Photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling

Abstract

The invention discloses a photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling, and belongs to the technical field of photoacoustic sensors. The shell is provided with a notch and a waterproof film; the excitation optical fiber and the perforated plate are mounted in the shell; a first cavity is formed between the perforated plate and the waterproof film, and a first through hole is formed in the perforated plate; and an acoustic wave detector. The waterproof film can enable the shell to be directly inserted into a liquid sample to form a gas-liquid phase interface, a light beam of the excitation optical fiber penetrates through the first through hole and the first cavity and penetrates through the waterproof film to irradiate the liquid sample, so that sound waves are generated, when the sound wave frequency is close to the working frequency of the first cavity, local resonance occurs in the first cavity, and local sound pressure is remarkably enhanced; therefore, the sound wave transmissivity across the gas-liquid interface is improved. The sound signal spans the gas-liquid phase interface with small reflection to be propagated into the first cavity, and then the sound signal is detected by the sound wave detector to obtain the characteristic parameters of the sample, so that the detection sensitivity of the characteristics of the liquid sample can be improved.

Description

Technical Field

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

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

[0003] In recent years, the advancement of optical technology has promoted the application of PAS in liquid detection, such as biological fluid detection, chemical solution analysis, and industrial sewage monitoring. However, the photoacoustic signal in the liquid must be transmitted through the gas-liquid interface before it is transmitted to the air and captured by the acoustic sensor. Since the acoustic impedance between water and air differs by 3600 times, this huge impedance mismatch causes 99.9% of the sound energy to be reflected at the gas-liquid interface, and only 0.1% of the sound energy is transmitted through the gas-liquid interface, which greatly limits the liquid detection sensitivity of 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 is as follows: a photoacoustic sensor based on multi-cavity coupling to detect liquid molecules, which is used to detect the characteristics of liquid samples. The photoacoustic sensor comprises: a shell, a notch is opened at the bottom, a waterproof film is installed at the bottom of the shell, and the waterproof film closes the notch; an excitation optical fiber is installed in the shell, and the light beam emitted by the excitation optical fiber can pass through the waterproof film; a perforated plate is installed inside the shell and is 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 is installed in the shell, 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 into the sample, so that the sample generates an acoustic wave and propagates through the waterproof film to the first cavity, and the acoustic wave detector detects the acoustic wave 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 directly contact the liquid sample, and the liquid sample is isolated outside the first cavity by the waterproof film to form a gas-liquid interface. The light beam emitted by the exciting optical fiber passes through the first through hole and the first cavity and irradiates the liquid sample through the waterproof film. The molecules of the liquid sample are excited by the photoacoustic effect and absorb light energy to generate sound waves. When the sound wave frequency is close to the working frequency of the first cavity, the first cavity resonates locally, 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 across the gas-liquid interface to the first cavity 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 the sample characteristic parameters, thereby improving the detection sensitivity of the liquid sample characteristics.

[0007] As a further improvement of the above technical solution, the acoustic 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 in the second cavity, a mounting hole connected to the second cavity is provided outside the mounting block, a cantilever beam slice parallel to the detection end face of the detection optical fiber is installed in the mounting hole, the side of the cantilever beam slice away from the second cavity is connected to the first cavity, the light beam emitted by the detection optical fiber is reflected on the detection end face and the cantilever beam slice to form interference light, the spectrometer is used to capture the interference light and obtain interference spectrum information related to the characteristics of the liquid sample. The acoustic wave in the first cavity acts on the cantilever beam slice, the cantilever beam slice is forced to vibrate, and the end face of the detection optical fiber and the cantilever beam slice form an FP interferometer, the light beam emitted by the detection optical fiber is reflected on the end face of the detection optical fiber and the cantilever beam slice, and the two beams of light are coupled to form FP interference and captured by the spectrometer. The cantilever beam sheet vibrates due to the sound waves in the first cavity, causing the cavity length of the FP interference cavity to change. The change in the cavity length reflects the characteristics of the liquid sample being measured, such as concentration, thereby realizing the detection of the sound waves in the first cavity.

[0008] As a further improvement of the above technical solution, a third cavity is provided in the housing, the side of the cantilever beam sheet away from the detection end face of the detection optical fiber is connected to the third cavity, the housing is equipped with a connecting tube, one end of the connecting tube is connected to the third cavity, and the other end is connected to the first cavity, and the cross-sectional area of ​​the connecting tube is smaller than the cross-sectional area of ​​the third cavity. The acoustic signal received by the first cavity can resonate and be enhanced in the third cavity, thereby achieving the effect of enhancing the acoustic wave, so as to improve the detection sensitivity of the acoustic 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 sheet, and a first driving member for driving the mounting block to slide is installed in the housing, and 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 connected to a first threaded screw, and the first threaded screw is threadedly connected to the mounting block. The first motor drives the first threaded screw to rotate, and the position of the mounting block can be slightly adjusted, so that the height adjustment of the third cavity has a higher degree of precision, and the resonant frequency of the third cavity can be accurately controlled.

