CN113466147A - Rectangular quartz tuning fork and trace gas detection device based on same - Google Patents
Rectangular quartz tuning fork and trace gas detection device based on same Download PDFInfo
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- 239000010453 quartz Substances 0.000 title claims abstract description 111
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 111
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- 230000005284 excitation Effects 0.000 claims description 21
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- 230000035945 sensitivity Effects 0.000 claims description 9
- 238000004891 communication Methods 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 24
- 238000004867 photoacoustic spectroscopy Methods 0.000 description 10
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- 238000010586 diagram Methods 0.000 description 4
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000001834 photoacoustic spectrum Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- MIMUSZHMZBJBPO-UHFFFAOYSA-N 6-methoxy-8-nitroquinoline Chemical compound N1=CC=CC2=CC(OC)=CC([N+]([O-])=O)=C21 MIMUSZHMZBJBPO-UHFFFAOYSA-N 0.000 description 1
- 229910018487 Ni—Cr Inorganic materials 0.000 description 1
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- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 1
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- 229920002120 photoresistant polymer Polymers 0.000 description 1
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
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Abstract
The invention belongs to the technical field of gas sensing, and particularly relates to a rectangular quartz tuning fork and a trace gas detection device based on the rectangular quartz tuning fork, wherein the rectangular quartz tuning fork comprises the following components in parts by weight: the rectangular through holes are designed on the inner sides of the vibrating arms, so that the rectangular quartz tuning fork realizes the clean passing of a wide light beam under a very small size, and the miniaturization characteristic of the quartz reinforced photoacoustic sensor is kept; the problem that the combination application of the quartz tuning fork and a quantum cascade laser or a terahertz light source with a large divergence angle is limited due to the narrow vibrating arm distance of the commercial standard quartz tuning fork is solved.
Description
Technical Field
The invention belongs to the technical field of gas sensing, and particularly relates to a rectangular quartz tuning fork and a trace gas detection device based on the rectangular quartz tuning fork.
Background
Chemical gas phase analysis techniques in physics, chemistry, atmospheric sciences, space sciences, bioengineering, life sciences and medicineHas an extremely important position in the application of science. The basic requirements of gas sensing are sensitivity, selectivity and stability, which are well met by photoacoustic spectroscopy, such as conventional photoacoustic spectroscopy, which can obtain the concentration level of trace gases by detecting the intensity of sound waves with a broadband microphone. The quartz enhanced photoacoustic spectrum is a variation of photoacoustic spectrum technology, uses a tuning fork type quartz crystal oscillator to replace a traditional microphone to detect sound waves, and has the characteristics of small volume and strong noise resistance. The specific principle of quartz enhanced photoacoustic spectroscopy is as follows: a beam of modulated laser penetrates through the miniature sound resonant cavity and the quartz tuning fork, and the population number of gas molecules in a low energy level state and an excited state is periodically modulated, so that the temperature of the measured gas molecules is periodically changed, the expansion and contraction of gas in a light path are caused, and further, sound waves are generated; the sound waves in the light path are collected by the miniature sound resonant cavity, the two vibrating arms of the quartz tuning fork are pushed to vibrate symmetrically, the tuning fork converts the vibration amplitude into an electric signal in direct proportion to the vibration amplitude through the piezoelectric effect, and therefore the concentration of the gas to be measured can be inverted. Quartz enhanced photoacoustic spectroscopy has two very significant advantages over other optical sensing technologies: its detection sensitivity is in direct proportion to the exciting light power; since acoustic waves are measured, this technique is not selective to the wavelength of the excitation light. By means of the first advantage, novel high-power light sources which continuously emerge in the market can be fully utilized, and cheap and high-sensitivity gas detection is realized; by utilizing the second advantage, the detection wavelength can be selected to be a gas fundamental frequency vibration band with stronger absorption, namely a mid-infrared gas fingerprint spectrum band, even a terahertz band, so that ultrahigh sensitive detection is realized. However, whether the high-power LED light source, the intermediate infrared quantum cascade laser source or the terahertz light source are used, the common characteristics of the high-power LED light source, the intermediate infrared quantum cascade laser source and the terahertz light source are that the divergence angle of light beams is large, and the quality of the light beams is far inferior to that of a near infrared light source. Especially, the light emitting mechanism of light sources such as quantum cascade lasers, LEDs and the like enables the emergent light of the novel light source to be mostly in a strip shape. The sensitive area between the two vibrating arms of the standard quartz tuning fork is only about 0.3 multiplied by 3mm3Such a small acoustic response area enables a sensing system based on such a quartz tuning fork to have a small size and a compact structureMeanwhile, harsh requirements are also put forward on the beam quality of a light source used by the system and the light path collimation link. In the quartz enhanced photoacoustic spectroscopy technology, the light beam of the excitation light source must be strictly prohibited from contacting the quartz tuning fork, otherwise, stray light irradiating on the tuning fork vibrating arm can cause background noise with interference-like shape 5 to 10 times higher than the signal, and the noise directly affects the detection sensitivity of the sensor system. In fact, it is the narrow arm spacing of the commercial standard quartz tuning fork that limits its combined application with high power light sources with large spot size or mid-infrared and terahertz light sources. Therefore, the above-mentioned limitations can be solved well by designing a rectangular quartz tuning fork suitable for the new excitation light source.
