CN101539588B - Half-bridge test method for modal resonance frequency of piezoresistive acceleration sensor - Google Patents

Abstract

The invention relates to a method for testing the modal resonance frequency of a piezoresistive acceleration sensor. It is characterized in that on the basis of maintaining the original full-bridge circuit connection structure of the piezoresistive acceleration sensor, it uses the rich frequency spectrum generated by the impact of metal collisions as the excitation source, and adopts the form of half-bridge output through an appropriate external circuit to obtain the acceleration sensor model. The resonant frequency information of the state is obtained, and the frequency spectrum analysis is performed using the obtained raw data to obtain the modal resonant frequency of the microstructure. The resonance frequency of the acceleration sensor mode includes different resonance frequencies of the same structure of the device in the sensitive direction and the non-sensitive direction. By determining the first-order resonance frequency of different modes of the acceleration sensor, the structural parameters of the microstructure manufacturing can also be obtained to verify the correctness of the structural size design, which can be used to analyze the working state of the device. The test method is suitable for high-range piezoresistive, capacitive and other types of acceleration sensors and pressure sensors with a full-bridge structure.

Description

Half-bridge test method for modal resonance frequency of piezoresistive acceleration sensor

technical field

The present invention relates to providing a test method based on the modal resonance frequency of a piezoresistive acceleration sensor, more precisely, it relates to a half-bridge test method for the modal resonance frequency of a piezoresistive acceleration sensor manufactured by micro-processing in the medium and high range, and belongs to micro sensors The field of mechanical testing analysis.

Background technique

In micro-nano electromechanical systems (MEMS), mode refers to the vibration mode of a structure, and different vibration modes correspond to different characteristic vibration frequencies. The modal analysis of the microstructure is an important analysis method to obtain the geometric structure information of the device and verify the working state of the device [Huang Weidong, Caixia Xu Bu, Lu Chengzhaonian, The influence of packaging on the performance of MEMS high-G value sensors, Journal of Functional Materials and Devices, 2002, 8 (3), pp251-258]. The piezoresistive acceleration sensor manufactured by micromachining with a range of 2000g (g=9.8m/s ² ) has important applications in many fields and is a main aspect of current research [VTSrikar, Stephen D. Senturia, The reliability of microelectromechanical systems ( MEMS) in shock environments, Journal of microelectromechanical systems, 2002, V11(3), pp206-214]. The resonant frequency of the first-order mode in the sensitive direction of the acceleration sensor is an important parameter to measure its working bandwidth. The higher the first-order resonance frequency, the wider the operating frequency range of the device. Therefore, different methods are often used to obtain important information about the resonance frequency of the device. However, the acquisition of resonance frequency information of other modes of the microstructure plays an important role in the design, implementation and application of devices and materials [R.Rabe, K.Janser, and W.Arnold, Vibrations of free and surface-coupled atomic force microscope Cantilevers: theory and experiment, Rev. Sci. Instrum. 67(9), 1996, pp3281-3293]. Because different modes correspond to different motion forms of the same structure of the device, from related experiments and simulation tests, the mechanical structure information of the device and the useful information stimulated during the working process can be obtained. Because there is a big difference between the test of the device under laboratory conditions and the test in the real working environment. Therefore, obtaining the resonant frequency of the acceleration sensor is an important analysis method, which is of great significance for identifying the intrinsic vibration of the device and obtaining the external characteristic vibration and shock.

