Learn How Metal Detectors Work - Science, History and Use in Modern Times
By Michael and Daniel Bernzweig
Over the years, one of the most asked questions we receive is, how does a metal detector work? A metal detector is a device that detects the presence of metal nearby. Metal detectors are useful for finding metallic objects that could be dangerous, like weapons--or valuable, such as scrap metal or buried coins.
Metal detectors consist of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field; if the circuit is interrupted by any conductive object, however small, some of the alternating currents will flow through it and magnetize it slightly.
In this article, we'll look at the real-life applications for metal detectors and how they work. Additionally, we'll explore how metal detectors are used for multiple purposes and what makes a unit more or less appropriate for each application. For a revised version of how metal detectors work, check out our more recent post on the topic.
How Do Metal Detectors Work?
Alexander Graham Bell was the inventor of the metal detector, which was designed to find a bullet that had struck US President James Garfield during an assassination attempt. Though this early model wasn't nearly as advanced as modern metal detectors, In general, metal detectors are now used to detect buried metals just under the surface, or even deeper than 65 feet below the surface, even underwater!
Metal detectors function by sending an electromagnetic wave into the ground via the search coil. Any metal items (targets) within the electromagnetic field will become energized and emit their own electromagnetic signal.
All metal detectors work on the principle that metal has different magnetic properties than the surrounding ground and other substances around it. Current is sent down a wire coil to produce an electromagnetic field.
When something made of metal passes through this field, its unique atomic structure causes the current to either speed up or slow down and emit changes in the magnetic flux lines, which give rise to detectable electrical signals that indicate there is a piece of metal nearby. Metal Detector Systems can identify all forms of metal. There are three basic types: Ferrous metal (magnetic), Non-Ferrous metal (non-magnetic), and Stainless Steel.
The strength of these signals changes as the object moves closer to or further from the coil because their elemental makeup can be used to determine how far away they are and where exactly they are located.
What Are the Parts of a Metal Detector?
The control panel contains all the knobs and switches necessary to make the detector work. The coil, which consists of loops of wire, is the part that emits the electromagnetic field that detects metal objects.
The main parts of a metal detector are the sensor, the control, the signal processor, and the output device.
A circuit called an oscillator produces high-frequency AC power that feeds into the transmitting coil when it's switched on. The circuitry connected to the receiving coil converts this signal back into audio form to hear where things are in your path.
The Search Coil
The sensor of a metal detector is usually composed of a transmitter coil, which emits the electromagnetic field that detects metal objects. The sensor is attached to the control unit, including all of the knobs and switches necessary to make the detector work. The receiver coil in a metal detector is located very close (inches) to the transmitter coil. The receiver coil will receive the induced voltage of the same frequency as the transmitted signal.
The metal detector's sensor is usually contained in plastic and is a small disc plate that emits an electromagnetic field into the ground that varies according to the conductivity of any object it encounters. At your end of the detector, another small disc detects this field and sends its variations to the circuitry inside the detector's control unit.
When you switch on a metal detector, it first emits a high-pitched tone to tell you it's working and then transmits a magnetic field for a few seconds. The receiver coil's function is to detect the magnetic field and, utilizing the same method as before in reverse, generates a current through a circuit, which produces a speaker on a basic metal detector. If something metal is in your path, the detector detects this and emits another audible signal.
The Control Unit
The control unit is connected to the input jack of your detector. It directs the electromagnetic field emitted from the transmitter coil and sends it to the receiving coil inside your metal detector.
Some units have meter displays with LEDs, LCDs, bars, or numbers that tell you how strong a detected object's field is. Those units are more expensive, but they are beneficial for finding metals on different types of ground where their signal strength can vary greatly.
There are also some specialty machines on the market today that are designed to find specific types of metals, such as gold nuggets or lost coins in the sand on the beachfront property where there are no mineralized soils. These detectors contain sensors for specialized purposes and can be outfitted with coils dedicated to particular purposes, so they will only respond to the frequencies associated with the type of search being done.
