Gas detection device and method based on 3D printing Helmholtz photoacoustic cell

Abstract

The invention relates to the technical field of photoacoustic spectrometry, in particular to a gas detection device and method based on a 3D printing Helmholtz photoacoustic cell, and is suitable for the fields with load requirements such as unmanned aerial vehicle-mounted gas monitoring platforms. In order to overcome the problems of large volume, heavy weight, complex structure and low integration level of a photoacoustic gas sensor in the prior art, the lightweight Helmholtz photoacoustic cell structure manufactured based on 3D printing comprises a sound wave generation cavity, a small-diameter connecting pipe and a detection cavity which are integrally formed, an optical reflection unit is integrated in the sound wave generation cavity, and the optical reflection unit is integrated in the detection cavity. Two concave reflectors are arranged to reflect incident light beams for 160 times, a laser, an optical fiber collimator, a pre-amplifier, a lock-in amplification circuit board, a notebook computer and a current temperature control module are arranged outside, and the concentration of gas to be detected is obtained through analysis and processing of the notebook computer.

Description

Technical Field

[0001] The present invention relates to the field of photoacoustic spectroscopy (PAS) technology, and in particular to a gas detection device and method based on a 3D-printed Helmholtz photoacoustic cell, which is suitable for fields with load requirements such as unmanned aerial vehicle (UAV)-borne gas monitoring platforms. Background Art

[0002] Due to their ease of deployment, high maneuverability, and moderate flight altitude, drone platforms have become a core technology in fields such as environmental monitoring and industrial safety, playing a particularly important role in pollution monitoring and greenhouse gas detection. Therefore, the development of highly sensitive and accurate drone-borne greenhouse gas sensing equipment is crucial for building a database of atmospheric vertical distribution prior profiles and improving an integrated sky-ground-ocean carbon monitoring network.

[0003] UAV-based gas sensing and monitoring technology enables real-time monitoring of gas concentrations over large areas by deploying gas sensors on UAV platforms. Currently, the main types of gas sensors used on UAV platforms include electrochemical sensors, semiconductor sensors, and infrared optical sensors. The first two sensors are widely used in low-sensitivity and low-precision gas monitoring tasks due to their light weight and low power consumption. However, they suffer from defects such as baseline drift, long response time, and susceptibility to interference from other gases, resulting in poor measurement accuracy. In contrast, infrared optical sensing technology, especially multi-channel sensing technology based on laser absorption spectroscopy, has become the primary technical means for greenhouse gas monitoring due to its high sensitivity, high selectivity, and rapid response. However, existing infrared optical sensors generally face problems such as large size, heavy weight, complex structure, and high platform requirements, which limit their widespread application on portable platforms such as UAVs.

[0004] Photoacoustic spectroscopy (PAS) technology has become an important technical path to solve the above problems due to its advantages of high sensitivity, low detection limit and no need for complex sample pretreatment. Photoacoustic spectroscopy measures gas concentration by utilizing the acoustic wave signals generated by gas molecules after absorbing light radiation. It not only has excellent sensitivity and selectivity, but also can perform accurate gas monitoring in complex environments. However, traditional photoacoustic spectroscopy technology usually relies on large and heavy photoacoustic cells and independent optical systems, resulting in bulky equipment that is not suitable for use on UAV platforms with strict requirements on weight, volume and integration. Most existing photoacoustic sensor designs use single-channel resonant cavities with limited signal amplification capabilities, which cannot fully meet the needs of high-sensitivity detection.

[0005] Therefore, how to use advanced integration technology to achieve the miniaturization and integration of photoacoustic spectroscopic sensors while ensuring their high sensitivity, stability and low weight has become a key technical problem that needs to be urgently solved in the field of UAV-borne gas sensors. Summary of the Invention

[0006] The present invention aims to overcome the problems of large size, heavy weight, complex structure and low integration of existing photoacoustic gas sensors. It provides a gas detection device and method based on a 3D-printed Helmholtz photoacoustic cell. The device is based on a lightweight Helmholtz photoacoustic cell structure manufactured by 3D printing, achieving lightweight, miniaturized, highly integrated and highly sensitive sensors, and is suitable for environmental gas monitoring tasks on platforms such as drones.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0008] The present invention provides a gas detection device based on a 3D printed Helmholtz photoacoustic cell, comprising a Helmholtz photoacoustic cell, a laser, a fiber collimator, a preamplifier, a phase-locked amplifier circuit board, a laptop computer, and a current and temperature control module;

[0009] The Helmholtz photoacoustic cell is formed in one step by 3D printing of high-strength lightweight materials, and includes a sound wave generating chamber and a detection chamber, which are connected by a thin-diameter connecting tube. An optical reflection unit is provided in the sound wave generating chamber, and a microphone is provided on the detection chamber.