The piezoresistive acceleration sensor generally adopts the connection mode of Wheatstone full bridge or half bridge circuit for the extraction of acceleration information. For example, the piezoresistive acceleration sensor, in the full-bridge measurement circuit, connects the piezoresistive with the same force property to the opposite side of the bridge, and connects the different piezoresistive to the adjacent side, and its output sensitivity is doubled compared with the half-bridge structure. Both non-linear error and temperature error are improved. Therefore, the sensitive resistor full-bridge circuit structure is widely used in the acquisition of various signals. The reason is that the structure output of the full-bridge form has many advantages: one has a larger output signal, that is, has a larger sensitivity output, and the other The more important reason is that the full-bridge structure can electrically eliminate the input signal and noise of the common mode component, so that the input of the useful differential signal can be effectively output. At present, in the design and implementation of micro-electro-mechanical systems, the sensitive structure or sensitive method is generally designed in the form of a full-bridge circuit, or the micro-mechanical inertial device is designed as a pair of identical micro-mechanical structures, and then the entire body is processed and manufactured on it. The sensitive resistance or capacitance structure of the bridge is also used to eliminate the common mode effect caused by vibration and shock. The full-bridge structure also has the characteristics of simple implementation and is the main way to obtain effective and sensitive information from the outside world.

Although the full-bridge structure is usually an effective way to suppress common-mode components, some relevant dynamic information about the interior of the device is concealed during the information extraction process. The test found that in the middle and high-range acceleration sensors, the resonance waves of other modes of the piezoresistive acceleration sensor are generally suppressed. In the half-bridge experiment, piezoresistors with different force directions are connected to the bridge as the adjacent side, and the output of the bridge has the characteristics of high sensitivity and good nonlinearity. However, it has no inhibitory effect on the common mode component, so the half-bridge output form can be used to obtain richer microstructure mode information.

General simulation tools such as finite element analysis software ANSYS can analyze the first few modes of microstructures. In terms of implementation, the modal information of the microstructure can be obtained by methods such as vibration table or laser strobe test, which are also limited by the driving mode and driving frequency. These methods are more effective for structures with relatively small elastic coefficients, and for medium and high-range acceleration sensors. There is a certain difficulty in obtaining the modal. Therefore, without changing the circuit structure of the original acceleration sensor, the present invention adopts an external half-bridge output mode, utilizes the metal collision resonance excitation mode, and combines Fourier transform analysis and other means to extract and analyze the original data to obtain the sensitive direction of the acceleration sensor. The modal information of the vibrating structure is related to the non-sensitive direction.

Contents of the invention

In summary, the purpose of the present invention is to provide a method for testing the modal resonance frequency of a piezoresistive acceleration sensor with a medium to high range. The present invention is characterized in that on the basis of maintaining the original full-bridge circuit connection structure of the piezoresistive acceleration sensor, a rich frequency spectrum generated by metal collision impact is used as an excitation source, and a half-bridge output form is adopted through an appropriate external circuit to obtain a device model. The resonant frequency information of the state is obtained, and then the spectrum analysis is performed using the obtained original data, and then the theoretical analysis and the corresponding test data are combined to obtain the modal resonant frequency of the microstructure. The resonant frequencies of the modes include the different resonant frequencies of the same structure of the device in the sensitive direction and the non-sensitive direction. The invention not only provides a test method for the modal resonance frequency of the medium-high range acceleration sensor device, but also determines the first-order resonance frequency of different modes of the acceleration sensor, thereby obtaining the structural parameters of the microstructure processing and verifying the design of the structural size The correctness, and the correctness of analyzing the working state of the device. This test does not exclude the results of the full-bridge structure test, and is suitable for high-range piezoresistive, capacitive and other types of acceleration sensors and pressure sensors with a full-bridge structure.

The resonant frequencies of different sensitive structures have different mathematical expressions. Figure 1 is a schematic diagram of the structure of the simplest cantilever beam acceleration sensor. The cantilever beam structure has modes such as deflection and torsion. Number 1 in Figure 1 indicates the cantilever beam, number 2 indicates the four sensitive resistive areas on the cantilever beam, number 3 indicates the sensitive normal direction of the sensor, and number 4 indicates the non-sensitive lateral direction of the sensor. For this cantilever beam structure, the resonant frequency of the first-order deflection form in sensitive direction 3, that is, the resonant frequency of mode 1, is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1.015</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.162</span>}\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h\; L"\; filenames="H2009100496345E00011.png,H2009100496345E00013.png"\; state="\{\{state\}\}">h</figure-callout></span><figure-callout\; id="2"\; label="h\; L"\; filenames="H2009100496345E00011.png,H2009100496345E00013.png"\; state="\{\{state\}\}">\; </figure-callout>}}{{\mathrm{<span\; class="notranslate">\; </span>}}^{}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; E.</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; ,</span>$

where k is the normal elastic coefficient of the cantilever beam, m is the effective mass of the cantilever beam, h is the thickness of the cantilever beam, L is the length, E and ρ are the Young’s modulus and density of silicon, respectively.

