Gas sensor based on Fano resonance and gas detection method thereof

Abstract

The invention discloses a gas sensor based on Fano resonance and a gas detection method thereof. The gas sensor is composed of a phononic crystal circular thin plate, a circular piezoelectric plate, a rectangular gas cavity and a barometer. The front surface and the back surface of the rectangular air cavity are open and are fixed with acrylic plates; round holes are formed in a left side plate and a right side plate of the rectangular air cavity, the two round holes are fixedly sealed by round photonic crystal thin plates, and a round piezoelectric plate is adhered to the outer surface of the round photonic crystal thin plate on one side; barometers are fixed on the inner surfaces of top plates of the rectangular air cavities. The normal frequency of gas to be measured in the rectangular gas cavity in the left-right direction of the rectangular gas cavity is close to the normal frequency of the gas to be measured in the height direction of the rectangular gas cavity, so that two normal modes appear and are coupled to generate Fano resonance, and after the signal generator emits frequency sweep excitation, the sound pressure is measured through the barometer to obtain the sound pressure spectrum in the rectangular gas cavity. Therefore, the gas components are judged.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, in particular to a gas sensor and a gas detection method thereof based on Fano resonance formed by coupling of a phononic crystal and an acoustic cavity normal mode. Background Art

[0002] In recent years, with the continuous expansion of industrial production, exhaust gas composition monitoring has become a top priority in the field of environmental protection. Traditional gas detection instruments such as spectrometers and chromatographs are costly, bulky, and inconvenient to move. Phononic crystal sensors have the characteristics of low cost, simple structure, and good portability, but the Q value of phononic crystal sensors is low, and it is difficult to accurately distinguish subtle changes in gas composition. Therefore, it is necessary to develop a gas sensor that is low in cost, simple in structure, easy to carry, and can be used to monitor gas composition. Summary of the invention

[0003] The present invention proposes a gas sensor based on Fano resonance and a gas detection method thereof, which realizes that two normal modes of gas appear at similar frequencies and forms Fano resonance, thereby achieving different response frequencies for gases with different densities and sound propagation speeds.

[0004] The present invention discloses a gas sensor based on Fano resonance, which is composed of a phononic crystal circular thin plate, a circular piezoelectric piece, a rectangular air cavity and a barometer; the rectangular air cavity is made of stainless steel; the front and back of the rectangular air cavity are both open and fixed with an acrylic plate. Circular holes are opened on the left and right side plates of the rectangular air cavity, and the two circular holes are fixed and sealed with a phononic crystal circular thin plate, and a circular piezoelectric piece is adhered to the outer surface of the phononic crystal circular thin plate on one side; a barometer is fixed on the inner surface of the top plate of the rectangular air cavity.

[0005] Preferably, the lead wire of the barometer passes through an opening of a side plate of the rectangular air cavity, and the opening is sealed.

[0006] Preferably, the length of the inner wall of the rectangular air cavity is 10 cm, the height of the inner wall of the rectangular air cavity is 15 cm, and the depth of the inner wall of the rectangular air cavity is 6.5 cm.

[0007] Preferably, the acrylic plate is transparent.

[0008] Preferably, the two phononic crystal circular thin plates are completely identical and are made of aluminum.

[0009] Preferably, the diameter of the circular phononic crystal thin plate is 5 cm, which is 2 mm larger than the diameter of the circular hole, and the thickness is 3 mm.

[0010] The gas detection method of the gas sensor based on Fano resonance is as follows:

[0011] The signal generator is connected to the circular piezoelectric piece through a power amplifier. The signal generator generates a sinusoidal signal. The sinusoidal signal is amplified by the power amplifier and transmitted to the circular piezoelectric piece. The circular piezoelectric piece vibrates to form a sound wave, which is first transmitted to the circular thin plate of the phononic crystal. When passing through the junction of the circular thin plate of the phononic crystal and the gas to be measured in the rectangular air cavity, a part is reflected and the other part continues to propagate. Therefore, the vibration of the circular thin plate of the phononic crystal drives the vibration of the gas to be measured in the rectangular air cavity. The height of the inner wall of the rectangular air cavity is designed to be a multiple of half the length of the inner wall of the rectangular air cavity, so that the normal frequency of the gas to be measured in the rectangular air cavity in the left and right directions of the rectangular air cavity is close to the normal frequency in the height direction of the rectangular air cavity, so that two normal modes appear and couple, generating Fano resonance. After the signal generator sends out a sweep frequency excitation, the sound pressure is measured by a barometer to obtain the sound pressure spectrum in the rectangular air cavity, so as to judge the gas composition.