[0011] As a further improvement of the above technical solution, the perforated plate is slidably connected to the shell, and a second driving member for driving the perforated plate to slide is installed in the shell, and 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 connected to a second threaded screw, and the second threaded screw is threadedly connected to the perforated plate. The second motor drives the second threaded screw to rotate, and the position of the perforated plate can be slightly adjusted, so that the height adjustment of the first cavity has a higher degree of precision, and the resonant frequency of the first cavity can be accurately controlled.

[0013] As a further improvement of the above technical solution, the mounting block includes a mounting seat and two cantilever beam fixing plates, the second cavity is arranged on the outside of the mounting seat and has an opening formed on the mounting seat, the two cantilever beam fixing plates are stacked and installed on the outside of the mounting seat and close the opening, the mounting hole is arranged in the middle of the two cantilever beam fixing plates, and the cantilever beam thin plate is clamped between the two cantilever beam fixing plates. The cantilever beam thin plate is clamped and installed between the two cantilever beam fixing plates, so that the structure of the cantilever beam thin plate 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 sheet and the output light modulation frequency of the excitation optical fiber are equal, so as to maximize the amplification of the photoacoustic signal.

[0015] As a further improvement of the above technical solution, the shell 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 in the cavity sleeve, the outer side of the sealing sleeve is ringed with a convex edge, the cavity sleeve is sleeved outside the sealing sleeve, and the top surface of the cavity sleeve is in contact with the bottom surface of the convex edge, the fixing ring is sleeved on the outer side of the convex edge and clamps the cavity sleeve, the waterproof film is covered on the outer side of the cavity sleeve, and the edge of the waterproof film is clamped between the fixing ring and the cavity sleeve, so that the shell can be waterproof. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present invention; Figure 2 This is a schematic diagram of the disassembled structure of a housing according to an embodiment of the present invention; Figure 3 In the embodiment of the present invention, the positioning sleeve and the cavity sleeve are Figure 2 A schematic diagram of the cross-sectional three-dimensional structure in the QQ direction; Figure 4 A schematic diagram of the structure of an acoustic wave detector in an embodiment of the present invention; Figure 5 A top view of an embodiment of the present invention; Figure 6 for Figure 5 Schematic diagram of the cross-sectional structure of II; Figure 7 for Figure 5 Schematic diagram of the cross-sectional structure of JJ; Figure 8 for Figure 5 Schematic diagram of the cross-sectional structure of KK; Fig. 9 for Figure 5 Schematic diagram of the cross-sectional three-dimensional structure of II.

[0017] 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, semicircular arc 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 plate; 330, mounting screw; 400, detection optical fiber; 410, second cavity; 420, mounting hole; 430, cantilever beam sheet; 440, third cavity; 450, connecting tube; 500, first motor; 510, first threaded screw; 600, second motor; 610, second threaded screw. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0019] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply 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 understood as a limitation on the present invention.

[0020] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0021] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0022] Reference Figure 1-9 The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling 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 an acoustic wave detector.

[0023] Reference Figure 1-5 The housing 100 includes a sealing sleeve 110 , a cavity sleeve 140 and a fixing ring 160 .

[0024] The sealing sleeve 110 includes a waterproof sleeve 111 and a positioning sleeve 112. The bottom of the waterproof sleeve 111 is missing to allow the top of the positioning sleeve 112 to be inserted. The inner side of the waterproof sleeve 111 is provided with an internal thread, and the outer side of the positioning sleeve 112 is provided with an external thread, so that the waterproof sleeve 111 is threadedly connected with the positioning sleeve 112. A convex edge 120 is provided around the middle position of the outer side of the positioning sleeve 112. After the waterproof sleeve 111 and the positioning sleeve 112 are threadedly connected, 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. The top surface of the convex edge 120 is provided with a rubber sealing ring, which is squeezed by the waterproof sleeve 111 and provides friction force to react to the waterproof sleeve 111, 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.

