CN101034144A - Full-automatic measurement device for magnetoelectric properties of magnetoelectric material and measuring method thereof - Google Patents

Abstract

The invention belongs to the field of magnetoelectric materials, and in particular relates to a computer-controlled method and device for measuring the magnetoelectric properties of materials by utilizing the principle of virtual multi-channel phase-locked amplification. The present invention virtualizes the lock-in amplifier, that is, the computer software realizes the function of the lock-in amplifier, and utilizes the virtual lock-in amplifier to conveniently carry out lock-in amplification processing on any multi-channel signal, so that not only the simultaneous and accurate dynamic measurement The dE and dH improve the measurement accuracy of the magnetoelectric performance, and the upper limit of the operating frequency of the hardware lock-in amplifier is greatly improved, and at the same time, the manufacturing cost of the magnetoelectric measurement equipment is reduced. The invention also combines the control and measurement of the external DC bias magnetic field to further improve the automation degree of the magnetoelectric measurement equipment, thereby improving the magnetoelectric measurement accuracy and efficiency.

Description

A fully automatic magnetoelectric material magnetoelectric property measurement device and its measurement method

technical field

The invention belongs to the field of magnetoelectric materials, and relates to a measurement technology of magnetoelectric properties of magnetoelectric materials, in particular to a fully computer-controlled device for measuring magnetoelectric properties of magnetoelectric materials and a measurement method thereof realized by using the principle of virtual multi-channel phase-locked amplification.

Background technique

Magnetoelectric properties refer to the dielectric polarization of a material induced by an external magnetic field, or the magnetization induced by an external electric field. Generally speaking, the magnetoelectric properties refer to the magnetic field-induced dielectric polarization unless otherwise specified. Magnetoelectric properties have broad application prospects in many high-performance magnetoelectric functional components. Specifically, it can be used in many fields such as magnetic field detection, magnetoelectric energy exchange, information storage, and driving. The measurement of the magnetoelectric properties of materials is the most critical link in the research, development and application of magnetoelectric materials. The commonly used index to characterize the magnetoelectric performance is the magnetoelectric voltage coefficient, which is defined as α _ME =dV/(tdH), where dH is the AC differential magnetic field superimposed on the DC bias magnetic field, and dV is the two ends of the sample generated under the action of the differential magnetic field The voltage, t is the thickness of the sample.

Usually the test conditions are at kHz or MHz frequency. In this frequency range, the differential magnetic field generated by the Helmhertz coil is usually very small, that is to say, the current passing through the Helmhertz coil is very weak, and the two ends of the sample The voltage generated is also very small. Therefore, the measurement of the magnetoelectric response signal of the magnetoelectric material involves weak signal detection, and the precise magnetoelectric measurement equipment must use a lock-in amplifier. Due to the high price of the lock-in amplifier, the cost of the existing magnetoelectric measurement equipment at home and abroad expensive. On the other hand, from α _ME =dV/(tdH), it can be seen that the acquisition of magnetoelectric properties requires simultaneous measurement of dV and dH, but each common commercial lock-in amplifier can only perform lock-in amplification processing on the signal of one channel , it is impossible to measure dV and dH at the same time, so the common practice at home and abroad is to only measure dV and nominally fix dH [1-2]. In actual measurement, especially when the frequency of the AC magnetic field changes, it is not easy to completely fix dH, so it is impossible to do accurate dynamic monitoring of the magnetic field, and thus it is impossible to obtain accurate magnetoelectric properties. The operating frequency range of the lock-in amplifier is also an important indicator of the measurement capability of the magnetoelectric test system. The operating frequency of the general lock-in amplifier is below 200kHz. If the test conditions exceed this operating frequency range, then the lock-in amplifier cannot be used. The test cannot be performed because the test requirements are met. If the test frequency of the equipment is to be expanded, a more expensive broadband lock-in amplifier is required, which will undoubtedly further increase the equipment cost. In addition, the change of the magnetoelectric properties with the applied DC bias magnetic field and the change of the magnetoelectric properties with the frequency of the applied AC magnetic field must be measured separately [1-2]. frequency changes. It can be seen that the existing magnetoelectric measurement equipment at home and abroad is expensive, the accuracy and frequency upper limit are not high enough, and the degree of automation of the measurement process needs to be improved urgently.

