A metal detector is a tool that is used to detect the presence of metal not too far away. There are several types of metal detectors, and they are used for different purposes.
Some are installed in the entrance of public institutions like banks and schools. They are meant to prevent criminals from coming in with weapons like handguns and knives.
Some metal detectors are installed on the ground, and they scan people as they walk across. It is for the same purpose. To prevent people from passing through with metallic objects.
This type can be seen in airports. They are also used in drug manufacturing and food production processes. They are meant to scan for the presence of metals. The most common type is the one used by metal hunters. They are used to find relics, coins, and treasures buried in the ground. These metal detectors are used by metal detectorists.
If you are among the people that always ask – How do metal detectors work, here are all you should know about how metal detectors work.
Main types of metal detectors:
While there are numerous brands and models of metal detectors, there are only three types of the device, and they are Beat-Frequency Oscillation (BFO), Very Low Frequency (VLF), and Pulse Induction (PI) metal detectors.
Beat-Frequency Oscillation is commonly used in stores, and the type of detectors in this category can detect metal about 2 feet underground.
Very Low-Frequency detectors are mostly used by treasure hunters because they can detect metals very deep down the earth. They also allow users to narrow down their search to only gold and silver. The three types have been discussed in details below.
1) Major parts of a metal detector
Regardless of the type, brand, and model of a metal detector, all-metal detectors have certain major parts:
- Search coil: This is also known as the search head. It is the part at the base of a metal detector that senses the presence of any of the targets. On detecting the presence of a metal, it will send a signal to the control box.
- Control box: This part is made of the microprocessor, batteries, speaker, controls, and the circuitry.
- Shaft: This is the adjustable rod that connects the control box to the search coil.
- Stabilizer: You don’t have to use this component. It is meant to keep your metal detector steady as you move the search coil back and forth in search of targets.
- Headphone Jack: This component is self-explanatory. However, not all metal detectors have a headphone jack.
2) Very Low-Frequency Metal Detectors
This type of metal detector is the most popular. It is known for having two distinct coils which are the receiver coil and the transmitter coil. The transmitter coil transmits the signal received too by the receiver coil to the control box for processing. The receiver coil picks up signals from the detected metal.
3) Phase Shifting
Phase shifting is the phenomenon used by VLF metal detectors to differentiate some detected metals from others. Remember, with some detectors, you can refine your search to a particular kind of metal through the settings.
Phase shifting is the difference between the frequency of the detected metal and the frequency of the transmitter coil.
Different metals have different phase shifts. For example, small nails and soda cans (both of them are worthless) have their different phase shifts, and hunters can filter them out so that the detector will not make a sound when it senses their presence.
Imagine how annoying and frustrating it can be, to dig for several minutes only to discover that the detected metal is just a small rusted nail.
4) Pulse Induction Metal Detectors
These metal detectors are not so popular. However, they are equally valid. While VLF detectors have two coils (receiver and transmitter), this one has just a single coil that works together as receiver and transmitter.
According to pulse induction technology, it sends short bursts of current, known as pulses through the coil of wire. Every pulse generates a brief magnetic field, and the field reverses when the pulse ends, thereby resulting in a very sharp electrical spike.
PI metal detectors send up to 100 pulses per second on the average. Once the device detects a metal, it sends a pulse that will create an opposite magnetic field in the object.
This magnetic field makes the pulses longer. Longer pulses are the major signal that there is metal around and its magnetic field is causing the pulses longer.
5) Beat-Frequency Oscillator Metal Detectors
Although these detectors are also useful, they don’t offer the level of precision and accuracy offered by both Pulse Induction and Very Low-Frequency Metal Detectors.
These detectors have two large coils – one in the search head and the other in the control box. Both coils are connected to an oscillator. This oscillator generates several thousands of pulses of current per second.
The coil generates radio waves as the pulses travel through it. A receiver in the control box creates audible tones (known as beats) based on the difference between the frequencies.
If metal is detected, a magnetic field is created around the detected object, and the magnetic field will interfere with the frequency of the radio waves that are being generated by the search coil.
6) Factors that affect detection of metals
Once there is a difference between the frequency of the waves generated by the search coil and that of the frequency of the coil in the control box, audible sounds will be generated to alert the user.
- How easy or hard it is to detect some metals depends on the following factors.
- Interference from other objects like power lines, cables, and pipes. If they are above the metal, it will be difficult to detect the metal.
- Soil composition also matters. Some soil types have a lot of minerals that are natural conductors. These minerals will interfere with metal detection.
- Larger metallic objects are often easier to detect than smaller ones.
- Type of metal also matters. Metals like iron create stronger magnetic fields than many other metals.
- Type of metal detector is the biggest determinant. Some detectors operate at a higher frequency than others.
7) 4 basic types of metal hunting
Metal detectorists carry out four basic types of metal hunting, and they are:
- Treasure Hunting – This is the act of searching for treasures rumored or thought to have been lost or buried somewhere.
- Relic Hunting – This is the search for significant metals like the ones that have historical value. A good example is weapons used in any war fought in the United States.
- Prospecting: This the process of wild-searching for gold or any other valuable metals.
- Coin Shooting: This is the act of searching for different types of coins or a particular kind of coin.
Now when people ask you – how do metal detectors work? You should be able to explain to them in details. When planning to buy a metal detector, it is better to consider what you intend to do with it before purchasing yours. It will guide you on the type of metal detector to buy. Don’t always base your choice at the lowest price.
It could be the wrong one for you. There is no point buying a product you won’t use no matter how cheap it may be. Finally, it is a good idea to go for the ones manufactured by a reputable brand like Garrett.