CN114166934A - Gas detection device and method based on graphene film-coated quartz tuning fork - Google Patents
Gas detection device and method based on graphene film-coated quartz tuning fork Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/02—Analysing fluids
- G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G—PHYSICS
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Abstract
According to the gas detection device and method based on the graphene-coated quartz tuning fork, the adopted graphene and the derivatives thereof have excellent adsorbability on characteristic gas, meanwhile, the Q value of the quartz tuning fork is extremely high, quantitative information of gas concentration can be well reflected on frequency deviation, and gas detection can be completed only by detecting the change of the resonance frequency of the quartz tuning fork. Compared with the prior art, the invention has the advantages of simple peripheral circuit, small volume and low power consumption, and can ensure better detection sensitivity; expensive and huge light sources are not needed as excitation sources, complicated and time-consuming light beam collimation is not needed, the cost is low, and the operation is simple; the quartz tuning fork with the graphene coating films and different coatings and frequency response characteristics can be connected in parallel, and multi-point remote detection of different gases can be completed through time division/frequency division. The invention has wide application prospect in the gas detection field sensitive to detection distance, monitoring range, portability and cost.
Description
Technical Field
The invention relates to the technical field of gas measurement, in particular to a gas detection device and method based on a graphene film-coated quartz tuning fork.
Background
Under the circumstances of rapid development of economy and productivity of the society, environmental pollution is increasingly serious, and various environmental deterioration problems inevitably occur in various regions around the world due to the over-standard emission of various toxic and harmful gases. Among them, gases such as methane, sulfur dioxide, nitrogen dioxide, ozone, etc. are the main causes of environmental problems such as global warming, photochemical pollution, ozone layer cavities, acid rain, etc. Therefore, qualitative and quantitative detection is carried out on various gases in the working and living environment of people, the concentration information of various gases in the surrounding atmospheric environment is mastered in real time, and the method has great significance for protecting the atmospheric environment and maintaining the life and property safety of people. Meanwhile, gas detection is widely applied in the fields of industrial processes, biomedicine and the like. For example, the insulation system of the transformer is aged in long-term operation, gases such as ethylene, acetylene, carbon monoxide and the like are generated, and the aging degree of the insulation system can be effectively reflected by detecting the gases, so that the fault of the transformer is prevented. For example, the content of ammonia gas in the respiratory gas of a patient can be detected, so that whether the patient has diabetes, liver dysfunction, cancer and other diseases can be well judged in an auxiliary manner.
The quartz tuning fork refers to a crystal oscillator made of quartz material and having a tuning fork structure, and is originally used in electronic products as a standard frequency source or a pulse signal source to provide a frequency reference. In recent years, quartz tuning forks have been widely used in the field of gas detection due to their advantages of superior mechanical and electrical characteristics, high quality factor, immunity to environmental noise, small size, low cost, etc., and most typically quartz enhanced photoacoustic spectroscopy (QEPAS). The quartz enhanced photoacoustic spectrometry technology has extremely high sensitivity and can meet the requirement of trace gas detection. However, the quartz enhanced photoacoustic spectroscopy technology generally needs to use an expensive and bulky laser as a light source to vibrate the tuning fork to realize measurement, and meanwhile, the laser has high requirements on the collimation of laser beams, so that the equipment of the technology is large in size, high in cost and inconvenient to use.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a gas detection device and method based on a graphene-coated quartz tuning fork. The technical problem to be solved by the invention is realized by the following technical scheme:
in a first aspect, the gas detection device based on the graphene-coated quartz tuning fork provided by the invention comprises the graphene-coated quartz tuning fork, a detection circuit, a digital lock-in amplifier and an upper computer;
the electrode at one end of the graphene film-coated quartz tuning fork is connected with the detection circuit, the electrode at the other end of the graphene film-coated quartz tuning fork is connected with the digital lock-in amplifier, and the graphene film-coated quartz tuning fork is used for adsorbing gas to be detected through a graphene film on the quartz tuning fork, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed; the upper computer is used for setting a sine wave frequency scanning range of the digital phase-locked amplifier; the digital phase-locked amplifier is used for generating a sine wave signal with periodically changed frequency in a scanning range to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, the detection circuit is used for amplifying the piezoelectric signal and outputting the piezoelectric signal to the digital phase-locked amplifier, the digital phase-locked amplifier is used for performing phase-locked demodulation on the amplified piezoelectric signal, and the upper computer is used for processing the piezoelectric signal after the phase-locked demodulation to obtain the gas concentration of the gas to be detected.
