A photoacoustic gas measurement method and system based on series sensitization technology

Abstract

The application provides a photoacoustic gas measurement method and system based on a series sensitization technology, relates to the technical field of optical gas sensing, and adopts decoupling of generation and primary amplification of a photoacoustic signal in a physical space, a first-stage light absorption enhancement structure is used for maximizing photoacoustic conversion of a target gas to generate an initial photoacoustic pressure signal, a second-stage acoustic resonance structure is introduced to resonate and amplify an acoustic wave of a specific frequency, a series cascade sensitization architecture of light absorption enhancement and acoustic resonance amplification is constructed, coherence outside preset noise analysis frequency band data is calculated through mutual verification analysis, common-mode noise interference caused by environmental vibration and the like is identified and suppressed, a feedback control parameter is generated while calculating a final gas concentration, and intensity modulation frequency and wavelength modulation depth are adaptively adjusted, so that the measurement reliability, the dynamic range and the adaptive ability of the system under complex working conditions are improved, a multiplicative breakthrough in system sensitivity and a performance synergistic optimization are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical gas sensing, in particular to a photoacoustic gas measurement method and system based on a series sensitization technology. BACKGROUND

[0002] Photoacoustic spectroscopy technology is based on the photoacoustic effect, which inverses the concentration by detecting the sound wave generated after the gas absorbs and modulates the light energy. It has become an important means for trace gas detection due to its high sensitivity and high selectivity. At present, the research on improving gas measurement mainly follows two independent directions: enhancing the interaction between light and gas or optimizing the detection of acoustic signals. One mainly focuses on the enhancement of light interaction, and the other focuses on the optimization of acoustic signal detection. However, there are the following problems in actual use:

[0003] Problem one, the existing technology mainly adopts the method of sensitization in a single physical link. For example, in the signal generation link, a multi-pass absorption cell is constructed to increase the effective optical path, thereby enhancing the photoacoustic effect. Or in the signal detection link, a high-Q value tuning fork resonant detector is used to improve the sensitivity of the acoustic-electric conversion. The existing technology focuses on the independent optimization of the "light-sound" or "sound-electricity" single conversion process. Its performance improvement has a physical upper limit, and it is difficult to achieve a magnitude breakthrough. Pursuing high performance in a single link often leads to complex system, large volume or reduced anti-interference ability, which is not conducive to actual use.

[0004] Problem two, the existing measurement method usually relies on a single type of detector to obtain signals, which is effective in a specific concentration range, but is limited by the performance characteristics of the detector itself. It is difficult to simultaneously meet the dual requirements of sensitive detection of low-concentration gas and wide linearity and non-saturation measurement of medium and high-concentration gas in a complex noise background. At the same time, there is a lack of real-time evaluation mechanism for signal quality, which cannot effectively distinguish and suppress environmental common-mode noise, lacks adaptive parameter adjustment capability when the working point drifts or the concentration changes dramatically, resulting in limited measurement dynamic range and insufficient long-term reliability. SUMMARY

[0005] To achieve the above purpose, the present application realizes the following technical scheme: a photoacoustic gas measurement method based on a series sensitization technology, the method comprising:

[0006] acquiring a target gas, generating a modulated laser based on wavelength modulation of the target gas, coupling the modulated laser to a first-stage light absorption enhancement structure, and generating an initial photoacoustic pressure signal by interacting with the target gas;

[0007] introducing the initial photoacoustic pressure signal into a second-stage acoustic resonant structure for frequency-selective acoustic resonance amplification to generate an amplified acoustic signal;

[0008] The first probe and the second probe are used to synchronously collect the amplified acoustic signal, and the first electric signal and the second electric signal are generated based on the amplified acoustic signal;

[0009] The first electric signal and the second electric signal are subjected to digital phase-locked processing, and the first harmonic component and the second harmonic component are extracted, respectively, and the gas concentration value is generated based on the first harmonic component and the second harmonic component through a signal fusion and mutual checking algorithm;

[0010] The second harmonic component and the second electric signal are analyzed to generate a feedback control parameter, and the wavelength modulation parameter of the modulated laser is adjusted based on the feedback control parameter.

[0011] Further, the modulated laser is coupled to the first-stage light absorption enhancement structure, and the modulated laser interacts with the target gas to generate an initial photoacoustic pressure signal.

[0012] The modulated laser is coupled to the first-stage light absorption enhancement structure, and the modulated laser forms an N-reflection enhanced light path region inside the first-stage light absorption enhancement structure.

[0013] The target gas flows through the enhanced light path region in sequence, absorbs the modulated laser energy in the enhanced light path region, and generates an initial photoacoustic pressure signal proportional to the gas concentration.

[0014] Further, the initial photoacoustic pressure signal is introduced into the second-stage acoustic resonance structure, and frequency-selective acoustic resonance amplification is performed to generate an amplified acoustic signal, which includes:

[0015] The acoustic resonance frequency of the second-stage acoustic resonance structure is set, and the intensity modulation frequency of the modulated laser is configured to be consistent with the acoustic resonance frequency.

[0016] The initial photoacoustic pressure signal is transmitted to the second-stage acoustic resonance structure, and the second-stage acoustic resonance structure resonantly amplifies the sound wave with a frequency component matching the acoustic resonance frequency, and outputs the amplified acoustic signal.

[0017] Further, the first probe and the second probe are used to synchronously collect the amplified acoustic signal, and the first electric signal and the second electric signal are generated based on the amplified acoustic signal, which includes:

[0018] The first probe and the second probe are arranged at the output region of the second-stage acoustic resonance structure; the first probe is an acoustic resonance type probe, and the second probe is a wide dynamic range sound pressure sensor.

[0019] The first probe is used to convert the acquired amplified acoustic signal into a first raw electric signal, and the first raw electric signal is subjected to band-pass filtering to generate a first electric signal containing narrow-band resonance acoustic characteristics.

[0020] The second probe converts the amplified acoustic signal obtained into a second electric signal containing a wideband sound pressure amplitude.

[0021] Further, the first electric signal and the second electric signal are subjected to digital phase-locked processing, and first harmonic components and second harmonic components are extracted, respectively, including:

[0022] The intensity modulation frequency of the modulated laser is obtained as a reference frequency, the first electric signal is subjected to first digital phase-locked amplification processing, and the amplitude of the second harmonic component is demodulated and output as the first harmonic component.

[0023] The second electric signal is subjected to second digital phase-locked amplification processing, and the amplitude of the second harmonic component is demodulated and output.

[0024] Further, the first harmonic component and the second harmonic component are used to generate a gas concentration value through a signal fusion and mutual verification algorithm, including:

[0025] Data of the first electric signal and the second electric signal in a preset noise analysis frequency band outside the intensity modulation frequency of the modulated laser is obtained.

[0026] The coherence coefficient of the first electric signal and the second electric signal in the preset noise analysis frequency band data is calculated, and the coherence coefficient is compared with a preset coherence threshold.

[0027] If the coherence coefficient exceeds the preset coherence threshold, it is determined that common-mode noise interference exists, filter parameters are generated based on the preset noise analysis frequency band data, and the first harmonic component and the second harmonic component are subjected to digital filtering before signal fusion.

