 50 of that of stainless steel, and the sensitivity at a frequency of 4.1 kHz is 957.7 mV / Pa.

[0016] Further, the reflectivity of the gold-plated layer is 85%, which is 1600% higher than the reflectivity of 5% of the uncoated polyimide (PI) film.

[0017] Further, the frequency response range of the sensor is 500 Hz to 8 kHz, and the resonant frequency is 4.1 kHz.

[0018] Further, the stainless steel ring-shaped substrate and the optical fiber ceramic core are fixed by the Liantian 9005 epoxy resin AB glue.

[0019] Further, the polyimide (PI) cantilever beam film is processed into a triangular-rectangular composite structure by a laser marking machine.

[0020] The optical fiber cantilever beam acoustic sensor based on the polyimide (PI) film has the following advantages compared with the prior art:

[0021] 1. High sensitivity: at a resonant frequency of 4.1 kHz, the sensitivity reaches 957.7 mV / Pa, which is about 21.6% higher than that of the traditional stainless steel cantilever beam sensor (787.6 mV / Pa).

[0022] 2. Wide frequency response: the frequency response range is 500 Hz-8 kHz, which is suitable for various acoustic detection scenarios.

[0023] 3. High temperature stability: thanks to the high temperature resistance of the polyimide (PI) film, the sensor can work stably at 120℃ environment, and the sensitivity fluctuation is less than 3%.

[0024] 4. Anti-interference: all-optical fiber structure design, no electrical components, strong anti-electromagnetic interference ability. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor, wherein:

[0026] Figure 1 The overall structure schematic diagram of a fiber cantilever beam acoustic sensor based on a polyimide (PI) film according to the present application;

[0027] Figure 2 The cross-sectional view part in the above-mentioned structure schematic diagram of the cantilever beam; Figure 1

[0028] Figure 3 The optical path schematic diagram of a fiber cantilever beam acoustic sensor based on a polyimide (PI) film according to the present application based on the Fabry-Perot interference principle;

[0029] Figure 4 The reflectivity comparison bar chart of a fiber cantilever beam acoustic sensor based on a polyimide (PI) film according to the present application before and after gold plating. DETAILED DESCRIPTION

[0030] The following will combine specific embodiments to make a detailed description of the implementation details of a fiber cantilever beam acoustic sensor based on a polyimide (PI) film according to the present application, so as to enable those skilled in the art to implement the present application.

[0031] As shown in Figures 1-4 , a fiber cantilever beam acoustic sensor based on a polyimide (PI) film.

[0032] Embodiment one: preparation of the sensor

[0033] 1) Gold plating of the polyimide (PI) film: a polyimide (PI) film (Kapton® HN type) with a thickness of 25 µm and a size of 20 mm × 20 mm is selected; a magnetron sputtering machine (model: DCT-600) is used to plate a 200 nm thick gold film on the surface of the polyimide (PI) film; process parameters: vacuum degree 10⁻ 4 Pa, sputtering power 200 W, plating time 30 minutes; reflectivity test after gold plating (using a spectrometer): 85% (wavelength 1550 nm).

[0034] ​2) Cantilever beam processing: Place the gold-plated polyimide (PI) film in a laser marking machine (Model: FiberMark 24); set the laser parameters: wavelength 1064 nm, power 20 W, scanning speed 100 mm / s; cut out the cantilever beam structure: total length 1.5 mm, total width 0.8 mm, top is an isosceles triangle (base 0.8 mm, height 0.5 mm), bottom is a rectangular arm (1 mm x 0.5 mm).

[0035] 3) Assembly: Prepare two stainless steel ring substrates (thickness 100 µm, inner diameter 2 mm, outer diameter 10 mm); clamp the cut polyimide (PI) cantilever beam film between the two substrates, use the blue Tian 9005 epoxy resin AB glue (mixing ratio 1:1) to fix; align the fiber ceramic core (inner diameter 125 µm) with the single-mode optical fiber (Corning SMF-28) and insert it into the center of the stainless steel substrate; use a 3D printer (Model: Form 3) to print the shell (material: ABS resin), with a size of diameter 15 mm, length 10 mm; place the assembled substrate and fiber ceramic core in the shell and seal it with epoxy glue.

[0036] Example Two: Performance Test

[0037] 1) Frequency response test: Place the sensor on the acoustic test platform, connect the signal generator (Model: Agilent 33220A) and the photoelectric converter; input the sound wave signal with a frequency range of 500 Hz-8 kHz and a sound pressure level of 1 Pa; record the change of output voltage with frequency, the resonant frequency is 4.1 kHz, and the sensitivity is 957.7 mV / Pa.

[0038] 2) High temperature stability test: Place the sensor in a high temperature oven (Model: DHG-9070A), set the temperature to 120°C; work continuously for 24 hours, measure the sensitivity every 4 hours; the result shows that the sensitivity fluctuation is less than 3%, proving the stable performance at high temperature.

[0039] 3) Reflectivity test: Use a spectrum analyzer (Model: Yokogawa AQ6370D) to test the reflectivity of the gold-plated polyimide (PI) film; the measured reflectivity is 85% (wavelength 1550 nm), and the uncoated polyimide (PI) film is 5%.

[0040] Example Three: Application Verification

[0041] 1) Geological exploration application: Deploy the sensor in a simulated seismic wave detection scene; successfully capture the weak vibration signal in the range of 500 Hz-8 kHz, with better sensitivity than traditional sensors.