Optionally, the gas detection device further comprises a gas chamber, wherein the gas chamber comprises a tuning fork fixing frame, a gas inlet and a gas outlet and is used for storing gas to be detected and the graphene film-coated quartz tuning fork, so that the graphene film-coated quartz tuning fork is in a gas environment to be detected to fully contact and adsorb the gas to be detected.
Optionally, the quartz tuning fork with the graphene coating comprises a substrate quartz tuning fork and graphene, wherein the graphene coating is applied to the substrate quartz tuning fork, and the surface of the substrate quartz tuning fork is plated with an electrode.
Optionally, the Q value of the graphene-coated quartz tuning fork is not less than 5000.
Optionally, the mode of coating the substrate quartz tuning fork with the graphene includes partial coating or complete coating;
in the partial film coating mode, a graphene film is attached to the surface of a quartz tuning fork without electrodes; in all film covering modes, the surface of the quartz tuning fork substrate is completely covered by the graphene film, and a layer of insulating layer is covered between the graphene film and the surface of the quartz tuning fork electrode.
Optionally, the detection circuit includes a transimpedance amplification circuit and a capacitance compensation circuit;
the mutual impedance amplifying circuit amplifies a current signal generated by the graphene film-coated quartz tuning fork through a piezoelectric effect into a voltage signal, the capacitance compensating circuit enables the capacitance compensating circuit to be equal to the parasitic capacitance by adjusting the size of the self compensating capacitance, and enables the phase of the current flowing through the compensating capacitance to be opposite to the phase of the current flowing through the parasitic capacitance, so that the influence of the parasitic capacitance in a quartz tuning fork detection loop on a frequency effect curve is eliminated, and the signal-to-noise ratio is effectively improved.
Optionally, the digital phase-locked amplifier generates a sine wave signal with periodically changing frequency by using a Direct Digital Synthesis (DDS) technology, and uses the sine wave signal as an excitation signal of the piezoelectric effect of the graphene film-coated quartz tuning fork and a reference signal for phase-locked demodulation, and the digital phase-locked amplifier is configured to perform phase-locked demodulation on the piezoelectric signal output by the graphene film-coated quartz tuning fork according to the piezoelectric signal and the sine wave reference signal generated by the graphene film-coated quartz tuning fork, and output the demodulated piezoelectric signal.
Optionally, the upper computer is configured to control an integration time of the digital lock-in amplifier, adjust a demodulation bandwidth of the digital lock-in amplifier, set a sine wave signal frequency scanning range, receive a piezoelectric signal output after demodulation by the digital lock-in amplifier, perform signal processing on the demodulated piezoelectric signal, and obtain a type and a concentration of the gas to be detected for display.
In a second aspect, the invention provides a gas detection method based on a graphene coated quartz tuning fork, which uses the gas detection device based on a graphene coated quartz tuning fork of the first aspect, and the gas detection method includes:
the first step is as follows: placing the gas detection device based on the graphene film-coated quartz tuning fork in a background gas environment without gas to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the second step is that: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a first resonant frequency of the graphene film-coated quartz tuning fork in a background gas environment;
the third step: placing the graphene film-coated quartz tuning fork in a gas environment to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the fourth step: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a second resonance frequency of the graphene film-coated quartz tuning fork in a gas environment to be measured;
the fifth step: and the upper computer establishes a quantitative relation between the resonance frequency variation of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference value of the first resonance frequency and the second resonance frequency, so that the gas concentration detection is realized.
