Thermal conductivity vs depth profiling using the hot disk technique-Analysis of anisotropic, inhomogeneous structures.

A recently developed method for analyzing the thermal conductivity vs depth variation near a sample surface has been extended to include inhomogeneous samples with anisotropy. If not considered, the anisotropy ratio in the sample structure can distort the depth-position data of the original test method. The anisotropy ratio is introduced in the original computational scheme in order to improve the depth-position estimations for inhomogeneous structures with anisotropy. The proposed approach has been tested in experiments and shown to improve depth position mapping.

Thermal conductivity versus depth profiling of inhomogeneous materials using the hot disc technique.

Transient measurements of thermal conductivity are performed with hot disc sensors on samples having a thermal conductivity variation adjacent to the sample surface. A modified computational approach is introduced, which provides a method of connecting the time-variable to a corresponding depth-position. This allows highly approximate-yet reproducible-estimations of the thermal conductivity vs. depth. Tests are made on samples incorporating different degrees of sharp structural defects at a certain depth position inside a sample. The proposed methodology opens up new possibilities to perform non-destructive testing; for instance, verifying thermal conductivity homogeneity in a sample, or estimating the thickness of a deviating zone near the sample surface (such as a skin tumor), or testing for presence of other defects.

Pulse transient hot strip technique adapted for slab sample geometry to study anisotropic thermal transport properties of µm-thin crystalline films.

A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample geometry has been developed for studying thermal conductivity and thermal diffusivity of anisotropic thin film materials (<50 µm) with thermal conductivity in the 0.01-100 W/mK range, deposited on thin substrates (i.e., wafers). Strength of this technique is that it provides a well-controlled thermal probing depth, making it possible to probe a predetermined depth of the sample layer and thereby avoiding the influence from material(s) deeper down in the sample. To verify the technique a series of measurements were conducted on a y-cut single crystal quartz wafer. A Hot Strip sensor (32-µm wide, 3.2-mm long) was deposited along two orthogonal crystallographic (x- and z-) directions and two independent pulse transients were recorded. Thereafter, the data was fitted to our theoretical model, and the anisotropic thermal transport properties were determined. Using a thermal probing depth of only 30 µm, we obtained a thermal conductivity along the perpendicular (parallel) direction to the z-, i.e., optic axis of 6.48 (11.4) W/mK, and a thermal diffusivity of 3.62 (6.52) mm(2)/s. This yields a volumetric specific heat of 1.79 MJ/mK. These values agree well with tabulated data on bulk crystalline quartz supporting the accuracy of the technique, and the obtained standard deviation of less than 2.7% demonstrates the precision of this new measurement technique.

Analytical calculation of the skin temperature distribution due to subcutaneous heat production in a spherical heat source.

An analytical solution of the thermal conductivity equation describing the surface temperature distribution over a buried heat source is given in tabular form. The solution is applicable to experimental models for studies of the surface temperature over an implanted artificial heat source. The results can also be used for the analysis of the skin temperature over biological heat sources such as breat tumours.

Refractive Index Measurements in Fused NaNO(3) and KNO(3) by a Modified Thermooptic Technique.

A thermooptic technique for studying the temperature dependence of refractive index of liquids at room temperature has been modified and applied to the study of molten NaNO(3) and KNO(3) within a temperature range of some 80 K above the melting point for five different wavelengths within the visible spectral range. The experiments show a temperature dependence of the polarizability for the two salts as calculated from the Lorentz-Lorenz formula, which cannot be explained by experimental inaccuracy.