How Does a Metal Detector Work?

How Does A Metal Detector Work

Different professionals and hobbyists use metal detecting for various purposes. The process can help find 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.

A metal detector emits a low-frequency electromagnetic field and detects the disturbance caused by metal objects within that field. When a metal object is brought close to the search coil of a metal detector, it creates a disturbance in the electromagnetic field, which is detected by the metal detector and indicated through an audio signal or a visual indication on the display screen.

Most metal detectors have a control panel or display screen that allows the user to adjust the detector’s sensitivity and select the type of metal they are searching for. Some metal detectors also have a ground balance feature that helps to eliminate false signals caused by minerals in the ground.

Overall, a metal detector works by emitting an electromagnetic field and detecting the disturbance caused by metal objects within that field, allowing the user to locate metal objects that may be buried or hidden.

Most people using a metal detector have a basic knowledge of how it works. It is not necessary to know the device’s mechanics 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 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, jewelry, and coins. These people should have basic skills in this tool 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 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 with different engineers and scientists. They began using their expanding electrical theory knowledge to create a device capable of locating and discovering metal items.

The intention was to support the miners who searched for ore-bearing rocks in different areas of the country. The scientists wanted to accelerate the exploration of various areas and maximize the results with an efficient tool.

The first metal detectors were pretty basic and not so ideal. They used a lot of energy, so very few batteries could support their work normally. 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 successfully produced a handheld machine for detecting and locating metal items in human bodies. This tool was mostly used to discover bullets in wounded patients’ bodies.

The success of this inventor inspired Alexander Graham Bell, so he created a similar device attempting to detect similar things and improve the medical capabilities of that time. James A Garfield, an American president, was the first patient subjected to the investigation with that newly developed device.

The bullet was detected in his chest, and the machine worked properly. However, it was impossible 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 lasted for several years, and Fisher applied for the registration of the first metal detector patent of this type.

The responsible authorities accepted the application, and the inventor became the first scientist with a granted patent. 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, which 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 occurred at the bottom of Lake Nemi in Italy in 1929.

Herr’s device had, however, quite a wider purpose, and various investigation expeditions used it 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.

Clearly, the detector is a very practical and useful tool that could be used for various explorations. The military noticed the machine’s capabilities, so they used it as a mine detector on the battlefield. Lieutenant Jozef Stanislaw Kosacki was the first to perform 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 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 to work continuously.

The further development of metal detectors has continued to this day, and at the 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 that each new model will be stronger than the current ones.

How Detectors Work

These devices can transmit an electromagnetic field directly into the ground. The metal objects become energized, creating and retransmitting their small electromagnetic fields.

The search coil receives the impulses of retransmitted signal, which is when it sends a notification to the user in the form of a specific sound or tone. Metal detectors have different 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 only allows a researcher to focus on valuable discoveries. 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 pass up a gold ring.

Metal detectors have several important parts, each of which has a specific purpose.

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

The Search Coil aims to send the electromagnetic field to the ground and catch the field of a targeted object. This metal detector part is 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 time.

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

The Receive Electromagnetic Field is technically not part of the metal detector, but the signal 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 determining the device’s efficiency. It is usually a rule that high frequency is more sensitive to small objects, while low frequency is far better for discovering big objects hidden in the ground.

Different metal detectors might use different frequency technologies depending on the producer’s choice. However, some new and advanced models transmit multiple frequencies simultaneously, so they may successfully discover all 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, some of which might be overly mineralized by various natural influences.

For example, the ground can contain a lot of salt, 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. A metal detector would be unable to locate them in those conditions.

Fortunately, the Ground Balance feature allows you 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 differ depending on the particular model you currently use, and there are generally three types of Ground Balance.

Manual Ground Balance is the first one, allowing you 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 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, allowing the device to adjust appropriate settings following the ground’s conditions. It means the researcher does not need to do anything for themselves because the detector can resolve a potential issue independently.

One thing to keep in mind about ground balancing your metal detector, is 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 useful feature that helps you improve your performance and get the best results. The ground may contain a lot of potential targets. However, some might be 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 allows them to avoid the iron trash from the ground.

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

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

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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. Today’s three most common types are low-frequency, multi-frequency, and pulse-induction metal detectors.

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 your particular model. These detectors are usually affordable, easy to use, lightweight, and with a strong battery.

Multi-frequency detectors are even better. They can successfully discover large and small objects, making them a better solution for professional use.

Pulse induction metal detectors are, however, the best on the list. They can also successfully identify targets of various sizes and are 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 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 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 its tones.

Chapter 6 – How To Use a Metal Detector

Go here to read our Beginners Guide To Metal Detecting.

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