CN114777905B - Low-noise thermal particle vibration velocity sensor and implementation method thereof - Google Patents
Low-noise thermal particle vibration velocity sensor and implementation method thereof Download PDFInfo
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- 230000008859 change Effects 0.000 claims abstract description 13
- 230000035945 sensitivity Effects 0.000 claims abstract description 10
- 239000000758 substrate Substances 0.000 claims description 26
- 238000002955 isolation Methods 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 239000010703 silicon Substances 0.000 claims description 3
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 3
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 2
- 239000011521 glass Substances 0.000 claims description 2
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910001120 nichrome Inorganic materials 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H11/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties
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Abstract
The invention discloses a low-noise thermal particle vibration velocity sensor and an implementation method thereof. According to the invention, an even number of temperature measuring resistors are arranged on a flow channel, and an odd number of heating resistors are arranged in the temperature measuring resistors, so that the temperature resistance coefficient TCR of the heating resistors is reduced by selecting the materials of the heating resistors, and meanwhile, the width w of the heating resistors is increased, and the equivalent thermal noise resistance of the heating resistors is reduced, so that the thermal noise of a low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced; meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity and is used for sensing micro temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved; the invention can eliminate closed loop feedback caused by resistance change and reduce low-frequency thermal noise of the sensor.
Description
Technical Field
The invention relates to a low-noise thermal particle vibration velocity sensor and an implementation method thereof.
Background
The thermal particle vibration velocity sensor is a novel acoustic vector sensor, and consists of a heating resistor and a temperature measuring resistor, wherein the heating resistor heats a medium, medium molecules vibrate under the action of sound waves, and the temperature measuring resistor directly measures the vibration velocity of acoustic particles by sensing tiny temperature disturbance. Under the condition that the structural size of the sensor is fixed, improving the heating power of the heating resistor is the most direct and effective method for improving the sensitivity of the sensor. This method has the following disadvantages:
The noise floor of a thermal particle velocity sensor is mainly derived from the thermal noise of the resistor, which is usually only related to the size and temperature of the resistor and is independent of frequency. But the heating resistor of the thermal particle vibration velocity sensor has the characteristics of high temperature resistivity and low thermal mass, so that the sensor is very sensitive to temperature disturbance. The thermal noise at the two ends of the heating resistor can cause disturbance of the heating power, and the disturbance of the heating power is fed back to the temperature to further influence the thermal noise of the resistor, so that the thermal noise of the resistor can be amplified after the closed loop feedback is formed. Especially for low-frequency disturbance, the temperature of the heating resistor can be changed along with low-frequency voltage, and at a high frequency, the temperature of the heating resistor is limited by thermal mass and is stable and is not influenced by high-frequency voltage fluctuation. Therefore, the thermal noise of the heating resistor of the thermal particle vibration velocity sensor is related to frequency, and the thermal noise generated by temperature disturbance at low frequency can rise rapidly along with the improvement of heating power, so that the improvement of the heating resistor power can not increase the signal to noise ratio of the low frequency band.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a low-noise thermal particle vibration velocity sensor and an implementation method thereof; the heating structure can eliminate closed loop feedback caused by resistance change and reduce low-frequency thermal noise of the sensor.
It is an object of the present invention to provide a low noise thermal particle velocity sensor.
