Frequency analysis of transient electromagnetic wave caused by low voltage ESD in spherical electrode

Frequency spectra of transient electromagnetic wave caused by electrostatic discharge in spherical electrode were examined by experimental study. The experimental system consists of a pair of spherical electrodes with different diameters, a 1-18 GHz band width horn antenna and a 20 GHz bandwidth digitizing oscilloscope. Discharge voltage is less than 600 V in this experiment. Frequency spectra and waveforms of received voltages caused by ESDs were measured in order to clarify an EM radiation mechanism. As a result, we found that the waveform duration and first peaks of the EM field radiation can be explained from a dipole antenna structure which makes the spark part of spherical electrodes. Furthermore, as the excitation factors of the EM radiation from electrode elements are mentioned the current path length of the electrodes, and transient speed di/dt of discharge current. In addition, the frequency spectrum distribution of the received voltage was found to be related to the excitation path length determined by the size of the spherical electrode.