Miniature photoacoustic spectrometry gas detection device

Abstract

The utility model provides a miniature photoacoustic spectrometry gas detection device, and belongs to the technical field of photoacoustic spectrometry gas detection. The device comprises a signal processing board, a laser device and a photoacoustic cell, the signal processing board is connected with the laser device, the laser device corresponds to the photoacoustic cell through an optical assembly, an MEMS microphone is arranged in the middle of the photoacoustic cell, a microprocessor, a laser driving temperature control module and a transimpedance amplification filtering module are arranged on the signal processing board, and the transimpedance amplification filtering module is arranged on the signal processing board. The laser driving temperature control module and the transimpedance amplification filtering module are both connected with the microprocessor, the laser driving temperature control module is connected with the laser, and the MEMS microphone is connected with the transimpedance amplification filtering module. According to the utility model, the TO packaging distributed feedback type semiconductor laser is combined with the photoacoustic spectrum system of the MEMS microphone, so that the volume is small, the process is simple, and the large-scale production is facilitated.

Description

Technical Field

[0001] The utility model relates to the technical field of photoacoustic spectroscopy gas detection, in particular to a micro photoacoustic spectroscopy gas detection device. Background Art

[0002] Photoacoustic spectroscopy gas detection is a spectroscopic technique based on the photoacoustic effect. When monochromatic light with a modulated wavelength in the "fingerprint" absorption peak of the gas irradiates the gas sealed in the photoacoustic cell, the gas molecules absorb light energy and jump to the excited state, and then return to the ground state by releasing heat energy, causing the pressure in the cell to change periodically with the modulation frequency of the monochromatic light, thereby forming a sound pressure signal. The sound pressure signal is detected by a microphone such as a tuning fork or a cantilever beam type, and the photoacoustic signal is obtained. After signal processing, the type and concentration of the gas in the photoacoustic cell can be calculated.

[0003] Currently, in the research of photoacoustic spectroscopy gas detection technology, most use a butterfly distributed feedback semiconductor laser as the system light source, and adopt a fiber coupling method. After the light is collimated by a fiber collimator, it irradiates the gas sealed in the photoacoustic cell. The microphone mainly uses a tuning fork or a cantilever beam type vibration sensor. Due to the high manufacturing cost and complex process, it is not conducive to large-scale application. Gas sensors are currently developing towards the trend of miniaturization and low cost. In order to reduce the overall size of the sensor, therefore, it is of great practical significance to design a micro photoacoustic spectroscopy gas detection system.

[0004] The invention patent with the application number 202210466124.3 discloses a micro photoacoustic spectroscopy gas sensor, which includes a MEMS microphone, a MEMS infrared light source, a substrate and a photoacoustic cell. The MEMS microphone, the MEMS infrared light source and the substrate are stacked in sequence. A photoacoustic cell is arranged in the MEMS microphone and the MEMS infrared light source for receiving gas. The MEMS infrared light source emits intermittent infrared radiation, and the MEMS microphone receives the acoustic wave signal generated by the gas absorbing the pulsed radiation of the infrared rays for detecting the gas. The above invention uses the MEMS microphone cavity and the MEMS infrared light source cavity to form a photoacoustic cell, reducing the size of the sensor. The sensor is composed of a MEMS microphone, a MEMS infrared light source and a substrate, with low complexity. When using a silicon substrate with an integrated ASIC circuit, all parts of the sensor are prepared by semiconductor manufacturing processes, reducing costs. However, using the MEMS microphone cavity and the MEMS infrared light source cavity to form a photoacoustic cell to reduce the size has a slow response speed, low sensitivity, and is susceptible to cross-interference from other gases. Summary of the Utility Model

[0005] Aiming at the technical problems of complex manufacturing process and high manufacturing cost of existing photoacoustic spectroscopy gas detection devices, the utility model provides a micro photoacoustic spectroscopy gas detection device, which adopts a TO-packaged distributed feedback semiconductor laser combined with a MEMS process microphone to realize photoacoustic spectroscopy detection, with small volume and simple process.