The low noise thermal particle velocity sensor of the present invention comprises: the device comprises a substrate, a runner, a temperature measuring resistor, a heating resistor and an electrode; wherein, the substrate is in a flat plate shape, and the substrate is hollowed out, so that a flow channel is formed on the substrate; an even number of temperature measuring resistors are arranged on the flow channel, and the temperature measuring resistors are symmetrically distributed about the central axis of the flow channel; the heating resistors are symmetrically distributed about the central axis of the flow channel, the heating resistors cannot be positioned on the outer sides of the temperature measuring resistors, the width of the heating resistors is w, and the temperature resistance coefficient of the heating resistors is TCR; a plurality of electrodes are arranged on the substrate, and each temperature measuring resistor and each heating resistor respectively correspond to one electrode; each temperature measuring resistor is connected to an external temperature measuring circuit through a corresponding electrode; each heating resistor is connected to an external heating circuit through a corresponding electrode; the heating circuit is used for heating the heating resistor, and when sound particles vibrate in the flow channel, the heating resistor generates temperature field distribution disturbance, and the temperature field distribution disturbance causes the resistance value of the temperature measuring resistor to change; the temperature measuring circuit collects the change of the resistance value of the temperature measuring resistor, so that the acoustic particle vibration speed is obtained; wherein the disturbance of the temperature field distribution comprises a disturbance caused by acoustic particle vibration and a disturbance caused by thermal noise N;
the thermal noise N of the low noise thermal particle velocity sensor satisfies:
Wherein k is Boltzmann constant, T is the temperature of a heating resistor, B is the working bandwidth of the low-noise thermal particle vibration velocity sensor, and R e is the equivalent thermal noise resistor of the heating resistor; the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced along with the reduction of the equivalent thermal noise resistance R e of the heating resistor;
The equivalent thermal noise resistance R e of the heating resistor satisfies the following equation:
Wherein a=tcr× (T-T 0), TCR is the temperature resistivity of the heating resistor, T 0 is room temperature, R 0 is the resistance of the heating resistor at a temperature of T 0, ω is the angular frequency of the equivalent thermal noise of the heating resistor, ω=2pi f, f is the frequency of the equivalent thermal noise of the heating resistor, and T is the thermal time constant of the heating resistor; the thermal time constant t of the heating resistor satisfies:
Wherein ρ is the density of the heating resistor, c p is the specific heat capacity of the heating resistor, h is the convective heat transfer coefficient of the ambient medium, V is the volume of the heating resistor w×d×l, L is the length of the heating resistor, d is the thickness of the heating resistor, a is the surface area of the heating resistor, a=2× (w×h+w×l+h×l); because the length and the thickness of the heating resistor are not easy to adjust, increasing the width w of the heating resistor can improve the thermal time constant t of the sensor, so that the equivalent thermal noise resistor R e of the heating resistor is reduced; and the equivalent thermal noise resistance R e of the heating resistor can be reduced by reducing the temperature resistance coefficient TCR of the heating resistor;
By selecting the material of the heating resistor, the temperature resistance coefficient TCR of the heating resistor is reduced, and the width w of the heating resistor is increased, so that the equivalent thermal noise resistance R e≤R0 of the heating resistor is reduced, the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced;
meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity larger than 1000ppm/K and is used for sensing tiny temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved.
Further, a heating resistor is arranged near the temperature measuring resistor, the heating resistor is located below the temperature measuring resistor or the distance between the heating resistor and the temperature measuring resistor is smaller than 10 mu m, an electric bridge is formed by the temperature measuring resistor and an external temperature measuring circuit, power is applied to the temperature measuring resistor by the power supply voltage of the electric bridge, the power applied to the temperature measuring resistor is smaller than the power applied by the heating resistor, therefore, thermal noise disturbance caused by the fact that the temperature measuring resistor adopts a material with a high temperature resistance coefficient is reduced, stable power is provided by the heating resistor with a low temperature resistance coefficient nearby, and low-frequency thermal noise is restrained while the sensitivity is further improved. When the heating resistor is positioned below the temperature measuring resistor, the temperature measuring resistor further comprises an isolation layer, and the isolation layer is arranged between the heating resistor and the temperature measuring resistor. The isolation layer is made of silicon oxide and silicon nitride.
The substrate is made of silicon or glass; the length of the flow channel is 1-5 mm, and the width is 500-2000 mu m.
The width of the temperature measuring resistor is 1-10 mu m; the length is 500-2000 mu m.
The material of the heating resistor adopts a material with a temperature resistivity TCR <100 ppm/K.
