The Faraday Cage Effect

The Computer Corner

By Charles Miller

The Faraday Cage Effect means that an electric charge on a conductor sits on the outer surface, such that little electrostatic field is present within the container. In 1755, long before Internet connectivity problems existed, it was Benjamin Franklin who observed the effect on a ball suspended in an electrically charged metal can. The English scientist Sir Michael Faraday later invented the eponymous cage in 1836. This cage is a problem some people have today with their home Wi-Fi connections.

If you want to see what a Faraday cage looks like, go to the kitchen and have a look at the window of your microwave oven. That metal grid you see is part of the Faraday Cage, intended to contain the radio interference the oven would otherwise emit. The Sistine Chapel was enclosed in a Faraday Cage during the secret papal conclave to elect Pope Francis. That was done by design to block wireless access, but what is more common is to encounter the Faraday Cage effect causing unwanted blocking of Wi-Fi signals.

Experienced computer network technicians know to look for the Faraday Cage effect when troubleshooting Wi-Fi connectivity problems. What is usually encountered is part of a cage formed by things such as steel rebar in concrete walls blocking part of a signal.

Over lunch recently, one of my fellow professionals related to me that he had experienced an encounter with a Faraday Cage that was not just figuratively, but literally, a cage. One of his clients was experiencing Wi-Fi problems with a dead area in her home. Located between the wireless modem and that dead area was a large wire-metal birdcage. It was apparent the metal bars of the cage were entrapping the Wi-Fi signal because according to the formula provided by Noble Prize winner Hans Bethe, diameter divided by wavelength to the sixth power, a wire mesh of one centimeter spacing should block 2.4-gigahertz radio signals used by Wi-Fi. In this case the client found that wireless devices such as laptops or tablets could not connect because the birdcage was soaking up the entire Wi-Fi signal like a sponge!

Over the course of the last few weeks I have tried to explain to readers just a few of the many possible unseen problems that can have a negative impact on their Internet connectivity. Even if you have read this column every other week for the last few months, let me assure you that we have only scratched the surface. I intend to leave this subject for a while, not because I have exhausted all the possibilities, just the most entertaining ones.

What I hope readers will take away from this series of columns is that computer networking is very complex. The do-it-yourself simplicity promised by modem and router manufacturers is misleading and does not accurately portray the results consumers usually get. Still, the incredible fault tolerance designed into networking protocols means that no matter how badly installed or incorrectly configured, the networks sometimes still function at a reduced level. When you have issues with Internet connectivity you should consult with a networking professional who has the training to understand networking issues and the field experience to be able to recognize them.

Charles Miller is a freelance computer consultant, a frequent visitor to San Miguel since 1981 and now practically a full-time resident. He may be contacted at 415 101 8528 or email FAQ8 (at) SMAguru.com.

 

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