How Does a Metal Detector Work?


Metal detecting is used by different professionals and hobbyists for various purposes. The process can help in finding hidden metal objects, gold, coins, and jewelry below the ground’s surface. A metal detector is the main tool used for that purpose. The good part is that you do not even need to know how a metal detector works to use it correctly.

The real simple answer is the metal detector transmits an electromagnetic field from the search coil at the end into the ground, and any metal objects, gold, coins, or jewelry within that field will send a tone or a signal back to the detector. That tone sent back will have its own unique properties depending on what kind of metal it is.

Most people that use a metal detector just have a very basic knowledge of how it works. It is not necessary to know the mechanics of the device if you want to be a successful operator, however, a better understanding can help you to master the skills and achieve maximal results. That’s why you should definitely continue reading.

Who Can Use a Metal Detector?

The simple answer is virtually anyone can pick up one and within a short time frame can learn how to use it and find hidden objects below the ground. Metal detecting is an activity performed by military and law enforcement. For example, they usually use metal detectors to discover mines and bombs hidden below the ground. Also, they might search for any other potentially dangerous item or material in the same way. A metal detector is also a popular tool of various archeologists who use it to find historically important artifacts and items that stay below the ground.

Also, many adventurers and hobbyists use the tool on beaches, yards, and parks in search of lost people’s valuable items, such as gold, pieces of jewelry, and coins for example. These people should have basic skills about this tool in order to operate it successfully. Metal detecting is, fortunately, simple to learn and master so virtually anyone can gain those skills. Still, very few of those people really know the details and inner workings of the device.

Development of Metal Detectors Throughout History

The development of metal detectors started at the end of the 19th century by different engineers and scientists. They began using their expanding knowledge about electrical theory trying to create a device with the capabilities of locating and discovering metal items. The intention was to support the miners who searched for ore-bearing rocks in different areas in the country. The scientists wanted to accelerate the exploration of various areas and maximize the results with an efficient tool of that kind.

First metal detectors were pretty basic and not so ideal. They used a lot of energy so very few batteries could support their work in a normal way. That’s one of the reasons why these devices worked in a limited range.

Gustave Trouve was one of the first inventors of a metal detector. In 1874, he achieved success by producing a handheld machine for detecting and locating metal items in human bodies. This tool was mostly used to discover bullets in the bodies of patients who were wounded.

Alexander Graham Bell was inspired by the success of this inventor so he created a similar device attempting to detect similar things and improve the medicine capabilities of that time. James A Garfield, an American president, was the first patient who was subjected to the investigation with that newly developed device. The bullet was detected in his chest, and the machine worked properly. However, it was not possible to complete the operation by locating the bullet precisely because the device was confused by the metal construction of a bed that the president used during the exploration.

These were some of the first devices of this kind, however, further, development continued throughout the 20th century. Gerhard Fisher, for example, created a device based on radio-direction exploration in 1920. The machine was extremely successful and the most powerful metal detector ever made. However, the inventor noticed particular anomalies at locations with ore-bearing rocks.

Fisher concluded that it would be achievable to develop a device with abilities to detect metal objects utilizing a search coil echoing a radio frequency if metal distorted a radio beam. The development of this product was lasting for several years and Fisher applied for the registration of a first metal detector patent of this type.

The application was accepted by the responsible authorities, and the inventor became the first scientist with a granted patent of that type. However, Shirl Herr was the first engineer who applied for the metal detector patent almost one year earlier than Fisher. Still, his application waited for more than four years to get accepted by the authorities and that happened in July 1928.

Shirl Herr was an assistant of Italian Prime Minister Benito Mussolini in discovering metal artifacts and items remaining from the period of Emperor Caligula. The exploration took place at the bottom of Lake Nemi in Italy in 1929.

Herr’s device had, however, quite a wider purpose, and it was used by various investigation expeditions during the early 20th century. Admiral Richard Byrd was, for example, one of them. He used the machine during the Second Antarctic Expedition that occurred in 1933. The main intention was to discover items and objects lost by previous expeditors in the area. Herr’s machine was efficient at a depth of 8 feet.

It was clear the detector is a very practical and useful tool that could be used for various explorations. The military noticed the capabilities of the machine so they started using it as a mine detector on the battlefield. Lieutenant Jozef Stanislaw Kosacki was the first one who performed such a task with the Herr’s detector and from then on the Polish army used the device for that purpose.

However, the device still needed some modifications and improvements that happened later on. For example, the detector units were pretty heavy so they took a lot of energy during the operations. They also needed a lot of battery power so separate packs were a necessity in order to work continuously.

The further development of metal detectors has continued to this very day, and at a moment, there are pretty efficient models on the market. They have excellent specifications and provide great results. It is good to expect the development of these devices will proceed further and each new model will be stronger than the current ones.

How Detectors Work

These devices have the capability to transmit an electromagnetic field directly into the ground. The metal objects then become energized, and they start creating and retransmitting their own small electromagnetic fields. The search coil receives the impulses of retransmitted signal, and that’s the moment when it sends a notification to the user in a form of a specific sound or tone. Metal detectors have different kinds of settings and features so they might locate only some specific items developed of some particular type of metal while avoiding all others.

That’s a very suitable option because it gives a researcher a chance to focus on valuable discoveries only. The ground is always full of trash, so it is good to ignore such objects, but ignoring the trash can also lead to not finding something valuable. For example old pull tabs are in the same tone range as a gold ring, so if you do not ‘dig for trash’ you could be passing up a gold ring.

