EMI shielding is a barrier designed to stop leakage of strong electromagnetic fields that negatively interfere with sensitive signals and devices. They can be installed in most devices to isolate electromagnetic fields. They are also used as enclosures for devices that need protection. Electromagnetic interference is a consistent and growing problem electrical engineers must continually deal with. Ignoring the issue or underestimating it often causes devices and systems to malfunction or break.
All EMI is bad for electronics. Electromagnetic interference corrupts signals from one system to another. Within electronic devices, there are three primary sources responsible for creating EMI. These include:
- Path
- Receiver
- Source
There are also four different types of electromagnetic interference, and each is detrimental. It is crucial to recognize and understand the distinctions between the four.
Radiated EMI occurs in open spaces between the source and the receiver. Sources omit EMI waves that are intentionally or unintentionally transmitted to the circuit. Common conductors (cables, circuit board traces) Functions as the antenna that transmits and receives external EMI.
As its name suggests, conducted EMI occurs in the presence of a conductive path that lies between two circuits (where currents or stray signals travel). Conducted EMI is broken down into standard mode and differential mode. Common mode allows straight currents from two systems to travel in one direction through grounded connections. This grounded connection functions as a common return path. In the differential mode, all unwanted current flows through the two systems opposite the common mode. Just passed leads through the power supply lines, independent from the ground.
Although less common, magnetic EMI is a problem to be mindful of. This type of EMI occurs when signal transfers happen by creating a secondary current through electromagnetic induction. This is only possible when the first conductor changes or oscillates.
Capacitive EMI happens between two conductors that are near each other. The rule of thumb is to be no more than a wavelength apart. The small area between the two conductors engenders parasitic capacitance to store electrical charges and transfer them through charge differentials. Electric fields that conductors emit are chiefly responsible for creating charge differentials.