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

Abstract

The invention provides a two-parameter detection device and method for a quartz crystal microbalance. The two-parameter detection device comprises a driving 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 driving signal unit is used for generating cosine signals with a fixed peak-to-peak value. The series circuit unit comprises the quartz crystal microbalance to be detected and a resistor in series connection with the quartz crystal microbalance, and is used for converting admittance information of the quartz crystal microbalance into voltage signals which are output under driving of the driving signal unit. The signal processing unit is used for extracting the amplitude and phase difference information of signals generated by the series circuit unit. The signal switching unit is used for switching signals generated by the signal processing unit. The A/D conversion unit is used for converting analog signals output by the signal switching signal into digital signals. The control unit is used for controlling a bottom circuit and forwarding data signals. The drawing unit has a processing function and is used for achieving sweeping frequency setting and curve drawing.

Description

A kind of two-parameter pick-up unit of QCM (Quartz Crystal Microbalance) and method

Technical field

The present invention relates to resonant transducer technology, particularly the two-parameter pick-up unit of a kind of QCM (Quartz Crystal Microbalance) and method.

Background technology

QCM (Quartz Crystal Microbalance) (QuartzCrystalMicrobalance, be called for short QCM) be a kind of resonant transducer measuring technique grown up the sixties in 20th century, its measuring accuracy is Gao Keda nanogram level very, medical analysis is widely used in as a kind of mass sensor, environment measuring, analytical chemistry etc. require higher field to measuring.QCM is that the upper and lower surface by cutting quartz wafer at AT plates metal electrode and the high-resolution piezoelectric sensor of one formed.Crystal can produce vibration under the effect of applied alternating field, when vibration frequency is consistent with the natural frequency of quartz crystal, just can produce resonance, now vibrational stabilization and strong, namely piezoelectric resonator occurs.

When the electrode of QCM contacts with test substance, the character (as: quality, viscosity, density etc.) of test substance will change the resonance frequency of QCM.GuenterSauerbrey and Kanazawa derives respectively and demonstrates in gas phase and formula in liquid phase between quartz crystal resonant frequency and quality of adsorption, the frequency change of the bright quartz crystal of formula table becomes simple linear relationship with plane of crystal mass change, therefore the change that crystal oscillation frequency change just can record plane of crystal quality need only be detected, thus realize mass change change into frequency change export however when QCM detects for memory fluid, adsorbability due to viscoelasticity film presents obvious flexible characterization of adsorption, only the change of record resonance frequency can make result produce very large error, the analysis result even led to errors.Now logical record dissipation factor D can know that what be adsorbed on surface is the soft film that viscosity is very large, or rigid structure, therefore can reflect more structural information.Two-parameter detection method to be adopted in memory fluid detects, namely obtain resonance frequency changing value Δ f and dissipation factor D simultaneously.

The measurement mechanism that simultaneously can obtain Δ f and D of current main flow is the QCM-D that the people such as Sweden scholar Kasemo, Rodahl propose on Voigt model and hydromechanical basis.Measure block diagram as shown in Figure 1.Its ultimate principle is: be periodically communicated with, disconnect the switch be connected with signal source with qcm sensor, with the frequency of its output voltage signal of digital oscilloscope record and decay time delay.After drive singal disconnects, the oscillation amplitude exponentially form decay of QCM.The attenuation of this QCM oscillation amplitude can obtain with the high resistant of digital oscilloscope or low-resistance probe measurement respectively, so just can ensure that the decay of crystal goes on record in its series connection or parallel resonance frequency place.The signal of record is imported in computing machine, by data fitting, can obtain following form: wherein, frequency shift (FS) directly obtains, Δ f=f ₀-f.And dissipation factor D is obtained by following relation:

The method uses often at present, but the method exists certain defect, is mainly manifested in:

(1) in QCM-D, dissipation factor adopts the mode of pulse excitation to allow qcm sensor vibrate, then measurement oscillatory extinction Time Calculation obtains, this is a kind of transient measurement method, is easily subject to the impact of external disturbance, and extraneous subtle disruption all likely causes the inaccurate of test data.Meanwhile, because oscillator die-away time is generally 10 ^-6s magnitude, therefore the resolution of testing tool and accuracy requirement are very high.

