Photoacoustic Sensor for Detecting Liquid Molecules Based on Multi-Cavity Coupling

Abstract

The present invention discloses a photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling, belonging to the technical field of photoacoustic sensors. It includes: a housing provided with a notch and a waterproof film; an excitation optical fiber and a perforated plate installed in the housing; a first cavity is formed between the perforated plate and the waterproof film, and the perforated plate is provided with a first through hole; a sound wave detector. The waterproof film enables the housing to be directly inserted into the liquid sample to form a gas-liquid interface. The light beam of the excitation optical fiber passes through the first through hole and the first cavity and irradiates the liquid sample through the waterproof film, thereby generating sound waves. When the sound wave frequency approaches the working frequency of the first cavity, local resonance occurs in the first cavity, and the local sound pressure is significantly enhanced, thereby improving the sound wave transmittance across the gas-liquid interface. The sound signal propagates into the first cavity across the gas-liquid interface with a small reflection, and then the sound wave detector detects the sound signal to obtain the sample characteristic parameters, thereby improving the detection sensitivity of the liquid sample characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic sensors, and particularly to a photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling. Background Art

[0002] Photoacoustic spectroscopy (PAS) is a new type of spectroscopic analysis technology that uses the photoacoustic effect to detect molecular information. A modulated laser covering the absorption line is used to excite target molecules to generate acoustic wave signals, and the acoustic waves caused by absorption are measured by an acoustic sensor to detect the molecular concentration. Compared with other absorption spectroscopy technologies, PAS is a zero-background measurement technology with the advantages of high sensitivity and selectivity. It was first applied to trace gas detection, including petrochemical analysis, environmental pollution monitoring, and industrial production detection.

[0003] In recent years, with the progress of optical technology, it has promoted the application of PAS in liquid detection such as biological fluid detection, chemical solution analysis, and industrial sewage monitoring. However, before the photoacoustic signal in the liquid is transmitted to the air and captured by the acoustic sensor, it must be transmitted through the gas-liquid interface. Since the acoustic impedance between water and air differs by 3600 times, this huge impedance mismatch causes 99.9% of the acoustic energy to be reflected at the gas-liquid interface, and only 0.1% of the acoustic energy can pass through the gas-liquid interface, which greatly limits the liquid detection sensitivity of the PAS technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling, so as to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0005] The technical solution adopted to solve the above technical problems: A photoacoustic sensor for detecting liquid sample characteristics based on multi-cavity coupling, the photoacoustic sensor includes: a housing with a notch opened at the bottom, a waterproof film is installed at the bottom of the housing, and the waterproof film closes the notch; an excitation optical fiber installed in the housing, and the light beam emitted by the excitation optical fiber can pass through the waterproof film; a perforated plate installed inside the housing and located between the excitation optical fiber and the waterproof film, a first cavity is formed between the perforated plate and the waterproof film, and the perforated plate is provided with a first through hole for the light beam of the excitation light to pass through; an acoustic wave detector installed in the housing, and the acoustic wave detector is used to detect the acoustic wave signal in the first cavity; wherein, the light beam emitted by the excitation optical fiber passes through the first through hole and the first cavity, then passes through the waterproof film and irradiates the sample, causing the sample to generate acoustic waves and transmit through the waterproof film to the first cavity, and the acoustic wave detector detects the acoustic waves in the first cavity to obtain an acoustic wave signal related to the characteristics of the liquid sample.

[0006] The technical solution has at least the following beneficial effects: The waterproof film can be in direct contact with the liquid sample. The liquid sample is isolated outside the first cavity through the waterproof film, forming a gas-liquid interface. The light beam emitted by the excitation optical fiber passes through the first through hole and the first cavity and irradiates the liquid sample through the waterproof film. The molecules excited by the liquid sample due to the photoacoustic effect absorb light energy to generate sound waves. When the sound wave frequency approaches the operating frequency of the first cavity, local resonance occurs in the first cavity, and the local sound pressure is significantly enhanced, thereby improving the sound wave transmittance across the gas-liquid interface. That is, the first cavity receives the sound signal excited by the sample, and the sound signal propagates into the first cavity across the gas-liquid interface with a small reflection, and then the sound signal is detected by the sound wave detector to obtain a sound wave signal related to the characteristics of the liquid sample, so as to obtain sample characteristic parameters, thereby improving the detection sensitivity of the liquid sample characteristics.

