CN105043922A - Two-parameter detection device and method for quartz crystal microbalance - Google Patents

Abstract

The invention provides a dual-parameter detection device for a quartz crystal microbalance, comprising a drive signal unit, a series circuit unit, a signal processing unit, a signal switching unit, an A/D conversion unit, a control unit, and a drawing unit; a drive signal unit for generating A cosine signal with a fixed peak value; a series circuit unit, including the measured quartz crystal microbalance and a resistor connected in series with it, used to convert the admittance information of the quartz crystal microbalance into a voltage signal output under the drive of the drive signal unit; signal processing The unit is used to extract the amplitude and phase difference information of the signal generated by the series circuit unit; the signal switching unit is used to switch the signal generated by the signal processing unit; the A/D conversion unit is used to convert the analog signal output by the signal switching unit Converted into digital signals; the control unit is used for the control of the underlying circuit and the forwarding of data signals; the drawing unit has processing functions and is used for frequency sweep setting and curve drawing.

Description

A dual-parameter detection device and method for a quartz crystal microbalance

technical field

The invention relates to a resonant sensor technology, in particular to a dual-parameter detection device and method for a quartz crystal microbalance.

Background technique

Quartz Crystal Microbalance (QCM for short) is a resonant sensor measurement technology developed in the 1960s. Its measurement accuracy is as high as nanograms. It is widely used as a quality sensor in medical analysis and environmental detection. , Analytical chemistry and other fields that require high measurement. QCM is a high-resolution piezoelectric sensor formed by plating metal electrodes on the upper and lower surfaces of an AT-cut quartz wafer. The crystal will oscillate under the action of an external alternating electric field. When the vibration frequency is consistent with the natural frequency of the quartz crystal, resonance will occur. At this time, the oscillation is stable and strong, that is, piezoelectric resonance occurs.

When the electrodes of the QCM are in contact with the substance to be measured, the properties of the substance to be measured (such as mass, viscosity, density, etc.) will change the resonant frequency of the QCM. GuenterSauerbrey and Kanazawa deduced and verified the formulas between the resonance frequency and adsorption mass of quartz crystals in the gas phase and liquid phase respectively. The formula shows that the frequency change of the quartz crystal has a simple linear relationship with the change of the crystal surface quality, so it is only necessary to detect the crystal oscillation frequency change The change of the surface mass of the crystal can be measured, so as to realize the conversion of mass change into frequency change output. However, when the QCM is used for viscoelastic liquid detection, due to the obvious flexible adsorption characteristics of the viscoelastic film, only the resonance frequency is recorded. Variations can cause large errors in results and even lead to erroneous analysis results. At this time, by recording the dissipation factor D, it can be known whether it is a soft film with a high viscosity or a rigid structure that is adsorbed on the surface, so more structural information can be reflected. In the detection of viscoelastic liquids, a double-parameter detection method is used, that is, the change value of the resonance frequency Δf and the dissipation factor D are simultaneously obtained.

At present, the mainstream measurement device that can simultaneously obtain Δf and D is the QCM-D proposed by Swedish scholars Kasemo, Rodahl, etc. on the basis of Voigt model and fluid mechanics. The measurement block diagram is shown in Figure 1. The basic principle is: periodically connect and disconnect the switch connected to the QCM sensor and signal source, and record the frequency and decay delay time of the output voltage signal with a digital oscilloscope. When the driving signal is disconnected, the oscillation amplitude of the QCM decays exponentially. The attenuation of the QCM oscillation amplitude can be measured with a high-impedance or low-impedance probe of a digital oscilloscope, so as to ensure that the attenuation of the crystal is recorded at its series or parallel resonance frequency. The recorded signal is input into the computer, and through data fitting, the following form can be obtained: Wherein, the frequency offset is obtained directly, Δf=f ₀ -f. And the dissipation factor D is obtained from the following relationship:

This method is widely used at present, but there are certain defects in this method, mainly in:

(1) The dissipation factor in QCM-D is calculated by making the QCM sensor oscillate by means of pulse excitation, and then measuring the oscillation decay time. This is an instantaneous measurement method, which is easily affected by external disturbances. It may lead to inaccurate test data. At the same time, because the decay time of the oscillator is generally on the order of 10 ^-6 s, the resolution and precision of the test instrument are required to be very high.

