Blog_FurtherEMI

We live in a world today surrounded by electromagnetic fields. Unseen to our eyes, these fields exists everywhere, from every electronic device we use to all the electrical cables around us. These fields could be from the rotating magnetic fields in our every-day motor use, from the radiation inherit in electronic devices, from kitchen items and from the trams & trains that run our world. Not only are these fields spread across different frequency spectrum but also interact with each other in the same frequency spectrums. This interaction of electromagnetic fields can be either through direct cables currents or through radio interference.

But the question is in spite of having innumerable devices, how are these electromagnetic fields existing so seamlessly with each other? Should not they be interfering within each other and wreaking havoc in what seems to be a rather harmonious environment for all devices?

The answer to this is – Electromagnetic Compatibility. All the electronic and electrical devices we use have been subjected to rigorous testing and filtering so that the interference between them can be removed or at best minimised.

In formal education for engineers, the subject of Electromagnetic Compatibility (EMC) is often neglected or ignored in Electrical and Electronics engineering coursework throughout much of the university curriculums. EMC is basically concerned with the generation, transmission, and reception of electromagnetic energy and uses fundamental theorems and equations applied to empirical circuits rather than theoretical ones.

Electromagnetic Compatibility (EMC) of an electronic system can be defined as – “its ability to function compatibly with other electronic and electrical systems in its vicinity, and not produce or be susceptible to interference”. If the electronic equipment achieves this, its is deemed to be ‘electromagnetically compatible’. Further, as per Clayton.R.Paul in his book, ‘Introduction to Electromagnetic Compatibility’, broadly the system is electromagnetically compatible if –

• It does not cause interference with other systems.

• It is not susceptible to emissions from other systems

• It does not cause interference with itself.

Through formal education, electrical & electronic engineers tend to think about circuits in a linear view. Simply put, all the electromagnetic interferences that a cable or a device could be subjected to from its source to its reception are ignored, since lumped parameters modelling makes it simpler to predict system behaviour. However, the theoretical understanding falls short in empirical application of electrical circuits.

In the figure, form the source to the receptor, practically there exists interference from emissions arising from ‘Coupling’ and ‘Radiations’ mechanisms. The coupling emissions are termed as Conducted Emissions while those from radiations are termed as Radiated Emissions. Both these emissions affect the source and the receptor at different frequency spectrum and introduce unwanted currents that affect the system’s overall performance. These unwanted currents tend to mix with the power currents and together the current is deemed to have emissions.

The word ‘emission’ in terms of EMC can be roughly considered analogous to ‘noise’ in the signals. In terms of forming an idea, noise in power signals can be thought of as emissions. However, in terms of forming a concept, the emissions in power signals differ from noise in control signals.

The EMC is based out of the four Maxwell’s equations. But further, it has many terms that might have not been introduced to training Electrical and Electronic Engineers. Some of the basics are -

1. Conducted Emissions - as those conduced from one electric circuit to another using through copper cables.

2. Radiated Emissions – as those conducted from one electric circuit to another using radio interference

3. Conducted Susceptibility – is the ability of a device to be influenced by conducted emissions for an electrically interconnected device in its vicinity.

4. Radiated Susceptibility - is the ability of a device to be influenced by radiated emissions for a radio interconnected device in its vicinity.

The ability of a device to be immune to conducted radiation and emission determines its susceptibility. Hence, devices with lower immunity to emissions are deemed better compatible with other devices in their vicinity.

Given the increasing number of electronic devices in our environments and their interactions within each other and with the electrical grid at large, the subject of EMC will become increasingly important in the coming decades. As of now, there seems to be a lack of understanding amongst engineers about EMC and its basic aspects, and needs to be rectified.

Further on Fundamentals of EMI and Introduction to Theoretical Concepts.