CN106918380A - A high-sensitivity micro-mass testing method and portable mass testing device - Google Patents

Abstract

The present invention discloses a high-sensitivity micro-mass testing method and a portable mass testing device, wherein the micro-mass testing method is as follows: a specific frequency within a certain range before and after the resonant frequency of the micro-mass sensor is used as the detection frequency, and the impedance difference of the micro-mass sensor equivalent circuit before and after the mass is loaded is measured at the detection frequency, and the difference is converted by calculation to obtain the loaded micro-mass. The portable micro-mass testing device using this method includes a micro-mass sensor, a signal generating module and an impedance reading module, and the micro-mass sensor is a piezoelectric cantilever beam sensor. The measurement method described in the present invention has a sensitivity that is more than 100 times higher than that of the frequency measurement method, has a simple measurement principle, and requires low-cost equipment and is highly portable, so it can be widely used in the precise measurement of tiny masses such as air dust pollution, environmental pollution, leakage of hazardous chemicals, and microorganisms such as bacteria or viruses.

Description

A high-sensitivity micro-mass testing method and portable mass testing device

technical field

The invention relates to the technical field of portable detection sensors, in particular to a high-sensitivity micro-mass testing method and a portable quality testing device.

Background technique

Piezoelectric cantilever beam micromass sensor is a new type of sensor integrating excitation and sensing, which has been widely used in the detection and identification of air dust, microbial germs and other fields. Piezoelectric cantilever sensor consists of two parts: piezoelectric film and elastic element.

At present, the measurement of micromass is mainly realized by the method of frequency offset detection. Its working principle is to convert the micromass change adsorbed in the detection area into the change of resonance frequency, and deduce the micromass change according to the frequency difference before and after the mass adsorption, that is, Δm =-Δf Me/fn, where fn is the structural resonance frequency corresponding to the nth order mode, Me is the equivalent mass of the cantilever beam, Δm is the mass of the object to be detected, and Δf is the variation of the resonance frequency. A large number of existing technologies are based on the frequency difference method, for example, US patent US 6389877 B1, WO 2005/043126 A2 domestic patents CN1250156A, CN2011101177772, CN201110216323.0, ZL2013100145951, ZL2013103177028, etc., all identify the frequency difference of the cantilever structure by measuring different tiny mass. In addition, the documents "Higher modes of vibration increase mass sensitivity in nanomechanical microcantilevers" and "An alternative solution to improve sensitivity of resonant microcantilever chemical sensors: comparison between using high-order modes and reducing dimensions" according to the principle of frequency difference method measurement, need to pass a certain range Only frequency sweep measurements can determine the frequency difference caused by micromass changes. Identify tiny masses by measuring the frequency difference of higher-order vibration modes. Frequency offset detection of micromass. It should be noted that the frequency difference method has obvious shortcomings in practical applications, that is, its micromass frequency sweep measurement process based on frequency difference relies heavily on the impedance analyzer, and the impedance analyzer is expensive, and the measurement accuracy is limited by the quality factor. Both resolution and resolution are affected by instrument and environmental damping, and the frequency sweep measurement process is complex.

In order to simplify the measurement process and improve the sensitivity of micro-mass detection, a more effective and easier-to-implement micro-mass measurement method is urgently needed to meet the requirements of air dust pollution, environmental pollution, leakage of hazardous chemicals, and microorganisms such as bacteria or viruses. precision measurement needs.

Contents of the invention

Aiming at the deficiencies in the traditional frequency-difference micromass detection method, the purpose of the present invention is to provide a high-sensitivity micromass detection method with accurate detection and convenient application.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A high-sensitivity micro-mass testing method, characterized in that: a specific frequency within a certain range before and after the resonant frequency of the micro-mass sensor is used as the detection frequency, and the loaded micro-mass size is obtained by calculating the impedance change of the micro-mass sensor before and after loading the mass , whose steps include:

S1. Taking a specific frequency within a certain range before and after the vibration frequency of the micromass sensor as the detection frequency, measure the output voltage of the detection circuit before and after loading the mass;

S2. Calculate the change of the output voltage and obtain the impedance change of the micro-mass sensor before and after loading the mass through calculation processing;

S3. According to the linear relationship between the impedance change of the micromass sensor and the loaded mass at the detection frequency, the magnitude of the loaded mass is obtained by calculation.

