Weak pressure measurement method and system based on film reflection

Abstract

The invention relates to a weak pressure measurement method and system based on film reflection, the system comprises a light source, an optical fiber pressure probe, a signal acquisition module, a signal processing module and a signal display module, the optical fiber pressure probe comprises a film, a dual-optical fiber coupler and a sleeve, and the signal acquisition module comprises a photosensitive transistor and a driving circuit. And the signal processing module comprises a signal amplification circuit and a signal demodulation circuit. The method comprises the steps that when light beams emitted by the light source are projected to the surface of the film through the emission optical fiber, the film deforms under the action of external pressure, reflection light spot distribution and reflection angle change are caused, and signal modulation is achieved. The emergent optical fiber receives the reflected signal, the signal acquisition module acquires a light intensity signal of the emergent optical fiber and converts the light intensity signal into an electric signal, the signal processing module amplifies and processes the acquired information to realize signal demodulation, and the signal display module displays a processing result. The micro-pressure sensor has the advantages that micro-pressure measurement with low cost and excellent linearity is realized through a simple zero-point adjustment mechanism and a compact double-optical-fiber design.

Description

Technical Field

[0001] This invention relates to a method and system for measuring weak pressure based on thin-film reflection, and particularly to a method and system for measuring weak pressure based on thin-film deformation and reflection, optical fiber coupling, and signal modulation and demodulation. Background Technology

[0002] With the rapid development of society, modern industrial technology has increasingly higher demands for information acquisition technologies. Sensor technology, communication technology, and computer technology are the three major technologies for information acquisition. Among them, fiber optic sensing technology, as an important branch of sensor technology, has matured and has a wide range of market applications. Miniature pressure sensors are a rapidly developing cutting-edge technology in recent years, whose core lies in their ability to accurately measure minute pressures (typically from a few Pascals to several kilopascals). The main driving force behind their application comes from the demand for miniaturized sensors, high sensitivity, low power consumption, low cost, and new application forms.

[0003] In recent years, with the development of optical fiber communication technology, optical fiber-based sensing technology has gradually developed and been widely used. Its principle is that during optical pulse transmission, the distribution of the reflected light spot and the reflection angle are modulated by pressure. The measuring end uses demodulation equipment to analyze the reflected light information and indirectly calculate the pressure at the monitoring point. Due to its advantages such as high accuracy, small size, resistance to electromagnetic interference and corrosion, optical fiber sensors are used in fields such as medicine, construction, and aerospace. Summary of the Invention

[0004] The technical problem solved by this invention is to design a method and system for measuring weak pressure based on thin-film reflection, providing an effective and reliable method and system for measuring weak pressure.

[0005] The technical solution adopted in this invention is as follows: A method and system for measuring weak pressure based on thin-film reflection, comprising a light source, an optical fiber pressure probe, a signal acquisition module, a signal processing module, and a signal display module. The optical fiber pressure probe includes a thin film, a dual-fiber coupler, and a sleeve. The signal acquisition module includes a phototransistor and a driving circuit. The signal processing module includes a signal amplification circuit and a signal demodulation circuit. The method steps are as follows: When the light beam emitted by the light source is projected onto the surface of the thin film through the emitting optical fiber, the thin film deforms under external pressure, causing changes in the distribution of the reflected light spot and the reflection angle, thus achieving signal modulation. The emitting optical fiber receives the reflected signal. The signal acquisition module acquires the light intensity signal from the emitting optical fiber and converts it into an electrical signal. The signal processing module amplifies and processes the acquired information, achieving signal demodulation. The signal display module displays the processing result, thus achieving the purpose of presenting the weak pressure result.

[0006] The core formula design method of the above signal processing module, and the specific steps are as follows:

[0007] The elastic deformation of a thin film follows the thin-plate small deflection theory. ,in Central displacement It is directly proportional to the pressure P, R is the film radius, E is the elastic modulus, h is the thickness, and ν is Poisson's ratio.

