CN120275298B - A photoacoustic spectroscopy gas analysis method and system based on multidimensional modulation - Google Patents
A photoacoustic spectroscopy gas analysis method and system based on multidimensional modulationInfo
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- CN120275298B CN120275298B CN202510412647.3A CN202510412647A CN120275298B CN 120275298 B CN120275298 B CN 120275298B CN 202510412647 A CN202510412647 A CN 202510412647A CN 120275298 B CN120275298 B CN 120275298B
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Abstract
The invention discloses a modulation method for photoacoustic spectrum gas analysis based on multidimensional modulation, which comprises the following steps of S100, initializing various parameters of a light source, S200, inputting various action parameters into a preset modulation algorithm, outputting the modulation parameters for modulating the light source by the modulation algorithm, S300, converting the modulation parameters output by the modulation algorithm into modulation signals, and controlling and simultaneously adjusting various parameters of an optical signal sent by the light source based on the modulation signals. Therefore, the modulation algorithm obtains all output parameters as modulation parameters according to the input action parameters, and the adjustment of the light source is realized based on the modulation parameters. Therefore, after the light source is initialized and regulated, various parameters in the light signal of the light source can be regulated continuously based on the modulation signal, so that the simultaneous regulation of various parameters of the light source can be realized by accurately controlling the frequency, the wavelength and the amplitude of the light source, and the sensitivity and the selectivity of the regulation can be improved.
Description
Technical Field
The invention relates to the technical field of trace detection, in particular to a photoacoustic spectrum gas analysis method and system based on multidimensional modulation.
Background
Photoacoustic spectroscopy (PAS, photo Acoustic Spectroscopy) detection techniques (e.g., laser photoacoustic spectroscopy detection techniques) are a type of spectroscopic detection method based on the photoacoustic effect. When the substance absorbs the periodically modulated light energy, the light energy is converted to heat energy in the form of heat, resulting in a periodic change in the temperature of the substance. Such temperature changes cause periodic changes in the volume of the substance due to thermal expansion and contraction, thereby generating pressure waves, i.e., acoustic signals. This process is the photoacoustic effect. The gas can be detected very accurately and selectively by photoacoustic spectroscopy (PAS). The basic measurement principle is that if a gas sample in a measurement cell is irradiated with a pulsed light source, the gas molecules will absorb light and the gas sample will heat up. In the case of a constant cell volume, this will produce sound waves with a frequency matching the modulation frequency of the light source. These sound waves, i.e. photoacoustic signals, can be detected with a sound sensor. The signal amplitude of the photoacoustic signal is related to the absorption intensity and thus provides information about the concentration of gas in the measurement cell. The high-performance photoacoustic spectroscopy technology is favored by people because of the advantages of high sensitivity, quick response, high selectivity, non-contact real-time continuous measurement and the like.
In the existing photoacoustic spectrum detection gas analysis, after the photoacoustic cell starts to generate the photoacoustic effect, in order to obtain a better detection result, a certain parameter is usually adjusted by adopting modes such as amplitude adjustment and wavelength adjustment, for example, the amplitude or the frequency of a light source is adjusted according to different photoacoustic effect conditions and characteristic gases.
Therefore, the adjustment mode in the prior art needs to select specific parameters and adjust each parameter one by one, and has low efficiency and poor sensitivity, and the adjustment mode is based on the specific parameters, so that the selectivity and the accuracy in the adjustment process are insufficient.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a photoacoustic spectrum gas analysis method and a photoacoustic spectrum gas analysis system based on multidimensional modulation, which can automatically carry out multidimensional modulation on an optical signal after initializing and adjusting the optical signal of a light source, so that the detection efficiency, sensitivity, selectivity and accuracy are improved.
The aim of the invention is realized by the following technical scheme:
The application discloses a modulation method for photoacoustic spectrum gas analysis based on multidimensional modulation, which comprises the following steps of S100, initializing various parameters of a light source, introducing characteristic gas to enable light emitted by the light source and the characteristic gas to interact in a photoacoustic cell, S200, obtaining acoustic wave signals currently generated by the photoacoustic cell, calculating various action parameters according to the acoustic wave signals, inputting the various action parameters into a preset modulation algorithm, outputting the modulation parameters for modulating the light source by the modulation algorithm, S300, converting the modulation parameters output by the modulation algorithm into modulation signals, and controlling and simultaneously adjusting various parameters of the optical signals sent by the light source based on the modulation signals.