[0012] Preferably, the gas to be measured in the rectangular air cavity vibrates at the normal frequency in the left and right directions of the rectangular air cavity. When the sound waves continue to be transmitted to the junction of the gas to be measured in the rectangular air cavity and the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece, most of them are reflected, and a small part is transmitted to the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece. Then, most of the sound waves transmitted to the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece are output.

[0013] Preferably, when the composition of the gas to be measured changes, the density and sound propagation speed of the gas to be measured change, the relative impedance between the circular thin plate of the phononic crystal and the gas to be measured changes, and the normal frequency of the gas to be measured in the rectangular air cavity also changes, causing changes in the frequency of occurrence and width of the resonance peak.

[0014] Preferably, the thickness of the top plate and the bottom plate of the rectangular air cavity is changed to change the relative impedance of the top plate and the bottom plate to the gas to be measured, thereby changing the propagation law of the sound wave at the top plate and the bottom plate; the larger the relative impedance, the sharper the resonance peak formed, and the higher the Q value of the gas sensor.

[0015] Beneficial effects of the present invention:

[0016] 1. The present invention uses a combination of phononic crystal and air cavity to excite Fano resonance, so that the sensor has an extremely high Q value and high sensitivity, and can produce a significant output response under extremely small input changes, which is significantly improved compared with the traditional phononic crystal sensor performance. After the signal generator emits a sweep frequency (for example, from 1kHz to 5kHz) excitation, the present invention measures the sound pressure by installing a barometer at the midpoint of the top of the air cavity to obtain the sound pressure spectrum in the air cavity, so as to judge the sound propagation speed and density of the gas to be measured, and then obtain the composition of the gas.

[0017] 2. The phononic crystal used in the present invention is an aluminum plate and the rectangular air cavity is stainless steel, both of which are easy to obtain and process, and the material cost is low. The overall cost is lower than that of gas identification instruments such as chromatographs. The present invention is simple to operate, has a long service life, and can be used multiple times. The present invention is small in size, light in weight, and easy to carry, and is suitable for gas detection in multiple scenarios such as chemical plants and laboratories. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 For the present invention Figure 1 The sound pressure spectrum diagram in the rectangular air cavity when the gas to be tested is air and the excitation makes the air vibrate at the normal frequency.

[0020] Figure 3 For the present invention Figure 1 The sound pressure spectrum in the rectangular air cavity when the gas to be tested is carbon dioxide and the carbon dioxide is excited to vibrate at the normal frequency.

[0021] Figure 4 To increase Figure 1 The thickness of the top and bottom plates of the rectangular air cavity, the sound pressure spectrum in the rectangular air cavity when the gas to be measured is air and the excitation makes the air vibrate at the normal frequency.

[0022] Figure 5 for Figure 4 Sound pressure distribution diagram in the rectangular air cavity corresponding to the narrow resonance peak in the rectangular air cavity sound pressure spectrum diagram.

[0023] Figure 6 for Figure 4 Sound pressure distribution diagram in the rectangular air cavity corresponding to the wide resonance peak in the rectangular air cavity sound pressure spectrum diagram. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] like Figure 1As shown, a gas sensor based on Fano resonance is composed of a phononic crystal circular thin plate 1, a circular piezoelectric piece, a rectangular air cavity 2 and a barometer (the lead of the barometer passes through the opening of the side plate of the rectangular air cavity, and the opening is sealed). The front and back of the rectangular air cavity are open and fixed with a transparent acrylic plate. The length of the inner wall of the rectangular air cavity is 10 cm, the height of the inner wall of the rectangular air cavity is 15 cm, and the depth of the inner wall of the rectangular air cavity is 6.5 cm; the rectangular air cavity is made of stainless steel. There are circular holes on the left and right side plates of the rectangular air cavity, and the two circular holes are fixed and sealed with phononic crystal circular thin plates, and a circular piezoelectric piece is adhered to the outer surface of the phononic crystal circular thin plate on one side; the two phononic crystal circular thin plates are exactly the same, made of aluminum, with a diameter of 5 cm, 2 mm larger than the diameter of the circular hole, and a thickness of 3 mm; a barometer is fixed on the inner surface of the top plate of the rectangular air cavity.