[0007] As a further improvement of the above technical solution, the sound wave detector includes a spectrometer, a mounting block and a detection optical fiber installed inside the housing. A second cavity is formed inside the mounting block. The detection end face of the detection optical fiber is located inside the second cavity. An installation hole communicating with the second cavity is formed outside the mounting block. A cantilever beam thin plate parallel to the detection end face of the detection optical fiber is installed in the installation hole. The side of the cantilever beam thin plate facing away from the second cavity communicates with the first cavity. The light beam emitted by the detection optical fiber forms interference light after being reflected on the detection end face and the cantilever beam thin plate. The spectrometer is used to capture the interference light to obtain interference spectrum information related to the characteristics of the liquid sample. The sound wave in the first cavity acts on the cantilever beam thin plate, and the cantilever beam thin plate vibrates under forced vibration. An F-P interferometer is formed between the end face of the detection optical fiber and the cantilever beam thin plate. The light beam emitted by the detection optical fiber is reflected on the end face of the detection optical fiber and the cantilever beam thin plate, and the two beams of light are coupled to form F-P interference and captured by the spectrometer. Among them, the cantilever beam thin plate vibrates due to the sound wave in the first cavity, causing the cavity length of the F-P interference cavity to change. The change amplitude of the cavity length reflects the characteristics of the measured liquid sample, such as concentration, thereby realizing the detection of the sound wave in the first cavity.

[0008] As a further improvement of the above technical solution, a third cavity is provided inside the housing. The side of the cantilever beam thin plate away from the detection end face of the detection optical fiber communicates with the third cavity. The housing is provided with a connecting pipe. One end of the connecting pipe communicates with the third cavity, and the other end communicates with the first cavity. The cross-sectional area of the connecting pipe is smaller than the cross-sectional area of the third cavity. The sound signal received by the first cavity can resonate and enhance in the third cavity, thereby achieving the effect of enhancing the sound wave and improving the detection sensitivity of the sound wave.

[0009] As a further improvement of the above technical solution, the mounting block is slidably arranged in the third cavity along a direction perpendicular to the cantilever beam thin sheet, and a first driving member for driving the mounting block to slide is installed in the housing. When the mounting block slides, the volume of the third cavity can be changed. By changing the height of the third cavity, the resonance frequency of the third cavity can be adjusted.

[0010] As a further improvement of the above technical solution, the first driving member includes a first motor installed in the housing. The output end of the first motor is drivingly connected to a first threaded rod, and the first threaded rod is threadedly connected to the mounting block. By driving the first threaded rod to rotate through the first motor, the position of the mounting block can be finely adjusted, so that the height adjustment of the third cavity has a high fineness, and the precise control of the resonance frequency of the third cavity can be realized.

[0011] As a further improvement of the above technical solution, the perforated plate is slidably connected to the housing, and a second driving member for driving the perforated plate to slide is installed in the housing. When the perforated plate slides, the volume of the first cavity can be changed. By changing the height of the first cavity, the resonance frequency of the first cavity can be adjusted.

[0012] As a further improvement of the above technical solution, the second driving member includes a second motor installed in the housing. The output end of the second motor is drivingly connected to a second threaded rod, and the second threaded rod is threadedly connected to the perforated plate. By driving the second threaded rod to rotate through the second motor, the position of the perforated plate can be finely adjusted, so that the height adjustment of the first cavity has a high fineness, and the precise control of the resonance frequency of the first cavity can be realized.

[0013] As a further improvement of the above technical solution, the mounting block includes a mounting seat and two cantilever beam fixing pieces. The second cavity is arranged outside the mounting seat and has an opening formed in the mounting seat. The two cantilever beam fixing pieces are stacked and installed outside the mounting seat to close the opening. The mounting hole is arranged in the middle of the two cantilever beam fixing pieces, and the cantilever beam thin sheet is clamped between the two cantilever beam fixing pieces. The cantilever beam thin sheet is clamped and installed between the two cantilever beam fixing pieces, so that the structure of the cantilever beam thin sheet has high stability and can achieve high installation accuracy, thereby improving the detection accuracy of the acoustic wave detector.

