Metal Detecting Advice

How Do Metal Detectors Work?

12 Mins read

Whether you’re doing it for the sake of science, preserving history, or seeking monetary gains, there’s always something fascinating about metal detecting. If you’re new to the world of metal detecting or even the concept itself, then this is the tell-all resource that won’t leave any stone unturned.

Reasons Why People Go Metal Detecting

Metal detecting offers a variety of advantages and benefits that are more than just looking up rare and valuable items.

1.   You Can Make Some Quick Cash For Yourself

Arguably, the biggest reason people go metal detecting is to look for rare items to sell off to a pawn shop to make a quick buck for themselves. The best part about this is that the world is full of items that you never know what will be worth when you dig them up. This could be either a box of historic Spanish doubloons, a diamond ring that may have slipped off and was never found, or a rare relic that was left behind by its previous owner for whatever reason. The bottom line, anything you find with your detector is yours to keep (most of the time, unless the actual owner shows up that is).

2.   It Gives You a Pretty Good Workout

Now we’re not saying that metal detecting will give you a six-pack or compete for the Arnold Classic, but it does build character to a certain degree that will prevent you from seeing the world walk you by as you sit on your comfy chair and bed most of the time. Swinging a 3 lb-piece of equipment around constantly can be straining for one hand before you switch over to the next. Doing this for consecutive hours as you search for precious finds will result in your arms burning, and do you know what that means? It means you’re getting the workout.

3.   The Thrill of a Great Find Eliminates Stress

The act of constantly waving your metal detector back and forth and the beeping sound you hear whenever you pick something up is almost therapeutic to most detectorists. Having something to do and then accomplishing your goal in this manner pretty much takes away whatever stress we accumulate in our lives. To give the relaxation part more context, you can take your metal-detecting ventures out on the beach so that you can hunt for valuable items and relax at the same time.

4.   Learning About History

Let’s face it; learning about history from school was more of a drag than offering us any practical value. Fortunately, metal detecting does just that. The historical side of metal detecting can come off as a secret second hobby because of coin collecting. Collecting items related to the events that your history teacher drilled into your head can finally help you learn to appreciate the subject.

5.   Inspect Whether Food is Contaminated

Metal detectors can be used as an important tool for a variety of industries, including plastics, pharmaceuticals, mining, and food, among others. When it comes to food, detectors can help staff members perform checkups to see whether they have been contaminated with any metal from machinery.

6.   Security Scanning

Most public places, including airports or malls, use metal detectors to inspect passengers or shoppers. This works by having passengers or shoppers go through gantries that use alternating current and pulse detectors, while handheld detectors are used to scan purses, pockets, or wallets. Most detectors available these days don’t just pick up metal objects; they can also detect items of various materials.

7.   Fun Activity for the Family or Friends

Be it at a local club or an online forum for metal detectorists; there’s always going to be someone that you can connect to when it comes to metal detecting. Better yet, you can go out with other like-minded metal detectorists on a plant treasure hunt or just have a fun outing with your kids if you have any. This way, you won’t relish in the items you dig up all by yourself and come off more as a winner.

If you’re curious about the functioning of metal detecting itself or simply wish to know how it works, then we can help you out with that.

How do Metal Detectors Work?

Although the equipment has been around for a long time, most treasure hunters don’t know how a metal detector works. Well, the concept behind that is pretty simple, and it revolves around the principle of electromagnetism.

What is Electromagnetism?

As its name suggests, electromagnetism is a combination of both magnetism and electricity. What happens is that the electromagnetic force is carried off by electromagnetic fields that are made of magnetic fields and electric fields, which is also responsible for electromagnetic radiation like the lights in our houses.

To give you a more practical example, let’s start with an electromagnet. You can makeshift an electromagnet for yourself by taking a coil of wire and then wrapping it around a nail before hooking it up to a battery. Upon doing that, you’ll notice how intermingled electricity and magnetism can really be. In other words, if you find electricity, you’ll likely find magnetism as well.

As a matter of fact, most of society uses the concept of electromagnetism on an everyday basis. The most glaring example of this is the electrical appliances we use, which always rely on magnetism and electricity all the time. The electricity that powers those appliances comes from power plants and is produced by a generator, which one you look carefully, is a massive drum of copper wire.

Compared to that, the appliances in our house (be it the heating iron, washing machine, or vacuum cleaner) consist of an electric motor that works oppositely to a power generator. When electricity flows into these devices, it produces a changing magnetic field in a coiled wire that pushes against a permanent magnet’s field, allowing the motor to spin.

When it comes to metal detectors, the concept of electromagnetism varies depending on the type of metal detector that you have. Let’s take the example of how a VLF detector, which is the most common model used these days, uses electromagnetism.

How Electromagnetism is Used in a VLF Detector

Very low-frequency (VLF) metal detectors consist of two coils, including a transmitter and a receiver coil.

