CN115683384A - Acoustic temperature sensor and temperature measuring method - Google Patents
Acoustic temperature sensor and temperature measuring method Download PDFInfo
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Abstract
An acoustic temperature sensor and a temperature measuring method comprise a microphone, an acoustic waveguide, a power supply and a signal processing module. The microphone is used for detecting sound waves; the first port of the sound wave guide pipe is blocked by the microphone and then forms a sound wave Fabry-Perot resonator with the second port, the first reflecting surface of the sound wave Fabry-Perot resonator is a sound sensing surface of the microphone, and the second reflecting surface is an interface between the air at the inner side and the air at the outer side of the second port; after the background noise of the tested environment is transmitted into the acoustic waveguide tube from the second port, the background noise is modulated by the acoustic Fabry-Perot resonator, and the modulated background noise signal is converted into an electric signal by a microphone and then is output; the power supply and signal processing module is used for supplying power to the microphone and processing an electric signal output by the microphone to obtain the temperature of the detected environment. The invention has the advantages of simple sensor structure, convenient use, wide temperature measuring range, low power consumption, quick response, high precision, no influence of air pressure and the like.
Description
Technical Field
The invention relates to the technical field of environmental noise detection and acoustic temperature measurement, in particular to an acoustic temperature sensor based on an acoustic wave Fabry-Perot resonator and a temperature measurement method.
Background
The acoustic temperature measurement technology is a non-contact indirect temperature measurement technology which is based on the temperature dependence of sound velocity and obtains the ambient gas temperature by measuring the sound velocity, has the advantages of fast response, high precision, good robustness, wide temperature measurement range and the like, and is suitable for measuring the temperature of complex and severe environments, such as a casting hearth, a plasma chamber, a nuclear reactor and the like. According to literature reports, the existing acoustic thermometry technologies mainly include two types: one is to measure the time required for the sound pulse emitted from the sound source to reach the sound detector with a given distance, then calculate the sound velocity, and then use the temperature dependence of the sound velocity to calculate the environment temperature; the other method is to place the sound source and the sound detector in an acoustic resonator to detect the resonance frequency, and then use the correlation between the resonance frequency and the sound velocity to calculate the sound velocity, so as to obtain the ambient temperature. Both methods need to use a known sound source, and have the disadvantages of high power consumption, complex structure of a measuring device, harsh signal control conditions, high operation difficulty and inconvenience in realizing temperature measurement anytime and anywhere.
Disclosure of Invention
In view of the above, the present invention is directed to an acoustic temperature sensor and a temperature measuring method, which are designed to at least partially solve at least one of the above-mentioned problems.
According to an aspect of the present invention, there is provided an acoustic temperature sensor including: the microphone is used for detecting sound waves and is provided with a sound sensing surface; the acoustic wave guide tube is provided with a first port and a second port, wherein the port faces of the first port and the second port are flush, the first port and the second port form an acoustic wave Fabry-Perot resonator after being blocked by the microphone, a first reflecting face of the acoustic wave Fabry-Perot resonator is a sound sensing face of the microphone, and a second reflecting face of the acoustic wave Fabry-Perot resonator is an interface between inside air and outside air of the second port; after the background noise of the tested environment is transmitted into the sound wave guide pipe from the second port, the background noise is modulated by the sound wave Fabry-Perot resonator, and a background noise signal obtained through modulation is converted into an electric signal by the microphone and then is output; and the power supply and signal processing module is electrically connected with the microphone and used for supplying power to the microphone and processing the electric signal output by the microphone to obtain the temperature of the detected environment.
According to another aspect of the present invention, there is provided a method of measuring temperature using an acoustic temperature sensor as described above, comprising the steps of: step A: the acoustic wave Fabry-Perot resonator is placed in a tested environment, and a power supply and signal processing module supplies power to the acoustic wave Fabry-Perot resonator; and B: continuously detecting background noise of a detected environment for multiple times by using the acoustic wave Fabry-Perot resonator, and outputting multiple background noise time domain spectrums; and C: processing the plurality of background noise time domain spectrums by using the power supply and signal processing module to obtain a background noise frequency spectrum, wherein the processing comprises frequency spectrum conversion and frequency spectrum superposition; step D: determining frequencies and orders corresponding to a plurality of resonance peaks from the background noise spectrum by using the power supply and signal processing module; step E: and solving the temperature of the measured environment according to the linear regression slope between the frequency and the order of the resonance peaks.
Compared with the prior art, the acoustic temperature sensor and the temperature measuring method have at least one or part of the following beneficial effects:
(1) The invention utilizes the characteristic that the background noise of the tested environment is relatively uniform in power spectral density distribution in a wider frequency domain range, and can determine the relation between the resonant frequency and the temperature based on the resonance phenomenon generated by the environment background noise in the acoustic wave Fabry-Perot resonator, thereby realizing temperature measurement without knowing a sound source, and having simple structure, low power consumption, quick response, low cost and high sensitivity;
(2) The acoustic temperature sensor can realize temperature measurement only based on the acoustic waveguide and the microphone blocked on the acoustic waveguide, has the advantages of small volume, light weight, convenience in carrying and convenience in operation, and can measure temperature at any time and any place;
(3) Compared with the existing temperature measurement mode which needs to be calibrated before use, such as a mercury thermometer needs to calibrate the temperature and the scale, the acoustic wave Fabry-Perot resonator of the invention can realize temperature measurement without the calibration process, namely, without making a frequency-temperature standard curve or a slope-temperature standard curve in advance, and has high accuracy;
(4) The acoustic wave Fabry-Perot resonator has multiple functions, can measure temperature, monitor noise and measure sound velocity, is not influenced by air pressure, and is suitable for temperature measurement in severe environments such as adjacent space and the like.