Optionally, the establishing a quantitative relationship between the resonance frequency variation of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference between the first resonance frequency and the second resonance frequency, and implementing the gas concentration detection includes:
calculating a resonance frequency variation between the first resonance frequency and the second resonance frequency and a mass variation of the first mass and the second mass;
establishing a change expression of the resonance frequency variation and the mass variation;
determining the concentration of the gas to be detected according to the mass variation and the variation expression;
wherein the variation expression is expressed as:
F(c)＝f1-f0＝-2f0 2M(c)/Aρv
wherein A represents the area of the tuning fork surface with piezoelectric activity, ρ is the density of the tuning fork, v is the propagation velocity of the sound wave in the tuning fork, f1Representing the second resonance frequency, f0And M (c) represents the variable quantity of the graphene film-coated quartz tuning fork from the first mass to the second mass, the first mass is the mass of the graphene film-coated quartz tuning fork after being placed in a background gas environment without the gas to be detected for a certain time, and the second mass is the mass of the graphene film-coated quartz tuning fork after being placed in the gas environment to be detected for a certain time.
According to the gas detection device and method based on the graphene-coated quartz tuning fork, the adopted graphene and the derivatives thereof have excellent adsorbability on characteristic gas, meanwhile, the Q value of the quartz tuning fork is extremely high, quantitative information of gas concentration can be well reflected on frequency deviation, and gas detection can be completed only by detecting the change of the resonance frequency of the quartz tuning fork. Compared with the prior art, the invention has the advantages of simple peripheral circuit, small volume and low power consumption, and can ensure better detection sensitivity; expensive and huge light sources are not needed as excitation sources, complicated and time-consuming light beam collimation is not needed, the cost is low, and the operation is simple; the quartz tuning fork with the graphene coating films and different coatings and frequency response characteristics can be connected in parallel, and multi-point remote detection of different gases can be completed through time division/frequency division. The invention has wide application prospect in the gas detection field sensitive to detection distance, monitoring range, portability and cost.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a schematic diagram of a gas detection device based on a graphene-coated quartz tuning fork according to an embodiment of the present invention;
FIG. 2 is a schematic view of a partially-coated graphene-coated quartz tuning fork according to an embodiment of the present invention;
fig. 3a is a schematic view of a partially-coated graphene-coated quartz tuning fork according to an embodiment of the present invention;
FIG. 3b is a schematic diagram of a partially-coated graphene-coated quartz tuning fork according to an embodiment of the present invention;
FIG. 4 is a schematic view of a partially-coated graphene-coated quartz tuning fork according to an embodiment of the present invention;
FIG. 5 is a schematic view of a quartz tuning fork with a complete film-covered graphene film according to an embodiment of the present invention;
FIG. 6 is a flowchart of a gas detection method based on a graphene-coated quartz tuning fork according to an embodiment of the present invention;
FIG. 7a is a graph showing the relationship between the mass increment of the quartz tuning fork and the gas concentration;
FIG. 7b is a graph of the resonant frequency of the tuning fork under different gas concentrations provided by an embodiment of the present invention;
FIG. 8 is a graph showing the relationship between the change in the tuning fork resonant frequency and the gas concentration according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.
Graphene is a new material prepared by british physicist in 2004. Since graphene has a high surface area, it can adsorb gas well, and thus is used for gas detection. However, the conventional graphene gas sensor detects gas by detecting resistance change of graphene based on the principle that the graphene absorbs electrons on the rear surface of gas, and the measurement scheme is susceptible to external temperature change, so that a special instrument is required to measure the resistance characteristic after adsorption, the structure is complex, and the input cost of the product is high.
As shown in fig. 1, the gas detection device based on the graphene-coated quartz tuning fork provided by the invention comprises a graphene-coated quartz tuning fork 2, a detection circuit 3, a digital lock-in amplifier 4 and an upper computer 5;
one end of the graphene-coated quartz tuning fork 2 is connected with the detection circuit 2, the other end of the graphene-coated quartz tuning fork 2 is connected with the digital lock-in amplifier 4, and the graphene-coated quartz tuning fork 2 is used for adsorbing gas to be detected through a graphene coating on the quartz tuning fork, so that the mass and the resonance frequency of the graphene-coated quartz tuning fork 2 are changed; the upper computer 5 is used for setting a sine wave frequency scanning range of the digital lock-in amplifier 4; the digital phase-locked amplifier 4 is used for generating a sine wave signal with periodically changing frequency in the scanning range to one electrode of the graphene film-coated quartz tuning fork 2, exciting the graphene film-coated quartz tuning fork 2 to vibrate through a piezoelectric effect to generate a piezoelectric signal, the detection circuit 3 is used for amplifying the piezoelectric signal and outputting the piezoelectric signal to the digital phase-locked amplifier 4, and the digital phase-locked amplifier 4 is used for performing phase-locked demodulation on the amplified piezoelectric signal; and the upper computer 5 is used for processing the piezoelectric signal demodulated by the phase lock to obtain the gas concentration of the gas to be detected.