[0010] The laser serves as a light source to emit a light beam, which passes through a fiber collimator and enters an acoustic wave generating cavity. The acoustic wave generating cavity generates an acoustic wave signal, which enters a detection cavity through a thin-diameter connecting tube. The microphone converts the acoustic wave signal into an electrical signal, which passes through a preamplifier to a phase-locked amplifier circuit board. The signal demodulated by the phase-locked amplifier circuit board is sent to a laptop computer, and the concentration of the gas to be measured is obtained through analysis and processing. The laptop computer outputs a control signal to a current and temperature control module, and the current and temperature control module outputs a modulation signal to the laser and a synchronization signal to the phase-locked amplifier circuit board.

[0011] Furthermore, the optical reflection unit includes two oppositely arranged concave reflectors. By placing two concave reflectors, the incident light beam can be reflected up to 160 times, which significantly increases the optical path, thereby enhancing the light-gas interaction and increasing the generation of sound pressure.

[0012] Furthermore, the high-strength and lightweight material is a nylon composite material or a resin composite material, which is different from traditional metal materials (the density of stainless steel is generally 7.9g / cm 3 ), the weight of the photoacoustic pool structure is reduced by at least 70%, meeting the load-bearing requirements of the UAV platform.

[0013] Furthermore, the laser uses a continuous wave fiber coupled DFB laser with a central wavelength of 1572 nm.

[0014] The present invention also provides a gas detection method based on the gas detection device, comprising the following steps:

[0015] Step 1: The laptop computer outputs a control signal to the current and temperature control module, which outputs a modulation signal to the laser. The laser outputs a laser beam of the corresponding wavelength. After being collimated by a fiber collimator, the laser beam enters the acoustic wave generating cavity in the Helmholtz photoacoustic cell.

[0016] Step 2: In the acoustic wave generating cavity, the gas molecules to be measured absorb energy from the periodically modulated laser beam, causing a photoacoustic effect, thereby generating acoustic wave signals. The microphone on the detection cavity converts these acoustic wave signals into electrical signals.

[0017] Step 3: The electrical signal passes through a preamplifier to a phase-locked amplifier circuit board, and the phase-locked amplifier circuit board demodulates the signal according to the synchronization signal from the current and temperature control module to obtain a demodulated signal.

[0018] Step 4: The demodulated signal is sent to a laptop computer, and the concentration of the gas to be measured is obtained through analysis and processing.

[0019] Furthermore, the Helmholtz photoacoustic cell is made of high-strength and lightweight materials and is formed in one step through selective laser sintering or light-curing 3D printing technology. The one-piece molding design can improve mechanical stability and vibration resistance, ensuring stable operation during flight.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. Small size and light weight, with an overall volume of no more than 30mL, suitable for a variety of small flight platforms such as drones.

[0022] 2. The optical path is greatly extended (≥159 reflections). Compared with the traditional photoacoustic cell sensing device, the photoacoustic signal intensity of the present invention is increased by 21 times, and the detection sensitivity is significantly improved.

[0023] 3. The one-piece molding structure improves the overall stability and vibration resistance, suitable for dynamic flight environments.

[0024] 4. Use 3D printing to simplify the manufacturing process, shorten the production cycle and reduce system costs;

[0025] 5. Highly integrated design reduces the difficulty of installation and debugging, improves system reliability, and facilitates mass production and application promotion.

[0026] 6. Compared with metal materials, 3D printing materials have the advantage of light weight. Compared with the photoacoustic cell made of metal materials, the weight of the photoacoustic cell made of 3D printing materials is reduced by 3 / 4. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of the Helmholtz photoacoustic cell.

[0028] Figure 2 Schematic diagram of the structure of the gas detection device based on the 3D printed Helmholtz photoacoustic cell.

[0029] Figure 3 This is a physical picture of the Helmholtz photoacoustic cell.

[0030] Figure 4 Three days of atmospheric CO2 concentration measurement data.

[0031] Figure 5 This is the 2f spectrum of 2500ppmv CO2 concentration at normal pressure.

[0032] Figure 6 This is the 2f spectrum of 380ppmvCO2 concentration at normal pressure.

[0033] Figure 7 Allan deviation stability diagram for the 380 ppmv CO2 sensor.

[0034] Figure 8 This is the CO2 concentration response linearity test chart (100-1250ppmv).

[0035] Figure 9 Resonant frequency diagram of the 3D-printed integrated Helmholtz photoacoustic cell. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical solution of the present invention, the present invention is further described below through examples.