Disclosure of Invention
The invention provides a rectangular quartz tuning fork and a trace gas detection device based on the rectangular quartz tuning fork, which aim to solve the problem of low detection sensitivity when a standard quartz tuning fork is combined with a quantum cascade laser, an LED and other novel light sources with strip-shaped light spots as emergent light spots in a quartz reinforced photoacoustic spectroscopy technology.
In order to achieve the purpose, the invention adopts the following technical scheme:
the inner sides of the two vibrating arms are provided with mutually symmetrical rectangular through holes. When the sound source is positioned in the center of the tuning fork vibrating arm, the photoacoustic signals can push the two vibrating arms of the quartz tuning fork to symmetrically vibrate in opposite directions, so that the two vibrating arms of the tuning fork must be symmetrically modified to effectively push the vibrating arms of the tuning fork to vibrate, and the sensitivity of photoacoustic detection is improved.
Furthermore, the top end of the vibrating arm is provided with a hammer-shaped structure, so that the top end mass of the vibrating arm is increased, the mass center of the vibrating arm is moved upwards, the quality factor of the rectangular quartz tuning fork is greatly increased, and the detection sensitivity of the sensor is improved.
Still further, two the clearance between the arm of shaking is 0.8-1mm, the thickness of the arm of shaking is 0.2-0.3mm, and the overall height is 9.4mm, and the width at lower part and middle part is 1.6mm, the width in rectangle quartz tuning fork bottom region is 5.2-5.4mm, and highly is 5.2mm, the width of hammer-shaped structure is 2mm, highly is 2.4mm, the width of rectangle via hole is 0.5mm, highly is 1mm, the distance of the center of rectangle via hole apart from the arm top of shaking is 1-2 mm.
The trace gas detection device based on the rectangular quartz tuning fork comprises a photoacoustic signal detection module, a light source module and a data acquisition module;
the photoacoustic signal detection module comprises a rectangular quartz tuning fork and an air chamber, wherein two opposite side walls of the air chamber are respectively provided with a light incident window and a light emergent window, the other two side walls of the air chamber are provided with an air inlet and an air outlet, the rectangular quartz tuning fork is placed in an inner cavity of the air chamber through a support, the light incident window, the midpoint of the central connecting line of the two rectangular through holes and the light emergent window are all positioned on the same light path, the horizontal included angle between the axis of the light incident window and the light path is 5 degrees, and the horizontal included angle between the axis of the light emergent window and the light path is-5 degrees;
the light source module comprises an excitation light source, a first function generator, a second function generator, an adder circuit, a light source temperature controller and a light source current controller, wherein the signal output end of the first function generator is connected with the first input port of the adder circuit, the signal output end of the second function generator is connected with the second input port of the adder circuit, the synchronous signal output end of the second function generator is connected with the synchronous signal input port of the lock-in amplifier, the output port of the adder circuit is connected with the input port of the light source current controller, and the light source current controller and the light source temperature controller are connected with the excitation light source and used for controlling the excitation light source to output a modulated light beam with a specific wavelength;
the data acquisition module comprises a transimpedance preamplifier, a phase-locked amplifier and a computer, wherein two signal input ends of the transimpedance preamplifier are respectively connected with two electrode output ends of the rectangular quartz tuning fork, one signal input end of the transimpedance preamplifier is connected with the electrode output end of the rectangular quartz tuning fork and then grounded, the signal input end of the phase-locked amplifier is connected with the signal output end of the transimpedance preamplifier, the synchronous signal input end of the phase-locked amplifier is connected with the synchronous signal output end of the second function generator, and the signal output end of the phase-locked amplifier is connected with a signal acquisition port of the computer through an RS232 serial port communication port so as to read and process signals.