[0014] As a further improvement of the above technical solution, the first-order resonance frequency of the first cavity, the first-order resonance frequency of the third cavity, the first-order resonance frequency of the cantilever beam thin sheet are equal to the modulation frequency of the outgoing light of the excitation optical fiber. The photoacoustic signal can be maximally amplified.

[0015] As a further improvement of the above technical solution, the housing includes a sealing sleeve, a cavity sleeve and a fixing ring. The excitation optical fiber and the acoustic wave detector are both installed in the sealing sleeve. The perforated plate and the notch are both arranged on the cavity sleeve. The outer side of the sealing sleeve is provided with a convex edge. The cavity sleeve is sleeved outside the sealing sleeve, and the top surface of the cavity sleeve abuts against the bottom surface of the convex edge. The fixing ring is sleeved outside the convex edge and clamps the cavity sleeve. The waterproof film is coated on the outside of the cavity sleeve, and the edge of the waterproof film is clamped between the fixing ring and the cavity sleeve, so that the housing can achieve waterproofing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, in which:

[0017] Figure 1 is a schematic diagram of the overall structure of an embodiment of the present invention;

[0018] Figure 2 is a schematic diagram of the disassembled structure of the housing of an embodiment of the present invention;

[0019] Figure 3 is a schematic diagram of the sectional three-dimensional structure of the positioning sleeve and the cavity sleeve in the Figure 2 Q-Q direction of an embodiment of the present invention;

[0020] Figure 4 is a schematic diagram of the structure of the acoustic wave detector of an embodiment of the present invention;

[0021] Figure 5 is a top view of an embodiment of the present invention;

[0022] Figure 6 is Figure 5 a schematic diagram of the sectional structure of I-I in

[0023] Figure 7 is Figure 5 a schematic diagram of the sectional structure of J-J in

[0024] Figure 8 is Figure 5 a schematic diagram of the sectional structure of K-K in

[0025] Figure 9 is Figure 5 a schematic diagram of the sectional three-dimensional structure of I-I in

[0026] 100, housing; 110, sealing sleeve; 111, waterproof sleeve; 112, positioning sleeve; 120, convex edge; 130, main cavity; 131, cover plate; 132, motor bracket; 133, first guide rod; 134, second guide rod; 140, cavity sleeve; 141, notch; 150, waterproof film; 160, fixing ring; 161, semi-circular strip; 162, fastening screw; 200, excitation optical fiber; 210, perforated plate; 211, first through hole; 220, first cavity; 300, mounting block; 310, mounting seat; 320, cantilever beam fixing piece; 330, mounting screw; 400, detection optical fiber; 410, second cavity; 420, mounting hole; 430, cantilever beam thin plate; 440, third cavity; 450, connecting pipe; 500, first motor; 510, first threaded lead screw; 600, second motor; 610, second threaded lead screw. Detailed implementation mode

[0027] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0028] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0029] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is two or more, and understandings such as greater than, less than, exceeding, etc. do not include the present number, and understandings such as above, below, within, etc. include the present number. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0030] In the description of the present invention, unless otherwise clearly defined, words such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0031] Refer to Figures 1-9 , a photoacoustic sensor for detecting liquid molecular characteristics based on multi-cavity coupling, which is used to detect the characteristics of liquid samples. The photoacoustic sensor includes a housing 100, an excitation optical fiber 200, a perforated plate 210 and a sound wave detector.

[0032] Refer to Figures 1-5 , the housing 100 includes a sealing sleeve 110, a cavity sleeve 140, and a fixing ring 160.

