Sándor Ress

A procedure to correct the error in the structure function based thermal measuring methods

In this paper a methodology is presented to correct the systematic error of structure function based thermal material parameter measuring methods. This error stems from the fact that it is practically impossible to avoid parallel heat-flow paths in case of forced one-dimensional heat conduction. With the presented method we show how to subtract the effect of the parallel heat-flow paths from the measured structure function. With this correction methodology the systematic error of structure function based thermal material parameter measuring methods can be practically eliminated. Application examples demonstrate the accuracy increase obtained with the use of the method.

Chemical images by artificial olfactory epithelia

Abstract Creating olfactory images is an attractive method for selective gas analysis. These images can be considered as response patterns of a sensor matrix. The scanning version of the vibrating capacitor has been used as a simple and accurate tool for measuring the adsorption induced change of the work function at the surface of different gas sensing layers. The work function maps (olfactory images) characterise the gas compositions (H2 in air, alcohol vapour, ammonium, and chloroform) over the receptor area (Pd-Ag-Au-Pt-V-Pt-SnO2 and Pt-Pd-Cu-Fe-Ni-Pt strips at different temperatures). The present paper details this new analytical tool and different olfactory images obtained by the scanning Kelvin method.

Issues of thermal transient testing on photovoltaic modules

The thermal behavior of mass production terrestrial solar modules is a somehow neglected but very important issue of photovoltaics. Despite its significant influence on the power generation, the thermal properties of solar modules are mostly not taken into account in daily applications. In recent literature thermal transient testing was suggested as a possible solution to proper thermal characterization of photovoltaic devices. In this paper we give a short overview on the known issues of the thermal transient testing of photovoltaic devices and address the issue of the variation of the structure function at different heating currents. It is shown that for small current densities the increasing forward driving current (i.e. the heating current) can have a strong influence on the size of the active area that on the other hand determines the volume of the heat path. Due to this an increasing heating current results in the decrease of the Junction to ambient thermal resistance, with the thermal resistance converging to a minimum value at high heating currents. The phenomenon was investigated by Kelvin probe potential mapping, thermal imaging and thermal simulations which uniformly supported our explanation.

Investigation of the thermal behaviour of thin crystalline silicon solar cells

This paper investigates the thermal behaviour of thin crystalline silicon solar cells and determines whether the decrease in cell thickness affects the temperature dependences of the solar cell parameters. For the investigation crystalline solar cells with different photoactive layer thicknesses were processed. Sample cells were formed on n+-substrate wafers with n epitaxial layers where due to the low minority carrier lifetime in the n+-substrate only the epitaxial layer participates effectively in the photocurrent generation. The thin photoactive layers were achieved by the etching of the epitaxial layer. On the samples I-V curves and spectral response functions were measured at different temperatures, and the temperature dependence the solar cell parameters were determined. Most of the parameters showed no differences in their temperature behaviour, but the temperature dependence of the short circuit current and the fill factor differed on all sample cells. From the results it can be concluded, that decreasing the thickness of the solar cells will have practically no effect on the temperature dependence of the performance and the efficiency of crystalline silicon solar cells. However the dependence of in the temperature coefficients for the short circuit currents on the thickness of the photoactive layer could be of interest in sensor applications, e.g. for the thermal compensation of light sensors.

Chemical Images by an Artificial Olfactory Bulb

Creating olfactory images is an attractive method for selective gas analysis. These images can be considered as response patterns of a sensor matrix. The scanning version of the vibrating capacitor have been used as a simple and accurate tool for measuring the adsorption induced change of the work function at the surface of different gas sensing layers. The work function maps (olfactory images) characterise the gas compositions (H2 in air, alcohol vapour) over the receptor area (Pd, Ag, Au, Pt, V, SnO2 strips at different temperatures). In the paper this new analytical tool is discussed in details, and different olfactory images obtained by the scanning Kelvin method are presented.