Experimental study of the thermal probing depth of a skin calorimeter

Abstract

In this work we perform an experimental study of the thermal probing depth of a skin calorimeter developed to measure in vivo the heat capacity and the thermal resistance of a 4 cm2 skin region. To determine these properties, a small thermal excitation is applied to the skin and then, the static and dynamic response of the calorimetric signal is studied. This excitation consists of a periodic change of the calorimeter thermostat temperature while the device is applied on the skin. We have found that the thermal penetration depth depends mainly on the period of this periodic thermal excitation. This time dependence is exponential for non-semi-infinite domains. Using a time–variant model, we performed measurements on the dorsal and volar areas of the left wrist of a healthy 64-year-old male subject. For a 4 cm2 region of skin, the results show that the heat capacity in both zones are of the same order of magnitude. Its initial value is 4 J/K and increases exponentially up to 7 J/K with a time constant of 6.5 min. Thermal resistance also increases exponentially with time: from 27 to 36 K/W for the volar zone, and from 32 to 45 K/W for the dorsal zone.