Drawings
Fig. 1 is a schematic structural diagram of an acoustic temperature sensor based on an acoustic fabry-perot resonator according to a first embodiment of the present invention;
FIG. 2 is a flowchart illustrating a method for measuring temperature using an acoustic temperature sensor based on an acoustic Fabry-Perot resonator according to a first embodiment of the present invention;
fig. 3 is a simulation result of the first four-order resonant frequency of the acoustic fabry-perot resonator structure according to the second embodiment of the present invention varying with temperature based on the first embodiment;
FIG. 4 is a graph showing the frequency spectrum of the ambient background noise measured by a laboratory-prepared acoustic Fabry-Perot resonator according to a third embodiment of the present invention;
FIG. 5 is a schematic diagram of an apparatus for testing the variation of resonant frequency of each stage of a lab-prepared acoustic Fabry-Perot resonator with temperature in a temperature-controlled chamber environment according to a fourth embodiment of the present invention;
FIG. 6 is a graph showing the variation of the resonant frequency, the test temperature and the test error of each stage of the Fabry-Perot resonator according to the fourth embodiment of the present invention with the ambient temperature in the environment of the temperature control chamber;
FIG. 7 is a graph showing the variation of the resonant frequency and the test temperature at different environmental temperatures in the environment of the thermal control chamber according to the fourth embodiment of the present invention;
fig. 8 is a graph showing a background noise spectrum and a linear variation of a resonant frequency with an order number measured by using a lab-prepared acoustic fabry-perot resonator in a total anechoic chamber according to a fifth embodiment of the present invention.
In the above drawings, the reference numerals have the following meanings:
1-a microphone; 2-an acoustic waveguide;
10-acoustic fabry-perot resonator; 20-a preamplifier;
30-a reference microphone; 40-temperature control box;
50-data acquisition card.
Detailed Description
The invention discloses an acoustic temperature sensor and a temperature measuring method. The microphone and the acoustic waveguide tube form an acoustic wave Fabry-Perot resonator, background noise of a detected environment is modulated and detected by the acoustic wave Fabry-Perot resonator, a measured modulated background noise signal is processed by the power supply and signal processing module, and the temperature of the detected environment can be measured based on the corresponding relation between the resonant peak frequency and the temperature in a background noise signal frequency spectrum obtained by signal processing. The temperature sensor has the advantages of simple structure, convenient use, non-contact type, wide temperature measurement range, low power consumption, quick response, high precision and no influence of air pressure, and is suitable for temperature measurement in severe environments such as adjacent space and the like.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings. It should be noted that in the drawings or description, the same reference numerals are used for similar or identical parts. Implementations not depicted or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints. Directional phrases referred to in the embodiments, such as "upper," "lower," "front," "rear," "left," "right," etc., refer only to the orientation of the figure. Accordingly, the directional terminology used is intended to be illustrative and is not intended to be limiting of the scope of the present invention.
First embodiment
In a first exemplary embodiment of the present invention, an acoustic temperature sensor based on an acoustic wave fabry-perot resonator is provided. Fig. 1 is a schematic structural diagram of a temperature sensor based on an acoustic fabry-perot resonator according to a first embodiment of the present invention. As shown in fig. 1, the acoustic temperature sensor includes: a microphone 1, an acoustic waveguide 2, and a power and signal processing module (not shown), wherein the microphone 1 is used for detecting acoustic waves, and the microphone 1 has a sound sensing surface; the acoustic wave guide tube 2 is provided with a first port and a second port, the port surfaces of the first port and the second port are flush, the first port and the second port form an acoustic wave Fabry-Perot resonator after being blocked by the microphone 1, a first reflecting surface of the acoustic wave Fabry-Perot resonator is a sound sensing surface of the microphone 1, and a second reflecting surface is an interface between inside air and outside air of the second port; after the background noise of the tested environment is transmitted into the acoustic waveguide 2 from the second port, the background noise is modulated by the acoustic wave Fabry-Perot resonator, and a background noise signal obtained by modulation is converted into an electric signal by the microphone 1 and then is output; and the power supply and signal processing module is electrically connected with the microphone 1 and used for supplying power to the microphone 1 and processing the electric signal output by the microphone 1 to obtain the temperature of the detected environment.
It should be noted that the background noise in the present invention can be understood as white noise or background noise of the surrounding environment when no specific sound source is generated, and the power spectral density of the background noise is distributed as uniform noise in a wide frequency domain.
