Indirect type universal photoacoustic gas concentration sensor and application thereof

Abstract

The invention relates to an indirect type universal photoacoustic gas concentration sensor and application thereof, and belongs to the technical field of sensors. The sensor comprises a sound pressure detection unit, a light wave generation unit, a sound pressure detector, a light source and a micro-ring resonator, the sound pressure detector and the light wave generation unit are arranged in the sound pressure detection unit, and the light source and the micro-ring resonator are arranged in the light wave generation unit. The micro-ring resonator of which the refractive index is changed by heating is arranged behind the light source, so that the change of the wavelength of the detection light is realized, and the concentration detection of various gases is further realized; meanwhile, through an indirect measurement method, the contact between the sound pressure detector and various gases is avoided, and the reliability of the sensor is improved.

Description

Technical Field

[0001] The invention relates to an indirect universal photoacoustic gas concentration sensor and application thereof, belonging to the technical field of sensors. Background Art

[0002] Gas concentration detection has a wide range of applications in environmental monitoring, industrial safety, medical diagnosis and other fields. Most of the current gas detection methods rely on the absorption characteristics of a light source with a specific wavelength and the gas to be tested. In traditional gas concentration sensors based on the photoacoustic effect, light of a specific wavelength is used to irradiate the gas sample. Different gases have specific absorption characteristics for light of different wavelengths. When gas molecules absorb light energy, they undergo temperature changes, resulting in periodic expansion and contraction of the gas volume. This periodic expansion and contraction generates sound waves in the gas. Highly sensitive microphones or piezoelectric sensors are used to detect and measure the intensity of these sound waves. The intensity of the sound waves is proportional to the concentration of the gas, but this type of gas concentration detector will inevitably produce the following problems:

[0003] First, the stability of the light source is very high: the environment in which the photoacoustic gas concentration sensor is located is very complex. Under the influence of internal gas flow, the temperature of the light source will change, resulting in unstable wavelength of the light source, affecting the absorption of specific wavelengths by specific gases.

[0004] Second, it can only measure the concentration of a single type of gas: The principle of traditional photoacoustic gas concentration sensors is based on the photoacoustic effect produced by the absorption of light of a specific wavelength by a specific gas to achieve detection. However, when the gas composition becomes complex and one wants to detect new specific gases by changing the specific wavelength of light, the system becomes complex and there is no way to directly adjust the wavelength of the light source.

[0005] Third, background noise has a great influence on the measurement results: since the photoacoustic measurement method is used to measure the gas concentration, it is inevitable to measure the sound generated by the photoacoustic effect, but the background noise has a great influence on the measurement results, and the traditional photoacoustic concentration sensor has a poor shielding effect against external noise. For this reason, the present invention is proposed. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides an indirect universal photoacoustic gas concentration sensor, in which a microring resonator whose refractive index is changed by heating is arranged behind a light source, so as to change the wavelength of the detection light and further realize the detection of the concentrations of various types of gases; at the same time, through the indirect measurement method, the contact between the acoustic pressure detector and various gases is avoided, thereby improving the reliability of the sensor.

[0007] The present invention also provides application of the above-mentioned indirect universal photoacoustic gas concentration sensor.

[0008] The technical solution of the present invention is as follows:

[0009] An indirect universal photoacoustic gas concentration sensor comprises a sound pressure detection unit, a light wave generating unit, a sound pressure detector, a light source and a microring resonator, wherein the sound pressure detection unit is provided with a sound pressure detector and a light wave generating unit, and the light wave generating unit is provided with a light source and a microring resonator.

[0010] Preferably according to the present invention, the sound pressure detection unit includes a first substrate, a first shell and a separation membrane, the first substrate is sealed with the first shell on the upper side, the separation membrane is arranged in the middle of the first shell, the separation membrane divides the interior of the first shell into a first air chamber and a second air chamber, the first air chamber is provided with a sound pressure detector, the second air chamber side wall is provided with air holes, and the second air chamber is provided with a light wave generating unit.

[0011] Preferably according to the present invention, a sound insulation layer is provided on the outside of the first shell, the number of air holes is at least 1, and the shape is circular, polygonal or other irregular shapes, without limitation, and a waterproof breathable membrane is provided on the outside of the air hole.

[0012] Preferably, according to the present invention, the waterproof and breathable membrane is a molecular sieve membrane having the function of screening molecules, and the separation membrane is an inorganic or organic membrane that is opaque and has good ductility and strength.

[0013] Preferably according to the present invention, the light wave generating unit includes a second substrate, a second shell and a light-transmitting sheet, the second substrate is fixed on the first substrate, a second shell is arranged on the upper side of the second substrate, a light source is arranged in the middle of the second substrate, a micro-ring resonator is fixed above the light source, and a light-transmitting sheet is arranged on the second shell above the micro-ring resonator.

