Miniaturized high-frequency sensing detection system based on photoacoustic spectrum

Abstract

The invention belongs to the technical field of photoacoustic spectrum sensors, and particularly relates to a miniaturized high-frequency photoacoustic spectrum-based sensing detection system, which comprises a photoacoustic cell, and a light source module, a sound wave detection module and a driving and signal processing module which are arranged in the photoacoustic cell, the light source module comprises a light source and a galvanometer, and the galvanometer is used for modulating a path of an optical signal emitted by the light source and then reflecting the optical signal back into the photoacoustic cell so as to excite transition of an object to be detected in the photoacoustic cell to generate a photoacoustic signal; and the driving and signal processing module is used for driving the light source to emit a light signal, receiving a photoacoustic signal detected by the sound wave detection module and processing the signal to obtain the concentration of an object to be detected. The high modulation frequency of the galvanometer and the characteristics of a deflection light path are utilized, pressure waves with high frequency are obtained, the response speed is shortened, and the measurement precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoacoustic spectroscopy sensors, and in particular relates to a miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system. Background Art

[0002] As a highly sensitive and selective gas detection method, photoacoustic spectroscopy sensing technology has shown great potential in environmental monitoring, industrial process control, medical diagnosis and other fields in recent years. Its core principle is to generate photoacoustic signals by exciting gas molecules with lasers, and then capture the signals through acoustic sensors to achieve quantitative analysis. For example, photoacoustic spectroscopy technology uses CO2 gas molecules to absorb light energy of a specific 4.26μm wavelength and transition from the ground state to the excited state. Subsequently, the excited state molecules release heat energy and kinetic energy through non-radiative relaxation (such as collisions), causing the local temperature of the gas to rise and the volume to expand. If the incident light is modulated so that the light signal has a modulation frequency, the temperature and volume of the gas inside the photoacoustic cell will change periodically with the modulation frequency of the light signal, resulting in periodic changes in pressure, and ultimately generating photoacoustic signals (pressure waves).

[0003] Compared to electrochemical or infrared gas sensor technologies, photoacoustic spectroscopy is a background-free spectral measurement technology with advantages such as long life, strong anti-interference ability, and good selectivity. However, the mainstream gas sensors based on photoacoustic spectroscopy currently on the market have the disadvantages of high cost, complex structure, high energy consumption, and inability to be applied to vehicle-mounted systems or precision instruments due to the use of large equipment such as cascade lasers, resonant photoacoustic cells, and photoacoustic spectrometers. In addition, existing miniaturized gas sensors based on photoacoustic spectroscopy all obtain photoacoustic signals by modulating MEMS light sources to obtain frequency optical signals. Due to the long thermal response time of MEMS light sources, mostly about 10ms-20ms, the frequency of the obtained photoacoustic signals is low, resulting in poor sensitivity and accuracy of the entire system. Summary of the Invention

[0004] The purpose of the present invention is to provide a miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system, which utilizes the high modulation frequency and deflection optical path characteristics of the galvanometer to solve the problems of slow response speed and low accuracy of existing photoacoustic spectroscopy sensing.

[0005] To achieve the above object, the present invention provides a sensing detection system based on photoacoustic spectroscopy technology, comprising a photoacoustic cell and a light source module, an acoustic wave detection module, and a driving and signal processing module arranged in the photoacoustic cell;

[0006] The light source module includes a light source and a galvanometer, wherein the galvanometer is used to modulate the path of the light signal emitted by the light source and reflect it back into the photoacoustic cell to stimulate the transition of the object to be measured in the photoacoustic cell to generate a photoacoustic signal;

[0007] The driving and signal processing module is used to drive the light source to emit a light signal, and to receive the photoacoustic signal detected by the acoustic wave detection module, and to process the signal to obtain the concentration of the object to be detected.

[0008] Furthermore, the rotation frequency of the galvanometer is 500-2000 Hz.