The transmitter coil (as its name suggests) ‘transmits’ a magnetic field around the metal detector. Electromagnetic current drives through the coil to generate an electromagnetic field. The current flow’s direction is reversed thousands of times each second; the detector’s transmit frequency, otherwise known as ‘operating frequency,’ is how many times the current flow ranges from clockwise to counterclockwise and vice versa every second.

When the metal detector moves over a particular metallic object, the magnetic field that moves around the device affects the metal atoms. This changes the way the electrons (small particles that orbit around the atoms) move. This develops a changing electric field, which establishes a changing magnetic field around the detector’s metal.

To put it simply, moving a metal detector near anything that’s metal results in a new magnetic field that surrounds the metal.

For this new magnetic field, the receiver coil comes into play. The receiver coil is the second coil of wire right around the metal detector’s head directly connected to its loudspeaker. When the receiver coil moves through the new magnetic field surrounding the metal, an electric current is produced in the coil. As a result, the loudspeaker connected to the receiver coil alerts users with a click or a beep.

The receiver wire needs to be arranged in a manner that it doesn’t end up getting affected by the transmitter coil’s magnetic field. If this isn’t done, any signal from the metal would be overwhelmed by the transmitter coil’s current.

An additional observation is that when you bring the detector closer to the target metal object, the stronger the magnetic field will become, resulting in a stronger click or beep.

What Types of Metal Does a VLF Detector Detect?

A VLF detector can pick up a variety of metals, including iron, gold, aluminum, and so on. But how is this possible? This is made possible because of a principle known as phase shifting.

Instead of going into more detail about what face shifting is, all you need to know is that a transmitter coil’s frequency is different from the one picked up by the receiver coil. That’s due to the varying electric resistance of a particular metal. That resistance can easily affect the flow of electricity through that metal.

When you know the resistance of a certain material and the phase shift, the detector lets users know what type of metal is underneath their searching area. This process is known as discrimination.

Most VLF detectors enable users to also filter out metals that they don’t want to be picked up by their devices. This can be done with a knob that allows us to configure a specific phase shift threshold. If there is a certain range you want your device to detect, you’ll find that most VLF models enable you to make notches (phase shift ranges) or also various notches.

Other Types of Metal Detectors

Although most detectors typically function in the same manner – converting electricity into magnetism and then vice versa – these devices come in three different types. We’ve already talked about the most common one, which is VLF detectors, as they use a fixed, single detecting frequency that ranges between 6 to 20 kilohertz (usually lower than 30 kilohertz). Another type of detector is one that uses pulse induction (PI) technology that is known for using pulsed signals and higher frequencies.

The third type of detector uses the beat frequency oscillator technology. This particular detector is the least complicated and most affordable option of them all. Although they’re not going to give you any accurate readings like the PI or VLF detectors, and won’t provide you with the same type of controls, they’re more than enough to get the job done for those who have recently been introduced to the world of metal detecting.

Pulse Induction Detector

A pulse induction detector can pick up objects that are deeper than those picked up by VLF devices. This detector makes looking for items on saltwater beaches relatively easier.

A pulse induction detector is especially preferred if you’re hunting for tiny gold nuggets or huge flakes. But besides that, it can also detect other kinds of precious metals, widening one’s earning range, if you’re seeking to profit from it.

This device works because it uses one coil as not only a transmitter but also a receiver. It sends electrical pulses into the ground, which produces a magnetic field. Pulse induction detectors typically send around 100 pulses per second. As soon the pulse impacts the targeted metal object, the field becomes reversed, allowing the detector to catch the signal.

If you’re going to be hunting in a high ground mineralized area, then it is highly pivotal you take a metal detector that uses pulse induction technology. Other areas where you’ll mostly come across magnetite hot rocks are also where a PI metal detector comes in handy.

BFO Detector

The beat frequency oscillation detector is the most basic detector out of all of them. It is mainly used by introductory detectorists or those who have recently gotten into metal detecting.

The BFO detector is used mostly in electronic stores. It can pick up items that are about 2 ft underground.

A detector that uses BFO technology comes with two wire coils. One coil that’s the largest of the two, is located in the detector’s search head, while the smaller one is inside the control box. Every coil is connected to an oscillator that produces thousands of current pulses in a second. The frequency in these pulses is slightly balanced between the two coils.

When the pulse goes through a coil, the latter produces radio waves. There’s a small receiver within the control box that picks those radio waves up and then creates a series of audible tones, which is based on the frequency differences.

If the search head coil goes over a metal item, the magnetic field created by the flowing current from the coil develops a magnetic field around the item. The magnetic field from the object causes an interference with the search head coil’s radio wave frequency. Once the frequency separates from the control box coil’s frequency, you’ll notice the audible beats alternate in tone and duration.