[0028] If the coherence coefficient does not exceed the preset coherence threshold, the first harmonic component and the second harmonic component are directly subjected to signal fusion without digital filtering.

[0029] Further, the first harmonic component and the second harmonic component are used to generate a gas concentration value through a signal fusion and mutual verification algorithm, including:

[0030] The amplitude of the first harmonic component is obtained as a main concentration calculation value, and the amplitude of the second harmonic component is obtained as a reference concentration calculation value.

[0031] A first concentration threshold and a second concentration threshold are set, and the first concentration threshold is less than the second concentration threshold.

[0032] The numerical relationship between the main concentration calculation value and the first concentration threshold and the second concentration threshold is determined, a determination result is generated, and a final concentration calculation value is generated based on the determination result.

[0033] The final concentration calculation value is multiplied by a preset system calibration coefficient to obtain a final output gas concentration value.

[0034] Further, the final concentration calculation value is generated based on the judgment result, and the final concentration calculation value comprises:

[0035] When the judgment result is that the main concentration calculation value is less than the first concentration threshold value, the main concentration calculation value is used as the final concentration calculation value.

[0036] When the judgment result is that the main concentration calculation value is greater than the second concentration threshold value, the reference concentration calculation value is used as the final concentration calculation value.

[0037] When the judgment result is that the main concentration calculation value is between the first concentration threshold value and the second concentration threshold value, the main concentration calculation value and the reference concentration calculation value are linearly weighted and summed, and the sum result is used as the final concentration calculation value.

[0038] Further, the feedback control parameter is generated based on analysis of the second harmonic component and the second electric signal, and the wavelength modulation parameter of the modulation laser is adjusted based on the feedback control parameter, and the wavelength modulation parameter comprises:

[0039] The real-time amplitude of the second harmonic component is obtained, the real-time amplitude is compared with a preset amplitude threshold value, and a depth adjustment parameter is generated;

[0040] The second electric signal is subjected to frequency spectrum analysis, the current optimal resonance frequency of the second-order acoustic resonance structure is identified, and the current optimal resonance frequency is compared with the intensity modulation frequency of the modulation laser, and a frequency adjustment parameter is generated;

[0041] The wavelength modulation parameter comprises a wavelength modulation depth and an intensity modulation frequency, the wavelength modulation depth of the modulation laser is adjusted based on the depth adjustment parameter, and the intensity modulation frequency of the modulation laser is adjusted based on the frequency adjustment parameter.

[0042] An optoacoustic gas measurement system based on a series connection sensitization technology, the system comprising:

[0043] A tunable laser source module for generating a modulation laser based on a target gas by wavelength modulation;

[0044] A series connection cascade sensitization module for receiving a target gas and coupling the modulation laser to a first-order light absorption enhancement structure to interact with the target gas to generate an initial optoacoustic pressure signal, and guiding the initial optoacoustic pressure signal into a second-order acoustic resonance structure for frequency-selective acoustic resonance amplification to generate an amplified acoustic signal;

[0045] A dual-mode detection module for synchronously collecting the amplified acoustic signal based on a first detector and a second detector, and generating a first electric signal and a second electric signal based on the amplified acoustic signal;

[0046] The signal processing and feedback control module is used for carrying out digital phase-locked processing on the first electric signal and the second electric signal, extracting a first harmonic component and a second harmonic component respectively, generating a gas concentration value through a signal fusion and mutual checking algorithm based on the first harmonic component and the second harmonic component, analyzing the second harmonic component and the second electric signal to generate a feedback control parameter, and adjusting a wavelength modulation parameter of the modulated laser based on the feedback control parameter.

[0047] The application provides a photoacoustic gas measurement method and system based on a series connection sensitization technology.

[0048] 1. The application decouples the generation of a photoacoustic signal and a primary amplification process in a physical space, a first-stage light absorption enhancement structure is used to maximize photoacoustic conversion efficiency, an enhanced light path area with a long light path is formed through internal multiple reflections, a target gas absorbs modulated laser energy to generate an initial photoacoustic pressure signal, the initial photoacoustic pressure signal is introduced into a second-stage acoustic resonance structure to resonate and amplify an acoustic wave of a specific frequency, a series connection cascading sensitization architecture of light absorption enhancement and acoustic resonance amplification is constructed, the gains of the two-stage structure are independent of each other and can be optimized respectively, the first stage can adopt a compact design such as an optical fiber, and the second stage focuses on acoustic optimization, thereby balancing the contradiction between high performance and system integration while breaking through the sensitivity limit, and realizing a multiplicative breakthrough in system sensitivity and a synergistic optimization in performance.

[0049] 2. The application synchronously collects signals by using a parallel high-sensitivity acoustic resonance detector and a wide dynamic range acoustic pressure sensor, converts the acquired amplified acoustic signals into first and second electric signals for mutual checking analysis, calculates the coherence outside the preset noise analysis frequency band data, identifies and suppresses common mode noise interference caused by environmental vibration and the like, thereby greatly improving the signal-to-noise ratio and anti-interference ability, through intelligent signal fusion, the harmonic component extracted by the high-sensitivity detector is preferentially used in the low concentration interval to ensure the detection lower limit, and as the concentration increases, the wide linearity detector signal is mainly used for smooth transition, thereby seamlessly covering an ultra-wide dynamic range from trace to high concentration, through real-time analysis of the real-time amplitude and spectrum acquired by the second detector, feedback control parameters are adaptively generated, the wavelength modulation depth of the laser is dynamically adjusted to prevent signal saturation, and the intensity modulation frequency is finely adjusted to track the optimal resonance point of the acoustic resonance cavity, through the introduction of the double-mode detection and intelligent feedback control mechanism, the system can automatically maintain the optimal working state, and the measurement reliability, dynamic range and adaptive ability of the system under complex working conditions are improved. BRIEF DESCRIPTION OF DRAWINGS

[0050] Fig. 1 A flowchart of the application, a photoacoustic gas measurement method based on a series connection sensitization technology;

[0051] Fig. 2A data transmission flowchart of a photoacoustic gas measurement method based on a series of sensitization technologies according to the present application;

[0052] Fig. 3 An architecture diagram of a photoacoustic gas measurement system based on a series of sensitization technologies according to the present application. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0054] As shown in Figs. 1-2 A photoacoustic gas measurement method based on a series of sensitization technologies, the method comprising:

[0055] In step S100, a target gas is obtained, a wavelength-modulated modulation laser is generated based on the target gas, the modulation laser is coupled to a first-stage light absorption enhancement structure, and an initial photoacoustic pressure signal is generated by the interaction of the target gas; wherein the target gas is a to-be-measured gas component capable of absorbing a specific wavelength laser, such as methane, carbon monoxide, carbon dioxide, ammonia, water vapor, etc.; the modulation laser is generated by an external tunable laser, such as a distributed feedback laser diode; the wavelength of the modulation laser is slowly scanned or stably controlled near the center frequency of the target gas absorption spectrum, which ensures that the modulation laser spectrum is aligned with the target gas absorption line; the output intensity of the modulation laser is sinusoidally modulated at a specific low frequency (such as 2.05 kHz); the wavelength characteristics of the modulation laser ensure that the laser can be effectively absorbed by the target gas; the intensity modulation frequency provides a periodic energy injection source for the entire system, and the intensity modulation frequency ultimately determines the frequency of the photoacoustic signal and provides a reference benchmark for subsequent lock-in amplification;