[1] M.Mahesh Kumar et al, An experimental setup for dynamic measurement of magnetoelectric effect, Bull.Mater.Sci., 21(3), 251-255(1998)

[2] Shuxiang Dong, Jie-Fang Li, and D.Viehland, Characterization of magnetoelectriclaminate composites operated in longitudinal-transverse and transverse-transverse modes, J.Appl.Phys., 95(5), 2625-2630(2004)

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of high cost of existing measuring instruments, low measurement accuracy, upper frequency limit and low degree of automation. For this reason, the lock-in amplifier is virtualized, that is, the function of the lock-in amplifier is realized by computer software, because the phase-lock The amplifier is virtual, and it is very convenient to implement lock-in amplification processing on multi-channel signals. In this way, not only can dynamic measurement of dV and dH be performed accurately at the same time, which improves the measurement accuracy of magnetoelectric performance, but also greatly improves the upper limit of operating frequency compared with hardware lock-in amplifiers, and at the same time reduces the manufacturing cost of magnetoelectric measurement equipment. In addition, The invention combines the control and measurement of the external DC bias magnetic field to further improve the automation degree of the magnetoelectric measurement equipment, thereby improving the precision and efficiency of the magnetoelectric measurement.

A fully automatic measuring device for magnetoelectric properties of magnetoelectric materials, comprising an electromagnet 1, a Helmertz coil 2, a Tesla meter 3, a DC power supply 4, a test sample 5, a computer 8, a differential instrument 11, a data acquisition front end 12, Signal generator 13, power amplifier 14. The front end of data acquisition is an A/D card or digital oscilloscope capable of multi-channel synchronous sampling. The computer 8 is equipped with a virtual magnetic field closed-loop control unit 6 , a recording unit 7 of magnetoelectric coupling performance, a virtual signal generation control unit 9 , and a correlator 10 .

The electromagnet 1 is used to generate a DC bias magnetic field; the Helmertz coil 2 placed in the middle of the DC magnetic field is used to generate an AC magnetic field; the strength of the applied bias magnetic field is read by the Tesla meter 3 and sent to the computer. The DC power supply 4 controls the external bias magnetic field; the virtual magnetic field closed-loop control unit 6 in the computer can read the strength of the DC bias magnetic field transmitted from 3; the control signal of the DC bias magnetic field is transmitted to the power supply 4 through the D/A card . The virtual signal generation control unit 9 in the computer 8 amplifies the signal through the signal generator 13 through the power amplifier 14 and provides it to the Helmertz coil 2 as its driving signal. The strength of the alternating magnetic field is converted into a voltage signal by the resistor R connected in series with the Helmertz coil 2 and input to the data acquisition front end 12 . The magnetoelectric response signal generated on the sample 5 to be tested in the magnetic field is connected to the differential instrument 11 through two coaxial lines; the input signal line of the differential instrument 11 improves the signal-to-noise ratio through the floating connection method, and its output is connected to the data acquisition front end 12 on. The virtual signal generation control unit 9, the correlator 10, and the data acquisition front end 12 are the three main parts of the virtual lock-in amplifier. The correlator 10 is the core component of the virtual multi-channel lock-in amplifier. The magnetoelectric response signal input by the data acquisition front end 12, the signal of the AC magnetic field strength and the reference signal input by the signal generation control unit 9 are used for correlation calculation to obtain the magnetoelectric coupling strength and phase difference and other information and output the result to the recording unit 7 of the magnetoelectric coupling performance. The magnetoelectric coupling performance recording unit 7 can dynamically record the magnitude of the DC bias magnetic field intensity from the input of the magnetic field control unit 6; and the information and other experimental information of the magnetoelectric response intensity and phase lag introduced by the correlator 10, thereby completing continuous Fully automated measurement.

The use premise of the correlator among the present invention is that the measured signal is a weak sinusoidal signal with a certain period, and its mathematical form is s(t)=Asin(ωt+φ), and noise n is mixed in the measurement signal of the data acquisition front end (t), that is, the measurement signal Vs(t)=s(t)+n(t). The reference signals in the correlator are two sinusoidal signals Vr(t)=sin(ωt) and Vr'(t)=sin(ωt+π/2) with an amplitude of 1 and a phase difference of π/2. Solving the simultaneous equations of the discrete signal cross-correlation function, we can get $\mathrm{\φ}=\arctan \left\{\underset{k}{\overset{N}{\mathrm{\Σ}}}\right[\mathrm{vs.}\left(k\right)V{r}^{\′}\left(k\right)/\underset{k}{\overset{N}{\mathrm{\Σ}}}\left[\mathrm{vs.}\left(k\right)\mathrm{VR}\left(k\right)\right]\},$ $A=2\underset{k}{\overset{N}{\mathrm{\Σ}}}\left[\mathrm{vs.}\left(k\right)\mathrm{VR}\left(k\right)\right]/\cos \mathrm{\φ}$ where N is the total number of discrete sampling points of the sampling signal or virtual reference signal entering the correlator.

