CN103411904A - Opto-acoustic gas sensing device based on polyvinylidene fluoride piezoelectric film - Google Patents

Abstract

The invention discloses a photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film. It consists of a light source (1) and a tubular acoustic resonant cavity (6) on its optical path (2), and a photoacoustic gas sensor placed at the side opening of the tubular acoustic resonant cavity (6). Demodulation components, especially the pipe length of the tubular acoustic resonant cavity (6) is 20-150 mm, the inner diameter of the tube is 3-10 mm, the opening on the side of the tubular acoustic resonant cavity (6) is a small hole (4) connected to it, The hole depth is 1.5-2.5mm, and the hole diameter is 1.5-2.5mm. The photoacoustic gas sensor is a polyvinylidene fluoride piezoelectric film (5), and the distance between the film plane and the end plane of the small hole (4) is 0.1-3mm , the output terminal is electrically connected to the input terminal of the lock-in amplifier (8) of the modulation and demodulation part through the preamplifier (7). It has the characteristics of simple structure, wide response bandwidth and stable operation, and can be widely used to detect and determine gas concentration or chemical composition.

Description

Photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film

technical field

The invention relates to a photoacoustic gas sensing device, in particular to a photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film. the

Background technique

Detecting and determining the concentration or chemical composition of gases has a wide range of applications in environmental monitoring, climate, agriculture, security, medical diagnostics, and industry. With the development of laser technology and weak signal detection technology, photoacoustic spectroscopy technology has also been developed rapidly, and photoacoustic spectroscopy technology is considered to be a spectral technology with zero background, high sensitivity and high selectivity. the

Photoacoustic spectroscopy is a unique spectroscopic technique that is different from traditional absorption spectroscopy based on the Beer-Lambert absorption law. It is a spectroscopic technique based on the photoacoustic effect. light intensity. When a light source in the molecular absorption band irradiates the sample, the sample molecules absorb light energy and transition to an excited state, and the molecules in the excited state return to the ground state through collision relaxation, and the absorbed light energy is converted into the internal energy of the molecule, and This results in an increase in the local temperature of the molecule. So when the light irradiated on the sample molecules is modulated, the local temperature of the molecules changes periodically, thus generating periodic pressure changes, namely sound waves. When people use an acoustic sensor such as a microphone to record the relationship between the acoustic signal and the wavelength of the light source, the photoacoustic spectral signal is obtained. Compared with the general traditional absorption spectroscopy technology based on the Beer-Lambert (Beer-Lambert) absorption law, photoacoustic spectroscopy has the following characteristics: First, photoacoustic spectroscopy measures the light energy absorbed by molecules, so photoacoustic spectroscopy signals It is only related to the light energy absorbed by the molecule (rather than the transmitted light intensity or reflected light intensity), so there is no signal without absorption. There is no wavelength-dependent characteristic; third, photoacoustic spectroscopy has the characteristics of good linearity and wide response range, and theoretically one calibration point is enough to reflect the sensor response characteristics; fourth, photoacoustic spectroscopy has high sensitivity and small system size, which is easy to develop into a portable Features of gas sensors. In view of these characteristics of photoacoustic spectroscopy, in addition to traditional microphone-based photoacoustic spectroscopy, new photoacoustic spectroscopy techniques continue to emerge. For example, a "quartz tuning fork enhanced photoacoustic spectroscopy gas sensing device based on an acoustic resonant cavity" is described in the Chinese invention patent specification CN101813621B published on April 25, 2012. The gas sensing device consists of a focusing lens on the laser optical path, a tubular acoustic resonant cavity whose cavity axis is coaxial with the optical path, a quartz tuning fork placed at the side opening slit of the acoustic resonant cavity, and a laser source and a quartz tuning fork. Circuit composition. Although this gas sensing device using a quartz tuning fork has the characteristics of strong anti-interference ability, because the response bandwidth of the quartz tuning fork is generally less than 5Hz, and the accuracy of the modulation frequency of the laser source is very high, the deviation should be less than 0.1Hz. When the environmental conditions of the detection - temperature, carrier gas composition, etc. change, the modulation frequency of the laser source needs to be corrected in time to ensure accurate signal output. the

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film with simple structure and wide response bandwidth. the

In order to solve the technical problem of the present invention, the adopted technical scheme is: the photoacoustic gas sensing device based on the polyvinylidene fluoride piezoelectric film consists of a light source and a tubular acoustic resonant cavity on its optical path, and a tube-shaped acoustic resonant cavity placed on the side of the tubular acoustic resonant cavity. The photoacoustic gas sensor at the opening is composed of modulation and demodulation components matched with the photoacoustic gas sensor, especially,

The tube length of the tubular acoustic resonant cavity is 20-150 mm, and the inner diameter of the tube is 3-10 mm;

The opening on the side of the tubular acoustic resonator is a small hole communicating with it, the hole depth is 1.5-2.5mm, and the hole diameter is 1.5-2.5mm;

