Talk:Faraday cage

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Are electromagnetic waves (aka light) blocked by a Faraday cage?

Are electromagnetic waves blocked by a Faraday cage? Electromagnetic waves like the ones used by cell phones and microwave ovens are essentially light in different frequencies. They are different from a electric field. Would loss of reception of cell phone in elevator and microwave oven be right examples of a Faraday cage?

Yes, and no. The difference between light and say cell phone microwaves, as you pointed out, is in the frequencies. Now, the wavelength and frequency have a relationship (in electromagnetic waves), which can be stated as, "wavelength multiplied by frequency is equal to the speed of light" (you can rearrange this equation to solve for wavelength or frequency). Ok so getting to the point: the holes in the faraday cage are too small for the wavelengths to pass through. So, being that light has much, much smaller wavelengths than say microwaves or radio waves or whatever else might be used for communication, it passes through the faraday cage easily. In conclusion most forms of electromagnetic waves are blocked by faraday cages, and I would even venture to say that 'all' traditional forms of communication using electromagnetic waves are blocked by a faraday cage (now as a small point there have been attempts to make a communication device which utilizes lasers to pass the information on, and these would not be blocked by a faraday cage, but these devices are usually considered impractical because it is necessary for there to be a line of sight for the device to work). Hope this answers your question. Mjs072 (talk) 02:23, 3 April 2008 (UTC)

There's a paragraph in the "Examples" section that is really bothering me and it's related to the RF vs Light discussion. To whit:

A shopping bag lined with aluminum foil acts as a Faraday cage. It is often used by shoplifters to steal RFID tagged items.[citation needed] In this case, the use of the bags as a Faraday cage is intentional, though paper bags lined with foil are made also for the purposes of blocking light and moisture. (Light blocking by metal foil is actually related to the Faraday shielding effect—it arises from the fact that electrical fields cannot pass through good conductors, because the electrical field across an ideal conductor is always zero, due to its conductivity. Light is electromagnetic radiation just like radio waves, infrared, low-frequency electromagnetic pulses, etc.

What bothers me here is that it implies that anything that blocks light does so because it's a good conductor. Something that is patently false. The initial example of using a foil lined bag to block RFID tags may well be valid, but relating the light blocking properties of a foil bag used for consumer products to this effect is really a stretch.

Is there any objection to removing that example? Bagheera (talk) 19:55, 23 July 2009 (UTC)

I would object to removing the whole thing. I agree that a correction is needed, but as you say, the initial example is valid; remove only the offending digression. 67.162.34.172 (talk) 16:26, 4 November 2009 (UTC)

Is a magnetic field blocked by a Faraday cage?

For instance, will a magnetic compass in a Faraday cage still point toward magetic north? Suggest such knowledge be added to the main page. Andrew8

No. Magnetic field is not blocked by a Faraday cage. I discovered this the hard way as a student when someone re-located a CRT computer monitor in an adjacent lab. So their computer monitor was 2-3 feet away from the experiment area, but on the opposite side of a wall -- took forever to figure out where the interference was coming from....

—The preceding unsigned comment was added by 203.38.122.195 (talk) 01:34, 12 March 2007 (UTC).

Faraday cage is not effective for static and low frequency magnetic field. —Preceding unsigned comment added by Fsyap73 (talk • contribs) 09:03, 17 July 2009 (UTC)

Faraday cage = a metal enclosure?

Is it just me or is this Faraday cage just a metal enclosure? I suggest someone add to the article that a Faraday cage is actually just a metal enclosure. There seems to be an epidemic in science of easily-reducible-to-a-generalized-name concepts still being called by their original discovers or inventors' last names even one hundred years after they discovered or invented it. I think 30 years of calling a new discovery by the last name of its discoverer is appropriate but not one hundred years plus. Foober 22:18, 18 February 2007 (UTC)

It's more than just a metal enclosure. It depends upon the frequencies that you are considering - for example bridges are Faraday cages at radio frequencies but certainly not at optical frequencies.Flying fish 02:26, 6 March 2007 (UTC)

No, it need not be metal. Conducting non-metalic material can also create a Faraday cage. Andrew8 —The preceding unsigned comment was added by 203.38.122.195 (talk) 01:32, 12 March 2007 (UTC).