The acoustic temperature sensor based on the acoustic wave Fabry-Perot resonator can realize temperature measurement according to the following principle:
one reflectivity R of the acoustic fabry-perot resonator formed by the diaphragm (i.e. the sound-sensing surface) of the microphone 1 1 And the other port of the acoustic waveguide 2 is in communication with the outside air to accelerate heat exchange. Although the acoustic waveguide 2 is connected to the outside air, since the inner diameter of the pipe is not matched with the acoustic impedance of the near-infinite space outside, the other port of the acoustic waveguide 2 can be equivalent to another reflectivity R of the acoustic fabry-perot resonator 2 The air reflection surface of (2). The sound wave entering the sound wave guide tube from the outside is reflected when reaching the diaphragm of the microphone 1, and the reflected sound wave returns to the outlet and is reflected by the air reflection surface, and meanwhile, the phase shift of pi is added. Therefore, the sound waves are repeatedly reflected and superposed in the sound wave Fabry-Perot resonator to form interference, and the phase difference of adjacent reflected waves can be expressed as:
where L is the length of the acoustic waveguide between the two reflective surfaces, k is the propagation constant of the acoustic wave within the tube, and can be expressed as k =2 pi f/c, where f is the acoustic frequency and c is the acoustic velocity. Considering that transmission loss is caused by the transmission of the acoustic wave in the acoustic waveguide, the propagation constant k is expressed as: k =2 pi f/c-j α, where α is a loss factor, which is proportional to the square of the acoustic frequency. Therefore, when the sound pressure amplitude is P 0 When the sound wave of (2) is incident into the sound wave guide, the sound pressure received by the microphone sound sensing surface can be expressed as:
the sound pressure amplitude of formula (I) can be expressed as:
as can be seen from formula (II), when the incident sound frequency satisfies the relationship shown in formula (III):
and when the sound pressure amplitude is at an extreme value, the sound wave Fabry-Perot resonator is in a resonance state. At this time, f m The frequency corresponding to the mth order resonance peak can also be called as the mth order resonance frequency. It will be appreciated that the 1 st harmonic peak is the first harmonic peak in the background noise spectrum that occurs from low to high frequencies, and so on.
In addition, according to an acoustic basic theory, the relationship that the sound velocity and the temperature satisfy the formula (IV) can be obtained:
the simultaneous formulas (III) and (IV) can obtain the relation between the resonant frequency and the temperature of the acoustic wave Fabry-Perot resonator as follows:
where B is a constant, for airborne sound, B =20.05. Therefore, by utilizing the relation between the resonant frequency and the temperature, the temperature of the measured environment can be measured based on the measured sound wave frequency spectrum of the sound wave Fabry-Perot resonator placed in the measured environment.
Further, as can be seen from the above equation (1), the resonant frequency f of the acoustic fabry-perot resonator at a given temperature m The slope of the linear relation with the corresponding resonance peak order m can be expressed as follows:
as can be seen from equation (2), the slope SL is proportional to the square root of the temperature T, so that, in the test process, the resonant frequency of the resonant peak with different orders is firstly measured, and then the linear regression slope between the resonant frequency and the resonant order is used to obtain the temperature to be measured. It is to be noted here that the temperature T in the above formula is a kelvin temperature.
The following respectively describes the components of the acoustic temperature sensor based on the acoustic fabry-perot resonator according to the present embodiment in detail.
As shown in fig. 1, the microphone 1 is a one-half inch Electret Condenser Microphone (ECM), but not limited thereto, and in other embodiments, the microphone 1 may be one of a piezoelectric microphone, an electromagnetic microphone, a fiber-optic microphone, a grating microphone, and a MEMS microphone. In this embodiment, the lower limit of the frequency response of the microphone is not greater than 50Hz, so as to satisfy the measurement of the environmental background noise in the low frequency part.
In the present embodiment, the sonic waveguide 2 is a stainless steel cylindrical sonic waveguide with a length L =0.38m and an inner diameter d =25mm, but is not limited thereto, and in other embodiments, the sonic waveguide 2 may be other sizes; the acoustic waveguide 2 may be a metal tube, a ceramic tube, a hard wood tube, a glass tube, a PVC tube, or the like. The shape of the acoustic waveguide 2 is not limited to the straight shape shown in fig. 1, and may be a curved shape or a combination of straight and curved shapes, and the specific shape of the acoustic waveguide 2 does not affect the resonance interference effect of the acoustic wave generated in the fabry-perot resonator.
In the present embodiment, the cross-sectional shape of the acoustic waveguide 2 is circular to match the microphone 1, so that the microphone 1 is blocked at the first port of the acoustic waveguide 2, and the two are tightly assembled to form a sealed structure, thereby avoiding acoustic crosstalk and improving the measurement accuracy. However, the cross-sectional shape of the acoustic waveguide 2 may be other regular or irregular shapes such as square, triangle, etc. in other embodiments, as long as the cross-sectional shape is adapted to the microphone 1. Further, in other embodiments, the microphone 1 is a MEMS microphone and the acoustic waveguide 2 is a micro-acoustic waveguide compatible with the MEMS microphone, such that the resulting acoustic temperature sensor can be a highly integrated on-chip acoustic thermometer.
