How Do Metal Detectors Work – Simple Explanation

The ability of metal detectors to detect metal buried several inches or feet beneath the ground is a remarkable achievement in modern science. 

For years, these simple devices have been used for cultural explorations, high-level security, and treasure hunting. 

But have you ever wondered – how does a metal detector work? What helps them discover metals that are situated so deep?

Here we’ll discuss how metal detectors work, what types are available, how you can use them, and more. 

How Do Metal Detectors Work – Electromagnetism

To understand how metal detectors can find valuable buried treasure, you need to understand the physics behind all this. 

Metal detectors work by following the simple law of electromagnetism. 

Electromagnetism and its use in metal detectors is very simple; let’s take a look. 

Electromagnetism is a combination of electricity and magnetism. To create electricity inside a basic generator, a drum of copper wire spins through a magnetic field. 

The electricity generated inside the wire is a result of the presence of a magnetic field. 

Electric motors follow a similar process; however, their parts function in a reverse cycle.

Based on the above examples, you can say that electricity can make magnetism, and magnetism can be used to create electricity. Both variables are closely linked to each other.

The presence of both variables together is termed as ‘electromagnetism’. 

How Does A Metal Detector Detect Metal?

The first-ever metal detector was created in the year 1874 by Gustave Trouve. It was a handheld detector with limited abilities. 

Later, Alexander Graham Bell invented his own version when trying to detect a bullet lodged in the 20th President of the United States, James A. Garfield.

Many inventors have tried to create their versions of metal detectors. However, Gerhard Fischer, the founder of Fisher Labs, was the one to acquire the patent for the first metal detector.

Today countless machines and devices can find metal quickly. Let’s understand how they work and what it is that locates the metal.

In metal detectors, electromagnetism is the foundation of the entire metal hunting process. Its magnetic abilities guide the machine and help it reach closer to the target. 

The construction of a metal detector is designed to facilitate the transfer of these electric and magnetic signals. 

Wires are wound in the form of a coil and wrapped around the circular coil, which is attached to the end of the handle. 

This part is known as the ‘Transmitter coil’. It creates a magnetic field around it when electricity is passed through.

When the metal detector is moved around, its magnetic field moves around with it too.

As the machine is moved over a metal object, its magnetic field impacts the atoms present in the metal buried underground. 

The machine’s magnetic field changes the way electrons move in the piece of metal while orbiting around the atoms. 

According to James Maxwell, If a piece of metal has a changing magnetic field, it will also have a moving electric current. Furthermore, this moving current can create magnetism. 

James Clerk Maxwell

This leads us to the idea that a detector can create electrical activity in the metal object to some extent. 

Therefore, when you move a metal detecting device over a metal object, the magnetic field created by the detector causes a second magnetic field to be created around the metal.

So when you hear a metal detector beep on detecting an object, it’s the second magnetic field that the machine reacts to. 

There is another wired coil in the head i.e. receiver coil. It connects to the main circuit where the loudspeaker is located. 

When the detector is moved over a piece of metal, the metal buried underground creates a magnetic field that passes through the coil.

As this piece of metal is moved through a magnetic field, the electricity passes through it the same way as the generator works. 

This electricity passes through the receiver coil and reaches the circuit which then triggers the loudspeaker to create a sound. 

When the detector’s transmitter coil is moved nearer to the piece of metal, a stronger magnetic field is created in it. 

This strong magnetic field results in the increase of current flowing through the receiver to the circuit. 

Due to this excessive current flow, the speaker makes a louder noise to signal the target is near.

Make sure the wire connecting the receiver coil does not interfere with the transmitter’s magnetic field. 

How Do Metal Detectors Differentiate Between Metals?

Electromagnetism helps machines find metal; however, other components and controlling mechanisms open up new possibilities. 

Read on to learn how metal detectors can differentiate between metals. 