Metal detectors and the concept of metal detection have many uses outside security and safety applications. They're great for helping hobbyists find many cool things, especially to help keep kids entertained by going on metal detecting hunts for lost coins and other hidden treasures. Geologists and archeologists also use them to locate artifacts or buried treasure deep underground, as well as for military purposes.
The Signal Processor
The signal processor is the most important part of a metal detector. This is the unit that actually sends out a signal, analyzes it, and returns a result to the machine's readout. The metal detector itself only detects the presence or absence of metal, so this processor has to decide what kind of metals are being detected from their electrical conductivity.
The Output Device
An output device is usually a meter or LCD display that shows what is found by the metal detector. This device is usually incorporated into an apparatus that shows what is found by the metal detector. As an example, the output device can be as simple as a speaker for an audio alert, or it can be more sophisticated and even have visual aids such as LCDs and meters that are built into metal detectors.
What Can Metal Detectors Be Used For?
Metal detectors are used in many environments and for many different reasons. A metal detector can be used as a simple tool to detect the presence of metal like nails and pull tabs in a yard, or it can be part of a high-tech security system that detects weapons and contraband. They can even be used to detect a metal contaminant in food processing plants. Another application for metal detectors is finding underground utilities, such as pipes and cables.
Metal detectors can be used in many different fields to find hidden metallic objects such as tools, scrap metal, copper wire, weapons, and ammunition. Metal detectors can also be used to check if items are made from valuable metals such as silver or gold.
Metal detectors can also tell the difference between different types of metals to distinguish between valuable targets and undesirable metal objects like iron trash. They do this using a multi-frequency system that sends out different frequencies (frequently referred to as "tones") in rapid succession through the coil.
When the target is made of one type of metal, it will speed up, slow down or emit no change at all compared with other objects in the surrounding environment, depending on its makeup. This means that by listening for distinct tones coming from inside the coil, you see whether there's something worth picking up or just junk to be discarded.
What Substances Can't Be Detected by a Metal Detector?
Metal detectors have a hard time detecting metals with such low electrical conductivity as stainless steel. As stainless steel has a low magnetic permeability, it does not produce a strong signal to be easily detected, making it a poor conductor. In contrast, other metals like silver, gold, and platinum are much more conductive and are much easier to detect than other metals.
Materials that a metal detector can't detect include:
● Gemstones
● Paper
● Pearls
● Bones
● Stone figures
These items can't be detected because they do not contain a large enough percentage of conductive material.
How Do You Use a Metal Detector for Beach Hunting?
You can use a metal detector to search for metals both in the water and on land, depending on the type of metal detector you have. The methods used to find precious items on the beach are more advanced, and some metal detectors are superior to others when it comes to beach metal detecting.
The best metal detector for beaches or deeper treasure hunting will be those that use PI technology. Metal detectors with very low frequencies operate underwater and on wet surfaces, but mineralized ground circuit deterioration is more severe.
The PI detector (Pulse Indication) metal detector's sampling circuit is set to monitor the length of the reflected pulse. By comparing expected and actual lengths, the circuit can determine what metal the pi metal detector's search coil is approaching. The most important thing when beach hunting with a metal detector is understanding how your machine works and where to look for treasure. Gold nuggets can be found at extraordinary depths with the pulse Induction detector due to its ability to ignore the toughest ground mineral conditions. Metal detectorists who are more serious about their hobby will want to consider a PI metal detector. With a PI gold metal detector, you can search much deeper in the ground than with a VLF. The advantage of this is that the gold can be located even if it is buried deeper in the ground. In addition to this, pulse detectors are capable of handling more challenging ground conditions as well. This can make it more fun for you as you are learning to metal detect.
Due to the vastness of a beach, there are many beaches across the world where you can search for these hidden treasures, as a beach is such a huge place. When it comes to beach hunting, it is ideal to use all-terrain gear that gives you stability and grip in loose sand, which is one of the best places to start. It is also important to choose the right device for the job to achieve the best results. As a matter of fact, having fun on the beach comes down to knowing what you are going to encounter out there, so make sure you read up on any local finds before heading out onto the beach.
How Do You Use a Metal Detector to Find Coins & Jewelry?
Metal detectors can find many different things such as coins, gold jewelry, and even lost tools. However, each type of item requires a slightly different technique for finding it.
