CN109490215A - Utilize the system and method for photocaustic spectroscopy detection methyl bromide gas concentration - Google Patents
Utilize the system and method for photocaustic spectroscopy detection methyl bromide gas concentration Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- 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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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- 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
Abstract
A kind of method and system using photocaustic spectroscopy detection methyl bromide gas concentration proposed by the present invention, including antimonide laser light source, chopper, photoacoustic cell, microphone and signal processing unit；Wherein antimonide laser light source connects chopper, is arranged in photoacoustic cell side；The bottom of photoacoustic cell is arranged in microphone, and laser light source is emitted to chopper, cuts light by chopper, forms modulation light；Antimonide laser emits light and forms the modulated spectrum in narrowband, is irradiated into photoacoustic cell.The present invention has high sensitivity, high stability, the shielding strong point that interference is good and device volume is small.Photocaustic spectroscopy surveys the principle of bromomethane without adding any chemical substance, and the invention method once dispatch from the factory after calibration calibration, and optical texture is stable, the shortcomings that without doing secondary or multiple calibration, also avoiding electrical conductivity method.
Description
Technical field
The invention belongs to trace gas detection technical fields, and in particular to a kind of to detect Bromide first using photocaustic spectroscopy
The system and method for alkane gas concentration is suitable for such as remaining detection of inspection and quarantine fumigating gas.
Background technique
Bromomethane, molecular formula CH3Br, relative density 1.730 (0/4 DEG C) are also known as bromomethane, a bromomethane or methyl bromide,
It is a kind of gas of colorless and odorless.It has strong fumigation action, and energy is efficient, kills to wide spectrum various harmful organisms.Bromine first
Alkane is usually used in the stifling of the cargo that need to be stored and perishable, is also sometimes used as the disinfectant of building, ship and aircraft.By
In bromomethane colorless and odorless, in order to guarantee the safety of user, about 2% dacryagogue is usually added in this fumigant, uses
Make alarm agent.
But remaining methyl bromide gas has certain toxic action, exposure limit 1mg/m to human body3, acute poisoning feelings
Having under condition slightly has headache, dizziness, nausea, a general weakness, drowsiness, tremble；Occur excited, delirium, mutual aid mistake compared with severe one
It adjusts, muscle spasmus, and can be with polyneuritis and liver, renal damage；When serious poisoning, because brain edema has a convulsion, mania, dusk
Fan；Or there is cyanosis because of pulmonary edema or circulatory failure.It can seriously be damaged because of pulmonary edema or nervous system or circulatory failure due to causes
It is dead.Slow poisoning then often has headache, malaise, drowsiness, failure of memory etc..It also can be with peripheral neuritis or plant mind
Through unbalance of system symptom.Therefore, we will strictly monitor remaining, micro methyl bromide gas concentration, to ensure personal safety.
Meanwhile bromomethane is also a kind of potent greenhouse gases, serious greenhouse effects, Ren Menxu caused by environment
Micro bromomethane is monitored, be prevented the pollution of the environment.
For the detection of micro methyl bromide gas, three kinds of detection methods of China's standard main definitions: gas chromatography, heat
Inducing defecation by enema and suppository and infrared detection method.
Chromatographic basic principle above-mentioned is to make to be analyzed in sample gas injection chromatographic column.Gas sample containing bromomethane by
Under inert carrier gas carries, slowly by reaching detector after chromatographic column, the temperature of control chromatographic column is needed, therebetween in order to which gas sample is logical
Classes of compounds is precipitated time difference and achievees the purpose that separate it when crossing chromatographic column.Then, the change that will be obtained by detector
It closes after the parameters such as time, the area of map and the compound known concentration spectral contrast is precipitated in object and obtains its concentration value.The method is
The domestic common method of experimental determination bromomethane, its advantage is that high sensitivity, anti-interference ability are good.The disadvantage is that live cannot examine
Survey, analysis time is long, bulky, need to rely on and be continuously passed through carrier gas.
Thermal conductivity method above-mentioned is the characteristic for having different thermal conductivities based on gas with various, is detected according to the variation of thermal conductivity
Gas concentration.Thermal conductivity method core is thermal conductivity sensor, has been internally integrated a resistive heater in thermal conductivity sensor.Work as bromine
When methane gas flows through resistance wire, because methyl bromide gas has certain thermal conductivity, a degree of heat can be taken away, electricity is caused
Resistance silk temperature changes.The heat that the methyl bromide gas of various concentration is taken away can be different, will cause wire temperature
Different change, by detection resistance silk temperature variations, to obtain the corresponding concentration value of methyl bromide gas.This detection
The advantages of method is high sensitivity；The disadvantage is that poor anti jamming capability, sensor service life is short, needs frequent calibrating instrument.
