Abstract
Sensitive and quick-response nonlinear inductance characteristics are found for high Tc superconducting (YBa2Cu3O7-x bulk) disk cores with tightly wound coils at 77K in which soft magnetic BH hysteresis loops are observed. The permeability changes from nearly zero (Meissner effect) to the vacuum permeability applying a coil-current magnetic field H or an external magnetic field Hex due to flux penetration effect. Theoretical curves of permeability versus field characteristics and initial magnetization curve are obtained using a flux penetration model.
The magnetizing frequency can be set to more than 20MHz due to the absence of eddy current losses, which is difficult for conventional ferromagnetic cores made of Permalloy, amorphous materials, and ferrite. New quick-response fluxgate magnetic-field sensors are constructed using modulator circuits with AC or DC voltage sources. The former is used for second-harmonic type sensors and DC output type sensors, while the latter is for voltage-output multivibrator bridge type sensors. The sensitivity is about 10-4A/m for AC fields and the cut-off frequency is about 100kHz for several MHz excitation.