[0025] The top of the cavity sleeve 140 is sleeved on the bottom of the positioning sleeve 112, and the top surface of the cavity sleeve contacts the bottom surface of the convex edge 120, and the convex edge 120 can limit the cavity sleeve 140. The fixing ring 160 includes two semicircular arc strips 161, one end of the two semicircular arc strips 161 is penetrated by a fastening screw 162, and the other end is provided with a threaded hole for the fastening screw 162 to be screwed in, so that the two semicircular arc strips 161 can be combined to form a ring and then sleeved on the outside of the convex edge 120, and then the two ends of the two semicircular arc 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 semicircular arc strips 161 clamp 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 a nearly full-circle annular buckle, 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.

[0026] Reference Figure 5-9A 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 facing the inside of the cavity sleeve 140 is larger than the diameter at the end facing 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 a waterproof effect. The waterproof film 150 is a flexible film made of polyethylene terephthalate (PET). The thickness of the waterproof film 150 is between 0.05 mm and 0.1 mm. The loss of light energy transmission by the waterproof film 150 with a smaller thickness can be ignored. It can be understood that the waterproof sleeve 111, the positioning sleeve 112 and the cavity sleeve 140 form a sealed space inside, thereby protecting 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.

[0027] The main cavity 130 is installed inside the positioning sleeve 112, and the outer cross section of the main cavity 130 is the same as the inner cavity cross section of the positioning sleeve 112 to ensure the sealing of 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 in the cavity sleeve 140, and 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 where the perforated plate 210 is far away from the waterproof film 150, and 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 opened on the perforated plate 210. After the excitation light beam emitted by the excitation optical fiber 200 passes through the first through hole 211 and the first cavity 220, it is irradiated into the external liquid sample through the waterproof film 150.

[0028] The detection end of the acoustic wave detector is in the first cavity 220, so that the acoustic wave detector can detect the acoustic wave signal of the first cavity 220. When the excitation light is irradiated to the liquid sample, the liquid sample generates an acoustic wave with the same modulation frequency as the outgoing light due to the photoacoustic effect. The acoustic wave is reflected and received by the first cavity 220 with a smaller gas-liquid phase interface through the waterproof film 150. Through local resonance at the resonance frequency, the acoustic wave can be efficiently transmitted between media with extremely large differences in acoustic impedance such as the gas-liquid phase interface, 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 obtain the characteristics of the liquid sample such as the concentration of the liquid sample. This makes the photoacoustic sensor of this technical solution have a higher detection sensitivity.‌

[0029] 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 .

[0030] The mounting block 300 includes a mounting base 310 and two cantilever beam fixing plates 320. A second cavity 410 is provided on the bottom surface of the mounting base 310. The second cavity 410 has an opening formed on the bottom surface of the mounting base 310. The two cantilever beam fixing plates 320 are stacked and installed on the bottom surface of the mounting base 310 by means of mounting screws 330, so that the two cantilever beam fixing plates 320 close the opening of the second cavity 410. A mounting hole 420 connected to the second cavity 410 is provided in the middle of the two cantilever beam fixing plates 320. A cantilever beam sheet 430 is sandwiched between the two cantilever beam fixing plates 320, that is, one side of the cantilever beam sheet 430 is connected to the second cavity 410, and the other side is connected to the outside of the mounting base 310. The cantilever beam sheet 430 and the upper and lower cantilever beam fixing sheets 320 have the same shape as the bottom edge of the mounting base 310. After the cantilever beam sheet 430 is clamped between the two cantilever beam fixing sheets 320 and then fixed to the bottom surface of the mounting base 310 by bolts, the installation of the cantilever beam sheet 430 can be facilitated and the installation of the cantilever beam sheet 430 has higher stability.

[0031] One end of the detection optical fiber 400 is inserted into the top of the mounting block 300 through a hollow pin, and the hollow pin is a ceramic ferrule, so that the detection end face of the detection optical fiber 400 is in the second cavity 410, and the bottom of the ceramic ferrule is directly opposite to the position of the mounting hole 420. The cantilever beam slice 430 is parallel to the detection end face of the detection optical fiber 400. The bottom of the mounting seat 310 is inserted into the perforated plate 210, so that the side of the cantilever beam slice 430 away from the second cavity 410 is connected to the first cavity 220. The detection light beam emitted by the detection optical fiber 400 is reflected on the detection end face and the cantilever beam slice 430 to form interference light. The spectrometer is outside the waterproof sleeve 111 and the measuring end of the spectrometer is connected to the mounting seat 310 through the optical fiber. The spectrometer is used to capture the interference light. Since the cantilever beam slice 430 is sensitive to the sound waves in the first cavity 220, the interference spectrum information of the interference light is associated with the characteristics of the liquid sample.

