Studies and computing techniques in the spectral characterisation of solids

Abstract

A new rapid technique for the measurement of permittivity and dielectric loss has been developed by utilising the concept of Fourier methods of analysis. In the equipment developed an input signal, characterised by having known harmonic components, was fed (in a coaxial system) to a solid sample and the distorted output waveform could either be Fourier analysed by a computer whose output was programmed to give directly the variations of permittivity and dielectric loss with frequency or compared directly with reference waveforms stored in the computer. Trials made with standard materials showed that the results obtained by the Fourier computerised technique were in very good agreement with those obtained by the more conventional methods. The Fourier technique, together with an improved cavity perturbation method at 9.4GHz., has been used to make an extended study of the dielectric properties of reaction bonded silicon nitride (RBSN). Attention was particularly directed to the situation in partially nitrided materials, a region which has not been fully explored in previous studies. The salient feature of the experimental results is the presence of a peak in the variation of permittivity with weight gain. This effect has been discussed in terms of structural and microstructural studies which have shown the presence of impurity phases of iron silicide {FeSi(_2)) and calcium silicide (CaSi(_2)) in addition to the expected silicon and voids. [brace not closed]