Thermal Design of High-T Superconductor Radiometers

This paper investigates the feasibility of constructing electrical substitution radiometers operating near liquid-nitrogen temperature using high-temperature (T,) superconductors. Three design examples that utilize micromachining techniques and a YBa 2 CU 3 O 7-δ superconductor meander line are presented and evaluated. The key performance parameters of a radiometer, such as the power noise level, the maximum measurable power, the time constant, and the spatial uniformity, are predicted based on the design geometry and materials properties. A finite element method is employed to calculate the temperature distribution on the receiver. The temperature responsivity is obtained for different heating methods. The spatial nonuniformity and the nonequivalence between radiative heating and electrical heating are determined. A time constant of about I s, a measurable power ranging from 150 nW to 150 μW, and a nonequivalence (between radiative and electrical heating) of 0.36% are predicted for a design that uses a thin silicon substrate sustained by a yttria-stabilized zirconia membrane. A time constant of about 2 s, a measurable power ranging from l.3 μW to 1.3 mW, and a nonequivalence of 0.18% are predicted for a design that uses a 25-μm-thick sapphire plate.