[0009] Furthermore, the galvanometer is driven by a PWM modulation signal with a duty cycle of 20%-80%, and the vibration frequency f1 of the galvanometer and the frequency f2 of the PWM modulation signal satisfy f2=f1×d, where d represents the duty cycle.

[0010] Furthermore, the galvanometer includes a rectangular frame and a support beam arranged on the rectangular frame, a mirror surface is set on the support beam, and the rotation of the mirror surface is achieved by driving the support beam to twist.

[0011] Furthermore, the oscillating mirror is a MEMS oscillating mirror, and the oscillating mirror is fixedly arranged between the inner wall of the photoacoustic cell and the light source.

[0012] Furthermore, the light source is a MEMS infrared radiation light source, and the surface of the light source is covered with a filter for modulating the wavelength of the light signal to be consistent with the absorption wavelength of the object to be measured.

[0013] Furthermore, the acoustic wave detection module includes a microphone for converting the photoacoustic signal into an electrical signal, and preferably also includes a lock-in amplifier.

[0014] Furthermore, the object to be detected is gas, and a microporous membrane is provided on the photoacoustic cell for gas exchange with the outside world.

[0015] Furthermore, the photoacoustic cell is a non-resonant photoacoustic cell.

[0016] Furthermore, a temperature and humidity sensor is provided in the photoacoustic cell for transmitting temperature and humidity signals back to the driving and signal processing module for concentration calculation and compensation of the object to be measured.

[0017] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0018] 1. The sensing detection system based on photoacoustic spectroscopy technology provided by the present invention drives the galvanometer to change the optical path and obtain a light signal with a higher modulation frequency. The resulting photoacoustic signal also has a higher frequency, which enables the sensor to have higher accuracy and shorter response time. In addition, by deflecting the path and periodically scanning different areas, it helps to improve the signal strength.

[0019] 2. The present invention drives the galvanometer through a signal with a preset duty cycle, so that the galvanometer vibrates and stops periodically in each modulation cycle, thereby producing non-uniform irradiation and absorption of the gas in the photoacoustic cell, causing changes in gas expansion and further generating periodic pressure waves.

[0020] 3. The present invention uses a non-resonant photoacoustic cell and an MCU chip to drive the entire sensor, achieving miniaturization and intelligence of the entire sensor, making the sensor based on photoacoustic spectroscopy smaller and less expensive. Furthermore, through the temperature and humidity sensor, the humidity and temperature of the working environment are monitored in real time and the measurement accuracy is compensated. The present invention has the advantages of miniaturization, intelligence, strong selectivity, high accuracy, short response time, strong anti-interference ability, long life, and low cost, making it suitable for use in vehicle-mounted systems or precision instruments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the module structure of the miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system in the present invention.

[0022] Figure 2 This is a schematic diagram of the appearance and structure of the miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system in the present invention.

[0023] Figure 3 Schematic diagram of the internal structure of the miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system in the present invention.

[0024] Figure 4 This is a schematic diagram of the structure of the MEMS galvanometer of the miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system in the present invention.

[0025] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0026] 1-MEMS light source; 2-MEMS galvanometer; 3-temperature and humidity sensor; 4-microphone; 5-MCU; 6-non-resonant photoacoustic cell; 7-microporous membrane. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0028] The present invention uses a MEMS galvanometer to partially deflect the radiated light generated by a MEMS light source, and then drives the MEMS light source to make the partially deflected light signal obtain a higher frequency, thereby obtaining a higher-frequency photoacoustic signal, solving the problems of existing photoacoustic spectroscopy sensing, such as slow response speed, low accuracy, and complex structure. The details are as follows:

[0029] See also Figure 1-4 The present invention provides a miniaturized high-frequency sensing detection system based on photoacoustic spectroscopy, which mainly includes a photoacoustic cell and a light source module, an acoustic wave detection module, and a driving and signal processing module arranged in the photoacoustic cell.

