PNNL

Abstract

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments (high temperature, pressure, and corrosive environments). PNNL’s state-of-the-art dual channel millimeter-wave passive radiometer with active interferometric capabilities allows for radiometric measurements of sample temperature and emissivity up to at least 1600°C. Interferometric capabilities through the mixed “video” channels at 137 GHz allow simultaneous measurement of additional parameters, e.g., volume expansion/level change and viscosity. These capabilities have been used to demonstrate measurement of melting of simulated lunar regolith. The paper presents the theoretical background and basis for the dual-receiver system, describes the hardware in detail, and demonstrates the data analysis. Observed phenomena include melting and foaming of regolith with oxygen evolution. Post-experiment analysis of emissivity versus temperature allows further extraction from the radiometric data of millimeter wave coupling factors, which provide corroboratory evidence to the interferometric data of the processes observed. These results show the promise of the MMW system for extracting quantitative and qualitative process parameters for industrial processes and access to real-time dynamics of materials behavior in extreme environments.