(2) pumping signal of upper figure QCM is the fixed frequency signal produced by signal generator.When after QCM surface attachment film, its series resonance frequency there occurs change (new resonance frequency is unknown), if still use original fixed frequency signal de-energisation QCM, the data obtained differ and accurately reflect the genuine property of film surely.

Summary of the invention

The object of the present invention is to provide the two-parameter pick-up unit of a kind of QCM (Quartz Crystal Microbalance) and method, the present invention is based on steady state method to realize the measurement to frequency change and dissipation factor before and after QCM adsorbent.

The two-parameter pick-up unit of a kind of QCM (Quartz Crystal Microbalance), comprises drive singal unit, series circuit unit, signal processing unit, signal switch unit, A/D converting unit, control module, drawing unit.Described drive singal unit, for generation of the cosine signal that peak-to-peak value is fixing; Described series circuit unit, comprises the resistance of tested QCM (Quartz Crystal Microbalance) and series connection with it, for by the admittance convert information of QCM (Quartz Crystal Microbalance) being voltage signal output under the driving of drive singal unit; Described signal processing unit, for extracting amplitude and the phase information of the signal that series circuit unit produces; Described signal switch unit, for the signal switching produced by signal processing unit; Described A/D converting unit, converts digital signal to for simulating signal signal switch unit exported; Described control module, for the control of bottom circuit, and the forwarding of data-signal; Described drawing unit, has processing capacity, for realizing frequency sweep setting and Drawing of Curve.

According to said apparatus, the present invention adopts and completes the two-parameter detection of QCM (Quartz Crystal Microbalance) with the following method, and concrete grammar is: carry out following process to the two-way cosine signal that the QCM (Quartz Crystal Microbalance) under unloaded and load condition produces:

(1) determine a frequency, adopt auto-correlation and cross correlation process, obtain the respective amplitude of two-way cosine signal and both phase differential, obtain the electric conductivity value under this frequency according to the amplitude of two-way cosine signal and phase differential,

(2) change frequency, obtain the electric conductivity value under different frequency,

(3) relation between electric conductivity value and frequency is built,

(4) resonance frequency change is obtained, and dissipation factor under unloaded or load condition.

Through said apparatus and method, obtain the resonance frequency of QCM (Quartz Crystal Microbalance) and to be changed under zero load and load condition difference on the frequency between conductance peaks;

Through said apparatus and method, under the light condition of acquisition QCM (Quartz Crystal Microbalance), dissipation factor is the ratio of half of half-power bandwidth twice and resonance frequency under light condition;

Through said apparatus and method, under the load condition of acquisition QCM (Quartz Crystal Microbalance), dissipation factor is the ratio of half of half-power bandwidth twice and resonance frequency under load condition.

The present invention compared with prior art, has the following advantages:

(1) viscoelasticity film just directly can be reflected by frequency change and half-power bandwidth change the impact of QCM, more can reflect the property of thin film that QCM surface is adsorbed really, ensure that the accuracy analyzing data theoretically.

(2) stabilization signal that during data of analyzing and processing, qcm sensor produces under the effect of driving circuit.Its resonance frequency and half of half-power bandwidth obtain all in the steady state, and the data recorded are all occur in the mode of frequency, and resonance frequency and half of half-power bandwidth are respectively 10 ⁶hz and 10 ³the Hz order of magnitude.This obtains than transient measurement method decay time delay 10 ^-6s magnitude more easily accomplishes accurate measurement.

Below in conjunction with Figure of description, the present invention is described further.

Accompanying drawing explanation

Structural representation when Fig. 1 is QCM-D work.

Fig. 2 is the concrete structure figure of the two-parameter pick-up unit of QCM (Quartz Crystal Microbalance) of the present invention.

Fig. 3 is method flow diagram of the present invention.

Fig. 4 is half of half-power bandwidth acquisition methods schematic diagram in the two-parameter detection method of QCM (Quartz Crystal Microbalance) of the present invention.

Fig. 5 is resonance frequency change acquisition methods schematic diagram in the two-parameter detection method of QCM (Quartz Crystal Microbalance) of the present invention.

