CN113218901B - Cavity enhanced spectrum gas detection device and method based on micro quartz crystal oscillator array detector - Google Patents
Cavity enhanced spectrum gas detection device and method based on micro quartz crystal oscillator array detector Download PDFInfo
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Abstract
The invention discloses a cavity enhanced spectrum gas detection device and method based on a micro quartz crystal array detector, and relates to the technical field of laser spectrum and photoelectric detection. The invention comprises a modulatable LED light source, a collimating lens, a sample cell, a focusing lens, a miniature quartz crystal oscillator array, a conversion circuit, a digital-to-analog conversion module, a computer control unit and a laser control module. The invention utilizes the piezoelectric effect and the resonance characteristic of the micro quartz crystal oscillator array, a vacuum sealing shell-free structure and a high-sensitivity ring-down cavity enhanced spectrum technology, and realizes a simple and convenient high-sensitivity gas detection scheme by using the micro quartz crystal oscillator array as a photoelectric signal detector.
Description
Technical Field
The invention relates to the technical field of laser spectroscopy and photoelectric detection, in particular to a cavity enhanced spectroscopy gas detection device and method based on a micro quartz crystal oscillator array.
Background
The laser spectroscopy technology has important significance in the fields of atmospheric environment monitoring, industrial process control, combustion diagnosis, respiratory gas component diagnosis and the like. Conventional laser spectroscopy techniques mainly include direct absorption spectroscopy and photoacoustic spectroscopy. In 2002, quartz tuning forks were first reported to be successfully applied in photoacoustic spectroscopy systems as acoustic signal detectors instead of traditional microphones, from which quartz enhanced photoacoustic spectroscopy comes. Since then, quartz tuning forks have been extensively studied. In recent years, a quartz tuning fork is applied to an absorption spectroscopy technology as a photodetector, and unlike a photoacoustic spectroscopy technology, the quartz tuning fork is applied to the absorption spectroscopy technology as a photodetector based on the resonance characteristics and the piezoelectric effect of the quartz tuning fork. The laser spectrum technology based on the quartz tuning fork is rapidly developed due to the advantages of small interference of environmental factors, high detection sensitivity, low price, no wavelength response limitation and the like.
Currently, the laser spectroscopy technology based on quartz tuning forks generally uses two types, one is a standard commercial cylindrical quartz crystal oscillator with an eigenfrequency of about 32kHz. The other is a custom tuning fork with lower frequency and larger size made by self-processing. When the quartz tuning fork is applied to gas detection, the performance of the tuning fork is influenced by the quality factor of the tuning fork, and the higher the quality factor is, the better the detection performance is. When the former tuning fork is used for gas detection, the metal shell of the quartz tuning fork needs to be removed so that the tuning fork can be coupled with an optical path to detect an acoustic signal or an optical signal, but the quality factor of the tuning fork with the shell removed is greatly reduced. The latter tuning fork is limited due to the complex manufacturing process and high development cost. The two exposed tuning forks are easy to be polluted and corroded, and cannot meet the requirements of harsh environments and long-term application. In addition, the photoelectric conversion efficiency of the quartz tuning fork is limited, and the quartz tuning fork cannot be used for high-sensitivity measurement of weak-power light sources, especially non-stimulated radiation light sources such as LEDs and laser light sources in ultraviolet and terahertz wave bands.
Aiming at the defects of the traditional quartz tuning fork or the customized quartz tuning fork at present, the invention provides a high-sensitivity gas detection device and method based on a micro-nano quartz crystal oscillator array. The micro quartz crystal oscillator completely seals the micro quartz tuning fork in a vacuum environment through a micro-nano processing technology, is not easy to be polluted and corroded, and can be directly used for photoelectric signal measurement without a shell. Compared with the traditional standardized commercial crystal oscillator and the large-scale crystal oscillator, the micro crystal oscillator is not easily disturbed by external environment noise, has higher quality factor and narrower response bandwidth. In order to enhance the signal intensity, the signal superposition enhancement can be realized by integrating a plurality of crystal oscillators in an array mode, and the detection sensitivity can be obviously improved. In addition, the absorption optical path of the interaction of light and substances is increased by combining the high-precision optical ring-down cavity, so that the gas sensor is more suitable for ultrahigh-precision and ultrahigh-sensitivity gas detection application.