Further, the excitation light source is an LED light source, a quantum cascade laser or a terahertz light source.
Compared with the prior art, the invention has the following advantages:
according to the invention, the rectangular through hole is designed on the inner side of the vibrating arm, so that the rectangular quartz tuning fork realizes the clean passing of a wide light beam under a very small size, and the miniaturization characteristic of the quartz reinforced photoacoustic sensor is kept; the problem that the combination application of the quartz tuning fork and a quantum cascade laser or a terahertz light source with a large divergence angle is limited due to the narrow vibrating arm distance of the commercial standard quartz tuning fork is solved; the introduction of the rectangular via hole structure combines quartz enhanced photoacoustic spectroscopy with a strip-shaped high-power LED light source, so that a trace gas detector with high cost performance is realized; the lower resonance frequency of the rectangular quartz tuning fork solves the problem that a QEPAS sensing system using a standard quartz tuning fork cannot effectively measure gas with lower molecular relaxation rate.
Drawings
FIG. 1 is a schematic structural diagram of a rectangular quartz tuning fork according to the present invention;
FIG. 2 is a diagram showing the simulation of the vibration effect of the rectangular quartz tuning fork according to the present invention;
FIG. 3 is a circuit diagram of a transimpedance preamplifier according to the present invention;
FIG. 4 is a schematic diagram of the structure of the trace gas detection device according to the present invention;
FIG. 5 is a schematic view of the angle between the light path and the axis of the light entrance window and the light exit window according to the present invention;
FIG. 6 is a frequency sweep graph of a rectangular quartz tuning fork of the present invention;
FIG. 7 is a graph comparing photoacoustic signals of a sensing system based on a rectangular quartz tuning fork of the present invention and a standard quartz tuning fork;
FIG. 8 is a graph comparing the noise level of a sensing system based on a rectangular quartz tuning fork according to the present invention with that of a standard quartz tuning fork;
in the figure, a rectangular quartz tuning fork-1, a gas chamber-2, a laser light source-3, a first function generator-4, a second function generator-5, an adder circuit-6, a light source temperature controller-7, a light source current controller-8, a transimpedance preamplifier-9, a lock-in amplifier-10, a computer-11, a vibrating arm-101, a rectangular through hole-102 and a hammer-shaped structure-103.
Detailed Description
In order to further illustrate the technical solution of the present invention, the present invention is further illustrated by the following examples.
The rectangular quartz tuning fork is realized by adopting the following technical scheme: for quartz etching, an opening is limited through a negative photoresist photoetching method, then the quartz wafer is etched in an ammonium bifluoride saturated solution so as to selectively remove an unnecessary area in the quartz wafer, finally, a designed tuning fork structure is etched, the surface of a vibrating arm and the surface of a base are coated with a gold coating in an electron beam evaporator, a gold thin layer with a specific shape is designed and electroplated to collect charges generated by the quartz tuning fork due to a piezoelectric effect, and a side wall electrode is added by adopting a hollow mask process and a nickel-chromium oblique evaporation process so as to improve the charge collection capability.
In the quartz enhanced photoacoustic spectroscopy technology, the modulation frequency needs to be far lower than the vibration-translation relaxation rate of target gas molecules, otherwise the relaxation process of the molecules cannot follow the external modulation process; secondly, the modulation frequency should be increased as much as possible to suppress low-frequency noise in the environment, so the resonance frequency of the rectangular quartz tuning fork of the invention is selected to be 15kHz, and the resonance frequency can find the best balance point between the aspect of low-frequency noise suppression and most molecular relaxation processes. The target resonant frequency is obtained by setting basic geometric parameters of the vibration arm, and for the damping motion of the rectangular cantilever beam structure, the target resonant frequency is generally described by an Euler-Bernoulli beam equation:
wherein y represents the length from the base of the vibrating arm along the vibrating armThe distance in the axial direction, f (y, t) represents the force density acting on the vibrating arm of the quartz tuning fork at the point y, u (y, t) is the displacement amount of the point y at the moment t, and rho is 2,650kg/m3The density of the quartz material is E, 72GPa is the Young modulus of the vibrating arm of the quartz tuning fork in a vibrating state, A and I are respectively the cross-sectional area and the sectional inertia moment at the y point, and beta is the damping coefficient of air.
