Evaluation of thermal diffusivity variations in multi-layered structures
Marcin Hryciuk, Antoni Nowakowski
Department of Medical and Ecological Electronics,
Technical University of Gdansk, Narutowicza 11/12, 80-952 Gdansk, Poland;
Phone: +48 58 3472785, fax +48 58 3471757
E-mail: onufry@biomed.eti.pg.gda.pl, antowak@eti.pg.gda.pl
Keywords: thermal diffusivity, thermal models, skin burns
Non destructive evaluation of objects using thermal excitation has been widely described in
literature but only in relation to a narrow class of simple shape objects under investigation.
Most authors refer only to uniform objects with an inclusion inside or to a layer of unknown
depth covering a homogenous substrate. We are interested in analysing multi-layered
structures. The objective of the research is to determine thermal diffusivity of subsequent
layers of complex biological objects, as the skin with subcutaneous layers.
The reconstruction of internal structure of a tested object should be based on the surface
temperature response measurements using external thermal excitation. The aim of
reconstruction of thermal diffusivity of the skin is the burn diagnostics – evaluation of the
burn degree and it’s depth and extension.
Two methods of excitation of a tested object are analysed:
1. A single step excitation resulting in a change of the object’s surface temperature. The
value of the heat flux necessary to keep the temperature constant is measured. The
temperature change is forced by application of a heater controlled by a dedicated
electronic circuit. The value of heat flux is equal to the ratio of the electrical power
delivered to the heater divided by the heater’s area.
2. Constant heat flux passing through the surface of a tested object. The temperature of the
surface is measured using a thermovision camera and the value of the heat flux is
calculated for the steady state.
Matlab’s functions are used for reconstruction of a tested structure. The non-linear least
square optimisation procedure is applied. The results of the simulation and the effects of the
analysis of data taken from in vivo measurements over skin burns are presented and compared
for verification of the model validity.