Infrared Detection Method above-mentioned is dense in the light absorption progress of mid infrared region (6.82~9 μm) using methyl bromide gas
Degree measurement, when a branch of 6.82~9 μm constant of infrared light is by medium containing methyl bromide gas, the energy of light is by bromine first
Alkane gas absorbs, and luminous flux is attenuated, measures the light energy attenuated, can find out the concentration of methyl bromide gas.The method application
It is more universal, but led when measurement since mid infrared region is there is also the absorption spectra of other gases, such as moisture, carbon dioxide etc.
Cause bromomethane detection accuracy and lower limit will receive interference, can not detect the dense of micro methyl bromide gas very well in this way
Degree.
In view of above-mentioned prior art, it is necessary to be explored more preferably to the detection side of methyl bromide gas residual concentration
Method.
Summary of the invention
1, the purpose of the present invention
The present invention provides a kind of method of photocaustic spectroscopy detection methyl bromide gas residual concentration, just solves bromomethane gas
The test problems of bulk concentration.
2, the technical solution adopted in the present invention
The invention proposes it is a kind of using photocaustic spectroscopy detection methyl bromide gas concentration method, chopper, photoacoustic cell,
Microphone and peripheral circuit, wherein light source connects chopper；It is configured at photoacoustic cell side；Microphone is embedded in the bottom of photoacoustic cell
Portion；Data acquisition circuit is sent into after amplifying electric signal by the lock-in amplifier in peripheral circuit again, which is characterized in that uses antimony
Object laser light source and the quantitative analysis detection for completing bromomethane residual concentration according to the following steps:
Step 1, when light beam is with voice modulation, air pressure just forms sound wave by modulation at the same frequency, for work
The amplitude A of photoacoustic signal under low frequency non-resonant behavior0(w)
It indicates are as follows:
WhereinFor the absorption coefficient of gas, Pa is the partial pressure of gas,For the specific heat ratio of gas,
For the modulating frequency of light,It is motivated the service life to disappear, I is beam intensity, and wherein r is the radial distance of photon；W is spot radius, V
For the volume of photoacoustic cell, i is imaginary unit；
Step 2, for photoacoustic cell, using disresonance cylindrical structure, in the case where gas weak absorbing, it is believed that light
Strong I is evenly distributed in photoacoustic cell, i.e. I (r, w)=I (w)；The power that light beam is arranged again is W, then I=Wl/V, and wherein l is light
The length in sound pond, V are volume；To in formula (1) light intensity carry out space integral after it follows that
The cross section for reducing photoacoustic cell cavity it can be seen from formula (2) formula help to obtain higher photoacoustic signal amplitude；
Step 3, using the micro- microphone of silicon for detecting acoustic pressure using silicon thin film, on chip integrate an analog-to-digital conversion
Device forms the microphone with numeral output；By the acoustic-electric conversion coefficient S of the micro- microphone of this siliconm(w) it substitutes into formula (2)
Obtain the amplitude A of photoacoustic signalm(w):
As can be seen that the lower photoacoustic signal amplitude of modulating frequency of light beam is bigger in formula (3), since tested concentration C is gas
The intrinsic standoff ratio of body, C=Pa/P0, this formula substitution formula (3) can be calculated to finally tested gas concentration.
Further, for 3.5 micron waveband of antimonide laser light source, realize multiple quantum well laser 80 degree with
Lower continuous work, optical power reach 1W.
Further, photoacoustic cell internal diameter 15mm, length 50mm.
Further, light beam is with voice modulation range in tens hertz to several kilohertz ranges.