The principle of virtual multi-channel lock-in amplification used in the present invention is to transmit the synchronous voltage signal dV and magnetic field signal dH into the correlator at the same time, and the calculation results obtain the amplitude A _dE and phase φ _dE of the voltage signal and the amplitude of the magnetic field signal respectively A _dH and phase φ _dH , and then calculate the magnitude of the magnetoelectric coupling performance and the amplitude α _ME and phase difference φ _ME of the magnetoelectric coupling.

Because the DC magnetic field generated by the power supply 4 does not change with time, the magnetic field is calibrated before the magnetoelectric measurement to generate a table. When it is necessary to load a DC bias magnetic field of a specific strength, the DC magnetic field is directly set by looking up the table. During the dynamic magnetoelectric measurement process, the instantaneous DC bias magnetic field value corresponding to each magnetoelectric performance measurement moment is tracked in real time, and the difference between the DC bias magnetic field value and the set DC bias magnetic field value is less than 5%.

The principle of virtual phase-locked amplification used in the present invention is to perform phase-sensitive detection on the AC signal of the magnetoelectric response, that is, to use the measured signal and the reference signal to have the same frequency and a certain phase relationship, and only use the same frequency as the reference signal in the measured signal The part of the signal component has a response, and the part of the measured signal with a frequency different from the reference signal is suppressed as noise, so the signal-to-noise ratio of the magnetoelectric measurement can be greatly improved.

The magnetoelectric measuring device built by the principle of virtual multi-channel lock-in amplification adopted in the present invention has the following technical effects:

(1) Synchronously and dynamically accurately measure the two parameters dV and dH in the formula of the magnetoelectric voltage coefficient, thereby improving the measurement accuracy of the magnetoelectric performance, which is not available in other magnetoelectric measuring devices.

(2) Due to the adoption of virtual lock-in amplification technology, the control degree of freedom for the entire process of lock-in amplification is quite large, thus increasing the automatic control level of the magnetoelectric measuring equipment. No one has introduced virtual lock-in amplification technology in other magnetoelectric measuring equipment at home and abroad.

(3) No real lock-in amplifier is used in the present invention, thereby greatly reducing the cost of the magnetoelectric measuring equipment.

(4) Due to the use of a virtual lock-in amplifier, its operating frequency will be greatly expanded without being limited by the operating frequency of the hardware lock-in amplifier.

(5) The virtual lock-in amplifier collects and calculates the generated signal and the generated signal at the same time, and can directly calculate the phase of the two, thus providing the possibility for phase research.

(6) The present invention combines the virtual multi-channel lock-in amplifier with the closed-loop control system of the virtual DC magnetic field, and can automatically measure the three-dimensional image of the magnetoelectric properties of the material changing with the frequency of the external DC bias magnetic field and alternating magnetic field. The three-dimensional images of the magnetic and electrical properties of materials changing with the frequency of the applied DC bias magnetic field and the applied AC magnetic field have not been measured so far at home and abroad.

Description of drawings

Fig. 1 is a structural schematic diagram of a fully automatic magnetoelectric measuring device utilizing the principle of virtual multi-channel lock-in amplification according to the present invention.

Fig. 2 is a measurement curve of the variation of transverse magnetoelectric coupling strength of Ni/PZT/Ni layered composite material with external DC bias magnetic field according to the present invention.

Fig. 3 is the variation of the phase lag of the transverse magnetoelectric coupling strength and magnetoelectric response of the Ni/PZT/Ni layered composite material with the frequency of the applied AC magnetic field according to the present invention.

FIG. 4 is a partial variation of FIG. 3 .

Fig. 5 is a three-dimensional image of the variation of the magnetoelectric coupling strength of the Ni/PZT/Ni layered composite material with the frequency of the applied bias magnetic field and the applied AC magnetic field according to the present invention.

Fig. 6 is a three-dimensional image of the phase lag of the magnetoelectric response of the Ni/PZT/Ni layered composite material according to the present invention as a function of the frequency of the applied bias magnetic field and the applied AC magnetic field.

Detailed ways

Further description will be given below through implementation examples and accompanying drawings.

In embodiment 1, a typical test sample 5 uses a Ni/PZT/Ni layered composite material. The transverse magnetoelectric coupling coefficient α _ME,31 and the corresponding phase lag of the magnetoelectricity of Ni/PZT/Ni layered composites were measured.

