Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Optimum signal-to-noise ratios and voltmeter source resistances at input frequencies are obtained by using a planar series-parallel transformer to couple pick-up loop inductance and that of the input coil to a superconducting quantum interference device (SQUID). In DC SQUID magnetometers, the most favorable signal-to-noise ratio is obtained when pick-up coil inductance equals the SQUID input coil inductance. In DC SQUID voltmeters, the preferred source resistance is proportional to the product of the signal frequency and the input coil inductance. These relationships can be obtained by planar transformer in the figure, where the primary winding includes a plurality of smaller windings LP1-LP4 in series to increase inductance and is coupled to the pick-up coil L .