To find coins with a metal detector, you should do some research on the types of coins that are commonly found in your area so that you know what kind of metals they're composed of and roughly how old they might be.
For example, older coins will most likely not contain silver and instead will be made up of copper and nickel or bronze alloys which produce weaker signals than sterling silver. Charles Garrett, the creator of Garrett Metal Detectors, was a major player in developing today's metal detectors. Product reviews of the Top-Performing Garrett ACE metal detectors prove they have a variety of applications. Most models typically have a powerful performance when hunting for coins, jewelry, and artifacts.
You need to take into account the conductivity of the ground where you might be searching because if it is highly conductive (i.e., wet sand), then iron objects may be mistaken for silver, and the older the coin is, the more it will resemble iron or some other conductive material.
For jewelry items such as pearls that aren't too deep in the ground, carefully check areas of high-mineralization where objects can become stuck quite easily. Also, avoid searching over saltwater because this will interfere with the ability of your metal detector to get accurate readings.
Deep Seeking 2 Box Metal Detectors
Metal detectors for deep seeking need to be able to distinguish between treasures buried several feet under the surface and items lying on top of the ground. Choose the best metal detector that you can afford when it comes to picking out a deep-searching, 2-box metal detector that will allow you to conduct deep searches. Your financial commitment can provide a great return. Depending on the unit that you're looking for, you might be able to get it for around $1,000.
These detectors are much more expensive than their more shallow-seeking counterparts. Price ranges from around $1000 for a decent model up to several thousand dollars for a top model with 3D capabilities. A general all-purpose metal detector with a regular or small search coil won't cut it if you want to search for larger, deep treasures. You need a deep-seeking metal detector for finding gold veins and deeply buried containers. It is possible for a treasure cache to be located as deep as three to four feet or even deeper. The types of detectors and search coils that are made specifically for this purpose will only be able to detect large objects and offer the greatest depth of detection possible.
For deep seeking, you'll need a metal detector with the ability to identify or discriminate targets precisely and at great depth. Consequently, it ignores small pieces of foil and small unwanted targets in favor of large deep precious metal treasures. In many of these models, a color display or iPhone or Android device shows the targets in real time. Some detectors have several different search modes, so you might want to try the various settings to see which one yields the best results for your particular location.
Gold Prospecting Metal Detectors
You should ensure that if you plan to operate a high-end metal detector for gold prospecting, treasure hunting, or gold detecting, it offers manual ground balance as well as adjustable discrimination settings so you can eliminate the troublesome sources of interference from ground minerals. It is through the use of such features that you will be able to obtain more accurate readings when it comes to finding valuable finds, such as gold nuggets or large veins of gold buried in the ground.
To search for gold with a gold metal detector, you'll need to be able to distinguish between gold and other metals. For this reason, you should set the discrimination low on your metal detector to focus on signals from small gold nuggets. This will also help filter out any trash items you come across, so you don't have to dig them up.
There are two superior types of gold detector types: very low frequency or VLF metal detector and pulse induction (PI). VLF detector models are designed to find gold and have a higher operating frequency than other models to detect smaller golden nuggets.
Nokta Makro is one example of an ideal metal detector brand to use for gold detecting. Nokta Makro is a global leader in metal detecting technology and innovation, providing the finest metal detectors for the pursuit of coin, relic gold, and hunting.
Using Metal Detectors for Relic Hunting
For metal detectorists interested in relic hunting, you should set the discrimination on your metal detector low to identify iron and steel objects which may be valuable relics like civil war bullets, buckles, buttons, or other military weapons. This will allow you to find more of the type of relics that are valuable to your particular site of interest. The Teknetics T2 and the XP DEUS are top choices for relic hunting.
Due to the low conductivity of most relics, detectors with frequencies below 10 kHz are required to detect them. It is important to invest in a variety of search coils when looking for relics that are deeper or larger. The larger the coil, the more ground it covers and the deeper it goes. With the smaller coils, you will be able to isolate trash targets on top of trash near foundations and trash targets within areas that are cluttered with trash.