[0026] The gas detection method of the gas sensor based on Fano resonance is as follows:

[0027] The signal generator is connected to the circular piezoelectric piece through a power amplifier. The signal generator generates a sinusoidal signal. The sinusoidal signal is amplified by the power amplifier and then transmitted to the circular piezoelectric piece. The circular piezoelectric piece vibrates to form a sound wave (longitudinal wave), which is first transmitted to the circular thin plate of the phononic crystal. When passing through the junction of the circular thin plate of the phononic crystal and the gas to be measured in the rectangular air cavity, a part is reflected (when the reflected sound wave passes through the junction of the circular thin plate of the phononic crystal and the sound wave attenuation area 3 in the air on the same side of the circular piezoelectric piece, a small part is reflected and continues to propagate in an oscillating attenuation manner, and most of it is transmitted to the sound wave attenuation area in the air on the same side of the circular piezoelectric piece), and the other part continues to propagate, so that the vibration of the circular thin plate of the phononic crystal drives the vibration of the gas to be measured in the rectangular air cavity. When the gas to be measured in the rectangular air cavity vibrates at the normal frequency (the resonant frequency of the gas to be measured in the rectangular air cavity), a standing wave is generated in the rectangular air cavity, forming a normal mode corresponding to the normal frequency. Since the impedance of the circular thin plate (aluminum) of the phononic crystal is much larger than that of the gas to be measured, the frequency band of the normal mode generated in the rectangular air cavity is relatively narrow, and the excitation of most frequency bands cannot cause the rectangular air cavity to generate a normal mode. However, there are relatively thick stainless steel walls on the top and bottom plates of the rectangular air cavity, so the sound waves rarely leak from the height direction of the rectangular air cavity, resulting in a narrower frequency band for the normal mode in the height direction of the rectangular air cavity. However, by designing the geometric dimensions of the rectangular air cavity (the height of the inner wall of the rectangular air cavity is a multiple of half the length of the inner wall of the rectangular air cavity), no matter what kind of gas to be measured, two normal modes can be achieved at similar frequencies. The frequency of the normal mode in the left and right directions is relatively wide, called the dark mode, and the frequency of the normal mode in the height direction of the rectangular air cavity is extremely narrow, called the bright mode. When the two normal frequencies are close, coupling can occur to produce Fano resonance, and its resonance peak has a higher Q value than that of a single normal mode. When the gas to be measured in the rectangular air cavity vibrates at the normal frequency in the left and right directions and continues to transmit the sound waves to the junction of the gas to be measured in the rectangular air cavity and the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece, most of the sound waves are reflected, and a small part is transmitted to the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece. Then, most of the sound waves transmitted to the circular thin plate of the phononic crystal continue to be transmitted to the sound wave attenuation area in the air on the opposite side of the circular piezoelectric piece.

[0028] When the composition of the gas to be measured changes, the density of the gas to be measured and the speed of sound propagation change, and the relative impedance between the circular thin plate of the phononic crystal and the gas to be measured changes; the corresponding normal frequency in the rectangular air cavity also changes, causing the frequency of the resonance peak and the width of the resonance peak to change. After the signal generator sends out a sweep frequency (for example, from 1kHz to 5kHz) excitation, the sound pressure is measured by the barometer to obtain the sound pressure spectrum in the rectangular air cavity, thereby determining the gas composition. For example, in Figure 1 Under the geometric dimensions of the circular thin plate and rectangular air cavity of the phononic crystal shown in FIG, when the gas to be measured in the rectangular air cavity is air and the air in the rectangular air cavity is excited to vibrate at the normal frequency, the sound pressure spectrum in the rectangular air cavity is as follows: Figure 2As shown, the normal frequency is about 3.43kHz. Figure 1 Under the geometric dimensions of the circular thin plate and rectangular air cavity of the phononic crystal shown in FIG, when the gas to be measured in the rectangular air cavity is carbon dioxide gas, and the carbon dioxide gas in the rectangular air cavity is excited to vibrate at the normal frequency, the sound pressure spectrum in the rectangular air cavity is as follows: Figure 3 As shown in the figure, the normal frequency is about 2.58kHz. It can be seen that the resonance peak occurrence frequency and the resonance peak width of the two are different.

[0029] In addition, by controlling the thickness of the top and bottom plates of the rectangular air cavity, the relative impedance of the top and bottom plates to the gas to be measured can be changed, thereby changing the propagation law of the sound wave at the top and bottom plates. The larger the relative impedance, the sharper the resonance peak, and the higher the Q value of the gas sensor of the present invention. For example, keeping Figure 1 When the other geometric dimensions of the circular thin plate and rectangular air cavity of the phononic crystal shown in the figure remain unchanged and only the thickness of the top plate and the bottom plate of the rectangular air cavity is increased, the resonance peak ratio of the air in the rectangular air cavity is Figure 2 The resonance peak of the air in the middle rectangular air cavity is sharper, e.g. Figure 4 As shown, at this time, the Q value of the gas sensor is higher than Figure 2 Q value of the gas sensor.

