Thermal Modeling of Absolute Cryogenic Radiometers

This work consists of a detailed thermal modeling of two different radiometers operated at cryogenic temperatures. Both employ a temperature sensor and an electrical-substitution technique to determine the absolute radiant power entering the aperture of a receiver. Their sensing elements are different: One is a germanium resistance thermometer, and the other is a superconducting kinetic-inductance thermometer. The finite element method is used to predict the transient and steady-state temperature distribution in the receiver. The nonequivalence between the radiant power and the electrical power due to the temperature gradient in the receiver is shown to be small and is minimzed by placing the thermometer near the thermal impedance