CN109814152A

CN109814152A - A kind of infrasound sensor and its realization method

Info

Publication number: CN109814152A
Application number: CN201910159712.0A
Authority: CN
Inventors: 邵建龙; 薛春; 邵馨叶; 金建辉; 刘羽升; 王奕文; 李重
Original assignee: Kunming University of Science and Technology
Current assignee: Kunming University of Science and Technology
Priority date: 2019-03-04
Filing date: 2019-03-04
Publication date: 2019-05-28
Anticipated expiration: 2039-03-04
Also published as: CN109814152B

Abstract

The invention relates to an infrasound sensor and a realization method thereof, belonging to the technical field of earthquake monitoring. The infrasound sensor of the invention comprises a plastic casing, a circuit board containing a single chip microcomputer and an acceleration sensor, and a lead wire; the acceleration sensor on the circuit board is connected with the single chip computer, and the circuit board is hermetically packaged by a plastic casing with strong airtightness and waterproofness. The implementation method of the present invention includes: mode setting; installing a device; reading infrasound signals; infrasound signal de-interference; The invention is hermetically packaged and placed in the underground or deep water to detect the precursor infrasound of an underground earthquake. The device has the characteristics of low cost, convenient use, simple and reliable, small size, and easy portability and installation.

Description

A kind of infrasound sensor and its implementation

Technical field

The present invention relates to a kind of infrasound sensor and its implementation, belong to seismic monitoring system field.

Background technique

Violent earthquake causes great disaster to the mankind, and 21 century violent earthquake is increased, and the prediction of violent earthquake is very anxious Compel.As research of the mankind to earthquake is more and more deep, numerous studies data shows to send out ground in Seismogenic Process Shake infrasound.If can the infrasonic characteristic of earthquake be analyzed and be monitored, this will be the hair shake of foreseeing earthquake in advance Moment, earthquake centre and earthquake magnitude provide very big help, this will also will be greatly reduced the harm of earthquake, so we are detection the earth Shake omen infrasound provides a solution.Numerous scholars carry out research and have found the infrasonic feature of violent earthquake omen: 7 Grade or more violent earthquake shake first 10 days or so in can receive infrasonic sound abnormal signal；The infrasonic sound abnormal signal of the overwhelming majority is maximum Acoustic pressure is more than 100dB；The abnormal frequency range of earthquake abnormal infrasonic wave signal is 10^-3Hz magnitude；From the point of view of the Energy distribution of spectrogram, Energy focuses mostly in 0.0015~0.0045Hz.It can be distinguished with other natural infrasonic sounds and artificial infrasonic sound by these characteristics Come.Existing infrasound sensor volume is big, at high cost, uses complex, thus leads to existing seismic monitoring mode It is at high cost, it uses complex, has more interference, so detecting the method for earthquake in the world using infrasonic monitoring mode It is still a very stubborn problem.Therefore, designing a suitable infrasound sensor is urgent for seismic monitoring etc. It is essential and wants.

Summary of the invention

The technical problem to be solved by the present invention is the present invention provides a kind of infrasound sensor and its implementation, to be used for It is at high cost to solve existing seismic monitoring mode, uses complex, there is the problem of more interference.

The technical scheme is that: a kind of infrasound sensor, including plastic shell 1, single-chip microcontroller 2, acceleration transducer 3； Wherein acceleration transducer 3 is connected with single-chip microcontroller 2, and acceleration transducer 3 and single-chip microcontroller 2 pass through 1 enclosed package of plastic shell simultaneously It is embedded in underground, the plastic shell strong using leakproofness and waterproofness of plastic shell 1.

Further, the acceleration transducer 3 uses nine axle sensor of MPU-9250.

Further, the acceleration transducer 3 can be replaced with three analog acceleration sensors, instead of rear, sensing Device can according to need addition low-pass filter circuit and amplifying circuit, can collect infrasonic sound in analog acceleration sensor in this way It after signal, is filtered out by the other signals that low-pass filter circuit will be above required infrasound signals highest frequency, using putting Big circuit carries out signal amplification, can control the sensitivity of sensor as needed, by three analog acceleration sensors with Orthogonal mode is put, to simulate the detection that 3-axis acceleration sensor carries out sound source amplitude, frequency, orientation.

