What is Faraday cage: Definition and 97 Discussions

A Faraday cage or Faraday shield is an enclosure used to block electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after scientist Michael Faraday, who invented them in 1836.

A Faraday cage operates because an external electrical field causes the electric charges within the cage's conducting material to be distributed so that they cancel the field's effect in the cage's interior. This phenomenon is used to protect sensitive electronic equipment (for example RF receivers) from external radio frequency interference (RFI) often during testing or alignment of the device. They are also used to protect people and equipment against actual electric currents such as lightning strikes and electrostatic discharges, since the enclosing cage conducts current around the outside of the enclosed space and none passes through the interior.
Faraday cages cannot block stable or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screened room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference. See also electromagnetic shielding. They provide less attenuation of outgoing transmissions than incoming: they can block EMP waves from natural phenomena very effectively, but a tracking device, especially in upper frequencies, may be able to penetrate from within the cage (e.g., some cell phones operate at various radio frequencies so while one frequency may not work, another one will).
The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage; however, a Faraday cage has varied attenuation depending on wave form, frequency, or distance from receiver/transmitter, and receiver/transmitter power. Near-field, high-powered frequency transmissions like HF RFID are more likely to penetrate. Solid cages generally attenuate fields over a broader range of frequencies than mesh cages.

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  1. S

    Gauss' law and Faraday cage problem

    Is this a good response? The lift is a conductor, therefore electrons can move freely. The charges on a conductor reside on the outer surface as they like to be as far from each other as they possibly can be due to the repulsive coulomb force. There is no charge between the inner and the outer...
  2. vytautas_k

    I Faraday cage continuity question

    We have built a faraday cage out of 1,5mm thick galvanized steel sheets. Size is 1.5m*1.25m*1.5m. The steel got powder coated and was assembled on a frame. Each side of the cage is made from separate sheets that are joined using rivets. All of the separate sheets are connected with grounding...
  3. C

    I A and ϕ inside a Faraday cage?

    Are A and ϕ always zero inside a Faraday cage, like E and B are? If not, can its design be modified to accomplish that? If not, is there an analogous mechanism that'd always have A=0 and ϕ=0 inside?
  4. C

    I Faraday cage made of a real conductor

    A faraday cage made of a perfect conductor would theoretically have a zero E field inside. However, are there cases where a faraday cage made of a real conductor like copper wouldn't block out all EM radiation, like very high or low frequencies? How can the design be improved to make a real...
  5. A13579

    B Does a Faraday Cage trap EMF inside and increase exposure?

    Hi All, I’d like you to weigh in on a debate I’ve been having. I’ve been thinking about a Faraday Cage (FC from now on) but from the opposite perspective. Sure it stops EMF getting in. But does that also mean, if there are items emitting EMF in there, that gets trapped within the room. Taking...
  6. I

    B Protecting Your Computer from Solar Storms - Is a Faraday Cage Enough?

    How did you find PF?: Via Google search From what I understand in scientific publications, if there is a strong solar storm directed towards the Earth, the effects would be such that any electronic equipment would suffer irreparable damage. I ask, if I put my computer inside a Faraday cage...
  7. A

    Electric Field Shielding: Does a Conductor Shield Inside?

    Hi. I was reading about conductors in electrostatic equilibrium and how it makes sense that they have zero electric field inside the material even when an external charge is brought near. The charge density of the material just rearranges itself to cancel. Then I searched for hollow conductors...
  8. E

    An electron inside a Faraday cage

    I came across a problem that seemed fairly interesting; it asks what would be the trajectory of an electron released from rest inside a Faraday cage (which is itself within a uniform gravitational field ##\vec{g} = -g\hat{y}##). I didn't quite understand their explanation. They say that...
  9. stanley

    Impact of frequency on Faraday cages

    I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0. Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able...
  10. E

    How do we show that the interior of a Faraday cage is an equipotential?

