Community Research and Development Information Service - CORDIS

Sensitive bolometric detector

The basic idea for the detector rests on a system of two coupled microwave resonators, one of which acts as a stable reference frequency but the other of which has a strong temperature dependent frequency (in the present prototype this is made of SrTiO3 (STO), which has a very strong temperature dependence of its permittivity. A key property of this resonator is that if the correct mode is chosen the frequency shift of the coupled mode with temperature does not depend on the volume of the temperature dependent resonator, at least to first order.

Thus when energy is absorbed by the STO resonator its temperature changes, resulting in a frequency shift in the coupled resonance. Since extremely small frequency shifts are relatively easily detected this temperature sensor can have nK sensitivity.

It also possesses other potential advantages over other sensors types. It is essentially non-contacting, in that interrogation of the temperature is done by the microwave field itself, no cables are required to contact the sensor. Secondly the sensor is an insulator. Its thermal capacity is due only to phonon contributions and there is no electronic contribution.

At temperatures below 1K the electronic contribution to the specific heat of metals far outweighs the lattice contribution. Thus an insulating sensor of a particular mass can have a much smaller heat capacity than a metal of similar mass at the same temperature so it may have higher resolution than a metallic one or could be operated at a higher temperature with the same resolution.

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