How Do Metal Detectors Work?

why would Want to detect metal? Oh, I don’t know… maybe you want to find some gold in the ground. You can dig all the dirt, or you can find the location that has gold before You dig. Or maybe you’re looking for buried metal meteorites. You can even use a metal detector to find your lost ring on the beach. These devices are quite useful.

But do you know how they work? Aha! When you think about it, it’s not obvious. There are different types of detectors, but they all draw on the same cool physics of electric and magnetic fields. Let’s take a look, what do we do?

Go with the flow

First, what makes metals different from other materials? Any solid is made up of atoms, each of which has negatively charged electrons buzzing around a positive nucleus. In nonmetals such as plastic or glass, electrons stick very closely to their original atoms.

In a metal like copper, however, the outer electrons swim around freely and are shared by all the atoms. This is why electricity can flow through a metal – if you apply an electric field, you get a flow of electrons in a certain direction, which we call electric current. metal conductors.

Faraday’s law

So how do you create an electric field? The simplest way is to apply a charge by just adding some electrons to the surface of a metal object – this is what a battery does. Obviously this won’t work for our purposes, though. You’ll need access to metal before you can find it, which makes no sense.

But there are other ways to go. It appears that a Change in magnetic field Also creates an electric field. This is the basic concept of Faraday’s law. If you move a magnet near a metal conductor, the motion will create a changing magnetic field that creates an electric field. If that electric field is in a metal — boom: you get what’s called eddy current.

And vice versa

It also goes the other way: just as a changing magnetic field creates an electric current, an electric current creates a magnetic field. Remember that old science fair project where you wrap a wire around an iron nail and connect the ends to a battery? When the juice flows, the nail temporarily becomes magnetized and can pick up the paper clip.

But as we’ve seen, you don’t need batteries. A changing magnetic field creates eddy currents in a metal and these eddy currents create their own magnetic field. Wait! It’s even crazier. Because these eddy currents create magnetic fields, there will be an interaction between a metal and matter that creates a changing magnetic field.

You are now ready for your first, very simple metal detector. We’re just going to use a moving magnet to create a changing magnetic field. In the demo below, I placed a magnet on top of a coin and then quickly pulled it. The movement creates eddy currents in the coin and these currents create a magnetic field that interacts with the magnet. see? The coins bounce up.