The first-order flexural resonant frequency of the insensitive transverse direction 4, that is, the resonant frequency of mode 2 is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; tr</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1.015</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; tr</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.162</span>}\frac{\mathrm{<span\; class="notranslate">\; w</span>}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L"\; filenames="H2009100496345E00011.png,H2009100496345E00013.png"\; state="\{\{state\}\}">L</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; E.</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}$

In the formula, k _tr is the transverse elastic coefficient of the cantilever beam, and w is the width of the cantilever beam. Because the width w is much larger than the thickness h, that is to say, the transverse resonance frequency _ftr of the cantilever beam is much higher than the resonance frequency f in the sensitive direction, so the transverse resonance frequency wave and high-order frequency wave of the cantilever beam are not easily excited ; Especially the output form of the full-bridge structure, to some extent, will suppress the appearance of high-order frequencies electrically and mechanically.

The piezoresistive acceleration sensor is composed of four sensitive resistors. The four sensitive resistors of the acceleration sensor and the corresponding amplifying circuit are connected as shown in Figure 2 and Figure 3, where the voltage (usually 5V) is applied to the sensitive resistor composed of sensitive resistors. on Stone Bridge. Fig. 2 is a schematic diagram of the output of the acceleration sensor and the operational amplifier connected with a full-bridge signal. In a full-bridge connection, connect the middle outputs of the two pairs of same-side sense resistors to the two inputs of an op amp. For the sensitive structure of the full bridge, it has a common-mode suppression effect on vibration and shock, especially for high-order modes. Therefore, on the basis of maintaining the full-bridge structure of the original acceleration sensor, a half-bridge output form is used to obtain the output characteristics of the sensitive structure on the circuit. Figure 3 is a schematic diagram of the output of a sensor and an operational amplifier connected in a half-bridge form. In the half-bridge output, the connection between the four sensitive resistors and the operational amplifier is the same as that of the full-bridge, except that one of the two input terminals connected to the operational amplifier is connected to the ground to form a half-bridge output. In this way, in fact, only half of the bridge signal is input to the operational amplifier, which means that only half of the bridge is working in the sensor. The result of this is that the signal amplitude output by the half bridge will be lost by half, because the characteristics of the output waveform in the sensitive direction of the sensor can be fully reflected by the device response caused by vibration and shock, and will not be suppressed. This method does not exclude the way that the full-bridge structure can obtain the modal resonance frequency, but it is easier to observe the natural waveform characteristics of the sensor and obtain the resonance frequency of the vibration mode through the half-bridge form, which is an effective method.

In the present invention, a metal rod collides with a metal steel anvil on the ground as an excitation source for generating high-acceleration and high-frequency component waves when falling. The collision end face of the metal rod is first decelerated and then accelerated upwards. The velocity change of the colliding end face produces a stress wave (sound wave in a solid), which propagates to the other end of the metal rod. When t=L/C (L is the length of the metal rod, C is the speed of sound in the metal rod), the sound wave travels to the sensor end of the metal rod. If the sensor is rigidly connected directly to the metal rod, the sound waves are fully transmitted to the sensor.

Figure 4 is a schematic diagram of three installations of the device. Along the pin direction (y direction in the figure) is the sensitive direction of the acceleration sensor. Figure 4(a) is when the direction of the installed device pin 12 is consistent with the axial direction of the metal rod 10, that is, along the y direction of the gravitational acceleration direction, when the metal rod falls freely and collides with the metal anvil, the acceleration sensor in the sensitive direction is recorded. Output; Similarly, Fig. 4(b) is when the direction of the pin 12 is perpendicular to the metal rod 10, the output of the device in the non-sensitive direction, that is, the lateral direction (x direction), is obtained. Figure 4(c) is a schematic diagram of the device installed in the non-sensitive z direction on the top of the metal rod; Figure 4(d) shows the coordinates of the device.