The invention proposes it is a kind of using photocaustic spectroscopy detection methyl bromide gas concentration system, chopper, photoacoustic cell,
Microphone and peripheral circuit, wherein light source connects chopper；It is configured at photoacoustic cell side；Microphone is embedded in the bottom of photoacoustic cell
Portion；Data acquisition circuit is sent into after amplifying electric signal by the lock-in amplifier in peripheral circuit again, which is characterized in that uses antimony
Object laser light source simultaneously uses the quantitative analysis detection that bromomethane residual concentration is completed with lower module:
The amplitude module of photoacoustic signal:
When light beam is with voice modulation, air pressure just forms sound wave by modulation at the same frequency, for working in low frequency
The amplitude A of photoacoustic signal under non-resonant behavior0(w)
It indicates are as follows:
WhereinFor the absorption coefficient of gas, Pa is the partial pressure of gas,For the specific heat ratio of gas,
For the modulating frequency of light,It is motivated the service life to disappear, I is beam intensity, and wherein r is the radial distance of photon；W is spot radius, V
For the volume of photoacoustic cell (3), i is imaginary unit；
Space integral module:
For photoacoustic cell (3), using disresonance cylindrical structure, in the case where gas weak absorbing, it is believed that light intensity I
It is evenly distributed in photoacoustic cell (3), i.e. I (r, w)=I (w)；The power that light beam is arranged again is W, then I=Wl/V, and wherein l is light
The length in sound pond (3), V are volume；To in formula (1) light intensity carry out space integral after it follows that
The cross section for reducing photoacoustic cell (3) cavity it can be seen from formula (2) formula help to obtain higher photoacoustic signal vibration
Width；
The micro- microphone acoustic-electric conversion module of silicon:
Using the micro- microphone of silicon for detecting acoustic pressure using silicon thin film, an analog-digital converter is integrated on chip, is formed
Microphone with numeral output；By the acoustic-electric conversion coefficient S of the micro- microphone of this siliconm(w) substituting into formula (2) can be obtained optoacoustic
The amplitude A of signalm(w):
As can be seen that the lower photoacoustic signal amplitude of modulating frequency of light beam is bigger in formula (3), since tested concentration C is gas
The intrinsic standoff ratio of body, C=Pa/P0, this formula substitution formula (3) can be calculated to finally tested gas concentration.
Further, for 3.5 micron waveband of antimonide laser light source, realize multiple quantum well laser 80 degree with
Lower continuous work, optical power reach 1W.
Further, photoacoustic cell internal diameter 15mm, length 50mm.
Further, light beam is with voice modulation range in tens hertz to several kilohertz ranges.
3, beneficial effect of the present invention
(1) methyl bromide gas of the present invention has relatively high intensity and density, it can be achieved that bromomethane is dense at 3.5 microns
The accurate detection of degree, it is dense for methyl bromide gas that 3.5 micron wavebands of transmitting of antimonide laser light source 1 can effectively shield steam
The interference signal that degree detection generates.
(2) present invention has high sensitivity, high stability, the shielding strong point that interference is good and device volume is small.Optoacoustic light
Spectrometry surveys the principle of bromomethane without adding any chemical substance, and the invention method is once dispatched from the factory after demarcating calibration, optics knot
Structure is stablized, the shortcomings that without doing secondary or multiple calibration, also avoiding electrical conductivity method.
(3) present invention is compared with non-dispersion infrared analytic approach, and optical signal is effectively converted into acoustical signal by it, and passes through precision
Final gas concentration is calculated to the detection of voice signal in microphone.Due to optoacoustic spectroscopy special optical structure with
And the specific calculations process in signal acquisition, signal processing, so that the method is effectively collected faint photoacoustic signal, and have
Effect rejects the interference of background signal, is highly suitable for trace gas concentration detection field, and noiseless in complex environment
Detection
Detailed description of the invention
Fig. 1 is the structural schematic diagram of testing principle used in the present invention.
Fig. 2 is absorption spectrogram of the methyl bromide gas at 2~5 micron wavebands in range.
Fig. 3 is absorption spectrogram of the gaseous state steam at 2~5 micron wavebands in range.
Specific embodiment
A kind of device using photocaustic spectroscopy detection methyl bromide gas residual concentration proposed by the present invention, including antimonide
Laser light source, chopper, photoacoustic cell, microphone and signal processing unit；Wherein antimonide laser light source connects chopper,
It is arranged in photoacoustic cell side；The bottom of photoacoustic cell is arranged in microphone, and laser light source is emitted to chopper, is cut by chopper
Light forms modulation light；Antimonide laser emits light and forms the modulated spectrum in narrowband, is irradiated into photoacoustic cell.
