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Pet trackers, and lots of other electronics, have little cylinders inside them called ferrite beads. If they didn’t, they’d probably be picking up the local traffic report instead.

Hosted by: Hank Green
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(text: "QQs: Why is there a magnet inside my dog?")

Hank: This is a USB cable. It’s just a normal USB cable. The- the information goes down the wire and that’s all it does, right? Except what’s this- what the heck? Why’s this? What? Why?

This thing is called a ferrite bead, and it’s a type of iron-containing magnet designed to block interference so that you only get the electric signals you want to come through. You see them on various chargers, and on some connector cables too. I use this one with my fancy microphone so that I don’t get any extra noise when I’m recording music and podcasts. But they’re also hiding in plenty of other places too -- there’s probably one at the base of your car’s radio antenna, and if you’ve microchipped your pet? Well, Fluffy might have one, too.

In some cases, like those computer cables, the interference comes from having the cable too close to circuits in your computer. Circuits are just loops of different types of parts that let electricity flow through in a current. But when current flows, it can create an electromagnetic field around it -- and sometimes, that can be picked up by your nearby cable. And you probably want your cables to do what they were designed to do, like charge your laptop, instead of picking up stray signals from circuits inside your computer.

In things like radios or that chip inside your pet -- called an RFID tag -- the interference comes from other, nearby wireless devices that are also transmitting signals. When you activate the tag because you’re trying to find your lost dog, you don’t want your tracker to fail because it’s picking up the local traffic report instead. This kind of interference is also one of the reasons they’ll ask you to turn off your cell phone in a theater -- besides the possibility for your phone ringing and being loud and disruptive- and never ever ever do that- getting a phone call can create interference that messes with their sound system.

If the manufacturer tests the cable or RFID tag and realizes that they have an interference problem, one of the easiest ways to deal with it is by installing one of those ferrite beads. Ferrite is especially useful because it acts as a resistor, or something that absorbs electric energy by turning it into heat. When the ferrite surrounds the cable, it blocks interfering signals that try to pass through it and releases the energy as heat instead.

So you can thank those little, behind-the-scenes beads for keeping your electronics in line -- and for making sure you can find Fluffy the next time he wanders off. Maybe you should build a fence.

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