Another object of the present invention is to provide a portable micro-mass testing device based on the above-mentioned quality testing method, the micro-mass testing device includes a micro-mass sensor, a signal generating module, a detection circuit and an impedance reading module;

The micromass sensor is a piezoelectric cantilever beam sensor, which includes a fixed block, a cantilever beam connected to the fixed block, and a piezoelectric sheet pasted on the cantilever beam and having the same width as the cantilever beam, and the length of the piezoelectric sheet is shorter than that of the cantilever beam. length, the cantilever beam and the piezoelectric sheet are combined to form a composite section of the cantilever beam and the piezoelectric sheet, and the part of the cantilever beam that is not combined with the piezoelectric sheet is an extension section of the cantilever beam;

The signal generation module includes a signal generation circuit and a power amplifier, the output of the power amplifier is connected to the lead-out line of the piezoelectric sheet of the micro-mass sensor, and the piezoelectric sheet is connected in parallel with the additional capacitor _Cp after being connected in series with the resistor R;

The impedance reading module is connected in parallel with both ends of the additional capacitor _Cp .

Further, the resonant frequency of each order of the micromass sensor is

in, is the amplitude function of the composite section of the cantilever beam and the piezoelectric sheet; Is the amplitude function of the extension section of the cantilever beam; _l1 is the length of the composite section of the cantilever beam and the piezoelectric sheet; _l2 is the length of the extension section of the cantilever beam; m ₁ =(ρ _p t _p +ρ _np t _np )w; m ₂ =ρ _np t _np w; E _p is the modulus of elasticity of the piezoelectric sheet; t _p is the thickness of the piezoelectric sheet; ρ _p is the density of the piezoelectric sheet; E _np is the modulus of elasticity of the cantilever beam; t _np is the thickness of the cantilever beam; ρ _np is the density of the cantilever beam; w is the piezoelectric sheet and The width of the cantilever beam.

Further, the adjustment of the range of the device and the measurement sensitivity of the device is realized by adjusting the additional capacitance C _p .

Further, the measurement sensitivity of the device adjusted by adjusting the additional capacitance _Cp is:

Among them, R _m is the dynamic resistance of the piezoelectric cantilever sensor, C _m is the dynamic capacitance of the piezoelectric cantilever sensor, L _m is the dynamic inductance of the piezoelectric cantilever sensor, ω _n is the input voltage frequency, C _p is the additional capacitance, and Δm is Load quality.

Compared with prior art, the beneficial effect of the present invention:

1. From a theoretical point of view, the present invention verifies the feasibility of the impedance measurement method, and the sensitivity is increased by more than 100 times compared with the frequency measurement method with the same structure.

2. From the perspective of portability, the present invention designs a new measurement circuit, and changes the complicated frequency measurement into a simple resistance measurement. The measurement equipment is small in size, strong in portability, and low in price.

3. The present invention adjusts the measurement range and measurement sensitivity of the sensor without changing the structure and size of the sensor by connecting the piezoelectric cantilever sensor in series and parallel and adding an external circuit.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is a flow chart of the quality testing method of the present invention.

Fig. 2 is a structural diagram of a piezoelectric cantilever sensor of the present invention;

3 is a schematic diagram of a detection circuit of a portable micromass measuring device of the present invention;

Fig. 4 is a schematic diagram of a portable micromass measuring device of the present invention;

Fig. 5 is embodiment 1 impedance change curve;

Fig. 6 is the curve of the portable micromass measuring device of embodiment 2 impedance change;

Fig. 7 is the impedance change curve of embodiment 3;

Explanation of reference numbers:

1. Fixed block, 2. Piezoelectric sheet, 3. Cantilever beam.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

When the frequency f _i of the sensor input voltage U _i is a specific frequency within a certain range near the resonant frequency f _n of each order, the impedance changes approximately linearly with the frequency, and the magnitude of the loaded mass can be obtained by changing the impedance before and after loading the mass.