It uses antimonide laser as light source 1, launches 3.5 microns of monochromatic light, by mechanical chopper 2, obtain strong
It spends modulated monochromatic light exposure to enter in the photoacoustic cell 3 of sealing, be excited after gas molecules sorb electromagnetic radiation in photoacoustic cell 3, jumped
Adjourn the excitation state of higher level.The electronic state of molecule, vibration and rotary state are all quantized.In general, gas molecule
Ground state can be returned to by transmitting fluorescence or vibration, vibration causes the raising of gas temperature, and transmits energy, referred to as without spoke
Penetrate relaxation phenomena.The premise that this Non-radiative relaxation processes generated by vibration occur is that the relaxation time compares lifetime of excited state
It is much faster.Attenuation is 10 in the usual time of visible light-7s.To generate radiationless decay, the relationship in relaxation time and pressure
Very close (die-away time t and pressure are inversely proportional) and great changes (10 can be generated under atmospheric pressure-3–10-8s)。
Radiation source is modulated to the acoustic frequency for making Temperature cycling variation, leads to the cyclically-varying of pressure, this variation
Voice signal can be generated, in gas detection, this voice signal is detected by the highly sensitive micro- microphone 4 of silicon.
It is namely based on this optoacoustic effect using photoacoustic spectrum sensor detection bromomethane residual concentration, this optoacoustic spectroscopy sensing
Device is as shown in Figure 1, comprising: light source 1, chopper 2, photoacoustic cell 3, microphone 4 and peripheral circuit, wherein light source 1 connects chopper
2；It is configured at 3 side of photoacoustic cell；Microphone 4 is embedded in the bottom of photoacoustic cell 3.Amplified again by the lock-in amplifier in peripheral circuit
It is sent into data acquisition circuit after electric signal, is calculated finally by formula (1) formula (2) formula (3) formula and completes bromomethane residual concentration
The detection of bromomethane concentration is completed in quantitative analysis with this.When light beam is with audio frequency (tens hertz are arrived several kHz) modulation, gas
Pressure just forms sound wave by modulation at the same frequency, for the amplitude A for the photoacoustic signal under low frequency non-resonant behavior that works0
(w)
It indicates are as follows:
WhereinFor the absorption coefficient of gas, Pa is the partial pressure of gas,For the specific heat ratio of gas,
For the modulating frequency of light,It is motivated the service life to disappear, I is beam intensity, and wherein r is the radial distance of photon；W is spot radius, V
For the volume of photoacoustic cell 3, i is imaginary unit.For specific gas, the amplitude of photoacoustic signal and the light intensity of excitation light and Spectral Properties
The factors such as the modulating frequency of property, 3 structure of photoacoustic cell and light are related.
For antimonide laser light source 1, we select 3.5 micron wavebands, realize multiple quantum well laser 80 degree with
Lower continuous work, optical power reach 1W.From the point of view of absorbing spectrogram such as Fig. 2 bromomethane, the absorption spectrogram of methyl bromide gas is at 3.5 microns
Locate that there is relatively high intensity and density the accurate detection, it can be achieved that bromomethane concentration.As Fig. 3 gaseous state steam absorption spectra figure comes
It sees, steam absorption line intensity at 3.5 microns is very low, so we select antimonide laser light source 1 to emit 3.5 micron waves
Section can effectively shield the interference signal that steam generates methyl bromide gas Concentration Testing.
For photoacoustic cell 3, the present invention uses disresonance cylindrical structure, in the case where gas weak absorbing, it is believed that
Light intensity I is evenly distributed in photoacoustic cell 3, i.e. I (r, w)=I (w).The power that light beam is arranged again is W, then I=Wl/V, and wherein l is
The length of photoacoustic cell 3, V are volume.To in formula (1) light intensity carry out space integral after it follows that
The cross section for reducing 3 cavity of photoacoustic cell it can be seen from formula (2) formula help to obtain higher photoacoustic signal vibration
Width.But since the size of photoacoustic cell 3 also depends on the installation site of microphone 4, with greater need in view of light beam coupling effect with
And the collimation adjustment difficulty of light beam.Transverse heat transfer effect can be also set to decline and cause to disappear sharp if the volume of photoacoustic cell 3 is too small
Encourage the service lifeIncrease, as a result reduces photoacoustic signal.The present invention takes photoacoustic cell 3 internal diameter 15mm, length 50mm in the present system,
To reduce because of coherent noise caused by window absorption.