The light source 1 has the advantages that the modulation algorithm obtains various output parameters as modulation parameters according to the input action parameters, wherein the parameters comprise wavelength, frequency and amplitude, and therefore the light source 1 is adjusted based on the modulation parameters. Therefore, after the light source 1 is initialized and regulated, various parameters in the light signal of the light source 1 can be regulated based on the modulation signal to simultaneously control the frequency, the wavelength and the amplitude of the light source 1, so that the efficiency is improved, and the modulation parameters are obtained based on interaction parameters acquired in real time in the photoacoustic cell, so that the modulation parameters are most consistent with the interaction conditions in the current photoacoustic cell, the method not only can realize simultaneous regulation of various parameters of the light source 1, but also can improve the sensitivity and the accuracy of regulation.
Preferably, the action parameters comprise the concentration of characteristic gases, and the modulation algorithm comprises amplitude modulation, frequency modulation and wavelength modulation;
in the process of the amplitude modulation by the modulation algorithm, when the input numerical value of the concentration is lower than a preset value, the low concentration is judged, and the amplitude is modulated based on the following relation:
Wherein: the method comprises the steps of representing the proportionality coefficient of the concentration and amplitude modulation of the characteristic gas, S representing the absorption intensity of the photoacoustic signal, A representing the amplitude of the optical signal, C representing the concentration of the characteristic gas;
when the inputted concentration value is higher than the preset value, it is determined as a high concentration, and the amplitude is modulated based on the following relation:
Wherein: 、 The method comprises the steps of representing the proportionality coefficient of characteristic gas concentration and amplitude modulation, S representing the absorption intensity of a photoacoustic signal, A representing the amplitude of an optical signal, C representing the characteristic gas concentration and extracting photoacoustic effect parameters obtained from a resonant cavity;
in the process of the modulation algorithm for carrying out the wavelength modulation, the relation between the concentration and the wavelength modulation is represented by the following formula:
wherein E represents the light energy absorbed by the gas; Indicating the light absorption coefficient, which is the wavelength Is a function of (2); L represents the optical path length;
in the process of the modulation algorithm for the frequency modulation, the relationship between the concentration and the frequency modulation is represented by the following formula:
Wherein: f represents modulation frequency; the signal strength at resonance is indicated, Representing the resonant frequency; Representing half-width;
When (when) Complete modulation at maximum, and。
Specifically, the S100 includes:
And S120, modulating the wavelength of the light source to be consistent with any absorption wavelength of the characteristic gas, and controlling the light source to emit the light signal with the absorption wavelength and the preset frequency and amplitude so as to finish the initialization of the light source.
Preferably, the method further comprises S210 performed after S200;
S210, acquiring one of the action parameters, namely the absorption intensity of the characteristic gas, and judging that the characteristic gas reaches an absorption peak and locking the wavelength after the absorption intensity reaches a threshold value.
The application discloses a modulation system for photoacoustic spectrometry gas analysis based on multidimensional modulation, which is used for a modulation method for photoacoustic spectrometry gas analysis based on multidimensional modulation, and comprises a controller, a modulator and a modulator, wherein the controller is used for acquiring acoustic signals currently generated by a photoacoustic cell, calculating various action parameters according to the acoustic signals, inputting the various action parameters into a preset modulation algorithm, outputting the modulation parameters for modulating a light source by the modulation algorithm, converting the modulation parameters output by the modulation algorithm into modulation signals, and sending the modulation signals to the modulator, and controlling and simultaneously adjusting the various parameters of an optical signal sent by the light source by the modulator based on the modulation signals.
The modulator comprises an electric signal processing part and an optical signal processing part, wherein the electric signal processing part is used for receiving the modulation signal and generating corresponding modulation parameters according to the modulation signal, and the optical signal processing part is used for receiving the optical signal sent by the light source and adjusting all parameters of the optical signal to be consistent with the modulation parameters.
Preferably, the device further comprises a demodulator, wherein the demodulator is connected to the photoacoustic cell and used for acquiring an acoustic wave signal of the photoacoustic cell, demodulating the acoustic wave signal to obtain the interaction parameter, and sending the interaction parameter to the controller.
Specifically, the demodulator is connected to the photoacoustic cell through a microphone, and an audio acquisition end of the microphone is in contact with a resonant cavity of the photoacoustic cell.