Metal detectors are composed of several important parts and each of those components has some specific purpose.

The Control Box is, for example, the place where the electronics are housed. This part of the detector is responsible for transmitting the signal to potential objects and receive a signal from those targets in a form of response. That means it is the brain of the device in charge of the main part of work.

The Search Coil has the purpose of sending the electromagnetic field to the ground and catch the field of a targeted object. This part of the metal detector acts as a helping component of the control box.

The Target is any metal object that might be a potential find depending on a researcher’s selection. People usually want to discover valuable items so you may want to limit your search to maximize efficiency and save your time.

Unwanted Targets are normally considered to be ferrous objects, which just means they are attracted to magnets.  These are normally things like nails, but there are items that are non-ferrous that are attracted to magnets like bottle caps.

The Receive Electromagnetic Field is technically not part of the metal detector, but it is the signal that is sent back by the item, thus giving you a tone once it reaches the control box.

The detector’s frequency is one of the most important aspects when it comes to determining the efficiency of the device. It is usually a rule that high frequency is more sensitive to small objects while the low frequency is far better for discovering big objects hidden in the ground.

Different metal detectors might use different frequency technologies and it depends on the producer’s choice. There are, however, some new and advanced models that transmit multiple frequencies at once so they may successfully discover all types of targets regardless of their sizes and other related aspects.

Important Features and Settings

Ground Balance is also one of the important features that every good metal detector possesses. As you know, there are different kinds of grounds and some of those might be overly mineralized by various nature influences. For example, such a ground can contain a lot of salts like wet beach sand or red earth. These minerals are, however, not very helpful when it comes to metal detecting because they can mask and hide various small objects and a metal detector would be unable to locate them in those conditions.

Fortunately, the Ground Balance feature gives you the possibility to correct this issue by removing the ground signals. When you do this, the interference stops, and the metal detector can fully focus exclusively on the targets. The settings might be different depending on a particular model you currently use, and there are generally three types of Ground Balance.

Manual Ground Balance is the first one, and it gives you a chance to set-up that option manually. It is an efficient type that maximally reduces the sound of mineral soil.

Automatic Ground Balance provides an option to perform the same task automatically. That’s definitely a hassle-free procedure so it is quicker and more accurate than the manual settings.

Tracking Ground Balance is the third type on the list, and it gives a possibility to the device to adjust appropriate settings in accordance with the ground’s conditions. It means the researcher does not need to do anything for themselves because the detector is capable of resolving a potential issue on its own.

One thing to keep in mind about ground balancing your metal detector, normally, but not always, you have to do a ground balance every time you turn your metal detector on.  Also when you move to a different type of ground it is best to ground balance again.  For example, if you are at a park and you move from the sand around the playground to the grass in the park it is best to ground balance in the new area, or moving from the grass to a beach, you will need to run a ground balance again.

Discrimination is also a very useful feature that helps you improve the performance and get the best results. The ground may contain a lot of potential targets, however, some might be totally unusable for the purpose. This feature exists to help you avoid unwanted targets by setting appropriate adjustments. It is necessary to mention, there are four types of discrimination, and they are explained better further in the text.

Variable Discrimination is the first one, and it is the easiest sort of discrimination that allows you to use a control knob to make appropriate adjustments.

Iron Mask is the second type, and it is usually used by detectors that search for gold. The feature gives them an opportunity to avoid the iron trash from the ground.

Notch Discrimination third on the list, and it serves to allow or reject a potential target based on their characteristics.

Smartfind is the last discrimination type, and it is the most advanced sort of all four different types. The feature provides a visualization of targets on a small display so it is far easier to make the right selection during detection.

Different Types of Metal Detectors

Of course, it is necessary to understand not all metal detectors have the same features and capabilities. That’s because there are different types of metal detectors, and the newest models are typically the most efficient and best. Some of those sorts are very common on the market, while others might appear as a real rarity. Very low frequency, multi-frequency, and pulse induction metal detectors are the three most common types today.

Very low-frequency metal detectors are good when it comes to detecting bigger targets in the ground. They might have a display where the objects are visualized, but it depends on the particular model you use. These detectors are usually affordable, easy to use, lightweight, and with a strong battery.

Multi-frequency detectors are even better. They can successfully discover both large and small objects so they are definitely a better solution when it comes to professional use.

Pulse induction metal detectors are, however, the best on the list. They can also successfully identify targets of various sizes and are totally immune to ground mineralization. They allow deep detection and that’s why they are excellent for gold hunting.

So as you can see, you can fairly easily use your metal detector without really knowing all the details of how it actually works.  At the same time, some of the higher-end metal detectors have many different features and settings that can be used and adjusted to fine-tune your searches.

It is always best to read through your manual for the metal detector that you are using to get familiar with its specific settings.  Then practice, practice, practice.  Once you have dug about 100 targets out of the ground you should be at a point where you are very familiar and comfortable with your particular metal detector, its settings, and tones.

Jason Smith

Former Marine, IT Guy & Builder of Websites.  I have 5 US states left to visit. I enjoy hot springs, adventures, hiking, photography, sci-fi, wine, coffee & whiskey.  I am fluent in sarcasm, name that tune, & speak in movie quotes.  I spend most of my time building websites, fixing computers, metal detecting, magnet fishing, and gaming occasionally.

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