Further, the acceleration transducer 3 is communicated by i2c and is connected with single-chip microcontroller 2, and single-chip microcontroller 2 uses STM32F103；Wherein, the SCL mouth of MPU-9250 connects the PB5 mouth of single-chip microcontroller 2, and the SDA mouthfuls of PB6 mouths for connecing single-chip microcontroller 2, VCC mouthfuls connect VCC, GND mouthfuls of power supply ground connection.

Further, the acceleration transducer 3 is connected by SPI communication with single-chip microcontroller 2, and single-chip microcontroller 2 uses STM32F103；Wherein, the SCLK mouth of MPU-9250 connects the PA15 mouth of single-chip microcontroller 2, the SDI mouthfuls of PB3 mouths for connecing single-chip microcontroller 2, and SDO mouthfuls Connect the PB4 mouth of single-chip microcontroller 2, the NCS mouthfuls of PB7 mouths for connecing single-chip microcontroller 2, VCC mouthfuls connect power supply VCC, GND mouthfuls of ground connection.

Further, the connection of the acceleration transducer 3, single-chip microcontroller 2 and plastic shell 1 is dry connection, and uses spiral shell Silk is fixed, and the power supply of single-chip microcontroller 2 and serial ports are exported by USB line, when infrasound sensor is embedded in more than earth's surface 5 When at the underground of meter Shen or deep water, USB line needs plus repeater, and the junction of plastic shell 1 is then carried out heat-seal processing, The junction of plastic shell 1 and USB line package tinfoil and gluing processing are simultaneously placed desiccant in inside and are fixed, then will dress It sets and is embedded at underground or deep water.

A kind of implementation method of infrasound sensor, specific step is as follows for the implementation method:

A, mode setting: there are three types of operating modes for sensor, are general sound detection mode, general infrasound detection mould respectively Formula and low frequency infrasound detection mode, the audio detection range of general sound detection mode accelerate in 20Hz to 800Hz for detecting Spend the quality of sensor 3, the audio detection range of general infrasound detection mode is low for detecting earthquake infrasonic sound in 1Hz to 20Hz The audio detection range of frequency sound detection mode is in 0.001Hz to 0.005Hz, for detecting seismic precursor infrasound signals, is passing After sensor powers on, the initial operation mode of default is low frequency infrasound detection mode, sends character string to sensor by serial ports " mode1 ", operating mode will be set as general sound detection mode, send character string " mode2 " to device by serial ports, work Mode will be set as general infrasound detection mode, send character string " mode3 " to device by serial ports, operating mode will be set as Low frequency infrasound detection mode；

B, mounting device: being set as general sound detection mode in operating mode, and having detected acceleration transducer 3 can be normal After use, acceleration transducer 3 is connect with single-chip microcontroller 2 it is errorless after be placed on leakproofness and the strong plastic shell of waterproofness In 1, and the connection of acceleration transducer 3, single-chip microcontroller 2 and plastic shell 1 is dry connection, and is fixed with screw, and will The power supply and serial ports of single-chip microcontroller 2 are exported by USB line, convenient to power and transmit data to device, when device needs are embedded in When more than at the underground of 5 meters of depths of earth's surface or deep water, USB line needs plus repeater, and the junction of plastic shell is then carried out heat The junction package tinfoil and gluing of encapsulation process, plastic shell and USB line handle and place desiccant in inside and fix, Reach waterproof, dampproof effect, because sound propagation loss in solid and liquid is far below in gas propagation loss, then Device is embedded at underground or deep water, Lai Zengjia device detects the sensitivity of infrasonic sound, sets after placing, then by operating mode It is set to low frequency infrasound detection mode, and character string " RESET " is sent to device by serial ports, is initialized；