This is an excellent observation, it made me wonder what types of conductors are non-metallic (graphite, some salts and all plasmas), but i think people often forget they exist (like i did). Although, I have yet to see one made of a non-metal, I suggest that the article should emphasize this, avoiding the use of the word metal unless it is specifing the nature of the conductor as so: ...conducting material (metal or non metal). Chibby0ne (talk) 11:44, 2 July 2010 (UTC)

As others have indicated, it doesn't have to be metal, but it does in some sense need to be an enclosure. The idea of the Faraday cage is more about the shielding effect or restriction of charge to the surface of a conductor. The cage is just the practical realization of the surface of such a conductor. 70.247.169.197 (talk) 03:23, 1 August 2010 (UTC)

Old relocated conversations

The last part of this article is written in German!

The bit about holes is inaccurate: EM radiation with a wavelength comparable or smaller to the size of the hole gets through easily. That's why the mesh in microwave oven windows has to be so fine. The Anome

I think 'hole' refers to the inside, not to a hole in the mantle. Patrick 14:03 Nov 25, 2002 (UTC)

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This whole article has a "subtly wrong" feel to it: it conflates several things as if they are one, such as:

• ground plane
• Faraday cage principle (exclusion of electric field)
• preferential / sacrificial conductor
• skin effect
• RF shielding

Can people with a physics / EE background please take a look at the article and try to sort this out?

The article refers to a Faraday cage and a Faraday shield as one and the same. I believe when experimenting with capacitors, Faraday discovered that a simple grounded plate could be used to shield electric fields and those are known as Faraday shields. I believe that the cage is a hybrid he discovered later and that is known as the Faraday cage.

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Perhaps we need to break this article into several sections:

• Idealised Faraday cage
• Mathematics of the Faraday cage
• Faraday cage in practice
• --> article on Electrostatic shielding and earthing
• --> article on RF shielding and earthing

Starting to rework: but it's still wrong... hmmm... The Anome

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"Since like electrical charges repel each other, they accumulate where they can be furthest apart, on the outside layer of the Faraday cage." ... This is a description of the electrostatic principle that the electric field inside a conductor is zero; it is not applicable to changing EMFs. I'm rewriting the paragraph... --hb

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The excited fields oppose the applied fields, in concord with the law of conservation of energy.

The relationship is not clear to me. Patrick 11:11 Nov 26, 2002 (UTC)

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a current that cancels the applied field inside the conductor

This may create the impression that as long as the electric field is outside, the current flows to cancel it inside; however, in the case of a static field, the charge distribution (+ here, - there) takes care of it, the current is there only very shortly to create this charge distribution. Patrick 11:56 Nov 26, 2002 (UTC)

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I agree that the article seems to include stuff that isn't strictly within the original definition of the Faraday cage effect. I added some historical info at the beginning to show where the idea started. Perhaps with more research we can trace how the concept has been broadened to RF etc., and whether the later additions deserve to be part of this article. -- Heron

The concept doesn't have to be "broadened" to include RF. It includes all electrical energy. In practical F Cages, instead of smooth walls, a mesh is used to save metal/cost (or for visibility), and in that case the wavelength of the electrical energy becomes significant vis a vis the mesh size; obviously, the EM energy at the optical wavelengths are meant to get through. If the cage is completely closed and smooth (e.g., a closed sphere), classical EM theory predicts zero field inside everywhere. Of course, quantum considerations change everything...

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There has been some back and forth about FCs on (ironically) the tin-foil hat page. Take a look at the discussion (and the talk page) for some more information about skin effect, partial FCs, etc., that could be usefully integrated.

What exactly is the difference between the concept of a Faraday Cage and the Skin Effect? They both seem very very simular, except that the skin effect is based on alternating current.

I have read that the real reason why a person is safe in a car during lightning is the skin effect, as a lighning bolt acts as alternating current, although only one half wave of it.