[0037] like Figure 1-3 As shown, a gas detection device based on a 3D printed Helmholtz photoacoustic cell of this embodiment includes a Helmholtz photoacoustic cell 1, a laser 2, a fiber collimator 3, a preamplifier 4, a phase-locked amplifier circuit board 5, a laptop computer 6, and a current and temperature control module 7;

[0038] The Helmholtz photoacoustic cell 1 is formed in one step by 3D printing of high-strength lightweight materials, and includes a sound wave generating chamber 11 and a detection chamber 12, which are connected by a thin-diameter connecting tube 14. An optical reflection unit 13 is provided in the sound wave generating chamber 11, and a microphone 15 is provided on the detection chamber 12.

[0039] The optical reflection unit 13 includes two oppositely arranged concave reflection mirrors. Each concave reflection mirror has a diameter of 1 inch and a focal length of 25 mm. The distance between the concave reflection mirrors is set to 36.4 mm.

[0040] The laser 1 serves as a light source to emit a light beam, which passes through a fiber collimator 3 and enters an acoustic wave generating cavity 11. The acoustic wave generating cavity 11 generates an acoustic wave signal, which enters a detection cavity 12 through a thin-diameter connecting tube 14. The microphone 15 converts the acoustic wave signal into an electrical signal, which passes through a preamplifier 4 to a phase-locked amplifier circuit board 5. The demodulated signal of the phase-locked amplifier circuit board 5 is sent to a laptop computer 6, and the concentration of the gas to be measured (e.g., CO2) is obtained through analysis and processing. The laptop computer 6 outputs a control signal to a current and temperature control module 7, which outputs a modulation signal to the laser 2 and a synchronization signal to the phase-locked amplifier circuit board 5.

[0041] In this embodiment, the acoustic wave generating chamber 11 has a volume of 30 mL, and the diameter of the thin connecting tube 14 is 6 mm. The total weight is controlled within 50 grams, and the surface is precision polished and airtight to ensure acoustic performance. The high-strength, lightweight material is a nylon composite (such as PA12) or a resin composite.

[0042] Laser 2 uses a continuous-wave fiber-coupled DFB laser with a central wavelength of 1572 nm. According to the HITRAN 2016 database, this wavelength corresponds to the CO2 absorption line, which is not affected by other substances in the ambient air. The operating current and temperature of laser 2 are controlled by a custom-designed current-temperature control module 7. By adjusting the operating current and temperature, the wave number of the emitted laser 2 can be precisely adjusted to target 6361.25 cm -1 At this specific wavenumber, when the operating current and temperature are set to 220 mA and 30.51°C, respectively, laser 2 can provide 40 mW of single-mode radiation.

[0043] Assembling a fiber optic collimator can effectively avoid the complex optical path coupling process. By replacing the appropriate light source, highly sensitive detection of trace gases can be achieved.

[0044] Based on the above-mentioned gas detection device, a gas detection method of this embodiment includes the following steps:

[0045] Step 1: The laptop computer 6 outputs a control signal to the current and temperature control module 7, which outputs a modulation signal to the laser 2. The laser 2 outputs a laser beam of a corresponding wavelength. After being collimated by the fiber collimator 3, the laser beam enters the acoustic wave generating cavity 11 in the Helmholtz photoacoustic cell 1.

[0046] Step 2: In the acoustic wave generating cavity 11, the gas molecules to be measured absorb energy from the periodically modulated laser beam, generating a photoacoustic effect, thereby generating acoustic wave signals. The microphone 15 on the detection cavity 12 converts these acoustic wave signals into electrical signals.

[0047] Step 3: The electrical signal passes through the preamplifier 4 to the phase-locked amplifier circuit board 5, and the phase-locked amplifier circuit board (5) demodulates the signal according to the synchronization signal from the current temperature control module 7 to obtain a demodulated signal;

[0048] Step 4: The demodulated signal is sent to the laptop computer 6, and the concentration of the gas to be measured is obtained through analysis and processing.

[0049] To improve detection sensitivity, wavelength modulation technology based on second harmonic (2f) detection was employed. Laser wavelength scanning and modulation were controlled by a laptop computer 6, with the modulation signal frequency set to half the resonant frequency of the Helmholtz photoacoustic cell 1. The integration time of the detection device was set to 1 second. The phase-locked amplifier circuit board 5 demodulated the signal in 2f mode, synchronized with the synchronization signal. The equivalent noise bandwidth (ENBW) of the phase-locked amplifier circuit board 5 was set to 1.25 Hz.