C, read infrasound signals: Setting pattern and after installing device reads signal by acceleration transducer, The value of reading is the value of the acceleration of three fluctuations on three-dimensional cartesian coordinate system direction, due to defaulting the acceleration transducer used It is nine axle sensor of MPU-9250, it is capacitance acceleration transducer, its principle is when sensor is in the feelings of acceleration Under condition, internal mass block can cause to deviate due to inertia force, so that the capacitance of its internal capacitance is changed, pass through capacitance Variable quantity detects the value of acceleration, and the propagation of sound is also the propagation of energy, will cause the matter inside acceleration transducer Gauge block carries out forced vibration, causes the capacitance of its internal capacitance to change, allows to detect acceleration value, forced vibration Amplitude it is related with the amplitude of sound source, frequency, the frequency of forced vibration and the frequency of sound source are identical, when frequency is constant, are forced to The amplitude of vibration and the amplitude of sound source are directly proportional, and the frequency of sound source is closer to the intrinsic frequency of forced vibration object, forced oscillation Dynamic amplitude is bigger, and the amplitude of the acoustic pressure of sound source and sound source, frequency relation are as follows:

P=2 π crhoAf

Wherein, P is the acoustic pressure of focus, and c is the velocity of sound, and rho is sound source density, and A is the amplitude of sound source, and f is the frequency of sound source, As can be seen that the amplitude of acoustic pressure and sound source is directly proportional when frequency is identical, so when frequency is identical, acoustic pressure and forced vibration Amplitude it is also directly proportional, and amplitude of the acceleration transducer Internal moving mass in forced vibration and its detect the acceleration of fluctuation The amplitude of angle value is also directly proportional, so acoustic pressure and acceleration transducer detect that the amplitude of the acceleration value of fluctuation is also directly proportional, Its relationship is as follows:

P=ka

Wherein P is the acoustic pressure of focus, and a is the amplitude of the acceleration value of detected fluctuation, and k is proportionality coefficient, and sound For the frequency in source closer to the intrinsic frequency of forced vibration object, the amplitude of forced vibration is bigger, so ratio at different frequencies Example coefficient k is different, and its proportionality coefficient of different acceleration transducers k is also different in addition sensor locating for geography Position is different, and proportionality coefficient k is also different, and the acceleration transducer inside device and plastic shell are dry connection, institute With when detecting infrasonic sound, the shell and plastic shell of internal acceleration transducer can take the lead in that forced vibration occurs, and internal Acceleration transducer Internal moving mass can and plastic shell occur forced vibration, also will increase the sensitive of sensor in this way Degree, but can also change its proportionality coefficient k, it so needing to test it, can determine proportionality coefficient k, be embedded in sensor With rear at underground or deep water, sending character string " record " to device by serial ports makes sensor enter recording mode, then uses One can produce 0 to 0.005Hz infrasonic instrument to generate the infrasound that pressure is 10Pa, since 0.0015Hz, often Every two seconds frequency increments 0.00015Hz, until 0.0045Hz, sensor can calculate the proportionality coefficient k of this 21 groups of frequencies Value, and stored, then sending character string " normal " to device by serial ports makes sensor come back to low frequency Infrasound detection mode starts to read infrasound signals；

D, infrasound signals go to interfere: single-chip microcontroller 2 is after receiving the data come transmitted by acceleration transducer 3, when adding Velocity sensor 3 be MPU9250 sensor when, can by second-order low-pass filter algorithm to the signal detected on three directions into Row filtering calculates, and the acoustic signals other than the maximum value more than required frequency is filtered out, second-order low-pass filter algorithm is as follows:

Wherein, Y_nFor this filtered value, x_nFor this sampled value, Y_n-1For last time filtered value, Y_n-2It is upper Secondary filtered value, a and b are filter factor, and the value of a is as follows:

Wherein f_HFor cutoff frequency, so, as long as determining cutoff frequency, it can determine that the value of filter factor a, the value of b is such as Under:

B=T²

Wherein T is sampling interval duration, so just can determine that filter factor after program sets sampling interval duration The value of b, when acceleration transducer 3 is three analog acceleration sensors put with orthogonal manner, directly to each simulation Acceleration transducer is filtered using low-pass filter circuit, and uses amplifying circuit as needed, no matter uses step low-pass Filtering algorithm or low-pass filter circuit, cutoff frequency are disposed as 0.0045Hz, when using second-order low-pass filter algorithm, Its sample frequency is set as 0.0096Hz；