Contradiction tag added

The first paragraph seems to contradict itself, defining a faraday cage as shielding from electromagnetic radiation and then talking about Michael Faraday experimenting with electrostatics. Obviously the cage will shield both, but this does not make clear what the definition of the term is (i.e. perhaps it was initially an electrostatic shield and then discovered to also be an electromagnetic shield). Either way, as mentioned above, the article could probably do with a rewrite by someone with a background in the area. --postglock 08:36, 18 July 2005 (UTC)

I hope interested readers can discern that the Postglock's post was addressed shortly after his post. The article is correct. See also skin effect for the RF (i.e. Electromagnetic version) --Ancheta Wis 00:01, 18 December 2005 (UTC)

magnetic fields

needs more details on the differences between magnetic, electric, and electromagnetic fields, frequency, near field vs far field, and which of those a faraday cage shields against. and real-life, resistive cages vs ideal perfect conductors. — Omegatron 03:22, 22 December 2005 (UTC)

Is this description correct?

Magnetostatic fields would not be blocked by such a shield, but changing magnetic fields would create eddy currents in the surface that create their own fields and cancel them out, so the magnetic shielding gets more effective at higher frequencies?

Changing electric fields would not be blocked as much as electrostatic (which are blocked perfectly), since the charges have to move around to cancel them out, and charges can't move instantaneously, so the shield would be less effective against electric fields as frequency increases? — Omegatron 16:10, 23 March 2006 (UTC)

Faraday cages do not block DC or slowly-changing magnetic fields. A magnetic compass will work inside a Faraday cage.

From <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations">Maxwell's Equations</a>, however, a changing magnetic field creates an electric field (and vice versa), and the walls suppress the electric field. They therefore also suppress the magnetic field. Whether the changes are "fast" (and therefore suppressed) or "slow" (and transmitted) is set by the wall materials' thickness and <a href="http://en.wikipedia.org/wiki/Skin_depth">skin depth</a>.

Faraday cages large enough to people, furniture, etc. are often called "screen rooms".

They're also used in pulsed high-voltage experiments to protect sensitive electronics from electromagnetic pulses created by the experiment.

I'll note all this in the article.SMesser 01:09, 6 June 2007 (UTC)

Do true Faraday cages need to be grounded?

It seems that a Faraday Cage requires a completely enclosed cage so that there are clear "inner" and "outer" surfaces. However, one of the links on the bottom goes to a site that talks about grounding a conductive shield and specifically says that the Faraday Cage does NOT have to closed on all sides. It seems to me that if the cage is NOT closed on all sides, then the conductor has only a single surface and the electrical charge is free to propogate to any point on that surface. (The linked site also credits scientists working with Einstein or at least in the same era for creating the first Faraday Cage, but I digress.)

So is this a different property than Faraday's enclosure? Is this more simply, shunting the electrical charge away and dissipating it to ground? Does a Faraday Cage need to be grounded? Is a Faraday Cage more effective either for blocking electrical fields or as an RF shield if the cage is grounded? If the cage is not fully closed on all sides, is it a "Faraday Cage"? --JJLatWiki 16:08, 8 June 2006 (UTC)

A Faraday cage does not need to be grounded the shield the inside from external EM. The reason cages are connected to an internal circuit's ground is to prevent the cage from capacitively coupling parts of the circuit to each other, and to prevent crosstalk from cables. Connecting the shield to ground causes them to capacitively couple to ground instead. There's a very clear description and picture in ISBN 0-7506-7403-2, which we should mimic. — Omegatron 06:26, 25 November 2006 (UTC)

From the current article "If the cage is grounded, the excess charges will go to the ground instead of the outer face, so the inner face and the inner charge will cancel each other out and the rest of the cage would remain neutral." Is this not a mistake? I would think that the charge needed to nullify the field created by the internal charge (inside the conductor) would be supplied by the ground - not the other way around (as in the above citation) --Qff (talk) 09:33, 29 August 2010 (UTC)

Vehicle safety

Added to the list item indicating occupants in a car were safe from lightning. The truth is more conditional than that and cars don't provide complete safety.

