RU2522128C1 - Measuring method of constant magnetic field - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: capacitor, the dielectric of which is represented with a magnetostriction-piezoelectric composite, is placed into a measured constant magnetic field; the specified alternating magnetic field is applied, and difference of neighbouring amplitudes of an output harmonic signal is measured, which is equal to a product of intensity of constant magnetic field by a value characterising the structure sensitivity.

EFFECT: higher accuracy.

1 tbl, 3 dwg

Description

The invention relates to measuring technique and can be used to measure the intensity of a constant magnetic field.

Several methods are currently used to measure the constant magnetic field strength [see Electrical measurements. Means and methods of measurement. Ed. E.G.Shramkova. -M., High School, 1972, 520 pp.] The main of which are the following:

1 is a magnetometric method based on the action of a magnetic field on a magnetic needle;

2 - a method based on the measurement of the emf resulting from the phenomenon of electromagnetic induction. This method includes a ballistic method based on measuring the charge induced in a magnetic coil when the magnetic flux penetrating it changes;

3 - ponderomotive method based on measuring the force acting on a sample in an inhomogeneous magnetic field;

4 is a method based on measuring the Hall emf resulting from the Hall effect.

A method based on the action of a magnetic field on a magnetic needle is simple to implement, but it has a large error.

A method based on measuring the emf resulting from electromagnetic induction is associated with the need to rotate or move the circuit and also has little sensitivity.

The method based on the measurement of the Hall emf has a maximum sensitivity of up to 1 mV / O [see Baranochnikov M.L. Micromagnetoelectronics. -M .: DMK Press, 2001, 554 pp.] And is based on the measurement of a constant signal, which significantly reduces its noise immunity.

There is also a known method [see Barone A., Paterno J. Josephson Effect. Physics and application. -M .: Mir, 1984, 639 p.], Based on measuring the phase difference that occurs when electrons pass through a superconducting ring with two Josephson junctions in a magnetic field. This method has maximum sensitivity, however, its use is associated with the use of substances in the superconducting state, which greatly complicates its use in the measurement.

The closest technical solution adopted for the prototype is a method of measuring the magnetic field, based on measuring the voltage occurring on the plates of a capacitor, the dielectric of which is a magnetoelectric material, when a current pulse is applied to a magnetizing coil [see Patent RU No. 2244318, G01R 33/02, 01/10/2005].

The disadvantage of this method is the use of a large current pulse when measuring, so that it is necessary to ensure good heat transfer with the substrate.

The objective of the invention is to simplify the method, increase the sensitivity and noise immunity of measuring the intensity of a constant magnetic field at ordinary temperatures.

To solve this problem, a method is proposed for measuring a constant magnetic field by measuring the alternating voltage arising on the plates of a capacitor, the dielectric of which is a magnetostrictive piezoelectric composite, when it is placed in an alternating and constant magnetic field, and the difference between two adjacent maxima of the harmonic signal, which is equal to the product of the constant magnetic field strength by an amount characterizing the sensitivity of the structure.

When a capacitor is placed in a magnetic field in the magnetostrictive phase of the composite, mechanical stresses arise, which are transferred to the piezoelectric phase, as a result of which a potential difference arises on the plates of the capacitor. Since magnetostriction is a quadratic magnetization effect [Belov K.P. Magnetostrictive phenomena and their technical applications. -M: Nauka, 1987, 160 pp.], Then in a region far from saturation, the magnitude of mechanical stresses is proportional to the square of the magnetic field strength. As a result of this, the electric field arising on the capacitor plates will also be proportional to the square of the magnetic field strength. This leads to the fact that when a capacitor is placed in an alternating magnetic field with a frequency ω, an electric voltage with a double frequency occurs on the plates of the capacitor.

Using the equations of motion of the medium and material equations, we can show [Filippov D.A. The theory of the magnetoelectric effect in heterogeneous structures based on a ferromagnet-piezoelectric // FTT, 2005, v. 47, No. 6, pp. 1082-1084], that the value of the potential difference U arising on the capacitor plates is determined by the expression:

$$U=\frac{Y_{p}d}{p_{\epsilon }{\Delta }_D}\frac{Y_m{t}_m}{Y_m{t}_m+Y_p{t}_p}{t}_p{\left(H\right)}^2,\left(\mathrm{one}\right)$$

- безразмерный параметр, $$K_p^2=Y_p{d}^2/p_{\epsilon }$$

- квадрат коэффициента электромеханической связи.here H is the magnetic field strength, t _m , t _p is the thickness of the magnetostrictive and piezoelectric layer, Y _m , Y _p are Young's moduli of the magnetic and piezoelectric phases, respectively, d is the piezoelectric module, p _ε is the dielectric constant of the piezoelectric, g = δ ² λ / (δH) ² is the magnetostrictive coefficient, λ is the magnetostrictive deformation, $${\Delta }_D=l-K_p^2(\frac{Y_m{t}_m}{Y_m{t}_m+Y_p{t}_p})$$

- dimensionless parameter, $${\mathrm{<figure-callout\; id="2"\; label="K\; p"\; filenames="00000011.png"\; state="\{\{state\}\}">K\; </figure-callout>}}_p^{}={\mathrm{<figure-callout\; id="2"\; label="Y\; p\; d"\; filenames="00000011.png"\; state="\{\{state\}\}">Y\; </figure-callout>}}_p{d}^{}{}^2/p_{\epsilon }$$

- squared coefficient of electromechanical coupling.