Based on the above principles, the present invention provides a high-sensitivity micromass testing method, which is characterized in that a specific frequency within a certain range before and after the resonant frequency of the micromass sensor is used as the detection frequency, and the micromass sensor before and after the loading mass is equivalent The change of circuit impedance is calculated to obtain the size of the loaded micromass. The test process is shown in Figure 1. The steps include:

S1. Taking a specific frequency within a certain range before and after the resonant frequency of the micromass sensor as the detection frequency, measure the output voltage of the detection circuit before and after loading the mass. The specific detection frequency is generally adjusted before the equipment leaves the factory, and no additional frequency adjustment work is required during use. The resonant frequency of the sensor used in this embodiment is:

in, is the amplitude function of the composite section of the cantilever beam and the piezoelectric film; Is the amplitude function of the extension section of the cantilever beam; _l1 is the length of the composite section of the cantilever beam and the piezoelectric sheet; _l2 is the length of the extension section of the cantilever beam; m ₁ =(ρ _p t _p +ρ _np t _np )w; m ₂ =ρ _np t _np w; E _p is the modulus of elasticity of the piezoelectric sheet; t _p is the thickness of the piezoelectric sheet; ρ _p is the density of the piezoelectric sheet; E _np is the modulus of elasticity of the cantilever beam; t _np is the thickness of the cantilever beam; ρ _np is the density of the cantilever beam; w is the piezoelectric sheet and The width of the cantilever beam.

S2. Calculate the change of the output voltage and obtain the impedance difference of the micro-sensor before and after loading the mass through calculation processing.

S3. According to the linear relationship between the impedance and the loaded mass at the detection frequency, the magnitude of the loaded mass is obtained by calculation.

This embodiment provides a portable micro-mass testing device based on the above-mentioned quality testing method, the micro-mass testing device includes a micro-mass sensor, a signal generation module, a detection circuit and an impedance reading module;

The micromass sensor is a piezoelectric cantilever beam sensor, and the structure of the piezoelectric cantilever beam sensor is shown in Figure 2, which includes a cantilever beam 3 connected to a fixed block 1, and a piezoelectric sheet 2 pasted on the cantilever beam 3 , the cantilever beam is made of highly elastic material, and the piezoelectric sheet is made into a thin film and closely attached to the cantilever beam. Wherein, the piezoelectric sheet 2 is as wide as the cantilever beam 3 and the length of the piezoelectric sheet 2 is less than the length of the cantilever beam 3. The cantilever beam and the piezoelectric sheet are combined to form a composite section of the cantilever beam and the piezoelectric sheet. The junction part of the electric sheet is the extension section of the cantilever beam;

The signal generating module includes a signal generating circuit and a power amplifier connected to the signal generating circuit, the output of the power amplifier is connected to the lead-out line of the piezoelectric sheet of the micro-mass sensor, and the piezoelectric sheet is connected in series with a resistor R Afterwards, connect in parallel with the additional capacitor C _p ;

The impedance reading module is connected in parallel with the two ends of the additional capacitor C _p , the sinusoidal input voltage of U _i =u _i e ^jωt is applied to the two ends of b and d, and the output voltage U _o is applied to the two ends of a and c.

In this embodiment, a Wheatstone bridge is used to measure the total impedance Z of the sensor. Figure 3 is a schematic diagram of the detection circuit. A sinusoidal input voltage of U _i =u _i e ^jωt is applied to both ends of bd, and the output voltage U _o is output at both ends of ac. When the bridge is balanced, the products of the resistances of the opposite arms of the bridge are equal, that is, ZR ₃ =R ₂ R ₄ . When the sensor absorbs mass Δm, it will cause a change in the total impedance. After absorbing the mass, the total impedance of the sensor is Z', then the sensor adsorption mass Δm causes a change in the total impedance ΔZ, and the impedance change ΔZ=ΔU is obtained by detecting the change of the output voltage U _{o o} Z/U _i . According to the impedance change curve of the piezoelectric cantilever beam sensor, when the frequency f _i of the input voltage U _i is a certain frequency within a certain range near the resonant frequency f _n of each order, the impedance changes approximately linearly with the frequency, and the impedance change ΔZ before and after passing through the loading mass The size of the loaded mass Δm can be obtained.

The piezoelectric cantilever sensor impedance Z= _{Re +jX e ,}

Among them: R _e is the resistance component, X _e is the reactance component.

