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.