A gas sensor based on fano resonance and a gas detection method thereof

Abstract

The application discloses a kind of gas sensor based on Fano resonance and its gas detection method, and the gas sensor is composed of phononic crystal circular sheet, circular piezoelectric sheet, rectangular air cavity and barometer;The front and back of rectangular air cavity are open and fixed acrylic plate;Two circular holes are opened on the left and right side plates of rectangular air cavity, two circular holes are fixed and closed by phononic crystal circular sheet, and the outer surface of one side phononic crystal circular sheet adheres circular piezoelectric sheet;The inner surface of the top plate of rectangular air cavity is fixed with barometer.The application realizes that the normal frequency of the gas to be measured in rectangular air cavity in the left and right direction of rectangular air cavity and the normal frequency in the height direction of rectangular air cavity are close, so that two normal modes appear and coupling occurs, Fano resonance is generated, after sweep excitation is sent by signal generator, the sound pressure spectrum in rectangular air cavity is obtained by measuring sound pressure through barometer, so as to judge gas composition.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically a gas sensor and its gas detection method based on the coupling of phonon crystal and acoustic cavity normal modes to form Fano resonance. Background Technology

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

[0003] This invention proposes a gas sensor based on Fano resonance and its gas detection method, which enables the gas to exhibit two normal modes at similar frequencies and form Fano resonance, thereby generating different response frequencies for gases with different densities and sound propagation speeds.

[0004] This invention discloses a gas sensor based on Fano resonance, comprising a circular phonon crystal plate, a circular piezoelectric element, a rectangular gas cavity, and a barometer. The rectangular gas cavity is made of stainless steel. Both the front and rear of the rectangular gas cavity are open and fixed with acrylic plates. Circular holes are formed on the left and right side plates of the rectangular gas cavity, and both holes are sealed by the circular phonon crystal plate. A circular piezoelectric element is adhered to the outer surface of one side of the circular phonon crystal plate. A barometer is fixed to the inner surface of the top plate of the rectangular gas cavity.

[0005] Preferably, the barometer's lead wires pass through an opening in the side plate of the rectangular air chamber, and the opening is sealed.

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

[0007] Preferably, the acrylic sheet is transparent.

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

[0009] Preferably, the diameter of the phonon crystal circular 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 based on the Fano resonance gas sensor is as follows:

[0011] A signal generator is connected to a circular piezoelectric element via a power amplifier. The signal generator produces a sinusoidal signal, which is amplified by the power amplifier and then transmitted to the circular piezoelectric element. The piezoelectric element vibrates, generating a sound wave. This wave first travels to a circular phonon crystal plate. At the interface between the phonon crystal plate and the gas to be measured in the rectangular cavity, part of the wave is reflected, while the rest continues to propagate. Thus, the vibration of the phonon crystal plate drives the vibration of the gas to be measured in the rectangular cavity. The height of the inner wall of the rectangular cavity is designed to be a multiple of half its length. This ensures that the normal frequencies of the gas to be measured in the rectangular cavity are close to the normal frequencies in the horizontal direction and the vertical direction, resulting in two normal modes that couple and produce Fano resonance. After the signal generator sends a sweep excitation, the sound pressure is measured using a barometer to obtain the sound pressure spectrum in the rectangular cavity, thereby determining the gas composition.

[0012] Preferably, the gas to be tested in the rectangular gas cavity vibrates at the normal frequency in the left-right direction of the rectangular gas cavity. When the sound wave continues to be transmitted to the junction of the gas to be tested in the rectangular gas cavity and the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet, most of it is reflected, a small part is transmitted to the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet, and then most of the sound wave transmitted to the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet is output.

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

[0014] Preferably, the thickness of the top and bottom plates of the rectangular gas cavity is changed to alter the specific impedance between the top and bottom plates and the gas to be measured, thereby changing the propagation pattern of the sound wave at the top and bottom plates; the greater the specific impedance, the sharper the resonance peak, and the higher the Q value of the gas sensor.

[0015] The beneficial effects of this invention are:

[0016] 1. This invention employs a combination of phonon crystal and gas cavity to excite Fano resonance, resulting in a sensor with an extremely high Q value and high sensitivity. It can produce a significant output response with minimal input changes, representing a significant performance improvement over traditional phonon crystal sensors. After the signal generator emits a frequency sweep excitation (e.g., from 1kHz to 5kHz), the sound pressure spectrum within the gas cavity can be obtained by measuring the sound pressure using a barometer installed at the midpoint of the top of the gas cavity. This allows for the determination of the sound propagation speed and density of the gas being tested, thereby obtaining the gas composition.

[0017] 2. The phonon crystal used in this invention is made of aluminum plate, and the rectangular gas chamber is made of stainless steel, both of which are readily available and easy to process, resulting in low material costs and an overall cost lower than gas identification instruments such as chromatographs. This invention is simple to operate, has a long service life, and can be used multiple times. It is small in size, lightweight, and portable, making it suitable for gas detection in various scenarios such as chemical plants and laboratories. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

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

[0020] Figure 3 For the present invention in Figure 1 The sound pressure spectrum in a rectangular gas 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 gas to be measured is air, and the excitation causes the air to vibrate at the normal frequency. The sound pressure spectrum in the rectangular air cavity is shown.

