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Cryogenic calorimeters with superconducting phase transition (SPT) thermometers are extremely sensitive particle detectors. Some characteristics of SPT calorimeters such as linearity and dynamic range often suffer from the superconducting transition shape. The common way to improve the performances is to use the voltage bias to operate the SPT calorimeter in strong electrothermal feedback mode. This method does not allow us to optimize the noise, linearity and dynamic properties simultaneously. We have developed a novel SQUID circuit with thermal feedback which allows to improve the linearity, dynamic range and speed of the SPT calorimeter. Results obtained with a cryogenic calorimeter based on a tungsten thermometer are presented.

The results of an investigation of YBa2Cu3O7-x Josephson contacts applied to practical devices are reported. The ceramics preparation technology, the fabrication method of stable Josephson contacts with low critical currents and experimental methods and techniques are described. An estimate of the limiting energy resolution of the superconducting quantum interferometer, based on described contacts, is given.

A magnetocardiometer based on a single-hole SQUID made from high-Tc YBa2Cu3O7-x ceramic, operating without magnetic shielding is described. It has enabled the authors to measure a magnetocardiogram in real time in a 60 Hz bandwidth. Spectra for the intrinsic noise of the SQUID and the ambient noise of the magnetocardiogram measurement site are given.