[0030] Among them, the light source module includes a light source and a galvanometer. The galvanometer is used to modulate the path of the light signal emitted by the light source and reflect it back into the photoacoustic cell to stimulate the transition of the object to be measured in the photoacoustic cell to generate a photoacoustic signal; the driving and signal processing module is used to drive the light source to emit a light signal, and receive the photoacoustic signal detected by the acoustic wave detection module, and process the signal to obtain the concentration of the object to be measured.

[0031] This setup, utilizing the higher modulation frequency of the galvanometer and the characteristics of the deflection optical path, can solve the problems of existing photoacoustic spectroscopy sensing, such as slow response speed, low accuracy, and complex structure.

[0032] The analyte is preferably a target gas in a liquid or gaseous environment, such as carbon dioxide, nitrogen, hydrogen, or methane. The photoacoustic cell exchanges gas with the outside world through vents covered by a microporous breathable membrane. The membrane is provided with micropores with a diameter of several microns and is made of expanded polytetrafluoroethylene. This ensures effective gas exchange between the inside and outside of the photoacoustic cell while also preventing leakage of acoustic signals.

[0033] Preferably, a temperature and humidity compensation module is further provided in the photoacoustic cell, such as a temperature and humidity sensor, which can monitor the humidity and temperature of the working environment in real time, thereby effectively compensating for the gas measurement accuracy.

[0034] Preferably, the rotation frequency of the galvanometer is 500-2000 Hz. By utilizing the high frequency of the galvanometer, the photoacoustic signal finally obtained also has a higher frequency, thereby improving the detection accuracy and shortening the response time.

[0035] Specifically, the galvanometer is driven by a PWM modulation signal with a duty cycle of 20%-80%. The galvanometer's vibration frequency f1 and the PWM modulation signal's frequency f2 satisfy f2 = f1 × d, where d represents the duty cycle. For example, if the galvanometer's vibration frequency f1 is 1000 Hz and the duty cycle is 50%, the PWM modulation signal's frequency f2 is 500 Hz. If the duty cycle is 60%, f2 is 600 Hz. In practical applications, the appropriate frequency and duty cycle can be selected based on the thermal delay time of the gas to be measured.

[0036] This setting makes the power-on time of each cycle the same as the time of one vibration cycle of the galvanometer, so that the galvanometer vibrates and stops periodically, and dual frequency control is implemented to improve signal integration and thus improve detection sensitivity.

[0037] In particular, the present invention can also further increase the integration of photoacoustic signals by adding intensity frequency modulation. The scanning path can also be regulated by adjusting the shape of the photoacoustic pool and the position of the galvanometer in the photoacoustic pool, and then the non-uniform scanning can be regulated, thereby realizing the regulation of the photoacoustic signal. For example, the part of the photoacoustic pool covered by the galvanometer scanning path is set to an arc shape, and the focus of the galvanometer is set at the center of the arc shape, so that the distance of the entire scanning path is the same. Alternatively, the photoacoustic pool is set to a rectangular parallelepiped or cubic structure, so that the path distance of a single scan is different, the absorption non-uniformity is improved, and the generation of photoacoustic signals is promoted. The signal is then processed in combination with the path information to obtain the gas concentration.

[0038] In some specific embodiments, the galvanometer is a MEMS galvanometer, which is fixedly arranged between the inner wall of the photoacoustic pool and the light source. The MEMS galvanometer includes a rectangular frame and a support beam arranged on the rectangular frame, and a mirror is set on the support beam. The rotation of the mirror is achieved by driving the torsion of the support beam. For example, the vibration frequency of the MEMS galvanometer is set to 1000Hz, the length of the support beam is about 100μm, the width is about 20μm, and the thickness is about 10μm. The diameter of the mirror is about 1mm and the thickness is about 50μm. The MEMS galvanometer is driven by a PWM modulation signal with a duty cycle of 50% and a frequency of 500Hz, so that it obtains a vibration frequency of about 1kHz.

