Analysis of the ac SQUID with low inductance and low critical current

The properties of the ac SQUID magnetometer has been analyzed. The results are valid in the low‐inductance low‐critical‐current regime, where the Lri0 producted is belowthe value at which the relation between the enclosed and externally applied magnetic dc flux becomes reentrant. The effects of the screening current circulating in the SQUID ring as well as of the SQUID‐ring time constant, τ‐Lr/R9 are taken into account. Here LR IS THE SQUID‐ring inductance, and R is the shunt resistance in the shunted junction model assumed to describe the weak link. It is shown that for finite values of ωτ, where ω/2π is the pump frequency, the magnetometer response is due to both the flux dependence of the dispersion and f the dissipation in the tank circuit, and that, generally, the two mechanisms contribute simultaneously. Furthermore, for appropriately chosen ac bias conditions theyt may add constriuctively with the result that the optimal response occurs at a definite and finite value of ωτ. If ωτ is increased beyon...