The photoacoustic gas sensor is a polyvinylidene fluoride piezoelectric film, the distance between the film plane of the polyvinylidene fluoride piezoelectric film and the hole end plane is 0.1-3 mm, and its output terminal is connected to the modulated The input terminal of the lock-in amplifier of the demodulation part is electrically connected. the

As a further improvement of the photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film:

A focusing lens whose focal point is located at the midpoint of the tubular acoustic resonant cavity is placed on the optical path between the light source and the tubular acoustic resonant cavity. the

The light source is a laser, and its output wavelength is the light absorption wavelength of the gas to be measured. the

The tube axis of the tubular acoustic resonant cavity is coaxial with the optical axis of the optical path. the

The small hole is located at the midpoint of the tubular acoustic resonant cavity and is vertically connected to it. the

The film length of the polyvinylidene fluoride piezoelectric film is 20-30 mm, the film width is 9-19 mm, and the film thickness is 0.1-0.3 mm. the

The modulation and demodulation part is composed of an electrically connected lock-in amplifier and a function generator, wherein the output end of the function generator is respectively electrically connected to the power control end of the light source and the input end of the lock-in amplifier. the

The modulation and demodulation part is composed of an electrically connected lock-in amplifier and a chopper, wherein the aperture of the chopper is located on the optical path between the light source and the tubular acoustic resonant cavity, and the output ends of the control unit are respectively connected to the optical The input terminals of the drive motor and the lock-in amplifier are electrically connected. the

The beneficial effect relative to prior art is:

First, the structure of the tubular acoustic resonant cavity, that is, the length of the tube, the inner diameter of the tube and the depth and diameter of the small hole, make it have an excellent resonance effect in the normal pressure atmospheric environment, which is not only to achieve high detection sensitivity The foundation is laid, the structure is simple, the work is stable, and the modulation and demodulation components are easy to determine the modulation signal frequency. the

Second, polyvinylidene fluoride piezoelectric film is used as an acoustic sensor to detect photoacoustic absorption, because it has a wide frequency response characteristic and can be linearly output in the frequency range of 0.01Hz to 100MHz, so it not only makes the present invention applicable The range is quite wide, and there is no requirement for the accuracy of the light source modulation frequency, which greatly expands the application occasions and can fully meet the application requirements of specific occasions. It is also very convenient to adjust and use the modulation signal frequency of the modulation and demodulation components. Features, so that it can be widely used to detect the composition or content of gas. In addition, the polyvinylidene fluoride piezoelectric film has the advantages of good flexibility, strong drop resistance, good water resistance and high chemical stability, and the price is low, which greatly reduces the cost of manufacture, use and maintenance of the present invention. the

As a further manifestation of beneficial effects:

One is the setting of the focusing lens, which is conducive to the further improvement of the detection sensitivity. the

The second is to choose a laser whose output wavelength is the light absorption wavelength of the gas to be measured as the light source, which is easy to improve the detection sensitivity. the

The third is to choose the polyvinylidene fluoride piezoelectric film with a film length of 20-30 mm, a film width of 9-19 mm, and a film thickness of 0.1-0.3 mm, so as to facilitate its optimal matching with the small hole. the

Description of drawings

The preferred modes of the present invention will be further described in detail below in conjunction with the accompanying drawings. the

Fig. 1 is a kind of basic structure schematic diagram of the present invention. the

Fig. 2 is a schematic diagram of a basic structure when a chopper is selected as the modulator in the present invention. the

Fig. 3 is a basic topographic view of the polyvinylidene fluoride piezoelectric film used in the present invention. the

Fig. 4 is a signal spectrogram obtained when the present invention is used to measure water vapor in the atmosphere. the

Detailed ways

Referring to Figure 1, Figure 3 and Figure 4, the composition of the photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film is as follows:

The optical path 2 of the light source 1 is provided with a focusing lens 3 and a tubular acoustic resonant cavity 6 in sequence; wherein,

The light source 1 is preferably a laser, and its output wavelength is the light absorption wavelength of the gas to be measured. the

The focal point of the focusing lens 3 is located at the midpoint of the tubular acoustic resonant cavity 6 . the

The tube length of the tubular acoustic resonator 6 is preferably 30 (can be 20-150) mm, the inner diameter of the tube is preferably 5 (can be 3-10) mm, and the tube axis is coaxial with the optical axis of the optical path 2 . Its working frequency is about 5800Hz under normal pressure atmospheric environment. the

The midpoint of the tubular acoustic resonant cavity 6 is provided with a small hole 4 vertically connected to it. The hole depth of the small hole 4 is preferably 2 (can be 1.5-2.5 mm), and the hole diameter is preferably 2 (can be 1.5-2.5) mm. . the

