With the proliferation of wearable terminals and internet of things (IoT) equipment, electrostatic discharges (ESDs) due to electrification of humans and objects can cause electromagnetic malfunction to these devices, which is called intra-EMC (Electromagnetic Compatibility). This type of the ESD/EMC issues would come from a steep transient electromagnetic near fields generated by spark discharges between micro-gaps. To clarify the underlying mechanism of micro-gap sparks, it is indispensable to quantitatively grasp the spark phenomena of such micro-gap ESDs. For this purpose, different two spark-resistance laws proposed by Toepler and Rompe-Weizel have often been used so far; however, the applicability to micro-gap ESDs is not being fully understood. In this study, a spark current is derived for an electric dipole sparking model in closed forms from the above spark resistance formulae to show the characteristics of spark discharges theoretically. Measurements of spark currents due to the sparks between parallel disk electrodes with a micro-gap are conducted at charge voltages from 300 V to 7000 V in order to verify the validity and applicability of Toepler's and Rompe-Weizel's formulae. As a result, spark constants derived from the measured results can be independent of spark lengths, and agree fairly with those empirically obtained for both the formulae. In comparison with the Toepler's formula, however, the Rompe-Weizel's formula can better explain the charge voltage dependence of spark characteristics such as nominal duration times, peaks and frequency spectra of spark currents.
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