Human body impedance modelling for ESD simulations

Motivated by understanding the ESD-induced currents from body-worn, wire and hose connected medical equipment is exposed to, a computer simulation is presented to estimate the impedance of a human body relative to ground. This 3D model is the basis for transient field calculation. A Method of Moments (MoM) frequency domain solution is transformed into time domain via IFFT for further circuit level time domain simulations. The human body is modeled as a homogeneous dielectric with frequency-dependent complex permittivity. Dependence of the impedance on the position of discharge and posture of the human body is investigated. The simulation results are compared with measurements and demonstrate capturing of general tendencies of measured curves.

I. Introduction

Approximate system-level ESD models for predicting discharge current have been created based on measured discharge currents from handheld metal pieces. These models are not based on an electromagnetic analysis of the charge distribution and current flow on the body, but instead relied on intuitive equivalent circuits [1]–[3]. However, at higher frequencies the human body behaves as a distributed system and hence human ESD must be viewed as a traveling wave process [1].