You might have noticed billboards and posters advertising EMI shielding facilities at affordable prices. If you are new to the industry, it might confuse you a little, and rightfully so. What is EMI and what does shielding do? Simply put, EMI stands for electromagnetic interference and it refers to the coupling of signals from one system to the other.
There are 3 aspects to creating an EMI- the source, the path, and the receiver. The 2 systems are the source and the receiver. The source is typically the external circuit or a phenomenon that creates a disturbance. It can be naturally occurring, such as lightning, cosmic microwave background, auroras, and solar flares, or artificial, such as cellular networks, power transmission lines, AM/FM radio waves, measurement, and control devices.
The receiver is the sensitive signal or the device in which the output signal is distorted by electromagnetic interference. The path is where the signal coupling occurs, and it can be through any of 4 distinct modes.
The Four Pathways of EMI
These are the four pathways of electromagnetic interference:
Caused by a conductive path present between 2 circuits where stray currents or signals can travel, this can be classified as either common-mode or differential-mode. When in the common-mode, these stray currents from the systems will travel in the same direction via a grounding connection that serves as a common return route. When in the differential-mode, the unwanted current flows across the systems in opposing directions via the power supply lines and are generally independent of the ground.
This propagates through the free space in between the source and the receiver. Here’s what happens- the source emits an electromagnetic wave and it is unintentionally transmitted to a circuit. Cables, circuit boards, and similar conductors serve as antennae that transmit and receive external electromagnetic waves.
This takes place between 2 conductors in a system in very close proximity, generally merely a wavelength apart. The tiny area makes room for a parasitic capacitance where the electric charge is duly stored and then transferred through the charge differentials created by the electric fields that the conductors emit. This parasitic capacitance turns into a pathway for transferring all stray signals.
Almost the same as capacitive coupling that occurs at close distances, signal transfer is done through the creation of a current across a different conductor by means of electromagnetic induction. This can only be possible if the current in the first conductor alters or oscillates.
What is EMI Shielding?
EMI shielding is a technique that involves creating a barrier that averts leakage of strong electromagnetic fields which could otherwise interfere with sensitive signals and devices. They could be installed as an enclosure for a sensitive device or to isolate the electromagnetic field source.
Electromagnetic interference is a problem for most electronics as it decreases the performance of the circuit, sometimes even causing it to fail. Electronics tackle small currents and voltages that an electromagnetic field can disrupt effortlessly. EMI shielding is one efficient way to get EMC barring filtering, grounding, and bonding techniques. It involves forming enclosures with the right materials, form, and structure to alter the pathway of most unwanted electromagnetic waves that come in or go out of any equipment. Here, ferromagnetic or other conductive materials reflect or absorb the electromagnetic wave to alter its path.
One of the most cost-effective modes of EMC compatibility, EMI shielding can bring down the use of intra-equipment devices to tackle unwanted signals, given only experienced EMI shielding professionals take over the project.