See http://www.lightningsafety.com/nlsi_pls/vehicle_strike.html (National Lightning Safety Institute) for example.

-Michael

Question: What does this comment "Faraday cages are not good to use outside in the event of a lightning strike." mean? The cited source does not support the assertion. Perhaps it can be reworded. --69.3.237.169 21:03, 24 November 2006 (UTC)

Is protection from electrical currents really an aspect of a Faraday cage? I mean, I know that Faraday cages protect against currents, but is that really relevant? The key point of Faraday cages is that they prevent electric fields from penetrating. Protection from currents is related more to the skin effect, no? — Omegatron 07:41, 25 November 2006 (UTC)

Mesh size; explanation; magnetic fields

The intro says that Faraday cages keep out "electromagnetic fields". Do they indeed keep out magnetic fields? Naively, I would assume that they keep out electric fields, and therefore electromagnetic radiation, but not necessarily magnetic fields (unless the conductor happens to be magnetizable, but that's not part of the definition of a Faraday cage).

The intro gives as core reason for the operation of a Faraday cage that repelling charges will accumulate on the surface of a conductor. While that is true, it doesn't explain how a Faraday cage blocks an electric field. The explanation further down in the article (moving charges creating a field that cancels the original one inside the cage) is much more to the point. I would argue to remove the intuitive explanation in the intro, or replace it with a better one.

I'm also interested in the relationship between the mesh size of a Faraday cage and the wave length of the radiation that it blocks. Does the mesh size have to be significantly smaller than the wave length? My little hand-held radio can receive radiation with wave length of over 3m just fine in a car (whose mesh size as a Faraday cage is smaller than one meter). AxelBoldt 21:40, 19 September 2006 (UTC)

I don't understand this either, and I should. From what I understand, a Faraday cage keeps out static electric fields but not static magnetic fields. It also keeps out changing electric fields, though not as well, and worse at higher frequencies, due to resistance of the material, and also blocks changing magnetic fields, better at higher frequencies, due to induced eddy currents. And those are all near field. Far field EM I don't know about, and I'm sketchy on the difference between near and far field anyway.

But that's just a hunch/gut feeling kind of thing. I could be thinking about it wrong. I'm going to look in some books. — Omegatron 22:40, 24 November 2006 (UTC)

As for your radio working inside the car, blame it on the tires. Rubber tires. Unless you're dragging a grounding strip, your car body is very very poorly grounded. Ungrounded faraday cages are only practically effective against static EM. While it is technically blocking the signal arriving from the radio transmitter, in your case, all that RF energy goes into inducing currents in the cage, just like any other antenna, and since there's no ground for that current to dissipate into, enough of it ends up re-emitting into the inside of the cage for your radio to still get decent reception. You'll weaken the signal non-negligibly, and introduce a lot of extra RF noise, but standing between 2 skyscrapers does that. Your radio has circuits to filter out the noise, and the signal coming in is apparently strong enough to afford the energy loss. 67.162.34.172 (talk) 16:58, 4 November 2009 (UTC)

Summary of facts from ISBN 0-7506-7403-2:

• Near field shielding
  • Electric fields
    • Created by high voltage/low current devices, like dipole or monopole antennas, sparks, or high-impedance circuits
    • Wave impedance is very high, while conductor's impedance is low, so
    • Shielding is perfect for an electrostatic field, diminishes as frequency increases
  • Magnetic fields
    • Created by motors and loop antennas (and power transformers?)
    • Wave impedance is low, while conductor's impedance is low, so
    • Not much reflection occurs; shielding must be by absorption
      • Needs to be several skin depths thick
      • Shielding gets better at higher frequencies
    • At low frequencies, even absorption shielding is useless.
      • For low frequencies, use high-permeability shielding to re-route the magnetic field lines, like mu-metal

Summary of facts from ISBN 0-521-37095-7: Low frequency magnetic fields are not shielded well by metal enclosures. Instead, try not to create loops in the circuit layout, and if you do, don't let them cover a large area. Use twisted pairs to connect things, since they minimize loop area and each successive twist picks up the opposite field of the last, canceling out. Can also use mu-metal shielding. — Omegatron 07:11, 25 November 2006 (UTC)

I can't argue with any of that.

