EMI and ESD Relationship

At the time of an ESD discharge occurring, which may take a very short time perhaps in the order of a dozen ns, there is a release of energy very similar to that produced when lightning occurs. This energy release is accompanied by heat and also electromagnetic radiation which has been found to be somewhere in the frequency range of a few MHz to a couple of GHz. Some complex equipment is susceptible to this radiation release which is in fact a variety of Electro Magnetic Interference (EMI). Also most electrical cabling around the place will operate like receiver antennas so shielding is most important. The ESD discharge could be said is in fact a micro lightning.

The latter property of an ESD discharge of producing EMI is in practice harnessed into one of the principles used to detect, count and measure ESD events on a particular location, a major advantage of using this principle is that is non intrusive. As a very rudimentary EMI detector we can use a transistor radio that need to be placed near the ESD suspect point, proceed to tune it in the AM band just off a station where a hissing background noise can be heard, when an ESD event occurs a popping noise should be heard. Of course more complex arrangements can be organised to measure ESD events, for example, by using a digital CRO with a memory storage feature or some other GHz wideband instrument. There are a few types of commercial handheld devices out there that use directional antennas as to pin-point the location of the event they also have speakers so the events can be heard.

Newer electronics PCB design techniques allow for more than two layer PCBs so there is opportunity for inserting EMI susceptibility loops and inhibiting layers in between, for example a couple of copper layers, one being ground the other providing the power perhaps would greatly reduce EMI interference to the more sensitive PCB components. Of course there are many techniques out there available to handle this. Another latent problem is the induction of voltages on earth loops, if they are not well designed.

Mobile phones are also badly affected on their audio quality by the EMI/ESD events. Their design includes a variety of ESD supressors and also EMI filters