Characteristics of electrostatic discharges (ESD) based on current,optical and magnetic radiation fields

Abstract: In this thesis parameters characterising electrostatic discharges such as the current, the magnetic fieldand the optical radiation are investigated. Optical radiation and magnetic fields generated by ESD aremeasured together with their current signatures in the time domain. Observations show that during theinitial growth, the temporal variation of the optical pulse is similar to that of the current. The peakcurrent is linearly correlated to the peak optical radiation, with a correlation coefficient of about 0.9.The results show that both the optical radiation and the magnetic fields can be used to remote sense thecurrents in electrostatic discharges, which is difficult to measure directly.It is shown that magnetic fields very close to an ESD can be predicted by modelling theradiating discharge current path as a sequence of electric dipoles. Time domain measurements of thecurrent and the magnetic fields generated by human-metal electrostatic discharges produced by an ESDgenerator are used for verification. An ESD current with a peak of 28 A and a risetime of 10 ns cancreate magnetic flux density derivative of about 105 T/s at a distance of 10 mm from the discharge. Current generated by ESD events between metal electrodes and a finitely conducting mediumwere measured simultaneously with their magnetic fields and optical radiation in the time domain.Finitely conducting water was used as the medium. The conductivity of water was changed by addingsalt (NaCl) and an ESD was applied through a point plane electrode configuration with a fixed gapdistance. For a given voltage, the peak current and the peak magnetic field derivative increases withincreasing conductivity. The duration of the ESD current also varies with the conductivity of water. Itincreases with decreasing conductivity initially but reaches a maximum and then starts to decreaseagain. It is shown that an RLC model canpredict the general features of the experimental results. Magnetic fields and optical radiation generated by ESD from metal objects held by peopletogether with their current signatures are also measured in the time domain. The peak measured currentwaveforms are between 25-50 A and the risetime is about 10 ns for a 10 kV discharge, which wassimilar to the current measured from the human body model ESD generator (IEC 801-2). The resultscan be used to estimate the RLC circuit components of the human body model ESD generator.