[0006] In order to achieve the above object, the technical solution of the utility model is realized as follows: A micro photoacoustic spectroscopy gas detection device includes a signal processing board, a laser, and a photoacoustic cell. The signal processing board is connected to the laser, and the laser corresponds to the photoacoustic cell through an optical component. A MEMS microphone is provided in the middle of the photoacoustic cell. A microprocessor, a laser drive temperature control module, and a transimpedance amplification and filtering module are provided on the signal processing board. Both the laser drive temperature control module and the transimpedance amplification and filtering module are connected to the microprocessor. The laser drive temperature control module is connected to the laser, and the MEMS microphone is connected to the transimpedance amplification and filtering module.

[0007] Preferably, the laser is a TO-packaged distributed feedback semiconductor laser.

[0008] Preferably, an input / output module is further provided on the signal processing board, and the input / output module is connected to the microprocessor.

[0009] Preferably, a cavity is provided in the middle of the photoacoustic cell. A first window mirror and a second window mirror are respectively fixed on both sides of the cavity. The light source emitted by the laser, the center of the optical component, the first window mirror, the cavity, and the center of the second window mirror are on the same straight line.

[0010] Preferably, the cavity includes a resonance cavity and a buffer cavity. Buffer cavities are provided on both sides of the resonance cavity. The MEMS microphone is arranged in the middle of the resonance cavity and the MEMS microphone is communicated with the resonance cavity. The MEMS microphone is fixed on a microphone fixing plate, and the microphone fixing plate is fixed on the outside of the photoacoustic cell. An air inlet is provided on one buffer cavity and an air outlet is provided on the other buffer cavity.

[0011] Preferably, the laser is fixed on a laser fixing plate, the optical component is fixed on the laser, and the laser relies on an external heat sink for heat dissipation and direction adjustment. A retaining ring is provided on the front side of the first window mirror and the second window mirror, and the retaining ring corresponds to both sides of the photoacoustic cell. The first window mirror and the second window mirror are connected to the buffer cavity through an O-ring.

[0012] Preferably, the laser is fixed on the signal processing board.

[0013] Preferably, a first reflecting mirror is provided between the laser and the optical component, and the laser and the optical component are respectively arranged on the optical paths on both sides of the first reflecting mirror.

[0014] Preferably, a first reflector is provided at the rear side of the optical component. The laser and the optical component are arranged on the incident light path of the first reflector, and the center of the photoacoustic cell is arranged on the reflected light path of the first reflector.

[0015] Preferably, a second reflector is provided at the rear side of the second window mirror away from the laser. The second reflector faces the center of the photoacoustic cell and is inclined.

[0016] Compared with the prior art, the beneficial effects of the present utility model are as follows: The photoacoustic spectroscopy system using a TO-packaged distributed feedback semiconductor laser combined with a MEMS microphone adopts the tunable semiconductor laser absorption spectroscopy technology, which has a fast response speed, high sensitivity, effectively resists cross-interference of other gases, is small in size, simple in process, and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 It is the principle block diagram of Embodiment 1 of the present utility model.

[0019] Figure 2 It is Figure 1 the exploded view shown.

[0020] Figure 3 It is the principle block diagram of Embodiment 2 of the present utility model.

[0021] Figure 4 It is the principle block diagram of Embodiment 3 of the present utility model.

[0022] Figure 5 It is the principle block diagram of Embodiment 4 of the present utility model.

[0023] Figure 6 It is the principle block diagram of Embodiment 5 of the present utility model.

[0024] Figure 7 It is the principle block diagram of Embodiment 6 of the present utility model.