(2) The excitation signal of the QCM in the above figure is a fixed frequency signal generated by a signal generator. When a film is attached to the surface of the QCM, its series resonance frequency changes (the new resonance frequency is unknown). If the original fixed frequency signal is still used to excite the QCM, the obtained data may not accurately reflect the true characteristics of the film.

Contents of the invention

The object of the present invention is to provide a quartz crystal microbalance dual-parameter detection device and method. The present invention is based on the steady-state method to realize the measurement of the frequency change and dissipation factor before and after QCM adsorbed substances.

A quartz crystal microbalance dual-parameter detection device includes a drive signal unit, a series circuit unit, a signal processing unit, a signal switching unit, an A/D conversion unit, a control unit, and a drawing unit. The drive signal unit is used to generate a cosine signal with a fixed peak-to-peak value; the series circuit unit includes the measured quartz crystal microbalance and a resistor connected in series with it, and is used to drive the quartz crystal microbalance to The admittance information is converted into a voltage signal output; the signal processing unit is used to extract the amplitude and phase difference information of the signal generated by the series circuit unit; the signal switching unit is used to switch the signal generated by the signal processing unit; The A/D conversion unit is used to convert the analog signal output by the signal switching unit into a digital signal; the control unit is used for the control of the underlying circuit and the forwarding of the data signal; the drawing unit has a processing function and uses It is used to realize frequency sweep setting and curve drawing.

According to the above-mentioned device, the present invention adopts the following method to complete the dual parameter detection of the quartz crystal microbalance, and the specific method is: the two-way cosine signals produced by the quartz crystal microbalance under no-load and load states are processed as follows:

(1) Determine a frequency, adopt autocorrelation and cross-correlation processing, obtain the respective amplitudes and phase differences of the two cosine signals, and obtain the conductance value at the frequency according to the amplitude and phase difference of the two cosine signals,

(2) Change the frequency to obtain the conductance value at different frequencies,

(3) Construct the relationship between conductance value and frequency,

(4) Obtain the change of resonant frequency, and the dissipation factor under no-load or load state.

Through the above-mentioned device and method, the resonant frequency change of the quartz crystal microbalance is obtained as the frequency difference between the conductance peak values under no-load and load states;

Through the above-mentioned device and method, the dissipation factor of the quartz crystal microbalance under the no-load state is obtained as the ratio of half half power bandwidth twice to the resonant frequency under the no-load state;

Through the above device and method, the dissipation factor of the quartz crystal microbalance under load is obtained as the ratio of twice the half power bandwidth under load to the resonant frequency.

Compared with the prior art, the present invention has the following advantages:

(1) The influence of the viscoelastic film on the QCM can be directly reflected by the frequency change and the half-power bandwidth change, which can more truly reflect the properties of the film adsorbed on the surface of the QCM, and theoretically ensure the accuracy of the analytical data.

(2) The stable signal generated by the QCM sensor under the action of the drive circuit when analyzing the processed data. Its resonant frequency and half-half power bandwidth are obtained in a steady state, and the recorded data appear in the form of frequency. The resonant frequency and half-half power bandwidth are on the order of 10 ⁶ Hz and 10 ³ Hz, respectively. This is easier to measure accurately than the 10 ^-6 s decay delay time obtained by the instantaneous measurement method.

The present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

Figure 1 is a schematic diagram of the structure of QCM-D when it is working.

Fig. 2 is a specific structural diagram of the quartz crystal microbalance dual-parameter detection device of the present invention.

Fig. 3 is a flow chart of the method of the present invention.

Fig. 4 is a schematic diagram of a method for obtaining a half-power half-power bandwidth in the dual-parameter detection method of the quartz crystal microbalance of the present invention.

