Low-noise magnetometers with asymmetric superconducting quantum interference devices

Fully integrated low-critical-temperature magnetometers based on asymmetric superconducting quantum interference devices have been designed, fabricate d, and characterized. The large value of the flux to voltage transfer coeff icient, typical of such configurations, allow a direct coupling to an exter nal preamplifier without the need of an impedance matching flux transformer or additional positive feedback circuitry. This simplifies the read-out el ectronics, as required in multichannel systems for low-noise measurements. The values of the magnetic flux noise and field sensitivity, obtained so fa r, are 3-5 mu Phi (0)/Hz(1/2) and 6-7 fT/Hz(1/2), respectively. These resul ts are already suitable for biomagnetic applications and can be further imp roved by properly optimizing the device parameters. (C) 2001 American Insti tute of Physics.