For microphone 4, the present invention selects the micro- microphone of silicon.Since traditional capacitor microphone does not have any power supply to press down
The mains fluctuations of ability processed, very little can result in intermittent noise.And in terms of Machine Design, conventional condenser microphony
Device can not only detect voice signal, moreover it is possible to and it detects mechanical oscillation, and vibration is finally converted to low frequency sound signals, this
Sample, when such microphone is placed in vibration environment, vibration will become the dominant noise source of audio system.The silicon that the present invention uses
Micro- microphone is to detect acoustic pressure using silicon thin film, it can integrate an analog-digital converter on chip, and being formed has number
The microphone of output.Compared with traditional capacitor microphone, the micro- microphone sound pressure level of silicon is high, and chip interior generally have it is pre-
Amplifying circuit, therefore sensitivity is very high；Its Hz-KHz is wide, generally in 100~10KHZ；And distortion is small, total harmonic distortion <
1% (in 1KHZ, 500mV p-p)；Vibration sensing degree is less than < 1dB.In addition to this, there are also excellent anti-electromagnetism for the micro- microphone of silicon
Interference characteristic, and moisture resistance wet environment and temperature shock.We are by the acoustic-electric conversion coefficient S of the micro- microphone of this siliconm(w) formula is substituted into
(2) amplitude A of photoacoustic signal can be obtained inm(w):
As can be seen that the lower photoacoustic signal amplitude of modulating frequency of light beam is bigger in formula (3), but for general microphony
Device, when w < 100Hz, acousto-electric-index Sm(w) it will decreased significantly, when in addition modulating frequency is too low, the 1/f of electronic amplification system
Noise also obviously increases.Due to being tested the intrinsic standoff ratio that concentration C is gas, C=Pa/P0, this formula substitution formula (3) can be calculated
Finally tested gas concentration.
The working principle of the invention
A method of methyl bromide gas residual concentration is detected using photocaustic spectroscopy:
1, light source uses antimonide laser, cuts light by chopper and optical filter filters, obtain the modulated list of intensity
Coloured light；
2, on micro methyl bromide gas of the modulated spectral illumination in the photoacoustic cell of sealing, methyl bromide gas molecule absorption
It is excited after electromagnetic radiation, transits to the excitation state of higher level, and ground state is returned to by stretching vibration and deformation vibration；
3, vibration causes the raising of gas temperature, and discharges thermal energy, and the thermal energy of release makes bromomethane molecule by the modulation of light
Frequency generates periodic heat, to generate periodic pressure fluctuation；
4, pressure oscillation is less than the < micro- microphone detection of the silicon of 1dB using vibration sensing degree, and passes through conversion circuit amplification letter
Photoacoustic signal number is obtained, photoacoustic signal is converted into electric signal by peripheral circuit, then is amplified by the lock-in amplifier in peripheral circuit
It is sent into data acquisition circuit after electric signal, finally calculates and completes bromomethane residual concentration.
Antimonide laser light source fundamental vibration area infrared generally in 2-5 micron waveband is in, comprising very
The characteristic spectral line of more gas molecules also includes very important atmospheric window.The forbidden bandwidth of antimonide determines that antimonide swashs
The wave-length coverage of light device can cover this wave band, therefore antimonide laser also just becomes an important light source of Trace gas detection
Selection.We select 3.5 micron wavebands in the present invention, realize multiple quantum well laser in 80 degree or less continuous works, light
Power reaches 1W, the Concentration Testing applied to methyl bromide gas.It is emphasized simultaneously in the Absorption Line of 3.5 micron waveband region steam non-
It is often low, it can effectively shield the interference signal that steam generates methyl bromide gas Concentration Testing.
Claims (8)
1. a kind of method using photocaustic spectroscopy detection methyl bromide gas concentration, chopper (2), photoacoustic cell (3), microphone
(4) and peripheral circuit, wherein light source (1) connection chopper (2)；It is configured at photoacoustic cell (3) side；Microphone (4) is embedded in light
The bottom in sound pond (3)；It is sent into data acquisition circuit after amplifying electric signal by the lock-in amplifier in peripheral circuit again, feature exists
In completing the quantitative analysis detection of bromomethane residual concentration using antimonide laser light source (1) and according to the following steps:
Step 1, when light beam is with voice modulation, air pressure just forms sound wave by modulation at the same frequency, for work low
The amplitude of photoacoustic signal under frequency non-resonant behavior
It indicates are as follows:
WhereinFor the absorption coefficient of gas, Pa is the partial pressure of gas,For the specific heat ratio of gas,/ Cv,For light
Modulating frequency,It is motivated the service life to disappear, I is beam intensity, and wherein r is the radial distance of photon；W is spot radius, and V is light
The volume in sound pond (3), i are imaginary unit；
Step 2, for photoacoustic cell (3), using disresonance cylindrical structure, in the case where gas weak absorbing, it is believed that light
Strong I is evenly distributed in photoacoustic cell (3), i.e. I (r, w)=I (w)；The power that light beam is arranged again is W, then I=Wl/V, and wherein l is
The length of photoacoustic cell (3), V are volume；To in formula (1) light intensity carry out space integral after it follows that
The cross section for reducing photoacoustic cell (3) cavity it can be seen from formula (2) formula help to obtain higher photoacoustic signal amplitude；
Step 3, using the micro- microphone of silicon for detecting acoustic pressure using silicon thin film, on chip integrate an analog-digital converter, shape
At the microphone with numeral output；By the acoustic-electric conversion coefficient of the micro- microphone of this siliconSubstitution formula can be obtained in (2)
The amplitude of photoacoustic signal
It is gas due to being tested concentration C as can be seen that the lower photoacoustic signal amplitude of modulating frequency of light beam is bigger in formula (3)
Intrinsic standoff ratio, C=Pa/P0, this formula substitution formula (3) can be calculated to finally tested gas concentration.