A schematic diagram of the entire test setup is shown in Figure 5. In the experiment, the sensor is fixed on the end of the metal rod in a certain way. A strain wave is generated during the collision of the metal anvil, and the strain wave will be transmitted along the metal rod to the acceleration sensor, and the acceleration sensor will record the collision process. Finally, the Fourier transform analysis is performed on the data to obtain the power spectrum of the device output, that is, the relationship between the square of the amplitude and the frequency, which can be judged from the peak position of the spectrum, from which the required device mode and corresponding resonance frequency can be obtained.

Specific implementation steps:

(1) The overall layout of the installation and connection of the acceleration sensor:

First, the piezoresistive acceleration sensor to be tested is installed according to one of the three installation methods shown in Figure 4, and the acceleration sensor 11 is installed and fixed on the metal aluminum rod 10 of a certain length and diameter by using double-sided adhesive tape or 502 adhesive. on the tail end. Then, the acceleration sensor is connected with the amplifying circuit 5 to form a full bridge or a half bridge; the connection according to FIG. 2 is the full bridge output form, and the connection according to FIG. 3 is the half bridge output mode. Finally, the amplifying circuit 5 is connected to the computer data acquisition system 18, and the overall layout is shown in FIG. 5 . Start the computer and the corresponding software for controlling the data acquisition system is Topview400, turn on the corresponding power supply to make the device, operational amplifier and computer in normal working condition.

(2) Experimental process:

In the experiment, according to FIG. 5 , the metal aluminum rod 10 on which the acceleration sensor was fixed was dropped freely from a certain height and impacted against a metal anvil 17 fixed on the ground. The impact of the collision between the metal rod and the metal steel anvil on the ground produces high acceleration and frequency-rich excitation signals. The excited high-frequency waves contain waves with the same frequency as the resonance frequency of the acceleration sensor, so that the device can be adjusted in different directions in the sensitive direction and the lateral direction. The resonant wave of the mode is excited, so as to obtain the resonant frequency information of the acceleration sensor in different modes in the sensitive direction and the non-sensitive lateral direction. Figure 6 and Figure 8 are the relationship between the output voltage signal amplitude and time of the acceleration sensor under the sensitive direction and lateral impact respectively.

The size of the metal steel anvil in the test is: length 29.8cm, width 26.7cm, height 19.2cm; metal aluminum rod length 1m, diameter 1.5cm; sensor 13 (or position 14) is installed and fixed on the tail end of the metal aluminum rod, the sensor The generated small signal is connected to the operational amplifier 5 through the thin flexible cable 7, and the amplified signal is connected to the computer 18 with data acquisition function through the cable, and the waveform generated during the collision process is displayed on the computer screen.

(3) Data collection and analysis:

Strain waves are generated during the metal collision process, and the strain waves will be transmitted to the acceleration sensor along the metal aluminum rod. When the stress waves generated by mutual collision are higher than the threshold level set by the data acquisition system, the computer data acquisition system will start to automatically record the output. voltage waveform.

Figure 6 and Figure 8 are the original data relationship between the output voltage signal amplitude and time of the acceleration sensor under the sensitive direction and lateral impact obtained by the computer data acquisition system. This original data is the relationship between the amplitude of the output voltage signal and time, that is, the corresponding relationship in the time domain, where the magnitude of the voltage signal directly corresponds to the magnitude of the acceleration. In order to obtain the relationship between the corresponding frequency and output characteristics, it is also necessary to convert the data. That is to use the data analysis function in the data acquisition system to analyze the original data obtained by using the Fourier transform analysis method to obtain the corresponding relationship between the output intensity and frequency in the frequency domain, that is, to obtain the power spectrum, as shown in Figure 7 and Figure 9 is the power spectrum obtained after the Fourier transform of Figure 6 and Figure 8, respectively. From the analysis of the power frequency, it can be found that the wave intensity and other information corresponding to different frequency positions are obviously corresponding, and the information of the final modal resonance frequency of the acceleration sensor can be obtained.

