MULTITURN FLUX TRANSFORMERS FOR YBA2CU3O7 RF SQUID MAGNETOMETERS

This work showed experimentally how the planar multiturn input coil of a flux transformer could be integrated with a coplanar resonator whil e still permitting one to couple radio frequency (rf) signals to an rf SQUID. A new layout of a multiturn flux transformer with one pickup l oop and two input coils, one single turn and one multiturn, has been f abricated on 10 x 10 mm(2) LaAlO3 (001) substrates and evaluated. A pl anar double-hole washer SQUID was inductively coupled to the two separ ate input coils via a flip chip configuration. With this layout the be st magnetometer showed magnetic field white noise of 22 fT Hz(-1/2) at 77 K (1.5 x 10(-5) Phi(0) Hz(-1/2)) in a magnetically shielded surrou nding.