Since the vibrating arm is in a fixed state at y-0 and in a free state at y-L, a boundary condition can be introduced that the displacement and slope at the fixed end of the vibrating arm is 0, i.e., u (0, t) is 0,
the bending moment and shear force at the free end of the horn are 0, i.e.
The displacement formula of each point on the vibrating arm under the excitation of sound waves can be obtained by solving the damping motion of the vibrating arm:
where ω is the frequency of the acoustic excitation, and in order to allow maximum vibrational displacement of the tuning fork, the acoustic excitation frequency is generally equal to the resonant frequency of the tuning fork, M1(y0) Inversely proportional to the density ρ of the quartz tuning fork and the cross-sectional area a at the y-point, we can obtain the following formula of resonance frequency:
where ρ is 2,650kg/m3The density of the quartz material is shown, E is 72GPa, the Young modulus of the vibrating arm of the quartz tuning fork in a vibrating state, and L and w are respectively the length and the width of the vibrating arm of the quartz tuning fork. The rectangular quartz tuning fork of the invention is determined to reserve the geometrical characteristics of symmetrical distribution of two vibrating arms of the standard tuning fork after calculation through a theoretical model and optimization through experiments, and the quartz tuning fork is a standard tuning forkCompared with the whole size, the excessively wide distance between the vibrating arms of the acoustic quadrupole vibration structure can cause the two vibrating arms which originally vibrate oppositely to gradually become independent cantilever beam structures, so that the noise suppression capability of the acoustic quadrupole vibration structure is weakened, and therefore, the distance between the two vibrating arms of the rectangular quartz tuning fork is 0.8-1mm, the total length of the vibrating arms is 9.4mm, and the thickness of the vibrating arms is 0.2-0.3 mm. As shown in fig. 1, the rectangular via hole structure of the rectangular quartz tuning fork of the present invention is: on the basis of keeping the vibration arm gap to be 0.8mm, rectangular through holes with the height of 1mm and the width of 0.5mm are formed in the inner sides of the two vibration arms respectively, the distance between the rectangular through holes can reach 1.8mm, and novel laser light sources such as high-power LED light sources with large-size strip-shaped light spots can penetrate through the vibration arm gap of the quartz tuning fork without collision. The center of the rectangular through hole is located at a position 1-2mm away from the top end of the vibrating arm, and the position is the optimal excitation position under the fundamental frequency vibration mode of the rectangular quartz tuning fork, and finally the dimension of the rectangular through hole structure of the rectangular quartz tuning fork designed by the invention can maximally allow strip-shaped light beams with the length of 1.8mm and the width of 1mm to pass through, so that the combined requirement of most high-power laser light sources capable of generating strip-shaped light spots and the quartz reinforced photoacoustic spectroscopy technology can be met.
Since the detection sensitivity of quartz enhanced photoacoustic spectroscopy is proportional to the quality factor Q, and the rectangular via hole shape of the designed quartz tuning fork can reduce part of the quality factor, the invention maintains the high quality factor characteristic by arranging the hammer-shaped structure at the top end of the vibrating arm. The hammer-shaped structure can greatly increase the quality factor of the quartz tuning fork due to the fact that the top mass of the hammer-shaped structure is increased, and the center of mass of the hammer-shaped structure is moved upwards. The width of the hammer-shaped structure at the top end of the rectangular quartz tuning fork is 2mm, and the height of the hammer-shaped structure is 2.4 mm; the width of the bottom end area of the rectangular quartz tuning fork is 5.2-5.4mm, and the height of the bottom end area of the rectangular quartz tuning fork is 5.2-5.4 mm.