Fig. 5 is a schematic diagram of a method for acquiring resonance frequency changes in the dual-parameter detection method of the quartz crystal microbalance of the present invention.

Detailed ways

2, a quartz crystal microbalance (QCM) dual-parameter detection device includes a drive signal unit, a series circuit unit, a signal processing unit, a signal switching unit, an A/D conversion unit, a control unit, and a drawing unit. The drive signal unit is used to generate a cosine signal with a fixed peak-to-peak value; the series circuit unit includes the measured quartz crystal microbalance and a resistor connected in series with it, and is used to drive the quartz crystal microbalance to The admittance information is converted into a voltage signal output; the signal processing unit is used to extract the amplitude and phase difference information of the signal generated by the series circuit unit; the signal switching unit is used to switch the signal generated by the signal processing unit; The A/D conversion unit is used to convert the analog signal output by the signal switching unit into a digital signal; the control unit is used for the control of the underlying circuit and the forwarding of the data signal; the drawing unit has a processing function and is used for Realize frequency sweep setting and curve drawing.

The driving signal unit includes a frequency synthesizer, an automatic control gainer, an amplifier, and a low-pass filter. The single-chip microcomputer sends a control signal to control the frequency synthesizer, and the frequency synthesizer is used to generate a cosine signal; the automatic control gainer is used for constant peak-to-peak value of the cosine signal; the amplifier is used to amplify the cosine signal; the low-pass Filter, used to filter out the noise signal in the cosine signal.

The signal processing unit includes a signal acquisition circuit in which a three-way multiplier and a low-pass filter are connected in series. The first signal acquisition circuit is connected to one end of the quartz crystal microbalance to realize autocorrelation processing of one cosine signal and obtain the DC voltage value; the second signal acquisition circuit is connected to the other end of the quartz crystal microbalance to realize another cosine signal Signal autocorrelation processing and obtaining a DC voltage value; the third signal acquisition circuit is connected to both ends of the quartz crystal microbalance for realizing cross-correlation processing of two cosine signals and obtaining phase difference information.

Specifically, the device uses the following components to achieve the purpose of the invention:

(1) The control unit in the quartz crystal microbalance dual-parameter detection device adopts the single-chip microcomputer Lingyang 061A;

(2) The drawing unit is a PC with computing functions;

(3) The DDS chip adopts AD9850 produced by AD Company. The innovative high-speed DDS core of AD9850 provides a 32-bit frequency control word. For 125MHz reference clock input, the output tuning resolution can reach 0.0291Hz;

(4) The AGC module adopts AD8367. AD8367 is a variable gain amplifier with integrated square-law detector (Square-Law Detector) on chip. Using this chip, it can be easily built into an automatic gain controller (AGC);

(5) The operational amplifier is AD9632;

(6) The low-pass filter uses an elliptical filter to filter out high-frequency signals above the required frequency;

(7) multiplier part adopts high-precision multiplier AD835, multi-way switch selects DG408 for use, and DG408 is 8 channels, and the voltage to be converted by AD in the present invention is that three roads can fully meet the requirements;

(8) The AD conversion chip is AD7711. AD7711 is a 24-bit high-precision AD conversion chip, which can directly receive low-level signals from the sensor and generate serial digital output, which can complete the circuit design requirements;

(9) The communication between 061A and PC is realized through RS232. If there is no serial port on the PC, communication can be realized through 232-USB conversion line.