The gas detection device further comprises a gas chamber 1, wherein the gas chamber 1 comprises a tuning fork fixing frame, a gas inlet and a gas outlet and is used for storing gas to be detected and a graphene film-coated quartz tuning fork, so that the graphene film-coated quartz tuning fork is in a gas environment to be detected to fully contact and adsorb the gas to be detected.
It is worth explaining that the tuning fork fixing frame is used for fixing the graphene film-coated quartz tuning fork, and the air chamber 1 is provided with an air outlet and an air inlet; the gas to be measured enters the gas chamber from the gas inlet, and the gas outlet is used for discharging gas.
The gas chamber is an unnecessary device and is used for storing gas to be detected and the graphene film-coated quartz tuning fork, and the graphene film-coated quartz tuning fork can be directly placed in a gas environment to be detected according to actual needs.
The graphene-coated quartz tuning fork comprises a substrate quartz tuning fork and graphene, wherein the graphene is coated on the substrate quartz tuning fork, and the surface of the substrate quartz tuning fork is plated with an electrode. The Q value of the graphene-coated quartz tuning fork is not less than 5000.
It is worth mentioning that: the surface of the tuning fork substrate is plated with electrodes for collecting electric charges generated by piezoelectric effect, and the electrode material can be good conductors such as gold, silver and the like. The type of graphene or its derivatives attached to the base tuning fork should be selected according to the type of gas to be detected. For example, carbon dioxide can be detected with alkynyl-modified graphene oxide.
In a specific embodiment, the way for coating the graphene on the substrate quartz tuning fork comprises a partial coating or a complete coating;
in the partial film coating mode, the graphene film is attached to the surface of the quartz tuning fork substrate without electrodes or is attached to an insulating layer; in all film covering modes, the surface of the quartz tuning fork substrate is completely covered by the graphene film, and a layer of insulating layer is covered between the graphene film and the surface of the quartz tuning fork electrode.
Referring to fig. 2, fig. 3a, fig. 3b and fig. 4, fig. 2, fig. 3a, fig. 3b and fig. 4 are schematic diagrams of partially coated graphene-coated quartz tuning forks at different positions of the quartz tuning forks. In the partial coating mode, the graphene film is attached to the surface of the quartz tuning fork substrate, and the graphene or the derivative thereof has conductivity, so that the graphene film is not influenced by two electrodes of the tuning fork, and the graphene film is coated on the surface of the tuning fork without the electrodes or is attached to an insulating layer. Referring to fig. 5, fig. 5 is a schematic view of a fully-coated graphene-coated quartz tuning fork. In all the film covering modes, in order to increase the surface area of the graphene film and increase the absorption of the graphene or the derivative thereof to the gas to be detected so as to improve the detection sensitivity, the surface of the base tuning fork is completely covered by the graphene film. Similarly, in order not to affect the electrodes on the tuning fork surface, an insulating layer is covered between the graphene film and the base tuning fork surface to isolate the electrodes from the graphene film by the insulating layer, and the insulating layer can be polydimethylsiloxane or the like. In addition, only the graphene film at the vibration arm position of the quartz tuning fork plays a role in gas detection, and whether the film is coated at other positions can be automatically selected according to the manufacturing process and the application scene.
In a specific embodiment, the detection circuit comprises a transimpedance amplification circuit and a capacitance compensation circuit;
the mutual impedance amplifying circuit amplifies a current signal generated by the graphene film-coated quartz tuning fork through a piezoelectric effect into a voltage signal, the capacitance compensating circuit enables the capacitance compensating circuit to be equal to the parasitic capacitance by adjusting the size of the self compensating capacitance, and enables the phase of the current flowing through the compensating capacitance to be opposite to the phase of the current flowing through the parasitic capacitance, so that the influence of the parasitic capacitance in a quartz tuning fork detection loop on a frequency effect curve is eliminated, and the signal-to-noise ratio is effectively improved.
