If you’re new to metal detecting and don’t yet grasp how it works, one idea you might have is that metal detectors have magnets that attract the metals buried underground as you search. This theory is a good guess but not quite correct.
Metal detectors do not have magnets in them. Metal detectors have inductor coils that use electromagnetic induction to interact with metallic objects and materials underground, so they use magnetism but do not have natural magnets.
In this article, I’ll explain how metal detectors use a form of magnetism called electromagnetic induction to detect metallic materials underground. Let’s get started.
How Electromagnetic Induction Works in Metal Detectors
Metal detectors don’t have natural magnets in them that attract metallic objects. Instead, they use the powers of electricity and magnetism together, called electromagnetism. In the 1860s, physicist James Clerk Maxwell declared that when there’s a changing electric field, so follows a changing magnetic field, and vice versa. Basically, electricity and magnetism are two parts of one whole: electromagnetism.
Metal detectors don’t just use magnetism; they use electromagnetism. Therefore, they don’t have natural magnets but one or multiple inductor coils. This coil (or coils) of wire is at the head of the handle. When some electricity goes through the coil from the metal detector, it creates a magnetic field around the coil.
At this point, when you swing your metal detector, you are essentially swinging around a magnetic field. Electricity goes through the coil initially thanks to the battery or batteries powering your metal detector.
When this magnetic field moves across a metal, it will interact with the atoms inside it, altering the electrons’ movements. This creates electric currents. As mentioned above, one of James Clerk Maxwell’s rules was that when there’s a changing electric field, a changing magnetic field follows.
Therefore, when you alter the electrical movement within a piece of metal by waving a magnetic field over it, the metal creates a magnetic field of its own. The interaction between the two magnetic fields generates yet another current, an opposite current, which goes through the receiver coil.
The receiver coil is a second wire on the metal detector’s head. This coil is connected to a circuit that has a loudspeaker inside. This loudspeaker will make some sort of noise every time the electricity goes through the receiver coil, every time the electromagnetism process explained above occurs or when you wave the metal detector over a piece of metal.
The signal will come through the speaker if you don’t have headphones. However, I always recommend metal detecting with a good pair of headphones because they block out excess noise, which makes the tones easier to hear and interpret. Using headphones also helps your metal detector batteries last longer.
Electromagnetism is an effective way to metal detect and find treasures, but it doesn’t always work. Sometimes the metal objects are buried too deep for the magnetic fields to interact with each other and trigger an electrical response. Other items are so old and oxidized that they’re more difficult for the metal detector to sense.
Finally, some metals are low electricity conductors, making them more difficult to find. These famously include stainless steel and titanium. I’ve compiled a comprehensive list of metals that metal detectors won’t find: 4 Metals that Metal Detectors Won’t Detect
For this reason, most metal detectors can’t sense objects buried more than twenty inches (50 centimeters) underground, and most can’t reach depths even close to that. The average Very Low Frequency (VLF) detector can only reach eight inches underground.
In conclusion, metal detectors rely on electromagnetism to work, not natural magnets themselves. Metal detectors do not have magnets but use magnetism’s powers to operate.
Parts of a Metal Detector
Many people find that knowing the different metal detector parts helps them understand how the electromagnetic process works and better prepares them for using a detector when starting out. Let’s take a look at the parts of an average metal detector:
- Control box. The control box is the part of the detector that holds all the electronic parts of the detector, including the circuitry, batteries, and controls. Not all metal detector control boxes are waterproof, so be careful if you are metal detecting when it rains.
- Coil. The coil is the most important part of the metal detector because it is the part that searches for the metal in the ground using electromagnetism. Larger coils can find objects buried deeper in the ground than smaller coils, but smaller coils are better at discrimination. If your coil is bad, you won’t be able to find anything underground or be successful in your metal detecting endeavors.
- Shaft. The shaft connects the coil to the control box. The shaft is usually adjustable, so you can alter the detector to your height to make it more comfortable.
- Grip. The grip is where the user holds the metal detector while using it. A good grip allows the user to keep the detector nice and steady as they swing it around.
Understanding the various parts of a metal detector helps enhance your knowledge of how the metal detector works. The most important thing is to protect the electronic components in the control boxes to keep your metal detector working as it should.
Types of Metal Detectors
Another aspect of understanding how metal detectors work is knowledge of the different types of metal detectors. There are two primary types of metal detectors you should know about:
Very Low Frequency (VLF)
You’ll probably get a VLF detector if you’re a metal detecting hobbyist. These are the most affordable and widely available metal detectors. They contain an inductor and receiver coil, which interact with metallic objects in the ground and communicate with one another to alert the user when there’s metal nearby.
VLF detectors effectively find coins, relics, and other items that metal detector hobbyists seek. If you’re curious about the most profitable metal detector finds, check out my full list: 12 Most Valuable Metal Detector Finds
Pulse Induction (PI) Detectors
The main difference between PI detectors and VLF detectors is that instead of having two coils, PI detectors only have one coil. The one-coil design is more effective in mineralized ground than VLF detectors, so many people who metal detect on beaches or underwater prefer PI detectors over VLF. However, this additional effectiveness usually comes with a higher price tag, so they aren’t as affordable as VLF models.
However, the downside to PI detectors is that they aren’t as good at discrimination. Therefore, if you primarily search in areas with lots of trash, I don’t recommend using a PI detector because you’ll get lots of chatter and alerts for undesirable items. Then, you’ll spend more time digging up trash than digging for the objects you want to find.
Another category of metal detectors is prospecting metal detectors, specifically designed to find gold. These detectors have a higher frequency range.
Conclusion
Metal detectors do not have full magnets but rely on electromagnetism to sense metallic objects buried underground. When electricity travels through the inductor coil, it creates a magnetic field that interacts with the magnetic field around metallic objects, which triggers a current through the receiver coil. The receiver coil then triggers the loudspeaker, alerting the user that something metallic is underneath.