[0025] In the figure, 1 is a signal processing board, 11 is a microprocessor, 12 is a laser drive temperature control module, 13 is a transimpedance amplification and filtering module, 14 is an input / output module, 2 is a laser, 3 is a photoacoustic cell, 31 is a MEMS microphone, 32 is a first window mirror, 33 is a second window mirror, 34 is an air inlet, 35 is an air outlet, 36 is an O-ring, 37 is a retaining ring, 38 is a microphone fixing plate, 39 is a tower head, 4 is an optical component, 5 is a first reflector, and 6 is a second reflector. Detailed implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] Embodiment 1

[0028] As Figure 1 shown, a micro photoacoustic spectroscopy gas detection device includes a signal processing board 1, a laser 2, and a photoacoustic cell 3. The signal processing board 1 is connected to the laser 2, and the laser 2 corresponds to the photoacoustic cell 3 through an optical component 4. It is characterized in that a MEMS microphone 31 is provided in the middle of the photoacoustic cell 3. A microprocessor 11, a laser drive temperature control module 12, and a transimpedance amplification and filtering module 13 are provided on the signal processing board 1. Both the laser drive temperature control module 12 and the transimpedance amplification and filtering module 13 are connected to the microprocessor 11. The laser drive temperature control module 12 is connected to the laser 2, and the MEMS microphone 31 is connected to the transimpedance amplification and filtering module 13. The laser 2 in this application is a TO-packaged distributed feedback semiconductor laser.

[0029] An input / output module 14 is further provided on the signal processing board 1, and the input / output module 14 is connected to the microprocessor 11. The input / output module 14 includes a liquid crystal display screen for data input and output. The liquid crystal display screen is a color dot matrix screen produced by companies such as Deven.

[0030] The microprocessor 11 is selected from STM32 series single-chip microcomputers or Xilinx FPGAs. The function of the laser drive temperature control module 12 is that the microprocessor 11 controls the internal temperature of the laser and drives the laser to emit light through a PID algorithm. The function of the transimpedance amplification and filtering module 13 is to convert the current signal of the MEMS microphone into a voltage signal and amplify and filter the voltage signal to facilitate subsequent acquisition by the microprocessor. The chip in the laser drive temperature control module 12 uses a TEC control chip from companies such as TI or ADI, and the chip in the transimpedance amplification and filtering module 13 uses a dedicated transimpedance amplification chip from companies such as TI or ADI.

[0031] The microprocessor 11 generates a modulation signal, which controls the temperature of the laser 2 through the laser driving and temperature control module 12 and drives the laser 2 to emit modulated light containing the wavelength of the "fingerprint" absorption peak of the gas. The modulated light is collimated by the optical component 4 and then irradiated onto the gas sealed in the photoacoustic cell 3 through the first window mirror 32 of the photoacoustic cell 3. The gas absorbs the modulated light to generate heat to form a sound pressure signal. The MEMS microphone 31 senses the sound pressure signal. The sound pressure signal sensed by the MEMS microphone is converted into a voltage signal by the transimpedance amplification and filtering module 13. The microprocessor 11 collects the voltage signal, calculates the concentration of the gas sealed in the photoacoustic cell through data processing and interpolation algorithm of the software / digital lock-in amplification technology, and communicates or displays externally through the input / output module 14.

[0032] The function of the second window mirror 33 is not only to transmit the light passing through the photoacoustic cell 3, but also to seal the photoacoustic cell, as Figure 1 shown. The optical component 4 includes a lens, which collimates the light emitted by the laser. The lens can be directly fixed on the outside of the TO package distributed feedback semiconductor laser to form a TO package laser with collimation function.

[0033] A cavity is provided in the middle of the photoacoustic cell 3. The first window mirror 32 and the second window mirror 33 are respectively fixed on both sides of the cavity. The light source emitted by the laser 2, the center of the optical component 4, the first window mirror 32, the cavity and the center of the second window mirror 33 are on a straight line to ensure the straight transmission of the modulated light emitted by the laser. The main functions of the first window mirror 32 and the second window mirror 33 are to seal the light inlet and outlet of the photoacoustic cell 3.