When searching for coins with a metal detector, you should use the Custom Mode to determine which setting will help you eliminate trash targets while still detecting gold and, unfortunately, aluminum foil, which is usually how people find gold targets and copper coins when they are using metal detectors. If you learn more about what your model has to offer and what settings work best in given areas, you will be able to make the most of your experience with a metal detector.
Using Metal Detectors for Underwater Hobby
Metal detectors that work underwater are divided into two categories: pulse induction (PI) metal detectors and exceptionally low frequency (VLF) metal detectors. Underwater operation of pulse induction metal detectors is achieved by sending signals in the form of electric current pulses into the ground. It is important to understand how to deal with the minerals you will find on the beach when hunting. You must deal with salt water and so-called "hot rocks" at the beach. In the presence of salt water, normal ground minerals are amplified, causing many land-based detectors to produce false signals and chatter.
If you are trying to have fun in the water and you are just trying to have a good time, this can be downright annoying. In order to deal with this problem, there are two ways to go about it. You may want to consider a Very Low Frequency (VLF) metal detector that can be adjusted to the ground if you are on a budget. You can tune your detector based on the level of mineralization on the beach by using the ground balance feature. It is common for entry level metal detectors to feature a preset ground adjustment feature. It is true that these units are good for most conditions on dry land, but they will prove to be frustrating to use while at the beach in most conditions. At the beach, you will have a much better chance of finding treasure with a metal detector that has a VLF circuit and a ground adjust control.
The best beach units use Pulse Induction (PI) circuitry if your budget is not limited. Electronic pulses are transmitted to the ground by a pulse induction metal detector. Salt sand and ground minerals do not affect these electronic currents, but precious metals do. For salt water beaches and diving, a pulse detector is best. For tough ground mineral conditions, the Pulse circuit is great. If you want to find as many precious items as possible, you will need to dig more trash items in order to compensate for the limited discrimination capabilities of the PI circuit. A pulse induction metal detector is recommended to be used either in freshwater or in seawater, depending on the situation. As they are able to see right through the tough saltwater minerals, they are the best option to make use of when dealing with saltwater. Due to their ease of use, pulse induction metal detectors are excellent choices for a treasure hunter and recreational users, even if the user is not an experienced underwater hobbyist.
Using Metal Detectors for Crime Scene Investigation
A major part of the investigation of a crime scene is the detection of metal. In some cases, detectives may be required to know what types of metals are present at the scene of an accident or break-in in order to collect samples for further analysis. It may even be necessary for them to isolate specific sections of a crime scene by looking for smaller pieces of metal, such as bullet fragments or knives, that had not been thrown as far as other pieces of metal.
Metal detectors allow investigators to narrow down the search area quickly and focus their attention on more relevant information. With ground penetrating radar detectors, law enforcement professionals can detect foreign objects buried beneath the surface without disturbing any evidence above it.
As a crime scene investigator, it can be very useful to detect metals underwater as part of the investigation in many ways. In the course of their search for metal fragments in human remains, detectives are likely to use VLF detectors in their search. There is a strong possibility that the victim was tied to weights or otherwise bound with metal before he or she was thrown into the water; therefore, finding this hardware under the water could be a tremendous help to investigators in finding the place where the body was.
Using a Security Walk Through Metal Detector
There are a number of reasons why organizations use security metal detectors in their schools, airports, and other facilities for a variety of purposes. The reason that these devices are used differs from one organization to another, but most organizations use them to prevent weapons and other types of metal from being brought on to an area that could be dangerous. The security personnel may also use them to search visitors to a particular area who are wishing to visit the area. Detectors can also be used in warehouse facilities to prevent items from being stolen by using them as a stop loss system.
Several types of metal detectors are available for use in security walk-throughs. In addition to the standard walk-through metal detector, there are also advanced imaging technology devices, which can be used for random checks or restricted areas, as well as portable/handheld devices that can be used for random checks. Additionally, handheld models can also be used to locate items that may need to be checked manually, not only for searching people who wish to enter an area but also for searching objects that may need to be checked manually.