FIG. 4 is a schematic diagram of the overall structure of the portable micromass measuring device.

Further, the adjustment of the range of the device and the measurement sensitivity of the device is realized by adjusting the additional capacitance C _p . When the maximum impedance frequency after loading the mass is less than the minimum impedance frequency of the original sensor, the measured mass exceeds the mass measurement range of the sensor. Without changing the size of the sensor structure, as shown in Figure 4, the quality measurement range is increased by adjusting the additional capacitance C _p and resistance R. Wherein, the additional capacitor C _p is an adjustable capacitor.

Change the sensitivity of the device by adjusting the additional capacitance _Cp method, the measurement sensitivity is

Among them, R _m is the dynamic resistance of the piezoelectric cantilever sensor, C _m is the dynamic capacitance of the piezoelectric cantilever sensor, L _m is the dynamic inductance of the piezoelectric cantilever sensor, ω _n is the input voltage frequency, C _p is the additional capacitance, and Δm is Load quality.

Specific examples:

Embodiment one

As shown in Figure 5, the impedance and phase angle of the piezoelectric cantilever sensor near the second-order mode before and after loading the mass vary with frequency. A specific frequency near the original resonance frequency is used as the detection frequency, and the impedance change at this frequency before and after loading the mass is measured to obtain the size of the loaded micromass. In this example, the original resonant frequency of the piezoelectric cantilever sensor is used as the detection frequency, and the impedance difference before and after loading 500μg mass is 520Ω, and the sensitivity is 1.04×10 ⁶ Ω/g, which is 16.2 times of the frequency measurement sensitivity of 6.43×10 ⁴ HZ/g .

Embodiment two

In this example, the size of the additional capacitor is adjusted to make the new additional capacitor C _p1 =0.5C _p , and the frequency change curve of impedance is shown in FIG. 6 . The resonant frequency before loading the mass is the detection frequency. Near the resonant frequency, the impedance changes approximately linearly with the frequency and gradually decreases. The size of the loaded micromass can be obtained by changing the impedance before and after loading the mass at a specific frequency. Using this device to measure the impedance difference before and after loading 500μg mass is 457Ω, and the sensitivity is 0.914×10 ⁶ Ω/g, which is 14.2 times of the measurement sensitivity of the frequency difference method.

Embodiment three

In this example, the size of the additional capacitor is adjusted so that the new additional capacitor C _p2 =2C _p , and the impedance frequency curve is shown in FIG. 7 . The measurement range of the piezoelectric cantilever sensor increases after the capacitance is connected in parallel. On both sides of the turning frequency f _turn , the impedance changes approximately linearly with the frequency. Taking the measurement frequency f=5900HZ as an example, the impedance difference before and after loading 500μg microgram mass is 1.233×10 ⁵ Ω, the sensitivity is 2.5×10 ⁸ Ω/g, which is 3888 times the sensitivity of frequency measurement.

The analysis of the above three examples shows that by adjusting the additional capacitance _Cp , the impedance can be linearly changed with the frequency on both sides of the resonant frequency of each order, which greatly improves the quality measurement range and measurement sensitivity of the sensor.

From a theoretical point of view, the present invention introduces the feasibility of the impedance measurement method and provides a specific measurement circuit, and adjusts the measurement range and sensitivity of the sensor without changing the structural size of the sensor by adding an external circuit to the sensor in series and parallel.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (5)

1. A high-sensitivity micro-quality test method is characterized in that: the method comprises the following steps of taking a specific frequency in a certain range before and after the resonance frequency of the micro mass sensor as a detection frequency, obtaining the loaded micro mass size through calculation according to the impedance change of the micro mass sensor before and after loading mass, and the steps comprise:

s1, measuring output voltages of the detection circuit before and after mass loading by taking a specific frequency in a certain range before and after the vibration frequency of the micro mass sensor as a detection frequency;

s2, calculating the change of the output voltage, and obtaining the impedance change of the micro mass sensor before and after loading mass through operation processing;

and S3, calculating to obtain the loading mass according to the linear relation between the impedance change of the micro mass sensor and the loading mass under the detection frequency.