Drawings
Fig. 1 is a flow chart of a photoacoustic optical frequency analysis method based on multi-dimensional modulation according to some embodiments of the present application;
Fig. 2 is a schematic structural diagram of a photoacoustic optical frequency analysis method system based on multi-dimensional modulation according to some embodiments of the present application;
In the figure:
1-light source, 2-modulator, 3-optical fiber, 4-photo-acoustic cell, 5-demodulator, 6-data processor, 7-controller, 8-light hole, 9-air inlet, 10-air outlet and 11-microphone.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by a person skilled in the art without any inventive effort, are intended to be within the scope of the present invention, based on the embodiments of the present invention.
Referring next to fig. 1-2, a modulation system and method of photoacoustic spectroscopy gas analysis based on multi-dimensional modulation is disclosed.
In the related art, an optical signal emitted by a modulated light source is generally initialized based on preset parameters, so that each parameter of the optical signal is matched with a characteristic gas to be detected, for example, a wavelength conforms to a certain absorption wavelength of the characteristic gas. The user further modulates each parameter of the optical signal one by one to enable the optical signal and the characteristic gas to generate better photoacoustic effect, but the efficiency is low due to the one by one modulation parameter, and the interaction condition in the photoacoustic cell also changes in real time in the modulation process, so that the accuracy and the sensitivity of the modulation mode are insufficient.
For this reason, the embodiment of the application discloses a modulation method for photoacoustic spectrum gas analysis based on multidimensional modulation, which comprises the following steps:
s100, initializing various parameters of the light source 1, wherein the light source 1 and the characteristic gas act in the photoacoustic cell 4.
Specifically, the light signal emitted by the light source 1 is transmitted through the optical fiber 3 and can enter the photoacoustic cell from the light through hole 8, and the corresponding characteristic gas can enter the photoacoustic cell 4 from the air inlet hole 9 on the photoacoustic cell 4. The characteristic gas introduced into the photoacoustic cell 4 strongly absorbs the energy of the optical signal and generates the photoacoustic signal, the wavelength of the laser emitted by the initialized light source 1 periodically changes, and the pressure fluctuation in the photoacoustic cell 4 caused by expansion with heat and contraction with cold becomes an acoustic wave, which also periodically changes along with the modulation frequency.
S200, acquiring sound wave signals currently generated in the photoacoustic cell 4, calculating according to the sound wave signals to obtain various action parameters, and then inputting the action parameters into a preset modulation algorithm, wherein the modulation algorithm outputs modulation parameters for modulating the light source 1.
The modulation algorithm is used for expressing mathematical relations between each acting parameter and each parameter of the optical signal, and when the acting parameter is used as input, the output of the modulation algorithm corresponds to each parameter corresponding to the optical signal output by the light source 1. The action parameters include, but are not limited to, the current concentration of the characteristic gas in the photoacoustic cell 4, the signal strength of the photoacoustic effect, the absorption strength, the resonant frequency, and the action parameters are obtained from the acoustic wave signals in the current photoacoustic cell 4, so that the situation within the current photoacoustic cell 4 can be acted upon.
That is, the action parameter is used as an input of the modulation algorithm, and since the modulation algorithm corresponds to an ideal mathematical model between the action parameter and each parameter of the light source 1, each parameter output by the modulation algorithm is each parameter ideal at the current time, and in this embodiment, the parameters are defined as modulation parameters. Therefore, the modulation parameters are matched with the action conditions in the photoacoustic cell 4 in real time, the optical signals of the light source can be modulated based on the feedback action parameters, and the accuracy and the sensitivity of modulation are improved.
Of course, the ideal parameters described herein are not assumed to be close to perfect in a broad physical sense, but rather are corresponding narrow ranges in the present embodiment.
S300, converting the modulation parameters output by the modulation algorithm into modulation signals. In particular, the control of the light source 1 needs to be implemented by means of a device such as the modulator 2, and thus the modulation parameters need to be converted into a signal form for transmission, for example, the modulation parameters are encoded and then transmitted.
And S400, controlling and simultaneously adjusting various parameters of the optical signal sent by the optical source 1 based on the modulation signal so that the modulated optical source 1 accords with the action condition of the current photoacoustic cell 4.
Therefore, the method can simultaneously obtain various parameters of the optical signal based on the output of the modulation function, and further uses the corresponding modulation signal for modulating the optical signal of the light source, so that multiple parameters of the optical signal can be simultaneously regulated, and compared with a single parameter regulation mode, the method has higher efficiency.