[0033] The sealing sleeve 110 includes a waterproof sleeve 111 and a positioning sleeve 112. The bottom of the waterproof sleeve 111 is missing for the top of the positioning sleeve 112 to be sleeved in. An internal thread is provided on the inner side of the waterproof sleeve 111, and an external thread is provided on the outer side of the positioning sleeve 112, so that the waterproof sleeve 111 is threadedly connected to the positioning sleeve 112. A convex edge 120 is provided in a circumferential manner at the middle position on the outer side of the positioning sleeve 112. After the waterproof sleeve 111 is threadedly connected to the positioning sleeve 112, the bottom wall of the waterproof sleeve 111 abuts against the top surface of the convex edge 120, and the convex edge 120 can limit the waterproof sleeve 111. Splitting the sealing sleeve 110 into the waterproof sleeve 111 and the positioning sleeve 112 can facilitate the installation of the internal structure. A rubber sealing ring is sleeved on the top surface of the convex edge 120. The rubber sealing ring is squeezed by the waterproof sleeve 111, providing a frictional force acting on the waterproof sleeve 111 in the opposite direction, thereby improving the tightening force of the thread of the waterproof sleeve 111 and ensuring effective sealing. In other embodiments, the waterproof sleeve 111 and the positioning sleeve 112 can also be made into an integral sealing sleeve 110.

[0034] The top of the cavity sleeve 140 is sleeved at the bottom position of the positioning sleeve 112, and the top surface of the cavity sleeve abuts against the bottom surface of the convex edge 120. The convex edge 120 can limit the cavity sleeve 140. The fixing ring 160 includes two semi-circular strips 161. One end of each of the two semi-circular strips 161 is provided with a fastening screw 162, and the other end is provided with a threaded hole for the fastening screw 162 to be screwed into, so that the two semi-circular strips 161 can be combined to form a ring and sleeved on the outside of the convex edge 120, and then the two ends of the two semi-circular strips 161 are connected by two fastening screws 162 to install the fixing ring 160 on the outside of the convex edge 120. The inner side of the fixing ring 160 also presses against the outer top of the cavity sleeve 140, that is, the upper half of the two semi-circular strips 161 clamps the convex edge 120, and the lower half also clamps the cavity sleeve 140, so that the cavity sleeve 140 is connected to the positioning sleeve 112. In other embodiments, the fixing ring 160 can also be an annular buckle close to a complete circle, and only one fastening screw 162 is used to connect the two ends of the annular buckle, so that the fixing ring 160 can be sleeved outside the convex edge 120 and the cavity sleeve 140 to connect the positioning sleeve 112 and the cavity sleeve 140.

[0035] Refer to Figures 5-9, a notch 141 is provided at the bottom of the cavity sleeve 140. The notch 141 is a circular structure and its diameter is slightly smaller than the inner diameter of the cavity sleeve 140. The side wall of the notch 141 is inclined so that the diameter of the notch 141 at the end towards the inside of the cavity sleeve 140 is larger than the diameter at the end towards the outside of the cavity sleeve 140. A waterproof film 150 is sleeved at the bottom of the cavity sleeve 140. The waterproof film 150 covers the position of the notch 141, and the edge of the waterproof film 150 extends to the side edge of the cavity sleeve 140 and is clamped between the inner side of the fixing ring 160 and the outer side of the cavity sleeve 140, so that the waterproof film 150 is closely attached to the bottom wall of the cavity sleeve 140, sealing the notch 141 to achieve the waterproof effect. Among them, the waterproof film 150 is a flexible film and its material is polyethylene terephthalate (Polyethylene terephthalate), abbreviated as PET. The thickness of the waterproof film 150 is between 0.05 mm and 0.1 mm, and the waterproof film 150 with a smaller thickness can be ignored for the loss of light energy transmission. It can be understood that the waterproof sleeve 111, the positioning sleeve 112 and the cavity sleeve 140 form a sealed space inside, so as to protect the internal structure from being penetrated by the sample liquid, so that the entire photoacoustic sensor can be completely immersed in the liquid for use.

[0036] A main cavity 130 is installed inside the positioning sleeve 112. The outer cross-section of the main cavity 130 is the same as the inner cross-section of the positioning sleeve 112 to ensure the sealing between the main cavity 130 and the positioning sleeve 112. The excitation optical fiber 200 and the acoustic wave detector are both installed in the main cavity 130. A perforated plate 210 is installed inside the cavity sleeve 140. A first cavity 220 is formed between the perforated plate 210 and the waterproof film 150. The excitation optical fiber 200 is located at a position away from the waterproof film 150 of the perforated plate 210. The excitation optical fiber 200 is an instrument that can emit excitation light. The emitting end of the excitation optical fiber 200 is arranged downward, and a first through hole 211 is provided on the perforated plate 210. The excitation light beam emitted by the excitation optical fiber 200 passes through the first through hole 211 and the first cavity 220, and then irradiates the external liquid sample through the waterproof film 150.

