Nonlinear amplification of the magnetic induction signal in a magnetomodulation sensor with an amorphous ferromagnetic core

The purpose of this work is to show the possibility of using a magnetic field-controlled nonlinearity of the amplitude change in an oscillatory LC-circuit containing a core made of an amorphous ferromagnetic alloy with compensated longitudinal magnetostriction, which makes it possible to obtain a high conversion coefficient of weak magnetic field sensors operating at room temperature. Methods. A practical method for constructing magnetomodulation sensors of magnetic induction with a fixed magnetic displacement field, which corresponds to the maximum steepness of the nonlinear characteristic of an oscillatory circuit with an amorphous ferromagnetic core in the region of autoparametric resonance, is considered. Results. It has been shown that the stable conversion factor of a 35 mm long sensor based on an oscillatory circuit with autoparametric amplification at a modulation frequency of 256 kHz can reach 10 mV/nT, which allows, with the available element base, to record signals of a weak alternating magnetic field with an amplitude of 0.03 pT/H$z^{1/2}$ in the frequency range 10... 1000 Hz. It is noted that the excitation of the sensor by a weak harmonic magnetic field of a high frequency and the constant presence of the amorphous ferromagnetic core near the state of technical saturation significantly reduces the level of intrinsic magnetic noise of the magnetomodulation sensor. Conclusion. Magnetomodulation sensors with autoparametric amplification of the magnetic induction signal can find application in geophysics, magnetobiology and biomedicine.