Ultrasonic Thermometry for Recession Measurements in Ablative Materials

Recent developments in ultrasonic instrumentation & sensors, improved signal processing, and high speed data acquisition have rekindled interest in ultrasonic thermometry and made temperature localization feasible and economically attractive to a wider range of applications. Ultrasound-based temperature measurements offer several advantages: they are non-intrusive, have high temporal response, isolate the sensor from explosive or chemically harsh environments and do not adversely influence thermal transport. Ultrasonic thermometry techniques rely on precise measurements of ultrasonic time-of-flight (ToF) which forms the basis for many applications including measurements of flow, heat flux, temperature, ablation and strain. In this report, we characterize the ultrasonic propagation characteristics of several ablative materials. Properties relevant to ultrasonic thermometry include backscattering properties, attenuation coefficient, ultrasonic velocity, and velocity-temperature coefficient. We will present preliminary experiments directed at developing ultrasonic methods for simultaneous temperature and recession measurements on ablators. Various approaches to measuring recession, heat flux, and internal temperature profiles in ablators will be described.