Design of thermistor probes for measurement of ultrasound intensity distributions

Thermistors coated with absorbing material provide small omnidirectional probes for measurement of ultrasound intensity distributions. They are simple and inexpensive to construct and can be made with dimensions less than 1 mm. The use of various glues, varnishes and resins for the ultrasound absorbing coating is considered. Heat is generated by shear viscosity in the neighbourhood of the boundary between the thermistor and coating material. The rate of temperature rise over the first one or two hundred milliseconds after the ultrasound is switched on is a reasonably linear function of intensity over the range used in physiotherapy.