E, infrasound signals Frenguency chage: after step D, single-chip microcontroller is to the signal on filtered three directions point Not carry out sample frequency 0.0096Hz, 64 points of FFT transform, i.e. Fast Fourier Transform (FFT), it can be transformed to time-domain signal Frequency-region signal both can guarantee that the frequency error of gained signal was lower, and also can guarantee that algorithm was gathered around using 64 points of FFT transform algorithm There is lower amount of storage, reduce the requirement to single-chip microcontroller, amplitude a corresponding to each frequency can be found out by following formula:

Wherein, a_x、a_y、a_zFor each frequency on three-dimensional cartesian coordinate system direction corresponding three amplitudes, then frequency Amplitude a corresponding to frequency in 0.0015Hz to 0.0045Hz is multiplied by the corresponding proportionality coefficient k stored in step C After, so that it may obtain the amplitude of infrasound signals corresponding to the frequency in 0.0015Hz to 0.0045Hz；

F, send data: single-chip microcontroller is after receiving the data come transmitted by acceleration transducer, by low-pass filtering After algorithm and fft algorithm, resulting data are three infrasound signals amplitudes and corresponding time on three-dimensional cartesian coordinate system direction Acoustical signal frequency can be calculated infrasound signals amplitude and specific infrasonic sound Sounnd source direction using algorithm, will measure number with serial ports According to being sent；

G, circulatory monitoring:

After sensor powers on and sets operating mode and installs, sensor can repeat step C, D, E, F.

The course of work of the invention is:

The first step, mode setting: there are three types of operating modes for sensor, are general sound detection mode, general infrasonic sound respectively Detection pattern and low frequency infrasound detection mode, the audio detection range of general sound detection mode is in 20Hz to 800Hz, for examining The quality of acceleration pick-up sensor, the audio detection range of general infrasound detection mode is in 1Hz to 20Hz, for detecting earthquake time Sound, the audio detection range of low frequency infrasound detection mode is in 0.001Hz to 0.005Hz, for detecting seismic precursor infrasound signals, On a sensor after electricity, the initial operation mode of default is low frequency infrasound detection mode, sends word to sensor by serial ports Symbol string " mode1 ", operating mode will be set as general sound detection mode, send character string " mode2 " to device by serial ports, Operating mode will be set as general infrasound detection mode, send character string " mode3 " to device by serial ports, operating mode will be set It is set to low frequency infrasound detection mode；

Second step, mounting device: it is set as general sound detection mode in operating mode, having detected acceleration transducer can After normal use, so that it may the installation for carrying out device, by the connection of each module it is errorless after be placed on leakproofness and waterproofness In strong plastic shell, and the connection of each module and plastic shell is dry connection, and is fixed with screw, and by single-chip microcontroller Power supply and serial ports exported by USB line, it is convenient to power and transmit data to device, when device needs are embedded in more than earth's surface When at the underground of 5 meters of depths or deep water, USB line needs plus repeater, then by the junction of plastic shell carry out heat-seal processing, The junction of plastic shell and USB line package tinfoil and gluing processing are simultaneously placed desiccant in inside and are fixed, anti-to reach Water, dampproof effect finally will dresses because sound propagation loss in solid and liquid is far below the propagation loss in gas It sets and is embedded at underground or deep water, the sensitivity of Lai Zengjia device detection infrasonic sound sets low for operating mode after placing Frequency sound detection mode, and character string " RESET " is sent to device by serial ports, it is initialized；

Third step reads infrasound signals: Setting pattern and after installing device, is read by acceleration transducer Signal, the value of reading are the value of the acceleration of three fluctuations on three-dimensional cartesian coordinate system direction, due to defaulting the acceleration used Sensor is nine axle sensor of MPU-9250, it is capacitance acceleration transducer, its principle is accelerated when sensor is in In the case where degree, internal mass block can cause to deviate due to inertia force, so that the capacitance of its internal capacitance is changed, pass through The variable quantity of capacitance detects the value of acceleration, and the propagation of sound is also the propagation of energy, be will cause in acceleration transducer The mass block in portion carries out forced vibration, causes the capacitance of its internal capacitance to change, allows to detect acceleration value, by The amplitude for compeling vibration is related with the amplitude of sound source, frequency, and the frequency of forced vibration and the frequency of sound source are identical, constant in frequency When, the amplitude of forced vibration and the amplitude of sound source are directly proportional, and the frequency of sound source is closer to the intrinsic frequency of forced vibration object, The amplitude of forced vibration is bigger, and the amplitude of the acoustic pressure of sound source and sound source, frequency relation are as follows:

