How do Signal Blockers Work? (Faraday Cages)

Many retailers now sell signal blockers to thwart digital snoops. How do they work, and are they really necessary?

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45 thoughts on “How do Signal Blockers Work? (Faraday Cages)

  • That was a very much overly complicated, if not wrong, way of defining Faraday law.
    Everything in nature strives towards stability. This is the so called "force free" state. This does not mean that there are by necessity no forces, but the only forces that remain are on average 0 newton.
    Metal conductors are very good att finding this "force free" state when it comes to the electric force. If a piece of metal is in the way of an electric field (force/charge) the electrons will move to cancel out that electric field. Getting as close as possible to finding this force free state. Since the electrons generally do not move outside of the conductor they can't truly cancel the electric field outside of the conductor. But inside the conductor the field is practically 0. This means that the field will be 0 on the other side.

    Another way of thinking of this is that when a lightning bolt hits a metal cage the cage as so much higher conductivity then the person inside of it that practically all of the current moves trough the cage instead of the person inside.

    There is another aspect of Faraday's cage, that only applies to electromagnetism. A "wave guide" is a metallic pipe with circular or quadratic dimensions. It guides electromagnetic waves, but only the waves with the right frequencies. It behaves similar to how sound waves oscillate in a pip, just in the opposite direction this time.
    While the magnetic field to the wave points along the wave guide the electric field of the wave points in the direction towards the sides. So the possible wave lengths are then limited by the width of the wave guide:
    So low frequencies tend to be blocked out, while high frequencies tends to pass. The waves with lengths between the ones you could see in that picture tend to lose a lot of energy really fast. So they do not penetrate the wave guide, instead they get absorbed and turned in to heat.
    Now think of the square holes in the Faraday's cage as a very short wave guides. The lowest frequency that can penetrate a rectangular hole is f=c/a.
    f is frequency (Herz).
    c is the speed of light (299 792 458 m/s).
    a is the length of the longest side (m). It is also the longest wave length that can penetrate the
    Lets say that a = 0.1 m, or about 4 inches. The lowest frequency that can penetrate this hole is then about Herz or 3 GHz. This is enough to block out the frequencies that are used in both radio apparats and mobil phones.
    If you want to block out any or all visible light then you have to have holes as wide as 390 to 700 nano meter.

  • In a 5+ minute video supposedly explaining how Faraday cages work, you spend only 40 seconds describing the physics. In that short time, your only visual is a nearly incomprehensible picture with far too much going on. Not very helpful.

  • read the article referenced why you don't need rfid protection in your wallet. while it may be true that you need a pin in Canada, in the US and other countries, you don't need a pin to use the card, meaning that hackers could steal your card's info from afar and use it in fraudulent purchases

  • Linus, WiFi and Cellphone radiation has been deemed a probable carcinogen by the World Health Organization. In a few years it will be widely known that WiFi is as bad if not worse than cigarette smoke. Hopefully you make your own research and create a video about the dangers of WiFi and the need to make one's home WiFi proof, (e.g. T98 and mesh) or better yet, research new technologies that will make WiFi obsolete. But 5G is looming at the horizon however, which will be even worse.

  • KFC protecting from emf and microwaves….while killing you with fried fast food..πŸ˜‚πŸ˜‚
    Reminds me to tell the right-wingers to eat more chicken….πŸ„πŸ„

  • so if I ground the F. cage the positive/negative cancelling doesnt work? And what about an other signal coming from the opposite side, doesnt it charge the other side back to where it was allowing the first signal to propagate? I dont think so but I think it works slightly different than you said

  • 0:45 that explanation is wrong, that explains how they work in electrostatics regime. What actually happens is that the electric field oscilates (due to the nature of the electromagnetic radiation itself), generating oscillating currents inside the conductor, witch dissipates energy by Joule effect.

  • maybe nice idea to construct such faraday cage like KFC but cheaper yet very effective, i think some techies will like that episode, to tune out, turn off, fade out once in a while πŸ™‚

  • Do Faraday cage protect your phone of data collection, but by inside apps ? (like : if I put my phone on a Faraday cage, can Google still collect my personal data ?)
    Sorry if my English is bad, I'm french 😁

  • Another way to think about this is the cage acting as an antenna. The antenna is driven by the incoming signal and emits a signal 180 deg out of phase into the cage and in phase back at the source reflecting the signal back like a mirror.
    A lot of lower level physics textbooks actually get this wrong and describe the process as the free electrons in the metal moving and then having their energy dissipated by resistance.

  • Wow they're going to be awwwwwfully busy when the metal detectors start goin off when every shopping card watch pocket knife or earring goes thru lol na this method would work perfect if u wanna steal

  • Do you think there are weapons that can be directed onto people that would do things to them that would do harm to people like cause vertigo?? and if so would a Faraday cage stop such a weapon??

  • This was great, I've been looking for "faraday cage cost" for a while now, and I think this has helped. Have you ever come across – Tennorra EMP Esterification – (do a search on google ) ? Ive heard some unbelievable things about it and my colleague got great success with it.

  • This was great, thanks, I've been looking for "emp faraday shield" for a while now, and I think this has helped. Have you ever come across – Tennorra EMP Esterification – (just google it ) ? Ive heard some amazing things about it and my partner got excellent success with it.

  • Winner of a video, I have been researching "homemade faraday room" for a while now, and I think this has helped. Have you heard people talk about – Tennorra EMP Esterification – (just google it ) ? Ive heard some unbelievable things about it and my work buddy got excellent success with it.

  • Winner of a video, I been tryin to find out about "how to make a faraday cage aluminum foil" for a while now, and I think this has helped. Have you ever come across – Tennorra EMP Esterification – (just google it ) ? Ive heard some extraordinary things about it and my work buddy got amazing success with it.

  • This is just superb, been searching for "faraday cage for solar flare" for a while now, and I think this has helped. You ever tried – Tennorra EMP Esterification – (just google it ) ? Ive heard some interesting things about it and my brother in law got great results with it.

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