In the present embodiment, the axes at the first and second ports of the acoustic waveguide 2 are perpendicular to the first and second reflective surfaces of the acoustic fabry-perot resonator, thereby facilitating the formation of the acoustic fabry-perot resonator at the microphone 1 at the first port and the second port.
In this embodiment, the quality factor of the resonance peak of the acoustic fabry-perot resonator is not less than 2, which is more favorable for accurately determining the resonance frequency, and thus is favorable for more accurately measuring the temperature. Here, quality factor (Q) = resonance frequency/bandwidth.
In the embodiment, the signal-to-noise ratio of the output signal of the acoustic wave fabry-perot resonator is not less than 5, and it can be understood that a higher signal-to-noise ratio is beneficial to accurately determining the position of the resonance peak and the frequency thereof.
In the present embodiment, the power supply and signal processing module may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer, the various component embodiments of which may be implemented in hardware, or in conventional software modules running on one or more processors, or in a combination thereof. For example, a preamplifier may be included for amplifying the output signal of the acoustic wave fabry-perot resonator; the data acquisition card is used for acquiring and carrying out analog-to-digital conversion on the output analog signal of the preamplifier; and a computer with LabVIEW program for processing the output signal of the data acquisition card. It will be appreciated by those skilled in the art that existing programming language or code may be used for a particular programming language, but that the present invention is not concerned with procedural modifications.
In a first exemplary embodiment of the present invention, a method for measuring temperature using the acoustic temperature sensor based on the acoustic wave fabry-perot resonator is also provided. Fig. 2 is a flowchart illustrating a method for measuring temperature using an acoustic temperature sensor based on an acoustic fabry-perot resonator according to a first embodiment of the present invention. As shown in fig. 2, the method comprises the steps of:
step A: the acoustic wave Fabry-Perot resonator is placed in a tested environment, and a power supply and signal processing module supplies power to the acoustic wave Fabry-Perot resonator.
And B: and continuously detecting background noise in the detected environment for multiple times by using the acoustic wave Fabry-Perot resonator, and outputting a plurality of background noise time domain spectrums.
Optionally, in step B, the frequency of continuously detecting the background noise in the detected environment by using the acoustic wave fabry-perot resonator is not less than 3 times, so as to improve the signal-to-noise ratio of the subsequently obtained background noise spectrum. The detection times in this step are the superposition times of the subsequent background noise spectrum.
Step C: and processing the plurality of background noise time domain spectrums by using a power supply and signal processing module to obtain a background noise frequency spectrum, wherein the processing comprises frequency spectrum conversion and frequency spectrum superposition.
Optionally, in this step C, the frequency spectrum conversion may be, for example, implemented by performing fourier transform on a time domain spectrum and a frequency spectrum, and performing frequency spectrum conversion on a plurality of background noise time domain spectrums to obtain a plurality of background noise frequency spectrums; and then, superposing the plurality of background noise spectrums to obtain a background noise spectrum with a high signal-to-noise ratio. The signal-to-noise ratio of the spectrum-superimposed background noise is preferably not less than 20.
In this embodiment, the method may further include: detecting background noise in a detected environment by using a reference microphone to obtain a reference background noise time domain spectrum; and performing frequency spectrum conversion on the reference background noise time domain spectrum by using the power supply and signal processing module to obtain a reference background noise frequency spectrum. Optionally, the reference microphone may be a microphone itself detached from the acoustic wave fabry-perot resonator, the step of detecting the reference microphone and the step of detecting the acoustic wave fabry-perot resonator (i.e., step B) may be performed at different times, the reference microphone may also be separately set, and in the case of separate setting, the two detection steps may be performed simultaneously, so as to improve accuracy and reliability of the differential operation result.
On the basis, the step C also comprises the following steps: and carrying out difference operation on the obtained background noise frequency spectrum and the reference background noise frequency spectrum to obtain the background noise frequency spectrum after the difference operation. Thereby performing the subsequent steps of processing based on the background noise spectrum after the difference operation.
Step D: determining frequencies and orders corresponding to a plurality of resonance peaks from a background noise spectrum by using a power supply and signal processing module;
step E: and solving the temperature of the detected environment according to the linear regression slope between the frequency and the order of the multiple resonance peaks. In this step E, the above formula (2) can also be utilized to determine the resonant frequency f m Solving the temperature of the measured environment by the slope SL determined by the linear curve corresponding to the order m of the resonance peakDegree T:
it is understood that the specific implementation of step E may include: substep E1: drawing a linear curve between frequencies and orders corresponding to a plurality of resonance peaks in the background noise frequency spectrum; substep E2: and (3) solving the temperature of the measured environment by using the formula (2) according to the slope of the linear curve. The following embodiments can confirm that the temperature determining method can accurately determine the temperature of the measured environment and has good robustness.
In other embodiments, instead of using the slope to solve the temperature in step E, step F: using equation (1) above to directly depend on the frequency f of the resonance peak m And (4) determining the temperature T of the detected environment only with accuracy which is not the same as the solution mode in the step E.