[0037] The detection end of the acoustic wave detector is located in the first cavity 220, so that the acoustic wave detector can detect the acoustic wave signal in the first cavity 220. When the excitation light irradiates the liquid sample, the liquid sample generates acoustic waves with the same modulation frequency as the outgoing light due to the photoacoustic effect. The acoustic waves are received by the first cavity 220 with a small gas-liquid interface reflection through the waterproof film 150. Through local resonance, the acoustic waves can be efficiently transmitted between media with extremely large acoustic impedance differences at the gas-liquid interface at the resonance frequency, that is, more acoustic waves can be received in the first cavity 220, and then the acoustic wave signal related to the characteristics of the liquid sample is obtained through the acoustic wave detector to know the characteristics of the liquid sample such as the concentration of the liquid sample. The photoacoustic sensor of the present technical solution has a high detection sensitivity.

[0038] Furthermore, the acoustic wave detector includes a mounting block 300, a detection optical fiber 400, and a spectrometer. The mounting block 300 and the detection optical fiber 400 are both mounted in the main cavity 130.

[0039] The mounting block 300 includes a mounting base 310 and two cantilever beam fixing pieces 320. A second cavity 410 is formed on the bottom surface of the mounting base 310, and the second cavity 410 has an opening on the bottom surface of the mounting base 310. After the two cantilever beam fixing pieces 320 are stacked, they are mounted on the bottom surface of the mounting base 310 through mounting screws 330, so that the two cantilever beam fixing pieces 320 close the opening of the second cavity 410. An installation hole 420 communicating with the second cavity 410 is formed in the middle of the two cantilever beam fixing pieces 320. A cantilever beam thin sheet 430 is clamped between the two cantilever beam fixing pieces 320, that is, one side of the cantilever beam thin sheet 430 communicates with the second cavity 410, and the other side communicates with the outside of the mounting base 310. The cantilever beam thin sheet 430 and the upper and lower two cantilever beam fixing pieces 320 have the same shape as the bottom edge of the mounting base 310. After the cantilever beam thin sheet 430 is clamped between the two cantilever beam fixing pieces 320, it is fixed to the bottom surface of the mounting base 310 through bolts, which is convenient for the installation of the cantilever beam thin sheet 430 and makes the installation of the cantilever beam thin sheet 430 have high stability.

[0040] One end of the detection optical fiber 400 is inserted into the top of the mounting block 300 through a hollow plug. The hollow plug is a ceramic ferrule, so that the detection end face of the detection optical fiber 400 is located in the second cavity 410, and the bottom of the ceramic ferrule is opposite to the position of the installation hole 420. The cantilever beam thin sheet 430 is parallel to the detection end face of the detection optical fiber 400. The bottom of the mounting base 310 is inserted into the perforated plate 210, so that the side of the cantilever beam thin sheet 430 facing away from the second cavity 410 communicates with the first cavity 220. The detection light beam emitted by the detection optical fiber 400 forms interference light after reflection on the detection end face and the cantilever beam thin sheet 430. The spectrometer is located outside the waterproof sleeve 111, and the measurement end of the spectrometer is connected into the mounting base 310 through an optical fiber. The spectrometer is used to capture the interference light. Since the cantilever beam thin sheet 430 is sensitive to the acoustic waves in the first cavity 220, the interference spectrum information of the interference light is associated with the characteristics of the liquid sample.

[0041] It can be understood that the probe light irradiates on the cantilever beam thin plate 430. The cantilever beam thin plate 430 and the ceramic ferrule form an optical fiber Fabry-Perot (F-P) interferometer. The probe light is reflected on two reflection surfaces respectively. After the two beams of light are coupled, F-P interference is formed and captured by the spectrometer. Using the spectral demodulation method, the concentration of the liquid sample can be measured by using the relationship between the phase of the measured interference spectrum and the cavity length of the F-P. The acoustic wave causes the cantilever beam thin plate 430 to vibrate forcedly, changing the length of the F-P cavity. The F-P cavity length reflected by the interference spectrum information can reflect the characteristics of the liquid sample, such as concentration. Among them, an arc-shaped through groove or a U-shaped through groove is formed on the cantilever beam thin plate 430 by laser processing to form a free end. The gap width of the cantilever beam thin plate 430 processed by laser is small, and the influence caused by air leakage can be ignored.

