Ultrasonic tomographic imaging of temperature and flow fields in gases using air-coupled capacitance transducers

A pair of air-coupled ultrasonic capacitance transducers with polished meta l backplates have been used to image temperature and Bow fields in gases us ing ultrasonic tomography. Using a filtered back-projection algorithm and a difference technique, cross-sectional images of spatially variant changes in ultrasonic attenuation and slowness caused by the presence of temperatur e and Bow fields were reconstructed. Temperature fields were produced in ai r by a commercial soldering iron, and the subsequent images of slowness var iations used to reconstruct the air temperature at various heights above th e iron. When compared to measurements made with a thermocouple, the tomogra phically reconstructed temperatures were found to be accurate to within 5%. The technique was also able to resolve multiple heat sources within the sc an area. Attenuation and Velocity images were likewise produced for flow fi elds created by an air-jet from a l-mm-diam nozzle, at both 90 and 45 degre es to the scanning plane. The fact that temperature and flow fields can be measured in a gas without the need to insert any measuring devices into the image region is an advantage that may have many useful applications. (C) 1 998 Acoustical Society of America. [S0001-4966(98)00412-3].