[0056] The first-stage light absorption enhancement structure is mainly composed of an anti-resonant hollow core fiber (AR-HCF), angle fiber collimators at both ends of the AR-HCF, and a precision clamp, and further includes a micro-hole array processed on the cladding of the AR-HCF; the first-stage light absorption enhancement structure provides an ultra-long effective light-gas interaction region for increasing the flow path of the target gas, improving the absorption time and efficiency of the target gas to the modulation laser energy, and amplifying the generated photoacoustic signal;

[0057] The core of the anti-resonant hollow core fiber is an air hole, and the cladding is composed of periodically arranged glass capillaries. The anti-resonant hollow core fiber uses the anti-resonant reflection principle to confine the light in the air core to propagate. The anti-resonant hollow core fiber has an ultra-long light path restrictor. The modulated laser is confined in the air core to realize long-distance transmission through the total reflection mechanism, and an enhanced light path region is created. The air core itself is an extremely thin gas channel, and the target gas can flow in it to realize the full action of light and gas. The air core structure also constitutes an acoustic waveguide, which helps to direct the initial photoacoustic pressure signal generated to reduce the diffusion loss of acoustic energy. The micro-hole array on the side wall further optimizes the exchange speed of the target gas.

[0058] In step S101, the modulated laser is coupled to the first-stage light absorption enhancement structure. The modulated laser forms an N-time-reflection enhanced light path region inside the first-stage light absorption enhancement structure, where N is an integer.

[0059] First, the modulated laser output by the tunable laser is introduced into a standard single-mode optical fiber for transmission. The end of the standard single-mode optical fiber is connected to a fiber collimator with a specific inclination angle (non-0 degree). The fiber collimator collimates and converts the Gaussian beam propagating in the standard single-mode optical fiber into a spatial beam, and emits it at a pre-calculated non-vertical angle. The spatial beam is accurately aligned and incident on the end face of the anti-resonant hollow core fiber (AR-HCF). A precision clamp is used to fix the fiber collimator and the anti-resonant hollow core fiber, ensuring the accuracy of the incident angle.

[0060] Then, when the spatial beam enters the air core of the anti-resonant hollow core fiber at the incident angle, due to the difference in refractive index between the air core wall material (usually glass) and the internal air, the spatial beam undergoes total reflection at the core wall interface, forming a zigzag light path that is much longer than the physical length of the fiber, i.e., an enhanced light path region. Through total reflection, the modulated laser is constrained in the air core and propagates along the zigzag path, rather than directly emitting from the other end, thereby completing the coupling.

[0061] The enhanced light path region refers to a continuous and zigzag light propagation path formed inside the anti-resonant hollow core fiber due to the N-time total reflection of the spatial beam at the core wall after being incident at a specific angle. The actual optical length of the enhanced light path region is much longer than the physical length of the anti-resonant hollow core fiber itself, greatly extending the effective length of the interaction between the target gas and the modulated laser. In a traditional straight-through gas cell, the optical path is equal to its physical length. In this embodiment, the light path is folded in a limited space through total reflection, so that the optical path per unit volume reaches meters or even tens of meters, thereby exponentially increasing the absorption probability of the target gas to photons and realizing the first-stage optical sensitization.

[0062] Step S102, the target gas flows through the enhanced light path region in sequence, absorbs the modulated laser energy in the enhanced light path region, and generates an initial photoacoustic pressure signal proportional to the gas concentration;

[0063] Firstly, the target gas flows into the air core of the anti-resonant hollow core fiber from one end or through the side wall micro-hole array under the driving of the micro-pump. The target gas molecules repeatedly cross the path of the modulated laser when flowing through the enhanced light path region, continuously absorbing the modulated laser energy. The target gas flows into or diffuses into the air core of the anti-resonant hollow core fiber under the driving, and fully contacts with the existing enhanced light path region inside. When the wavelength of the modulated laser matches a certain characteristic absorption spectrum of the target gas molecules, the target gas molecules flowing through the light path will absorb the photons passing through them. Since the output intensity of the modulated laser is low-frequency sinusoidal modulation, the rate of target gas absorbing light energy also synchronously changes sinusoidally. The excited molecules convert the absorbed light energy into translational energy, i.e. the thermal energy of the gas, through collision with other molecules in a very short time of picoseconds to nanoseconds, resulting in the periodic fluctuation of the local temperature of the gas synchronously with the modulation frequency.

[0064] Then, when the local temperature of the target gas periodically rises, thermal expansion generates pressure; when the temperature periodically decreases, contraction causes the pressure to decrease. The periodic thermal expansion and contraction of the target gas excite acoustic waves in the limited space of the anti-resonant hollow core fiber, forming an initial photoacoustic pressure signal. The initial photoacoustic pressure signal carries the concentration information of the target gas as the primary carrier, and its frequency is locked with the intensity modulation frequency of the modulated laser, while the amplitude carries the concentration information of the target gas.

[0065] Among them, the modulated laser energy refers to the photon energy carried by the modulated laser, which is selectively absorbed by the molecules of the target gas and converted into the internal energy of the molecules of the target gas;

[0066] The initial photoacoustic pressure signal is a weak acoustic pressure wave with the same frequency and amplitude proportional to the absorption intensity generated after the target gas absorbs the periodic modulated laser energy. The relationship between the initial photoacoustic pressure signal and the gas concentration is:

[0067] According to the basic principle of photoacoustic effect, under the condition of weak absorption, the amplitude P of the generated photoacoustic signal is proportional to the gas concentration C, the incident laser power I, the gas absorption coefficient a and the photoacoustic conversion efficiency η, that is, P∝η*α*C*I. In this scheme, due to the use of the enhanced light path, the effective interaction optical path L eff is greatly increased, so that the absorption term changes from the usual aCL to aCL eff , where the physical length of L eff is much larger than L, therefore, the amplitude of the initial photoacoustic pressure signal is not only proportional to the gas concentration C and the laser power I, but also to the super-long effective interaction optical path L effAmplification, for fixed system and fixed laser power, the signal amplitude can be simplified as P initial =K*C, where K is a huge constant that integrates the gas absorption coefficient, enhanced optical path, geometric structure and thermodynamic parameters, so that even for the gas concentration C is very low, can produce a relatively measurable P initial , the design of long optical path makes it possible to accumulate observable energy absorption and detection even for weakly absorbed target gas or low concentration.