In a specific embodiment, the digital lock-in amplifier generates a sine wave signal with a periodically changing frequency by using a Direct Digital Synthesis (DDS) technique, and uses the sine wave signal as an excitation signal of the piezoelectric effect of the graphene film-coated quartz tuning fork and a reference signal for lock-in demodulation, and the digital lock-in amplifier is configured to perform lock-in demodulation on the piezoelectric signal output by the graphene film-coated quartz tuning fork according to the piezoelectric signal and the sine wave reference signal generated by the graphene film-coated quartz tuning fork and output the demodulated piezoelectric signal.
Wherein the digital lock-in amplifier is based on a high-speed FPGA design. And the sine wave is used as an excitation signal of the piezoelectric effect of the graphene coated quartz tuning fork and a reference signal of phase-locked demodulation. The digital phase-locked amplifier can be used for phase-locked demodulation by combining the piezoelectric signal generated by the graphene film-coated quartz tuning fork and the sine wave reference signal.
In a specific implementation manner, the upper computer is configured to control an integration time of the digital lock-in amplifier, to adjust a demodulation bandwidth of the digital lock-in amplifier, and to set a sine wave signal frequency scanning range, receive a piezoelectric signal output by the digital lock-in amplifier after demodulation, perform signal processing on the demodulated piezoelectric signal, and obtain a type and a concentration of the gas to be measured for displaying.
It is worth mentioning that: the upper computer is used for controlling parameters such as the integration time of the digital lock-in amplifier, the attenuation slope of a low-pass filter in the upper computer, the sine wave frequency scanning range and the like. And meanwhile, the upper computer receives the piezoelectric signal output after the demodulation of the digital lock-in amplifier and performs signal processing, and finally displays the type and concentration of the gas to be detected.
According to the gas detection device based on the graphene-coated quartz tuning fork, the adopted graphene and the derivative thereof have excellent adsorbability on characteristic gas, meanwhile, the Q value of the quartz tuning fork is extremely high, the quantitative information of the gas concentration can be well reflected on frequency deviation, and the gas detection can be completed only by detecting the change of the resonance frequency of the quartz tuning fork. Compared with the prior art, the invention has the advantages of simple peripheral circuit, small volume and low power consumption, and can ensure better detection sensitivity; expensive and huge light sources are not needed as excitation sources, complicated and time-consuming light beam collimation is not needed, the cost is low, and the operation is simple; the quartz tuning fork with the graphene coating films and different coatings and frequency response characteristics can be connected in parallel, and multi-point remote detection of different gases can be completed through time division/frequency division. The invention has wide application prospect in the gas detection field sensitive to detection distance, monitoring range, portability and cost.
As shown in fig. 6, the gas detection method based on the graphene-coated quartz tuning fork provided by the present invention uses a gas detection device based on the graphene-coated quartz tuning fork, and the gas detection method includes:
the first step is as follows: placing the gas detection device based on the graphene film-coated quartz tuning fork in a background gas environment without gas to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the second step is that: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a first resonant frequency of the graphene film-coated quartz tuning fork in a background gas environment;
the third step: placing the graphene film-coated quartz tuning fork in a gas environment to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the fourth step: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a second resonance frequency of the graphene film-coated quartz tuning fork in a gas environment to be measured;
the fifth step: and the upper computer establishes a quantitative relation between the resonance frequency variation of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference value of the first resonance frequency and the second resonance frequency, so that the gas concentration detection is realized.
In a specific embodiment, the establishing a quantitative relationship between the variation of the resonant frequency of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference between the first resonant frequency and the second resonant frequency, and the implementing the gas concentration detection includes:
calculating a resonance frequency variation between the first resonance frequency and the second resonance frequency and a mass variation of the first mass and the second mass;
establishing a change expression of the resonance frequency variation and the mass variation;
determining the concentration of the gas to be detected according to the mass variation and the variation expression;
wherein the variation expression is expressed as:
F(c)＝f1-f0＝-2f0 2M(c)/Aρv
wherein A represents the area of the tuning fork surface having piezoelectric activity, ρ is the density of the tuning fork, and v is the acoustic wavePropagation velocity in the tuning fork, f1Representing the second resonance frequency, f0And M (c) represents the variable quantity of the graphene film-coated quartz tuning fork from the first mass to the second mass, the first mass is the mass of the graphene film-coated quartz tuning fork after being placed in a background gas environment without the gas to be detected for a certain time, and the second mass is the mass of the graphene film-coated quartz tuning fork after being placed in the gas environment to be detected for a certain time.