[0039] Preferably, the light source is a MEMS infrared radiation light source. The MEMS light source uses a frequency-modulated blackbody infrared radiation light source, which can emit infrared light in the range of 2 to 14 μm. The average emissivity is highest when the light source power is 250 mW. The cold state resistance is approximately 20 ohms, and the hot state resistance is approximately 25 ohms. The light source surface is covered with a 4.26 μm filter, which filters the infrared light emitted by the MEMS infrared radiation light source into mid-infrared light with a wavelength of 4.26 μm. The drive and signal processing system is an MCU microprocessor.

[0040] See also Figure 2 and 3 The bottom of the sensing detection system based on photoacoustic spectroscopy technology is a PCB board, and the photoacoustic cell is covered on it. All internal components are integrated on the bottom. Specifically, taking CO2 as an example, the non-resonant photoacoustic cell 6 adopts an aluminum rectangular metal shell with a smooth interior, which is attached to the bottom PCB board through thermal gel; the size of the photoacoustic cell is 12.7*12.7*11mm, and there is an air hole with a diameter of about 1mm on the top, and it is covered with a layer of microporous breathable membrane, and is made of expanded polytetrafluoroethylene material. It uses a multi-layer micro-nano film structure, which can effectively improve the anti-interference ability of the sensor. The entire photoacoustic cell is made of aluminum metal and is polished, which can enhance the interaction between light and gas molecules, greatly improve the reflectivity of infrared light, and reduce the loss of sound waves during transmission.

[0041] The MCU drives the light source system to generate light signals. The CO2 gas inside the photoacoustic pool generates photoacoustic signals after absorbing light molecules in a specific band. The signals are then transmitted to the microphone of the sound wave detection system controlled by the MCU for sampling and output, and then transmitted back to the MCU. At the same time, the MCU also drives the temperature and humidity compensation system to enable the temperature and humidity sensor to detect the temperature and humidity and transmit them back to the MCU for CO2 concentration calculation and compensation. Finally, the CO2 concentration is obtained through internal signal processing of the MCU, and the information is transmitted to another MCU and displayed on the broken code screen.

[0042] Preferably, the MEMS light source 1 in the light source system is installed at the bottom of the photoacoustic cell, and the MEMS galvanometer 2 is installed at a specific angle at the bottom of the photoacoustic cell, as shown in the schematic diagram. Figure 4 As shown, the length of the support beam is about 100μm, the width is about 20μm, and the thickness is about 10μm. The mirror is usually made of single crystal silicon or polycrystalline silicon and is metal-plated on the surface to improve the reflectivity of light. The diameter is about 1mm and the thickness is about 50μm. f0 is the resonant frequency of the galvanometer. Where, I is the moment of inertia, and I total =I mirror +I beam ,and Where m is the mass of the lens and r is the radius of the mirror. beam is the mass of the cantilever beam, L is the length of the cantilever beam. K is the torsional stiffness, and Where G is the shear modulus of the support beam material, and w, t, and L are the width, thickness, and length of the support beam. This can be calculated to achieve a modulation frequency of approximately 1 kHz.

[0043] In the acoustic wave detection system, the input and output ends of the microphone 4 are both connected to the MCU 5 , which drives and generates a clock signal to control the microphone to sample the photoacoustic signal and transmit it back to the MCU 5 for processing.

[0044] In the temperature and humidity compensation system, the clock line and data line of the temperature and humidity sensor are connected to the MCU. The MCU generates clock data to drive the temperature and humidity sensor to work, and transmits the temperature and humidity data back to the MCU for CO2 concentration calculation and compensation.