[0068] Step S200, the initial photoacoustic pressure signal is introduced into the second stage acoustic resonance structure, and the frequency selective acoustic resonance amplification is carried out to generate an amplified acoustic signal; the second stage acoustic resonance structure is a Helmholtz resonance cavity, which is composed of three parts of front cavity, neck pipe and rear cavity connected precisely, and the Helmholtz resonance cavity as an acoustic system has an inherent acoustic resonance frequency f res , which is determined by the volume of the front cavity, the size of the neck pipe and the volume of the rear cavity, when the frequency of the initial photoacoustic pressure signal is consistent with f res , strong acoustic resonance will be induced in the cavity;

[0069] Step S201, set the acoustic resonance frequency of the second stage acoustic resonance structure as the target frequency, and configure the intensity modulation frequency of the modulated laser to be consistent with the acoustic resonance frequency;

[0070] Wherein, the acoustic resonance frequency f res is the specific frequency that the second stage acoustic resonance structure responds most strongly to, which is generally set in the low frequency of audio frequency, for example, several hundred hertz to several thousand hertz, to avoid environmental noise, and at the same time, the response and size are considered: if the acoustic resonance frequency is too low, the volume of the Helmholtz resonance cavity needs to be too large, and if the frequency is too high, the sound wave loss increases, so the Q value and the best sound field distribution at the target frequency are obtained by theoretical calculation and simulation optimization considering the internal cavity volume, neck pipe length, etc;

[0071] The intensity modulation frequency f mod of the modulated laser is the frequency of the output power of the laser changing according to the sine wave rule, and the intensity modulation frequency is generated by a function generator or a digital signal processor (DSP) driving the laser, and the frequency of the sine wave signal output by the function generator is changed through software or circuit;

[0072] f mod is configured to be exactly consistent with f res , which is convenient for realizing acoustic resonance driving, and is a prerequisite for the second stage sensitization to take effect, only under this condition, the initial photoacoustic pressure signal with frequency f mod generated by the modulated laser can match the resonance frequency f resThis stimulates the strongest acoustic resonance, allowing the sound pressure signal of that frequency component to be amplified by a factor of Q. Conversely, if the two are mismatched, the signal cannot be effectively amplified, and the system sensitivity will drop sharply. Frequency locking ensures that the photoacoustic signal can be enhanced to the maximum extent through the acoustic resonant structure.

[0073] The Q value (quality factor) is a key parameter describing the frequency selectivity and energy storage efficiency of a resonant cavity, and is expressed as the resonant center frequency f. res The ratio of the full width at half maximum (FWHM) of the resonance peak to the full width at half maximum (bandwidth Δf), i.e., Q = f res / Δf, a higher Q value indicates a sharper resonance peak and a narrower bandwidth; in this scheme, a high Q value ensures that the Helmholtz resonator is only sensitive to f. res The photoacoustic signal generated by the absorption of the target gas is amplified significantly while the amplification effect on broadband noise of other frequencies in the environment (such as mechanical vibration and background noise) is minimal. This greatly improves the signal-to-noise ratio and anti-interference capability of the system. The Q value is directly related to the energy amplification factor. Theoretically, the acoustic pressure gain in the cavity is proportional to the Q value. A resonant cavity with a Q value of 50 can amplify the acoustic pressure signal of the target frequency by about 50 times, which is the core of realizing the second-stage acoustic sensitization.

[0074] Step S202: The initial photoacoustic pressure signal is transmitted to the second-stage acoustic resonant structure. Based on the second-stage acoustic resonant structure, the sound wave whose frequency components match the acoustic resonance frequency is resonantly amplified, and the amplified acoustic signal is output.

[0075] First, at a specific location at the end or side of the anti-resonant hollow fiber (AR-HCF), an acoustic coupling interface (such as a miniature, airtight acoustic conduit or adapter) is used to connect one end of the acoustic coupling interface to the air core of the AR-HCF, and the other end to the entrance of the front cavity of the Helmholtz resonant cavity. When the target gas absorbs light energy in the air core of the AR-HCF and generates an initial photoacoustic pressure signal, the pressure wave will propagate forward along the air core and the acoustic conduit, just like sound propagating in a pipe, and be injected directly into the front cavity of the Helmholtz resonant cavity with almost no obstruction.

[0076] Then, the frequency f mod The initial photoacoustic pressure signal is introduced into the front cavity of the Helmholtz resonant cavity through an acoustic conduit. The fluctuation of the initial photoacoustic pressure signal drives the gas piston at the cavity neck to reciprocate. Due to the system's inertia (mass of air in the neck) and elasticity (volume of gas in the cavity), resonance occurs when the driving frequency of the initial photoacoustic pressure signal equals the acoustic resonant frequency. The speed and amplitude of the gas vibration at the neck reach their maximum, thus efficiently accumulating and amplifying acoustic energy in the rear cavity. Finally, a frequency of f is output at the antinode of the rear cavity. mod, but the amplitude of the sound pressure is amplified by tens of times, that is, an amplified acoustic signal.

[0077] The amplified acoustic signal is an output sound pressure wave after resonance enhancement by the Helmholtz resonant cavity, and contains a frequency component, that is, a single frequency sound wave with the same frequency as the intensity modulation frequency f mod (equal to the acoustic resonance frequency f res ) of the modulated laser, and the amplitude has been amplified by Q times. The original weak and easily submerged initial photoacoustic pressure signal is converted into a strong amplified acoustic signal with a very clear characteristic frequency, so that the subsequent detector can convert it into an electrical signal with a higher signal-to-noise ratio, laying a solid foundation for the final high-precision inversion of the gas concentration. It is the output result of the acoustic sensitization link in the series sensitization.

[0078] Step S300, synchronously acquiring the amplified acoustic signal based on the parallelly arranged first detector and second detector, and generating a first electrical signal and a second electrical signal based on the amplified acoustic signal; the first detector and the second detector are arranged in parallel at the output area of the second acoustic resonant structure; the first detector is an acoustic resonance type detector, and the second detector is a wide dynamic range sound pressure sensor;

[0079] The first detector converts the obtained amplified acoustic signal into a first raw electrical signal, and the first raw electrical signal is bandpass filtered to generate a first electrical signal containing narrowband resonant acoustic characteristics; the first detector is a low-frequency quartz tuning fork (such as 32.768 kHz) in actual use, and a thin layer of polydimethylsiloxane is coated on the prongs to enhance the thermal elastic effect. The low-frequency quartz tuning fork is precisely positioned at the sound pressure antinode of the back cavity of the Helmholtz resonant cavity, and performs narrowband detection on the amplified acoustic signal with high sensitivity. When the amplified acoustic signal drives the tuning fork arm to vibrate, a weak current signal proportional to the vibration amplitude is generated on the electrodes of the low-frequency quartz tuning fork due to the piezoelectric effect and the thermal elastic effect, that is, the first raw electrical signal. The first raw electrical signal is immediately sent to a high-gain, narrow-bandwidth bandpass filter amplifier, the center frequency of the bandpass filter amplifier is strictly aligned with the target frequency of the system, and the bandwidth is only a few tens of hertz, so that most of the out-of-band noise is filtered out, and a pure first electrical signal whose amplitude is proportional to the sound pressure of the target frequency is finally output.

[0080] The second probe converts the amplified acoustic signal obtained into a second electric signal containing a wideband sound pressure amplitude. In actual use, the second probe uses a MEMS sound pressure sensor to directly and absolutely measure the sound pressure in the Helmholtz resonator, providing real sound pressure amplitude information that is not affected by the resonant characteristics of the probe itself. The MEMS sound pressure sensor is placed in the Helmholtz resonator, for example, near the neck pipe or the front cavity. Its sensitive diaphragm directly senses the instantaneous sound pressure in the cavity and produces deformation, causing the built-in Wheatstone bridge resistance to change, thereby directly outputting a standard voltage signal proportional to the instantaneous sound pressure, i.e., the second electric signal. The second electric signal is not filtered by a narrowband filter and contains the target frequency component and a wider background acoustic noise spectrum.

