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What is a Faraday cage and how does it work

2022/06/16 > Back

Magician David Blaine promoted his upcoming performance “Electrified” during a press briefing in New York, 2012.

A Faraday cage is a container or shield made of conductive material that blocks electromagnetic radiation around the exterior of the cage, protecting whatever is inside from any static or non-static charge or radiation. Faraday cages sometimes can be called faraday shields, RF (radio frequency) cages, or EMF (electromotive force) cages.

Faraday cage often look distinctly, regardless of their exact appearance, all faraday cages take electrostatic charges, or even certain types of electromagnetic radiation, and distribute them around the exterior of the cage. Faraday cages shield their contents from static electric fields*. As a faraday cage distributes that charge or radiation around the cage's exterior, it cancels out electric charges or radiation within the cage's interior. In short, a faraday cage is a hollow conductor, in which the charge remains on the external surface of the cage.
*An electric field is a force field surrounding a charged particle, such as an electron or proton.

Nowadays, this concept has all sorts of amazing applications:

1. Medical: You'll find faraday cages in the form of MRI (magnetic resonance scanning) rooms. MRI scans rely on powerful magnetic fields to create medically useful scans of the human body.

2. Military: Politicians may opt to discuss sensitive matters only in shielded rooms that can block out eavesdropping technologies. All modern armed forces depend on electronics for communications and weapons systems, but there's a catch --these systems are vulnerable to aggressive EMPs (electromagnetic pulses), which can be a result of a solar storm or even man-made EMP attacks. To safeguard critical systems, militaries sometimes use shielded bunkers and vehicles.

3. Household: Microwave ovens reverse the effect, trapping waves within a cage and quickly cooking your food. Your car is basically a faraday cage as well, it's the cage's effect, not the rubber tires, that protects you in case of a nearby lightning strike.

4. Aviation: It can be an airplane. Imagine flying in an airplane that's suddenly struck by lightning. Because the aluminum hull of the plane creates a faraday cage, the charge from the lightning can pass harmlessly over the surface of the plane without damaging the equipment or people inside.

5. Testing: Anechoic chambers are usually designed by implementing a faraday cage i.e., the entire chamber will be covered by a metallic or highly conductive layer. This prevents external waves from entering the chamber and causing interference.

Many anechoic chambers need to be equipped with single-phase or three-phase power line filters to guarantee the shielding effectiveness of the anechoic chamber.

The EMI filter adopts the π (pi) type filter network structure and security mechanism. On one hand, it guarantees the shielding effectiveness of the anechoic chamber. On the other hand, it effectively reduces the leakage current of the filter and ensures the safety of the filter.

In summary, as a power supply EMI design of high voltage anechoic chamber, the following parameters are mainly considered: Rated voltage, Max. THOU (Total Harmonic Voltage Distortion), Rated current, Maximum current, Leakage current calculated, Voltage drop, Power loss at 100Hz, Insulation withstand voltage. Among them, rated voltage and current, insertion loss are the general indicators of the filter. For testing high-power filters used in anechoic chamber for converter, special consideration should be given to leakage current, insulation withstand voltage, allowable voltage distortion rate and voltage drop.

Power Line EMI Filter for Anechoic Chamber / Shielded Room－ AS8 Series:

• High attenuation (shielding) performance up to 100 dB @ 150KHz～18GHz.
• Single-phase or 3-phase type power line filter.
• The circuit is designed as a multiple circuit with high-quality cores providing inductance.
• Suitable for use under extreme conditions (military applications) or TEMPEST areas.

Data sources: science.howstuffworks.com; researchgate.net; dawn.com