CS258764B1 - Method of measurement of constant saturated magnetostriction of magnetic strips - Google Patents

Abstract

The solution is based on measuring the saturated magnetostriction constant of magnetic strips using alternating magnetic susceptibility. The measured magnetic strip is subjected to a static magnetic field perpendicular to its longitudinal axis, an alternating magnetic field parallel to its longitudinal axis, and a mechanical stress parallel to the longitudinal axis of the magnetic strip. The components of the magnetic induction flux in the direction parallel to the longitudinal axis of the measured magnetic strip are measured, and these changes in the magnetic flux are a measure of the alternating magnetic susceptibility.

Description

The present invention relates to a method for measuring a saturated magnetostriction constant of magnetic strips by a simple induction method.

Magneto-elastic properties of ferromagnetic materials are important for their technical applications. For example, in materials intended for transformer cores or rotating electrical machines, magnetostriction is an undesirable phenomenon, as it causes vibration, increases noise, and magnetic losses in the material. In contrast, in other devices such as magnetomechanical transducers, ultrasound generators and the like, magnetostriction is used.

To determine the magnetoelastic properties of ferromagnetic materials, the knowledge of the JL _s saturation magnetostriction constant is necessary. · The methods used for its measurement can be divided into two groups:

1) For dilatation methods using changes in sample size during magnetization. Resistance or semiconductor extensometers are most often used for deformation measurements. However, these procedures are quite laborious and in some cases their accuracy and sensitivity may not be sufficient. Although it is possible to use more sensitive sample elongation sensors that meet even the most demanding requirements, the cost of these devices is relatively high.

2) The second group consists of methods that utilize changes in the magnetic properties that occur during the elastic deformation of the sample. Procedures based on this principle are known, but only some of them are universal, thus suitable for measuring the magnetostriction constants of both signs and arbitrary sizes. Recently, there has been a need to measure the saturation magnetostriction constant on thin-strip samples, particularly in connection with the expansion of the production of magnetic amorphous alloys. Thus, for example, a simple universal method for such measurements is known (A. Narita et al .: IEEE Trans. Magn. MAG-16 (1980). Two magnetic perpendicular magnetic fields are applied to a magnetic strip under tensile stress. The much weaker alternating field applied across the tape causes the saturation of the magnetization vector around the static field direction The frequency of the oscillations corresponds to the frequency of the alternating magnetic field The oscillation amplitude is determined from the voltage induced in the sensing coil through which the tape passes.

A disadvantage of this method is that the induced voltage is proportional to the time change of the longitudinal component of the tape magnetization. The frequency of the Induced voltage equals twice the frequency of the alternating magnetic field, and the amplitude of the induced voltage is proportional to the square of the amplitudes of the saturation magnetization vector. Accurate and sensitive determination of the vibration amplitude from which the saturation magnetostriction constant is determined is therefore somewhat complicated.

This method of measurement has not yet found wider application in practice. Most of the known methods of measuring the magnetistication constant are relatively expensive and complex, therefore the measurement of this important quantity is usually limited to some specialized laboratories.

These disadvantages are overcome by the invention, which is concerned with a method for measuring the saturation magnetostriction constant of magnetic strips by means of alternating magnetic susceptibility. SUMMARY OF THE INVENTION The magnetic tape being measured is subjected both to a static magnetic field having a direction parallel to the plane of the magnetic tape perpendicular to its longitudinal axis and having an intensity sufficient to saturate the measured magnetic tape and alternating magnetic field parallel to the longitudinal axis of the magnetic tape. . Further, the magnetic tape being measured is subjected to a mechanical stress parallel to the longitudinal axis of the magnetic tape, sensing the components of the magnetic flux in a direction parallel to the longitudinal axis of the measured magnetic tape, and these magnetic flux variations are a measure of alternating magnetic susceptibility.

To derive the relation between the longitudinal magnetic suseeptibility% and the saturation magnetostriction constant A. _s we start from the known expression for the free energy density E of the magnetic tape

E = -M _g cos 0 - M _g h sin £) coswt + 2 M ² (N sin ²⁰ + N cos ² $) + E ^, where M _g is saturated magnetization, N ,, and demagnetization factors along and across is the angle that at the instant of time t forms the saturation magnetization vector with the direction of the static field H, that is the circular frequency ah the amplitude of the alternating magnetic field.

For low values of the circular frequency uu, when at each moment the saturation magnetization vector has a direction corresponding to the thermodynamic equilibrium, the angle Θ can be determined from the condition of the minimum density of free energy

For small amplitudes of oscillations, ie small values of anglesΘ, the expression for longitudinal magnetic susoeptibility is obtained

M sin Θ M γ _ s_ s___ h coswt Η - Ηθ - (Nj. - N ") M _g where the effective anisotropic field H represents

I ^{H <F = M} s 3Θ ^{2] & = 0} ·

In the case of isotropic material, such as amorphous magnetic material or a polycrystalline material neorientovavaného valid and therefore 'in the ^M ·

6 * represents the amount of tensile stress applied to the tape. By measuring the changes of magnetic susceptibility X that occur when the tensile stress é changes, the magnitude of the saturation magnetostriction constant 3 can be determined.

By applying a static magnetic field across and an alternating magnetic field along the strip, the alternating component of the saturated magnetization vector is oriented predominantly in the direction along the strip and can therefore be readily read by the coil through which the strip passes. An advantage of this arrangement is that the voltage induced in the sensing coil has the same frequency as the alternating magnetic field and its amplitude is proportional to the amplitude of the oscillations of the saturated magnetization vector. Therefore, the advantages of the known AC bridge methods can be used to accurately and sensitively measure the induced voltage.

The attached drawing shows an exemplary embodiment of a device for measuring the saturation magnetostriction constant of magnetic strips according to the invention, showing the arrangement of the magnetizing, sensing and compensating coils and the method of positioning the measured tape.

The magnetic strip 2 to be measured is magnetized to saturation by a transverse static magnetic field 11, the direction of which is shown in the figure by an arrow. The alternating current passing through the magnetizing coil 2 generates a longitudinal alternating magnetic field. In the pick-up coil 2 ', the center of which passes through the strip 2, an alternating voltage is induced by changing the magnetic induction flux through the coil. The compensation coil 8, connected in reverse to the winding sense in series with the sensor coil 2, serves to compensate for the voltage induced in the sensor coil 2 ^{in the} absence of the measured tape 2.

The resulting voltage induced in the pair of coils 2 ^{and 3, and} P ^e is proportional to the longitudinal magnetic susceptibility X 2 · tape measuring tensile stress in the strip 2 is realized by attaching the one end of the strip 2 ^and applying ^a tensile force to the other end.

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Small variations in susceptibility when changing tensile stress can be very accurately and sensitively measured using bridge methods for measuring mutual inductance, such as a bridge

Hartshorn type.

Said method of measuring the saturation magnetostriction constant of the magnetic strips can be used, for example, to quickly and accurately check the properties of the magnetic materials produced in the form of sheets or strips directly at the factory.

Claims (1)

Method for measuring the saturation magnetostriction of magnetic strips by means of alternating magnetic susceptibility, characterized in that the measured magnetic tape is treated on the one hand by a static magnetic field with a direction parallel to the plane of the magnetic tape perpendicular to its longitudinal axis and having an intensity sufficient to saturate the measured magnetic tape. alternatively, by an alternating magnetic field parallel to the longitudinal axis of the magnetic tape and by a mechanical stress parallel to the longitudinal axis of the magnetic tape, sensing the components of the magnetic flux in a direction parallel to the longitudinal axis of the magnetic tape being measured.