P=2 π crhoAf

P=ka

4th step, infrasound signals go to interfere: single-chip microcontroller receive transmitted by acceleration transducer come data after, when It, can be by second-order low-pass filter algorithm to the signal detected on three directions when acceleration transducer is MPU9250 sensor It is filtered calculating, the acoustic signals other than the maximum value more than required frequency are filtered out, prevent from causing testing result Interference, second-order low-pass filter algorithm are as follows:

Wherein f_HFor cutoff frequency, so, as long as determining cutoff frequency, so that it may determine the value of filter factor a, the value of b It is as follows:

B=T²

Wherein T is sampling interval duration, so after program sets sampling interval duration, so that it may determine filtering system The value of number b, when acceleration transducer is three analog acceleration sensors put with orthogonal manner, directly to each simulation Acceleration transducer is filtered using low-pass filter circuit, and can use amplifying circuit as needed, no matter low using second order Pass filter algorithm or low-pass filter circuit, cutoff frequency are disposed as 0.0045Hz, are using second-order low-pass filter algorithm When, sample frequency is set as 0.0096Hz；

5th step, infrasound signals Frenguency chage: after the 4th step, single-chip microcontroller is on filtered three directions Signal carries out the FFT transform of sample frequency 0.0096Hz, at 64 points respectively, i.e. Fast Fourier Transform (FFT), it can be time-domain signal It is transformed to frequency-region signal, using 64 points of FFT transform algorithm, both can guarantee that the frequency error of gained signal was lower, and also can guarantee Algorithm possesses lower amount of storage, reduces the requirement to single-chip microcontroller, and amplitude a corresponding to each frequency can be asked by following formula Out:

Wherein, a_x、a_y、a_zFor each frequency on three-dimensional cartesian coordinate system direction corresponding three amplitudes, then frequency Amplitude a corresponding to frequency in 0.0015Hz to 0.0045Hz is multiplied by the corresponding proportionality coefficient stored in third step After k, so that it may obtain the amplitude of infrasound signals corresponding to the frequency in 0.0015Hz to 0.0045Hz；

6th step sends data: single-chip microcontroller is after receiving the data come transmitted by acceleration transducer, by low pass After filtering algorithm and fft algorithm, resulting data are three infrasound signals amplitudes and right on three-dimensional cartesian coordinate system direction Infrasound signals frequency is answered, can be calculated infrasound signals amplitude and specific infrasonic sound Sounnd source direction using algorithm, will be surveyed with serial ports Data are obtained to be sent；

7th step, circulatory monitoring:

After sensor powers on and sets operating mode and installs, sensor can repeat Step 3: four, Five, six.

The beneficial effects of the present invention are: the present invention is using sound, the propagation loss in solid and liquid is far below in gas Device enclosed package is placed at underground or deep water by the principle of propagation loss, and Lai Zengjia device detects the sensitivity of infrasonic sound, is made It is used lower cost, to reach the detection effect of high cost high accuracy infrasound sensor, the present invention possesses at low cost, user Just, simple and reliable, small in size, the features such as being easy to carry about with one and installing.

Detailed description of the invention

Fig. 1 is structural block diagram of the invention；

Fig. 2 is the circuit diagram of embodiment 1 in the present invention；

Fig. 3 is the circuit diagram of embodiment 2 in the present invention；

Each label in figure: 1- plastic shell, 2- single-chip microcontroller, 3- acceleration transducer.

Specific embodiment

In the following with reference to the drawings and specific embodiments, the invention will be further described.