Another object of the present invention is to provide a method for implementing a low noise thermal particle velocity sensor.
The invention discloses a realization method of a low-noise thermal particle vibration velocity sensor, which comprises the following steps:
1) The low-noise thermal particle vibration velocity sensor is connected with:
The substrate is in a flat plate shape, and hollowed-out treatment is carried out on the substrate, so that a flow channel is formed on the substrate; an even number of temperature measuring resistors are arranged on the flow channel, and the temperature measuring resistors are symmetrically distributed about the central axis of the flow channel; the heating resistors are symmetrically distributed about the central axis of the flow channel, the heating resistors cannot be positioned on the outer sides of the temperature measuring resistors, the width of the heating resistors is w, and the temperature resistance coefficient of the heating resistors is TCR; a plurality of electrodes are arranged on the substrate, and each temperature measuring resistor and each heating resistor respectively correspond to one electrode; each temperature measuring resistor is connected to an external temperature measuring circuit through a corresponding electrode; each heating resistor is connected to an external heating circuit through a corresponding electrode;
2) The heating circuit is used for heating the heating resistor, and when sound particles vibrate in the flow channel, the heating resistor generates temperature field distribution disturbance, and the temperature field distribution disturbance causes the resistance value of the temperature measuring resistor to change; the temperature measuring circuit collects the change of the resistance value of the temperature measuring resistor, so that the acoustic particle vibration speed is obtained; wherein the disturbance of the temperature field distribution comprises a disturbance caused by acoustic particle vibration and a disturbance caused by thermal noise N;
3) Parameter selection:
the thermal noise N of the low noise thermal particle velocity sensor satisfies:
Wherein k is Boltzmann constant, T is the temperature of a heating resistor, B is the working bandwidth of the low-noise thermal particle vibration velocity sensor, and R e is the equivalent thermal noise resistor of the heating resistor; the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced along with the reduction of the equivalent thermal noise resistance R e of the heating resistor;
The equivalent thermal noise resistance R e of the heating resistor satisfies the following equation:
Wherein a=tcr× (T-T 0), TCR is the temperature resistivity of the heating resistor, T 0 is room temperature, R 0 is the resistance of the heating resistor at a temperature of T 0, ω is the angular frequency of the equivalent thermal noise of the heating resistor, ω=2pi f, f is the frequency of the equivalent thermal noise of the heating resistor, and T is the thermal time constant of the heating resistor; the thermal time constant t of the heating resistor satisfies:
Wherein ρ is the density of the heating resistor, c p is the specific heat capacity of the heating resistor, h is the convective heat transfer coefficient of the ambient medium, V is the volume of the heating resistor w×d×l, L is the length of the heating resistor, d is the thickness of the heating resistor, a is the surface area of the heating resistor, a=2× (w×h+w×l+h×l); because the length and the thickness of the heating resistor are not easy to adjust, increasing the width w of the heating resistor can improve the thermal time constant t of the sensor, so that the equivalent thermal noise resistor R e of the heating resistor is reduced; and the equivalent thermal noise resistance R e of the heating resistor can be reduced by reducing the temperature resistance coefficient TCR of the heating resistor;
By selecting the material of the heating resistor, the temperature resistance coefficient TCR of the heating resistor is reduced, and the width w of the heating resistor is increased, so that the equivalent thermal noise resistance R e≤R0 of the heating resistor is reduced, the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced;
meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity larger than 1000ppm/K and is used for sensing tiny temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved.
The invention has the advantages that:
According to the invention, an even number of temperature measuring resistors are arranged on a flow channel, and an odd number of heating resistors are arranged in the temperature measuring resistors, so that the temperature resistance coefficient TCR of the heating resistors is reduced by selecting the materials of the heating resistors, and meanwhile, the width w of the heating resistors is increased, and the equivalent thermal noise resistance of the heating resistors is reduced, so that the thermal noise of a low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced; meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity and is used for sensing micro temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved; the invention can eliminate closed loop feedback caused by resistance change and reduce low-frequency thermal noise of the sensor.