[0014] Preferably, according to the present invention, the microring resonator includes a substrate, a linear waveguide, a ring waveguide and a heater, two linear waveguides are arranged in parallel on the substrate, the two linear waveguides are used to input and output optical signals, a ring waveguide is arranged on the substrate between the two linear waveguides, the ring waveguide is used for optical wave resonance, and a heater is arranged on the surface of the ring waveguide. The microring resonator can use the optical resonance effect to select a specific wavelength optical signal, and the temperature of the microring resonator is changed by the heater to adjust its resonant wavelength, thereby changing the wavelength of the selected optical signal.

[0015] Preferably according to the present invention, the light source adopts a MEMS infrared light source or an LED light source. The MEMS infrared light source can emit light in the infrared band, covering the absorption peaks of most gases. The light band of the LED light source is selected according to needs.

[0016] The application of the above-mentioned indirect universal photoacoustic gas concentration sensor is as follows:

[0017] (1) preparing a microring resonator, and then assembling a sound pressure detection unit, a light wave generating unit, a sound pressure detector, a light source and a microring resonator to form a gas concentration sensor, wherein a reference gas is sealed in the first gas chamber, and the reference gas is nitrogen, air or argon;

[0018] (2) The gas enters the second air chamber through the air hole, and the light waves emitted by the light source enter the microring resonator. The light of a specific wavelength (the strongest absorption peak of the gas to be measured) is screened out by the optical resonance effect. Then, the light passes through the light-transmitting sheet and enters the second air chamber of the sound pressure detection unit. The light is absorbed by the gas to be measured, causing the pressure in the second air chamber to change, which in turn causes the pressure in the first air chamber to change. The pressure change is detected by the sound pressure detector, and the concentration of the gas to be measured is calculated.

[0019] (3) When the gas to be measured changes, the microring resonator is heated and the resonant frequency is adjusted to meet the specific wavelength selection, and then step (2) is repeated to obtain the concentration of the gas to be measured.

[0020] Preferably, according to the present invention, in step (1), the microring resonator preparation process is:

[0021] S1, forming an insulating dielectric film on one side of the substrate by thermal oxidation;

[0022] S2, depositing a functional thin film on the insulating dielectric film by using a PECVD method;

[0023] S3, using dry etching to pattern the functional film to form a linear waveguide and a ring waveguide;

[0024] S4. Depositing a heater on the annular waveguide by using a lift-off process, a sputtering-etching combination process or an evaporation-etching combination process.

[0025] According to a further preferred embodiment of the present invention, the heater is made of Al, Au or Pt, and the functional film is made of silicon, silicon nitride, silicon oxide or gallium nitride.

[0026] The beneficial effects of the present invention are:

[0027] 1. According to the absorption peak requirements of the target gas, the present invention adjusts the resonant frequency by heating the microring resonator to achieve specific wavelength selection, thereby realizing the detection of different gases.

[0028] 2. The present invention adopts an indirect measurement method to avoid direct contact of the gas to be measured with the sound pressure detector, thereby improving the reliability of the sensor.

[0029] 3. The present invention provides a sound isolation layer on the outer shell of the sound pressure detection unit, which is beneficial to eliminating the influence of environmental noise and improving the detection signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the present invention;

[0031] Figure 2 It is a schematic diagram of the structure of the light wave generating unit of the present invention;

[0032] Figure 3 The present invention is a process flow chart for preparing a microring resonator;

[0033] Figure 4 A top view of the microring resonator of the present invention;

[0034] Among them: 1-sound pressure detection unit; 2-light wave generating unit; 3-sound pressure detector; 4-light source; 5-microring resonator;

[0035] 101-first substrate; 102-first shell; 103-air hole; 104-waterproof breathable membrane; 105-sound insulation layer; 106-separation membrane; 107-first air chamber; 108-second air chamber;

[0036] 201 - second substrate; 202 - second housing; 203 - light-transmitting sheet;

[0037] 501-straight waveguide; 502-annular waveguide; 503-heater. DETAILED DESCRIPTION

[0038] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0039] Embodiment 1:

[0040] like Figure 1-2 As shown, this embodiment provides an indirect universal photoacoustic gas concentration sensor, including a sound pressure detection unit 1, a light wave generating unit 2, a sound pressure detector 3, a light source 4 and a microring resonator 5, wherein the sound pressure detection unit 1 is provided with the sound pressure detector 3 and the light wave generating unit 2, and the light wave generating unit 2 is provided with the light source 4 and the microring resonator 5.

