Magnetic field sensor based on second harmonic response of polycrystallineYBCO pellets

A novel magnetic sensor, based on the non linear electromagnetic response o f the weak links present in superconducting YBCO polycrystalline bulk is re ported. The second harmonic response in YBCO sit 77 K in the low magnetic h eld region (0 <H-dc <4 G) has been found to be linear and has almost zero h ysterisis. The amplitude of this response is a strong function of the magni tude of the applied ac field and frequency. The noise limited resolution of the sensor was found to be similar to 1.8 x 10(-7) T H-1/2 for H-ac = 7.53 G and f = 15 kHz. The sensitivity of the sensor can be enhanced to similar to 10(-8) T with proper design of the coils, detection electronics and sam ple quality. (C) 1999 Elsevier Science S.A. All rights reserved.