Induction magnetometer using a high-T_c superconductor coil

摘要

An induction magnetometer consisting of a search coil and an inverting operational amplifier is simple in structure and in signal transferring mechanism from the magnetic field input to the voltage output. Because this magnetometer is based on Faraday's law of induction, it has a lower cutoff frequency r/ (2πL), where r is the resistance of the coil and L is its inductance. An attempt has been made to lower the cutoff frequency of the induction magnetometer by using a high-T_c superconductor coil. With a pancake coil (inner diameter ≈ 18 cm and outer diameter ≈ 23 cm, 92 turns, 3.23 mH) made of a Bismuth strontium calcium copper oxide (BSCCO) superconductor tape of 5 mm in width and 0.23 mm in thickness, the cutoff frequency achieved was 1.7 Hz which is much lower than that obtained with a bulky copper search coil which is typically in the range of 10-20 Hz. In the experiment, an inverting amplifier was made with a complementary metal-oxide semiconductor operational amplifier and was immersed in liquid nitrogen together with a BSCCO high-T_c superconducting coil. Discussion is made on the resolution of the induction magnetometer using a high-T_c superconductor search coil.