[0008] A fixed-wavelength light source emits a beam that travels through an incident fiber to illuminate a deformed thin film. Due to specular reflection caused by the metal coating, the beam is received by the end face of the exiting fiber. During this process, the thin film undergoes a normal displacement Δd, causing a change in the distance between the fiber end face and the reflecting surface, as well as a shift in the reflection angle. The overlap area between the reflected light spot and the end face of the exiting fiber determines the coupling efficiency, while the receiving power coefficient k is determined by the optical path geometry parameters. The radial displacement Δr and the effective receiving radius of the thin film are also considered. Satisfying Δr < 0.3 Within the linear working region, the formula can be simplified to This indicates that the change in light intensity is quasi-linear with respect to displacement (nonlinear error <2%), and the change in light intensity is negatively correlated with pressure.

[0009] Fiber optic pressure probe fabrication: During the fabrication of the fiber optic pressure probe, the initial distance between the fiber end face and the reflecting surface, i.e. the size of the cavity length, directly affects the sensor performance. By building a displacement platform to limit the appropriate step size scanning distance, and simultaneously comparing the cavity length with the voltage signal acquired by the signal acquisition module, based on the distance-voltage response characteristic analysis, the cavity length with stable signal slope in the adjacent interval is selected as the initial distance, and the cavity length value is determined.

[0010] After measuring several cavity lengths and power data using a fiber optic pressure probe, pressure-voltage characteristic analysis was performed, revealing a relationship between pressure and voltage. K represents the sensitivity in the pressure-voltage relationship, with units of V / Pa. Since the initial pressure voltage is zero, a calibration test using a standard pressure source is required, and the average value is then used to determine the value. This relationship is the core formula for the signal processing module to calculate the pressure value.

[0011] Compared with traditional pressure sensors, the advantages of this invention are that the incident and output optical fibers are arranged independently, eliminating the beam splitter loss and Rayleigh backscattering noise in the single-fiber scheme and improving the signal-to-noise ratio; the use of a metal-coated thin film as a deformation reflective surface, whose high mechanical resilience ensures reflection stability under strain and is not easily damaged; the manufacturing process is simple, green, safe and environmentally friendly, without the need for special treatment of the optical fiber itself, such as end-face coating, cutting, fusion splicing, etc., avoiding the environmental pollution (the film is recyclable and there is no heavy metal pollution) and processing risks (no need for high temperature conditions or use of hazardous chemical materials such as hydrofluoric acid) caused by the manufacturing and use of traditional optical fiber sensors. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the process of the present invention;

[0013] Figure 2 This is a schematic diagram of the structure of some components of the fiber optic pressure probe of the present invention;

[0014] Figure 3 This is a diagram illustrating the working effect of the fiber optic pressure probe of the present invention.

[0015] Figure 4 This is an overall effect diagram of the present invention;

[0016] Figure 5 This is a schematic diagram of the internal fiber distribution of the fiber optic pressure probe of the present invention. Detailed Implementation

[0017] The following is a detailed description of the implementation of the present invention with reference to the accompanying drawings.

[0018] A method and system for measuring weak pressure based on thin-film reflection is disclosed, comprising a light source, an optical fiber pressure probe, a signal acquisition module, a signal processing module, and a signal display module. The optical fiber pressure probe includes a thin film, a dual-fiber coupler, and a sleeve. The signal acquisition module includes a phototransistor and a driving circuit. The signal processing module includes a signal amplification circuit and a signal demodulation circuit. The specific preparations for this experiment are as follows:

[0019] The light source uses a single, fixed-wavelength 700nm light-emitting diode and a matching driving circuit. In the fabrication of the fiber optic pressure probe, a 75μm thick PET film (biaxially oriented polyester film) is used as the core sensitive material, with an aluminum reflective layer on the surface. The film is precisely machined into a circular structure with a diameter of Φ=2.5 mm using a precision rounding tool. A sleeve with annular grooves engraved on its end face is fabricated using polystyrene (PS). The edges of the PET film are fixed to the sleeve using UV-curable adhesive, and then cured using a UV lamp. The sleeves are then connected and installed to form the pressure probe.