Drawings
FIG. 1 is a schematic diagram of a first embodiment of a low noise thermal particle velocity sensor according to the invention, wherein (a) is a front view and (b) is a cross-sectional view;
FIG. 2 is a cross-sectional view of a second embodiment of a low noise thermal particle velocity sensor according to the invention;
FIG. 3 is a cross-sectional view of a third embodiment of a low noise thermal particle velocity sensor according to the invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in conjunction with the accompanying drawings.
Example 1
As shown in fig. 1, the low noise thermal particle velocity sensor of the present embodiment includes: the device comprises a substrate 1, a runner, a temperature measuring resistor 2, a heating resistor 3 and an electrode 4; wherein, the substrate is in a flat plate shape, and the substrate is hollowed out, so that a flow channel is formed on the substrate; two temperature measuring resistors 2 which are symmetrically distributed about the central axis of the flow channel are arranged on the flow channel, a heating resistor 3 is arranged on the central axis of the flow channel, the width of the heating resistor is w, and the temperature resistance coefficient of the heating resistor is TCR; a plurality of electrodes are arranged on the substrate, and each temperature measuring resistor and each heating resistor respectively correspond to one electrode; each temperature measuring resistor is connected to an external temperature measuring circuit through a corresponding electrode; each heating resistor is connected to an external heating circuit through a corresponding electrode; the heating circuit is used for heating the heating resistor, and when sound particles vibrate in the flow channel, the heating resistor generates temperature field distribution disturbance, and the temperature field distribution disturbance causes the resistance value of the temperature measuring resistor to change; the temperature measuring circuit collects the change of the resistance value of the temperature measuring resistor, so that the acoustic particle vibration speed is obtained; the disturbance of the temperature field distribution comprises disturbance caused by acoustic particle vibration and disturbance caused by thermal noise N, and the thermal noise N is inevitably reduced as much as possible.
In the embodiment, the substrate is made of silicon, and the length of the runner is 3mm and the width is 1000 μm; the width of the temperature measuring resistor is 5 μm, and the length is 1000 μm. The temperature measuring resistor is made of platinum, the temperature resistance coefficient TCR is 2000ppm/K, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved, the width w of the heating resistor is 4 mu m, and the temperature resistance coefficient TCR of the NiCr alloy is smaller than 100ppm/K, so that the equivalent thermal noise resistance R e≤R0 of the heating resistor is more stable, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced.
Example two
In this embodiment, in order to reduce thermal noise, the supply voltage of the temperature measuring resistor 2 needs to be reduced, and in order to improve the sensitivity of the sensor, a heating resistor 3 is added near 5 μm of each temperature measuring resistor, and the heating resistor 3 is also made of NiCr alloy with the temperature resistance coefficient TCR <100ppm/K, so that stable heating power is provided near the temperature measuring resistor. Other embodiments are the same as the first embodiment.
Example III
In the embodiment, the heating resistor is arranged below the temperature measuring resistor, the isolation layer 5 is arranged between the heating resistor and the temperature measuring resistor, the isolation layer is made of silicon oxide, and the heating resistor 3 can directly provide stable heating power for the temperature measuring resistor 2, so that the function of high temperature coefficient temperature measurement and low temperature coefficient heating of a single resistor is realized.