FIG. 7a is a graph showing the relationship between the mass increment of the quartz tuning fork and the gas concentration. According to the Freundlich equation: m (c) ═ kpn＝k(cp0)nWherein M (c) is the mass of the gas to be detected adsorbed by the graphene, p is the equilibrium partial pressure of the gas to be detected in the gas phase, and p is0Total gas pressure in gas phase environment, c ═ p/p0The relative pressure of the gas to be measured is the concentration of the gas to be measured. k and n are empirical constants, are related to graphene, the type of gas to be detected, the external temperature and the like, and need to be calibrated in advance. Therefore, according to the combination of the graph and the formula, the relationship between the graphene mass increase value and the gas can be determined to be linear, so as to obtain the concentration of the gas to be detected.
In a specific embodiment, the upper computer 5 and the digital phase-locked amplifier 4 can be connected to a plurality of graphene film-covered quartz tuning forks 2 with the same or different films and different frequency response characteristics, and the graphene film-covered quartz tuning forks 2 are placed in different gas environment detection points, so that multi-point remote detection of the same or different gases is realized by time division or frequency division.
In order to realize the concentration detection of X, Y, Z three polluted gases in three observation points of an industrial park, three groups of tuning fork arrays are selected, each group comprises one of three graphene-coated quartz tuning forks A, B, C with different frequency response characteristics, the surfaces of the three tuning forks are respectively coated with graphene or derivatives thereof which have characteristic absorption on X, Y, Z gas, and the three groups of tuning fork arrays are only connected with one digital phase-locked amplifier and an upper computer. The three tuning fork arrays are placed in an air environment without X, Y, Z three kinds of polluted gases, and the sine wave frequency scanning range of the digital lock-in amplifier is set through the upper computer. The upper computer commands the digital phase-locked amplifier to generate a set sine wave signal to the first group of tuning fork arrays at the time t1, electrodes of three graphene film-coated quartz tuning forks in the tuning fork arrays simultaneously receive the sine wave signal, one vibrating arm of the quartz tuning fork is excited by a piezoelectric effect to generate vibration with the same frequency or frequency multiplication as the sine wave, and the vibration excites the other vibrating arm to vibrate by coupling between the two vibrating arms of the tuning fork, so that piezoelectric current is generated. The piezoelectric currents generated by the three tuning forks are added and amplified into voltage signals through a detection circuit, the voltage signals are transmitted to the digital phase-locked amplifier, phase-locked demodulation is carried out by taking the sine wave as a reference signal, and quartz tuning fork piezoelectric signals with the same frequency or frequency multiplication with the sine wave are obtained. Since A, B, C three tuning forks only have response around their own resonant frequency, one sine wave frequency sweep can obtain the resonant frequencies of the three tuning forks of the first tuning fork array in the background gas environment at the same time. Finally, the resonance frequencies of A, B, C three tuning forks in the background gas were measured to be 8kHz, 16kHz, 32 kHz. Due to the manufacturing error, the resonant frequencies of tuning forks with the same size parameters can be slightly different. In order to improve the detection accuracy, the resonant frequencies of the tuning forks of the second and third tuning fork arrays under the background gas environment are obtained at the time t2 and t3 respectively by the method.
Then, the three tuning fork arrays are respectively placed in three observation points of an industrial park, X, Y, Z pollutant gases in the atmospheric environment of the observation points are respectively adsorbed by the graphene films on the surfaces of A, B, C three graphene-coated quartz tuning forks, so that the mass of the tuning forks is increased, and the resonance frequency of the tuning forks is changed, wherein the mass increase value is in positive correlation with the gas concentration. The resonance frequencies of A, B, C three graphene film-coated quartz tuning forks in the three tuning fork arrays in the gas environment to be measured can be respectively measured by adopting the method. The upper computer establishes a quantitative relation between the tuning fork resonance frequency change value and the concentration of the gas to be detected through data processing, and finally realizes the concentration detection of X, Y, Z three kinds of polluted gases in three observation points of the industrial park.
