Inverse fourier transform technique of measuring averaged absorption cross section in the reverberation chamber and Monte Carlo study of its uncertainty

Abstract

The averaged absorption cross section (ACS) of a lossy object characterises its ability to capture power from diffused electromagnetic waves. The averaged ACS is very important in many EMC research areas such as indoor wireless channel modelling and human safety exposure study. The measurement of averaged ACS in a reverberation chamber can be achieved by measuring the rate of power loss in the time domain, however this technique requires dense frequency sampling for taking the inverse Fourier transform, which is very time consuming. A new scenario which accelerates the measurement speed is presented in this paper. It combines the technique of non-linear curve fitting to the power delay profile, segmented frequency sweeping and continuous mode stirring. The scenario was validated by measuring the averaged ACS of a hollow plastic sphere filled with deionized water in an EMC reverberation chamber. Measurement results showed a good accordance with the simulations and the measurement uncertainty was studied numerically with the Monte Carlo method.

Effect of power state on absorption cross section of personal computer components: Applications to enclosure shielding

“…A measurement uncertainty of 20% was considered too high to allow small changes to ACS to be observed. Therefore, we also measured the ACS of the computer by using the time domain method, presented in the paper of Zhang et el [12], which allows significantly lower measurement uncertainty. The average ACS is determined from the average chamber time constants:…”

“…The chamber time constant is obtained by applying the non-linear curve fitting technique described in [13] to the average power delay profile (PDP) of the input energy at each frequency of interest. The PDP is given by: In [12], Zhang et al described how to estimate the measurement uncertainty. By using the Monte Carlo method, the uncertainty of the measured ACS is calculated to be approximately 1%.…”

Efficient Determination of Reverberation Chamber Time Constant

“…This problem can be demonstrated by transforming the PDP model into a logarithmic scale and then calculating its derivative. The PDP with a noise floor can be modelled by [13]:…”

“…where V s is the received signal voltage; N 1 (t) is a standard complex Gaussian random process with zero mean and variance of one. Equation (13) corresponds with Hill's idea that the transient behavior of an RC can be described by an exponential function [1]:…”

On the Estimated Measurement Uncertainty of the Insertion Loss in a Reverberation Chamber Including Frequency Stirring

“…In this paper, we consider the hybrid stirring as realized by a combination of frequency stirring (FS) and mechanical stirring (MS) [2]- [3]. The FS measurements also allow us to represent the measured quantity in time domain [8]- [10]. The MU of the insertion loss (IL) in an RC with hybrid MS and FS was addressed in [11], where a model was developed and achieved under conditions of well-stirred fields.…”