Ultrasound thermometry is based on the variation of the speed of sound with temperature in medium. The speed of sound is measured using the pulse-transit-time technique. A transducer on one side of the test section is used to generate a pulse, which travels across the test section and is monitored by a receiver on the opposite side at a known separation distance. The time taken for the transit of the pulse is related to the average temperature along the signal path. To visualize the temperature distribution within the test section, the principle of Computer Tomography is applied.
In the case of a gas, a non-uniform temperature field was measured by this method. It was compared with measurement data from a thermocouple array. The thermocouple data. indicated that the temperature of the central part of the heat source was lower than that of the region surrounding it. However, the ultrasound results yielded a uniform temperature for the heat source.