Embodiment 1: as shown in Figs. 1-2, a kind of infrasound sensor, including plastic shell 1, single-chip microcontroller 2, acceleration transducer 3；Wherein acceleration transducer 3 is connected with single-chip microcontroller 2, and acceleration transducer 3 and single-chip microcontroller 2 pass through 1 enclosed package of plastic shell And it is embedded in underground, the plastic shell strong using leakproofness and waterproofness of plastic shell 1.

Further, the acceleration transducer 3 uses nine axle sensor of MPU-9250.

Nine axle sensor of MPU-9250 (i.e. U2) is led to single-chip microcontroller 2 (i.e. U1) by a data wire and a clock line Letter, single-chip microcontroller U1 generates clock pulses, address signal, data-signal in bus, and nine axle sensor U2 of MPU-9250 is then Address wire, data line, control line are combined into the signal wire of a serially-transmitted data, this mode signal wire in a serial fashion Less, circuit connection is simple, saves system resource and board area；External AX5043 wireless transport module (i.e. U3) and monolithic Machine U1 is connected by way of serial ports, and another AX5043 wireless transport module is connected by way of serial ports with host computer It connects, host computer is also possible to other CPU devices either computer, so that the device can not only be used for an independent system System, can also be used as a sensor module to participate in other systems.

P=2 π crhoAf

P=ka

B=T²

F, send data: single-chip microcontroller is after receiving the data come transmitted by acceleration transducer, by low-pass filtering After algorithm and fft algorithm, resulting data are three infrasound signals amplitudes and corresponding time on three-dimensional cartesian coordinate system direction Acoustical signal frequency can be calculated infrasound signals amplitude and specific infrasonic sound Sounnd source direction using algorithm, be connected with serial ports AX5043 wireless transport module sends data measured, receives data with another AX5043 wireless transport module；

G, circulatory monitoring:

Embodiment 2: such as Fig. 1, shown in Fig. 3, a kind of infrasound sensor and its implementation, the present embodiment and 1 phase of embodiment Together, wherein the difference is that:

Nine axle sensor of MPU-9250 (i.e. U2) selects signal wire by two data lines, a heel piece with single-chip microcontroller 2 (i.e. U1) Communicated with a clock line, this mode transmission speed faster, and when needing multiple nine axle sensors of MPU-9250 only It needs to control each nine axle sensor of MPU-9250 by piece choosing with single-chip microcontroller U1；Air202 (i.e. U3) and single-chip microcontroller U1 passes through The mode of serial ports connects, and Air202U3 is the signal transmission module of Ali's cloud, it can be by an Internet of Things card directly by data It is sent in the account of Ali's cloud, display and other calculating is then carried out in Ali's cloud platform, this mode is easy to use, can To be checked and be arranged with computer and mobile communications device whenever and wherever possible, so that host computer is more flexible, do not have to limit It on a host computer, but can not be participated in sensor as a module in other systems, an independence can only be used as System come using.

Step F, send data: single-chip microcontroller is after receiving the data come transmitted by acceleration transducer, by low pass After filtering algorithm and fft algorithm, resulting data are three infrasound signals amplitudes and right on three-dimensional cartesian coordinate system direction Infrasound signals frequency is answered, infrasound signals amplitude and specific infrasonic sound Sounnd source direction is can be calculated using algorithm, is connected with serial ports Air202 module sends data measured, transmits data in specific Ali's cloud account, is further processed；

Embodiment 3: as shown in Figure 1-3, a kind of infrasound sensor and its implementation, the present embodiment is same as Example 1, Wherein the difference is that:

The advantages of this mode, is, according to the component model in self-designed low-pass filter circuit and amplifying circuit And parameter, transducer sensitivity required for oneself can be configured more flexiblely, and hardware filtering circuit not will receive and adopt The influence of sample frequency will not be influenced by the single-chip microcontroller speed of service, and filter effect can be more preferable, but hardware circuit becomes more, And ADC mouthfuls there are two general sensors, and which needs three analog acceleration sensors, so at least needing two lists Piece machine causes cost to become more, and sensor is bigger heavier.

Specific embodiments of the present invention are explained in detail above in conjunction with attached drawing, but the present invention is not limited to above-mentioned realities Example is applied, it within the knowledge of a person skilled in the art, can also be without departing from the purpose of the present invention Various changes can be made.