    It is possible to show via Gauss' law that the the net flux through a surface within the Faraday cage must be zero, however this is not a sufficient condition for the electric field to be zero. For the electric field to be zero in the interior of the cage, all points within the cage must be at...
  11. Ainokea

    Does My Router Need a Faraday Cage to Protect Me From Harmful Radiation?

    Is there a need to put a household router in a faraday cage to cut down on radiated signals that could damage the human body? I would think the manufacturer's would have shielded what needs to be shielded. I see these advertised on Amazon among other places. My router sits about 6 feet from...
  12. th078

    Radio frequency shielding for Raspberry Pi Zero

    So I'm trying to put together a Pi Zero mini computer to use for security-oriented applications, for example encrypting/decrypting messages, working with encryption keys, etc. It's cheap, very small and thus easy to carry around. However, I'm not entirely comfortable with the presence of the...
  13. B

    How to build a Faraday cage to keep a WiFi signal inside?

    I'm working on a wifi device testing box and made the first prototype of the Faraday cage. I need holes because of cooling. For this reason, the box has 3mm diameter holes on the top. The box made from steel, and have 2mm wall thickness. The wavelength around 12,5 cm for 2,4 GHz and 6 cm for...
  14. solzonmars

    How does a Faraday Cage block electric fields?

    Why does a Faraday Cage work? (or more generally, why does the inside of a conducting shell have no electric field if there are charges placed outside it?) I understand that this is the result of polarisation, but why does the polarisation happen to exactly cancel out the field? Could there be...
  15. S

    What is the optimal thickness for a Faraday cage to attenuate radio signals?

    Greetings, I have a question regarding the attenuation properties of Faraday cages. More specifically, I'm looking for a generalization I can use to better understand how thick they should be for a given frequency. I did a small experiment by taking a small enclosed aluminum box and placed an...
  16. F

    Does chromium oxide reduce conductivity in stainless steel?

    Does chromium oxide reduce the effectiveness of a faraday cage constructed from stainless steel mesh? I am using mesh that is like insect screen for windows. It will be in moist environment. I appreciate your help!
  17. H

    Can a Faraday cage protect you from electrocution in a nano second?

    In the Faraday cage, after injecting the charge, it takes about a nano second for charge to be distributed over the external surface. Why doesn't one become electrocuted in this very little time (nano second)?
  18. F

    Power line EMI filter + feedthrough filter for a Faraday cage

    Dear forumers, I need a 50hz 250VAC power line filter for an EMI shielding faraday cage. The filter should work between 100khz and 20ghz, attenuation should be >=60dB between 1mhz - 5ghz. Regular power line EMI filters like this don't seem to go that high (only up to a few hundreds of mhz...
  19. P

    Simulating a Faraday Cage

    Hi guys, I'm wanting to simulate faraday cage form, analysing mesh perforations defined by wavelengths of different electromagnetic spectra (eg. radio, microwave, UV etc). Are there any good analysis softwares which I could import a pre-made digital model with these perforations and simulate...
  20. P

    I Radiation modeling software (radiation blocking qualities)

    Hi guys, I'm wanting to test materials developed in CAD software for their radiation blocking qualities (EM Spectrum), I would ideally need to use a software where I can set the wavelength and frequency of the emitter and set up a receiver, allowing me to place different materials in the middle...
  21. G

    Is Faraday Cage able to stop all electromagnetic radiations?

    I'm trying to understand if it does exist something (material, construction) that shiled you against alll kind of electromagnetic radiations. Something that shields you from the lowest frequency radio waves up to the highest frequency gamma rays. I've read about faraday cage but it does not...
  22. M

    Faraday Cage Effectiveness versus Frequency

    If inside of a metal (for ex. Aluminum) enclosure, could it potentially create more harm than good if frequencies were able to penetrate due to an imperfectly sealed cage or due to a relatively high power level of frequencies that allowed them to penetrate the metal? If the power level was high...
  23. X

    The electrostatic field of the Faraday cage

    I have a function of the cartesian coordinates x, y, z such that: f = a * ln|sin(px + iqy)| + by + c This equation should be describing the electric field nearby the wall of the Faraday cage. I solved the Laplace equation Δf = 0 and got : p = +/- q, so p = q. I should choose the constants...
  24. J

