Micromachined hot-wire thermal conductivity probe for biomedical applications

A micro thin-film thermal conductivity probe is developed to measure thermal conductivity of biological tissues based on the principle of traditional hot-wire method. The design of this new micro probe consists of a resistive line heating element on a substrate and a RTD based temperature sensor. The transient time response of the heating element depends on the thermal conductivity of the surrounding medium and the substrate. A theoretical analysis of the transient conduction for this configuration where the heater source is sandwiched between two materials (the substrate and the surrounding medium) shows that the composite thermal conductivity calculated from the temperature versus time response is simply the average of the thermal conductivity of the two materials. The experiments conducted to measure thermal conductivity of Crisco and agar gel show a good match with the theoretical and numerical analyses. The technique demonstrates the potential of the microprobe for in vivo measurements of thermal conductivity of biological tissues.