It can be understood that in the modulation method based on the photoacoustic spectrum gas analysis of the multidimensional modulation, the modulation algorithm obtains various parameters of output as modulation parameters according to the input action parameters, for example, the parameters comprise wavelength, frequency and amplitude, so that the adjustment of the light source 1 is realized based on the modulation parameters. Therefore, after the light source 1 is initialized and regulated, various parameters in the light signal of the light source 1 can be regulated based on the modulation signal to simultaneously control the frequency, the wavelength and the amplitude of the light source 1, so that the efficiency is improved, and the modulation parameters are obtained based on interaction parameters acquired in real time in the photoacoustic cell 4, so that the modulation parameters are most consistent with the interaction conditions in the current photoacoustic cell 4, the method not only can realize simultaneous regulation of various parameters of the light source 1, but also can improve the sensitivity and the accuracy of regulation.
Next, a modulation method of photoacoustic spectroscopy gas analysis based on multidimensional modulation will be described in detail with reference to fig. 1.
The S100 includes:
S110, setting various parameters of the optical signal according to a preset value.
Illustratively, the initial frequency of the optical signal is set to the resonance frequency of the photoacoustic cell 4, the initial wavelength of the optical signal is set to the intermediate value of the characteristic gas absorption wavelength range, and the amplitude of the optical signal is set to the amplitude corresponding to the lowest absorption rate.
And S120, after the wavelength of the optical signal is modulated to be consistent with any absorption wavelength of the characteristic gas, controlling the light source 1 to emit the optical signal with the absorption wavelength and preset frequency and amplitude so as to finish the initialization of the light source 1.
It can be understood that the above method realizes multi-dimensional modulation (i.e. modulation of multiple parameters) on the light source 1, and needs various action parameters fed back by the photoacoustic cell 4, in this embodiment, when the user performs initialization, the user modulates the wavelength to any absorption wavelength according with the characteristic gas, and then the photoacoustic effect between the characteristic gas and the laser occurs, so that after the photoacoustic effect is ensured to have occurred in the photoacoustic cell 4, the photoacoustic cell 4 can feed back various action parameters.
Of course, the modulation of the wavelength during the initialization process in this embodiment is one possible way and should not be construed as the only way.
In some embodiments, the action parameter comprises a concentration of a characteristic gas.
The exact position of the characteristic gas absorption peak is determined by gradually changing the wavelength of the laser, based on the initialized wavelength parameters, when the wavelength modulation is performed. When the frequency modulation is carried out, the resonance characteristic of the photoacoustic cell is monitored in real time based on the initialized frequency parameters, and the frequency of the light source is dynamically adjusted to keep synchronization. When amplitude modulation is carried out, the amplitude of the light source is dynamically adjusted based on initialized amplitude parameters according to the intensity of the photoacoustic signal and the concentration change of the characteristic gas so as to maintain the optimal signal intensity.
Specifically, the relationship between the characteristic gas concentration and the modulation of the optical signal parameter includes:
Relationship between characteristic gas concentration and amplitude modulation:
When the gas concentration is low, the number of gas molecules is relatively small, the absorbed light energy is limited, and the generated photoacoustic signal is weak. In order to enhance the photoacoustic signal to increase the detection sensitivity, it is necessary to increase the radiant energy of the light source, i.e., to increase the amplitude.
Thus, modulation algorithms include amplitude modulation, frequency modulation, and wavelength modulation.
In the process of amplitude modulation by the modulation algorithm, when the input concentration value is lower than a preset value, the low concentration is judged, and the amplitude is modulated based on the following relation:
Wherein:
S represents the absorption intensity of the photoacoustic signal and is extracted from the action parameters obtained from the resonant cavity;
A is the amplitude of the optical signal;
And C, representing the concentration of the characteristic gas, and extracting the characteristic gas from the action parameters obtained from the resonant cavity. When the concentration of the gas is too high, too many gas molecules absorb a large amount of light energy, which may lead to an absorption saturation phenomenon, so that the photoacoustic signal no longer increases linearly with the concentration, and even signal distortion may occur. At this time, the amplitude is reduced to avoid saturated absorption, and the photoacoustic signal is ensured to be in a linear detection range.