• Static magnetic fields are not shielded at all by a Faraday cage.
• Far fields are those that have an E and an M component at right-angles to each other and to the direction of propagation, like EM waves in space. The wave impedance of free space is 377 ohms, while that of a conductor is low (milliohms, and a complex number [1]). If you short out the E component with a conductor, the M component gets clobbered too, since the two components generate each other. In near fields the two components aren't related in a simple way, so you have to consider them separately.
• The attenuation of a hole is proportional to the ratio of wavelength to diameter. There isn't a sharp cutoff. This source [2] (table on p2) shows that at half a wavelength you get -3 dB, so you shouldn't be surprised to get some leakage.
• "For circular apertures which have diameter much smaller than a wavelength, the radiation coupled through is proportional to the sixth power of the radius." [3] (right at the end), hence the microwave oven mesh. This seems to contradict the previous point, so I suppose the two statements apply to different ranges of λ/d.
• A thought experiment. If the cage were superconducting, it would keep out very LF magnetic fields, and even switching on an external DC electromagnet would count as changing the magnetic field, so the eddy currents induced in the cage would circulate for ever, cancelling out the field. --Heron 17:05, 26 May 2007 (UTC)

Recording Studios

I've heard that some recording facilities use a Faraday Cage. Can anyone verify this or provide more information? Mikebritt UTC

Lightning vs. a car?

A bolt of lightning has over a billion volts and a lot of amps, but if it hits a car, it won't penetrate through it, and kill the people inside? 64.236.245.243 14:35, 1 March 2007 (UTC)

In general it will not, yes. This lightning safety sheet calls a car the second safest place to be in a storm, after a proper building. Just make sure you don't touch any conductors connected to the metal body of the car. Algebraist 16:57, 14 November 2007 (UTC)

This was tested on the BBC's Top Gear. Richard Hammond sat in a car while an electrical charge was built up in a device high above it until the car was effectively struck by lightning several times. The electricity did penetrate the car a little since he reported feeling it in his fingers, but not enough to do any harm. 194.80.52.106 (talk) 14:12, 22 August 2008 (UTC)

Fry's Electronics

The article mentions that small electronic parts at Fry's are kept in a cage, inferring that the cage is used as a Faraday shield. What I've seen at any Fry's I've ever been to is nothing but a security cage made of chain-link fence. There would be no reason to keep parts in a Faraday cage; there would however be a reason to keep them in a secure area; CPU's and memory are valuable and easily stolen. 24.165.87.76 03:01, 14 May 2007 (UTC)

Faraday Suit

I saw a request for a picture of a Faraday Suit. This is a Russian "Radar Suit" that I photographed at Hack Green Secret Nuclear Bunker museum some years ago. Not sure if it is what is needed for the page. --jmb 15:12, 8 July 2007 (UTC)

Russian "Radar Suit"

Is this a faraday suit? The image is Creative Commons, so is suitable for uploading here. Marašmusïne_Talk 17:00, 29 July 2007 (UTC)

Comments

My thoughts: To get a "Faraday's cage effect" it can have big holes and must not be metal as long as it has low resistance (metal helps both because of thet the charges inside the metal extremely quickly re-distributes which in total makes the field 0 inside the cage, but also might help because of the low resistance since you get a voltage division vs the source), and it certainly does not have to be grounded. See my comments on "Antistatic bag" too. --88.131.22.138 (talk) 14:59, 11 March 2008 (UTC)

Microwave oven as shield?

At a business that was located across a two-lane street from one cell providers antenna, several employees including myself did an experiment on our lunch break that involved sticking the phone inside of the microwave, with it powered off the whole time, and seeing how many bars remained and/or calling the phones. Most phones went to out of service. Two rang, including the phone that matched the service provider on the antenna farm across the street. The matching-provider phone kept 100% of its bars during the entire time it was inside the microwave.

