Proceedings of the First European Workshop on Low Temperature Electronics
J. Phys. IV France 04 (1994) C6-255-C6-260
Magnetometers based on (double) relaxation oscillation SQUIDsM.J. van Duuren1, Y.H. Lee2, D. J. Adelerhof1, J. Flokstra1 and H. Rogalla1
1 University of Twente, Dept. of Applied Physics, Low Temperature Group, P.O. Box 217, 7500 AE Enschede, The Netherlands
2 Korea Research Institute of Standards and Science, P.O. Box 3, Taedok Science Town, Taejon 305-606, Republic of Korea
Relaxation Oscillation SQUIDs (ROS) and Double Relaxation Oscillation SQUIDS (DROS) combine the sensitivity of dc-SQUIDS with a large transfer, thus enabling flux locked loop operation with direct voltage readout by a room-temperature dc-amplifier, without flux modulation techniques. We fabricated several ROSs and DROSs with relaxation frequencies from 5 to 180 MHz. The experimental flux-to-frequency curves of the ROSs can well be fitted with theory, and the transfer (up to 170MHz/Φo) is large enough for practical use in a FLL without flux modulation. The experimental flux-to-voltage characteristics of the DROSs show very large transfer values of typically 10 to 30 mV/Φo. A DROS operated in a simple FLL with direct voltage readout showed a white noise level of about 2 µΦo/√Hz. A three channel DROS magnetometer system for biomagnetic measurements is under construction. In the DROSs that are to be used in this system, the signal flux is coupled to the SQUID by a tightly coupled 50-turn input coil.
© EDP Sciences 1994