As shown in FIG. 2, a fundamental frequency vibration mode of a rectangular quartz tuning fork with a rectangular through hole is simulated by using a COMSOL simulation software theory, the resonance frequency of the fundamental frequency vibration mode is 15kHz, and the measurement of gas molecules with low relaxation rate can be realized by using a low resonance frequency. To maximize the response of the quartz tuning fork, the modulation frequency of the external excitation signal should be equal to the resonance frequency of the quartz tuning fork or a harmonic frequency of the resonance frequency.
As shown in fig. 4, the trace gas detection device based on the rectangular quartz tuning fork comprises a photoacoustic signal detection module, a light source module and a data acquisition module;
the photoacoustic signal detection module comprises a rectangular quartz tuning fork 1 and an air chamber 2, wherein two opposite side walls of the air chamber 2 are respectively provided with a light incident window and a light emergent window, the other two side walls of the air chamber 2 are provided with an air inlet and an air outlet, the rectangular quartz tuning fork 1 is placed in an inner cavity of the air chamber 2 through a support, the light incident window, the midpoint of the central connecting line of the two rectangular through holes 102 and the light emergent window are all positioned on the same light path, the horizontal included angle between the axis of the light incident window and the light path is 5 degrees, and the horizontal included angle between the axis of the light emergent window and the light path is-5 degrees;
the light source module comprises an excitation light source 3, a first function generator 4, a second function generator 5, an adder circuit 6, a light source temperature controller 7 and a light source current controller 8, the excitation light source 3 is an LED light source, a quantum cascade laser or a terahertz light source, the signal output end of the first function generator 4 is connected with the first input port of the adder circuit 6, the signal output of the second function generator 5 is connected to the input port No. two of the adder circuit 6, the synchronization signal output of the second function generator 5 is connected to the synchronization signal input port of the lock-in amplifier 10, the output port of the adder circuit 6 is connected with the input port of a light source current controller 8, and the light source current controller 8 and a light source temperature controller 7 are connected with the excitation light source 3 and used for controlling the excitation light source 3 to output a modulated light beam with a specific wavelength;
the data acquisition module comprises a transimpedance preamplifier 9, a phase-locked amplifier 10 and a computer 11, wherein two signal input ends of the transimpedance preamplifier 9 are respectively connected with two electrode output ends of the rectangular quartz tuning fork 1, one signal input end of the transimpedance preamplifier 9 is connected with the electrode output end of the rectangular quartz tuning fork 1 and then grounded, the signal input end of the phase-locked amplifier 10 is connected with the signal output end of the transimpedance preamplifier 9, the synchronous signal input end of the phase-locked amplifier 10 is connected with the synchronous signal output end of the second function generator 5, and the signal output end of the phase-locked amplifier 10 is connected with a signal acquisition port of the computer 11 through an RS232 serial port communication port so as to read and process signals.
In FIG. 3, a circuit of a transimpedance preamplifier for detecting the weak signal of the rectangular quartz tuning fork is shown, and a gain resistor RfThe resistance value of 10M omega is selected, the feedback loop formed by the resistance value keeps the voltage difference between two electrodes of the rectangular quartz tuning fork to be zero, and the influence of parallel parasitic capacitance on a circuit system is effectively eliminated. The photoacoustic signal pushes two vibrating arms of the rectangular quartz tuning fork to vibrate symmetrically, alternating weak current I is formed by the vibration through the piezoelectric effect of the quartz material, and the current is transmitted to a transimpedance preamplifier through an electrode of the rectangular quartz tuning fork and then passes through a gain resistor RfAmplifies and converts into a voltage signal UoutThe voltage signal is demodulated by a phase-locked amplifier to obtain a harmonic signal corresponding to the photoacoustic signal.
FIG. 6 is a frequency spectrum curve obtained by the rectangular quartz tuning fork of the present invention through an electrical excitation method, the amplitude of the modulation voltage is 316mV, and the resonance frequency of the rectangular quartz tuning fork is 15265.2Hz when the modulation frequency is changed at a constant speed within the range of 15260 and 15270Hz in steps of 0.2Hz, and the resonance frequency can find the best balance point between the aspect of low frequency noise suppression and most molecular relaxation processes.
Fig. 7 is a photo-acoustic signal obtained by using the rectangular quartz tuning fork and the trace gas detection device of the present invention, and after comparing with a signal obtained by a standard quartz tuning fork under the same conditions, it shows that the rectangular quartz tuning fork signal with the rectangular via hole of the present invention is stronger than the standard quartz tuning fork signal by about 2.5 times, which shows that the introduction of the hammer-shaped structure can improve the detection sensitivity of the device.