When the sensitive direction is parallel to the acceleration direction, that is, when the pin direction is consistent with the axial direction of the metal rod (as shown in Figure 4(a)), the output of the acceleration sensor in the sensitive direction is recorded as shown in Figure 6. In order to verify the correct shape of the output results, the device can be placed in the horizontal direction for installation testing. When the pin direction of the acceleration sensor is perpendicular to the axial direction of the metal rod (as shown in Figure 4(b)), the record shown in Figure 8 The output of the acceleration sensor in the lateral direction, and then perform Fourier transform analysis on the data to obtain the power spectrum of the device output, that is, the relationship between the square of the amplitude and the frequency, and the corresponding modal resonance frequency of the acceleration sensor can be judged and analyzed from the peak position of the spectrum .

In summary, the half-bridge test method of the modal resonance frequency of the piezoresistive acceleration sensor of the present invention is characterized in that the test steps are:

a. Install the tested piezoresistive acceleration sensor on the tail end of the metal aluminum rod according to any of the following three installation methods:

(1) The pin direction of the acceleration sensor is consistent with the axial direction of the metal rod (sensitive direction);

(2) The pin direction of the acceleration sensor is perpendicular to the axial direction of the metal rod (non-sensitive direction);

(3) The acceleration sensor is placed horizontally and installed in the non-sensitive direction on the top of the metal rod;

b. Then, connect the acceleration sensor with the operational amplifier to form a half-bridge output form. In the described half-bridge output, the connection of the four sensitive resistors to the operational amplifier is the same as that of the full-bridge output, except that they are connected to two of the operational amplifiers. One of the input terminals is connected to the ground;

c. The metal aluminum rod installed with the acceleration sensor in step a freely falls and impacts the metal steel anvil fixed on the ground to generate a frequency-rich excitation signal;

d. the excitation signal produced by the acceleration sensor described in step c is connected with the operational amplifier through the cable, and the amplified signal is connected with the computer through the cable, and the voltage waveform of the output is automatically recorded by the data acquisition system of the computer, and is passed through the Fourier transform Analysis, the output power spectrum is obtained, and the required acceleration sensor mode and corresponding resonance frequency are obtained.

The measurement range of the piezoresistive acceleration sensor described in the present invention is a medium-to-high range greater than 2000g. By determining the first-order resonance frequency of different modes of the acceleration sensor, the structural parameters of the microstructure processing and manufacturing can also be obtained to verify the correctness of the structural size design. It can be used to analyze the working status of the device. The test method is suitable for high-range piezoresistive, capacitive and other types of acceleration sensors and pressure sensors with a full-bridge structure.

Description of drawings

Figure 1. Schematic diagram of the structure of a cantilever beam acceleration sensor; 1 indicates the cantilever beam, 2 indicates the four sensitive resistance areas on the cantilever beam, the external connection line is not drawn, 3 indicates the sensitive normal direction of the sensor, and 4 indicates the sensor insensitive to landscape orientation.

Figure 2. Schematic diagram of the full bridge connection mode of the sensor; 5 is the operational amplifier, 6 is the signal output terminal, 7 is the metal wire connection, 8 is the metal wire connection point, 9 is the ground, and Vdd is the power supply voltage applied to the operational amplifier.

Figure 3. Schematic diagram of the half-bridge connection mode of the sensor (each figure represents the same as Figure 2).

Figure 4. Three installation methods of the device. In the figure, the metal aluminum rod 10 and the acceleration sensor 11 are non-scale schematic diagrams. In Figure 4a, the device is installed on the side wall of the metal rod, and the sensitive y direction of the device is installed. The direction of the pin 12 is in line with the metal The rods are parallel; Figure 4b, the device is mounted on the side wall of the metal rod in the sensitive and non-sensitive x direction, and the pin direction is perpendicular to the metal rod; Figure 4c, the schematic diagram of the device mounted on the top of the metal rod in the non-sensitive z direction; Figure 4d, showing the coordinates of the device .

