Measurement of magnetostriction using a strain gauge bridge with alternating excitation

Objectives . Knowledge of the dependence of magnetostriction of various ferromagnetic materials on the magnetic field is important for studying the magnetoelectric effect in composite structures, in particular for calculating the shape of the field dependence of piezomagnetic moduli and for calculating magnetoelastic characteristics. However, the typical resolution level of known strain gauge setups for measuring magnetostriction is about 10 −6 , which is insufficient to obtain detailed information on the piezomagnetic coefficients of the materials under study. The paper describes the development of an automated setup for the precision measurement of the dependence of magnetostriction of ferromagnetic plates on a magnetic field in the range of ±5 kOe providing an improved strain resolution order of magnitude. Methods . The setup uses film strain gauges included in a Wheatstone bridge excited by alternating current. Thanks to the applied method of signal frequency shift, as well as the use of a low-noise preamplifier and temperature stabilization of the measuring cell, it was possible to reduce the level of noise referred to the input and zero drift of the measuring circuit. Results . The developed setup provides an accuracy of the magnetostriction measurement of ferromagnetic plates up to 10 −7 in the range of magnetic fields of ±5 kOe, which is an order of magnitude higher than known methods. The setup also allows measuring the electric and piezoelectric deformation of materials depending on the applied electrical voltage in the range of ±500 V. The measurement results can be used to more accurately calculate the field dependencies of the piezomagnetic and piezoelectric coefficients of materials, including materials with low magnetostriction, such as various ferrites, hematite, yttrium iron garnet, etc. Conclusions . The method of alternating excitation of the measuring bridge in combination with other measures can be used to increase the deformation resolution to about 10 −7 .