(1) Assemble the instrument according to the principle of Fig. 1, wherein the sensing resistance R=10Ω for generating the magnetic field. Data acquisition front end 12 is Rigol DS5062CA oscilloscope; signal generator 13 is Agilent 33220A; DC bias magnetic field system adopts WWL-LSX21 three-phase DC power supply and SB175 electromagnet; Tesla meter 3 uses HT100; (1.6GHz, 256MB, 40GB, WindowsXP) Install the evaluation version of Labview8.0 as the development platform of the control program. According to the above principles, the corresponding measurement control software is written under Labview.

(2) The sample tested is a Ni/PZT/Ni layered composite square plate with Ni electroplated on a PZT ferroelectric ceramic with a size of 25mm×25mm×0.8mm, where the thicknesses of Ni, PZT and Ni are 0.4mm and 0.8mm respectively. mm and 0.4mm. Put the two sides of the magnetoelectric composite sheet into the magnetic field as shown in Figure 1, and lead out the coaxial cable. The direction of placement ensures that the direction of the DC magnetic field, the direction of the AC magnetic field, and the direction of the side length of the square sheet are parallel. Since the direction of the magnetic field is within the square surface and is consistent with the side length of the square, it is recorded as the 1 direction, and because the output direction of the magnetically generated electric field is the direction perpendicular to the sheet, it is defined as the 3 direction, so the magnetoelectric coupling strength is recorded as α _ME,31 .

(3) After checking that all the power lines and signal lines are connected correctly, start to power on. The frequency of the driving signal of the AC magnetic field output from the signal generator 13 is set to 1kHz, and the amplitude is set to 1V, which remains unchanged. Then gradually increase the DC bias magnetic field, and observe the magnetoelectric output at the same time, as shown in Figure 2, it can be seen that the corresponding DC bias magnetic field value _HD = 150Oe when the magnetoelectric output peaks.

(4) The amplitude 1V of the output AC voltage of fixed DC bias magnetic field H _D =150Oe and signal generator 13 is constant, only changes the frequency of signal generator 13 output AC voltages, operation control program, automatically records magnetoelectric response output The amplitude and phase lag values are obtained in Figure 3. It is a measurement curve of the transverse magnetoelectric coupling strength of Ni/PZT/Ni layered composites and the phase lag of the magnetoelectric response as a function of the frequency of the applied AC magnetic field. It can be seen that the transverse magnetoelectric field coefficient α _{ME of the Ni/PZT/Ni layered composite material has a} maximum value of 41.5V/cm Oe at 85.3kHz. The other two resonant peaks are at 59.5kHz and 73.5kHz respectively. Although they cannot be distinguished as resonant peaks in terms of intensity, they can be confirmed to be two resonant peaks according to the phase lag curve of the magnetoelectric response.

(5) Analyze the position of the strongest peak of the magnetoelectric output intensity in Figure 3, keep other conditions unchanged, and perform a fine scan on the frequency near the peak to obtain Figure 4, which is the resonant frequency of the Ni/PZT/Ni layered composite Measurement curves of the nearby transverse magnetoelectric coupling strength and the phase lag of the magnetoelectric response as a function of the frequency of the applied AC magnetic field. By finely scanning the frequency near the strongest resonance peak, a more accurate resonance frequency can be obtained at 85.25kHz, and the corresponding α _{ME, 31} maximum also increases to 43.2V/cm Oe.

Example 2, measuring the three-dimensional image of the transverse magnetoelectric field coefficient α _{ME, 31} of the Ni/PZT/Ni layered composite material and the phase lag of the magnetoelectric response changing with the frequency of the applied bias magnetic field and the applied AC magnetic field.

(1) In order to increase the magnetic field automatic control module, AD/DA cards (AC6632 and AC6682) are installed in the PCI slot of the computer as the control interface of the DC bias magnetic field, and the hardware and software in the measurement system are correspondingly expanded. The rest are the same as Step 1 in Example 1

(2) The sample tested is the same as step 2 in Example 1.