[0020] Since the dual-fiber coupled signal is related to the cavity length, in the fabrication of the fiber optic pressure probe, a scanning interval of 0.1 mm was used to simultaneously acquire the output voltage and observe the signal curve. The initial spacing between the fiber end face and the PET reflective film (…) This directly affects sensor performance. Based on the spacing-voltage response characteristic analysis, the optimal value was selected. =0.8mm, the signal slope in this adjacent interval is stable, exhibiting both high sensitivity and good linearity. The sensor sensitivity remains highly consistent under different initial voltage settings, demonstrating excellent linearity. K is ultimately taken as the average sensitivity of -0.0215mV / Pa, yielding the sensor's pressure-voltage output relationship as follows: This relationship is the core formula for the signal processing module to calculate the pressure value.

[0021] In the signal processing module, the ESP8266 microcontroller was selected as the core processing unit for this project. The high-precision analog-to-digital converter ADS1115 was controlled through the I2C bus protocol to realize the acquisition and processing of weak voltage signals. Finally, the data was output to the signal display module for real-time display.

[0022] Using an embedded system, precise data acquisition and demodulation of the experimental setup were achieved, and pressure data was presented in real time. The symbols used are explained below:

[0023] Zero initial pressure voltage The voltage level under no-pressure input can be calibrated via command.

[0024] Current voltage Current device output voltage;

[0025] pressure value The pressure value calculated by the system ( ).

[0026] Calibration tests were performed using a standard pressure source, and multiple sets of measurements were taken. The data is 88.3mV. The values ​​were 79.1mV, 79.0mV, 79.0mV, 79.0mV, and 79.0mV, respectively. The average of these values ​​yielded the corresponding calculated output value. The pressure was 423 Pa, with an error of only 0.84% ​​compared to the standard pressure source setting of 426.4 Pa. The nonlinear error distribution mainly deviated in the low-pressure region (0-100 Pa), primarily due to the initial pretension of the membrane. The medium-pressure region (100-400 Pa) was the optimal linear region, with an error of <0.15%FS.

Claims

1. A method and system for measuring weak pressure based on thin-film reflection, comprising a light source, an optical fiber pressure probe, a signal acquisition module, a signal processing module, and a signal display module, characterized in that, The fiber optic pressure probe includes a thin film, a dual fiber optic coupler, and a sleeve; the signal acquisition module includes a phototransistor and a driving circuit; and the signal processing module includes a signal amplification circuit and a signal demodulation circuit.

2. The weak pressure measurement system based on thin-film reflection according to claim 1, characterized in that, The other end of the incident optical fiber is connected to a light source, and the other end of the output optical fiber is connected to a signal acquisition module. The signal acquisition module is connected to a signal processing module and a signal display module.

3. The weak pressure measurement system based on thin-film reflection according to claim 1, characterized in that, The film has good deformation and recovery capabilities, and the surface is coated with a reflective layer to effectively improve light reflectivity.

4. The weak pressure measurement system based on thin-film reflection according to claim 1, characterized in that, The dual fiber coupler is coupled in a Y-type structure and has the following characteristics: the two fiber cores are parallel and the spacing is between 0 and 700 μm, and the included angle of the end face axis near the thin film is between 0° and 180°.

5. A weak pressure measurement system based on thin-film reflection according to claim 1, characterized in that, The sleeve has an annular groove at the interface between the sleeve and the dual fiber optic coupling end, which encloses the thin film of claim 3 and the dual fiber optic coupler of claim 4 inside the sleeve.

6. The weak pressure measurement system based on thin-film reflection according to claim 1, characterized in that, The light source is a fixed wavelength light source, and the peak wavelength of the phototransistor response matches the wavelength of the light source.

7. A method for measuring weak pressure based on thin-film reflection according to claims 1-6, characterized in that, The method includes the following steps: (1) Signal modulation: When the light beam emitted by the light source is projected onto the surface of the thin film through the incident optical fiber, the thin film deforms under the action of external pressure, causing changes in the distribution of reflected light spots and the reflection angle, thereby realizing signal modulation. (2) Signal demodulation: The outgoing optical fiber receives the reflected signal, the signal acquisition module acquires the light intensity signal of the outgoing optical fiber and converts it into an electrical signal, the signal processing module amplifies and processes the acquired electrical information to realize signal demodulation, and the signal display module displays the processing result.

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