Erratic nature of product ESD immunity testing investigated using a dual TEM cell

Product ESD immunity testing to meet European EMC Directive is straight forward but sometimes the outcomes can be quite surprising; for example, indirect discharge can be more potent than direct discharge and contrary to preferred method air discharge causes failure whereas contact discharge passes. One of the key factors responsible for the surprises is the lack of information on the frequency contents associated with those ESD events. In this paper those ESD phenomena are investigated using a dual TEM cell (P.F. Wilson and M.T. Ma, 1985) connected to a spectrum analyzer simulating product under test; the spectrum plots collected from the different ESD test modes are then examined to gain insights into those anomalies. Some examples are given to demonstrate correlation between the spectrum plots and the surprises encountered during actual product testing