Shielding from electric/magnetic field using a metal box

Click For Summary

Discussion Overview

The discussion revolves around the effectiveness of using metal boxes or spheres, specifically Faraday cages, for shielding against electric and magnetic fields. Participants explore the concepts of electromagnetic shielding, attenuation, and the limitations of different shielding methods, including anechoic chambers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that a Faraday cage can shield electric fields and electromagnetic (EM) fields, but it cannot completely block them.
  • Others clarify that while a Faraday cage provides significant attenuation, it is not equivalent to complete shielding, which is only achievable with an anechoic chamber.
  • A participant notes that an anechoic chamber absorbs radiation to prevent reflections, distinguishing it from a Faraday cage, which prevents external EM radiation from entering.
  • There is a discussion about the limitations of Faraday cages in protecting against low-frequency magnetic fields, indicating that they may not be effective against inductive pick-up.
  • One participant suggests that superconductive cages could provide ideal shielding, while another counters that the shielding efficiency of superconductors varies with frequency, and mu-metal may perform better at high frequencies.
  • It is mentioned that effective shielding across all frequencies may require a combination of different materials, including mu-metal, superconductors, and regular conductors.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of Faraday cages and anechoic chambers, with no consensus reached on the completeness of shielding provided by these methods. The discussion remains unresolved regarding the best materials and methods for effective electromagnetic shielding.

Contextual Notes

Participants highlight the frequency dependence of shielding materials and the need for a combination of materials to achieve effective shielding across a range of frequencies. There is also mention of advancements in active RF cancellation technology.

manivas
Messages
7
Reaction score
0
Can electric fields can be completely shielded using a metal box or metal sphere,
please clarify the concept.
 
Physics news on Phys.org
Yes. The name of the concept is Faraday cage.
 
A faraday cage can give huge attenuation but it can't completely block an EM field it is by definition a shield effect.

The only way to completely block a signal is a anechoic chamber (http://en.wikipedia.org/wiki/Anechoic_chamber)

Look in the RF section.
 
Uglybb said:
The only way to completely block a signal is a anechoic chamber

The walls of an anechoic chamber absorb any radiation produced inside the chamber, so that measurements are not confused by reflections (echoes) from the walls

A Faraday cage stops radiation EM produced outside from getting inside.

These are two different issues. An anechoic chamber for EM radiation would normally be built inside a Faraday cage, as the Wiki link said.
 
manivas said:
Can electric fields can be completely shielded using a metal box or metal sphere,
please clarify the concept.

Yes, a Faraday cage will shield electric fields and EM fields. However, it won't protect you from inductive pick-up, i.e. it won't help against low-frequency magnetic fields (from say the mains).
 
Correct f95 and the better the conductivity the better the faraday cage. I guess a superconductive cage would give ideal shielding.

Most if not all RF anechoic chambers these days are for EMC testing and they are active suppression the same as noise cancellation headphones. If a signal is detected in the setup phase in the area of interest it will be actively canceled whether it is from inside or outside the wiki link is WAY WAY out of date. The cancellation will be to the sensitivity required for the compliance test.

I should say active RF cancelation has got so cheap and integrated that mobile phones are even carrying them on the antena to improve reception (http://www.intersil.com/signalintegrity/NoiseCancellingICs.asp)
 
Last edited:
Uglybb said:
I guess a superconductive cage would give ideal shielding.

Unfortunately not, the shielding efficiency of superconductors is frequency dependent. It gets worse as the frequency increases and mu-metal shields are actually better for screening magnetic fields at high frequencies.
Hence, the only way to make a shield that works well at all frequencies is to combine different types of materials (mu-metal, superconductors and good normal conductors).
 

Similar threads

Undergrad Shielding behavior of a steel cuboid in a DC magnetic field
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Building a Faraday cage with a conductive cloth and magnets
  • · Replies 10 ·
Replies
10
Views
2K
High School Curious about the uniform electric field between metal plates
  • · Replies 8 ·
Replies
8
Views
2K
High School What magnetic fields can this hollow rod shield?
  • · Replies 13 ·
Replies
13
Views
2K
High School Why does a magnet attract metal objects?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad What Materials Can Shield Electronics from a 3-Tesla MRI Magnetic Field?
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad Questions related to magnetic shielding separating two like poles
  • · Replies 6 ·
Replies
6
Views
1K
High School Can I use this method to charge a metal sphere?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Electric Field Shielding by Conducting Sheets
  • · Replies 3 ·
Replies
3
Views
2K
High School Electric Fields inside Conductors & Gauss' Law
  • · Replies 7 ·
Replies
7
Views
1K