Wherein, f m L is the acoustic waveguide length between the first and second reflective surfaces, and B is a constant, for airborne sound, B =20.05.
Optionally, in the case that the background noise spectrum includes a plurality of resonant peaks, a specific implementation of step F may include:
substep F1: substituting the frequency corresponding to each resonance peak in the background noise frequency spectrum into a formula (1) to obtain a corresponding temperature value; substep F2: and taking the average value of the plurality of obtained temperature values as the temperature of the measured environment.
Optionally, in a case where the background noise spectrum includes a plurality of harmonic peaks, another specific implementation of this step F may include:
substep F1': selecting a plurality of resonance peaks with quality factors close to a signal-to-noise ratio from a background noise spectrum; sub-step F2': substituting the frequency corresponding to each selected resonance peak into a formula (1) to obtain a corresponding temperature value; substep F3': and taking the average value of the plurality of obtained temperature values as the temperature of the measured environment.
So far, the acoustic temperature sensor based on the acoustic wave fabry-perot resonator and the method for measuring the temperature according to the first embodiment of the present invention have been described.
Second embodiment
In a second exemplary embodiment of the present invention, the acoustic temperature sensor based on the acoustic wave fabry-perot resonator in the first embodiment is used to perform a simulation test in a measured environment with temperature change, so as to verify that the response characteristic of the acoustic temperature sensor to the temperature change in the measured environment meets the measurement requirement.
Fig. 3 is a simulation result of the first four-step resonant frequency of the acoustic fabry-perot resonator structure according to the second embodiment of the present invention according to the first embodiment as a function of temperature. Wherein the graph (a) is a numerical simulation based on the above equation (1). It can be found that in the temperature range of-50 ℃ to 750 ℃, the first four-order resonance peak has monotonous nonlinear frequency shift with the increase of temperature, and the higher the order of the resonance frequency is, the higher the sensitivity is. For the same resonance peak, the rate of change of the resonance frequency with temperature gradually slows down with increasing temperature. Therefore, it is expected that the system is more suitable for temperature measurement in a low temperature range.
In many cases, the nonlinearity of the system complicates the back-end signal processing and is not conducive to temperature sensing. Therefore, many sensing applications require a linear response characteristic of the system. While any curve can be approximated by numerous straight lines. Therefore, when the selected temperature measurement range is not large, the operating curve of the system can be approximately regarded as linear.
To this end, the present example further simulates the response of an acoustic temperature sensor in the temperature range of-20 ℃ to 60 ℃. As shown in fig. 3 (b), the first four-order resonant frequency is well linearly related to the temperature. R2 of the linear fitting straight line is more than 0.999, which indicates that the system has high linearity, and the system can be regarded as a linear system at the moment, and the resonant frequency and the temperature are the sameThe degrees remain linear. The theoretical temperature sensitivity S of the first four-order resonant frequency can be obtained according to the slope of the fitting straight line 1 ＝0.39Hz/℃，S 2 ＝1.18Hz/℃，S 3 ＝1.97Hz/℃，S 4 =2.75 Hz/deg.c. Therefore, theoretically, the higher the order of the resonance frequency, the higher the temperature sensitivity, without considering the signal-to-noise ratio of the signal and the difficulty of picking up the resonance peak.
Third embodiment
In a third exemplary embodiment of the present invention, an acoustic wave fabry-perot resonator is prepared in a laboratory based on the structure described in the first embodiment, an environmental background noise spectrum is measured using the prepared acoustic fabry-perot resonator, and the effect of a signal processing manner is evaluated by testing the frequency response characteristics of the fabry-perot resonator. Fig. 4 is a spectrum of ambient background noise measured using a lab-prepared acoustic fabry-perot resonator according to a third embodiment of the present invention.
First, use B&K Acoustic calibration System (including loudspeaker (Visaton FR 9.15), reference microphone (B)&K，4193)、B&K PULSE Lab shop software, B&K LAN-3160 hardware), B&The K acoustic calibration system and the acoustic fabry-perot resonator are placed in the same measured environment, and a frequency spectrum measured by the acoustic fabry-perot resonator under excitation with a speaker as a sound source is shown in fig. 4 (a). Wherein the first order resonance frequency, i.e. fundamental frequency f 1 =226Hz, close to the theoretical value of 225.6Hz calculated by formula (III). The high-order resonant frequency is odd multiple of the fundamental frequency, and basically accords with the theory. These values can be used as a reference for evaluating the effect of the subsequent signal processing method.
The speaker was then turned off and the time domain signal from the microphone mounted at the end of the sonic tube was collected using a data acquisition card (SB 4431, national instruments, united States) to calculate a power spectrum, with the result that the sampling frequency and number of samples of the system was 50k and the power spectrum resolution was 1Hz, as shown in figure 4 (b). The power spectrum without signal processing may generate a plurality of resonance peaks similar to those shown in fig. 4 (a), because the fabry-perot resonator enhances background noise existing in the environment near the resonance frequency of the system. Therefore, the excitation of the sound source can be avoided, and the power consumption and the complexity of the system are reduced. Meanwhile, multimodal detection is allowed to be carried out simultaneously, and the working efficiency and the real-time performance of the system are improved. However, it should be noted that the average deviation of the resonant frequency of the obtained background noise power spectrum from the resonant frequency of the corresponding order shown in the graph (a) is 7Hz because the ambient background noise is weak. And the higher the resonant frequency, the greater the deviation, which means that the system can only operate with low accuracy at lower order resonant frequencies with a lower quality factor (Q) in this case. Obviously, this situation does not satisfy most application requirements.