As a general screening device, you can think of the walk-thru detector as a type of general screening device. Once you have identified that a person has a concealed item, you will need to be able to pinpoint exactly where the item is located. With the help of a metal detector wand, you will be able to locate the target in a matter of seconds. It is important to note that security wands will alert you to the target either using an audible tone, a target identification light, vibrations, or a combination of all three. To use the walk-through gate, a metal detector wand is a required accessory.
Metal Detectors for Marine Search & Recovery
To locate metallic objects in the ocean, metal detectors are used for marine search and recovery. One of the most popular types of detectors is a metal detector or magnetometer. All metal detectors are designed to be able to detect metal at a reasonable depth regardless of the metal. Iron and steel can be found at depths of more than 200 meters using magnetometers, which are used to search for them.
The accuracy of magnetometers is known to reach depths of up to 50 meters, while the accuracy of metal detectors is best at shallower depths. When used together, they can provide a little more depth and coverage. Metal detectors can also be mounted on ROVs while magnetometers can be towed behind them. As the magnetometer is set to max out at lower depths than the metal detector, it will not detect metallic targets such as gold or silver rings, which the metal detector would detect.
The use of handheld metal detectors for marine search and recovery is another popular option for marine salvage. For quick retrieval of gold, silver, and other metallic finds on the ocean floor or river bed, they are typically used with dredge pumps. When a metal detector finds an object, a dredge pump is often pre-programmed to move over the area, saving valuable time.
Metal detectors can also be helpful for removing debris from ports and harbors, as well as for determining the materials used in underwater structures submerged in oceans or rivers. There are many types of metal detectors available, so it is important to do some research before purchasing one for marine search and recovery.
Frequently Asked Questions
Here is a list of some of the most frequently asked questions about metal detectors, how they work, and which models are most commonly used.
How Does a Metal Detector Coil Work?
A coil is one of the most important components of a metal detector since it allows the user to detect and recover metallic items that are hidden under the ground, such as gold and other treasures, lost jewelry, and valuable coins that are hidden underground.
A metal detector uses an electromagnetic induction device called a search coil to detect metallic objects. A search coil is that part of the device that is responsible for creating the electromagnetic field that induces an eddy current in any metal object that passes through it, such as coins or gold, in the presence of the electromagnetic field.
How Does a Phone Metal Detector Work?
An iPhone or Android metal detector app uses the same technology that is used to drive your smartphone's compass, which is able to detect and measure the strength of magnetic fields around it. By sensing the presence of certain metals, your phone is able to identify certain metals.
A smartphone metal detector app uses the magnetic field around your phone. It can identify when something metallic changes that field after taking a baseline measurement from the sensitivity setting you pick.
How Does a Walk-Through Metal Detector Work?
A walk-through metal detector is a device that is used as a security measure to detect weapons or other items made from metal that might cause damage to people or property if they were handled.
A walk-through metal detector works by creating a stationary magnetic field with the use of electric coils, which are disrupted by the magnetic fields produced by objects passing through the scanners as they pass through it. Alarms are triggered as a result of this disruption.
How Far Down Does a Metal Detector Work?
Metal detectors can usually detect coin-sized objects about 4 - 12 + inches (10-25 cm) deep. A mid-range deep-seeking metal detector can achieve a detection depth of up to 12-18 feet (30-45 cm) underground in ideal circumstances. Some expert devices may reach 65 feet (20 meters).
Does a Metal Detector Work Underwater?
The majority of metal detectors are designed to work on land only. In spite of this, there are ways that divers can search for metal underwater using metal detectors specifically designed for this purpose. It is important to note that these fully sealed waterproof metal detector models are pressure rated to specific depths. As well as being able to filter out minerals in salt water conditions, they can also be equipped with specialized circuitry for that purpose.
Underwater metal detectors with pulse induction technology send electronic pulses that are unaffected by water and wet minerals. They transmit rapid electrical impulses that are sensitive to precious metals, allowing them to detect through wet or mineralized soil.
These PI models are very common for underwater metal detectors. Electrical pulses are sent out in pulse induction technology. Detectable electromagnetic fields are generated by this rapid pulse. As the device approaches buried metal, the field is disturbed, and the detector registers the change in signal strength. These models are the best designed for tough mineralized saltwater conditions.
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