Metal Detectors

Metal Detectors

We often see metal detectors in movies about treasure hunting or documentaries about archaeology, and generally, we only know one thing about them: that they can detect metal objects even in the deepest part of the ground.

But, aside from that common knowledge, what else do we know about metal detectors?

Read on and discover more amazing facts about metal detectors--- how they work, what they are made of, and a whole lot more.

Metal Detectors in a Nutshell

Metal Detectors Nutshell

For starters, a metal detector is a portable device that can, well, detect any metal object that is buried in the ground. With its magnetic power that can penetrate an estimated maximum depth of 20-50 centimeters, metal detectors can find anything--- from bombs to coins, to scrap metal and copper--- just as long as they are metal.

Over the years, metal detectors have been very essential for people who want to dig up valuable finds, such as coins, jewelry, and other treasures of yesteryears. They are mostly used on soil, but they can also work their magic on wood, sand, and grounds that are non-metallic. For treasure hunters and archaeologists, a metal detector is like a reliable best friend on the field.

History of Metal Detectors

Metal detectors, just like other inventions, did not start the way they are now. Believe it or not, they were not created for treasure hunting and stuff.

Alexander Graham Bell and the bullet

Alexander Gramham Bell

The first metal detector ever to be invented was not used for treasure-hunting purposes. Instead, it was used in an attempt to save a life.

On July 2, 1881, then US President James Garfield was shot in at the Baltimore and Potomac Railroad Station in Washington, D.C. by a man named Charles Guiteau. The doctors could not find the bullet on his back, so he was not treated completely.

Then, a visiting Alexander Graham Bell created a metal detector just so they can find the bullet and, hopefully, save the President’s life as soon as possible. Fortunately, it worked as it detected metal objects. Unfortunately, these metal objects were just the springs in the President’s bed.

In the end, they were not able to locate the bullet and the President died of wound infection on September 19, 1881.

Bell and Beyond


Even though Alexander Graham Bell’s metal detector was not successful in saving the President’s life, it still paved the way for future creators of metal detectors, such as Gerhard Fisher, founder of Fisher Metal Detectors.

In 1925, Fisher’s metal detector was patented. It was the first portable metal detector to be made, and it was the result of a discovery that he had while working on navigational systems.

One day, he discovered that his radio beams were being distorted every time an ore bearing rock was in the area. He tried to work it out and solve the mystery, but then, he realized that this could be very essential in detecting other metal objects. Thus, the first portable metal detector was born--- and sold to the public in 1931.

After Fisher

Charles Garret

After Fisher’s discovery and success, better and much-improved metal detectors were created.

Charles Garrett, founder of Garrett Metal Detectors, built his own metal detector after a series of unsatisfactory encounters with metal detectors in the market. His own creation not only had the ability to eliminate oscillator drift, but it also had unique search coils which he had patented.

As the years passed, more improvements to the metal detector have been made. From transistors to discriminators, to wireless technology and new designs for search coils, metal detectors nowadays serve as examples of how times have changed… and how much had been made to create the perfect modern metal detector.

How Does It Work?

How Metal Detectors Work

We all know that metal detectors find buried coins or other treasures. But, how do they exactly do that?

Here’s how:

  1. The electricity of the metal detector is passed by the transmitter circuit (which is activated by the battery on top of the metal detector) to the transmitter coil at the bottom of the device.
  2. Once the electricity is flowing through the transmitter coil, a magnetic field is automatically created around it.
  3. Once the metal detector is swiped on a buried metal object, the magnetic field automatically comes in contact with it. As a result, the magnetic field creates an electric current flow inside that certain metal object.
  4. This electric current flow generates another magnetic field around the metal object. As a result, the magnetic field goes through the receiver coil up to the receiver circuit, which will then alert the user about the metal object by beeping or buzzing.

Who Uses Them?

When we hear the term “metal detectors,” we usually associate it with buried treasure or archaeology. In the modern world, metal detectors are now being used by other people, too.

Here are all the people who make use of metal detectors:



Professionals in the field of science, especially archaeologists and geologists, use metal detectors in digging out metal artifacts, as well as metal components which can be found in soil and rocks.



Hobbyists--- people who collect interesting stuff and are on an endless chase for cool things--- also turn to metal detectors for their treasure adventures. Some of the people who belong to this group are those who search for gold, collect coins or relics (such as antique weapons), and hunt buried treasure.

Security Personnel

security personnel

Nowadays, it is easy to spot a security guard with a light metal detector in his hand. Malls and other big establishments, like airports and banks, now use metal detectors to sense possible threat, such as bombs, knives and other metal objects that could harm people.

Types of Metal Detectors

All metal detectors have one purpose (to sense metal objects, of course), but they actually have different types:

Very Low Frequency (VLF)

VLF Metal Detectors

The VLF metal detector is the most common type among users. It emits a very low-frequency magnetic field to detect metal objects--- even those covered in dirt. VLF metal detectors have two round coils (transmitter and receiver) and an electronic circuit that filters the signal coming from the receiver coil, so you can modify the signals for a more precise search result.

Pulse Induction (PI)

PI Metal Detectors

This type of metal detector is commonly used by treasure hunters, while larger versions of this are usually seen in buildings with security checkpoints. PI detectors are more specialized than VLF detectors. They use only one coil (which emits a magnetic field to the ground), then with its timed pulse method, a PI detector can quickly filter stray signals from the sent signals. This advanced mechanism makes the PI detector more accurate, but more expensive, too.

Beat Frequency Oscillation (BFO)

bfo metal detectors

A BFO metal detector is considered the cheapest and most simple type, which is usually great for beginners. Same as the VLF detector, this kind uses two detector coils--- this time with an oscillator that creates a continuous signal, which will be emitted by one of the wire coils. BFO detectors, however, are prone to inconsistency and inaccuracy due to its mechanism, which lacks filtering and fine-tuning.