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

[0023] Figure 6 for Figure 4 The sound pressure distribution within the rectangular air cavity corresponding to the broad resonance peak in the sound pressure spectrum diagram of the rectangular air cavity. Detailed Implementation

[0024] The invention will now be further described with reference to the accompanying drawings.

[0025] like Figure 1As shown, a gas sensor based on Fano resonance comprises a circular phonon crystal plate 1, a circular piezoelectric element, a rectangular gas cavity 2, and a barometer (the barometer's lead wire passes through an opening in the side plate of the rectangular gas cavity, and the opening is sealed). The front and back of the rectangular gas cavity are open and fixed with transparent acrylic plates. The length of the inner wall of the rectangular gas cavity is 10cm, the height is 15cm, and the depth is 6.5cm. The rectangular gas cavity is made of stainless steel. Circular holes are opened on both the left and right side plates of the rectangular gas cavity, and both holes are fixed and sealed by the circular phonon crystal plate. A circular piezoelectric element is adhered to the outer surface of one of the circular phonon crystal plates. The two circular phonon crystal plates are identical, made of aluminum, with a diameter of 5cm (2mm larger than the diameter of the circular hole), and a thickness of 3mm. A barometer is fixed to the inner surface of the top plate of the rectangular gas cavity.

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

[0027] A signal generator is connected to a circular piezoelectric plate via a power amplifier. The signal generator produces a sinusoidal signal, which is amplified by the power amplifier and then transmitted to the circular piezoelectric plate. The circular piezoelectric plate vibrates, forming a sound wave (longitudinal wave). This wave first travels to the phonon crystal circular plate. When it passes the boundary between the phonon crystal circular plate and the gas to be measured in the rectangular air cavity, part of it is reflected (the reflected sound wave passes through the sound wave attenuation region 3 in the air on the same side of the phonon crystal circular plate and the circular piezoelectric plate; a small portion is reflected and continues to propagate in an oscillating attenuation manner, while the majority enters the sound wave attenuation region in the air on the same side of the circular piezoelectric plate), and the other part continues to propagate. Thus, the vibration of the phonon crystal circular plate 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 its normal mode 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 the normal mode corresponding to the normal mode frequency. Because the impedance of the phonon crystal's circular thin plate (aluminum) is much greater than that of the gas being measured, the frequency band for generating normal modes within the rectangular gas cavity is narrow, and excitation in most frequency bands cannot induce normal modes in the rectangular gas cavity. Furthermore, the top and bottom plates of the rectangular gas cavity have thick stainless steel walls, resulting in minimal sound wave leakage along the height direction, leading to an even narrower frequency band for the normal modes in that direction. However, by designing the geometry of the rectangular gas cavity (the height of the inner wall is a multiple of half the length of the inner wall), it is possible to achieve two normal modes at similar frequencies regardless of the gas being measured. The normal mode in the left-right direction has a relatively wider frequency range, called the dark mode, while the normal mode in the height direction has an extremely narrow frequency range, called the bright mode. When the two normal frequencies are close, coupling occurs, producing Fano resonance, whose resonance peak has a higher Q value than a single normal mode. When the gas to be tested vibrates at its normal frequency in the left-right direction within the rectangular gas cavity, the sound waves continue to propagate to the junction between the gas to be tested within the rectangular gas cavity and the phononic crystal thin plate opposite the circular piezoelectric plate. Most of the sound waves are reflected, a small portion enters the phononic crystal thin plate opposite the circular piezoelectric plate, and then most of the sound waves that have entered the phononic crystal thin plate continue to propagate to the sound wave attenuation region in the air opposite the circular piezoelectric plate.

[0028] When the composition of the gas being tested changes, its density and the speed of sound propagation change, and the specific impedance between the phonon crystal's circular thin plate and the gas changes. The corresponding normal modes within the rectangular gas cavity also change, causing alterations in the frequency and width of the resonance peaks. After the signal generator issues a frequency sweep excitation (e.g., varying from 1kHz to 5kHz), the sound pressure spectrum within the rectangular gas cavity is obtained by measuring the sound pressure using a barometer, thus determining the gas composition. For example, in... Figure 1 Given the geometric dimensions of the circular thin plate and rectangular air cavity of the phonon crystal, when the gas to be measured in the rectangular air cavity is air, and the excitation causes the air in the rectangular air cavity to vibrate at its normal frequency, the sound pressure spectrum in the rectangular air cavity is as follows. Figure 2As shown, the normal mode frequency is approximately 3.43 kHz. For example, in... Figure 1 Given the geometric dimensions of the circular thin plate and rectangular gas cavity of the phonon crystal, when the gas to be measured in the rectangular gas cavity is carbon dioxide, and the excitation causes the carbon dioxide gas in the rectangular gas cavity to vibrate at its normal frequency, the sound pressure spectrum in the rectangular gas cavity is as follows. Figure 3 As shown, the normal mode frequency is approximately 2.58 kHz. It is evident that the frequency of the resonance peaks and the width of the resonance peaks differ between the two.