A polyvinylidene fluoride piezoelectric film 5 is attached to the small hole 4, which is preferably the model LDT0 produced by the American Measurement Specialties company, the film length is 25 (can be 20-30) mm, and the film width is 14 (can be 9-30) mm. 19mm), film thickness of 0.2 (can be 0.1 ~ 0.3) mm finished product. The distance between the film plane of the polyvinylidene fluoride piezoelectric film 5 and the end plane of the small hole 4 is preferably 1 (may be 0.1 to 3) mm, and its output terminal passes through the preamplifier 7 and the lock-in amplifier 8 of the modulation and demodulation component. The input terminals are electrically connected. the

The modulation and demodulation part is composed of an electrically connected lock-in amplifier 8 and a function generator 9, wherein the output terminal of the function generator 9 is electrically connected to the power control terminal of the light source 1 and the input terminal of the lock-in amplifier 8 respectively. the

Modulation and demodulation components can also choose the structure shown in Figure 2. At this time, the modulation and demodulation components are composed of an electrically connected lock-in amplifier 8 and a chopper 10, wherein the diaphragm of the chopper 10 is located on the optical path 2 between the light source 1 and the tubular acoustic resonant cavity 6, and its control unit The output ends of the aperture drive motor and the input end of the lock-in amplifier 8 are electrically connected respectively. the

When using the invention to measure water vapor in the atmosphere, when the modulated laser wave absorbs the water in the atmosphere, a photoacoustic signal will be generated and the PVDF piezoelectric film 5 will be excited to vibrate, so that it will generate an electric current signal and be detected Sent to the lock-in amplifier 8, after being demodulated by the lock-in amplifier 8, the absorption signal of the water vapor is obtained, that is, the signal spectrum of the water vapor in the atmosphere as shown in FIG. 4 is obtained. the

Obviously, those skilled in the art can make various changes and modifications to the photoacoustic gas sensing device based on the polyvinylidene fluoride piezoelectric film of the present invention without departing from the spirit and scope of the present invention. In this way, if these modifications and variations to the present invention belong to the scope of the claims of the present invention and equivalent technologies thereof, the present invention is also intended to include these modifications and variations. the

Claims (8)

1. The utility model provides a photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film, by tubular acoustic resonant cavity (6) on light source (1) and its light path (2) to and arrange the photoacoustic gas sensor of tubular acoustic resonant cavity (6) side opening part in, the modem part that connects with photoacoustic gas sensor constitutes its characterized in that:

the pipe length of the tubular acoustic resonant cavity (6) is 20-150 mm, and the inner diameter of the pipe is 3-10 mm;

the opening at the side of the tubular acoustic resonant cavity (6) is a small hole (4) communicated with the tubular acoustic resonant cavity, the hole depth is 1.5-2.5 mm, and the hole diameter is 1.5-2.5 mm;

the photoacoustic gas sensor is a polyvinylidene fluoride piezoelectric film (5), the distance between the film plane of the polyvinylidene fluoride piezoelectric film (5) and the end plane of the small hole (4) is 0.1-3 mm, and the output end of the photoacoustic gas sensor is electrically connected with the input end of a phase-locked amplifier (8) of the modulation and demodulation component through a preamplifier (7).

2. A photo-acoustic gas sensing device based on polyvinylidene fluoride piezoelectric film according to claim 1, wherein a focusing lens (3) with its focus at the midpoint of the tubular acoustic resonator (6) is disposed on the optical path (2) between the light source (1) and the tubular acoustic resonator (6).

3. A photo acoustic gas sensor device based on polyvinylidene fluoride piezoelectric film according to claim 2, characterized in that the light source (1) is a laser outputting a wavelength of light absorption of the gas to be measured.

4. A photo-acoustic gas sensing device based on polyvinylidene fluoride piezoelectric film according to claim 3, characterized in that the tube axis of the tubular acoustic resonator (6) is coaxial with the optical axis of the optical path (2).

5. A photo-acoustic gas sensing device based on polyvinylidene fluoride piezoelectric film according to claim 4, characterized in that the small hole (4) is located at the midpoint of the tubular acoustic resonator (6) and is connected to it perpendicularly.

6. A photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film as set forth in claim 1, wherein the polyvinylidene fluoride piezoelectric film (5) has a film length of 20 to 30mm, a film width of 9 to 19mm and a film thickness of 0.1 to 0.3 mm.

7. A photo-acoustic gas sensing device based on polyvinylidene fluoride piezoelectric film according to claim 1, wherein the modem part is composed of a phase-locked amplifier (8) and a function generator (9) which are electrically connected, wherein the output end of the function generator (9) is electrically connected with the power control end of the light source (1) and the input end of the phase-locked amplifier (8) respectively.

8. A photoacoustic gas sensing device based on polyvinylidene fluoride piezoelectric film as in claim 1, wherein the modem means consists of electrically connected lock-in amplifier (8) and chopper (10), wherein the diaphragm of chopper (10) is located on the optical path (2) between the light source (1) and the tubular acoustic resonator (6), and the output of its control unit is electrically connected to the input of the diaphragm driving motor and lock-in amplifier (8), respectively.

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