[0081] The first electric signal is an AC voltage signal amplified by high-Q narrowband filtering, mainly containing a single frequency component strictly synchronized with the intensity modulation frequency of the modulated laser. The amplitude accurately reflects the intensity of the sound pressure of the target frequency after acoustic resonance amplification and selective enhancement by the quartz tuning fork. It is the output of the high-sensitivity channel, providing extremely high signal-to-noise ratio at low concentrations. The narrowband resonant acoustic characteristics of the detection link effectively suppress the wideband environmental noise.

[0082] The second electric signal is a wide dynamic range voltage signal containing the sound pressure component of the target frequency and the real amplitude information of other frequencies of acoustic noise that may exist in the Helmholtz resonator (such as low-frequency noise coupled in by environmental vibration, airflow noise, etc.). The second electric signal is the output of the wide dynamic range channel, providing linear and reliable measurement at high concentrations and avoiding saturation problems that may occur with the quartz tuning fork. The wideband characteristics of the second electric signal facilitate subsequent noise analysis and system feedback control.

[0083] The narrowband resonant acoustic characteristics refer to the highly purified target frequency sound signal extracted by the first probe detection link. The frequency amplitude information is obtained through two levels of screening, i.e., the mechanical resonance of the quartz tuning fork and subsequent electronic narrowband bandpass filtering, at the cost of bandwidth and dynamic range, in exchange for the ultimate detection sensitivity at the target frequency. The wideband sound pressure amplitude is the time-domain or frequency-domain amplitude information of the total sound pressure in the Helmholtz resonator directly measured by the second probe. It contains the real sound pressure of the target frequency and other frequency components, providing a real and linear sound pressure absolute value reference to ensure the measurement accuracy of the system at high concentrations and provide data for system status monitoring. The wideband and flat frequency response characteristics of the MEMS sensor are directly obtained.

[0084] In step S400, the first electric signal and the second electric signal are subjected to digital lock-in processing, and the first harmonic component and the second harmonic component are extracted, respectively. Based on the first harmonic component and the second harmonic component, a gas concentration value is generated through signal fusion and mutual verification algorithm.

[0085] wherein, digital phase-locked processing is a signal extraction technology using software algorithm to simulate the function of traditional phase-locked amplifier, which is used to accurately demodulate the weak signal component related to the known reference frequency and in a specific second harmonic relationship from the first electrical signal and the second electrical signal, and output its amplitude and phase;

[0086] Both the first harmonic component and the second harmonic component specifically refer to the amplitude of the second harmonic component demodulated from the electrical signal of the respective channel, which is selected as the core intermediate variable for calculating the gas concentration. The second harmonic, rather than the fundamental wave, is selected because when the laser wavelength is small amplitude sinusoidal scanning modulation at the center of the gas absorption spectrum, the photoacoustic signal generated at the second harmonic presents a peak value, and the interference caused by the laser intensity fluctuation and the background light can be effectively suppressed, so as to more purely reflect the gas absorption information.

[0087] The gas concentration value directly quantitatively reflects the content of the target gas in the measured environment, which is the core data basis for environmental monitoring, industrial process control, safety warning or scientific research.

[0088] In step S401, the intensity modulation frequency of the modulated laser is obtained as a reference frequency, the first electrical signal is subjected to first digital phase-locked amplification processing, the amplitude of the second harmonic component is demodulated and output as the first harmonic component, and the second electrical signal is subjected to second digital phase-locked amplification processing, the amplitude of the second harmonic component is demodulated and output as the second harmonic component.

[0089] By taking the intensity modulation frequency f mod As a reference frequency, the first electrical signal and the second electrical signal are subjected to digital phase-locked amplification processing, the first electrical signal and the second electrical signal are subjected to high-speed analog-to-digital conversion (ADC) respectively to obtain digital sequences S1(t) and S2(t), the digital sequences S1(t) and S2(t) are multiplied by sin(4πf mod t) and cos(4πf mod t) respectively and integrated, the results after operation are low-pass filtered and amplitude calculated, thereby demodulating the in-phase component (X) and the quadrature component (Y) of the second harmonic component at double frequency (2f mod ), and the final first harmonic component and the second harmonic component are represented by their amplitudes Selecting the second harmonic can effectively suppress the direct current and the fundamental frequency noise caused by the background light;

[0090] Through calculation, the first digital phase-locked amplification processing is the phase-locked demodulation for the first electrical signal, which accurately extracts the second harmonic amplitude H a1 as the first harmonic component, ; the second digital phase-locked amplification processing is a phase-locked demodulation for the second electric signal, and the second harmonic amplitude H in the wideband channel signal is accurately extracted a2 as the second harmonic component, .

[0091] In step S402, the preset noise analysis frequency band data of the first electric signal and the second electric signal outside the intensity modulation frequency of the modulated laser is obtained, the coherence coefficient of the first electric signal and the second electric signal in the preset noise analysis frequency band data is calculated, and the coherence coefficient is compared with a preset coherence threshold value;

[0092] If the coherence coefficient exceeds the preset coherence threshold value, it is determined that common mode noise interference exists, filter parameters are generated based on the preset noise analysis frequency band data, and digital filtering is performed on the first harmonic component and the second harmonic component before signal fusion;

[0093] If the coherence coefficient does not exceed the preset coherence threshold value, digital filtering is not performed, and signal fusion of the first harmonic component and the second harmonic component is directly performed.

[0094] The preset noise analysis frequency band data includes the amplitude and phase information of various noises in the frequency band, which is directly extracted from the digital sequences S1(t) and S2(t) collected by the two-way ADC through digital band-pass filtering or spectrum analysis method. The preset noise analysis frequency band data is used to analyze whether there is common interference noise irrelevant to the target gas measurement in the two-way signal, and provides a basis for identifying and suppressing common mode noise;

[0095] The coherence coefficient generally refers to the cross-spectral coherence coefficient, which is a statistical quantity between 0 and 1, used to measure the linear correlation degree of two signals at a certain frequency (or frequency band), 0 represents no correlation, and 1 represents complete linear correlation, which is used to quantitatively judge whether the first electric signal and the second electric signal are affected by the same interference source in the non-target frequency band, i.e. noise frequency band;

[0096] The preset coherence threshold value is an empirical value used as a limit to determine whether common mode noise exists, and is generally between 0.7 and 0.9, for example, 0.8. By calculating the coherence coefficient of the two-way electric signal in the noise frequency band under the condition of no target gas but typical environmental interference (such as knocking the table surface and running the fan), the level of its increase is set as the preset coherence threshold value. It is considered that the common mode noise has been seriously affected to the extent that the suppression measures need to be started if it exceeds the preset coherence threshold value;

[0097] The filtering parameter refers to the center frequency and bandwidth of the digital notch filter. When the coherence coefficient exceeds the standard, more detailed spectrum analysis is performed on the noise analysis data, such as fast Fourier transform, to accurately find the discrete frequency points (such as 50 Hz and 100 Hz) with the strongest coherence, take the discrete frequency points as the center frequency of the notch filter, set the stop band bandwidth of the filter according to the width of the noise peak, and generate a digital notch filter with a specified stop band bandwidth. The generated digital notch filter is applied to the first harmonic component sequence H a1 (t) and the second harmonic component sequence H a2 (t) to filter out abnormal fluctuation components caused by common mode noise and falling within the notch frequency band in the output data, thereby smoothing the final concentration output curve and improving its stability and accuracy in the presence of periodic environmental interference.