[0029] Furthermore, by controlling the thickness of the top and bottom plates of the rectangular gas cavity, the specific impedance between the top and bottom plates and the gas to be measured can be changed, thereby altering the propagation pattern of sound waves at the top and bottom plates. A higher specific impedance results in a sharper resonance peak, leading to a higher Q value for the gas sensor of this invention. For example, maintaining... Figure 1 The circular thin plate of the phonon crystal and the rectangular gas cavity are shown. With other geometric dimensions unchanged, only the thickness of the top and bottom plates of the rectangular gas cavity is increased. The resonance peak ratio of the air inside the rectangular gas cavity is... Figure 2 The resonance peaks of the air within the rectangular air cavity are sharper, such as... Figure 4 As shown, the Q value of the gas sensor is higher at this time. Figure 2 The Q value of the gas sensor.

[0030] like Figure 4 The sound pressure spectrum diagram of the rectangular air cavity shown shows the sound pressure distribution within the rectangular air cavity when the excitation frequency is at a narrow resonant peak (3433.98Hz). Figure 5 As shown, the sound pressure distribution within the rectangular air cavity corresponding to the broad resonance peak (3434.02Hz) is as follows: Figure 6 As shown, under the narrow resonance peak condition, the Fano resonance of the air in the rectangular air cavity is mainly manifested in the formation of normal modes in the height direction of the rectangular air cavity, while under the wide resonance peak condition, the Fano resonance of the air in the rectangular air cavity is mainly manifested in the formation of normal modes in the left and right directions of the rectangular air cavity.

Claims

1. A gas sensor based on Fano resonance, characterized in that: It consists of a circular phonon crystal plate, a circular piezoelectric sheet, 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; there are circular holes on the left and right side plates of the rectangular air cavity, and both circular holes are fixed and sealed by the circular phonon crystal plate, and a circular piezoelectric sheet is attached to the outer surface of one side of the circular phonon crystal plate; a barometer is fixed to the inner surface of the top plate of the rectangular air cavity. The inner wall of the rectangular air cavity has a length of 10cm, a height of 15cm, and a depth of 6.5cm. The two phonon crystal circular plates are identical and made of aluminum. The diameter of the phononic crystal circular thin plate is 5cm, which is 2mm larger than the diameter of the circular hole, and the thickness is 3mm. The height of the inner wall of the rectangular gas cavity is designed to be a multiple of half the length of the inner wall of the rectangular gas cavity. This makes the normal modes of the gas to be tested in the rectangular gas cavity in the left and right directions of the rectangular gas cavity close to the normal modes in the height direction of the rectangular gas cavity, so that two normal modes appear and couple, producing Fano resonance.

2. The gas sensor based on Fano resonance according to claim 1, characterized in that: The barometer's lead wires pass through an opening in the side plate of the rectangular air chamber, and the opening is sealed.

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

4. A gas detection method based on a Fano resonance gas sensor according to any one of claims 1 to 3, characterized in that: The method is as follows: A signal generator is connected to a circular piezoelectric element via a power amplifier. The signal generator produces a sinusoidal signal, which is amplified by the power amplifier and then transmitted to the circular piezoelectric element. The circular piezoelectric element vibrates, forming a sound wave. This wave first travels to a circular phonon crystal plate. When it passes the boundary between the circular phonon crystal plate and the gas to be measured in the rectangular air cavity, part of the wave is reflected, while the other part continues to propagate. Thus, the vibration of the circular phonon crystal plate 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. This ensures that the normal modes of the gas to be measured in the rectangular air cavity are close to the normal modes in the left-right direction and the height direction, resulting in two normal modes that couple and produce 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, thereby determining the gas composition.

5. The gas detection method based on a Fano resonance gas sensor according to claim 4, characterized in that: The gas to be tested in the rectangular gas cavity vibrates at the normal frequency in the left-right direction of the rectangular gas cavity. When the sound wave continues to be transmitted to the junction of the gas to be tested in the rectangular gas cavity and the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet, most of it is reflected, a small part is transmitted to the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet, and then most of the sound wave transmitted to the phononic crystal thin plate on the opposite side of the circular piezoelectric sheet is output.

6. The gas detection method based on a Fano resonance gas sensor according to claim 4, characterized in that: When the composition of the gas to be tested changes, the density of the gas to be tested and the speed of sound propagation change, the specific impedance between the phonon crystal circular thin plate and the gas to be tested changes, and the normal mode frequency of the gas to be tested in the rectangular gas cavity also changes, causing changes in the frequency and width of the resonance peak.

7. The gas detection method based on a Fano resonance gas sensor according to claim 4, characterized in that: Changing the thickness of the top and bottom plates of the rectangular gas cavity alters the specific impedance between the top and bottom plates and the gas being measured, thereby changing the propagation pattern of sound waves at the top and bottom plates. The greater the specific impedance, the sharper the resonance peak, and the higher the Q value of the gas sensor.

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