This problem is improved by a two-step signal processing approach, first, suppressing random noise at high frequencies by superposition summing of the signals. After the processing, the pickup precision of the high-order resonant frequency of the system is obviously improved. As shown in fig. 4 (c), the background noise power spectrum is obtained when the number of times of superposition is 10, 30, and 60, respectively, and the average deviation of the third-order resonance frequency is reduced from 10Hz to 6Hz. This is because the superposition summation greatly enhances the signal at the resonant peak, while the superposition of random noise at other frequencies tends to be constant. At fourth order resonance frequency f 4 For example, the signal-to-noise ratio is improved by 1.08 times. However, superposition summing does not significantly improve or even degrade the signal-to-noise ratio at lower order resonant frequencies because of the strong trending term of the power spectrum itself due to the presence of significant non-random noise at low frequencies. In addition, if strong nonrandom noise exists outside, a plurality of resonance peaks at nonresonant frequencies appear on the power spectrum, which can also make the system misjudge.
In order to solve the problem, another reference microphone can be further used to collect the background noise signal, obtain a reference background noise power spectrum, and then perform a difference operation on the superimposed background noise power spectrum and the reference background noise power spectrum to suppress low-frequency non-random noise and strong random noise. As shown in the graph (d) of fig. 4, it can be seen that after the two-step process, a relatively sharp resonance peak can be observed from the power spectrum, and the average deviation of the resonance frequency of each step of the system from the result shown in the graph (a) of fig. 4 is only 3Hz. Compared with the original signal，f 4 The signal-to-noise ratio of (A) is improved by 2.3 times. This result confirms the feasibility and accuracy of the proposed signal processing method. It should be noted that the increase of the number of overlapping times does not significantly improve the performance of the system, but increases the calculation time of the system, and reduces the real-time performance of the system. Therefore, the number of times of superposition processing is selected to be 10, the time for one measurement of the system is 10s (the sampling rate is the same as the number of sampling points), and the high signal-to-noise ratio of the resonance peak and the real-time performance of the system are considered.
It should be noted that, according to the technical features of the proposed method, compared with the conventional acoustic resonance temperature measurement method, the method can perform temperature sensing by using multiple resonance peaks as reference quantities, and the real-time performance of the system is not affected too much. The multimodal working mode enables the system to have higher temperature measurement accuracy and robustness.
Fourth embodiment
In a fourth exemplary embodiment of the present invention, the acoustic fabry-perot resonator with the structure described in the first embodiment is prepared in a laboratory, and is placed in a temperature control box environment to measure changes of resonant frequencies of various orders with temperature, so as to verify that in practical application, the response characteristic of the acoustic temperature sensor to temperature changes in the measured environment can meet the measurement requirement.
Fig. 5 is a schematic diagram of an apparatus for testing the variation of resonant frequency of each step of a lab-prepared acoustic fabry-perot resonator with temperature in a temperature controlled chamber environment according to a fourth embodiment of the present invention. As shown in fig. 5, during signal acquisition, a reference microphone 30 (AWA 14423, hangzhou Aihua Instruments, china) and an acoustic fabry-perot resonator 10 are placed in a temperature chamber of a temperature-controlled box 40 (JJ-36l, dongguan Jingte Instruments, china). The temperature in the temperature cavity is controlled by heating and refrigerating devices of the temperature control box, and is calibrated by a thermometer arranged in the temperature cavity. The analog acoustic signal sensed by the microphone diaphragm is converted to a digital signal by a preamplifier and data acquisition card (USB 4431, national instruments, united States). The signal was processed by LabVIEW (National Instruments, united States) under computer control. The signal processing process specifically comprises the following steps: firstly, fourier transform (FFT) calculation is carried out on a time domain signal from two channels to obtain a power spectrum of background noise; then, accumulating and summing are respectively carried out to filter out random noise; then, carrying out differential operation on the two superposed signals to achieve the purpose of filtering additive noise; and finally, carrying out peak value detection on the processed signal to obtain the resonant peak frequency of each order.
It should be noted that the proposed real-time acquisition of the background noise spectrum by the reference microphone is a convenient technical means for application. The method aims at complex and time-varying noise fields which are difficult to predict in the actual working environment. Most of the external noise can be resisted by the technical means. The robustness of the system is greatly improved. However, if the background noise of the applied environment is relatively uniform and stable, in other embodiments, the working environment background noise spectrum may be estimated in advance through a microphone, and then filtering of noise and improvement of the signal-to-noise ratio may be achieved through signal processing means such as spectral subtraction. The complexity and cost of the system can be reduced even further by this approach.