When the amplitude of the signal received by the upper computer is maximum, the frequency of the corresponding graphene film-coated quartz tuning fork is the resonance frequency. Referring to fig. 7b, a frequency plot of the graphene-coated quartz tuning fork at gas concentrations of 0ppm, 1000ppm, 2000ppm, 3000ppm, and 4000ppm in fig. 7 b.
Referring to fig. 8, fig. 8 is a graph of gas concentration versus change in resonant frequency. The gas concentration can be known from the amount of change in the resonance frequency.
According to the gas detection method based on the graphene-coated quartz tuning fork, the adopted graphene and the derivative thereof have excellent adsorbability on characteristic gas, meanwhile, the Q value of the quartz tuning fork is extremely high, the quantitative information of the gas concentration can be well reflected on frequency deviation, and the gas detection can be completed only by detecting the change of the resonance frequency of the quartz tuning fork. Compared with the prior art, the invention has the advantages of simple peripheral circuit, small volume and low power consumption, and can ensure better detection sensitivity; expensive and huge light sources are not needed as excitation sources, complicated and time-consuming light beam collimation is not needed, the cost is low, and the operation is simple; the quartz tuning fork with the graphene coating films and different coatings and frequency response characteristics can be connected in parallel, and multi-point remote detection of different gases can be completed through time division/frequency division. The invention has wide application prospect in the gas detection field sensitive to detection distance, monitoring range, portability and cost.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.
While the present application has been described in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a review of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (10)
1. A gas detection device based on a graphene film-coated quartz tuning fork is characterized by comprising a graphene film-coated quartz tuning fork, a detection circuit, a digital phase-locked amplifier and an upper computer;
the electrode at one end of the graphene film-coated quartz tuning fork is connected with the detection circuit, the electrode at the other end of the graphene film-coated quartz tuning fork is connected with the digital lock-in amplifier, and the graphene film-coated quartz tuning fork is used for adsorbing gas to be detected through a graphene film on the quartz tuning fork, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed; the upper computer is used for setting a sine wave frequency scanning range of the digital phase-locked amplifier; the digital phase-locked amplifier is used for generating a sine wave signal with periodically changed frequency in a scanning range to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, the detection circuit is used for amplifying the piezoelectric signal and outputting the piezoelectric signal to the digital phase-locked amplifier, the digital phase-locked amplifier is used for performing phase-locked demodulation on the amplified piezoelectric signal, and the upper computer is used for processing the piezoelectric signal after the phase-locked demodulation to obtain the gas concentration of the gas to be detected.
2. The gas detection device based on the graphene film-covered quartz tuning fork as claimed in claim 1, further comprising a gas chamber, wherein the gas chamber comprises a tuning fork fixing frame, a gas inlet and a gas outlet and is used for storing gas to be detected and the graphene film-covered quartz tuning fork, so that the graphene film-covered quartz tuning fork is in a gas environment to be detected to fully contact and adsorb the gas to be detected.
3. The gas detection device based on the graphene-coated quartz tuning fork of claim 1, wherein the graphene-coated quartz tuning fork comprises a base quartz tuning fork and graphene, the graphene is coated on the base quartz tuning fork, and the surface of the base quartz tuning fork is plated with an electrode.
4. The gas detection device based on the graphene coated quartz tuning fork of claim 3, wherein the Q value of the graphene coated quartz tuning fork is not less than 5000.
5. The gas detection device based on the graphene-coated quartz tuning fork as claimed in claim 3, wherein the manner of coating the substrate quartz tuning fork with graphene comprises partial coating or full coating;
in the partial film coating mode, a graphene film is attached to the surface of a quartz tuning fork without electrodes; in all film covering modes, the surface of the quartz tuning fork substrate is completely covered by the graphene film, and a layer of insulating layer is covered between the graphene film and the surface of the quartz tuning fork electrode.
