Techinfo
Technical Information
EMC Solutions (Noise suppression)
What is EMC ?
Electromagnetic Compatibility
The concept of EMC (electromagnetic compatibility) is the basis for noise suppression.
For this reason, noise suppression and EMC suppression are often used interchangeably.
How does EMC relate to you?
In our everyday life, there are countless electrical and electronic devices.
They are indispensable to operate household appliances, infrastructure of factory production lines, medical equipment, communication equipment, as well as railways, airplanes, and automobiles.
However, these devices may malfunction or break down due to EMC noise.
There is the potential to cause a serious injury or endanger human life.
Therefore, noise suppression is required for electrical and electronic devices to work properly.
How to Suppress Electromagnetic Noise
EMC (Electromagnetic Compatibility) is to maintain an environment where electrical and electronic devices are resistant to noise.
Both EMI and EMS countermeasures are implemented to ensure a device's stable performance.
There are two approaches to noise suppression.
*EMI (Electromagnetic Interference) suppression is to prevent noise from being emitted from devices.
*EMS (Electromagnetic Susceptibility) or immunity design is to enhance the resilience of devices from external interference.
Grounding
The ground in an electronic circuit functions as the reference point of the operating voltage and serves as the return path of the current. Poorly designed ground planes can destabilize the reference voltage, resulting in unwanted radiations, device malfunctions due to external noise, and electrostatic discharge.
A ground plane is ideally wide and short to keep the reference voltage stable.
This can be seen in cases where multilayered printed circuit boards (PCBs) with ground planes are used along with a metal frame/chassis.
The next important point is how to connect the grounds.
To ensure the proper return path of the current, it is necessary to make the connection wide and short.
Connecting the ground of an electronic circuit to a metal frame is called a frame ground (FG).
Frame grounds are often used for noise suppression.
FG effectiveness is determined by the width, shortness, and multiple FG of the connections.
Filtering
Filtering is the process of sorting signals based on their characteristics.
A high-pass filter allows signals higher than a certain frequency to pass through, while a bandpass filter allows signals only in a specific frequency band to pass through.
Filtering is not just performed based on the frequency of the electrical signal.
Filtering that makes use of differences in transmission modes is an essential technology for noise suppression.
The purpose of filtering is to separate signals from the noise.
Harmonic noise in the clock of a digital circuit and switching noise generated in control circuits propagate and radiate through circuits and/or cables in common mode.
By contrast, signals that should be transmitted are passed between devices in differential mode.
Ferrite cores and common mode choke coils separate signals from noise by blocking signals in common mode and allowing only differential mode signals to pass.
Shielding
Electromagnetic noise is classified into two categories: radiated emissions that travel through space and conducted emissions that travel through cables and sheet metals. Shielding is a strong suppression technique that is effective for radiated emissions.
Shielding refers to covering a noisy part of a circuit or an entire device with a metal shield.
This allows radiated emissions to be confined within a space and in turn suppresses radiation to the outside.
In addition, metal shields can prevent external noise from entering and causing malfunctions in electronic circuits.
Shielding effectively controls noise for both emission and immunity, but it’s important to prevent electromagnetic waves from leaking or passing through.
It is necessary to ensure electrical continuity at the joints of metal housings, apertures, ventilation holes, and connections between cable shields and metal enclosures.
To control EMC noise, solution materials such as conductive FoF gaskets, shielding tapes, wire mesh (wire netting), conductive cable shields, and electrically conductive clamps are highly recommended.