Embodiment

Composition graphs 2, a kind of QCM (Quartz Crystal Microbalance) (QCM) two-parameter pick-up unit, comprises drive singal unit, series circuit unit, signal processing unit, signal switch unit, A/D converting unit, control module, drawing unit.Described drive singal unit, for generation of the cosine signal that peak-to-peak value is fixing; Described series circuit unit, comprises the resistance of tested QCM (Quartz Crystal Microbalance) and series connection with it, for by the admittance convert information of QCM (Quartz Crystal Microbalance) being voltage signal output under the driving of drive singal unit; Described signal processing unit, for extracting amplitude and the phase information of the signal that series circuit unit produces; Described signal switch unit, for the signal switching produced by signal processing unit; Described A/D converting unit, converts digital signal to for simulating signal signal switch unit exported; Described control module, for the control of bottom circuit and the forwarding of data-signal; Described drawing unit, has processing capacity, for realizing frequency sweep setting and Drawing of Curve.

Described drive singal unit comprises frequency synthesizer, automatically ride gain device, amplifier, low-pass filter.Single-chip microcomputer sends control signal controlled frequency compositor, and described frequency synthesizer, for generation of cosine signal; Described automatic ride gain device, for constant cosine signal peak-to-peak value; Described amplifier, for amplifying cosine signal; Described low-pass filter, for the noise signal in filtering cosine signal.

Described signal processing unit comprises the signal acquisition circuit of No. three multipliers and low-pass filter series connection.First via signal acquisition circuit is connected with QCM (Quartz Crystal Microbalance) one end, for realizing a road cosine signal auto-correlation processing and obtaining DC voltage value; Second road signal acquisition circuit is connected with the QCM (Quartz Crystal Microbalance) other end, for realizing another road cosine signal auto-correlation processing and obtaining DC voltage value; 3rd road signal acquisition circuit is connected with QCM (Quartz Crystal Microbalance) two ends, for realizing two-way cosine signal cross correlation process and obtaining phase information.

Concrete, this device adopts following parts to realize goal of the invention:

(1) in the two-parameter pick-up unit of QCM (Quartz Crystal Microbalance), control module adopts single-chip microcomputer Ling Yang 061A;

(2) drawing unit is the PC with calculation function;

(3) DDS chip adopts the AD9850 that AD company produces, and the innovative high-speed DDS kernel of AD9850 provides 32 bit frequency control words, and for the input of 125MHz reference clock, exporting tuning resolution can reach 0.0291Hz;

(4) employing of AGC module AD8367, AD8367 are the variable gain amplifiers of a upper integrated square-law detector (Square-LawDetector), use this chip can be barricaded as automatic gain controller (AGC) easily;

(5) that operational amplifier is selected is AD9632;

(6) low-pass filter adopts elliptic filter, high-frequency signal more than frequency needed for filtering;

(7) multiplier portion adopts high precision multiplier AD835, and DG408 selected by multi-way switch, and DG408 is 8 passages, treats that the voltage of AD conversion is that three tunnels can meet the demands completely in the present invention;

(8) AD conversion chip selects AD7711, and AD7711 is 24 high-precision AD conversion chips, can directly accept the low level signal of sensor, and produces serial digital output, energy completing circuit design requirement;

(9) communication between 061A and PC is realized by RS232, as on PC without serial ports, then can by 232-USB conversion line realize communication.

Composition graphs 2, particularly, the connected mode of said apparatus is as follows:

Single-chip microcomputer output terminal rate of connections compositor DDS input end, frequency synthesizer DDS output terminal connects automatic ride gain device AGC input end, automatic ride gain device AGC output terminal connects amplifier AMP input end, amplifier AMP output terminal connects low-pass filter LPF input end, low-pass filter LPF output terminal connects QCM (Quartz Crystal Microbalance) QCM first end, QCM (Quartz Crystal Microbalance) QCM second end contact resistance R, in described three road signal acquisition circuits, two input ends of first via multiplier all connect QCM (Quartz Crystal Microbalance) QCM first end, two input ends of No. second multiplier connect QCM (Quartz Crystal Microbalance) QCM first end and the second end respectively, No. three multiplier two input end all connects QCM (Quartz Crystal Microbalance) (QCM) second end, low-pass filter in described three road signal acquisition circuits connects from the different switches in three-way switch respectively, three-way switch output terminal is connected with A/D converter, A/D converter output terminal is connected with single-chip microcomputer, single-chip microcomputer is connected with PC.