[0042] Further, a third cavity 440 is formed in the main cavity 130. The bottom of the mounting seat 310 is inserted into the top of the third cavity 440, so that the side of the cantilever beam thin plate 430 away from the second cavity 410 communicates with the third cavity 440. A connecting pipe 450 is also vertically installed in the main cavity 130. The connecting pipe 450 is a hollow metal thin pipe. One end of the connecting pipe 450 is arranged at the bottom of the third cavity 440, and the other end passes through the perforated plate 210, so that the connecting pipe 450 connects the third cavity 440 with the first cavity 220. The cross sections of the bottom of the mounting seat 310, the third cavity 440 and the connecting pipe 450 are all circular, and the inner diameter of the connecting pipe 450 is smaller than the diameter of the third cavity 440.

[0043] It can be understood that the third cavity 440 is equivalent to a Helmholtz resonance cavity. The connecting pipe 450 forms the neck of the Helmholtz resonance cavity. The acoustic wave in the first cavity 220 compresses the air in the connecting pipe 450. The air enters the third cavity 440, causing the air pressure in the third cavity 440 to rise. Then, an outward reaction force is given to the air in the connecting pipe 450 to discharge the air, causing the air pressure in the third cavity 440 to drop. The acoustic wave continues to compress the gas in the connecting pipe 450 and enter the third cavity 440. Repeating like this, the movement of the air in the third cavity 440 can be simplified as a spring harmonic oscillator. When the frequency of the acoustic wave resonates with the frequency of the spring resonance, the amplitude of the acoustic wave signal will be amplified, enhancing the acoustic wave signal, and thus improving the sensitivity of the photoacoustic sensor.

[0044] Furthermore, the cross-section of the mounting base 310 is the same as that of the third cavity 440, and the mounting base 310 can slide vertically in the third cavity 440. The sliding direction of the mounting base 310 is perpendicular to the cantilever beam thin plate 430. A first driving member is installed at the top of the main cavity 130. The first driving member can drive the mounting base 310 to slide, so as to adjust the height of the third cavity 440, change the volume of the third cavity 440, and further adjust the resonance frequency of the third cavity 440. Specifically, the first driving member includes a first motor 500 and a first threaded lead screw 510. A cover plate 131 is installed at the top of the main cavity 130, and a motor bracket 132 is installed at the top of the cover plate 131. The first motor 500 is installed on the motor bracket 132 with its output end facing vertically downward. The first threaded lead screw 510 is connected to the output end of the first motor 500. The first threaded lead screw 510 passes through the cover plate 131 and is threadedly connected to the mounting base 310. By driving the first motor 500 to drive the first threaded lead screw 510 to rotate, the mounting base 310 can be driven to move slightly up and down, so as to finely adjust the volume of the third cavity 440, and further finely adjust the resonance frequency of the third cavity 440.

[0045] Wherein, a first guide rod 133 is installed on the cover plate 131. The first guide rod 133 passes through the mounting base 310, so that the mounting base 310 can slide along the first guide rod 133 to improve the sliding stability of the mounting base 310. During actual manufacturing and installation, sealing measures such as rubber rings can be added between the bottom of the outer side of the mounting base 310 and the side wall of the third cavity 440 to avoid excessive leakage when the air in the third cavity 440 undergoes elastic vibration, and reduce the occurrence of situations such as resonance peak broadening, frequency shift, and sound pressure amplitude decrease. In other embodiments, the first driving member can be an electric push rod. The electric push rod is installed on the motor bracket 132, and the output end of the electric push rod is fixedly connected to the mounting base 310 through a connecting rod, so that the mounting base 310 can be driven to slide by driving the electric push rod.

[0046] Furthermore, the cross-section of the perforated plate 210 is the same as that inside the cavity sleeve 140, so that the perforated plate 210 can slide vertically relative to the cavity sleeve 140. A second driving member is installed on the main cavity 130. The second driving member can drive the perforated plate 210 to slide inside the cavity sleeve 140, so as to adjust the height of the first cavity 220, change the volume of the first cavity 220, and further adjust the resonance frequency of the first cavity 220. Specifically, the second driving member includes a second motor 600 and a second threaded lead screw 610.