[0030] like Figure 4 In the rectangular air cavity sound pressure spectrum shown in the figure, the corresponding sound pressure distribution in the rectangular air cavity when the excitation frequency is at the narrow resonance peak (3433.98Hz) is as follows Figure 5 As shown, the sound pressure distribution in the rectangular air cavity corresponding to the broad resonance peak (3434.02Hz) is as follows Figure 6 As shown, it can be seen that in the case of narrow resonance peak, the Fano resonance of the air in the rectangular air cavity is mainly reflected in the height direction of the rectangular air cavity to form a normal mode. In the case of wide resonance peak, the Fano resonance of the air in the rectangular air cavity is mainly reflected in the left and right directions of the rectangular air cavity to form a normal mode.

Claims

1. A gas sensor based on Fano resonance, characterized in that: The device is composed of a phononic crystal circular thin plate, a circular piezoelectric piece, a rectangular air cavity and a barometer; the rectangular air cavity is made of stainless steel; the front and back of the rectangular air cavity are open and fixed with acrylic plates; circular holes are opened on the left and right side plates of the rectangular air cavity, and the two circular holes are fixed and sealed with a phononic crystal circular thin plate, and a circular piezoelectric piece is adhered to the outer surface of the phononic crystal circular thin plate on one side; a barometer is fixed on the inner surface of the top plate of the rectangular air cavity.

2. A gas sensor based on Fano resonance according to claim 1, characterized in that: The lead wire of the barometer passes through the opening of the side plate of the rectangular air cavity, and the opening is sealed.

3. A gas sensor based on Fano resonance according to claim 1, characterized in that: The length of the inner wall of the rectangular air cavity is 10 cm, the height of the inner wall of the rectangular air cavity is 15 cm, and the depth of the inner wall of the rectangular air cavity is 6.5 cm.

4. A gas sensor based on Fano resonance according to claim 1, characterized in that: The acrylic plate is transparent.

5. A gas sensor based on Fano resonance according to claim 1, characterized in that: The two phononic crystal circular plates are identical and made of aluminum.

6. A gas sensor based on Fano resonance according to claim 1, characterized in that: The diameter of the circular phononic crystal thin plate is 5 cm, which is 2 mm larger than the diameter of the circular hole, and the thickness is 3 mm.

7. A gas detection method of a gas sensor based on Fano resonance according to any one of claims 1 to 6, characterized in that: The method is as follows: The signal generator is connected to the circular piezoelectric piece via a power amplifier. The signal generator generates a sinusoidal signal. The sinusoidal signal is amplified by the power amplifier and then transmitted to the circular piezoelectric piece. The circular piezoelectric piece vibrates to form a sound wave, which is first transmitted to the phononic crystal circular thin plate. When passing through the junction of the phononic crystal circular thin plate and the gas to be measured in the rectangular air cavity, a part is reflected and the other part continues to propagate, so that the vibration of the phononic crystal circular thin plate drives the gas to be measured in the rectangular air cavity to vibrate; the height of the inner wall of the rectangular air cavity is designed to be a multiple of half the length of the inner wall of the rectangular air cavity, so that the normal frequency of the gas to be measured in the rectangular air cavity in the left and right directions of the rectangular air cavity is close to the normal frequency in the height direction of the rectangular air cavity, so that two normal modes appear and couple, and Fano resonance is generated; after the signal generator sends out a sweep frequency excitation, the sound pressure is measured by a barometer to obtain the sound pressure spectrum in the rectangular air cavity, so as to judge the gas composition.

8. A gas detection method of a gas sensor based on Fano resonance according to claim 7, characterized in that: The gas to be measured in the rectangular air cavity vibrates at the normal frequency in the left and right directions of the rectangular air cavity. When the sound waves continue to be transmitted to the junction of the gas to be measured in the rectangular air cavity and the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece, most of them are reflected, and a small part is transmitted to the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece. Then, most of the sound waves transmitted to the circular thin plate of the phononic crystal on the opposite side of the circular piezoelectric piece are output.

9. A gas detection method of a gas sensor based on Fano resonance according to claim 7, characterized in that: When the composition of the gas to be measured changes, the density and sound propagation speed of the gas to be measured change, the relative impedance between the circular thin plate of the phononic crystal and the gas to be measured changes, and the normal frequency of the gas to be measured in the rectangular air cavity also changes, causing changes in the frequency and width of the resonance peak.

10. A gas detection method of a gas sensor based on Fano resonance according to claim 7, characterized in that: Changing the thickness of the top and bottom plates of the rectangular air cavity changes the relative impedance between the top and bottom plates and the gas to be measured, thereby changing the propagation law of sound waves at the top and bottom plates; the larger the relative impedance, the sharper the resonance peak, and the higher the Q value of the gas sensor.

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