Accurate Measurement of Intradecoupling Characteristics for Noise Suppression Sheets on Conducting Plates in Low-Frequency Range

In this article, a test method is proposed for accurately evaluating the intradecoupling characteristics of noise suppression sheets (NSSs) on a conducting plate using two loop probes placed perpendicularly to the NSS on the same side. The effectiveness of the proposed method is discussed in comparison with the standard test method from IEC 62333-2, particularly by examining the underlying mechanisms based on the image method. To establish a test setup for measuring intradecoupling at frequencies below 100 MHz, the effects of various factors including the distance between the two loop probes, the distance from the probes to the NSS, and the size of the NSS were investigated using three-dimensional full-wave numerical simulations and design of experiments. For validation, intradecoupling ratios of commercial NSSs were measured using both the IEC 62333-2 method and the proposed method with two rectangular loop probes. In addition, regression analysis based on the measurement results was used to derive linear equations for predicting the intradecoupling ratio based on the real relative permeability and thickness, within the frequency range where real permeability is constant. The intradecoupling ratios at 1 MHz predicted by these regression equations showed an average deviation of 0.36<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> from the measured values of real NSSs on conducting plates.