ESD in electronic equipment: coupling mechanisms and compliance testing

The paper analyses several ways for an electrostatic discharge (ESD) to produce an effect on electronic equipment. In particular, they are classified into direct and indirect coupling mechanisms, also following the standard rules for compliance testing. A direct coupling arises when the discharge occurs on the equipment enclosure or on cables, that penetrating the shield, lead the ESD current on PCB traces and components. On the other hand, a distant ESD produces an indirect coupling by its strong radiated field, which impinges on the equipment. Particularly dangerous are those discharges occurring inside the shielding enclosure: in this case the radiated field directly couples with the internal electronics, and is enhanced by the resonant behaviour of the enclosure itself. Each situation is treated. from a theoretical point of view, adopting the more efficient technique: circuital approach, frequency or time domain numerical methods, and hybrid techniques. All simulations are experimentally confirmed showing a satisfactory agreement.