Transformers to readout arrays of microcalorimeters

We investigated the possibility of using transformers to replace SQUIDs for the readout of microcalorimeters. This simple scheme has been used in the past for bolometers, however it was discarded for the use with TES microcalorimeters because of the inadequate performance. Our work shows that, with a few simple changes, the performance of transformers as current transducers, while still not comparable to that of SQUIDs, is sufficient to read out the signal from TES microcalorimeters without any degradation in speed or energy resolution. In contrast to SQUIDs, transformers do not dissipate any power and their working principle makes them natural candidates for frequency multiplexing. Their extension to several channels is therefore straightforward.