Disclosure of Invention
The invention aims to provide a cavity enhanced spectrum gas detection device and method based on a micro quartz crystal oscillator array detector, which solve the defects of a traditional standard quartz tuning fork or a large-size quartz tuning fork in the background technology.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the invention relates to a cavity enhanced spectrum gas detection device based on a miniature quartz crystal oscillator array detector, which comprises a light source, a collimating lens, a sample cell, a focusing lens, a miniature quartz crystal oscillator array, a conversion circuit, a digital-to-analog conversion module, a computer control unit and a light source drive control module, wherein the light source is connected with the collimating lens;
the output of computer control unit is connected with light source drive control module input, light source drive control module's output is connected with the light source, the emergent light of light source passes through collimating lens and passes the sample cell, set up focusing lens at the back in the sample cell, focusing lens is equipped with miniature quartz crystal oscillator array at the back, miniature quartz crystal oscillator array is connected with converting circuit, converting circuit's output and digital-to-analog conversion module are connected, digital-to-analog conversion module connects computer control unit.
Further, the light source is a modulatable LED light source.
Further, the sample cell is a ring down cavity with a high reflectivity cavity mirror.
Furthermore, the micro quartz crystal oscillator array is formed by integrally packaging a plurality of micro quartz tuning forks with the same model through micro-nano processing, and the specific number of the tuning forks in the array can be set according to the actual application requirements.
Furthermore, each micro quartz crystal oscillator in the micro quartz crystal oscillator array has the size of only 3.2 × 1.3 × 0.8mm, and the eigenfrequency of each micro quartz crystal oscillator is 32.763kHz.
Furthermore, the micro quartz tuning fork is sealed in a vacuum shell made of quartz, and the dielectric material can be selected according to the highest transmittance corresponding to the wavelength band of the used light source, for example, calcium fluoride material can be selected in the mid-infrared band. Furthermore, the micro quartz crystal oscillator is processed by a micro quartz tuning fork through a micro nano technology and is sealed in a vacuum shell made of quartz; the size of the miniature quartz tuning fork is selected to be 1097 × 253um.
Furthermore, the computer control unit comprises a light source modulation algorithm written by Labview software and a signal demodulation analysis algorithm module written by Labview software.
The detection method of the cavity enhanced spectrum gas detection device based on the micro quartz crystal oscillator array comprises the following steps:
[01] a light source modulation digital signal output module compiled by Labview software in the computer control unit outputs a modulation signal with a specific frequency or a pulse driving voltage signal, the modulation signal or the pulse driving voltage signal is converted into an analog signal through a digital-to-analog conversion module and then is input into a light source through a light source driving control module, and the modulation luminescence of the light source is realized;
[02] modulated light emitted by the light source passes through the sample cell after being collimated by the collimating lens, is focused by the focusing lens, is incident to the micro quartz crystal oscillator array and irradiates the surface of the internal micro quartz tuning fork through the quartz shell;
[03] the micro quartz tuning fork is excited by modulated light, and piezoelectric current is generated due to the piezoelectric effect and the resonance effect of the micro quartz tuning fork;
[04] piezoelectric current generated by each micro quartz tuning fork in the micro quartz crystal oscillator array is input to a conversion circuit after being superposed and is converted into a voltage signal after being filtered and amplified;
[05] the voltage signal output by the conversion circuit is input into a signal demodulation analysis algorithm module compiled by Labview software in a computer control unit through a digital-to-analog conversion module for relevant processing;
[06] and gas concentration information can be inverted according to the Lambert-Beer law satisfied by the cavity enhanced absorption spectrum and a correction curve between the amplitude of the resonance curve and the gas concentration.
Furthermore, in the step [05], the algorithm of the signal demodulation analysis algorithm module based on Labview software comprises the following steps: firstly, carrying out spectrum analysis on an original time domain signal output by a miniature quartz crystal oscillator array through a fast Fourier transform algorithm, and demodulating a frequency signal responded by a surface-mounted quartz crystal oscillator; then, carrying out extreme value taking algorithm, and analyzing the corresponding relation between the frequency domain signal amplitude and the laser modulation frequency change; and finally, obtaining a crystal oscillator frequency response curve with a certain bandwidth near the eigenfrequency.
