Measurement of the thermal diffusivity of human epidermis by studying thermal wave propagation.

The thermal diffusivity of dry human epidermis was determined in vitro by studying thermal wave propagation in thin epidermal layers at frequencies between 10 and 200 Hz. Transmission measurements were performed on samples applied to a plane copper support at the underside of which thermal waves were generated by means of a square voltage controlled power transistor. Additionally, measurements were performed on epidermal layers with metal and air backing, in which thermal waves were generated by the absorption of intensity modulated light in a thin, superficially applied graphite layer (short and open circuit measurements). Thermal waves were detected by means of the laser beam deflection technique which allows the contactless measurement of the oscillatory surface temperature of a sample with respect to amplitude and phase. A critical discussion of methods shows that the thermal diffusivity is most reliably determined by transmission experiments. From experimental data obtained by this method a mean value alpha = (2.8 +/- 0.9) x 10(-4) cm2 s-1 was evaluated for the thermal diffusivity of dry epidermis.