Finally, it should be noted that the examples are disclosed for the purpose of aiding in the further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (8)
1. A low noise thermal particle velocity sensor, the low noise thermal particle velocity sensor comprising: the device comprises a substrate, a runner, a temperature measuring resistor, a heating resistor and an electrode; wherein, the substrate is in a flat plate shape, and the substrate is hollowed out, so that a flow channel is formed on the substrate; an even number of temperature measuring resistors are arranged on the flow channel, and the temperature measuring resistors are symmetrically distributed about the central axis of the flow channel; the heating resistors are symmetrically distributed about the central axis of the flow channel, the heating resistors cannot be positioned on the outer sides of the temperature measuring resistors, the width of the heating resistors is w, and the temperature resistance coefficient of the heating resistors is TCR; a plurality of electrodes are arranged on the substrate, and each temperature measuring resistor and each heating resistor respectively correspond to one electrode; each temperature measuring resistor is connected to an external temperature measuring circuit through a corresponding electrode; each heating resistor is connected to an external heating circuit through a corresponding electrode; the heating circuit is used for heating the heating resistor, and when sound particles vibrate in the flow channel, the heating resistor generates temperature field distribution disturbance, and the temperature field distribution disturbance causes the resistance value of the temperature measuring resistor to change; the temperature measuring circuit collects the change of the resistance value of the temperature measuring resistor, so that the acoustic particle vibration speed is obtained; wherein the disturbance of the temperature field distribution comprises a disturbance caused by acoustic particle vibration and a disturbance caused by thermal noise N;
the thermal noise N of the low noise thermal particle velocity sensor satisfies:
Wherein k is Boltzmann constant, T is the temperature of a heating resistor, B is the working bandwidth of the low-noise thermal particle vibration velocity sensor, and R e is the equivalent thermal noise resistor of the heating resistor; the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced along with the reduction of the equivalent thermal noise resistance R e of the heating resistor;
The equivalent thermal noise resistance R e of the heating resistor satisfies the following equation:
Wherein a=tcr× (T-T 0), TCR is the temperature resistivity of the heating resistor, T 0 is room temperature, R 0 is the resistance of the heating resistor at a temperature of T 0, ω is the angular frequency of the equivalent thermal noise of the heating resistor, ω=2pi f, f is the frequency of the equivalent thermal noise of the heating resistor, and T is the thermal time constant of the heating resistor; the thermal time constant t of the heating resistor satisfies:
Wherein ρ is the density of the heating resistor, c p is the specific heat capacity of the heating resistor, h is the convective heat transfer coefficient of the ambient medium, V is the volume of the heating resistor w×d×l, L is the length of the heating resistor, d is the thickness of the heating resistor, a is the surface area of the heating resistor, a=2× (w×h+w×l+h×l); because the length and the thickness of the heating resistor are not easy to adjust, increasing the width w of the heating resistor can improve the thermal time constant t of the sensor, so that the equivalent thermal noise resistor R e of the heating resistor is reduced; and the equivalent thermal noise resistance R e of the heating resistor can be reduced by reducing the temperature resistance coefficient TCR of the heating resistor;
By selecting the material of the heating resistor, the temperature resistance coefficient TCR of the heating resistor is reduced, and the width w of the heating resistor is increased, so that the equivalent thermal noise resistance R e≤R0 of the heating resistor is reduced, the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced;
meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity larger than 1000ppm/K and is used for sensing tiny temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved.
2. The low noise thermal particle velocity sensor of claim 1 wherein the substrate is made of silicon or glass.
3. A low noise thermal particle velocity sensor according to claim 1 wherein the length of the flow channel is 1 to 5mm and the width is 500 to 2000 μm.
4. The low noise thermal particle velocity sensor of claim 1 wherein the temperature sensing resistor has a width of 1 to 10 μm; the length is 500-2000 mu m.
5. The low noise thermal particle velocity sensor of claim 1, wherein a heating resistor is disposed near the temperature measuring resistor, the heating resistor is located below the temperature measuring resistor or a distance between the heating resistor and the temperature measuring resistor is less than 10 μm, the temperature measuring resistor and an external temperature measuring circuit form a bridge, a power supply voltage of the bridge also applies power to the temperature measuring resistor, and the power applied to the temperature measuring resistor is less than the power applied by the heating resistor, thereby reducing thermal noise disturbance caused by using a material with a high temperature resistivity for the temperature measuring resistor.
6. The low noise thermal particle velocity sensor of claim 5, wherein the heating resistor is located below the temperature sensing resistor, further comprising an isolation layer disposed between the heating resistor and the temperature sensing resistor.
