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In this article, we will discuss EMI and EMS. We would like to provide you with basic knowledge of EMI and EMS first by explaining what (electromagnetic) noise is and why noise is the source of many problems.

Noise is a constant annoyance for electronic devices. You need to have a fundamental understanding of noise and take measures to reduce it.

Noise is the result of unintended deformation of electric signals. It's not an overstatement to say that every current-carrying electronic device creates some form of noise. Such noise interferes with electric signals, which can cause equipment to malfunction or fail.

As mentioned above, noise is, in essence, an undesired form of electric signals, being indistinguishable from normal electric signals. So, it is troublesome, giving us a headache in coming up with effective countermeasures.

Roughly speaking, there are two types of noise. One is conductive noise, and the other is radiation noise.

The former is the noise that is transmitted through wires, printed circuits, etc., while the latter is one that propagates through the air.

Fig. 1 Conductive noise and radiation noise

Fig. 1 shows a way in which noise is transmitted in an electric circuit.

As shown in Fig. 1, in addition to noise transmitted in the electric circuit, there is also noise generated by the electric device itself, which exerts a negative effect on other devices in the circuit.

This leads us to a basic anti-noise policy based on two principles: "not being affected by noise" and "do not generate noise."



This is an anti-noise measure in which an electronic circuit is covered with a metal shield to block incoming noise or, even if noise manages to enter the circuit, lead noise to the ground (a route along which electricity returns to the source).

Fig. 2 Shielding



This is an anti-noise measure that eliminates unnecessary noise while letting necessary electric signals pass through. A capacitor or anti-noise filter incorporated in the circuit filters out noise from incoming electric signals.


Thermal conversion

This is an anti-noise measure using a resistor or ferrite, which absorbs noise that has entered the circuit and turns the noise into heat. 

The above-mentioned anti-noise measures are just a few examples of various anti-noise measures we can implement with specific components. 

We have briefly explained the basic idea of noise and anti-noise measures.
Anti-noise measures are an integrated part of your equipment designing. I hope this article will be helpful in your future design work.