[0098] Step S403: Take the amplitude of the first harmonic component as the main concentration calculation value H a1 , and take the amplitude of the second harmonic component as the reference concentration calculation value H a2 ; set the first concentration threshold T low and the second concentration threshold T high , and T low <T high ; judge the numerical relationship between the main concentration calculation value and the first and second concentration thresholds, and generate a judgment result.

[0099] When the judgment result is H a1 <T low , it means that the gas concentration is extremely low, and the signal-to-noise ratio of the second electric signal obtained by the second detector is insufficient. When the gas concentration is extremely low, the amplitude of the second harmonic component calculated cannot be clearly distinguished from the background fluctuation when the concentration is zero, that is, the effective signal is submerged in noise and fluctuates greatly, which is unreliable. However, the amplitude of the first detector can still maintain a high signal-to-noise ratio and accuracy, so the final concentration calculation value C end =H a1 is selected.

[0100] When the judgment result is H a1 >T high , it means that the gas concentration is high, the first detector tends to be saturated, the linearity is poor, and the vibration amplitude of the quartz tuning fork and the sound pressure no longer maintain a strict linear proportional relationship, resulting in low or distorted readings. However, the amplitude of the second detector is still within the linear working range, so the final concentration calculation value C end =H a2 is selected.

[0101] When the judgment result is T low ≤H a1 ≤Thigh When H a1 , it indicates that the gas concentration is in the middle section, the outputs of both detectors are relatively reliable, each has its own advantages, therefore, the linear weighted sum of the main concentration calculation value and the reference concentration calculation value is selected as the final concentration calculation value, and the final concentration calculation value C = w × H a2 + (1-w) × H a1 , wherein the weight w can be changed with H high . low Linearly increases from 0 to 1 to achieve a smooth transition, in the interval [T low , T high ], when H a1 = T low , the weight w is set to 1, when H a1 = T high , the weight w is set to 0, for any value of H a1 in the interval, the weight w is according to the formula: w = (T high -H a1 ) / (T high -T low ), thus, as the gas concentration increases from T low to T high , w smoothly linearly decreases from 1 to 0, and correspondingly, (1-w) smoothly linearly increases from 0 to 1, and the final concentration value C also smoothly transitions between H a1 and H a2 .

[0102] The final concentration calculation value C is multiplied by a preset system calibration coefficient K cal , and the final output gas concentration value is obtained.

[0103] Wherein, the first concentration threshold T low and the second concentration threshold T high are set based on the performance turning points of the two detectors, T low is set near the concentration point at which the signal-to-noise ratio of the second detector begins to become unacceptable (such as SNR < 3), and T high is set near the concentration point at which the output of the first detector begins to deviate from linearity (such as non-linear error > 1%) or approaches saturation, the specific value needs to be calibrated by experiment, for example, T low corresponds to 10 ppm, and T high corresponds to 1000 ppm (which varies depending on the specific gas and system design), which divides the three clear concentration working intervals for the dual-channel fusion algorithm;

[0104] The preset system calibration coefficient K calThis is a scaling factor that converts the final concentration calculation value C from the instrument reading into the true physical concentration value. It is set by using a standard gas of known concentration to measure the concentration of the standard gas, which is C. std At that time, the system output value of C is C. read Then K cal =C std / C read The preset system calibration coefficients encompass the effects of all inherent system parameters, including optical path enhancement factor, acoustic amplification factor, detector sensitivity, and electronic gain, and are therefore unique and essential.

[0105] Step S500: Analyze the second harmonic component and the second electrical signal to generate feedback control parameters, and adjust the wavelength modulation parameters of the modulated laser based on the feedback control parameters.

[0106] Step S501: Obtain the real-time amplitude H of the second harmonic component. a2 The real-time amplitude H a2 The depth adjustment parameters are generated by comparing the value with a preset amplitude threshold.

[0107] By continuously monitoring the real-time amplitude H of the second harmonic component a2 When the real-time amplitude H a2 If the preset amplitude threshold is exceeded in several consecutive measurement cycles (e.g., 10 cycles), it is determined that there is a risk of saturation. An instruction to reduce the wavelength modulation depth is generated, and a specific adjustment step size Δd is calculated (e.g., reduce the current wavelength modulation depth d by 5%). The instruction and step size Δd are sent to the wavelength modulation drive circuit that controls the laser to adjust the wavelength modulation depth.

[0108] The preset amplitude threshold is a warning value set to prevent signal saturation. It is usually expressed as a percentage of the full-scale range of the analog-to-digital converter (ADC). It provides the system with a standard to judge whether the signal is approaching the overload boundary, thereby triggering protective adjustments. The preset amplitude threshold is based on the dynamic range setting of the signal processing link in the system, especially the range of the ADC at the output of the lock-in amplifier. It is usually set between 70% and 90% of the upper limit of the ADC range, such as 80%. In order to ensure that the measurement is within the linear region and leave a safety margin, when the signal amplitude continuously exceeds this preset amplitude threshold, it is determined that there is a risk of entering the nonlinear region or saturation, and intervention is required.

[0109] The depth adjustment parameter is an instruction or value used to control the reduction in the wavelength modulation depth (i.e., the amplitude of wavelength swing) of the modulated laser. It is used to automatically reduce the amplitude of laser wavelength scanning in high concentration situations to avoid the generation of excessively strong photoacoustic signals that could saturate subsequent detection or amplification stages, thereby expanding the upper limit of the concentration that the system can measure.

[0110] Step S502, the second electrical signal is subjected to spectrum analysis, the current optimal resonance frequency of the second-order acoustic resonance structure is identified, the current optimal resonance frequency is compared with the intensity modulation frequency of the modulated laser, and a frequency adjustment parameter is generated; the second electrical signal is subjected to fast Fourier transform analysis, the peak frequency of the Helmholtz resonant cavity sound pressure response spectrum, i.e., the current optimal resonance frequency, is identified in real time, and is compared with the current intensity modulation frequency of the laser, if a drift occurs (e.g., due to temperature change), a fine adjustment instruction is generated to make the laser modulation frequency re-locked to the new resonance peak;

[0111] First, a discrete time sequence of the second electrical signal is obtained by continuous collection at a set sampling rate and time length, e.g., 1024 points per second for 0.1 seconds;

[0112] Then, the discrete time sequence is windowed (e.g., Hanning window) and subjected to fast Fourier transform operation to convert it from time domain to frequency domain, and an amplitude spectrum of the signal is obtained;

[0113] Finally, in the spectrum, a reasonable frequency band (e.g., ±50 Hz) centered on the theoretical acoustic resonance frequency f res (e.g., 2.05 kHz) is analyzed, which is used to directly observe the actual sound pressure response characteristics of the Helmholtz resonant cavity under the current environment (temperature, air pressure), and find the frequency value corresponding to the peak value of the amplitude spectrum, which is the current optimal resonance frequency f peak By calculating the difference Δf between the optimal resonance frequency and the intensity modulation frequency, Δf = f peak -f mod , it is judged whether the absolute value of Δf exceeds a preset allowable error threshold (e.g., 1 Hz), if it exceeds, a frequency adjustment instruction is generated, and contains a specific frequency adjustment value Δf or directly sets the target frequency to f peak The instruction is sent to a function generator or a digital frequency synthesizer that generates the laser intensity modulation signal.