Further, a modulatable LED light source with a center wavelength in the 440nm band is used for NO 2 Gas concentration measurement, or selection of modulatable LED light sources with center wavelengths near 760nm and 1653nm for O respectively 2 And CH 4 Measurement of gas concentration, etc.
Furthermore, a modulatable LED light source with a center wavelength in the 440nm band is used for NO 2 Gas concentration measurement: firstly, with N 2 Or zero air is background air, and a resonance response curve under the background condition of the sample pool of the ring-down cavity is recorded in a certain frequency range; the sample cell is then evacuated and then filled with different NO 2 A standard gas sample under the concentration is measured, and a resonance response curve of the standard gas sample is measured; finally, with different NO 2 And (3) dividing the signal amplitude and the background amplitude at the optimal central modulation frequency of the concentration sample, taking the negative logarithm to obtain the absorbance of the corresponding sample, establishing an experimental system correction curve by using the absorbance and the known sample concentration, measuring the absorbance of the sample gas with unknown concentration through the process, and substituting the measured absorbance into the correction curve to obtain the corresponding concentration information.
The cavity enhanced absorption spectrum principle analysis is as follows:
the cavity enhanced absorption spectrum is used for measuring the intensity of an optical signal penetrating through a resonant cavity, and the resonant cavity can be regarded as a Fabry-Perot cavity and a two-cavity mirror M in principle 1 ,M 2 Respectively, the transmittance and reflectance of 1 ,T 2 And R 1 ,R 2 . Let R be 1 ＝R 2 The amplitude transmission and reflection coefficients of the response are t 1 ,t 2 ,r 1 ,r 2 。
L is the cavity length, beta is the angle of incidence, n 2 The refractive index of the medium in the cavity.
Assuming a beam intensity of E 0 (v) The light is incident to the resonant cavity, and when the light beam passes through the resonant cavity with the medium for the first time through the two cavity mirrors, the amplitude E of the light beam 1 (v) Comprises the following steps:
when the beam is reflected N times in the cavity and N → ∞ passes through the cavity, the total field strength is:
it is expressed in light intensity form as:
in the formula
In cavity enhanced absorption spectroscopy, the phase term 2 n 2 vLcosi 2 The/c determines the constructive and destructive interference, when the laser is incident axially, cosi ≈ 1, the phase term is reduced to 2 π n 2 vL 2 C when 2 π n 2 vL 2 When/c = n pi, the intensity of the coherent constructive transmitted light is maximum, and the projected light intensity of the resonant cavity can be expressed as:
considering the effect of the pressure of the medium in the cavity on the absorption coefficient, the field strength expression can be expressed as:
where α' (v) is the absorption coefficient related to pressure and p is the pressure of the medium in the chamber.
When the laser resonates with the resonant cavity, and α' (v) pL < 1,r 1 ,r 2 When 1, the ratio between the intensity of the laser light transmitted through the cavity and the incident light can be written as:
assuming that the transmission loss of the cavity is due to absorption by the medium within the cavity, then:
if the absorption loss per pass of the cavity medium is much smaller than the projection loss, i.e., a ` (v) pL < 1-r 1 r 2 Then it can be simplified to:
in the cavity enhanced absorption spectroscopy technique, the optical fiber is prepared by mixing
Definition as the precision of the resonator, denoted by F
Compared with the Lambert-beer law obtained in the traditional direct absorption spectrum technology, the cavity enhanced absorption spectrum technology has one more coefficient term
The absorption path of the medium is enhanced compared to the cavity length L
And (4) doubling. The precision F of the resonant cavity is usually very high, so the effective path of the cavity enhanced absorption spectrum technology is very long and can reach km magnitude, and very high detection sensitivity can be obtained in actual detection.
In practical applications of cavity-enhanced absorption spectroscopy, the lambert beer law is transformed into:
the absorption coefficient a (v) of the transmitted absorption spectrum is proportional to the concentration C, and therefore, the absorbance of the medium can be expressed as:
the invention has the following beneficial effects:
(1) The invention utilizes the resonance characteristic and piezoelectric effect of a micro quartz crystal oscillator and the relation between different gas concentrations and the signal amplitude of the resonance curve of the crystal oscillator frequency to realize high-sensitivity gas detection. Compared with a laser spectrum technology sensing system based on a standard quartz crystal oscillator, the sensing system has the advantages of smaller size, simple structure, strong noise suppression capability, high quality factor, narrow bandwidth, high detection sensitivity and the like, solves the problems of low quality factor, high susceptibility to pollution and corrosion and the like of the traditional naked tuning fork, and can meet the requirement of long-term reliable application in harsh environments.
