# What is Cage: Definition and 121 Discussions

A cage is an enclosure often made of mesh, bars, or wires, used to confine, contain or protect something or someone. A cage can serve many purposes, including keeping an animal or person in captivity, capturing an animal or person, and displaying an animal at a zoo.

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1. ### Wood/Glass/Metal Batting Cage Steel Tubes - What size do I use

I am building a batting cage in my backyard. The cage will be 12x12x70. I'd like to use 4 steel posts. The posts will be 4 feet into the ground. I was considering using 4 x .120 A500/A513 post and cable. Can the posts handle the load? I believe the net weighs about 140 lbs.
2. ### Construction Steel cage weight load capacity needed

I have a VERTICAL standing square tube 1.25" x 1.25" x 1/16" thick. Length/Height = 79" Material = steel How do you determine its max load capacity for this tube when mounted vertically? I plan to use 18 of these vertical posts, evenly spaced, creating an 83" x 131" rectangular structure. They...
3. ### Calculating Load Capacity of Steel Cage with A-frame Roof

I have a steel cage 7 ft by 11 ft and 7 ft high. It's made out of standard 1 in square steel vertical tubing. Each vertical tube is spaced 18 inches apart all the way around the cage. All vertical posts are welded to a 2 in L-bar all the way around the top, and the bottom. I'm trying to...
4. ### 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?

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...
6. ### 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...
7. ### 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...
8. ### Engineering How to calculate rotor flux of the three phase squirrel cage induction motor?

Three phase squirrel cage induction motor with given parameters (stator winding connected in delta) nominal power: Pn=22.4kW nominal stator voltage: Vsn=230V nominal stator current: Isn=39.5A nominal stator frequency: fsn=60Hz nominal speed: nn=1168min−1 number of pole pairs: 3 stator...
9. 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...
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. ### 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. ### 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...
13. ### Why does a Faraday Cage work?

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...
14. ### Does an iron ring shield a static magnetic field?

Hi. This picture shows an iron ring shielding a static magnetic field: Does this really work, and why? I know that a conductor can shield an electric field (Faraday cage) and a changing magnetic field (Lenz's law), but why would it shield a static field? Especially since iron is a ferromagnet.
15. ### 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. ### Faraday cage and its risk

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)?
17. ### 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...
18. ### Nicolas Cage is going to Produce 3D Printers

They will be of the filament type. Short story here.
19. ### 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. G

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...
21. ### 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...
22. ### 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...
23. ### 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...
24. ### 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...
25. ### 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.
26. ### 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...
27. ### 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...
28. ### 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
29. ### Build a Baseball Batting Cage: Weight Requirements for Posts

Hi all, Not sure if I'm in the right section, but here is my problem: I would like to build a batting cage that is easy to take apart. I would use 4 * 10 foot steel post of 1 inch diameter. The netting weight about 50 lb and would be held with cables . The posts form a rectangle of 12 feets...
30. ### 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. ### 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. ### Faraday Cage & Microwave Mesh

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. ### 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...
34. ### 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...
35. ### Rotor EMF in squirrel cage induction motor

In a 3 phase induction motor,when stator rmf rotates, it cuts the rotor bars and induces an emf in them. Is this emf sinusoidal? I mean shouldn't it be a square wave since the rotor "bars" are being cut by the flux, like in case of concentrated stator windings of a synchronous generator? If the...
36. ### 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. ### 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 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. ### 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...
40. ### 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?

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...
42. ### 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...
43. ### 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.
44. ### 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...
45. ### Faraday's cage supposed to doesn't work for low frequency

Dear all, I’d like to ask your help concerning some doubts about electromagnetic waves, Faraday’s cage, and so on. I read recently that an instrument with a transmitter that emits a low frequency electromagnetic field (around 15 to 22 Hz) located inside a metal pipeline could communicate with...
46. ### Limit on Faraday's cage (rearranging charges)

Having a question regarding Faraday's cage,Applying a magnetic field over the cage, will cause the charges in the conducting cage to rearrange, thus causing another field which opposes the first field. This will give a net field inside the cage of zero (this is why we are safe in a car during a...
47. ### 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...
48. ### 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...
49. ### A puzzle on a Faraday cage "eating up" information

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. The charge +q induces an opposite charge -q on the wall of the cavity of the conductor, which distributes...
50. ### Why isn't my Faraday Cage blocking wifi signals?

So I made this Faraday Cage to block wifi in all directions but 1, to block it from my neighbor. Each side has 6 Layers of aluminum foil on it with no gaps, It looks sloppy because when I tried it and it didn't work I quickly added more trying to make it work. If I put my router inside this...