[0047] The second motor 600 is mounted on the motor bracket 132 with its output end vertically downward. The second threaded lead screw 610 is connected to the output end of the second motor 600. The second threaded lead screw 610 passes through the cover plate 131 and the main cavity 130 and is threadedly connected to the perforated plate 210. By driving the second motor 600 to drive the second threaded lead screw 610 to rotate, the mounting seat 310 can be driven to move slightly up and down, so that the volume of the first cavity 220 can be finely adjusted, and then the resonance frequency of the first cavity 220 can be finely adjusted. It should be noted that the bottom of the connecting pipe 450 is passed through the perforated plate 210 and is slidably connected to the perforated plate 210, so that the sliding adjustment of the perforated plate 210 does not interfere with the connecting pipe 450.

[0048] Wherein, two second guide rods 134 are mounted on the cover plate 131. Both of the two second guide rods 134 are passed through the perforated plate 210, so that the perforated plate 210 can slide along the second guide rods 134 to improve the sliding stability of the perforated plate 210. In other embodiments, the second driving member can be an electric push rod. The electric push rod is mounted on the motor bracket 132, and the output end of the electric push rod is fixedly connected to the perforated plate 210 through a connecting rod, so that the perforated plate 210 can be driven to slide by driving the electric push rod.

[0049] Wherein, both the first motor 500 and the second motor 600 adopt micro stepping motors. Both the first threaded lead screw 510 and the second threaded lead screw 610 adopt M2 threaded lead screws. In addition, by setting limiting members such as rubber gaskets in the corresponding components, the adjustable height of the perforated plate 210 is set to 2 mm, the height adjustment range of the first cavity 220 is 1 mm to 3 mm, and the movable distance of the mounting seat 310 is set to 7 mm.

[0050] It should be noted that a watertight connector is mounted on the top of the waterproof sleeve 111. The watertight connector is threadedly connected to the waterproof sleeve 111. The wiring of the excitation optical fiber 200, the detection optical fiber 400, the first motor 500 and the second motor 600 all extends to external computer equipment and other usage scenarios through the watertight connector. The measuring end of the spectrometer is connected to the inside of the waterproof sleeve 111 through an optical fiber passing through the watertight connector, so as to ensure the sealing performance of the housing 100.

[0051] The resonance frequencies of the first cavity 220, the cantilever beam thin plate 430 and the third cavity 440 are all determined by their own physical properties, so that the modulation frequency of the outgoing light of the excitation optical fiber 200, the first-order resonance frequency of the first cavity 220, the first-order resonance frequency of the third cavity 440 and the first-order resonance frequency of the cantilever beam thin plate 430 are equal to each other, that is, consistent, so that the resonance frequencies of the four are coupled with each other, and the liquid detection sensitivity can be improved by means of double enhancement of acoustics and detection.

[0052] Therefore, the resonance frequencies of the multi-cavities of the photoacoustic sensor of the present invention are coupled to increase the amplitude of the acoustic signal and the response of the cantilever beam thin plate 430. The liquid detection sensitivity is improved by means of double enhancement of acoustics and detection. The liquid molecule concentration is detected based on multi-cavity coupling, providing support for the application of the PAS technology to liquid molecule detection. The resonance frequencies of the first cavity 220 and the third cavity 440 are precisely regulated by a micro motor, so that the resonance frequencies of the first cavity 220, the third cavity 440 and the cantilever beam thin plate 430 are kept consistent, avoiding the resonance frequency shift caused by the coupling effect in different cavities, the installation precision error, and the liquid temperature, pressure, etc. in actual measurement.