[0114] Wherein, the optimal resonance frequency refers to the frequency point f peak with the largest amplitude of sound pressure response of the Helmholtz resonant cavity under the current actual working condition, which is identified through spectrum analysis of the second electrical signal, and is the final target of adjusting the intensity modulation frequency of the laser as the best frequency of acoustic amplification under the current state of the system.

[0115] The frequency adjustment parameter is an instruction or a numerical value for fine-tuning the intensity modulation frequency f mod of the modulated laser to re-align the identified optimal resonance frequency f peakThis enables real-time tracking and locking of the intensity modulation frequency to the acoustic resonance frequency, compensating for the inherent frequency drift of the resonant cavity caused by factors such as changes in ambient temperature, and ensuring that the acoustic sensitization circuit is always in the best working condition.

[0116] Step S503: The wavelength modulation parameters include wavelength modulation depth and intensity modulation frequency. The wavelength modulation depth of the modulated laser is adjusted based on the depth adjustment parameter, and the intensity modulation frequency of the modulated laser is adjusted based on the frequency adjustment parameter.

[0117] Wavelength modulation depth refers to the amplitude of the sinusoidal modulation signal applied to the current (or temperature) driving the laser. It determines the range of periodic scanning of the laser output wavelength near the center wavelength. A suitable modulation depth can maximize the second harmonic signal. An excessively large modulation depth will generate an excessively strong photoacoustic signal at high concentrations, leading to saturation. According to the depth adjustment parameters generated in step S501, the wavelength modulation signal input on the laser driver is modified through its control interface. The voltage or current amplitude of the sinusoidal modulation signal applied to the laser tuning port (usually the current input) is reduced proportionally by a step size Δd, thereby directly reducing the scanning amplitude of the laser wavelength.

[0118] Intensity modulation frequency refers to the frequency f of the low-frequency sinusoidal signal that directly controls the periodic variation of the laser's output power (intensity). mod This provides a time-domain synchronization reference for the entire system and ensures that the frequency of the photoacoustic signal matches the acoustic resonance frequency. Based on the frequency adjustment parameters generated in step S502, the function generator or direct digital frequency synthesizer that generates the intensity modulation signal is directly controlled for adjustment.

[0119] like Fig. 3 As shown, a photoacoustic gas measurement system based on tandem sensitization technology includes:

[0120] A tunable laser source module is used to generate modulated laser based on wavelength modulation of a target gas.

[0121] A series-cascaded sensitization module is used to receive the target gas and couple the modulated laser to the first-stage optical absorption enhancement structure. The laser interacts with the target gas to generate an initial photoacoustic pressure signal. The initial photoacoustic pressure signal is then introduced into the second-stage acoustic resonant structure for frequency-selective acoustic resonance amplification to generate an amplified acoustic signal.

[0122] The dual-mode detection module synchronously acquires and amplifies acoustic signals based on a first detector and a second detector connected in parallel, and generates a first electrical signal and a second electrical signal based on the amplified acoustic signals.

[0123] The signal processing and feedback control module is used for digital phase-locked processing of the first electric signal and the second electric signal, extracting the first harmonic component and the second harmonic component respectively, generating a gas concentration value through a signal fusion and mutual checking algorithm based on the first harmonic component and the second harmonic component, analyzing the second harmonic component and the second electric signal to generate a feedback control parameter, and adjusting a wavelength modulation parameter of the modulated laser based on the feedback control parameter.

[0124] In the embodiment, the generation of the photoacoustic signal and the primary amplification process are decoupled in physical space, the first-stage light absorption enhancement structure is used to maximize the photoacoustic conversion efficiency, the enhanced light path region with a long optical path is formed through internal multiple reflections, the target gas absorbs the modulated laser energy to generate an initial photoacoustic pressure signal, the initial photoacoustic pressure signal is introduced into the second-stage acoustic resonance structure to resonate and amplify the acoustic wave of a specific frequency, a series cascade sensitization architecture of light absorption enhancement and acoustic resonance amplification is constructed, the gains of the two-stage structures are independent of each other and can be optimized respectively, the first stage can adopt a compact design such as an optical fiber, and the second stage focuses on acoustic optimization, which balances the contradiction between high performance and system integration while breaking through the sensitivity limit, and realizes a multiplicative breakthrough in system sensitivity and a synergistic optimization in performance.

[0125] The high-sensitivity acoustic resonance detector and the wide dynamic range acoustic pressure sensor are used in parallel to synchronously collect signals, the acquired amplified acoustic signals are converted into the first electric signal and the second electric signal for mutual checking analysis, the coherence outside the preset noise analysis frequency band data is calculated, common-mode noise interference caused by environmental vibration and the like is identified and suppressed, thereby greatly improving the signal-to-noise ratio and the anti-interference ability, through intelligent signal fusion, the harmonic component extracted by the high-sensitivity detector is preferentially used in the low concentration interval to ensure the detection lower limit, and as the concentration increases, the wide linearity detector signal is mainly used for smooth transition, thereby seamlessly covering the ultra-wide dynamic range from trace to high concentration, through real-time analysis of the real-time amplitude and spectrum acquired by the second detector, feedback control parameters are adaptively generated, the wavelength modulation depth of the laser is dynamically adjusted to prevent signal saturation, and the intensity modulation frequency is finely adjusted to track the optimal resonance point of the acoustic resonance cavity, through the introduction of the dual-mode detection and intelligent feedback control mechanism, the system can automatically maintain the optimal working state, and the measurement reliability, dynamic range and adaptive ability of the system under complex working conditions are improved.

[0126] The application also provides an electronic device. The electronic device can include one or more processors and one or more memories. The memory stores computer-readable code which, when executed by the one or more processors, can perform a photoacoustic gas measurement method and system based on a series sensitization technology as described above.

[0127] The method and system according to the embodiments of the present application can also be implemented by means of the architecture of the electronic device shown in the present application. The electronic device can include a bus, one or more CPUs, ROM, RAM, a communication port connected to a network, input / output, a hard disk, etc. The storage device in the electronic device, such as the ROM or the hard disk, can store the photoacoustic gas measurement method and system based on the tandem amplification technology provided in the present application. Further, the electronic device can also include a user interface. Of course, the architecture shown in the present application is only exemplary, and when implementing different devices, one or more components of the electronic device shown in the present application can be omitted according to actual needs.

[0128] It should be noted that, in this document, the terms "first" and "second" and the like are used merely to distinguish one entity or action from another, and do not necessarily require or imply that these entities or actions occur in any temporal or chronological sequence. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by an indefinite article "a" does not exclude the existence of additional identical elements in the process, method, article, or apparatus including the element.