    Faraday Cage and a high voltage discharge arc

    In the following video: I understand how the Faraday Cage works, but what has me confused is the arching. If charge is building up on the sphere and then arching over to the cage, where then is that charge sunk to? You would think it would stop arching when there was sufficient charge on the...
  25. O

    Faraday Cage: Thickness of the conductor

    So i have learned about the ability of Faraday Cage for blocking an external electric field. But is the thickness of the conductor effect the ability? Is there any limit of its thickness so that the cage won't be able to block external electric field anymore? I have read and searched about this...
  26. Clara Chung

    Why must a Faraday cage be hollow?

    A metal piece has no E field inside too. Why must the microwave use a metal mesh with hollow spaces to block radiation? They can simply use a metal piece just like the interior part of the box.
  27. G

    Faraday cage from Gauss' law alone?

    Hi. Is it possible to derive the properties of a Faraday cage from Gauss' law alone? I found some "derivations" which I find rather unconvincing since they somehow conclude from a vanishing flux that the E field must vanish as well. Some slightly more elaborate derivations use a combination of...
  28. G

    Faraday cage in electrodynamics (with currents)

    Hi. Assume a long hollow wire that both carries a nonzero net charge and a current. Is it still true that all charge sits on the outer surface of the cable and that the empty space inside is field-free (Faraday cage)? I know proofs of those facts in electrostatics using Gauss' theorem, but they...
  29. S

    Faraday Cage: Surprising Facts from SIAM News

    This is an interesting short article from SIAM news that says the Feynman lectures are wrong about the Faraday cage: https://sinews.siam.org/DetailsPage/TabId/900/ArtMID/2243/ArticleID/757/Surprises-of-the-Faraday-Cage.aspx
  30. N

    Faraday cage, lower frequencies

    Faraday cages of the conducting type are not effective for lower frequencies; https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magnetic_shielding mentions a frequency of 100 kHz. The electromagnetic spectrum is composed of both an electrical, and a perpendicular magnetic field. If a...
  31. P

    Faraday cage to block cellphone/Wifi?

    Hi, I was wondering if I could make my house a big Faraday cage capable of blocking Wifi and cellphone signals from the outside by covering all of the inside walls with chicken wire? How big of a problem is it that windows would stay uncovered? Or that electrical wiring inside the wall (so...
  32. J

    Does Microwave Mesh Effectively Block Radiation Due to Wavelength or Amplitude?

    Hi pf, Please could someone provide an explanation of why the relationship between the wavelength and size of the gap is the significant factor for determining whether or not it blocks radiation in particular reference to the mesh on the door of a microwave oven. It seems very simple when a...
  33. T

    EM wave shielding & skin depth

    If I use 10mm (thickness) of a metal for the sides of a Faraday cage, with a 5mm skin depth at the frequency to be shielded, & increase the v/m of the EM wave to be blocked gradually, will there be a stage where the skin depth will increase to 6mm, or is 5mm the maximum limit?
  34. S

    Faraday Cage in Ionic Solution

    Another question and a another terrible illustration. So my question: do faraday cages interfere with dispersion of ionic solutions? In the illustration, a chemical reaction or some other cause for a lower concentration of ions is happening inside a faraday cage at B. Will the solution disperse...
  35. D

    Faraday Cage not blocking wifi

    In our school we made a submarine. The inner hull is a few cm thick metal, so it should be a good farady cage, but it does not act like one when blocking wifi from inside the hull. Wifi antenna is not touching the hull. The hull acts like a faraday cage when blocking a phone signal from the...
  36. B

    Having trouble understanding "Faraday cage"

    Homework Statement I am having trouble understanding how a Faraday cage works.Homework Equations $$\oint \vec{E}\cdot\,d\vec{A} = \dfrac{Q_{encl}}{\epsilon_{0}}$$ The Attempt at a Solution It says that Faraday cage is a hollow metallic conductor and hence, inside the cage, $$\vec{E} = 0$$ I am...
  37. Calpalned

    Exploring the Safety of a Faraday Cage: Conductivity and Hollow Design

    Here is what it looks like I have two questions. 1) What if the guy sticks a finger out of the cage? 2) The idea is that it doesn't matter if the cage is solid or hollow (has bars). As long as it's a conductor, the man inside is safe. What if I start removing the bars to make the cage...
  38. A

    Can a cylinder block magnetic fields in one direction like a Faraday cage?