[0053] The embodiments of the present invention have been described in detail above with reference to the drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. An optoacoustic sensor based on multi-cavity coupling for detecting liquid molecules, which is used to detect the characteristics of liquid samples, and is characterized in that The photoacoustic sensor includes: a housing with a notch formed at the bottom, a waterproof film for closing the notch is installed at the bottom of the housing, and the waterproof film is a flexible film; an excitation optical fiber installed in the housing, and the light beam emitted by the excitation optical fiber can pass through the waterproof film; a perforated plate installed inside the housing and located between the excitation optical fiber and the waterproof film, a first cavity is formed between the perforated plate and the waterproof film, and the perforated plate is provided with a first through hole for the light beam of the excitation optical fiber to pass through; an acoustic wave detector installed in the housing and connected to the first cavity, and the acoustic wave detector is used to detect the acoustic wave signal in the first cavity; wherein, after the light beam emitted by the excitation optical fiber passes through the first through hole and the first cavity, it passes through the waterproof film and irradiates the sample, causing the sample to generate acoustic waves and propagate through the waterproof film to the first cavity, and the acoustic wave detector detects the acoustic waves in the first cavity to obtain an acoustic wave signal related to the characteristics of the liquid sample.

2. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 1, wherein: The acoustic wave detector includes a spectrometer, a mounting block installed inside the housing, and a detection optical fiber. A second cavity is formed inside the mounting block, the detection end face of the detection optical fiber is located inside the second cavity, a mounting hole communicating with the second cavity is formed outside the mounting block, and a cantilever beam thin plate parallel to the detection end face of the detection optical fiber is installed in the mounting hole. One side of the cantilever beam thin plate facing away from the second cavity communicates with the first cavity, and the light beam emitted by the detection optical fiber forms interference light after being reflected on the detection end face and the cantilever beam thin plate. The spectrometer is used to capture the interference light to obtain interference spectral information related to the characteristics of the liquid sample.

3. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 2, wherein: A third cavity is arranged inside the housing, one side of the cantilever beam thin plate far away from the detection end face of the detection optical fiber communicates with the third cavity, a connecting pipe is installed on the housing, one end of the connecting pipe communicates with the third cavity, and the other end communicates with the first cavity. The cross-sectional area of the connecting pipe is smaller than the cross-sectional area of the third cavity.

4. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 3, characterized in that: The mounting block is slidably arranged in the third cavity along a direction perpendicular to the cantilever beam thin plate, and a first driving member for driving the mounting block to slide is installed inside the housing. When the mounting block slides, the volume of the third cavity can be changed.

5. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 4, characterized in that: The first driving member includes a first motor installed inside the housing, the output end of the first motor is drivingly connected with a first threaded lead screw, and the first threaded lead screw is threadedly connected with the mounting block.

6. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 1 or 4, characterized in that: The perforated plate is slidably connected with the housing, and a second driving member for driving the perforated plate to slide is installed inside the housing. When the perforated plate slides, the volume of the first cavity can be changed.

7. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 6, wherein: The second driving member includes a second motor installed inside the housing, the output end of the second motor is drivingly connected with a second threaded lead screw, and the second threaded lead screw is threadedly connected with the perforated plate.

8. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 2, characterized in that: The mounting block includes a mounting base and two cantilever beam fixing pieces. The second cavity is arranged on the outer side of the mounting base and has an opening formed in the mounting base. The two cantilever beam fixing pieces are stacked and mounted on the outer side of the mounting base to close the opening. The mounting hole is arranged in the middle of the two cantilever beam fixing pieces, and the cantilever beam thin sheet is clamped between the two cantilever beam fixing pieces.

9. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 3, wherein: The first-order resonance frequency of the first cavity, the first-order resonance frequency of the third cavity, and the first-order resonance frequency of the cantilever beam thin sheet are equal to the modulation frequency of the outgoing light of the excitation optical fiber.

10. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 1, characterized in that: The housing includes a sealing sleeve, a cavity sleeve, and a fixing ring. The excitation optical fiber and the acoustic wave detector are both mounted in the sealing sleeve. The perforated plate and the notch are both arranged in the cavity sleeve. A convex edge is provided on the outer circumference of the sealing sleeve. The cavity sleeve is sleeved outside the sealing sleeve, and the top surface of the cavity sleeve abuts against the bottom surface of the convex edge. The fixing ring is sleeved outside the convex edge and clamps the cavity sleeve. The waterproof film is coated on the outside of the cavity sleeve, and the edge of the waterproof film is clamped between the fixing ring and the cavity sleeve, so that the housing can achieve waterproofing.

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