Composition graphs 3, the two-parameter detection method of a kind of QCM (Quartz Crystal Microbalance), following process is carried out to the two-way cosine signal that the QCM (Quartz Crystal Microbalance) under unloaded and load condition produces:

Step S101, determines a frequency, carries out auto-correlation and cross correlation process to the two-way cosine signal that QCM produces, and obtains the respective amplitude of two-way cosine signal and both phase differential,

Step S102, obtains the electric conductivity value under this frequency according to the amplitude of two-way cosine signal and phase differential,

Step S103, change frequency, repeats step S101 and step S102, obtains the electric conductivity value under different frequency,

Step S104, builds the relation between electric conductivity value and frequency,

Step S105, obtains resonance frequency change, and dissipation factor under unloaded or load condition.

Particularly, after the high frequency noise in LPF filtered signal, so far signal produces complete, is set to voltage on resistance R simultaneously the now admittance of QCM can be expressed as:

$Y=\frac{1}{Z}=\frac{\stackrel{\·}{i}}{{\stackrel{\·}{u}}_1}=\frac{{\stackrel{\·}{u}}_1}{R}*\frac{1}{{\stackrel{\·}{u}}_1-{\stackrel{\·}{u}}_2}=\frac{1}{R}*\frac{1}{\frac{{\stackrel{\·}{u}}_1}{{\stackrel{\·}{u}}_2}-1}---\left(1\right)$

By u ₁and u ₂expression formula substitute into formula (1) obtain:

By plural number launch to obtain by Euler's formula:

Accordingly, electric conductivity value G and susceptance value B is

Shown in through type (4), (5).By amplitude u ₁, u ₂and the phase differential of two paths of signals just conductance and the susceptance of QCM can be obtained.Follow-up signal processing will complete the extraction of amplitude and phase information, what this part adopted is correlation principle, and the realization of correlation principle part is that multiplier adds low-pass filter, utilizes auto-correlation to realize the acquisition of amplitude information, utilizes cross-correlation to realize the extraction of phase information.

Auto-correlation part:

$\begin{array}{c}{u}_{11}=\frac{1}{T}{\∫}_0^T{u}_1{\left(t\right)}^{2}dt\\ =\frac{1}{T}{\∫}_0^T{\left(u_1\cos wt\right)}^{2}dt\\ =\frac{1}{2}{u}_1^2\end{array}---\left(7\right)$

Cross-correlation part:

Now

$u_1=\sqrt{2u_{11}}---\left(10\right)$

$u_2=\sqrt{2u_{22}}---\left(11\right)$

By formula (10), (11) and (13) substitute into formula (4) respectively, formula (5) obtains:

$G=\frac{1}{AR}(\frac{u_{12}}{u_{22}}-1)---\left(14\right)$

$B=\frac{1}{AR}\sqrt{\frac{u_{11}}{u_{22}}}\·\sqrt{1-\frac{u_{12}^2}{u_{11}{u}_{22}}}---\left(15\right)$

$A=\frac{u_{11}}{u_{22}}-2\frac{u_{12}}{u_{22}}+1---\left(16\right)$

Because R is known quantity, so only need u be recorded ₁₁, u ₁₂and u ₂₂just QCM conductance and susceptance value under this frequency can be obtained, when changing the frequency of signal, just can obtain the conductance under different frequency and susceptance value, take frequency values as horizontal ordinate, conductance susceptance value is that ordinate just can obtain the curve of conductance susceptance about frequency, can also obtain admittance circle.Analysis conductance and susceptance curve can obtain the information such as QCM resonance frequency now, half of half-power bandwidth.

When QCM is in running order (adsorption material), starts new one and take turns frequency sweeping and data acquisition, just can obtain the resonance frequency under duty, half of half-power bandwidth, then with making comparisons during zero load, just can obtain Δ f.

Composition graphs 4, the mechanical admittance curves obtained after supposing single pass as shown in Figure 3.Get the peak value of obtained conductance and cross this value and make a horizontal line, the point that now it and Curves are handed over is called half-power point, A, B 2 point in figure, and Γ is then called half of half-power bandwidth, wherein for electric conductivity value is its maximum conductance value G _max's time corresponding frequency, f is resonance frequency.According to now dissipation factor D can be obtained.