(2) According to the invention, the micro quartz tuning fork is integrated and packaged in vacuum to form an array, so that the light intensity utilization rate of light sources with higher divergence, such as LEDs, is effectively improved, the tuning fork quality factor is enhanced to improve the signal conversion efficiency, the mutual absorption process of light and a gas medium is improved by combining a high-precision long-optical-path ring-down optical cavity, and the ultrahigh-sensitivity gas measurement can be realized.
(3) The invention utilizes a light source modulation algorithm and a signal analysis processing algorithm compiled based on computer Labview to replace the traditional instrument equipment such as a signal generator, a lock-in amplifier and the like, so that the system is more compact and the cost is lower.
(4) The invention can be used for detecting and analyzing other gases by simply replacing LED light sources with other wave bands and ring-down cavity high-reflection lenses matched with the light sources without replacing a photoelectric detector. If the LED light sources with wavelengths of 760nm and 1653nm are selected, O can be respectively realized 2 And CH 4 Measurement of gas molecules.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a cavity enhanced spectrum gas detection device based on a micro quartz crystal oscillator array according to the present invention.
FIG. 2 is a schematic diagram of a micro quartz tuning fork used in the apparatus of the present invention.
FIG. 3 is a frequency resonance response curve of different NO2 gas concentrations detected by a micro quartz crystal array used in the device of the present invention.
FIG. 4 is a calibration curve between absorbance and gas concentration calculated from the amplitude of the micro quartz crystal oscillator spectrum signal.
In the figure: the device comprises a light source 1, a collimating lens 2, a sample cell 3, a focusing lens 4, a micro quartz crystal oscillator array 5, a conversion circuit 6, a digital-to-analog conversion module 7, a computer control unit 8 and a light source driving control module 9.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the device for detecting gas based on cavity enhanced spectrum of quartz crystal array detector of the present invention includes a light source 1, a collimating lens 2, a sample cell 3, a focusing lens 4, a micro quartz crystal array 5, a conversion circuit 6, a digital-to-analog conversion module 7, a computer control unit 8, and a light source driving control module 9; the output of computer control unit 8 is connected with the 9 inputs of light source drive control module, the output of light source drive control module 9 is connected with light source 1, the emergent light of light source passes through collimating lens 2 and passes sample cell 3, 3 back sets up focusing lens 4 in the sample cell, focusing lens 4 is equipped with miniature quartz crystal oscillator array 5 at the back, miniature quartz crystal oscillator array 5 is connected with converting circuit 6, converting circuit 6's output is connected with digital-to-analog conversion module 7, digital-to-analog conversion module 7 is connected computer control unit 8.
Furthermore, the light source is a modulatable LED light source.
Further, the sample cell 3 is a ring down cavity with a high reflectivity cavity mirror.
Furthermore, the micro quartz crystal oscillator array 5 is formed by integrally packaging a plurality of micro quartz tuning forks of the same type through micro-nano processing, and the specific number of the tuning forks in the array can be set according to the actual application requirements. .
Furthermore, each micro quartz crystal oscillator in the micro quartz crystal oscillator array has the size of only 3.2 × 1.3 × 0.8mm, and the eigenfrequency of each micro quartz crystal oscillator is 32.763kHz.
Furthermore, the micro quartz tuning fork is sealed in a vacuum shell made of quartz, and the dielectric material can be selected according to the highest transmittance corresponding to the wavelength band of the used light source, for example, calcium fluoride material can be selected in the mid-infrared band.
Furthermore, the micro quartz crystal oscillator is processed by a micro quartz tuning fork through a micro nano technology and is sealed in a vacuum shell made of quartz; the size of the miniature quartz tuning fork is selected to be 1097 × 253um.
Furthermore, the computer control unit 8 includes a light source modulation algorithm written by Labview software and a signal demodulation and analysis algorithm module written by Labview software.