Fig. 6 is a graph showing the variation of the resonant frequency, the test temperature, and the test error of each step of the acoustic fabry-perot resonator with the ambient temperature, which are measured in the environment of the temperature control box according to the fourth embodiment of the present invention. As shown in fig. 6, taking the second-order resonance peak as an example, it can be seen from the graph (a-1) in fig. 6 that the resonance frequency undergoes a significant monotonic frequency shift as the ambient temperature increases from-20 ℃ to 60 ℃. The quality factor Q value at different temperatures is basically kept consistent. The second to seventh order resonant frequencies are related to temperature as shown in the (a-1) to (f-1) diagrams of fig. 6, and the resonant frequencies of the respective orders increase nearly linearly with increasing temperature. R of a linearly fitted straight line 2 Basically all reach above 0.98. Indicating that the system has higher linearity. The sensitivity of the second-seventh order resonant frequency calculated according to the slope of the fitted straight line is S 2 ＝1.174Hz/℃、S 3 ＝1.805Hz/℃、S 4 ＝2.652Hz/℃、S 5 ＝3.366Hz/℃、S 6 =4.256 Hz/. Degree.C.and S 7 =4.950Hz/° c. The maximum deviation of the results from the theoretical sensitivity shown in fig. 3 is 8%. Generate this biasThe possible cause of the difference is non-uniformity of the temperature in the thermal chamber, and the temperature measured by the thermometer built in the thermal chamber deviates from the actual temperature at the waveguide. Calculating the average Q value of the front four-stage resonance peak in the temperature range of-20 ℃ to 60 ℃, and respectively obtaining Q 1 ＝4.47、Q 2 ＝9.34、Q 3 ＝13.11、Q 4 =26.04. Therefore, if only one resonant peak is selected as a reference for temperature sensing, a higher order resonant peak is a better choice because it has a higher Q value and higher sensitivity, which means that the resonant peak is sharper and it is easier to obtain the resonant frequency accurately. However, if the snr of the noise signal is considered, the snr of the higher order resonant frequency may be degraded, and the lower order resonant peak, such as 1 to 4 order resonant peak, is still preferably selected. Further, in the case of directly solving the test temperature by using the formula (1), the relationship between the second to seventh order test temperatures and the ambient temperature is shown in the (a-2) to (f-2) diagrams of fig. 6, it can be found that the test temperature and the ambient temperature are approximately linear, however, the deviation of the resonance peak of different orders relative to the ambient temperature is different, and the rule thereof cannot be determined, and further, as shown in the (a-3) to (f-3) diagrams of fig. 6, the error MAE of the test temperature obtained by the third order resonance peak relative to the ambient temperature is as high as 20 ℃.
In order to further improve the test accuracy and robustness, the temperature can be more accurately tested based on the linear relationship between the resonant frequency and the resonant peak order, and fig. 7 is a variation curve of the resonant frequency and the test temperature at different environmental temperatures measured in the environment of the temperature control box according to the fourth embodiment of the present invention. As shown in the graph (a) in FIG. 7, the resonance frequency is found to have a good linear relationship with the resonance peak order at different given ambient temperatures of-20 to 60 deg.C, and the graph (a) is inserted with SL 2 As a function of temperature T, it can be seen that R2 according to the fitted line reaches 0.999, indicating SL 2 Has good linearity with T, thereby showing that the method can be based on the slope
And solving to obtain the environmental temperature T to be measured. Such asAs shown in the graph (b) in fig. 7, the upper fitting straight line is a change curve of the test temperature with the ambient temperature obtained by solving a slope SL based on the change of the multiple resonance peaks with the orders, and the lower fitting straight line is a change curve of the test temperature with the ambient temperature obtained by solving the resonance frequency of the first-order resonance peak according to the formula (1), so that the linearity of the upper fitting straight line is better, and it can be seen from the illustration in the graph (b), the error MAE of the test temperature with respect to the ambient temperature obtained by using a single resonance peak in the upper fitting straight line is as high as 14 ℃, and the error of the test temperature with respect to the ambient temperature obtained by using the fitting slopes SL of the multiple resonance frequencies with the orders in the lower fitting straight line is within 2 ℃, so that the test accuracy is remarkably improved.
In summary, in the actual measurement process, the accuracy of temperature measurement may be improved by averaging the temperature values calculated by the respective harmonic peaks in the background noise spectrum, or averaging the temperature values calculated by the respective harmonic peaks with the quality factor and the signal-to-noise ratio close to each other, and more preferably, the accuracy of temperature measurement is higher by calculating the temperature values by using the fitting slope of the frequencies of the plurality of harmonic peaks along with the order, compared to the foregoing manner.
Fifth embodiment
In a fifth exemplary embodiment of the present invention, the acoustic fabry-perot resonator of the structure described in the first embodiment, which was prepared in the laboratory, was placed in a total anechoic chamber of size 6.4 mx 4.7 mx 4.2m and background noise less than 6dBA to measure the background noise spectrum.