[0045] The working principle of the present invention is as follows:

[0046] The entire system is driven by the MCU 5 of the drive and signal processing system. First, a stable driving voltage of 3.3V is supplied to the MEMS light source 1, so that the MEMS light source 1 is always on. Then, a stable driving voltage of 3.3V is supplied to the MEMS galvanometer 2 to drive the MEMS galvanometer 2 so that it has a modulation frequency of 1kHz. The 4.26μm infrared light emitted by the MEMS light source 1 also has a modulation frequency of 1kHz after being reflected by the MEMS galvanometer 2, and a 1kHz optical signal is obtained. After the CO2 gas inside the photoacoustic cell absorbs the optical signal, a corresponding photoacoustic signal is generated. The MCU 5 then drives the MEMS digital microphone 4 to operate and sample the photoacoustic signal and transmit it back to the MCU for data processing. Finally, the MCU 5 drives the temperature and humidity sensor 3 to operate, detect the temperature and humidity data, and transmit it back to the MCU. The CO2 concentration compensation calculation is performed with the data transmitted by the microphone, and finally the CO2 concentration value is obtained. This improves the accuracy of the CO2 concentration while also being able to detect the temperature and humidity of the working environment in real time. For a given infrared light source power, the higher the CO2 concentration, the stronger the generated photoacoustic signal, and the higher the resulting CO2 concentration value, forming a linear relationship. This linear relationship allows for real-time detection of CO2 concentration changes. Furthermore, because the frequency of the optical signal generated in the light source system is very high, the overall system response speed is shortened, improving the accuracy of concentration calculations.

[0047] In summary, the present invention drives the galvanometer to change the optical path and obtains a light signal with a higher modulation frequency, so that the final photoacoustic signal also has a higher frequency. Therefore, while ensuring the miniaturization and intelligence of the sensor, it can also improve the accuracy and shorten the response time. It can be used in vehicle-mounted systems or precision instruments to solve the problems of the current existing photoacoustic spectroscopy gas sensors, such as slow response speed, low accuracy, large size, high cost, complex structure, and high energy consumption.

[0048] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system, characterized in that: It includes a photoacoustic cell and a light source module, an acoustic wave detection module, and a driving and signal processing module, all of which are arranged in the photoacoustic cell; The light source module includes a light source and a galvanometer, wherein the galvanometer is used to modulate the path of the light signal emitted by the light source and reflect it back into the photoacoustic cell to stimulate the transition of the object to be measured in the photoacoustic cell to generate a photoacoustic signal; The driving and signal processing module is used to drive the light source to emit a light signal, and to receive the photoacoustic signal detected by the acoustic wave detection module, and to process the signal to obtain the concentration of the object to be detected.

2. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The rotation frequency of the galvanometer is 500-2000 Hz.

3. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 2, characterized in that: The galvanometer is driven by a PWM modulation signal with a duty cycle of 20%-80%. The vibration frequency f1 of the galvanometer and the frequency f2 of the PWM modulation signal satisfy f2=f1×d, where d represents the duty cycle.

4. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The galvanometer includes a rectangular frame and a support beam arranged on the rectangular frame. A mirror surface is set on the support beam. The rotation of the mirror surface is achieved by driving the support beam to twist.

5. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The oscillating mirror is a MEMS oscillating mirror, and the oscillating mirror is fixedly arranged between the inner wall of the photoacoustic cell and the light source.

6. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The light source is a MEMS infrared radiation light source, and the surface of the light source is covered with a filter for modulating the wavelength of the light signal to be consistent with the absorption wavelength of the object to be measured.

7. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The acoustic wave detection module includes a microphone for converting the photoacoustic signal into an electrical signal.

8. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The object to be detected is gas, and a microporous membrane is provided on the photoacoustic cell for gas exchange with the outside world.

9. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to claim 1, characterized in that: The photoacoustic cell is a non-resonant photoacoustic cell.

10. The miniaturized high-frequency photoacoustic spectroscopy-based sensing detection system according to any one of claims 1 to 9, characterized in that: The photoacoustic cell is also provided with a temperature and humidity sensor for transmitting temperature and humidity signals back to the driving and signal processing module for calculating and compensating the concentration of the object to be measured.

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