Composition graphs 5, the conductance plots obtained is scanned under zero load and load condition, wherein resonance frequency changes delta f is difference on the frequency between conductance peaks, and the obtain manner of half of half-power bandwidth as shown in Figure 4, can also obtain half of half-power bandwidth difference Δ Γ in twice sweep simultaneously in Fig. 5.

Claims (8)

1. the two-parameter pick-up unit of QCM (Quartz Crystal Microbalance), is characterized in that, comprising:

Drive singal unit, for generation of the cosine signal that peak-to-peak value is fixing;

Series circuit unit, comprises the resistance of tested QCM (Quartz Crystal Microbalance) and series connection with it, for by the admittance convert information of QCM (Quartz Crystal Microbalance) being voltage signal output under the driving of drive singal unit;

Signal processing unit, for extracting amplitude and the phase information of the signal that series circuit unit produces;

Signal switch unit, for the signal switching produced by signal processing unit;

A/D converting unit, converts digital signal to for simulating signal signal switch unit exported;

Control module, for the control of bottom circuit and the forwarding of data-signal; And

Drawing unit, has processing capacity, for realizing frequency sweep setting and Drawing of Curve.

2. the two-parameter pick-up unit of QCM (Quartz Crystal Microbalance) according to claim 1, is characterized in that, described drive singal unit comprises:

Frequency synthesizer, for generation of cosine signal;

Automatic gain controller, for constant cosine signal peak-to-peak value;

Amplifier, for amplifying cosine signal;

Low-pass filter, for the noise signal in filtering cosine signal.

3. the two-parameter pick-up unit of QCM (Quartz Crystal Microbalance) according to claim 1, is characterized in that, described signal processing unit comprises the signal acquisition circuit of No. three multipliers and low-pass filter series connection,

First via signal acquisition circuit is connected with QCM (Quartz Crystal Microbalance) one end, for realizing a road cosine signal auto-correlation processing and obtaining DC voltage value;

Second road signal acquisition circuit is connected with the QCM (Quartz Crystal Microbalance) other end, for realizing another road cosine signal auto-correlation processing and obtaining DC voltage value;

3rd road signal acquisition circuit is connected with QCM (Quartz Crystal Microbalance) two ends, for realizing two-way cosine signal cross correlation process and obtaining phase information.

4. adopt the two-parameter detection method of QCM (Quartz Crystal Microbalance) of device described in above-mentioned any one claim, it is characterized in that, following process is carried out to the two-way cosine signal that the QCM (Quartz Crystal Microbalance) under unloaded and load condition produces:

Determine a frequency, adopt auto-correlation and cross correlation process, obtain the respective amplitude of two-way cosine signal and both phase differential, obtain the electric conductivity value under this frequency according to the amplitude of two-way cosine signal and phase differential,

Change frequency, obtains the electric conductivity value under different frequency,

Build the relation between electric conductivity value and frequency, and

Acquisition resonance frequency changes, and dissipation factor under unloaded or load condition.

5. the two-parameter detection method of QCM (Quartz Crystal Microbalance) according to claim 4, is characterized in that,

Described resonance frequency to be changed under zero load and load condition difference on the frequency between conductance peaks;

Under described light condition, dissipation factor is the ratio of half of half-power bandwidth twice and resonance frequency under light condition;

Under described load condition, dissipation factor is the ratio of half of half-power bandwidth twice and resonance frequency under load condition.

6. the two-parameter detection method of QCM (Quartz Crystal Microbalance) according to claim 5, is characterized in that, described half of half-power bandwidth wherein for electric conductivity value is its maximum conductance value G _max's time corresponding frequency, f is resonance frequency.

7. the two-parameter detection method of QCM (Quartz Crystal Microbalance) according to claim 4, is characterized in that, the respective DC voltage value obtained after described two-way cosine signal auto-correlation processing is

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

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

Wherein, u ₁, u ₂for cosine signal amplitude;

The phase differential obtained after described two-way cosine signal cross correlation process

Wherein, u ₁₂for the direct current signal that cross-correlation exports.

8. the two-parameter detection method of QCM (Quartz Crystal Microbalance) according to claim 7, is characterized in that, electric conductivity value $G=\frac{1}{\mathrm{AR}}(\frac{u_{12}}{u_{22}}-1),$ Wherein, r is the resistance of connecting with QCM (Quartz Crystal Microbalance).