How does a metal detector work?

Measuring & Detection Tools

Metal detectors emit sounds to alert you to hidden treasures. Use headphones to be considerate to others and to keep your focus on what you find.

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The ins and outs of metal detection

When you picture a metal detector, you probably imagine a device that has a long shaft with something that looks like a small steering wheel attached to the bottom end. The user walks along the beach, moving the steering wheel end from side to side over the sand while listening through headphones.

Metal detectors have this peculiar shape for a reason. Once you learn how a metal detector works, you will understand why this shape is so important. You will also be able to quickly assess a metal detector’s general functionality from just a quick glance.

What is electromagnetism?

Before the 19th century, electricity and magnetism were considered two distinct forces. In 1905, however, Albert Einstein wrote a series of papers that changed how science viewed space, time, mass and energy. He established a theory that connected electricity and magnetism in his writings, revealing two aspects of the same phenomenon.

To understand how a metal detector works, we only need to understand two critical points of electromagnetism. 

  1. When electricity is applied to a coil, a magnetic field is created. 
  2. When a magnet is moved through a coil, voltage is generated. These are the two key principles on which the science of a metal detector is based.

How metal detectors work

The steering wheel shape at the bottom of a metal detector houses the unit’s coils: a search coil and a receiver coil. The search coil uses a current to create a magnetic field that extends into the ground to search for metal. The search coil also induces a small and precisely calibrated current in the receiver coil.

To keep the explanation simple, it can help to compare a metal detector to sonar. With sonar, a pulse of sound is emitted, hits an object and is reflected. However, with a metal detector, a magnetic pulse (not a sound wave) is emitted and is only reflected when it encounters a conductive target.

A more detailed explanation of metal detectors

Now that you have the basic idea of how a metal detector works, we can take a deeper dive to grasp what is going on when a metal detector detects metal.

When a conductive target is exposed to a magnetic field, it creates its magnetic field reflected to the metal detector’s receiver coil. This field, however, opposes the field already present in the receiver coil and causes the current to drop. The drop in current is measured by a sensor and can be used to approximate the type of metal that was detected.

The controls on a metal detector

Frequency

The frequency of a metal detector is essential in determining what you can find. Most hobby models operate in the 6-8 kilohertz range, which is suitable for all-around uses. However, some models range from 1-100 kHz.

In general, lower frequencies penetrate the ground more easily but are not suitable for small or low conductivity targets. Conversely, high frequencies may not penetrate the ground as deeply, but can pinpoint smaller items that a lower frequency model might miss. Because it’s more sensitive, there is a greater possibility of ground mineral interference.

Ground balance

Several elements in the ground, such as fine iron particles, may cause your metal detector to mask small targets. You can fine-tune a metal detector to ignore these smaller signals, making it easier to detect true treasures. Ground balance can either be done manually or automatically. Automatic continuous ground balancing produces the most accurate results.

Discrimination

A discrimination control allows the user to set parameters for when the metal detector will sound an alert. Using this feature can save time and increase efficiency by having your detector ignore non-valuable targets.

Factors that affect the range of a metal detector

While most models advertise a specific range, in reality, there are several factors that all work together to determine the range of your metal detector. In some instances, the range might be less than expected, but it may be greater than noted in others.

Coil size

The larger the coil size (the steering wheel-like object on the bottom of the metal detector), the deeper the magnetic waves will penetrate the ground.

Target material

Different metals have different levels of conductivity. For instance, silver is higher than gold. The higher the conductivity of a target, the deeper it can be found.

Best metal detectors

Garrett ACE 300 Metal Detector

Garrett ACE 300 Metal Detector

If you’re serious about your treasure hunting, this comprehensive kit from Garrett gives you everything you need. It’s a bit costly, but it offers a level of control and precision not found in lower-priced models.

Where to buy: Sold by Amazon

NATIONAL GEOGRAPHIC PRO Series Metal Detector

NATIONAL GEOGRAPHIC PRO Series Metal Detector

This model is perfect for the child who is interested in searching for buried items. It is lightweight, easy to operate and features a display that immediately lets you know what you’ve found: iron, aluminum, rings or coins.

Where to buy: Sold by Amazon

RM RICOMAX Professional Metal Detector

RM RICOMAX Professional Metal Detector

While this model might have a steeper learning curve, it also has many features typically found in higher-priced models. The shaft is adjustable, while the search coil is waterproof. The unit even has a notch mode to better target certain materials.

Where to buy: Sold by Amazon

Bounty Hunter Tracker IV Metal Detector

Bounty Hunter Tracker IV Metal Detector

Bounty Hunter is a popular brand of metal detectors that offers a balance of affordability and functionality. The detector allows you to distinguish between targets and unwanted metals, has a two-tone audio mode and the ground balance lets you focus on finding treasures instead of mineral content.

Where to buy: Sold by Amazon, Home Depot and Kohl’s

TACKLIFE Metal Detector

TACKLIFE Metal Detector

This affordable option is best for the casual user. The fun display quickly lets you know if you’ve found something of value based on the character’s expression.

Where to buy: Sold by Amazon

Allen Foster 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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