(3) The amplitude of the output AC voltage of the fixed signal generator 13 is 1V, remains unchanged, change the frequency of the signal generator 13 output AC voltage and the size of the DC bias magnetic field (seeing 1 among Fig. 1) simultaneously, run The control program automatically records the magnitude and phase lag of the magnetoelectric response output, and obtains Figures 5 and 6. They are three-dimensional images of the magnetoelectric coupling strength and response phase lag of Ni/PZT/Ni layered composites as a function of the frequency of the applied bias magnetic field and applied AC magnetic field, respectively. It can be seen from Figure 5 that the transverse magnetoelectric coupling performance of Ni/PZT/Ni layered composites is basically symmetrically distributed with the bias magnetic field at both positive and negative ends, and reaches a peak value at a certain absolute value of the bias magnetic field. It reflects that the magnetoelectric coupling properties of Ni/PZT/Ni layered composites come from the magnetostrictive properties of the Ni layer. In addition, the frequency of the AC magnetic field has a significantly stronger effect on the magnetoelectric coupling performance than the DC bias magnetic field. It can be seen from Figure 6 that the three frequency interfaces corresponding to Figure 3 are 59.5kHz, 73.5kHz and 85kHz, reflecting that the resonance characteristics do not change with the change of the bias magnetic field. In Fig. 6, there is also an interface introduced by a DC bias magnetic field, reflecting the sign change of the magnetoelectric coupling.

Claims (3)

1. full-automatic magnetoelectric properties of magnetoelectric material measurement mechanism, its pattern measurement device comprises electromagnet (1), helmholtz coil (2), teslameter (3), direct supply (4), specimen (5), computing machine (8), difference instrument (11), data acquisition front (12), signal generator (13), power amplifier (14); But data acquisition front is the A/D card or the digital oscilloscope of a multichannel synchronized sampling, and computing machine (8) is provided with record cell (7), virtual signal generation control module (9), the correlator (10) of closed-loop control unit, virtual magnetic field (6), magneto-electric coupled performance; Electromagnet (1) is used for producing direct current biasing magnetic field; The helmholtz coil of putting in the middle of D.C. magnetic field (2) is used for producing AC magnetic field; Add biased magnetic field strength and read and send into computing machine by teslameter (3).

2. a full-automatic magnetoelectric properties of magnetoelectric material measuring method is characterized in that adding bias magnetic field with direct supply (4) control; Closed-loop control unit, virtual magnetic field (6) in the computing machine reads in the intensity in the direct current biasing magnetic field of transmitting from (3), and the control signal of transmitting direct current biasing magnetic field by the D/A card arrives power supply (4); Virtual signal generation control module (9) in the computing machine (8) offers helmholtz coil (2) as its drive signal after by signal generator (13) signal being amplified through power amplifier (14); The intensity of alternating magnetic field converts voltage signal input data acquisition front (12) to by the resistance R that is connected in the helmholtz coil (2); Testing sample in the magnetic field (5) is gone up the magneto-electric response signal that produces and is connected to difference instrument (11) by two coaxial cables; The input signal cable of difference instrument (11) improves signal to noise ratio (S/N ratio) by floating ground connection, and its output is received on the data acquisition front (12); The magneto-electric response signal that correlator (10) utilizes data acquisition front (12) input and the reference signal that signal and the signal generation control module (9) of AC magnetic field intensity are imported carry out the relevant record cell (7) that calculates the information such as magneto-electric coupled intensity and phase difference and the result is outputed to magneto-electric coupled performance; Information and other experiment informations that magneto-electric coupled performance inventory unit (7) can dynamically note down the DC bias magnetic field intensity size of self-magnetic field control module (6) input and the magneto-electric response intensity of being imported into by correlator (10) and phase place to lag behind, thus the measurement of continuous full-automation finished.

3. as a kind of full-automatic magnetoelectric properties of magnetoelectric material measuring method as described in the claim 2, the use prerequisite that it is characterized in that correlator is that measured signal is the faint sinusoidal signal with some cycles, its mathematical form is s (t)=Asin (ω t+ φ), and in the measuring-signal of data acquisition front, be mixed with noise n (t), i.e. measuring-signal Vs (t)=s (t)+n (t); Reference signal in the correlator is that two amplitudes are 1, phase place differ sinusoidal signal Vr (the t)=sin (ω t) of pi/2 and Vr ' (t)=sin (ω t+ pi/2); Find the solution the simultaneous equations of discrete signal cross correlation function, obtain $\mathrm{\φ}=\arctan \left\{\underset{k}{\overset{N}{\mathrm{\Σ}}}\right[\mathrm{Vs}\left(k\right){\mathrm{Vr}}^{\′}\left(k\right)/\underset{k}{\overset{N}{\mathrm{\Σ}}}\left[\mathrm{Vs}\left(k\right)\mathrm{Vr}\left(k\right)\right]\},$ $A=2\underset{k}{\overset{N}{\mathrm{\Σ}}}\left[\mathrm{Vs}\left(k\right)\mathrm{Vr}\left(k\right)\right]/\cos \mathrm{\φ},$ Wherein N enters the sampled signal of correlator or the discrete sampling point total amount of virtual reference signal.

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