There are metal detectors on the market today that can distinguish between aluminum, iron, gold, and more. A principle called phase shifting is responsible for this ability. 

Metals have varying electric resistance that affects their ability to conduct electricity and let it flow through them. 

It determines the parity between the frequency conveyed by a transmitter coil and the one detected by the receiver coil. 

As the current and magnetic response from the target varies based on its composition.

The amount of phase shift created due to this response enables the machine to identify the target. 

This process is known as discrimination. 

You can use discrimination to eliminate the type of objects that you don’t want to find. To make this adjustment, you have to turn the knob to a specific phase shift threshold. 

Some metal detectors come with notches that make the phase shift range more specific. 

You can choose to create a single notch or multiple notches. 

Apart from electromagnetism and the basic characteristics, other things can impact a detector’s metal hunting abilities.

Here are the different components that control a metal detector:

• Control Unit: The control unit is the second most important part of a prospecting device. It houses the batteries, loudspeaker, processor, and other things that contribute to its performance.

• Shaft: The shaft is responsible for making the machine easier to use. Most of the devices come with long shafts, so the detectorists doesn’t have to bend when using them. Some devices also come with adjustable shafts.

• Search Head: The search head is the place where you plug the machine’s search coil. Normally, search heads are oval-shaped, while other variants include an antenna, a search coil, or a loop. 

• Stabilizer: Since metal detectors have to be swayed to and fro while being used, they can get out of control and slip off. Therefore, most detecting devices come with stabilizers. They are attached to the top of the device. 

This keeps the detector steady and gives you full control over the motion. 

In addition to these essential components, metal detectors come with a headphone jack and a display panel for convenience. 

The Different Types Of Metal Detectors

Detectors are available in different types. The most commonly used are Very Low Frequency Detectors (VLF) and Pulse Induction (PI) detectors. 

VLF detectors

The detectors are equipped with two coils that assist in detecting a target. They each have different functions, as one coil sends electricity while another one receives it. 

The sender coil creates a magnetic field that reacts with the metal object buried.

Once a target is located, the magnetic field creates a current, which is received by the receiver coil and amplified. 

This amplified signal reaches the circuit and triggers the speakers. 

Some VLF detectors have a Target ID display. The display interprets the signal into a series of numbers normally ranging between 0-99. The numbers indicate the signal strength. 

Owing to the information provided for the target, most metal detector manufacturers prefer sticking to VLF technology. 

In this entire process, the most important role is played by the control box.

It gives you a better understanding of the target by interpreting the signal along with audio and video cues to help you find it. 

If you have an advanced metal detector on your hands, you might come across more advanced features such as discrimination, target depth indicator, sensitivity adjustment, and more. 

Pulse Induction (PI)

Pulse Induction metal detectors differ greatly from VLF detectors. They have a single coil that works both as a transmitter and receiver. 

With PI detectors, current pulses are passed through a single wire to create the magnetic field. 

If this pulse is switched off, the magnetic field created by the device collapses and causes a short-lived electricity surge. 

When there is a metal object nearby, the sampling circuit detects the magnetic field lying in the opposite direction. 

The device detects reflected pulse from the object that takes longer to fade away. 

Pulse Induction detectors are quite impressive for depth reach and the amount of sensitivity required for finding gold. 

However, there are a few drawbacks to using PI detectors. 

Not all PI machines can ignore trash items such as iron which makes them unsuitable for use in urban areas.

Their discrimination ability is inferior compared to VLF detectors. 

Due to their deeper reach, they make excellent options for metal hunting in rural areas.

PI detectors work great in terrains with high mineralization or conductive materials such as beaches and hot rock plains. 

Beat-Frequency Oscillator (BFO)

BFOs are the most affordable and easy-to-use detectors. Since they have a basic construction, their accuracy is not the same as PI or VLF detectors. 

They don’t give the same amount of control. 

There are two coils in a BFO detector. The large coil is in the search head, and a smaller coil is placed in the control box. 