[0032] It can be understood that the detection light is irradiated onto the cantilever beam thin slice 430, and the cantilever beam thin slice 430 and the ceramic ferrule constitute an optical fiber Fabry-Perot (FP) interferometer. The detection light is reflected on two reflective surfaces respectively. After the two beams of light are coupled, FP interference is formed and captured by the spectrometer. The concentration of the liquid sample can be measured by using the spectral demodulation method and the relationship between the phase of the measured interference spectrum and the cavity length of the FP. The sound wave causes the cantilever beam thin slice 430 to vibrate under pressure, changing the length of the FP cavity. The FP cavity length reflected by the interference spectrum information can reflect the characteristics of the liquid sample, such as concentration. Among them, the cantilever beam thin slice 430 is formed with a free end by opening an arc-shaped through groove or a U-shaped through groove by laser processing. The gap width of the cantilever beam thin slice 430 processed by laser is small, and the impact on air leakage can be ignored.

[0033] Furthermore, a third cavity 440 is formed in the main cavity 130, and 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 sheet 430 away from the second cavity 410 is connected to 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 tube. One end of the connecting pipe 450 is arranged at the bottom of the third cavity 440, and the other end is penetrated on 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.

[0034] It can be understood that the third cavity 440 is equivalent to the Helmholtz resonant cavity, and the connecting tube 450 forms the neck of the Helmholtz resonant cavity. The sound waves of the first cavity 220 compress the air in the connecting tube 450, and the air enters the third cavity 440, causing the air pressure in the third cavity 440 to rise, which gives the air in the connecting tube 450 an outward reaction force to discharge the air, causing the air pressure in the third cavity 440 to drop. The sound waves continue to compress the gas in the connecting tube 450 and enter the third cavity 440. This is repeated, and the movement of the air in the third cavity 440 can be simplified to a spring resonator. When the frequency of the sound wave resonates with the frequency of the spring resonance, the amplitude of the sound wave signal will be amplified, the sound wave signal will be enhanced, and the sensitivity of the photoacoustic sensor will be improved.

[0035] Further, the cross section of the mounting seat 310 is the same as the cross section of the third cavity 440, and the mounting seat 310 can slide vertically in the third cavity 440, and the sliding direction of the mounting seat 310 is perpendicular to the cantilever beam sheet 430. A first driving member is installed on the top of the main cavity 130, and the first driving member can drive the mounting seat 310 to slide, thereby adjusting the height of the third cavity 440, so that the volume of the third cavity 440 changes, and then the resonance frequency of the third cavity 440 can be adjusted. Specifically, the first driving member includes a first motor 500 and a first threaded screw 510. A cover plate 131 is installed on the top of the main cavity 130, and a motor bracket 132 is installed on the top of the cover plate 131. The first motor 500 is installed on the motor bracket 132 with the output end facing vertically downward. The first threaded screw 510 is connected to the output end of the first motor 500. The first threaded 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 screw 510 to rotate, the mounting base 310 can be driven to move slightly up and down, so that the volume of the third cavity 440 can be finely adjusted, and then the resonance frequency of the third cavity 440 can be finely adjusted.

[0036] Among them, a first guide rod 133 is installed on the cover plate 131, and the first guide rod 133 is inserted into the mounting seat 310, so that the mounting seat 310 can slide along the first guide rod 133 to improve the sliding stability of the mounting seat 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 seat 310 and the side wall of the third cavity 440 to avoid excessive leakage of the air in the third cavity 440 when elastic vibration occurs, and to reduce the occurrence of resonance peak broadening, frequency shift, and sound pressure amplitude drop. In other embodiments, the first driving member can be an electric push rod, which is installed on the motor bracket 132, and the output end of the electric push rod is fixedly connected to the mounting seat 310 through a connecting rod, so that the mounting seat 310 can be driven to slide by driving the electric push rod.

[0037] Further, the cross section of the perforated plate 210 is the same as the cross section inside the cavity sleeve 140, so that the perforated plate 210 can slide in the vertical direction relative to the cavity sleeve 140, and a second driving member is installed on the main cavity 130, and the second driving member can drive the perforated plate 210 to slide in the cavity sleeve 140, thereby adjusting the height of the first cavity 220, changing the volume of the first cavity 220, and further adjusting the resonance frequency of the first cavity 220. Specifically, the second driving member includes a second motor 600 and a second threaded screw 610.

[0038] The second motor 600 is mounted on the motor bracket 132 with the output end facing vertically downward, and the second threaded screw 610 is connected to the output end of the second motor 600. The second threaded 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 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 resonant frequency of the first cavity 220 can be finely adjusted. It should be noted that the bottom of the connecting tube 450 is penetrated on 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 tube 450.