The detection method of the cavity enhanced spectrum gas detection device based on the micro quartz crystal oscillator array comprises the following steps:
[01] a light source modulation digital signal output module compiled by Labview software in the computer control unit 8 outputs a light source modulation signal or a pulse driving voltage signal with specific frequency, the light source modulation signal or the pulse driving voltage signal is converted into an analog signal through a digital-to-analog conversion module and then is input into an excitation light source through a light source driving control module 9, and the modulation luminescence of the light source (1) is realized;
[02] modulated light emitted by the light source 1 is collimated by the collimating lens 2, then passes through the sample cell 3, is focused by the focusing lens 4, then enters the micro quartz crystal oscillator array 5 and irradiates the surface of the internal micro quartz tuning fork through the quartz shell of the micro quartz crystal oscillator array;
[03] when the micro quartz tuning fork is excited by the modulated light, piezoelectric current is generated due to the piezoelectric effect and the resonance effect of the micro quartz tuning fork;
[04] piezoelectric current generated by each quartz tuning fork in the micro quartz crystal oscillator array 5 is input to a conversion circuit (6) after being superposed, and is converted into a voltage signal through filtering and amplification;
[05] the voltage signal output by the conversion circuit 6 is input into a signal demodulation and analysis algorithm module written by Labview software in a computer control unit 8 through a digital-to-analog conversion module 7 for relevant processing;
firstly, carrying out spectrum analysis on an original time domain signal output by a chip quartz crystal oscillator array 5 through a fast Fourier transform algorithm by a signal demodulation analysis algorithm module compiled based on Labview software, and demodulating a frequency signal responded by a miniature quartz crystal oscillator; then, carrying out extreme value taking algorithm, and analyzing the corresponding relation between the frequency domain signal amplitude and the laser modulation frequency change; finally, obtaining a crystal oscillator frequency response curve with a certain bandwidth near the eigenfrequency;
[06] and the gas concentration information can be inverted according to the Lambert-Beer law satisfied by the cavity enhanced absorption spectrum and a correction curve between the amplitude of the resonance curve and the gas concentration.
Specific example 1: use of an LED light source with a central wavelength in the 440nm band for NO 2 Taking gas concentration measurement as an example, first, N is taken 2 Or zero air is background air, and a resonance response curve under the background condition of the sample pool of the ring-down cavity is recorded in a certain frequency range; the sample cell is then evacuated and then filled with different NO 2 A standard gas sample at concentration and its resonance response curve measured, as shown in fig. 3; finally, with different NO 2 And (3) dividing the signal amplitude and the background amplitude at the optimal central modulation frequency of the concentration sample, taking the negative logarithm to obtain the absorbance of the corresponding sample, and establishing an experimental system correction curve by using the absorbance and the known sample concentration, as shown in fig. 4. In practical application, firstly, the method comprises the following stepsThe above process measures the absorbance of the sample gas with unknown concentration, and substitutes the absorbance into the calibration curve to obtain the corresponding concentration information.
Specific example 2: selection of modulatable LED light sources with center wavelength near 760nm for O 2 Measurement of gas concentration.
Specific example 3: selecting a modulatable LED light source with a center wavelength near 1653nm for CH 4 Measurement of gas concentration.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best understand the invention for and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims (6)
1. A cavity enhanced spectrum gas detection device based on a micro quartz crystal array detector is characterized by comprising a light source (1), a collimating lens (2), a sample cell (3), a focusing lens (4), a micro quartz crystal array (5), a conversion circuit (6), a digital-to-analog conversion module (7), a computer control unit (8) and a light source drive control module (9);
the output end of the computer control unit (8) is connected with the input end of a light source driving control module (9), the output end of the light source driving control module (9) is connected with a light source (1), emergent light of the light source passes through a collimating lens (2) and penetrates through a sample cell (3), a focusing lens (4) is arranged behind the sample cell (3), a micro quartz crystal oscillator array (5) is arranged behind the focusing lens (4), the micro quartz crystal oscillator array (5) is connected with a conversion circuit (6), the output end of the conversion circuit (6) is connected with a digital-to-analog conversion module (7), and the digital-to-analog conversion module (7) is connected with the computer control unit (8);
the light source (1) is a modulatable LED light source; the sample pool (3) is a ring-down cavity with a high-reflectivity cavity mirror;
the micro quartz crystal oscillator array (5) is formed by integrating a plurality of micro quartz crystal oscillators with the same model;
each micro quartz crystal oscillator in the micro quartz crystal oscillator array is 3.2 × 1.3 × 0.8mm in size, and the intrinsic frequencies are all 32.763kHz;
the micro quartz crystal oscillator is processed by a micro quartz tuning fork through a micro nano technology and is sealed in a vacuum shell made of quartz; the size of the miniature quartz tuning fork is selected to be 1097 × 253um.