The cellular band (1.8, 1.9GHz) isn't too far from the 2.5GHz used to actually cook the food. It does a pretty mediocre job of keeping these larger wavelengths out, but yes it did in fact block them somewhat. Just not as well as would be expected if the device were designed to do such, considering how frequently the signal is blocked unintentionally.

It seems like we should be able to get a citation on exactly how much of a shield a microwave oven is, or at least ought to be, considering that we are allowed to have 1W WiFi amplifiers on bookshelves and these ovens are usually between 400 and 1200 watts; I would think that somewhere, there ought to be a published guideline for shield effectiveness. —Preceding unsigned comment added by Zaphraud (talk • contribs) 20:27, 9 May 2008 (UTC)

While I'm not sure how much attenuation is needed to block a cell phone signal, I do know that I cannot get service inside a closed shipping container. Microwave ovens leak about 1mW/cm2, which is only about 40-50 db less than what is inside the microwave. —Preceding unsigned comment added by 24.74.206.8 (talk) 05:21, 18 December 2010 (UTC)

Badly formulated

The phrase "A Faraday cage is best understood as an approximation to an ideal hollow conductor" really puts me off. I hardly know anything about how Faraday cages work, but this is a very bad way to start a section to explain how something works. I myself don't understand them so I don't think I'll change this myself. If anyone who knows more about Faraday cages could fix this it would just be great --BiT (talk) 06:51, 14 January 2009 (UTC)

wavelength of lightning

In the article, we see

Cars and aircraft, when struck by lightning. The

metal frame and outer skin of the vehicle cause the electrical charge to travel safely away from the occupants. This differs from a popular urban legend that claims that a car's tires cause the lightning strike to reach the ground. However, radio and cellular phone signals can still reach inside the vehicle since their wavelengths are significantly smaller than the windows and other openings in the vehicle's conductive frame, though internal signal strength may be

diminished.

Kindly mention exactly how long the wavelength of lightning is.

Jidanni (talk) 03:20, 22 February 2009 (UTC)

Lightning is (basically) an example of direct current, so it does not have a wavelength or frequency. Indeterminate (talk) 07:52, 23 September 2009 (UTC)

SORRY. This statement is INCORRECT. AC or DC is actually irrelevant. An electrical current/signal does NOT have to change direction (AC) to have a Wavelength or frequency, it can be DC and still carry a varying waveform. It only has to change in strength ie. voltage over time. In many (most?) applications ie oscillators a signal will change direction.

It is usually depicted, as here in the Wavelength article, changing direction/polarity. BUT it does NOT have to reverse direction to have a wavelength. It could change from +5 to -5 Volts, or 0 to +10 Volts. As shown here, the measurement between 2 'equivalent' points on the waveform is the same irrespective of polarity. Are you perhaps thinking of DC in respect to a battery?

Lightning would cover a very wide range of RF frequencies and therefore a wide range of wavelengths. It would probably be referred to as 'white' noise ie. basically random. --220.101.28.25 (talk) 17:53, 22 November 2009 (UTC)

Can't pull the plug on rogue cellphone

Mention what to do in such cases, and if proposed solutions would be effective. Jidanni (talk) 03:20, 22 February 2009 (UTC)

Caves?

Mention if caves make good Faraday cages, and if they are well grounded (which I suppose is the case.) Jidanni (talk) 03:20, 22 February 2009 (UTC)

If they're wet enough, they can make a passable Faraday cage, and yes, an outstandingly well-grounded one. However, at this point, any faraday-cage-related, charge-distribution-based, shielding effects are totally insignificant compared to the sheer mind-boggling quantity of stone and dirt and hard water and other not-perfectly-transparent-at-useful-frequencies materials between the inside of the cave and the surface world, or even, in many cases, between rooms of the same cave.67.162.34.172 (talk) 17:37, 4 November 2009 (UTC)

Examples?