Most Important Features in a Metal Detector

Once you’ve decided to go metal detecting, you’ll obviously need a proper metal detector for the job. But before you go into a shop and buy the first one that catches your eye, there are certain essential factors that you need to keep in mind. The following characteristics are highly crucial successfully locating and digging out valuable or rate items:

1.   Discrimination

If you want to differentiate one target from the other, you must ensure that your metal detector features the ability to discriminate, otherwise known as discrimination. To put it simply, this characteristic lets you know whether your target is a piece of jewelry or a useless hunk of trash. Without this ability, it can be difficult to hunt for the item you have in mind, whether it be a relic, a coin, or jewelry. That’s because there’s plenty of material, metals, or even minerals to look into. Discrimination helps you save up time in digging out unnecessary finds or just plain garbage. Many detectors come with an auto adjustable feature or allow users to tune out garbage manually.

2.   Sensitivity

Many metal detectors that are on sale these days have been programmed to be highly sensitive. What this means is that a top-quality detector comes with a high operating frequency. This improves the metal detector’s ability to look for items under highly mineralized areas. It also allows users to pick up metal items that have been corroded upon being exposed to alternating weather conditions for a long time.

Operating frequencies normally range between 6.4 kilohertz to 20 kilohertz. Users can adjust the sensitivity controls based on the hunting area’s condition. We suggest using highly sensitive detectors to make the search process more comfortable and more rewarding.

3.   Ground Balance

This ability allows metal detectors to enhance their detection depth in mineralized grounds. The ground may consist of salts like those in when beaches or finer iron particles like those in the red earth. Much like the target item, minerals similarly respond to the detector’s transmitter field. Due to the ground’s much larger mass compared to the item you’re looking for underground, the mineralization effects can trick the detector’s tracking capability and prevent it from picking up small targets. Ground balance corrects this by removing the responding signals from the ground, allowing users to clearly hear their targets’ signals without letting ground noise distract them.

Ground balance is comprised of three types:

  1. Manual: users can manually adjust the ground balance setting to hear only a little ground signal.
  2. Automatic: the detector adjusts the ground balance automatically to the best setting. It’s a more convenient, quick solution and is usually more accurate than the manual setting.
  3. Tracking: while users track their designated item, the detector will constantly adjust its ground balance setting, ensuring that the setting always remains correct.

4.   Target Identification

Like the title suggests, this feature allows the detector to differentiate between coins like a dime or a penny, quarter, silver jewelry, a nickel, or junk/foil. When the detector picks up valuable items, it emits an audible high-pitched tone, while for junk items, it gives a low-grunt tone. This is more accurately known as tone identification. Target ID often offers a visual display that is seen on the LCD screen of a detector. Some numbers show on the screen, which you will eventually learn about, the more you use your metal detector.

5.   Coil Size and Shape

A coil’s shape and size greatly impact the amount of debt that emitted electromagnetic waves can reach. There are three kinds of coils, including spider, elliptical, and concentric. The coils vary in thickness, penetration ability, and depth. A coil’s penetration is also affected by the type of soil. This directly affects the detector’s work and its effectiveness in isolating a metal item’s position.

Who Invented The Metal Detector?

Many would argue that the concept of a metal detector was first brought up by James Maxwell, who came up with equations that explained their operation. Moreover, once electricity was invented, most scientists, scholars, and gold miners began to experiment with the concept of making a device that could help locate valuable buried items underground.  This was something that could help prospectors who were still on the hunt for gold after the end of the “gold rush” era, which would ultimately make them the first people to make a metal detector that made them very rich.

However, the first known invention capable of detecting metal dates back to the shooting of former US President James A. Garfield in July 1881. The president was shot in the back by Charles J. Guiteau, but the bullet wound hadn’t killed him at that point. The doctors tried to locate the position of the bullet, but couldn’t do anything about it.

It wasn’t until Alexander Graham Bell, a telephone pioneer and one of the President’s visitors during the time, built the first-ever metal detector to help Alexander locate the bullet within the President. Unfortunately, Bell’s attempts to save the President were in vain as the latter passed away later on due to an infection from his wound on September 19, 1881. Despite that, Bell’s version of the prototype would serve as a template for future metal detectors from that point on.

A German-based electronics engineer named Gerhard Fisher invented portable metal detectors while he was staying over in the United States. He would later apply for a patent on this concept in January 1933, which would later be known as the metalloscope, a device that would allow one to help them look for the presence of buried metals like pipes or something similar. During the same year, Fisher would later establish the Fisher Research Laboratory, which, interestingly, would become one of the leading metal detector manufacturers still to this day.

Later on, Dr.Charles L. Garrett, who founded Garrett Metal Detectors, would make the modern-day electronic detector in the early 1970s. After working for NASA, Garrett would focus his attention on amateur treasure hunting, which is where his company would then make a revolutionary innovation in the form of a computerized metal detector that included digital signal processing. This invention would be patented in 1987, and the rest is history.

Now that you are aware of how metal detectors work, what features you need to be mindful of before buying them, and how they came to be, we hope that we have created a newfound fascination within you regarding metal detecting as a whole.

About author
Hi, my name is Richard, I've been metal detecting for nearly 10 years now. I first got into it after running into an old friend on the beach who happened to be detecting (Mind he didn't actually find anything whilst I was there), it certainly got me curious. Since then it's been my biggest hobby so I decided to start this website and help other people get into it.
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