[0050] To verify the performance of the lightweight Helmholtz photoacoustic cell 1, the cell was integrated into a small unmanned aerial vehicle (UAV) platform and used to conduct multi-scenario carbon monitoring experiments. A near-infrared tunable laser and a micro-phase-locked amplifier circuit board were used to achieve highly selective detection of CO2's characteristic absorption peaks. The cell measured atmospheric CO2 concentrations over a three-day period. Figure 4 The data shows CO2 concentration measurements over three days. Peaks and valleys occur after sunrise and before sunset, with an average CO2 concentration of 426.44 ± 25.37 ppmv. The peak CO2 concentration reached 500 ppmv on November 8th, attributed to vehicle emissions during the Friday evening rush hour. This provides a reliable technical means for distributed greenhouse gas monitoring in line with the dual carbon goals.

[0051] like Figure 5 As shown, the signal amplitude of the Helmholtz photoacoustic cell 1 of the present invention is increased by 21 times compared with the conventional Helmholtz photoacoustic cell. -1 Laser 2 at the CO2 absorption line, such as Figure 6 As shown in Figure 2, the detection device achieved a minimum detectable limit (MDL) of 4.5 ppmv, and the corresponding NNEA was 3.0×10 -10 cm -1 W Hz -1 / 2 .like Figure 7 As shown, an optimal detection limit of 330 ppbv was achieved within an averaging time of 48 seconds. Figure 8 As shown, the linearity of the gas sensing device is verified. Figure 9As shown, the resonant frequency of the 3D printed integrated Helmholtz photoacoustic cell was evaluated.

[0052] The foregoing shows and describes the principal features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and all variations that come within the meaning and range of equivalents of the claims are intended to be embraced therein.

[0053] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A gas detection device based on a 3D printed Helmholtz photoacoustic cell, characterized in that: It includes a Helmholtz photoacoustic cell (1), a laser (2), a fiber collimator (3), a preamplifier (4), a phase-locked amplifier circuit board (5), a laptop computer (6), and a current and temperature control module (7); The Helmholtz photoacoustic cell (1) is formed in one step by 3D printing of high-strength and lightweight materials, and comprises a sound wave generating chamber (11) and a detection chamber (12), wherein the sound wave generating chamber (11) and the detection chamber (12) are connected via a thin-diameter connecting tube (14), an optical reflection unit (13) is provided in the sound wave generating chamber (11), and a microphone (15) is provided on the detection chamber (12); The laser (1) serves as a light source to emit a light beam, which passes through an optical fiber collimator (3) and enters a sound wave generating cavity (11). The sound wave generating cavity (11) generates a sound wave signal, which enters a detection cavity (12) through a thin-diameter connecting tube (14). The microphone (15) converts the sound wave signal into an electrical signal, which passes through a preamplifier (4) to a phase-locked amplifier circuit board (5). The signal demodulated by the phase-locked amplifier circuit board (5) is sent to a laptop computer (6), and the concentration of the gas to be measured is obtained through analysis and processing. The laptop computer (6) outputs a control signal to a current and temperature control module (7), which outputs a modulation signal to the laser (2) and a synchronization signal to the phase-locked amplifier circuit board (5).

2. A gas detection device based on a 3D printed Helmholtz photoacoustic cell according to claim 1, characterized in that: The optical reflection unit (13) comprises two concave reflection mirrors arranged opposite to each other.

3. A gas detection device based on a 3D printed Helmholtz photoacoustic cell according to claim 1, characterized in that: The high-strength and lightweight material is a nylon composite material or a resin composite material.

4. A gas detection device based on a 3D printed Helmholtz photoacoustic cell according to claim 1, characterized in that: The laser (2) uses a continuous wave fiber coupled DFB laser with a central wavelength of 1572 nm.

5. A gas detection method based on the gas detection device according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: The laptop computer (6) outputs a control signal to the current and temperature control module (7), the current and temperature control module (7) outputs a modulation signal to the laser (2), the laser (2) outputs a laser beam of a corresponding wavelength, the laser beam is collimated by the optical fiber collimator (3), and then enters the acoustic wave generating cavity (11) in the Helmholtz photoacoustic cell (1); Step 2: In the acoustic wave generating cavity (11), the gas molecules to be measured absorb energy from the periodically modulated laser beam, causing a photoacoustic effect, thereby generating acoustic wave signals, and the microphone (15) on the detection cavity (12) converts these acoustic wave signals into electrical signals; Step 3: The electrical signal passes through the preamplifier (4) to the phase-locked amplifier circuit board (5), and the phase-locked amplifier circuit board (5) demodulates the signal according to the synchronization signal from the current temperature control module (7) to obtain a demodulated signal; Step 4: The demodulated signal is sent to a laptop computer (6) and analyzed and processed to obtain the concentration of the gas to be measured.

6. The gas detection method according to claim 5, characterized in that: The Helmholtz photoacoustic cell (1) is made of high-strength and lightweight materials and is formed in one step by selective laser sintering or photocuring 3D printing technology.

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