I cannot understand why the only example offered on this page relates to a foil lined shopping bag. Surely there are other examples which can be offered to the reader to better understand this concept... 142.221.110.4 (talk) 19:14, 22 September 2009 (UTC)

Maybe not an example but a good reference in popular culture is the movie "Enemy Of the State". At one point in the movie, the ex-CIA agent steps into a Faraday cage to prevent eavesdropping/location. —Preceding unsigned comment added by 131.247.83.135 (talk) 13:33, 29 October 2009 (UTC)

• • That's a good example actually. Faraday cages are used in the electronics industry when 'aligning' RF (Radio Frequency) transmitters( TX) and receivers (RX). Stops the TX which may be off frequency from causing interference, allows RX to be tuned without interference from external TX sources etc. Also stops RF from test equipment causing interference to other external RX and electronic equipment.
  • Faraday cages also exist inside equipment. ie. inside a mobile/cell phone there is a lot of metal covers. At least some of this is for RF shielding. CRT TV/monitors (probably LCD/Plasma/LED displays too) have metal shields for various parts to stop interference getting out (& in too). This should fit the 'technical' definition of a Faraday Cage. Most often though, in my experience, it is merely referred to as 'shielding'. See Electromagnetic shielding. and try Practical Electromagnetic Shielding Tutorial [4]
  • The 'code room' in embassies and other places that use secure communications would use a type of Faraday cage to stop eavesdroppoing on communications. (Some of these are like bank vaults anyway!) The equipment itself would also be shielded to stop 'cleartext' signals getting out. ie being accidentally transmitted with the 'encrypted' text. This is a method that HAS been used against cypher equipment with poor 'shielding'. The technical codename (once classified) that 'Security agencies' ie NSA use for this area is TEMPEST.
  • Apart from books and websites user:Elonka is very much into deciphering encrypted messages. (She was once invited to the CIA to give a presentation!) She might also know a bit about this side of things. --220.101.28.25 (talk) 08:11, 22 November 2009 (UTC)

Unclear quote citation

From the first sentence of the second paragraph, under History:

The same effect was predicted earlier by Francesco Beccaria (1716–1781) at the University of Turin, a student of Benjamin Franklin, who stated that "all electricity goes up to the free surface of the bodies without diffusing in their interior substance."

I read this as attributing the "all electricity goes..." quote to Beccaria, not Franklin, but the phrasing is ambiguous on the matter. Could someone who knows for sure what it should say, please rephrase this sentence to be clearer? 67.162.34.172 (talk) 17:45, 4 November 2009 (UTC)

Franklin cage/Franklin shield

Since he discovered it first, should we name it after Franklin? Or as IP67 pointed out, should we name it after this Beccaria? Dictabeard (talk) 10:52, 2 February 2011 (UTC)

Faraday cage in microwave blocking outgoing EMR?

according to my memory of first year physics, a faraday cage only blocks incoming electromagnetic radiation - to block outgoing radiation would violate Gauss' Law. Considering removing the whole section but I'd like an expert's opinion first. — Preceding unsigned comment added by Akdor 1154 (talk • contribs) 03:46, 8 September 2011 (UTC)

Gauss' Theory Misquoted

The Operation section of the main article states that the position of a charge inside a hollow metallic conductor does not affect the field generated outside.

Again, this is an oft misquoted form of Gauss' Theory. Yes, the field outside will be identical to as if the conductor wasn't there - but moving the charge within this conductor, and RELATIVE to it, will change the strength of the field at a defined external point. — Preceding unsigned comment added by 123.238.25.145 (talk) 00:52, 26 September 2011 (UTC)

Electromagnetic Transparency

I think the main article, and several related ones could do with linking to an article on electromagnetic transparency.

Speaking of transparency, I've also got a question

> How are certain substances transparent at certain regions in the electromagnetic spectrum, but not in others - on EITHER SIDE of this permitted region? E.g. The Human body: X-rays get through, Radio waves pass through, but light does not.

Can both phenomena be explained with the same nature (i.e. particle or wave, but not one for each..)?