6. The gas detection device based on the graphene coated quartz tuning fork of claim 1, wherein the detection circuit comprises a transimpedance amplification circuit and a capacitance compensation circuit;
the mutual impedance amplifying circuit amplifies a current signal generated by the graphene film-coated quartz tuning fork through a piezoelectric effect into a voltage signal, the capacitance compensating circuit enables the capacitance compensating circuit to be equal to the parasitic capacitance by adjusting the size of the self compensating capacitance, and enables the phase of the current flowing through the compensating capacitance to be opposite to the phase of the current flowing through the parasitic capacitance, so that the influence of the parasitic capacitance in a quartz tuning fork detection loop on a frequency effect curve is eliminated, and the signal-to-noise ratio is effectively improved.
7. The gas detection device based on the graphene coated quartz tuning fork of claim 1, wherein the digital lock-in amplifier generates a sine wave signal with a periodically changing frequency by a Direct Digital Synthesis (DDS) technique, and uses the sine wave signal as an excitation signal of a piezoelectric effect of the graphene coated quartz tuning fork and a reference signal for lock-in demodulation, and the digital lock-in amplifier is configured to perform lock-in demodulation on the piezoelectric signal output by the graphene coated quartz tuning fork according to the piezoelectric signal and the sine wave reference signal generated by the graphene coated quartz tuning fork and output the demodulated piezoelectric signal.
8. The gas detection device based on the graphene coated quartz tuning fork as claimed in claim 7, wherein the upper computer is configured to control an integration time of the digital lock-in amplifier, to adjust a demodulation bandwidth of the digital lock-in amplifier, to set a sine wave signal frequency scanning range, to receive a piezoelectric signal output after demodulation by the digital lock-in amplifier, to perform signal processing on the demodulated piezoelectric signal, to obtain a type and a concentration of a gas to be detected, and to display the type and the concentration.
9. A gas detection method based on a graphene film-covered quartz tuning fork, which is characterized in that the gas detection device based on the graphene film-covered quartz tuning fork of any one of claims 1 to 8 is used, and the gas detection method comprises the following steps:
the first step is as follows: placing the gas detection device based on the graphene film-coated quartz tuning fork in a background gas environment without gas to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the second step is that: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a first resonant frequency of the graphene film-coated quartz tuning fork in a background gas environment;
the third step: placing the graphene film-coated quartz tuning fork in a gas environment to be detected for a certain time, so that the mass and the resonance frequency of the graphene film-coated quartz tuning fork are changed;
the fourth step: setting a sine wave frequency scanning range of the digital phase-locked amplifier through the upper computer, so that the digital phase-locked amplifier generates a sine wave signal with periodically changed frequency to one electrode of the graphene film-coated quartz tuning fork, exciting the graphene film-coated quartz tuning fork to vibrate through a piezoelectric effect to generate a piezoelectric signal, obtaining the amplified piezoelectric signal through a detection circuit by the digital phase-locked amplifier, performing phase-locked demodulation and outputting to the upper computer for processing, and measuring a second resonance frequency of the graphene film-coated quartz tuning fork in a gas environment to be measured;
the fifth step: and the upper computer establishes a quantitative relation between the resonance frequency variation of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference value of the first resonance frequency and the second resonance frequency, so that the gas concentration detection is realized.
10. The gas detection method according to claim 9, wherein the establishing a quantitative relationship between the variation of the resonant frequency of the graphene-coated quartz tuning fork and the concentration of the gas to be detected according to the difference between the first resonant frequency and the second resonant frequency to realize the gas concentration detection comprises:
calculating a resonance frequency variation between the first resonance frequency and the second resonance frequency and a mass variation of the first mass and the second mass;
establishing a change expression of the resonance frequency variation and the mass variation;
determining the concentration of the gas to be detected according to the mass variation and the variation expression;
wherein the variation expression is expressed as:
F(c)＝f1-f0＝-2f0 2M(c)/Aρv
wherein A represents the area of the tuning fork surface with piezoelectric activity, ρ is the density of the tuning fork, v is the propagation velocity of the sound wave in the tuning fork, f1Representing the second resonance frequency, f0And M (c) represents the variable quantity of the graphene film-coated quartz tuning fork from the first mass to the second mass, the first mass is the mass of the graphene film-coated quartz tuning fork after being placed in a background gas environment without the gas to be detected for a certain time, and the second mass is the mass of the graphene film-coated quartz tuning fork after being placed in the gas environment to be detected for a certain time.
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