Claims

1. An infrasound sensor, characterized in that: comprising a plastic casing (1), a single-chip microcomputer (2), and an acceleration sensor (3); wherein the acceleration sensor (3) is connected to the single-chip microcomputer (2), and the acceleration sensor (3) is connected to the single-chip microcomputer (2). (2) Hermetically encapsulated and buried in the ground through the plastic casing (1).

2 . The infrasound sensor according to claim 1 , wherein the acceleration sensor ( 3 ) adopts an MPU-9250 nine-axis sensor. 3 .

3. The infrasound sensor according to claim 1, characterized in that: the acceleration sensor (3) adopts three analog acceleration sensors placed in an orthogonal manner, and each analog acceleration sensor comprises a low-pass filter circuit and amplifying circuit.

4. The infrasound sensor according to claim 3, characterized in that: the acceleration sensor (3) is used to collect infrasound signals, and other signals higher than the highest frequency of the required infrasound signals are processed by a low-pass filter circuit. After filtering, the signal is amplified by the amplifying circuit, and the three analog acceleration sensors are placed in an orthogonal manner to simulate the three-axis acceleration sensor to detect the amplitude, frequency and orientation of the sound source.

5. The infrasound sensor according to claim 2, characterized in that: the acceleration sensor (3) is connected to the single-chip microcomputer (2) through i2c communication, and the single-chip microcomputer (2) adopts STM32F103; wherein, the SCL port of the MPU-9250 is connected to The PB5 port of the microcontroller (2), the SDA port is connected to the PB6 port of the microcontroller (2), the VCC port is connected to the power supply VCC, and the GND port is grounded.

6. The infrasound sensor according to claim 2, wherein the acceleration sensor (3) is connected to the single-chip microcomputer (2) through SPI communication, and the single-chip microcomputer (2) adopts STM32F103; wherein, the SCLK port of the MPU-9250 is connected to The PA15 port of the microcontroller (2), the SDI port is connected to the PB3 port of the microcontroller (2), the SDO port is connected to the PB4 port of the microcontroller (2), the NCS port is connected to the PB7 port of the microcontroller (2), the VCC port is connected to the power supply VCC, and the GND port is grounded .

7. The infrasound sensor according to claim 1, characterized in that: the acceleration sensor (3), the single-chip microcomputer (2) and the plastic casing (1) are connected by dry connection, and are fixed with screws, and the single-chip microcomputer is connected (2) The power supply and serial port are exported through the USB cable. When the infrasound sensor is buried in the ground or deep water more than 5 meters above the surface, the USB cable needs to be added with a repeater, and then the connection of the plastic shell (1) is connected. After heat sealing, the connection between the plastic casing (1) and the USB cable is wrapped with tin foil and glued, and a desiccant is placed inside and fixed, and then the device is buried underground or in deep water.

8. A realization method of an infrasound sensor, characterized in that: the concrete steps of the realization method are as follows:

A. Mode setting: The sensor has three working modes, namely the general sound detection mode, the general infrasound detection mode and the low-frequency infrasound detection mode. The audio detection range of the general sound detection mode is 20Hz to 800Hz, which is used to detect the acceleration sensor (3 ) is good or bad, the audio detection range of general infrasound detection mode is 1Hz to 20Hz, which is used to detect earthquake infrasound, and the audio detection range of low frequency infrasound detection mode is 0.001Hz to 0.005Hz, which is used to detect earthquake precursor infrasound signals , After the sensor is powered on, the default initial working mode is the low-frequency infrasound detection mode, send the string "mode1" to the sensor through the serial port, the working mode will be set to the general sound detection mode, and send the string "mode2" to the device through the serial port , the working mode will be set to the general infrasound detection mode, and the string "mode3" will be sent to the device through the serial port, and the working mode will be set to the low-frequency infrasound detection mode;