[0041] The sound pressure detector 3 adopts a MEMS microphone in a bare chip package form. The sound pressure detection unit is provided with an ASIC chip for controlling and preamplifying the sound pressure detector, as well as components for outputting the signal of the sound pressure detector.

[0042] The sound pressure detection unit 1 includes a first substrate 101, a first shell 102 and a separation membrane 106. The first shell 102 is sealed on the upper side of the first substrate 101, and a separation membrane 106 is arranged in the middle of the first shell 102. The separation membrane 106 divides the interior of the first shell 102 into a first air chamber 107 and a second air chamber 108. A sound pressure detector is arranged in the first air chamber 107, an air hole 103 is arranged on the side wall of the second air chamber 108, and a light wave generating unit 2 is arranged in the second air chamber 108.

[0043] A sound insulation layer 105 is arranged on the outside of the first shell 102. The material of the sound insulation layer 105 is polyester fiber or porous mineral wool. The number of the air hole 103 is 1, and the shape is circular, polygonal or other irregular shapes, without limitation. A waterproof and breathable membrane 104 is arranged on the outside of the air hole 103.

[0044] The waterproof and breathable membrane 104 is a molecular sieve membrane having the function of screening molecules, and the separation membrane 106 is an inorganic or organic membrane that is opaque and has good ductility and strength.

[0045] The light wave generating unit 2 includes a second substrate 201, a second shell 202 and a light-transmitting sheet 203. The second substrate 201 is fixed on the first substrate 101. The second shell 202 is arranged on the upper side of the second substrate 201. A light source 4 is arranged in the middle of the second substrate 201. A micro-ring resonator 5 is fixedly arranged above the light source 4. A light-transmitting sheet 203 is arranged on the second shell above the micro-ring resonator 5.

[0046] The first substrate 101 and the second substrate 201 are both PCB substrates. The first shell 102 and the second shell 202 are made of the same material, which is metal or plastic.

[0047] The microring resonator 5 includes a substrate, a linear waveguide 501, a ring waveguide 502 and a heater 503. Two linear waveguides 501 are arranged in parallel on the substrate, and the two linear waveguides 501 are used to input and output optical signals. A ring waveguide 502 is arranged on the substrate between the two linear waveguides 501, and the ring waveguide 502 is used for optical wave resonance. A heater 503 is arranged on the surface of the ring waveguide. The microring resonator can use the optical resonance effect to select a specific wavelength optical signal. The temperature of the microring resonator is changed by the heater to adjust its resonant wavelength, thereby changing the wavelength of the selected optical signal.

[0048] In specific applications, a heat conductive sheet may be used to replace the heater, and the heat conductive sheet may be set on the surface of the annular waveguide by pasting or adsorption.

[0049] The light source 4 adopts a MEMS infrared light source or an LED light source. The MEMS infrared light source can emit light in the infrared band, covering the absorption peaks of most gases. The light band of the LED light source is selected according to needs.

[0050] The application of the above-mentioned indirect universal photoacoustic gas concentration sensor is as follows:

[0051] (1) preparing a microring resonator 5, and then assembling a sound pressure detection unit 1, a light wave generating unit 2, a sound pressure detector 3, a light source 4 and the microring resonator 5 to form a gas concentration sensor, wherein a reference gas is sealed in the first gas chamber 107, and the reference gas is nitrogen, air or argon;

[0052] (2) The gas enters the second air chamber 108 through the air hole, and the light wave emitted by the light source 4 enters the microring resonator 5. The light of a specific wavelength (the strongest absorption peak of the gas to be measured) is screened out by the optical resonance effect, and then enters the second air chamber 108 of the sound pressure detection unit through the light-transmitting sheet 203, and is absorbed by the gas to be measured, causing the pressure of the second air chamber 108 to change, thereby causing the pressure in the first air chamber 107 to change. The pressure change is detected by the sound pressure detector 3, and the concentration of the gas to be measured is calculated (the calculation process is the existing gas concentration derivation process, which will not be repeated);

[0053] (3) When the gas to be measured changes, the microring resonator 5 is heated to adjust the resonant frequency to meet the specific wavelength selection, and then step (2) is repeated to obtain the concentration of the gas to be measured.

[0054] Embodiment 2:

[0055] This embodiment provides an application of an indirect universal photoacoustic gas concentration sensor. The steps are as described in Embodiment 1, except that in step (1), the microring resonator preparation process is as follows:

[0056] S1, forming an insulating dielectric film on one side of the substrate by thermal oxidation;

[0057] S2, depositing a functional thin film on the insulating dielectric film by using a PECVD method;

[0058] S3, using dry etching to pattern the functional film to form a linear waveguide and a ring waveguide;

[0059] S4. Depositing a heater on the annular waveguide by using a lift-off process, a sputtering-etching combination process or an evaporation-etching combination process.