With reference to Figure 2, specifically, the connection method of the above-mentioned devices is as follows:

The MCU output is connected to the frequency synthesizer DDS input, the frequency synthesizer DDS output is connected to the automatic gain control AGC input, the automatic gain control AGC output is connected to the amplifier AMP input, and the amplifier AMP output is connected to the low-pass filter LPF input end, the output end of the low-pass filter LPF is connected to the first end of the quartz crystal microbalance QCM, the second end of the quartz crystal microbalance QCM is connected to the resistor R, and the two input ends of the first multiplier in the three-way signal acquisition circuit are both Connect the first terminal of the quartz crystal microbalance QCM, the two input terminals of the second multiplier are respectively connected to the first terminal and the second terminal of the quartz crystal microbalance QCM, and the two input terminals of the third multiplier are connected to the quartz crystal microbalance (QCM) second end, the low-pass filter in the three-way signal acquisition circuit is respectively connected with different switches in the three-way switch, the three-way switch output terminal is connected with the A/D converter, and the A/D converter outputs The terminal is connected with the single-chip microcomputer, and the single-chip microcomputer is connected with the PC.

Combined with Figure 3, a dual-parameter detection method for a quartz crystal microbalance, the following processing is performed on the two-way cosine signals generated by the quartz crystal microbalance under no-load and load conditions:

Step S101, determining a frequency, performing autocorrelation and cross-correlation processing on the two cosine signals generated by the QCM, and obtaining the respective amplitudes and phase differences of the two cosine signals,

Step S102, obtaining the conductance value at the frequency according to the amplitude and phase difference of the two cosine signals,

Step S103, change the frequency, repeat step S101 and step S102, obtain conductance values at different frequencies,

Step S104, constructing the relationship between conductance value and frequency,

Step S105, obtaining the change of the resonant frequency, and the dissipation factor under no-load or load state.

Specifically, after the LPF filters out the high-frequency noise in the signal, the signal is generated so far, and it is set to At the same time, the voltage across the resistor R At this time, the admittance of the QCM can be expressed as:

$\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}<span\; class="notranslate">\; =</span>\frac{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\frac{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Substitute the expressions of u ₁ and u ₂ into formula (1) to get:

pluralize It can be expanded by Euler's formula:

Correspondingly, the conductance value G and the susceptance value B are

Through the formula (4), (5) shown. From the amplitude u ₁ , u ₂ and the phase difference of the two signals The conductance and susceptance of the QCM can be obtained. Subsequent signal processing part will be completed The extraction of amplitude and phase difference information, this part uses the correlation principle, the realization of the correlation principle part is a multiplier plus a low-pass filter, using autocorrelation to realize the acquisition of amplitude information, and using cross-correlation to realize the phase difference information extraction.

Autocorrelation part:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}\\ <span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}\\ <span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Cross-correlation part:

at this time

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

Substitute equations (10), (11) and (13) into equations (4) and (5) respectively to get:

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; R</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

Since R is a known quantity, it is only necessary to measure u ₁₁ , u ₁₂ and u ₂₂ to obtain the conductance and susceptance of QCM at this frequency. When changing the frequency of the signal, the conductance and susceptance at different frequencies can be obtained value, the frequency value is the abscissa, and the conductance value is the ordinate, the curve of the conductance relative to the frequency can be obtained, and the admittance circle can also be obtained. Analyzing the conductance and susceptance curves can obtain information such as the resonant frequency and half-power half-power bandwidth of the QCM at this time.

When the QCM is in the working state (that is, the surface adsorbed substances), start a new round of frequency scanning and data acquisition, and then you can get the resonant frequency and half-half power bandwidth in the working state, and compare them with those at no-load. Get Δf.

In combination with FIG. 4 , it is assumed that the admittance curve obtained after one scan is shown in FIG. 3 . Take the peak value of the conductance obtained as And pass this value to draw a horizontal line. At this time, the point where it intersects with the curve is called the half-power point. In the figure, A and B are two points, and Γ is called the half-side half-power bandwidth. in is the conductance value of the maximum conductance value G _max When the corresponding frequency, f is the resonant frequency. according to The dissipation factor D at this time can be obtained.

Combined with Figure 5, the conductance curves obtained by scanning under no-load and load conditions, in which the resonance frequency change Δf is the frequency difference between the conductance peaks, the half-power half-power bandwidth acquisition method is shown in Figure 4, and two can also be obtained in Figure 5 The half-power half-power bandwidth difference ΔΓ in the sub-scan.

