Oval photoacoustic cell for photoacoustic gas sensing detection system

Abstract

The utility model belongs to the technical field of spectral system design, and particularly relates to an elliptical photoacoustic cell for a photoacoustic gas sensing detection system, which comprises a gas inlet, a gas outlet, a light inlet and an elliptical cavity, the inner wall of the cavity is plated with a metal film, and two focuses in the elliptical cavity are respectively provided with a quartz tuning fork; the air inlet and the air outlet are located in the wall of the oval cavity, and the buffering cavity is formed in front of the air inlet. The extension line of the central axis of the light inlet just passes through the focus position of the ellipse; interdigital gaps of the two quartz tuning forks are perpendicular to the laser entering direction, and electric signals output by the two quartz tuning forks are added to form a photoacoustic signal output of the elliptical photoacoustic cell. According to the utility model, multiple reflection detection of optical and acoustic waves can be realized, the signal-to-noise ratio, the sensitivity and the detection limit of photoacoustic signals can be obviously improved, the enhancement of the optical and acoustic waves can be realized in one absorption cell, and the size of equipment can be obviously reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of spectrum system design, and in particular relates to an elliptical photoacoustic cell used in a photoacoustic gas sensing detection system. Background Art

[0002] Photoacoustic spectroscopy measures the acoustic signal generated by the thermal expansion of the gas in the absorption cell after absorbing light energy from the excited state to the ground state, that is, converting light energy into sound energy, and then detecting the signal through an acoustic sensor. This not only overcomes the wavelength response limitation of the photodetector, but is also theoretically not affected by background light. In addition, compared with photodetectors, acousto-optic sensors are usually more compact and cheaper. Among them, the most commonly used are quartz tuning fork enhanced photoacoustic spectroscopy and cantilever beam enhanced photoacoustic spectroscopy. Both essentially use mechanical resonance to increase the sensitivity of acoustic detection, that is, when the frequency of the modulated sound wave is consistent with the mechanical resonance frequency, the photoacoustic signal is the strongest.

[0003] Quartz tuning fork enhancement uses the piezoelectric effect to convert the mechanical vibration of quartz into an electrical signal when the frequency of the modulated sound wave is consistent with the resonant frequency of the tuning fork. Therefore, the quartz tuning fork can isolate external environmental noise in a large range. However, the natural frequency of the quartz tuning fork is usually fixed. For example, the commercial tuning fork is about 32.7kHz. For some molecules with slower relaxation, the photoacoustic signal will be weakened. The cantilever beam structure is a suspended cantilever structure that causes the cantilever to vibrate by detecting sound waves. Due to its simple structure, it is easy to integrate and miniaturize, and the resonant frequency can also be adjusted by adjusting the length, width and thickness of the diaphragm. In addition, the cantilever beam structure does not have to work at the resonant frequency and is more widely applicable.

[0004] Therefore, the improvement of the performance of photoacoustic spectroscopy mainly focuses on increasing the gas's absorption of laser energy and enhancing the acoustic signal. Utility Model Content

[0005] The existing photoacoustic cell structures are mainly cylindrical, circular and a small number of elliptical structures, and the photoacoustic cell mainly uses an acoustic resonance tube to enhance the photoacoustic signal. These structures have insufficient energy utilization for optics and acoustics. Therefore, in view of the shortcomings of the above-mentioned spectral technology detection, the utility model proposes an elliptical photoacoustic cell for a photoacoustic gas sensing detection system.

[0006] In order to achieve the above purpose, the following technical solutions are specifically adopted:

[0007] An elliptical photoacoustic cell for a photoacoustic gas sensing detection system comprises an air inlet, an air outlet, a light inlet and an elliptical cavity; the inner wall of the cavity is plated with a metal film, and a quartz tuning fork is placed on each of the two focal points in the elliptical cavity.

[0008] Preferably, the air inlet and the air outlet are located on the wall of the elliptical cavity.

[0009] Preferably, a buffer chamber is provided in front of the air inlet.

[0010] Preferably, an extension line of the central axis of the light inlet passes through the focus position of the ellipse.

[0011] Preferably, the interdigital gaps of the two quartz tuning forks are perpendicular to the extension line of the central axis of the light inlet.

[0012] Preferably, the electrical signals output by the two quartz tuning forks are added together to form the photoacoustic signal output by the elliptical photoacoustic cell.

[0013] By adopting the above technical solution, the utility model has the following beneficial effects:

[0014] 1. Realizing multiple reflection detection of optical and acoustic waves can significantly improve the signal-to-noise ratio, sensitivity and detection limit of photoacoustic signals.

[0015] 2. The ability to enhance optical and acoustic waves in one absorption cell can significantly reduce the size of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of an elliptical photoacoustic cell used in a photoacoustic gas sensing detection system;

[0017] Figure 2 This is a system structure diagram of an implementation example of the utility model.

[0018] In the figure: 1. light inlet; 2. air inlet; 3. air outlet; 4. elliptical cavity; 5. quartz tuning fork; 6. quartz tuning fork; 7. signal generator; 8. adder; 9. DFB laser; 10. phase-locked amplifier; 11. computer. DETAILED DESCRIPTION

[0019] The present embodiment will be further described in detail below with reference to the accompanying drawings.