Figure 5. Schematic diagram of the free fall rod impact test device, 13 indicates the installation in the sensitive direction of the device (rotate 90 degrees to obtain an installation in the non-sensitive direction), 14 indicates another installation in the non-sensitive direction, 15 indicates the acceleration direction, and 16 indicates The height difference between the metal rod and the metal anvil, 17 represents the metal anvil, and 18 represents the computer data acquisition system.

Figure 6. The half-bridge output waveform of an acceleration sensor with a measuring range of 6000g installed on a metal aluminum rod in the sensitive direction and falling freely from a height of 5cm.

Figure 7. The power spectrum (power spectrum for short) of the half-bridge output wave from the sensor in Figure 6 (bottom half).

Figure 8. The half-bridge output waveform of an acceleration sensor with a range of 6000g installed on a metal aluminum rod in the non-sensitive z direction and falling freely from a height of 5cm.

Figure 9. Power spectrum of the half-bridge output wave from the sensor in Figure 8 (bottom half).

Detailed ways

Embodiment 1. The modal resonance frequency of an acceleration sensor installed in a sensitive direction and with a range of 6000g

For the piezoresistive acceleration sensor with a measuring range of 6000g, the computer software Ansys is used for theoretical calculation and analysis, and the first-order resonance frequency corresponding to different modes of the acceleration sensor is obtained. Among them, the first-order resonance frequency in the sensitive direction is 24.1KHz, and the first-order resonance frequency in the transverse direction is 58.0KHz.

According to the method in Figure 4(a), use double-sided tape or 502 glue to install and fix the device on the metal rod in the sensitive direction. Bridge output (as shown in Figure 3), the amplifying circuit composed of operational amplifiers and corresponding resistors and capacitors has a wider frequency band. Then connect the output cable of the signal amplifier to the computer, start the computer and the corresponding control data acquisition software (Topview 400 data acquisition software), the sampling frequency is not less than 625KHz; release the metal aluminum rod freely and collide with the metal anvil from a height of 5cm ; After colliding with each other, when the generated stress wave is higher than the threshold level set by the data acquisition system, the data acquisition system of the computer will start to automatically record the output voltage waveform.

Fig. 6 and Fig. 7 are schematic diagrams of output waveforms of the acceleration sensor in the sensitive direction and corresponding power spectrum diagrams. In Figure 6, there is an obvious main wave in the output of the sensitive direction, and the aftermath after the main wave, and there is a regular waveform output in the aftermath. The power spectrum diagram 7 is obtained through the Fourier transform. In the spectrum diagram of the variation of intensity with frequency in Fig. 7, it can be found that there are two sharp peaks at frequencies below 100KHz, which are confirmed to be: the first order of the sensitive direction The resonance frequency is 24KHz, the first-order resonance frequency in the non-sensitive transverse direction is 58KHz, and the first-order formant intensity in the sensitive direction is higher than that in the transverse direction. The characteristic peaks are marked in the figure; while 100KHz to There are multiple peaks between 300KHz, but they are not very obvious. The resonant frequency of the higher order vibration mode needs to be verified by theoretical calculation, which will not be considered here.

Embodiment 2. The modal resonance frequency of an acceleration sensor installed in a non-sensitive lateral direction with a range of 6000g

The steps are the same as Example 1, keep the circuit connection of the sensor, but install the same sensor on the metal aluminum rod according to the non-sensitive direction in Figure 4(b). Also from a height of 5cm, the metal rod is freely released and collides with the metal anvil; the computer software automatically records the output waveform; the power spectrum is obtained through Fourier transform.