Therefore, when the inputted density value is higher than the preset value, it is determined that the density is high, and the amplitude is modulated based on the following relation:
Wherein:
、 the method is characterized in that the proportionality coefficient of the characteristic gas concentration and amplitude modulation is expressed and is a preset parameter;
s, representing the absorption intensity of the photoacoustic signal, and extracting photoacoustic effect parameters obtained from the resonant cavity;
A is the amplitude of the optical signal;
And C, representing the concentration of the characteristic gas, and extracting photoacoustic effect parameters obtained from the resonant cavity. Since each gas has its specific absorption spectrum, there is an absorption peak at a specific wavelength. In order for the gas molecules to absorb the light energy to the maximum, it is necessary to precisely tune the wavelength of the light source to the absorption peak position of the gas. When the wavelength drift is caused by the change of environmental factors or the characteristics of the light source, the absorption efficiency of the gas to the light can be influenced, and the intensity of the photoacoustic signal can be further influenced.
Therefore, in the course of wavelength modulation by the modulation algorithm, the relationship between the characteristic gas concentration and the wavelength modulation is represented by the following formula:
Wherein:
E, representing the light energy absorbed by the gas, extracting photoacoustic effect parameters obtained from the resonant cavity;
representing the light absorption coefficient, which is the wavelength Is a function of (2);
representing the incident light intensity, and determining according to the light intensity of laser emitted by the current light source;
L is the optical path length, and is determined according to the optical path length of the laser emitted by the current light source.
Since the photoacoustic cell has a specific resonant frequency, the photoacoustic signal is significantly enhanced when the modulation frequency of the light source matches the resonant frequency of the photoacoustic cell. The change in gas concentration affects the thermophysical properties of the gas within the photoacoustic cell, thereby changing the resonant frequency of the photoacoustic cell.
Therefore, in the course of frequency modulation by the modulation algorithm, the relationship between the characteristic gas concentration and the frequency modulation is represented by the following formula:
Wherein:
representing the intensity of a photoacoustic signal, and extracting photoacoustic effect parameters obtained from a resonant cavity;
f, represents modulation frequency;
representing the signal intensity at resonance, extracting photoacoustic effect parameters obtained from the resonant cavity;
Representing the resonant frequency, extracting photoacoustic effect parameters obtained from the resonant cavity;
Representing half-width as preset parameter;
The modulation algorithm modulates the frequency according to the current interaction parameters, records the intensity and the frequency of the photoacoustic signals corresponding to each timestamp, sorts the intensity of the photoacoustic signals corresponding to each timestamp according to the size, acquires the timestamp corresponding to the maximum photoacoustic signal intensity, and then invokes the corresponding frequency for output.
I.e. by adjusting f such that:
To obtain Is a maximum value of (a).
It will be appreciated that the modulator may change parameters according to the action parameters and based on the modulation algorithm described above, for example, adjust based on concentration information, and may adjust the frequency, wavelength, and amplitude of the light source in real time, thereby optimizing the photoacoustic signal strength and signal-to-noise ratio.
Further, in S200, the acoustic wave signal currently generated by the photoacoustic cell 4 is obtained, and the acoustic wave signal can be demodulated to form an acoustic wave signal generated by absorbing the optical signal by the characteristic gas in the photoacoustic cell 4, for example, through conversion, amplification, and other manners, so as to obtain the acoustic wave signal.
Further, the operation parameters are obtained by calculation from the photoacoustic signals, and for example, various operation parameters are obtained by using the relation of sound pressure change in the photoacoustic cell 4 expressed by the active Helmholtz equation.
In some embodiments, the method further comprises S210 performed after S200.
S210, acquiring one of the action parameters, namely the absorption intensity of the characteristic gas, and locking the wavelength after the absorption intensity reaches a threshold value.
In particular, the threshold is that the characteristic gas reaches the absorption peak and, after locking the wavelength, keeps track of any wavelength drift due to environmental changes or ageing of the light source 1. Therefore, when the system detects that the absorption intensity reaches a preset threshold value (namely, the characteristic absorption peak of the characteristic gas), the real-time feedback control loop is used for dynamically locking the wavelength of the light source, so that wavelength deviation caused by environmental temperature fluctuation, gas pressure change or laser thermal drift can be effectively eliminated, and the light signal is ensured to be always positioned at the central position of the gas absorption spectrum line.
It can be understood that the locking wavelength can enable the optical signal and the molecular energy level transition of the target gas to form optimal resonance matching by stabilizing the wavelength of the light source at the characteristic gas absorption peak, so that the energy conversion efficiency of the photoacoustic effect is maximized, the signal-to-noise ratio and the detection sensitivity of the photoacoustic signal are further remarkably enhanced, self-adaptive compensation can be realized by continuously tracking the wavelength drift, and signal attenuation caused by parameter mismatch is avoided.
