Noninvasive, locally resolved temperature monitoring via simultaneous measurement of sound velocity and distance

A locally resolved monitoring of temperature distribution allows to investigate and optimize many industrial processes, like mixing or chemical reactions, as well as medical therapy, like hyperthermia for cancer therapy. In this paper a new measurement technique is applied, which allows to measure sound velocity and distance simultaneously without any reflector at a known position. Instead, the echoes of moving scattering particles are used to determine distance and sound velocity simultaneously. The focal position, depending on sound velocity, can be used as additional information besides the time of flight. Averaging over a sufficient number of echo signal amplitudes, enables to suppose a uniform distribution of scattering particles. Thus. the maximum of average echo amplitude is correlated to the focal position. An annular array, whose elements are driven with calculated time lags, is used to move the focal point along the acoustic axis of the transducer. This allows to measure sound velocity locally resolved and noninvasively. As the sound velocity is well known as a function of temperature [1], a temperature gradient was generated in an experimental set-up with a heat source at the top and a cooling at the bottom. It has been shown that a reconstruction of a minor, approximately linear sound velocity gradient is possible with the measurement technique. The resulting temperature gradient was additionally monitored and confirmed by measurements with a linear array of temperature sensors.