Fig. 8 is a spectrum of background noise measured in a total anechoic chamber using a lab-prepared acoustic fabry-perot resonator according to a fifth embodiment of the present invention. When no sound is applied, a separate microphone is placed in the central area inside the total muffled chamber to estimate the ambient background noise, and the result is shown in fig. 8 (a). A flatter spectrum can be observed with the sound pressure amplitude of the noise floor substantially below 0 dB. An acoustic fabry-perot resonator is then placed near the reference microphone for background noise measurement and signal processing. The obtained power spectrum is shown in fig. 8 (b). The signal-to-noise ratio of the system operating in the total anechoic chamber is reduced compared to the results obtained in the third embodiment, but clear first seven-order formants are still visible. This indicates that the system can still function properly even in a relatively quiet environment. FIG. 8 (c) is a graph showing the linear change of the resonance frequencies according to the resonance peak order in the graph (b), the fitting linearity is 0.999, the slope is 0.451, and the measured ambient temperature is 18.41 ℃ in combination with the equation (2), which is slightly lower than 20.5 ℃ measured by a commercially available electronic thermometer (Testo 635-2, testo SE &Co. KGaA, germany).
So far, five embodiments of the present invention have been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly recognize that the acoustic temperature sensor and the temperature measuring method of the present invention are applicable.
In summary, the acoustic temperature sensor and the temperature measurement method of the invention can realize temperature measurement by measuring the ambient background noise without active sound source excitation, and have the advantages of simple structure and operation, high sensitivity, low power consumption, low cost, etc. By using a MEMS acoustic sensor and a miniature acoustic waveguide, the acoustic temperature sensor of the present invention can also be developed as a highly integrated on-chip acoustic thermometer.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An acoustic temperature sensor, comprising:
the microphone is used for detecting sound waves and is provided with a sound sensing surface;
the acoustic wave guide tube is provided with a first port and a second port, wherein the port faces of the first port and the second port are flush, the first port and the second port form an acoustic wave Fabry-Perot resonator after being blocked by the microphone, a first reflecting face of the acoustic wave Fabry-Perot resonator is a sound sensing face of the microphone, and a second reflecting face of the acoustic wave Fabry-Perot resonator is an interface between inside air and outside air of the second port;
after the background noise of the tested environment is transmitted into the sound wave guide pipe from the second port, the background noise is modulated by the sound wave Fabry-Perot resonator, and a background noise signal obtained through modulation is converted into an electric signal by the microphone and then is output;
and the power supply and signal processing module is electrically connected with the microphone and used for supplying power to the microphone and processing the electric signal output by the microphone to obtain the temperature of the detected environment.
2. The acoustic temperature sensor of claim 1, wherein the acoustic waveguide is one of a metal tube, a ceramic tube, a hardwood tube, a glass tube, a PVC tube.
3. The acoustic temperature sensor of claim 1, wherein the acoustic waveguide is linear, curved, or a combination of linear and curved.
4. The acoustic temperature sensor of claim 1 or 3, wherein axes at the first and second ports of the acoustic waveguide are perpendicular to the first and second reflective surfaces of the acoustic fabry-perot resonator.
5. The acoustic temperature sensor of claim 1, wherein the microphone is one of an electret condenser microphone, a piezoelectric microphone, an electromagnetic microphone, a fiber optic microphone, a grating microphone, and a MEMS microphone.
6. The acoustic temperature sensor of claim 1, wherein a lower frequency response limit of the microphone is no greater than 50Hz.
7. A method of measuring temperature using an acoustic temperature sensor according to any of claims 1 to 6, comprising the steps of:
step A: the acoustic wave Fabry-Perot resonator is placed in a tested environment, and a power supply and signal processing module supplies power to the acoustic wave Fabry-Perot resonator;
and B: continuously detecting background noise of a detected environment for multiple times by using the acoustic wave Fabry-Perot resonator, and outputting multiple background noise time domain spectrums;
step C: processing the plurality of background noise time domain spectrums by using the power supply and signal processing module to obtain a background noise frequency spectrum, wherein the processing comprises frequency spectrum conversion and frequency spectrum superposition;
step D: determining frequencies and orders corresponding to a plurality of resonance peaks from the background noise spectrum by using the power supply and signal processing module;
step E: and solving the temperature of the measured environment according to the linear regression slope between the frequency and the order of the resonance peaks.
8. The method according to claim 7, wherein step E specifically comprises:
substep E1: drawing a linear curve between the frequency and the order corresponding to the resonance peaks;
substep E2: solving the temperature of the measured environment according to the slope of the linear curve by using the following formula:
wherein SL is the slope of the linear curve, T is the Kelvin temperature of the measured environment, B is a constant, B =20.05 for airborne sound, L is the acoustic waveguide length between the first and second reflective surfaces.
9. The method of claim 7, further comprising:
detecting the background noise of the detected environment by using a reference microphone to obtain a reference background noise time domain spectrum; and
performing frequency spectrum conversion on the reference background noise time domain spectrum by using the power supply and signal processing module to obtain a reference background noise frequency spectrum;
step C also includes: and carrying out differential operation on the background noise frequency spectrum and the reference background noise frequency spectrum to obtain a background noise frequency spectrum after differential operation.
10. The method as claimed in claim 7, wherein the background noise of the measured environment is continuously detected not less than 3 times by using the acoustic fabry-perot resonator.
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