[0042] 2) Pipeline leak monitoring: In the pipeline leak simulation experiment, the sensor accurately locates the sound wave signal emitted by the leak point, and the detection distance reaches 50m.

[0043] 3) Underwater acoustic detection: In the underwater environment of 10m depth, the sensor stably outputs 4kHz sound wave signal, showing good underwater adaptability.

[0044] The working principle of the present application: The present sensor works based on the Fabry-Perot interference principle. The incident light is transmitted to the optical fiber ceramic core through a single-mode optical fiber, and a multi-beam interference is formed between the optical fiber end face and the gold-plated polyimide (PI) film. The interference spectrum characteristics are closely related to the interference cavity length. When the external sound wave acts on the polyimide (PI) cantilever film, the film vibrates, causing the change of the interference cavity length, and further causing the shift of the interference spectrum. By detecting the light intensity change of the reflected light, the accurate measurement of the sound signal can be realized.

[0045] The optical fiber cantilever beam acoustic sensor based on polyimide (PI) film of the present application has the following advantages compared with the prior art:

[0046] 1. High sensitivity: At a resonance frequency of 4.1kHz, the sensitivity reaches 957.7mV / Pa, which is about 21.6% higher than that of the traditional stainless steel cantilever beam sensor (787.6mV / Pa).

[0047] 2. Wide frequency response: The frequency response range is 500Hz-8kHz, which is suitable for various acoustic detection scenarios.

[0048] 3. High temperature stability: Due to the high temperature resistance of polyimide (PI) film, the sensor can work stably at 120℃ environment, and the sensitivity fluctuation is less than 3%.

[0049] 4. Anti-interference: The all-optical fiber structure design has no electrical components and has strong anti-electromagnetic interference ability.

[0050] The optical fiber cantilever beam acoustic sensor based on polyimide (PI) film of the present application has the following three major innovations:

[0051] 1. Material innovation: Polyimide (PI) film is used as the cantilever beam substrate, and its Young's modulus is only 1 / 50 of that of stainless steel, which greatly improves the vibration sensitivity.

[0052] 2. Process innovation: By magnetron sputtering to coat 200nm gold film, the reflectivity of polyimide (PI) film is increased from 5% to 85%, which significantly enhances the interference signal strength.

[0053] 3. Structural innovation: design a triangular-rectangular composite cantilever beam structure, optimize stress distribution, make the sensor have a flat frequency response in the range of 500Hz-8kHz, and the resonance frequency is 4 MoscaHz.

[0054] The polyimide (PI) film-based optical fiber cantilever beam acoustic sensor can be widely applied to the following fields:

[0055] 1) Seismic wave detection in geological exploration; 2) Acoustic positioning in pipeline leakage monitoring; 3) Underwater signal acquisition in underwater acoustic detection; 4) Gas analysis in photoacoustic spectroscopy. Especially in extreme environments such as high temperature and high noise, the sensor shows excellent adaptability and reliability.

[0056] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these specific embodiments are only illustrative, and those skilled in the art can make various omissions, substitutions and changes to the details of the above method and system without departing from the principles and essence of the present application. For example, combining the above method steps, performing substantially the same function in substantially the same way to achieve substantially the same result according to the same method belongs to the scope of the present application. Therefore, the scope of the present application is only limited by the appended claims.

Claims

1. A polyimide (PI) film based optical fiber cantilever beam acoustic sensor, characterized in that, Comprise the following components: Gold-plated polyimide (PI) cantilever beam film, the thickness of the polyimide (PI) cantilever beam film is 25µm; Two pieces of stainless steel ring substrate, the thickness of the stainless steel ring substrate is 100µm, used to fix the polyimide (PI) cantilever beam film; 3D printed shell, the size of the 3D printed shell is 15mm in diameter and 10mm in length, used to package the sensor assembly; Optical fiber ceramic core, connected with single-mode optical fiber; The polyimide (PI) cantilever beam film is plated with a gold film with a thickness of 200nm by magnetron sputtering, forming the reflecting surface of the Fabry-Perot interference cavity; The size of the cantilever beam is 1.5mm (long) x 0.8mm (wide), the top is an isosceles triangle with a base of 0.8mm and a height of 0.5mm, and the bottom is a rectangular arm with a length of 1mm and a width of 0.5mm; The Young's modulus of the polyimide (PI) cantilever beam film is 1 / 50 of that of stainless steel, and the sensitivity at a frequency of 4.1kHz is 957.7mV / Pa. The reflectivity of the gold-plated layer is 85%, which is 1600% higher than the reflectivity of the uncoated polyimide (PI) film, which is 5%.

2. The polyimide (PI) film-based optical fiber cantilever beam acoustic sensor according to claim 1, wherein, The frequency response range of the sensor is 500Hz to 8kHz, and the resonant frequency is 4.1kHz.

3. The polyimide (PI) film-based optical fiber cantilever beam acoustic sensor according to claim 1, wherein, The stainless steel ring substrate and the optical fiber ceramic core are fixed by blue Tian 9005 epoxy AB glue.

4. The polyimide (PI) film-based optical fiber cantilever beam acoustic sensor according to claim 1, wherein, The polyimide (PI) cantilever beam film is processed into a triangular-rectangular composite structure by a laser marking machine.

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