AUTHORS: Anna Stoynova, Borislav Bonev
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ABSTRACT: The aim is to study some factors influence on the contrast decreasing of the ampligram and phasegram obtained after lock-in thermography. It is analysed the effect of delay between excitation source modulated parameter changing and modulated signal. Two software corrections for decreasing the effect of these factors are developed. The offered corrections can be used with different types of excitation sources. In order to evaluate the effect of these corrections, lock-in thermography measurement is performed. Multiple results processing at different correction parameters’ values are studied for PCB samples. The contrast dependence from correction parameters in graphical form is presented. Multiple results processing with random correction parameters values using the both corrections are performed for determination of maximum possible contrast An iterative method with less number of results processing for choosing appropriate values of correction parameters using the both corrections is proposed. The effect of this method is presented and compared in tabular and graphic form. The investigated sample is PCB (evaluation of copper layers’ adhesion on FR-4).
KEYWORDS: lock-in thermography, excitation source, contrast increasing, digital lock-in correlation, Fourier transformation
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