Sequential read-out architecture for multi-channel SQUID systems

We describe a novel multi-channel sequential SQUID read-out technique that requires fewer wires than conventional units and also simplifies the electr onics significantly. We designed and experimentally tested the sequential r ead-out electronics with up to 8 channels using LTS 8 x 8 mm(2) magnetomete rs with better than 3 fT/root Hz field resolution. We have investigated noi se performance, amplitude-frequency characteristics, and cross-talk of the sequential read-out electronics for 2, 4, and 8 channels. We observed field resolution better than 4 fT/root Hz, 6 fT/root Hz, and 9 fT/root Hz for 2- , 4-, and 8-channel versions, respectively, We observed 10 kHz frequency ba ndwidth for the 8-channel version using 200 kHz modulation frequency. Cross -talk better than -90dB was measured for this system. A single-channel simu lation was used to estimate the field resolution for systems with up to 128 channels. We found that the expected field resolution can be better than 1 5 fT/root Hz, 20 fT/root Hz, and 30 fT/root Hz for 32-, 64-, and 128-channe l systems, respectively, with the sequential read-out technique.