2. The gas detection device based on the cavity enhanced spectrum of the miniature quartz crystal oscillator array detector as recited in claim 1, wherein the computer control unit (8) comprises an LED light source modulation algorithm and a signal demodulation and analysis algorithm module written by Labview software.
3. A method for detecting a cavity enhanced spectroscopy gas detection device based on a miniature quartz crystal oscillator array detector as set forth in claim 2, which comprises the following steps:
[01] an LED light source modulation digital signal output module compiled by Labview software in a computer control unit (8) outputs a modulation signal or a pulse driving voltage signal with specific frequency, the modulation signal or the pulse driving voltage signal is converted into an analog signal through a digital-to-analog conversion module and then is input into a light source (1) through a light source driving control module (9), so that the modulation luminescence of the light source (1) is realized;
[02] modulated light emitted by the light source (1) is collimated by the collimating lens (2), passes through the sample cell (3), is focused by the focusing lens (4), is incident to the micro quartz crystal oscillator array (5) and irradiates the surface of the internal micro quartz tuning fork through the quartz glass shell on the surface of the micro quartz crystal oscillator array;
[03] the micro quartz tuning fork is excited by the modulated light, and piezoelectric current is generated due to the piezoelectric effect and the resonance effect of the micro quartz tuning fork;
[04] piezoelectric current generated by each micro quartz tuning fork in the micro quartz crystal oscillator array (5) is input to the conversion circuit (6) after being superposed, amplified, filtered and converted into a voltage signal;
[05] the voltage signal output by the conversion circuit (6) is input into a signal demodulation analysis algorithm module written by Labview software in a computer control unit (8) through a digital-to-analog conversion module (7) for relevant processing;
[06] and gas concentration information can be inverted according to the Lambert beer law satisfied by the cavity enhanced absorption spectrum and a correction curve between the amplitude of the resonance curve and the gas concentration.
4. The detection method according to claim 3, wherein the step [05] is based on an algorithm step of a signal demodulation analysis algorithm module written by Labview software: firstly, carrying out frequency spectrum analysis on an original time domain signal output by a miniature quartz crystal oscillator array (5) through a fast Fourier transform algorithm, and demodulating a frequency signal responded by the miniature quartz crystal oscillator; then, carrying out an extreme value taking algorithm, and analyzing the corresponding relation between the frequency domain signal amplitude and the change of the laser modulation frequency; and finally, obtaining a crystal oscillator frequency response curve with a certain bandwidth near the eigenfrequency.
5. The detection method according to claim 4, wherein a modulatable LED light source with a center wavelength in the 440nm band is used for NO 2 Gas concentration measurement, or selection of modulatable LED light sources with center wavelengths near 760nm and 1653nm for O respectively 2 And CH 4 Measurement of gas concentration.
6. The method of claim 5Wherein a modulatable LED light source having a center wavelength in the 440nm band is used for NO 2 And (3) measuring the gas concentration: firstly, with N 2 Or zero air is background air, and a resonance response curve under the background condition of the sample pool of the ring-down cavity is recorded in a certain frequency range; the sample cell is then evacuated and refilled with different NO 2 A standard gas sample under the concentration is measured, and a resonance response curve of the standard gas sample is measured; finally, with different NO 2 And (3) dividing the signal amplitude and the background amplitude at the optimal central modulation frequency of the concentration sample, taking the negative logarithm to obtain the absorbance of the corresponding sample, establishing an experimental system correction curve by using the absorbance and the known sample concentration, measuring the absorbance of the sample gas with unknown concentration through the process, and substituting the absorbance into the correction curve to obtain the corresponding concentration information.
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| CN106596417A (en) * | 2016-12-16 | 2017-04-26 | 苏州亿科斯通电气有限公司 | Large-shaking-arm-spacing tuning-fork type quartz crystal oscillator and quartz enhanced photoacoustic spectrophone |
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