Calculated Waveform and Peculiarity of Radiated Electric Field due to Collision ESD between Metallic Spheres with Charging Voltages below 1000 V Using Spark Resistance Law

Collision ESD between charged metallic objects below 1000 V causes electromagnetic interference in electronic equipment and devices. This interference is being observed to intensify at lower charging voltages. The phenomenon was first identified by Masmitsu Honda, but its underlying mechanism remains unclear even today. Originally, the charging voltage and spark length of collision ESD are unknown due to measurement difficulties, making it extremely challenging to establish the relationship between the radiated electric field strength and the spark property in such cases. To clarify the above mentioned electromagnetic phenomenon in collision ESD, in this study, a method of calculating the radiated electric field along with a spark length estimated from the measurement strength of radiated field peak is presented using the spark resistance law developed by Rompe and Weizel. The validity is confirmed by our previous measurement data on radiated electric field due to the collision ESD between charged spherical electrodes with a diameter of 30 mm at charging voltages from 300 to 600 volts, employing an optical field probe with a wideband up to 10 GHz. The estimated spark length is verified by comparing it with the spark lengths based on an empirical Paschen's formula between fixed electrodes and the discharge data from past literature on metal electrodes, revealing the peculiarity effect of the radiated electric field strength caused by “constant breakdown potential gradient” that occurs at charging voltages below 1000 volts.