Fig. 8 is a noise signal obtained by using the rectangular quartz tuning fork and the trace gas detection device of the present invention, and a comparison with a noise signal obtained by a standard quartz tuning fork under the same conditions shows that the noise can be reduced by about 2 times by using the rectangular quartz tuning fork of the present invention due to the rectangular via hole structure.
While there have been shown and described what are at present considered to be the essential features and advantages of the invention, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but is capable of other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (5)
1. The quartz tuning fork of rectangle, its characterized in that: rectangular through holes (102) which are symmetrical to each other are arranged on the inner sides of the two vibrating arms (101).
2. The rectangular quartz tuning fork of claim 1, wherein: the top end of the vibrating arm (101) is provided with a hammer-shaped structure (103) so as to increase the top end mass of the vibrating arm (101) and move the mass center of the vibrating arm (101) upwards, thereby greatly increasing the quality factor of the rectangular quartz tuning fork (1) and improving the detection sensitivity of the sensor.
3. The rectangular quartz tuning fork of claim 2, wherein: two the clearance of shaking between the arm (101) is 0.8-1mm, the thickness of shaking arm (101) is 0.2-0.3mm, and the overall height is 9.4mm, and the width of middle part and lower part is 1.6mm, the width of rectangle quartz tuning fork (1) bottom region is 5.2-5.4mm, and highly is 5.2mm, the width of hammer structure (103) is 2mm, highly is 2.4mm, the width of rectangle via hole (102) is 0.5mm, highly is 1mm, the distance that the center distance of rectangle via hole (102) shakes arm (101) top is 1-2 mm.
4. The trace gas detection device based on the rectangular quartz tuning fork of claim 1, characterized in that: the device comprises a photoacoustic signal detection module, a light source module and a data acquisition module;
the photoacoustic signal detection module comprises a rectangular quartz tuning fork (1) and an air chamber (2), wherein two opposite side walls of the air chamber (2) are respectively provided with a light incident window and a light emergent window, the other two side walls of the air chamber (2) are provided with an air inlet and an air outlet, the rectangular quartz tuning fork (1) is placed in an inner cavity of the air chamber (2) through a support, the light incident window, the midpoint of the central connecting line of the two rectangular through holes (102) and the light emergent window are all positioned on the same light path, the horizontal included angle between the axis of the light incident window and the light path is 5 degrees, and the horizontal included angle between the axis of the light emergent window and the light path is-5 degrees;
the light source module comprises an excitation light source (3), a first function generator (4), a second function generator (5), an adder circuit (6), a light source temperature controller (7) and a light source current controller (8), the signal output end of the first function generator (4) is connected with the first input port of the adder circuit (6), the signal output end of the second function generator (5) is connected with the second input port of the adder circuit (6), the synchronous signal output end of the second function generator (5) is connected with the synchronous signal input end of the phase-locked amplifier (10), the output port of the adder circuit (6) is connected with the input port of a light source current controller (8), the light source current controller (8) and the light source temperature controller (7) are connected with the excitation light source (3) and used for controlling the excitation light source (3) to output a modulated light beam with a specific wavelength;
the data acquisition module comprises a transimpedance preamplifier (9), a phase-locked amplifier (10) and a computer (11), two signal input ends of the transimpedance preamplifier (9) are respectively connected with two electrode output ends of the rectangular quartz tuning fork (1), one signal input end of the transimpedance preamplifier (9) is connected with the electrode output end of the rectangular quartz tuning fork (1) and then grounded, the signal input end of the phase-locked amplifier (10) is connected with the signal output end of the transimpedance preamplifier (9), the synchronous signal input end of the phase-locked amplifier (10) is connected with the synchronous signal output end of the second function generator (5), and the signal output end of the phase-locked amplifier (10) is connected with the signal acquisition port of the computer (11) through an RS232 serial port communication port so as to read and process signals conveniently.
5. The trace gas detection device based on a rectangular quartz tuning fork according to claim 4, characterized in that: the excitation light source (3) is an LED light source, a quantum cascade laser or a terahertz light source.
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