All the Facts and Information You Should Know About RF Shielding Foil and the Shielding Process

The Fi-Foils RF Shield is a multi-layered specialty barrier with security shielding designed to resist electromagnetic (EM) and radio frequency (RF) interference and preserve extremely sensitive data. Designed for SCIF rooms, areas where a TEMPEST enclosure is required, or anywhere frequency blocking is necessary.

RF Shield is made in the United States and features two (2) outside layers of 99 percent pure aluminum foil with an inside layer of Fiberglass reinforcement and Kraft paper. As tested by an approved NSA Approved TEMPEST laboratory, RF Shield decreases sound attenuation and meets or surpasses minimum criteria for shielding efficacy at 378 frequencies. With an average RF Attenuation of 73 dB, RF Shielding foil delivers high-performance frequency shielding.


Shielding is a technique for reducing EMI by preventing noise signals from reaching the receiver from the source. Shields can be placed anywhere in between the source and the receiver. It is a function of the shield materials thickness, conductivity, and continuity in the case of electric fields, where it is most effective.

The shield on a cable’s purpose is to protect the inner conductor(s) from electric fields and so reduce the magnetic field’s size. Remember that when an electric field strikes a conductor, it generates a voltage that appears as noise on the victim circuitry; this is mostly due to high impedance circuits being more susceptible to induced noise.

As a result, decoupling capacitors and more complicated filtering, such as Pi filters, are the only ways to remove the noise. This technique generates a “low pass” filtering effect, allowing data to be transmitted while effectively suppressing higher frequency noise.

When a grounded shield is placed around the conductor, the electric field energy is usually drained away without affecting the conductors reducing or removing the noise.

Principle Mechanism in Shields

There are two principle mechanisms present in all shields, and these are reflection and absorption. Two things happen when an electromagnetic wave moving through space collides with a shield;

Much of the energy is reflected first, and then some of the energy that is not reflected is absorbed by the shield, leaving only the leftover energy on the other side. These two effects of reflection and absorption are independent of one another, but when combined, they constitute the full efficiency of the shield.

A third factor called re-reflection occurs in very thin shields. This re-reflection occurs at the shield boundary on the far side of the shield material.

Shielding Application Facts

The following are some facts about shield application:

  • Shields reduce Differential mode coupling
  • Shields reduce Electric field coupling onto wires
  • Shields Reduce voltage transients
  • Shields Reduce lightning transients
  • Shields, Supply a Faraday-Shield/Cage Return Reference
  • Shields, Control ESD path
  • Shields Enhance Filtering, and Isolation techniques

Impacts of RF Shielding

RF shields weaken interference and protect electronic circuits. RF shields establish enclosures that provide a shield between the emitter and susceptor of interference, thus diminishing the electromagnetic field strength.

RF shielding materials either absorb or reflect EMI radiations, ensuring the device is immune to RFI.

The higher the RF shielding effectiveness of the designed shield, the less of an impact the RFI has on the electronic device or circuit.


Post Author: Randall Callahan