Fig. 8 and Fig. 9 are the relationship of the output voltage waveform with time and the corresponding power spectrum after Fourier transform of the acceleration sensor under the non-sensitive lateral installation. In the spectrum diagram of the relationship between output intensity and frequency in Figure 9, it can be found that in the power spectrum diagram below 100KHz, there are two sharp peaks, which are resonance peaks. It is confirmed that the first-order resonance frequency in the sensitive direction is 24KHz, the first-order resonance frequency in the non-sensitive transverse direction is 58KHz, the result is consistent with Example 1. However, comparing Fig. 6 with Fig. 8, there is no obvious main collision wave (half-sine output waveform) in the output waveform of non-sensitive direction installation collision in Fig. 8; and in the comparison of power (intensity) spectrum between Fig. 7 and Fig. The resonant peak (58KHz) in the transverse direction is stronger than the resonant peak (28KHz) in the sensitive direction, which also verifies the correctness of the test results of the device. There is also a peak between 100KHz and 300KHz but it is not very obvious, and it needs to be further calibrated through theoretical calculations, which will not be considered here.

Claims (7)

1. The half-bridge test method of the modal resonance frequency of the piezoresistive acceleration sensor is characterized in that it maintains the basis of the full-bridge circuit connection structure of the piezoresistive acceleration sensor, utilizes the rich frequency spectrum generated by the impact of metal collisions as the excitation source, and through an external circuit, adopts The half-bridge output form obtains the information of the modal resonance frequency of the piezoresistive acceleration sensor, and obtains the modal and corresponding resonance frequency of the device through the analysis of the computer data acquisition system. The test steps are: a. Install the tested piezoresistive acceleration sensor on the tail end of the metal aluminum rod according to any of the following three installation methods: (1) The pin direction of the acceleration sensor is consistent with the axial direction of the metal aluminum rod; (2) The pin direction of the acceleration sensor is perpendicular to the axial direction of the metal aluminum rod; (3) The acceleration sensor is placed horizontally and installed in the non-sensitive direction on the top of the metal aluminum rod; b. Then, connect the acceleration sensor with the operational amplifier to form a half-bridge output form. In the described half-bridge output, the connection of the four sensitive resistors to the operational amplifier is the same as that of the full-bridge output, except that they are connected to two of the operational amplifiers. One of the input terminals is connected to the ground; c. The metal aluminum rod installed with the acceleration sensor in step a freely falls and impacts the metal steel anvil fixed on the ground to generate a frequency-rich excitation signal; d. the excitation signal produced by the acceleration sensor described in step c is connected with the operational amplifier through a cable, and the amplified signal is connected with a computer through a cable, and the voltage waveform of the output is automatically recorded by the data acquisition system of the computer, and is passed through Fourier Transform analysis, get the output power spectrum, and obtain the required acceleration sensor mode and corresponding resonance frequency. 2. by the half-bridge test method of the modal resonance frequency of piezoresistive acceleration sensor according to claim 1, it is characterized in that described modal resonance frequency comprises the different resonances of the same structure of acceleration sensor in sensitive direction and non-sensitive direction frequency. 3. by the half-bridge test method of the modal resonance frequency of the piezoresistive acceleration sensor claimed in claim 1, it is characterized in that the tested piezoresistive acceleration sensor is installed and fixed on the tail of the metal aluminum rod with double-sided tape or 502 glue serve. 4. by the half bridge test method of the modal resonance frequency of piezoresistive acceleration sensor according to claim 1, it is characterized in that described metal aluminum rod length is 1m, and diameter is 1.5cm. 5. by the half-bridge test method of the modal resonance frequency of piezoresistive acceleration sensor claimed in claim 1, it is characterized in that described metal steel anvil size is long 29.8cm, and width is 26.7cm, and height is 19.2cm. 6. by the half-bridge test method of the modal resonance frequency of piezoresistive acceleration sensor claimed in claim 1, it is characterized in that the software of described computer data acquisition system is Topview 400. 7. by the half bridge test method of the modal resonance frequency of piezoresistive acceleration sensor according to claim 1, it is characterized in that the measuring range of described piezoresistive acceleration sensor is greater than 2000g.

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