[0034] The schematic diagram of the structural explosion diagram of the present utility model is as Figure 2 shown, and mainly includes a signal processing board 1, a TO package laser, a first window mirror 32, a photoacoustic cell 3, and a MEMS microphone 31. The cavity includes a resonance cavity and a buffer cavity. Buffer cavities are provided on both sides of the resonance cavity. The MEMS microphone 31 is arranged in the middle of the resonance cavity and the MEMS microphone 31 is communicated with the resonance cavity. The MEMS microphone 31 is fixed on the microphone fixing plate 38, and the microphone fixing plate 38 is fixed on the outside of the photoacoustic cell 3. The main function of the MEMS microphone 31 is to collect the sound pressure signal in the photoacoustic cell. The size of the MEMS microphone is less than 5*3*1 (mm).

[0035] An air inlet 34 is provided on one buffer cavity, and an air outlet 35 is provided on the other buffer cavity. The main functions of the air inlet 34 and the air outlet 35 are that the gas in the photoacoustic cell 3 can interact with the outside. The air inlet 34 and the air outlet 35 are both connected to the buffer cavity of the photoacoustic cell 3 through a ferrule 39. The function of the ferrule 39 is to quickly connect the external air pipe.

[0036] As Figure 2As shown, the laser 2 is fixed on the laser fixing plate 21, and the optical component 4 is fixed on the laser 2 to form a collimated TO packaged laser. The laser 2 is disposed on the heat sink 22, and the function of the heat sink 22 is to dissipate heat from the laser 2. Moreover, the laser 2 can be finely adjusted by adjusting the screws on the heat sink, so that the light emitted by the laser passes through the photoacoustic cell. A retaining ring 37 is provided on the front sides of the first window mirror 32 and the second window mirror 33. The retaining ring 37 corresponds to both sides of the photoacoustic cell 3, and the first window mirror 32 and the second window mirror 33 are fixed on the photoacoustic cell 3 through the retaining ring 37. The first window mirror 32 and the second window mirror 33 are connected to the buffer cavity through an O-ring 36. The O-ring 36 ensures the sealed connection between the first window mirror 32 and the second window mirror 33 and the photoacoustic cell 3, does not affect the transmission of the modulated light, and ensures that the gas to be measured in the photoacoustic cell 3 does not leak.

[0037] TO packaged lasers with cooling and collimating lenses include TO46, TO60, etc. The specific size of TO60 is ø6*6.3 (mm), which directly collimates the light output and has a small volume. The specific size of a conventional 14-pin butterfly packaged laser with cooling and a pigtail is 30*12.7*8.2 (mm). If it is applied to a photoacoustic spectroscopy system, a fiber collimator needs to be added to collimate the light output. Coupled with the allowable coiling and bending radius of the optical fiber (greater than 20 mm), the volume is very large.

[0038] The main function of the TO packaged laser is to output light containing the wavelength of the "fingerprint" absorption peak of the gas. After being collimated by the optical component, it irradiates the inside of the photoacoustic cell 3. The main function of the signal processing board is to control the temperature of the laser 2 and drive the laser 2 to emit light through the laser drive temperature control module 12; the electrical signal generated by the MEMS microphone 31 is amplified by the transimpedance amplification and filtering module 12 and collected by the microprocessor 11. The gas concentration in the photoacoustic cell is calculated through data processing and interpolation algorithms inside the microprocessor 11. The main function of the photoacoustic cell 3 is that when the modulated monochromatic light at the "fingerprint" absorption peak of the gas irradiates the gas sealed in the photoacoustic cell, the gas molecules absorb light energy and will jump to the excited state, and return to the ground state by releasing heat energy, causing the pressure in the photoacoustic cell 3 to change periodically with the modulation frequency of the monochromatic light, thereby forming an acoustic pressure signal. The size of the photoacoustic cell is at the mm level. The photoacoustic spectroscopy gas detection device composed of the present application has a small size, and the overall size is much smaller than 10 cm, which is suitable for the development trend of miniaturization of gas sensors.

