Ultrasound thermometry for monitoring internal temperature gradient in heated material

An effective ultrasonic method for measuring internal temperature gradient of a heated material is proposed and its practical feasibility is demonstrated through experiments with a steel plate under heating or cooling. The method basically consists of an ultrasonic pulse-echo measurement and an inverse analysis coupled with a one-dimensional finite difference calculation. The advantage of the technique is that no boundary condition at the heating surface of a material is needed. Ultrasonic pulse-echo measurements are performed for the steel plate of 30 mm thickness whose single side is heated by a heater of 200°C and subsequently cooled down by water. The measured transit time of ultrasound across the steel is then used for the inverse analysis to determine temperature gradient in the steel. The variation in the estimated temperature gradient with elapsed time after heating starts is obtained. The temperature gradient and its variation estimated by the ultrasonic method almost agree with those measured using thermocouples installed in the steel. Thus, it is verified that the present method can be a promising means for real-time monitoring of temperature distributions in materials being heated or cooled.