2. the method according to claim 1 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: right
In (1) 3.5 micron waveband of antimonide laser light source, multiple quantum well laser is realized in 80 degree or less continuous works, light function
Rate reaches 1W.
3. the method according to claim 1 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: light
Sound pond (3) internal diameter 15mm, length 50mm.
4. the method according to claim 1 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: light
Beam is with voice modulation range in tens hertz to several kilohertz ranges.
5. a kind of system using photocaustic spectroscopy detection methyl bromide gas concentration, chopper (2), photoacoustic cell (3), microphone
(4) and peripheral circuit, wherein light source (1) connection chopper (2)；It is configured at photoacoustic cell (3) side；Microphone (4) is embedded in light
The bottom in sound pond (3)；It is sent into data acquisition circuit after amplifying electric signal by the lock-in amplifier in peripheral circuit again, feature exists
In, use antimonide laser light source (1) and use with lower module complete bromomethane residual concentration quantitative analysis detection:
The amplitude module of photoacoustic signal:
When light beam is with voice modulation, air pressure just forms sound wave by modulation at the same frequency, non-total in low frequency for working
The amplitude of photoacoustic signal under vibration state
It indicates are as follows:
WhereinFor the absorption coefficient of gas, Pa is the partial pressure of gas,For the specific heat ratio of gas,/ Cv,For light
Modulating frequency,It is motivated the service life to disappear, I is beam intensity, and wherein r is the radial distance of photon；W is spot radius, and V is light
The volume in sound pond (3), i are imaginary unit；
Space integral module:
For photoacoustic cell (3), using disresonance cylindrical structure, in the case where gas weak absorbing, it is believed that light intensity I is in light
It is evenly distributed in sound pond (3), i.e. I (r, w)=I (w)；The power that light beam is arranged again is W, then I=Wl/V, and wherein l is photoacoustic cell
(3) length, V are volume；To in formula (1) light intensity carry out space integral after it follows that
The cross section for reducing photoacoustic cell (3) cavity it can be seen from formula (2) formula help to obtain higher photoacoustic signal amplitude；
The micro- microphone acoustic-electric conversion module of silicon:
Using the micro- microphone of silicon for detecting acoustic pressure using silicon thin film, an analog-digital converter is integrated on chip, formation has
The microphone of numeral output；By the acoustic-electric conversion coefficient of the micro- microphone of this siliconOptoacoustic letter can be obtained in substitution formula (2)
Number amplitude
It is gas due to being tested concentration C as can be seen that the lower photoacoustic signal amplitude of modulating frequency of light beam is bigger in formula (3)
Intrinsic standoff ratio, C=Pa/P0, this formula substitution formula (3) can be calculated to finally tested gas concentration.
6. the system according to claim 5 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: right
In (1) 3.5 micron waveband of antimonide laser light source, multiple quantum well laser is realized in 80 degree or less continuous works, light function
Rate reaches 1W.
7. the system according to claim 1 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: light
Sound pond (3) internal diameter 15mm, length 50mm.
8. the system according to claim 1 using photocaustic spectroscopy detection methyl bromide gas concentration, it is characterised in that: light
Beam is with voice modulation range in tens hertz to several kilohertz ranges.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110208195A (en) * | 2019-06-25 | 2019-09-06 | 南京无书化工有限公司 | A kind of optoacoustic spectroscopy single channel locking phase amplifying device and method for gas detection |
| CN112504967A (en) * | 2020-12-09 | 2021-03-16 | 之江实验室 | Silicon tuning fork enhanced photoacoustic spectroscopy gas detection system |
| CN117665950A (en) * | 2024-01-31 | 2024-03-08 | 四川阳光上元科技有限公司 | Gas enrichment area detection method based on quantitative particles |
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