[0039] Embodiment 2

[0040] As Figure 3As shown in the figure, a micro photoacoustic spectroscopy gas detection device is provided. A second reflector 6 is provided at the rear side of the second window mirror 33 away from the laser 2. The second reflector 6 faces the center of the photoacoustic cell 3. The laser passing through the photoacoustic cell 3 is reflected back into the photoacoustic cell 3 after passing through the second reflector 6 and the second window mirror 33. According to the Lambert-Beer law, the concentration of the gas is proportional to the optical path. A second reflector 6 can be added behind the second window mirror 32. The main function is to reflect the outgoing light back into the photoacoustic cell 3, increase the optical path of the gas absorption in the photoacoustic cell 3, and thus improve the detection sensitivity of the system.

[0041] The second reflector 6 is inclined, which can prevent the reflected laser from being not on the same straight line as the modulated light emitted by the laser 2, and avoid the light reflected into the photoacoustic cell from irradiating the inner wall of the photoacoustic cell, so as to reduce unnecessary noise.

[0042] Other structures and principles are the same as those in Embodiment 1.

[0043] Embodiment 3

[0044] As Figure 4 shown in the figure, a micro photoacoustic spectroscopy gas detection device, the laser 2 is directly fixed on the signal processing board 1. A first reflector 5 is provided between the laser 2 and the optical component 4. The laser 2 and the optical component 4 are respectively arranged on the optical paths on both sides of the first reflector 5. The laser 2 is reflected by the first reflector 5 and reaches the photoacoustic cell 3 after being converged by the optical component 4. The advantage is that the laser 2 is fixed to the signal processing board, reducing the connection wires between the laser fixing board 21 and the signal processing board 1. However, compared with Embodiments 1 and 2, the added first reflector 5 results in a larger overall volume and a more complex process.

[0045] Other structures and principles are the same as those in Embodiment 1.

[0046] Embodiment 4

[0047] As Figure 5 shown in the figure, a micro photoacoustic spectroscopy gas detection device, a second reflector 6 is provided at the rear side of the second window mirror 33 away from the laser 2. The second reflector 6 faces the center of the photoacoustic cell 3 and the second reflector 6 is inclined, improving the reflection sensitivity. The main function of the second reflector 6 is to reflect the outgoing light back into the photoacoustic cell 3, increase the optical path of the gas absorption in the photoacoustic cell, and thus improve the detection sensitivity of the system.

[0048] Other structures and principles are the same as those in Embodiment 3.

[0049] Embodiment 5

[0050] As Figure 6As shown in the figure, a micro photoacoustic spectroscopy gas detection device, the laser 2 is fixed on the signal processing board 1, a first reflector 5 is provided at the rear side of the optical component 4, the laser 2 and the optical component 4 are arranged on the incident light path of the first reflector 5, and the center of the photoacoustic cell 3 is arranged on the reflected light path of the first reflector 5. The modulated light emitted by the laser 2 is converged by the optical component 4 and then reflected by the first reflector 5 to reach the photoacoustic cell 3. The advantage is that the laser 2 is fixed to the signal processing board, reducing the connection wires between the laser fixing board 21 and the signal processing board 1. The difficulty is that the added first reflector causes the volume to increase and the process to be complex.

[0051] Other structures and principles are the same as those in Embodiment 1.

[0052] Embodiment 6

[0053] As Figure 7 As shown in the figure, a micro photoacoustic spectroscopy gas detection device. In order to improve the sensitivity of the reflection micro photoacoustic spectroscopy system, a second reflector 6 is provided at the rear side of the second window mirror 33 away from the laser 2. The second reflector 6 is directly opposite to the center of the photoacoustic cell 3 and the second reflector 6 is inclined. The main function of the second reflector 6 is to reflect the outgoing light back to the photoacoustic cell again, increasing the optical path of the gas absorption in the photoacoustic cell, thereby improving the detection sensitivity of the system.

