Electromagnetic Interference and Compatibility

Bill Davis
AEI Cables Ltd

What is EMI ?

EMI is a type of environmental pollution but unlike the pollution that most of us understand involving water, air, noise, and other contaminants, EMI cannot be directly detected by sight, taste, smell, or touch yet it is pollution just the same. More appropriately it is radio frequency "spectrum pollution". We have all experienced some form of spectrum pollution. The radiated electrical noise from electric razors and from automobile ignition systems creates interference on our televisions
and radios. In these circumstances it is no more than a nuisance but there can be more serious side effects to EMI in certain circumstances. Consider the person with a heart pace maker. If in an environment where RF emitting sources are not properly shielded the effects could be disastrous.

In fact, EMI can be far more damaging and can affect more than just a single individual. It can negatively impact whole societies. Aircraft navigation systems, railway signalling systems, communications systems, computer networks, medical monitoring systems, fire detection systems, traffic control systems, are only a few of the critical systems that can be adversely
affected by spectrum pollution. If EMI were left unchecked our lives would be seriously disrupted and the economic consequences would be enormous. EMI is not just the domain of equipment and device manufacturers. Even the best designed device will fail to satisfy EMC (Electromagnetic Compatibility) compliance if the installation itself is not compliant. To understand the significance of this it's important to recognise the contributing elements to EMI in any installation.

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