Claims (8)

1. A quartz crystal microbalance double-parameter detection device is characterized by comprising:

the driving signal unit is used for generating a cosine signal with a fixed peak-to-peak value;

the series circuit unit comprises a tested quartz crystal microbalance and a resistor connected with the tested quartz crystal microbalance in series and is used for converting admittance information of the quartz crystal microbalance into a voltage signal to be output under the driving of the driving signal unit;

a signal processing unit for extracting amplitude and phase difference information of the signal generated by the series circuit unit;

the signal switching unit is used for switching the signal generated by the signal processing unit;

the A/D conversion unit is used for converting the analog signal output by the signal switching unit into a digital signal;

the control unit is used for controlling the bottom layer circuit and forwarding the data signal; and

and the drawing unit has a processing function and is used for realizing sweep frequency setting and curve drawing.

2. The quartz crystal microbalance dual parameter detection device of claim 1, wherein the driving signal unit comprises:

a frequency synthesizer for generating a cosine signal;

the automatic gain controller is used for keeping the peak value of the cosine signal constant;

an amplifier for amplifying the cosine signal;

and the low-pass filter is used for filtering the noise signal in the cosine signal.

3. The quartz crystal microbalance double-parameter detection device of claim 1, wherein the signal processing unit comprises a signal acquisition circuit with a three-way multiplier and a low-pass filter connected in series,

the first path of signal acquisition circuit is connected with one end of the quartz crystal microbalance and is used for realizing the autocorrelation processing of a path of cosine signals and acquiring a direct-current voltage value;

the second path of signal acquisition circuit is connected with the other end of the quartz crystal microbalance and is used for realizing the autocorrelation processing of the other path of cosine signal and acquiring a direct-current voltage value;

and the third signal acquisition circuit is connected with two ends of the quartz crystal microbalance and is used for realizing the cross-correlation processing of the two cosine signals and acquiring phase difference information.

4. The quartz crystal microbalance double-parameter detection method adopting the device of any one of the preceding claims is characterized in that the following processing is carried out on two paths of cosine signals generated by the quartz crystal microbalance under no-load and load states:

determining a frequency, obtaining respective amplitudes of the two cosine signals and a phase difference between the two cosine signals by adopting autocorrelation and cross-correlation processing, obtaining a conductance value under the frequency according to the amplitudes and the phase difference of the two cosine signals,

changing the frequency, obtaining the conductance values under different frequencies,

constructing a relationship between the conductance value and the frequency, an

And acquiring the change of the resonant frequency and the dissipation factor in the no-load or load state.

5. The quartz crystal microbalance double parameter detection method according to claim 4,

the resonance frequency changes into a frequency difference between conductance peak values in the no-load and load states;

the dissipation factor in the no-load state is the ratio of twice half-power bandwidth to resonant frequency in the no-load state;

the dissipation factor under the load state is the ratio of twice half-power bandwidth under the load state to the resonant frequency.

6. The quartz crystal microbalance double parameter detection method of claim 5, wherein the half-side half-power bandwidthWhereinThe conductance value is the maximum conductance value G_maxIs/are as followsThe frequency corresponding to the time, f is the resonance frequency.

7. The quartz crystal microbalance double-parameter detection method according to claim 4, wherein the respective direct current voltage values obtained after the autocorrelation processing of the two cosine signals are

$u_{11}=\frac{1}{2}{u}_1^2$

$u_{22}=\frac{1}{2}{u}_2^2$

Wherein u is₁、u₂Is the cosine signal amplitude;

the phase difference obtained after the two cosine signals are processed in a cross-correlation way

Wherein u is₁₂A dc signal output for cross-correlation.

8. The quartz crystal microbalance double parameter detection method of claim 7, wherein the conductance value is $G=\frac{1}{\mathrm{AR}}(\frac{u_{12}}{u_{22}}-1),$ Wherein,r is an and stoneResistance values of quartz crystal microbalances connected in series.