Volume 80, Issue 3, March 2009
Index of content:
- THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL AND PHOTOACOUSTIC
80(2009); http://dx.doi.org/10.1063/1.3097183View Description Hide Description
We present a contribution to a new mode of scanning thermal microscopy (SThM) based on the use of thermoelectric junction operating in ac active mode. This is the first alternative to operating mode of a resistive SThM probe for measuring thermophysical parameters of materials at micro- and nanoscale. Whereas a current at frequency generates by Joule effect a thermal oscillation along the wires, the junction thermoelectric voltage can be measured by means of a differential bridge scheme associated to a lock-in amplifier. A thermal model is presented that confirms measurements performed in different situations with different wire probes. Values of thermal contact conductance of different materials have been extracted and a comparison has been performed between this technique and the resistive mode.
Thermal-wave radar: A novel subsurface imaging modality with extended depth-resolution dynamic range80(2009); http://dx.doi.org/10.1063/1.3095560View Description Hide Description
Combining the ideas behind linear frequency modulated continuous waveradars and frequency domain photothermal radiometry (PTR), a novel PTR method is introduced. Analytical solutions to the heat diffusion problem for both opaque and transparent solids are provided. Simulations and experimental results suggest a significant improvement in the dynamic range when using the thermal-wave radar (TWR) instead of conventional PTR. A practical TWR image resolution augmentation method is proposed.
80(2009); http://dx.doi.org/10.1063/1.3103570View Description Hide Description
We present a theoreticalmodel for evaluating solid bilayered spherical samples (surfaces) that are heated by a frequency modulated light beam generating thermal waves. The Green’s function method is used as it provides a way of evaluating thermal-wave fields of bilayered spherical structures with arbitrary intensity distributions of incident laser beams. The specific thermal-wave Green’s function corresponding to the composite structure has been derived. The characteristics of the thermal-wave field with respect to the thermal diffusivity of the material, the diameter of the sample, the size of the incident beam, and the polar angle at which the thermal-wave field is measured on the surface are presented. Experimental results obtained with laser infrared photothermal radiometry are fitted to the theory and the thermal diffusivities of steel spheres are deduced.
Calibration of the thermoelastic constants for quantitative thermoelastic stress analysis on composites80(2009); http://dx.doi.org/10.1063/1.3090885View Description Hide Description
The application of thermoelastic stress analysis in composite materials is particularly complicated because of the anisotropy of the material, that determines the thermoelastic constant to be dependent on the direction of the fibers. A further difficulty depends on the constructive stratification of the material, whose mechanical properties vary with the depth from the surface and this causes thermoelastic constants to be dependent on the frequency of the load applied. By using an analytical two layer model, it has been possible to interpret experimental data, thus proposing an explanation of the dependence on the frequency of the measured thermoelastic constants. This has shown that the practical use of the thermoelastic effect for quantitative stress analysis on composites needs constants calibrated at the correct frequency, also considering the thin layer of superficial resin present in every composite material.