2. A portable micro-mass testing device based on the micro-mass testing method of claim 1, characterized in that: the micro-mass sensor comprises a micro-mass sensor, a signal generation module, a detection circuit and an impedance reading module;

the micro mass sensor is a piezoelectric cantilever beam sensor and comprises a fixed block, a cantilever beam connected with the fixed block and a piezoelectric sheet which is stuck on the cantilever beam and has the same width with the cantilever beam, the length of the piezoelectric sheet is less than that of the cantilever beam, the cantilever beam and the piezoelectric sheet are combined to form a cantilever beam and piezoelectric sheet composite section, and the part of the cantilever beam which is not combined with the piezoelectric sheet is a cantilever beam extension section;

the signal generation module comprises a signal generation circuit and a power amplifier, the output end of the power amplifier is connected with a piezoelectric plate outgoing line of the micro mass sensor, and the piezoelectric plate is connected with a resistor R in series and then connected with an additional capacitor C_pParallel connection;

the impedance reading module is connected in parallel with an additional capacitor C_pTwo ends.

3. The micro mass testing device of claim 2, wherein: the resonance frequency of each order of the micro mass sensor is

Wherein,obtaining an amplitude function of the composite section of the cantilever beam and the piezoelectric sheet;is that it isCantilever beam extension amplitude function; l₁The length of the composite section of the cantilever beam and the piezoelectric sheet is shown; l₂The length of the cantilever beam extension segment;m₁＝(ρ_pt_p+ρ_npt_np)w；m₂＝ρ_npt_npw；E_pis the elastic modulus of the piezoelectric sheet; t is t_pIs the thickness of the piezoelectric sheet; rho_pIs the density of the piezoelectric sheet; e_npIs the modulus of elasticity of the cantilever beam; t is t_npIs the thickness of the cantilever beam; rho_npIs the density of the cantilever beam; and w is the width of the piezoelectric sheet and the cantilever beam.

4. The quality test apparatus according to claim 2, wherein: by adjusting the additional capacitance C_pThe adjustment of the device range and the device measurement sensitivity is realized.

5. The micro mass testing device of claim 4, wherein: by adjusting the additional capacitance C_pThe measurement sensitivity of the device for realizing the adjustment is as follows:

$\begin{array}{c}S=(-\sqrt{(\frac{{R_m}^2}{{{\mathrm{\ω}}_n}^4{C_p}^2{({R_m}^2+{\left({\mathrm{\ω}}_n{L}_m-\frac{1}{{\mathrm{\ω}}_n{C}_p}\right)}^2)}^2}+\frac{{({R_m}^2+({\mathrm{\ω}}_n{L}_m-\frac{1}{{\mathrm{\ω}}_n{C}_m}\left)\right({\mathrm{\ω}}_n{L}_m-\frac{1}{{\mathrm{\ω}}_n{C}_p}\left)\right)}^2}{{{\mathrm{\ω}}_n}^2{C_p}^2{({R_m}^2+{\left({\mathrm{\ω}}_n{L}_m-\frac{1}{{\mathrm{\ω}}_n{C}_p}\right)}^2)}^2}+}\\ \sqrt{\frac{{({R_m^{\′}}^2+({\mathrm{\ω}}_n^{\′}{L}_m^{\′}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_m^{\′}}\left)\right({\mathrm{\ω}}_n^{\′}{L}_m^{\′}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_m^{\′}}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_p}\left)\right)}^2}{\left({\mathrm{\ω}}_n^{\′}{C}_p{\left({R_m^{\′}}^2+{\left({\mathrm{\ω}}_n^{\′}{L}_m^{\′}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_m^{\′}}\right)}^2\right)}^2\right)}+\frac{{R_m^{\′}}^2}{{{\mathrm{\ω}}_n^{\′}}^4{C_p}^4{({\mathrm{\ω}}_n^{\′}{L}_m^{\′}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_m^{\′}}-\frac{1}{{\mathrm{\ω}}_n^{\′}{C}_p})}^2})}/\mathrm{\Δ}m\end{array}$

wherein R is_mIs a piezoelectric cantilever sensor dynamic resistance, C_mIs a piezoelectric cantilever sensor dynamic capacitance, L_mIs a dynamic inductance, omega, of a piezoelectric cantilever sensor_nFor frequency of input voltage, C_pThe additional capacitance, Δ m, loads the mass.