    Can a cylinder with 1 side open act as a faredey cage (which do not allow passage of magnetic field) when magnetic field are only coming parallel to the curved part
  39. C

    Effect of electric field on a wire segment

    Hello. I was trying to understand the mathematics underlying Faraday cages. After hours of research on the web, It turns out that there are very few mathematical analysis related to Faraday cages, even in the electrostatic case, and those that I read do not satisfy me. So, I tried to solve the...
  40. J

    Will a Faraday cage affect the efficiency of motors inside?

    "A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of...
  41. G

    What happens on external surface of the Faraday cage?

    Hello. Let's say we build the Faraday cage which surround strong radiation such that no radiation can escape to outside world for safety. What happens on external surface of the Faraday cage in voltage during shielding? Is it fluctuated?
  42. G

    Can local voltage drop be developed over ground plane?

    Hello. The ground plane is sometimes used as current return path. If current is low frequency and amplitude is small then voltage rising due to current flow can be ignorable. However, what is return current is actually very high in both frequency and amplitude? In our lab, gas discharge...
  43. D

    Question about surface area of faraday cage

    Hi, I am making a faraday cage to be used in reactive ion etching of silicon. I was wondering if the size of the cage, or the surface area has any impact on it's effectiveness or how it works? I know the size of the mesh and the material I use, as well as whether or not it is grounded all...
  44. dreens

    Frequency Components of a Lightning Strike

    Hi there, I recently attended a physics demonstration (Lightning show at Boston Museum of Science, my favorite exhibit obviously), where the educator argued that the reason she could safely sit in a Faraday Cage while lightning was striking said cage was the skin effect. As I understand it...
  45. G

    Does AC current pass through perfectly shielded box?

    Hello. I've recently have a lot of question of building Faraday cage for our high voltage gas discharge lab. I think this question is a kind of fundamental question for such a job. Let's say I would make perfect Faraday cage with perfect shielding or have metal plate of infinity transverse...
  46. G

    Grounding of power line filter to Faraday cage chassis?

    Hello. I've uploaded similar question before but I think it is time to make this clear. I've seen the attached one during reading of grounding. In the picture, the body of the power line filter (or ground of the filter) is connected to inner surface of Faraday cage and signal ground is...
  47. TESL@

    Induced Electric Field inside Faraday Cage

    Imagine there is a hollow toroidal conducting chamber and a long solenoid in the middle. When we power the coil, does the induced electric field "propagate" inside the chamber? My prediction is that the changing flux will cause induction regardless of the cage. Thank you.
  48. anorlunda

    Faraday Cage For Lightning Protection

    A recent thread talked about a radio inside a metal box. That reminds me of a question I never resolved. 9 years ago my sailboat was struck by lightning. 6 people were on board, but nobody was hurt, luckily. My mast is grounded to an underwater plate via a thick copper cable inside a plastic...
  49. G

    Question for grounding of the electronics to Faraday cage

    Hello. Let's say there is a instrument needed to be EM wave-shielded in High voltage discharge lab. Building Faraday cage becomes necessary and the instrument is moved to inside the cage. The cage is grounded to lab ground and the frame ground of the instrument (it is also signal ground for the...
  50. H

    Detecting the charge distribution within a Faraday cage

    Imagine an uncharged solid spherical conductor. Inside this spherical conductor, there is a cavity of a weird shape carved out of it. And somewhere inside this cavity, there is a charge +q (or rather, a charge distribution of total charge +q). The charge +q induces an opposite charge -q on the...