7. The low noise thermal particle velocity sensor according to claim 6 wherein the isolation layer is made of silicon oxide or silicon nitride.
8. A method of implementing a low noise thermal particle velocity sensor according to claim 1, comprising the steps of:
1) The low-noise thermal particle vibration velocity sensor is connected with:
The substrate is in a flat plate shape, and hollowed-out treatment is carried out on the substrate, so that a flow channel is formed on the substrate; an even number of temperature measuring resistors are arranged on the flow channel, and the temperature measuring resistors are symmetrically distributed about the central axis of the flow channel; the heating resistors are symmetrically distributed about the central axis of the flow channel, the heating resistors cannot be positioned on the outer sides of the temperature measuring resistors, the width of the heating resistors is w, and the temperature resistance coefficient of the heating resistors is TCR; a plurality of electrodes are arranged on the substrate, and each temperature measuring resistor and each heating resistor respectively correspond to one electrode; each temperature measuring resistor is connected to an external temperature measuring circuit through a corresponding electrode; each heating resistor is connected to an external heating circuit through a corresponding electrode;
2) The heating circuit is used for heating the heating resistor, and when sound particles vibrate in the flow channel, the heating resistor generates temperature field distribution disturbance, and the temperature field distribution disturbance causes the resistance value of the temperature measuring resistor to change; the temperature measuring circuit collects the change of the resistance value of the temperature measuring resistor, so that the acoustic particle vibration speed is obtained; wherein the disturbance of the temperature field distribution comprises a disturbance caused by acoustic particle vibration and a disturbance caused by thermal noise N;
3) Parameter selection:
the thermal noise N of the low noise thermal particle velocity sensor satisfies:
Wherein k is Boltzmann constant, T is the temperature of a heating resistor, B is the working bandwidth of the low-noise thermal particle vibration velocity sensor, and R e is the equivalent thermal noise resistor of the heating resistor; the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced along with the reduction of the equivalent thermal noise resistance R e of the heating resistor;
The equivalent thermal noise resistance R e of the heating resistor satisfies the following equation:
Wherein a=tcr× (T-T 0), TCR is the temperature resistivity of the heating resistor, T 0 is room temperature, R 0 is the resistance of the heating resistor at a temperature of T 0, ω is the angular frequency of the equivalent thermal noise of the heating resistor, ω=2pi f, f is the frequency of the equivalent thermal noise of the heating resistor, and T is the thermal time constant of the heating resistor; the thermal time constant t of the heating resistor satisfies:
Wherein ρ is the density of the heating resistor, c p is the specific heat capacity of the heating resistor, h is the convective heat transfer coefficient of the ambient medium, V is the volume of the heating resistor w×d×l, L is the length of the heating resistor, d is the thickness of the heating resistor, a is the surface area of the heating resistor, a=2× (w×h+w×l+h×l); because the length and the thickness of the heating resistor are not easy to adjust, increasing the width w of the heating resistor can improve the thermal time constant t of the sensor, so that the equivalent thermal noise resistor R e of the heating resistor is reduced; and the equivalent thermal noise resistance R e of the heating resistor can be reduced by reducing the temperature resistance coefficient TCR of the heating resistor;
By selecting the material of the heating resistor, the temperature resistance coefficient TCR of the heating resistor is reduced, and the width w of the heating resistor is increased, so that the equivalent thermal noise resistance R e≤R0 of the heating resistor is reduced, the thermal noise N of the low-noise thermal particle vibration velocity sensor is reduced, the heating power is more stable, stable temperature field distribution is obtained, and the thermal noise disturbance of a low frequency band is reduced;
meanwhile, the temperature measuring resistor is made of a material with high temperature resistivity larger than 1000ppm/K and is used for sensing tiny temperature disturbance caused by sound waves, so that the sensitivity of the low-noise thermal particle vibration velocity sensor is improved.
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