[0060] The heater material is Al, Au or Pt, and the functional film material is silicon, silicon nitride, silicon oxide or gallium nitride.

[0061] The sound pressure detector adopts a pressure sensor in a bare chip package, and a component for outputting the sound pressure detector signal is arranged on the first substrate.

[0062] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any equivalent changes made to the present invention within the protection scope of the claims of the present invention shall fall within the protection scope of the present invention.

Claims

1. An indirect universal photoacoustic gas concentration sensor, characterized in that: The invention comprises a sound pressure detection unit, a light wave generating unit, a sound pressure detector, a light source and a micro-ring resonator, wherein the sound pressure detection unit is provided with the sound pressure detector and the light wave generating unit, and the light wave generating unit is provided with the light source and the micro-ring resonator.

2. The indirect universal photoacoustic gas concentration sensor according to claim 1, characterized in that: The sound pressure detection unit includes a first substrate, a first shell and a separation membrane. The first shell is sealed on the upper side of the first substrate, and a separation membrane is arranged in the middle of the first shell. The separation membrane divides the interior of the first shell into a first air chamber and a second air chamber. A sound pressure detector is arranged in the first air chamber, air holes are arranged on the side wall of the second air chamber, and a light wave generating unit is arranged in the second air chamber.

3. The indirect universal photoacoustic gas concentration sensor according to claim 2, characterized in that: A sound insulation layer is arranged on the outside of the first shell, the number of air holes is at least one, and a waterproof breathable membrane is arranged on the outside of the air hole.

4. The indirect universal photoacoustic gas concentration sensor according to claim 3, characterized in that: The waterproof and breathable membrane is a molecular sieve membrane with the function of screening molecules, and the separation membrane is an inorganic or organic membrane that is opaque.

5. The indirect universal photoacoustic gas concentration sensor according to claim 4, characterized in that: The light wave generating unit includes a second substrate, a second shell and a light-transmitting sheet. The second substrate is fixed on the first substrate. The second shell is arranged on the upper side of the second substrate. A light source is arranged in the middle of the second substrate. A micro-ring resonator is fixed above the light source. A light-transmitting sheet is arranged on the second shell above the micro-ring resonator.

6. The indirect universal photoacoustic gas concentration sensor according to claim 5, characterized in that: The microring resonator includes a substrate, a straight waveguide, a ring waveguide and a heater. Two straight waveguides are arranged in parallel on the substrate. The two straight waveguides are used to input and output optical signals. A ring waveguide is arranged on the substrate between the two straight waveguides. The ring waveguide is used for optical wave resonance. A heater is arranged on the surface of the ring waveguide.

7. The indirect universal photoacoustic gas concentration sensor according to claim 6, characterized in that: The light source adopts MEMS infrared light source or LED light source.

8. The use of the indirect universal photoacoustic gas concentration sensor as claimed in claim 7, characterized in that: Here are the steps: (1) preparing a microring resonator, and then assembling a sound pressure detection unit, a light wave generating unit, a sound pressure detector, a light source and the microring resonator to form a gas concentration sensor, wherein a reference gas is sealed in a first gas chamber; (2) The gas enters the second air chamber through the air hole, and the light waves emitted by the light source enter the microring resonator. The light of a specific wavelength is screened out by the optical resonance effect, and then enters the second air chamber of the sound pressure detection unit through the light-transmitting sheet, where it is absorbed by the gas to be measured, causing the pressure in the second air chamber to change, thereby causing the pressure in the first air chamber to change. The pressure change is detected by the sound pressure detector, and the concentration of the gas to be measured is calculated; (3) When the gas to be measured changes, the microring resonator is heated and the resonant frequency is adjusted to meet the specific wavelength selection, and then step (2) is repeated to obtain the concentration of the gas to be measured.

9. The use of the indirect universal photoacoustic gas concentration sensor as claimed in claim 8, characterized in that: In step (1), the microring resonator preparation process is: S1, forming an insulating dielectric film on one side of the substrate by thermal oxidation; S2, depositing a functional thin film on the insulating dielectric film by using a PECVD method; S3, using dry etching to pattern the functional film to form a linear waveguide and a ring waveguide; S4. Depositing a heater on the annular waveguide by using a lift-off process, a sputtering-etching combination process or an evaporation-etching combination process.

10. The use of the indirect universal photoacoustic gas concentration sensor as claimed in claim 9, characterized in that: The heater material is Al, Au or Pt, and the functional film material is silicon, silicon nitride, silicon oxide or gallium nitride.

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