[0020] Reference Figure 1 As shown, the utility model provides an elliptical photoacoustic cell for a photoacoustic gas sensing detection system, wherein an elliptical cavity 4 is machined in metal by mechanical processing, and the inner wall of the elliptical cavity 4 is plated with a metal film to achieve reflection and focusing of light and sound; a light inlet 1 is made outward at one of the focal points of the elliptical cavity 4, and the size is adjusted as needed. The light inlet 1 allows laser to enter, and is suitable for optical fiber and space light.

[0021] For example, if spatial light is used, an external lens is required for focusing, that is, a suitable lens is arranged outside the light inlet 1 so that the focus of the laser is located at the focal position of the elliptical cavity 4 after focusing.

[0022] Exemplarily, if applicable to optical fiber, the optical fiber can be directly focused to the focal position of the elliptical cavity 4 .

[0023] A quartz fork is placed at each of the two focal points of the elliptical cavity 4, and the interdigital gaps of the two quartz tuning forks are perpendicular to the direction of laser entry, i.e., the central axis of the light inlet 1, and the extension line of the central axis of the light inlet just passes through one of the quartz tuning forks 5. Two more through holes are opened on the surface of the elliptical cavity 4, an air inlet 2 and an air outlet 3. The gas in the elliptical cavity 4 absorbs laser energy to generate acoustic signals. In order to reduce the influence of air intake on the photoacoustic signal, a buffer chamber needs to be added before the air inlet 2, and the shape is not fixed.

[0024] Specifically, according to the properties of the ellipse, the rays emitted from one focus will inevitably pass through another focus. Therefore, the laser is detected once by the quartz tuning fork 5 at the first focus after entering the elliptical cavity 4. The laser and acoustic waves passing through the quartz tuning fork 5 are reflected by the inner wall of the elliptical cavity 4 and converge to the tuning fork 6 to be detected again. At the same time, the laser and acoustic waves passing through the quartz tuning fork 6 will converge to the quartz tuning fork 5 for detection. After this reciprocating process, the electrical signals output by the quartz tuning forks 5 and 6 are added together and output as the photoacoustic signal of the photoacoustic cell.

[0025] Reference Figure 2 As shown, one channel of the signal generator 7 outputs a sinusoidal signal for modulating the output of the DFB laser 9 ; and one channel outputs a sawtooth signal for realizing wavelength scanning of the DFB laser 9 .

[0026] The two channel outputs of the signal generator 7 are connected to the modulation port of the DFB laser 9 after passing through the adder 8. The output laser of the DFB laser 9 is connected to the photoacoustic cell of the utility model to excite the gas and detect the photoacoustic signal. In order to improve the signal-to-noise ratio of the signal, the sinusoidal signal of the signal generator 7 is connected to the reference signal input end of the phase-locked amplifier 10, and the sum of the output electrical signals of the two quartz tuning forks in the photoacoustic cell is connected to the signal input end of the phase-locked amplifier 10 to achieve phase-locked detection. Finally, the output signal of the phase-locked amplifier 10 is connected to the computer 11 for data storage, display and post-processing.

[0027] Optionally, the laser wavelength is determined by the absorption wavelength of the detection gas, and may be a DFB laser 9, a QCL laser, or other lasers.

[0028] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An elliptical photoacoustic cell for a photoacoustic gas sensing detection system, characterized in that: It comprises an air inlet (2), an air outlet (3), a light inlet (1) and an elliptical cavity (4); The inner wall of the elliptical cavity (4) is coated with a metal film, a quartz tuning fork is placed at each of the two focal points in the elliptical cavity (4), the light inlet (1) is formed outwardly from one of the focal points of the elliptical cavity (4), the interdigital gaps of the two quartz tuning forks are perpendicular to the central axis of the light inlet (1), and the extension line of the central axis of the light inlet (1) passes through one of the quartz tuning forks.

2. The elliptical photoacoustic cell for a photoacoustic gas sensing detection system according to claim 1, characterized in that: The air inlet (2) and the air outlet (3) are located on the wall of the elliptical cavity (4).

3. The elliptical photoacoustic cell for a photoacoustic gas sensing detection system according to claim 1, characterized in that: A buffer chamber is provided in front of the air inlet (2).

4. The elliptical photoacoustic cell for a photoacoustic gas sensing detection system according to claim 1, characterized in that: The extension line of the central axis of the light inlet (1) passes exactly through the focus position of the ellipse.

5. The elliptical photoacoustic cell for a photoacoustic gas sensing detection system according to claim 1, characterized in that: The interdigital gaps of the two quartz tuning forks are perpendicular to the extension line of the central axis of the light inlet (1).

6. The elliptical photoacoustic cell for a photoacoustic gas sensing detection system according to claim 1, characterized in that: The electrical signals output by the two quartz tuning forks are added to form the photoacoustic signal output by the elliptical photoacoustic cell.

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