The modulation system based on the multi-dimensional modulation photoacoustic spectrum gas analysis according to the embodiment of the application is connected to the photoacoustic cell 4 and the light source 1, wherein after the characteristic gas is introduced into the photoacoustic cell 4, the photoacoustic effect is generated in the photoacoustic cell 4 with the light emitted by the light source 1, and the modulation system comprises a controller 7 and a modulator 2.
Referring to fig. 2, the controller 7 is electrically connected to the modulator 2 to enable signal transmission therebetween, and in some examples, the controller 7 and the modulator 2 may be different devices connected by wires, antennas, or different modules in the same device to be connected by a circuit.
The controller 7 is configured to obtain each action parameter, and then input each action parameter into a preset modulation algorithm, where the modulation algorithm outputs a modulation parameter for modulating the light source 1, and converts the modulation parameter output by the modulation algorithm into a modulation signal. The controller 7 sends a modulation signal to the modulator 2, and the modulator 2 controls and simultaneously adjusts various parameters of the optical signal sent by the light source 1 based on the modulation signal.
It should be noted that, when the photoacoustic effect in the photoacoustic cell 4 has occurred for a period of time, the controller 7 can obtain the corresponding action parameter, and then generate a modulation signal according to the received action parameter so as to match the modulation signal with the current photoacoustic effect, so that, in the initial stage of detection, when the photoacoustic effect has not yet started, the modulator 2 needs to adjust the light source 1 according to the preset initial parameter, and then initially modulate the light signal generated by the light source 1 so as to basically match the current characteristic gas.
Specifically, the controller 7 transmits a modulation signal to the modulator 2, and the modulator 2 includes an electric signal processing unit and an optical signal processing unit. The electric signal processing part is used for receiving the modulation signal and generating corresponding modulation parameters according to the modulation signal. As in the previous method embodiment, the modulation parameters in this embodiment include at least two parameters, for example, the modulation parameters include the frequency, amplitude, and wavelength of the light source 1. The optical signal processing part is used for receiving the optical signal sent by the optical source 1 and adjusting various parameters of the optical signal to be consistent with the modulation parameters.
Of course, the controller 7 may be any hardware device capable of implementing computation processing, such as a single-chip microcomputer, a CPU, etc., and similarly, the electric signal processing part in the modulator 2 may be any electronic element capable of processing electric signals, and the optical signal processing part may be any component having the modulation function of the light source 1.
In this way, the modulator 2 firstly performs preliminary adjustment on the light source 1 according to the parameters preset by the user, namely, the light signal generated by the light source 1 is processed through the light signal processing part of the modulator, and then the controller 7 generates a modulation signal according to the action parameters acquired from the current photoacoustic cell 4, so that the controller 7 can generate a modulation signal or a control signal according to different situations to control and adjust the light source 1 through the controller 7.
Further, the system adjusts a plurality of parameters of the modulator 2, such as the amplitude, wavelength and frequency of the light source 1, simultaneously based on the modulation signals by sending the modulation signals to the modulator 2 through the controller 7, thereby realizing the function of adjusting a plurality of parameters of the light source 1 simultaneously.
Moreover, since the modulation signal is generated by the controller 7 based on the action parameters in the current photoacoustic cell 4, compared with the conventional photoacoustic spectroscopy gas analysis using the mode of modulating the specific parameters of the light source 1 by amplitude modulation or wavelength, the modulator 2 needs to be controlled separately and then each parameter is adjusted one by one, so that the processing efficiency is higher, the action is more sensitive, and the selectivity is stronger.
Next, a modulation system of photoacoustic spectroscopy gas analysis based on multi-dimensional modulation will be described in detail with reference to fig. 2.
The modulation system based on the photoacoustic spectrometry gas analysis of the multidimensional modulation further comprises a demodulator 5, wherein the demodulator 5 is connected to the photoacoustic cell 4 and is used for acquiring an acoustic wave signal of the photoacoustic cell 4, and the demodulator 5 demodulates the acoustic wave signal to obtain the action parameter and sends the action parameter to the controller 7. The demodulator 5 demodulates the acoustic wave signal using the control parameter of the light source 1 of the controller 7 as a reference signal.