[0039] Among them, two second guide rods 134 are installed on the cover plate 131, and the two second guide rods 134 are both arranged on 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, which is installed 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.

[0040] The first motor 500 and the second motor 600 are both micro-stepping motors. The first threaded screw 510 and the second threaded screw 610 are both M2 threaded screws. In addition, by setting limiting parts such as rubber washers in 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.

[0041] It should be noted that a watertight connector is installed on the top of the waterproof sleeve 111, and 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 are all extended to external computer equipment and other usage scenarios through the watertight connector. The measuring end of the spectrometer is connected to the waterproof sleeve 111 through the optical fiber through the watertight connector, thereby ensuring the sealing of the housing 100.

[0042] The resonance frequencies of the first cavity 220, the cantilever beam slice 430 and the third cavity 440 are all determined by their own physical properties, so that the output light modulation frequency 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 slice 430 are equal to each other, that is, they are kept consistent, so that the resonance frequencies of the four are coupled with each other, and the liquid detection sensitivity can be improved by dual enhancement of acoustics and detection.

[0043] Therefore, the photoacoustic sensor of the present invention couples the resonance frequency of multiple cavities to increase the amplitude of the acoustic signal and the response of the cantilever beam sheet 430, improves the liquid detection sensitivity by the method of dual enhancement of acoustics and detection, detects the concentration of liquid molecules based on multi-cavity coupling, and provides support for the application of PAS technology in 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 sheet 430 are kept consistent, avoiding the resonance frequency offset caused by coupling in different cavities, installation accuracy errors, and liquid temperature and pressure in actual measurement.

[0044] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling, used to detect the characteristics of liquid samples, characterized in that: The photoacoustic sensor comprises: The shell has a notch at the bottom, and a waterproof film is installed at the bottom of the shell to seal the notch; An excitation optical fiber is installed in the housing, and a light beam emitted by the excitation optical fiber can pass through the waterproof film; a perforated plate installed inside the housing and between the excitation optical fiber and the waterproof film, a first cavity being formed between the perforated plate and the waterproof film, and a first through hole being provided on the perforated plate for the light beam of the excitation light to pass through; An acoustic wave detector is installed in the shell, and 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 is irradiated into the sample through the waterproof film, so that the sample generates acoustic waves and propagates 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. According to claim 1, a photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling, characterized in that: The acoustic wave detector includes a spectrometer, a mounting block and a detection optical fiber installed inside the shell, a second cavity is formed inside the mounting block, a detection end face of the detection optical fiber is in the second cavity, a mounting hole connected to the second cavity is opened outside the mounting block, a cantilever beam sheet parallel to the detection end face of the detection optical fiber is installed in the mounting hole, the side of the cantilever beam sheet away from the second cavity is connected to the first cavity, the light beam emitted by the detection optical fiber is reflected on the detection end face and the cantilever beam sheet to form interference light, and the spectrometer is used to capture the interference light to obtain interference spectrum 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, characterized in that: A third cavity is provided in the shell, and a side of the cantilever beam sheet away from the detection end face of the detection optical fiber is connected to the third cavity. A connecting tube is installed on the shell, one end of the connecting tube is connected to the third cavity, and the other end is connected to the first cavity, and the cross-sectional area of ​​the connecting tube 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 sheet, and a first driving member for driving the mounting block to slide is installed in the shell. 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 comprises a first motor installed in the housing, an output end of the first motor is drivingly connected to a first threaded screw, and the first threaded screw is threadedly connected to the mounting block.

6. A 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 to the shell, and a second driving member for driving the perforated plate to slide is installed in the shell. 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, characterized in that: The second driving member includes a second motor installed in the housing, the output end of the second motor is transmission-connected with a second threaded screw, and the second threaded screw is threadedly connected to 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 seat and two cantilever beam fixing plates, the second cavity is arranged on the outside of the mounting seat and has an opening formed on the mounting seat, the two cantilever beam fixing plates are stacked and installed on the outside of the mounting seat and close the opening, the mounting hole is arranged in the middle of the two cantilever beam fixing plates, and the cantilever beam sheet is clamped between the two cantilever beam fixing plates.

9. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 3, characterized in that: 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 sheet and the output light modulation frequency of the excitation optical fiber are equal.

10. The photoacoustic sensor for detecting liquid molecules based on multi-cavity coupling according to claim 1, characterized in that: The shell 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 in the cavity sleeve. The outer side of the sealing sleeve is ringed 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 on the outer side of the convex edge and clamps the cavity sleeve. The waterproof film is coated on the outer side of the cavity sleeve, and the edge of the waterproof film is clamped between the fixing ring and the cavity sleeve, so that the shell can be waterproof.

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