How do metal detectors work?

Michael Pollick

More experienced metal detector hobbyists can actually distinguish between "junk" metals and precious metals based on subtle differences in the audio signal.

What makes metal detectors work

Consumer-grade metal detectors can help you discover everything from buried treasure to loose change or hidden wiring. Many people enjoy spending hours sweeping over beaches or abandoned property in hopes of finding interesting or potentially valuable trinkets. The process seems straightforward: when the metal detector “hits” on a metallic object, it generates a tone, and the operator digs up a sample for further investigation.

But how exactly does a metal detector determine there’s metal to be found among rocks, roots, sand and soil? There is a scientific principle at work, and it all has to do with electromagnetism and the properties of metal.

The science of metal detectors

Many pieces of scientific detection equipment are designed to exploit one difference between their target and everything else around it. In the case of a metal detector, an electromagnetic field “excites” any metallic atoms in the sampled area, but not organic material like dirt or mineral-based material like rocks. In essence, a metal detector makes metal elements glow at an atomic level.

Generating an electromagnetic field

The battery in a metal detector sends electricity to a large, coiled wire in the base. The coiled wire becomes an electromagnetic field strong enough to penetrate soil to a certain depth, usually measured in inches. This electromagnetic field triggers a response from any metal-based material in that field. Metal does not have to be magnetic in order to become energized by the electromagnetic field.

Picking up the signal

A second coiled wire in the base receives any transmissions generated by the energized metals in the charged field. Some signals are naturally stronger than others, based on the type and size of the metal target. These transmissions trigger an audible tone or beep, signaling a possible hit.

Metal discrimination

Different metals send back different reactions, and many metal detectors are equipped with a microprocessor that recognizes the unique signatures of target metals, such as gold or silver. So-called junk metals such as aluminum or iron can actually be filtered out to save time and effort. However, other models without discriminators alert whenever any form of metal is detected.

Types of metal detectors

Hobbyists searching for buried treasures generally use a portable metal detector with a smooth round base for sweeping scans of a field or beach. Some of these models also contain a smaller pinpoint detector to examine positive samples.

There are also handheld metal detectors that work on the same electromagnetic principle as their larger counterparts, but they’re more often employed to discover more mundane objects, such as electrical wiring, hidden plumbing and metal wall studs.

Accessories such as discreet headphones and digging tools can prove very useful for amateur metal hunters. Some metal-based digging tools can make the searching and scanning process more challenging. There are also waterproof metal detectors for use in rivers, lakes or oceans.

Potential search sites

Public beaches are popular search areas because of their accessibility and the potential for finding a range of valuables. Parks and fairgrounds are good choices because of their long histories. Older abandoned properties such as hospitals, schools, battlefields and stores can also be target-rich environments for hobbyists. Occasionally, an owner may hire metal detectorists to scan a property for valuables with the understanding that found objects will not be removed or sold.

Metal detection and the law

Owning a metal detector isn’t illegal, but there may be some legal restrictions concerning its use. Private property owners can grant permission to search their land but can also limit what can be done with any findings. Trespassing laws still apply to metal detectorists. Some areas are considered protected by state or federal agencies, so artifacts cannot be removed from the site. It falls on metal detectorists to determine if a potential site can be searched legally.

Michael Pollick is a writer for BestReviews. BestReviews is a product review company with a singular mission: to help simplify your purchasing decisions and save you time and money.

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