Illustratively, the demodulator 5 is connected with a microphone 11, the microphone 11 acquires the acoustic wave signal of the photoacoustic cell 4 and transmits the acoustic wave signal to the demodulator 5, and the modulation system based on the photoacoustic spectrum gas analysis of the multidimensional modulation further comprises a light source 1, an optical fiber 3, the photoacoustic cell 4 and a data processor 6.
As shown in fig. 2, a light source 1 provides an optical signal for photoacoustic spectrum detection by providing a photoacoustic effect, the light source 1 is connected with a modulator 2, the modulator 2 is connected with a photoacoustic cell 4 through an optical fiber 3, the optical signal emitted by the light source 1 is transmitted through the optical fiber 3 and then enters the photoacoustic cell 4 through a light through hole 8, and when the optical signal passes through the modulator 2, the modulator 2 modulates the optical signal.
Of these, the light source 1 is preferably a tunable continuous wave diode laser, which is capable of providing accurate wavelength adjustment, which is critical to matching the absorption wavelength of a specific gas, thereby improving the sensitivity and selectivity of detection.
The resonant cavity of the photoacoustic cell 4 is provided with a microphone 11, the microphone 11 is connected with a demodulator 5, and the demodulator 5 processes acoustic signals detected and transmitted by the microphone 11 through steps of conversion, amplification and the like to form photoacoustic signals generated by characteristic gas absorption optical signals in the photoacoustic cell 4.
Among them, the microphone 11 is preferably a condenser microphone, which has a wide frequency response range, can improve a signal-to-noise ratio, provides a clear signal in a noise environment, has a rapid transient response characteristic, and can rapidly respond to a change in sound waves. The demodulator 5, preferably a lock-in amplifier, has a high signal-to-noise ratio extraction capability, i.e. it is able to extract signal amplitude and phase information in an extremely noisy environment, and then by means of a phase sensitive detection technique it is possible to effectively extract a modulated signal with a known carrier from the noise, and has an extremely high frequency domain resolution capability, i.e. it is able to extract the amplitude and phase of an alternating signal buried in the noise even as weak as nanovolts. In addition, the lock-in amplifier has a dynamic reserve of up to 120 dB, meaning that this can achieve accurate measurement in the case where the noise amplitude exceeds the desired signal amplitude by a factor of million, and accurate measurement of the phase of the signal to be measured can be achieved by adjusting the phase of the reference signal.
The demodulator 5 is connected to a data processor 6, which data processor 6 is arranged to analyze the photoacoustic signals to determine the parameters of the effect within the photoacoustic cell 4.
The data processor 6 is connected with the controller 7, so that each action parameter obtained by the data processor 6 is input to the controller 7, the controller 7 adjusts the frequency, wavelength and amplitude of the optical signal emitted by the light source 1 according to the action parameter, and precisely controls the frequency, wavelength and amplitude of the optical signal to be the optimal light source 1 for generating the photoacoustic effect in the current characteristic gas state, and then outputs a modulation signal.
Correspondingly, the modulator 2 modulates the optical signal emitted by the light source 1 into the optimal optical signal of the current characteristic gas state to generate the photoacoustic effect according to the modulation signal.
Wherein the modulator 2 is preferably a silicon ring modulator which adopts a thermo-optic effect for modulation, has better thermal stability, lower insertion loss and higher integration level, can realize high-speed optical signal modulation,
In some examples, the photoacoustic cell 4 includes a light passing hole 8, an air inlet hole 9, and an air outlet hole 10;
the optical signal enters the photoacoustic cell 4 through the light through holes 8, the diameter of the light through holes 8 is preferably 3.0mm, the gas to be detected enters the photoacoustic cell 4 through the air inlet holes 9, and the gas after detection is discharged into the air or a specific unit through the air outlet holes 10. And, a resonant cavity is defined in the photoacoustic cell 4, the demodulator 5 is connected to the photoacoustic cell 4 through a microphone 11, and an audio collection end of the microphone 11 is in contact with the resonant cavity of the photoacoustic cell 4 to obtain an acoustic wave signal.
The foregoing is merely a preferred embodiment of the invention, and it is to be understood that the invention is not limited to the form disclosed herein but is not to be construed as excluding other embodiments, but is capable of numerous other combinations, modifications and environments and is capable of modifications within the scope of the inventive concept, either as taught or as a matter of routine skill or knowledge in the relevant art. And that modifications and variations which do not depart from the spirit and scope of the invention are intended to be within the scope of the appended claims.
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