Figure 1 shows the waveforms of the input voltage (1) on the Helmholtz coils, creating an alternating magnetic field, and the output voltage (2) on the capacitor plates. As can be seen from figure 1, the frequency of the output voltage is equal to twice the frequency of the input voltage.

If the magnetic field represents the sum of two fields, variable H (t) = H _m cos (ωt) and a constant value H ₀ , then the amplitude of the output signal on the capacitor will be proportional to the square of the resulting field, i.e. is proportional to (H _m cos (ωt) + Н ₀ ) ² , i.e.

$$U\left(t\right)=C\cdot {\left(H_m\cos \left(\omega t\right)+H_0\right)}^2,\left(2\right)$$

- постоянная величина, зависящая от магнитострикционных, пьезоэлектрических и упругих свойств структуры.Where $$C=\frac{Y_p{d}_{31}{g}_{331}}{p_{{\epsilon }_{zz}}\Delta D}\frac{Y_m{t}_m}{Y_m{t}_m+Y_p{t}_p}{t}_p$$

- a constant value, depending on the magnetostrictive, piezoelectric and elastic properties of the structure.

As a result, the output signal will represent the sum of two signals:

$$U\left(t\right)=U_{\mathrm{one}}\left(t\right)+U_2\left(t\right),\left(3\right)$$

where U ₁ (t) = С ( H _m cos (ωt)) ² is an alternating signal with a double frequency, U ₂ (t) = С · U _m cos (ωt) is an alternating signal with a usual frequency ω.

The difference of two adjacent amplitude values of the signal will in this case be proportional to the value of the constant magnetic field, i.e.

$$\Delta U_m=2C{H}_m{H}_0\left(\mathrm{four}\right)$$

Using formula (4, for the value of the constant magnetic field, we obtain the expression

$$\Delta U_m=k*{\mathrm{<figure-callout\; id="0"\; label="H"\; filenames="00000011.png"\; state="\{\{state\}\}">H</figure-callout>}}_0,\left(5\right)$$

where the sensitivity is k = 2CH _m .

On figa presents an oscillogram of the output voltage on the plates of the capacitor when it is placed in an alternating magnetic field with a frequency ω and a constant magnetic field with intensity H ₀ . Next, for comparison, Fig.2b presents a graph of the function f (x) = cos (2x) + 0.5 * cos (x).

The difference in signal magnitude at two adjacent maxima will be proportional to the magnitude of the dc magnetic field.

Table 1 presents the results of measuring the difference in the amplitude values of the voltage of two neighboring maxima depending on the magnitude of the constant magnetic field for various values of the intensity of the alternating magnetic field H _m . The structure of permendur-zirconate-titanate-lead-permendur was used as the dielectric of the capacitor. The samples had a rectangular shape. The length of the sample is 20 mm, the width is 5 mm, the thickness of the piezoelectric is 0.35 mm, and the thickness of one permendura plate is 0.175 mm.

Figure 3 presents graphs of the obtained dependences of the difference in the amplitude values of the voltage ΔU on the magnitude of the constant magnetic field H ₀ for various values of the amplitude of the alternating magnetic field H _m · 1-H _m = 10E, 2-H _m = 20E, 3-H _m = 30E , 4-H _m = 40 Oe.

As follows from the data presented in table 1 and the graphs presented in figure 3, in full accordance with formula (4), there is a linear dependence of the difference in the amplitude values of the voltage between adjacent maxima at different values of the amplitude of the alternating magnetic field. The sensitivity of the method depends on the magnitude of the intensity of the alternating magnetic field, increasing with its value. For these values of the magnetic field, it reaches 10 mV / Oe with amplitude values of the intensity of an alternating magnetic field of 40 Oe, which exceeds the sensitivity of Hall sensors.

Before taking measurements, the structure is first calibrated to determine its sensitivity. To do this, the difference in the amplitude values of the voltage is measured when the capacitor is placed in alternating and constant magnetic fields of known magnitude and the value C is determined. Then, knowing the sensitivity of the device, the potential difference is measured and the magnitude of the constant magnetic field is determined by formula (5).

It should be especially noted that since both signals (with a single and doubled frequency) are generated from the same source, the phase difference between them remains constant, which allows you to summarize the difference in amplitude values over a certain period of time, which significantly increases the sensitivity of the method.

Using the proposed method can increase the sensitivity of measurements and improve noise immunity during measurement.

Table 1 DC field strength H ₀ , Oe The difference in the amplitude values of the voltage ΔU, mV with an alternating field H _m = 10E H _m = 20E H _m = 30E H _m = 40E 0 0 0 0 0 0.34 0.6 1.38 2.0 3.33 0.68 1.15 2.75 4.25 6.66 1.03 1.75 4.0 6.75 10.0 1.71 2.9 6.63 11.25 16.7 2.39 4.2 9.13 16.0 24.4 3.42 6.25 13.25 23.0 34.4 5.13 9.13 20.0 34.0 51.4

Claims (1)

A method of measuring a constant magnetic field by measuring the alternating voltage arising on the plates of a capacitor whose dielectric is a magnetostrictive piezoelectric composite, when placed in an alternating and constant magnetic field, characterized in that the difference of two adjacent maxima of the harmonic signal is measured, the value of which is equal to the product of tension constant magnetic field by an amount characterizing the sensitivity of the structure.

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