[0129] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A photoacoustic gas measurement method based on a series enhancement technique, characterized by, The method comprises: acquiring a target gas, generating a modulated laser based on wavelength modulation of the target gas, coupling the modulated laser to a first-stage light absorption enhancement structure, forming an N-reflection enhanced light path region inside the first-stage light absorption enhancement structure by the modulated laser, and making the target gas flow through the enhanced light path region in sequence to absorb the modulated laser energy in the enhanced light path region and generate an initial photoacoustic pressure signal proportional to the gas concentration; setting an acoustic resonance frequency of a second-stage acoustic resonance structure, configuring an intensity modulation frequency of the modulated laser to be consistent with the acoustic resonance frequency, introducing the initial photoacoustic pressure signal into the second-stage acoustic resonance structure, and performing resonance amplification on sound waves with a frequency component matching the acoustic resonance frequency based on the second-stage acoustic resonance structure to generate an amplified acoustic signal; placing a first detector and a second detector in an output region of the second-stage acoustic resonance structure, the first detector being an acoustic resonance type detector, and the second detector being a wide dynamic range sound pressure sensor, synchronously collecting the amplified acoustic signal based on the first detector and the second detector, and generating a first electric signal and a second electric signal based on the amplified acoustic signal; performing digital phase-locked processing on the first electric signal and the second electric signal, extracting a first harmonic component and a second harmonic component respectively, and generating a gas concentration value through signal fusion and mutual verification algorithm based on the first harmonic component and the second harmonic component; analyzing the second harmonic component and the second electric signal to generate a feedback control parameter, and adjusting wavelength modulation parameters of the modulated laser based on the feedback control parameter.

2. The photoacoustic gas measurement method based on the series enhancement technology according to claim 1, characterized in that, The synchronous collection of the amplified acoustic signal based on the first detector and the second detector, and the generation of the first electric signal and the second electric signal based on the amplified acoustic signal, comprise: converting the acquired amplified acoustic signal into a first raw electric signal based on the first detector, performing band-pass filtering on the first raw electric signal, and generating a first electric signal containing narrowband resonance acoustic characteristics; converting the acquired amplified acoustic signal into a second electric signal containing wideband sound pressure amplitude based on the second detector.

3. The photoacoustic gas measurement method based on the series enhancement technology according to claim 1, characterized in that, The digital phase-locked processing of the first electric signal and the second electric signal, and the extraction of the first harmonic component and the second harmonic component respectively, comprise: acquiring the intensity modulation frequency of the modulated laser as a reference frequency, performing first digital phase-locked amplification processing on the first electric signal, demodulating and outputting the amplitude of the second harmonic component as the first harmonic component; performing second digital phase-locked amplification processing on the second electric signal, demodulating and outputting the amplitude of the second harmonic component as the second harmonic component.

4. The photoacoustic gas measurement method based on the series enhancement technology according to claim 3, characterized in that, The generation of the gas concentration value through signal fusion and mutual verification algorithm based on the first harmonic component and the second harmonic component, comprise: acquiring preset noise analysis frequency band data of the first electric signal and the second electric signal outside the intensity modulation frequency of the modulated laser; calculating the coherence coefficient of the first electric signal and the second electric signal in the preset noise analysis frequency band data, and comparing the coherence coefficient with a preset coherence threshold; if the coherence coefficient exceeds the preset coherence threshold, it is determined that there is common mode noise interference, filter parameters are generated based on the preset noise analysis frequency band data, and the first harmonic component and the second harmonic component are digitally filtered before signal fusion; If the coherence coefficient does not exceed the preset coherence threshold, digital filtering is not performed, and signal fusion of the first harmonic component and the second harmonic component is directly performed.

5. The photoacoustic gas measurement method based on the series enhancement technology according to claim 4, characterized in that, The gas concentration value is generated by the signal fusion and mutual verification algorithm, including: The amplitude of the first harmonic component is obtained as a main concentration calculation value, and the amplitude of the second harmonic component is obtained as a reference concentration calculation value. First and second concentration thresholds are set, and the first concentration threshold is smaller than the second concentration threshold. The numerical relationship between the main concentration calculation value and the first and second concentration thresholds is judged to generate a judgment result, and a final concentration calculation value is generated based on the judgment result. The final concentration calculation value is multiplied by a preset system calibration coefficient to obtain a final output gas concentration value.

6. The photoacoustic gas measurement method based on the series enhancement technology according to claim 5, characterized in that, The final concentration calculation value is generated based on the judgment result, including: When the judgment result is that the main concentration calculation value is less than the first concentration threshold, the main concentration calculation value is used as the final concentration calculation value; When the judgment result is that the main concentration calculation value is greater than the second concentration threshold, the reference concentration calculation value is used as the final concentration calculation value; When the judgment result is that the main concentration calculation value is between the first and second concentration thresholds, the main concentration calculation value and the reference concentration calculation value are linearly weighted and summed, and the sum result is used as the final concentration calculation value.

7. The photoacoustic gas measurement method based on the series enhancement technology according to claim 1, characterized in that, The second harmonic component and the second electric signal are analyzed to generate a feedback control parameter, and the wavelength modulation parameter of the modulation laser is adjusted based on the feedback control parameter, including: The real-time amplitude of the second harmonic component is obtained, and the real-time amplitude is compared with a preset amplitude threshold to generate a depth adjustment parameter; The second electric signal is subjected to frequency spectrum analysis, the current optimal resonance frequency of the second-order acoustic resonance structure is identified, and the current optimal resonance frequency is compared with the intensity modulation frequency of the modulation laser to generate a frequency adjustment parameter; The wavelength modulation parameter includes the wavelength modulation depth and the intensity modulation frequency, the wavelength modulation depth of the modulation laser is adjusted based on the depth adjustment parameter, and the intensity modulation frequency of the modulation laser is adjusted based on the frequency adjustment parameter.

8. A photoacoustic gas measurement system based on a tandem enhancement technique, characterized by The system includes: A tunable laser source module for generating a modulation laser based on a target gas by wavelength modulation; A series cascade sensitization module for receiving a target gas and coupling the modulation laser to a first-order light absorption enhancement structure, the modulation laser forming an N-reflection enhanced light path region inside the first-order light absorption enhancement structure, the target gas flowing through the enhanced light path region in turn to absorb the modulation laser energy in the enhanced light path region and generate an initial photoacoustic pressure signal proportional to the gas concentration, the acoustic resonance frequency of a second-order acoustic resonance structure being set, the intensity modulation frequency of the modulation laser being configured to be consistent with the acoustic resonance frequency, and the initial photoacoustic pressure signal being introduced into the second-order acoustic resonance structure to generate an amplified acoustic signal based on the second-order acoustic resonance structure resonating and amplifying the sound wave with a frequency component matching the acoustic resonance frequency. The dual-mode detection module sets the first detector and the second detector at the output area of the second-stage acoustic resonance structure, the first detector is an acoustic resonance type detector, the second detector is a wide dynamic range sound pressure sensor, and the amplified acoustic signal is synchronously collected based on the first detector and the second detector, and the first electric signal and the second electric signal are generated based on the amplified acoustic signal; The signal processing and feedback control module is used for performing digital phase-locked processing on the first electric signal and the second electric signal, extracting the first harmonic component and the second harmonic component respectively, generating the gas concentration value through a signal fusion and mutual checking algorithm based on the first harmonic component and the second harmonic component, performing analysis on the second harmonic component and the second electric signal to generate a feedback control parameter, and adjusting the wavelength modulation parameter of the modulated laser based on the feedback control parameter.

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