[0054] Other structures and principles are the same as those in Embodiment 5.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A micro photoacoustic spectroscopy gas detection device, comprising a signal processing board (1), a laser (2) and a photoacoustic cell (3), wherein the signal processing board (1) is connected to the laser (2), and the laser (2) corresponds to the photoacoustic cell (3) through an optical component (4), characterized in that: A MEMS microphone (31) is provided in the middle of the photoacoustic cell (3); a microprocessor (11), a laser-driven temperature control module (12) and a transimpedance amplification and filtering module (13) are provided on the signal processing board (1); the laser-driven temperature control module (12) and the transimpedance amplification and filtering module (13) are both connected to the microprocessor (11); the laser-driven temperature control module (12) is connected to the laser (2); and the MEMS microphone (31) is connected to the transimpedance amplification and filtering module (13).

2. The micro-photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The laser (2) is a TO-packaged distributed feedback semiconductor laser.

3. The micro-photoacoustic spectroscopy gas detection device according to claim 1 or 2, characterized in that: The signal processing board (1) is also provided with an input / output module (14), and the input / output module (14) is connected to the microprocessor (11).

4. The micro-photoacoustic spectroscopy gas detection device according to claim 1 or 2, characterized in that: A cavity is provided in the middle of the photoacoustic cell (3), a first window mirror (32) and a second window mirror (33) are respectively fixed on both sides of the cavity, and the light source emitted by the laser (2) is in a straight line with the center of the optical component (4), the first window mirror (32), the cavity and the center of the second window mirror (33).

5. The micro-photoacoustic spectroscopy gas detection device according to claim 4, characterized in that: The cavity comprises a resonance cavity and a buffer cavity, buffer cavities are provided on both sides of the resonance cavity, a MEMS microphone (31) is arranged in the middle of the resonance cavity and the MEMS microphone (31) is connected to the resonance cavity, the MEMS microphone (31) is fixed on a microphone fixing plate (38), and the microphone fixing plate (38) is fixed on the outside of the photoacoustic pool (3); an air inlet (34) is provided on one buffer cavity, and an air outlet (35) is provided on the other buffer cavity.

6. The micro-photoacoustic spectroscopy gas detection device according to claim 4, characterized in that: The laser (2) is fixed on a laser fixing plate (21), the optical component (4) is fixed on the laser (2), and the laser (2) relies on an external heat sink (22) to dissipate heat and adjust its direction; the front sides of the first window mirror (32) and the second window mirror (33) are provided with a pressing ring (37), the pressing ring (37) corresponds to the two sides of the photoacoustic cell (3), and the first window mirror (32) and the second window mirror (33) are connected to the buffer chamber via an O-ring (36).

7. The micro-photoacoustic spectroscopy gas detection device according to claim 4, characterized in that: The laser (2) is fixed on the signal processing board (1).

8. The micro-photoacoustic spectroscopy gas detection device according to claim 7, characterized in that: A first reflector (5) is provided between the laser (2) and the optical component (4), and the laser (2) and the optical component (4) are respectively arranged on the optical paths on both sides of the first reflector (5).

9. The micro-photoacoustic spectroscopy gas detection device according to claim 7, characterized in that: A first reflector (5) is provided on the rear side of the optical component (4), the laser (2) and the optical component (4) are arranged on the incident light path of the first reflector (5), and the center of the photoacoustic cell (3) is arranged on the reflected light path of the first reflector (5).

10. The micro-photoacoustic spectroscopy gas detection device according to any one of claims 5 to 9, characterized in that: A second reflector (6) is provided on the rear side of the second window mirror (33) away from the laser (2); the second reflector (6) faces the center of the photoacoustic pool (3) and is arranged at an angle.

Images