Both coils are connected to an oscillator that can generate thousands of pulses containing electrical current every second. 

The frequency is slightly offset between the pulses passed through both coils and creating radio waves in the process. There is a small receiver in the control box. 

It picks the radio waves to create a series of audible tones. The number of beats in the tone differs based on the frequency detected by the device. 

If a metal object comes within the range of the coil, the current passing through the coil that generates a magnetic field will also create a magnetic field around the object. 

The object’s magnetic field comes in contact with the radio wave frequencies created by the search-head coil. 

The number of beats and tones produced inside the control box changes as the proximity of both frequencies changes. 

Besides these metal detectors, some variants are used for industrial, commercial, and other hunts. 

Most of these detectors come with a three coil design which allows them to locate even the finest metal buried below. 

How Deep Can Metal Detectors Detect?

Considering that there are numerous metal detectors available in the market, it can be hard to come up with an exact answer to the question. 

There are many factors to be considered when determining the maximum depth of a detector. 

Here are some of them:

• The shape, size, and type of the buried metal item. Detectors can find bigger objects easily. Metal detectors do not detect objects that are made of non-metal materials such as gemstones, plastic, and glass. 

• The position of the object can make a difference too. Valuables that are buried in a flat position make a bigger target area. Therefore, sending the signal back to the detector becomes more effective. 

• Things buried for a long time can be difficult to find. When old objects are buried for a long time, they tend to rust and oxidize, losing their metallic properties and conductivity. 

• The composition of soil around the target.

• The detector device and the frequency it uses to locate objects. 

Generally, metal detectors have an average maximum depth reach of around 8-20 inches.

How Do You Use A Metal Detector For Beginners?

Metal detectors made for beginners are typically simple to use and have fewer features than advanced devices. 

If you’re using a metal detector for the first time, you can follow the tips mentioned below. 

Know And Understand The Settings

Whether you are handling a detector for the first time or using a basic metal detector for a while,  take time to understand the settings and the machine. 

Some entry-level metal detectors tend to come with multiple features and settings that can make your hunt quick and effortless.

Take the metal detector for a demo hunt in your backyard and try using features like discrimination, sensitivity, detection modes, ground balance, and more.

Prepare Your Kit

A detector device is not the only item you need to carry to a hunt. There are other things you need to do like digging the ground, getting the exact location of the object, and protecting your gear. 

• Gloves: Because you’ll be digging in the dirt, it is helpful to wear gloves that are rigid and suitable for digging. 

• Headphones: Most metal detectors have extremely powerful speakers capable of generating quite loud sounds. If you are planning to prospect in a public place, you will need headphones compatible with your detector. This will help you keep the sound down and also hunt with more precision. 

• Digging tools: When retrieving a target, you will need digging tools like a shovel, sand scoop, and Lesche digger to make sure you recover the target safely. 

• Coil Covers: Entry-level detectors do not come with waterproof coils. If these coils are submerged in water or are exposed to water, they can be damaged beyond repair. 

Choose A Hunting Area

When choosing a hunting area, you need to make sure that there are no restrictions for digging up treasure in that particular area. 

If you wish to go metal hunting in a normally out of bounds place, you can try applying for permission with the necessary authorities. 

Some common areas include beaches, parks, and woodlands. These areas don’t require special permissions for hunting. 

You can look for the best-hunting sites on the internet or by getting a detailed map of the city. 

These are the essential points that you need to keep in mind.

Among other things, you need to stay safe, be persistent and patient, and most importantly refrain from breaking any laws. 

Are Metal Detectors Expensive?

Not all metal detectors have to be expensive; some of them are quite affordable and simple. 

Entry-level detectors are becoming very sophisticated these days, but to understand how to make the best use of a metal detector, you will need a basic one. 

The best basic detectors offer a great deal of features and can be highly effective in hunting valuables. 

Frequently Asked Questions

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