B. Installation device: When the working mode is set to the general sound detection mode, after detecting that the acceleration sensor (3) can be used normally, connect the acceleration sensor (3) to the single-chip microcomputer (2) and place it in a strong airtight and waterproof place. Inside the plastic housing (1), and the connection between the acceleration sensor (3), the single-chip microcomputer (2) and the plastic housing (1) is a dry connection, and is fixed with screws, and the power supply and serial port of the single-chip microcomputer (2) are connected through the USB cable. Export, when the device needs to be buried in the ground or deep water more than 5 meters above the surface, the USB cable needs to be added with a repeater, and then the connection of the plastic casing is thermally packaged, and the connection between the plastic casing and the USB cable is wrapped with tin foil and Apply glue, place desiccant inside and fix it, then bury the device in the ground or deep water, set the working mode to low-frequency infrasound detection mode, and send the string "RESET" to the device through the serial port for initialization;

C. Read the infrasound signal: After setting the mode and installing the device, read the signal through the acceleration sensor (3). The relationship between the pressure and the detected fluctuating acceleration value is as follows:

P=ka

Among them, P is the sound pressure of the source, a is the amplitude of the detected acceleration value of the fluctuation, and k is the proportional coefficient. After the sensor is buried in the ground or in deep water, the string "record" is sent to the device through the serial port to make the sensor enter Recording mode, and then use an instrument that can generate infrasound waves from 0 to 0.005Hz to generate infrasound waves with a pressure of 10Pa. Starting from 0.0015Hz, the frequency increases by 0.00015Hz every two seconds until 0.0045Hz, the sensor calculates the 21 groups of frequencies. The value of the proportional coefficient k is stored, and then the string "normal" is sent to the device through the serial port to make the sensor return to the low-frequency infrasound detection mode and start to read the infrasound signal;

D. Infrasound signal de-interference: after the single chip microcomputer (2) receives the data sent by the acceleration sensor (3), when the acceleration sensor (3) is an MPU9250 sensor, it will pass the second-order low-pass filtering algorithm to the three directions. The detected signal is filtered and calculated, and the acoustic signal beyond the maximum value of the required frequency is filtered out. The second-order low-pass filtering algorithm is as follows:

Among them, Y _n is the value after filtering this time, x _n is the sampling value this time, Y _n-1 is the value after filtering last time, Y _n-2 is the value after filtering last time, a and b are Filter coefficient, the value of a is as follows:

Where f _H is the cutoff frequency, so as long as the cutoff frequency is determined, the value of the filter coefficient a can be determined, and the value of b is as follows:

b=T ²

Among them, T is the sampling interval time, so when the program sets the sampling interval time, the value of the filter coefficient b can be determined. When the acceleration sensor (3) is three analog acceleration sensors placed in an orthogonal manner, directly Each analog accelerometer is filtered by a low-pass filter circuit, and an amplifying circuit is used as needed. No matter whether the second-order low-pass filter algorithm or the low-pass filter circuit is used, the cut-off frequency is set to 0.0045Hz, and the second-order low-pass filter algorithm is used. , its sampling frequency is set to 0.0096Hz;

E. Amplitude-frequency conversion of infrasound signal: after step D, the single-chip microcomputer (2) performs FFT transformation with a sampling frequency of 0.0096Hz and 64 points on the filtered signals in the three directions, namely fast Fourier transform, and converts the The time domain signal changes into a frequency signal, and the amplitude a corresponding to each frequency is obtained by the following formula:

Among them, a _x , a _y , a _z are the three amplitudes corresponding to each frequency in the direction of the three-dimensional rectangular coordinate system, and then multiply the amplitude a corresponding to the frequency within 0.0015Hz to 0.0045Hz by step C After the corresponding proportional coefficient k stored in , the amplitude of the infrasound signal corresponding to the frequency within 0.0015Hz to 0.0045Hz is obtained;

F. Sending data: After the single-chip microcomputer (2) receives the data sent by the acceleration sensor (3), after the low-pass filtering algorithm and the FFT algorithm, the obtained data are three infrasound signals in the direction of the three-dimensional rectangular coordinate system. The amplitude and the corresponding frequency of the infrasound signal, and then through the algorithm calculation, the amplitude of the infrasound signal and the specific infrasound source direction can be obtained, and the measured data is sent through the serial port;

G. Cycle monitoring:

After the sensor is powered on and the working mode is set and installed, the sensor will repeat steps C, D, E, and F.