RF Interference Shielding: Explained

RF cable with ground surrounding the sensitive signal in the center — An intelligent form of RF interference shielding.

RF interference shielding involves creating a barrier between devices where electromagnetic coupling or radio frequency interference (RFI) may occur. In some cases, this involves constructing a protective enclosure around an electronic product, circuit board or specific component. For PCBs, there are several techniques used by RF engineers to maximize signal integrity and safeguard components from the effects of RF signals.

Types of RF Interference Shielding Components

Why RF Interference Shielding is Important

Without adequate RF shielding, electronic cables for serial and parallel signal transmission can become prone to signal corruption, leading to a degradation of the data transmitted through the device’s circuits. While this might primarily result in signal distortion and user frustration, it underscores the importance of effective shielding. An example of basic RF shielding is seen in the common microwave oven, where the metal interior acts as a Faraday cage.

RF signals pose various security and operational risks beyond just signal distortion. For instance, they can be exploited to gain unauthorized access to radio-frequency identification (RFID) chips found in biometric passports and other devices or disrupt cellular networks that facilitate communication and can adversely affect the functionality of medical equipment, such as MRI machines.

Where Does RFI Come From?

RFI comes from a diverse array of sources, both natural and artificial. Although radio signals were not created by humans, their discovery and subsequent manipulation have led to both human made sources and naturally occurring sources.

Natural RF signals are often generated by atmospheric phenomena such as lightning strikes, snowstorms, and dust storms. Additionally, sources like static electricity, solar flares, and cosmic noise contribute to natural RF emissions.

What Devices Cause RFI?

On the human-made side, unintentional RFI frequently originates from electrical infrastructure and equipment, including power transmission lines, generators, and electric motors. Conversely, intentional RFI, while not always aimed to disrupt maliciously, can be designed to interfere with radar systems and impact aerospace and defense technologies.

In today’s technological landscape, the sheer number of wireless networks and devices have become a significant source of RF interference. The RF spectrum can often become congested, where frequency bands overlap and cause interference. Devices operating on the same 2.4GHz frequency as Wi-Fi, in particular, are known to disrupt network connectivity.

RFI vs EMI Shielding

RFI shielding and electromagnetic interference (EMI) shielding are often used interchangeably. Although both are used to ensure PCB electromagnetic compatibility (EMC), they refer to protection against different frequency ranges. RFI shielding guards devices from frequencies typical of radio transmission–from 20 kHz to approximately 30 MHz, while EMI shielding covers all frequencies; including higher frequencies; such as microwave, used in broader applications.

RFI Shield Materials

Several materials excel in EMI/RFI shielding, with copper leading due to its high effectiveness, followed by bronze, aluminum, gold, and brass. The choice depends on the electronics and frequencies involved. The success of these materials in blocking interference is influenced by their thickness and application method.

Controlling EMI and EMC is essential for RF PCB design and critical for satisfying MIPI, HDMI and other data communication compliance standards. Understanding RF design principles is a prerequisite to devising an effective strategy to mitigate RFI. Incorporating these principles, along with employing the best RF simulation software is the solution for ensuring your board functions and performs to maximize signal integrity.