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What is a Metal Detector?

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  • Written By: Michael Pollick
  • Edited By: L. S. Wynn
  • Last Modified Date: 02 November 2016
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A metal detector is a portable electronic device that penetrates the ground magnetically in order to find traces of metal. This metal could either be discarded pieces of aluminum or valuable coins, jewelry, or other buried treasures. Part of the appeal of using the device is this unknown factor, keeping amateurs and professionals on a constant scan for new sources of metal and more promising locations. These tools can usually penetrate sand, soil, wood, and other non-metallic substances, making most areas fair game for treasure hunters.

A basic metal detector consists of an electronic box and battery case on one end, with a brace or handle for the operator's arm. An insulated wire wraps around a telescoping shaft and into a round plastic disk called the coil. This disk comes off the shaft at an angle, which allows it to be held parallel to the ground. The operator straps on or grips the electronic box and turns on the power. The idea is to slowly sweep the coil end over the ground until an electronic signal is heard. This lets the user know that some metallic element is buried directly beneath the area swept by the coil.

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Some devices can discriminate between various metals, allowing users to decide if a particular discovery would be worth digging up. A significant percentage of hits are indeed pieces of metallic trash or discarded building materials. Part of the appeal of this hobby, however, is discovering a lost class ring or a piece connected with local history. Some professional treasure hunters use very discriminating detectors set only for valuable metals, but hobbyists tend to explore even the less lucrative hits.

Metal detectors work on the principle of electromagnetics and their effects on conductive metals. There are actually two separate elements in the coil of a typical unit. The first is a high-powered coil of metal called the transmitter that uses the battery power to generate a penetrating magnetic field. As the elecromagnetic field enters the ground, anything metallic will become magnetized, similar to how a paper clip reacts after it comes into contact with a standard bar magnet.

The coil also contains a very sensitive wire array called the receiver. This receiver reacts to any charged magnetic field it passes over, especially the newly-magnetized metal elements. When the receiver detects the electromagnetic signature, it sends a signal to the electronic box. A speaker amplifies this signal and the operator hears a beep.

Microprocessors located in the electronic box can actually measure the time between the charging and the receiving (called a phase shift) and determine which metals may be present. This is how high-end metal detectors can be adjusted to only search for certain metals. The phase shifts of all other metallic elements are electronically squelched by the microprocessing unit.

These devices must also be adjusted to eliminate false positives generated by natural deposits of metal in the soil or sand itself. Most units allow users to change the sensitivity of the coil in order to cancel out the background clutter. Metal detecting technology is also used for security inspections at airports, government buildings, and other public places. Construction crews and woodworkers also use hand-held metal detectors to find dangerous nails or other metallic debris in reclaimed building materials and trees.

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TreeMan
Post 5

I like all of the different ways that metal detectors can be used outside of hobbyists searching for stuff on the beach.

I went on a tour of a local sawmill a while back for a group I was with, and they had a large metal detector that they ran every tree through before it got cut.

As trees grow near old fences or something, they can slowly start to wrap around the metal. When the trees are cut down, sometimes you can't see the metal that is inside of them. There is the same problem with people putting nails in trees for things like deer stands.

As you would expect, a big saw blade hitting one of these pieces of metal could cause a lot of damage to the machinery and the workers, so the logs go through a metal detector, and they cut around the metal before the final tree is processed.

cardsfan27
Post 4

I thought it was really interesting reading about how the whole metal detecting system works. I have never used one but have seen them at work. I always just suspected that the rings sent out a wave of electricity or something and that when the waves got disrupted it set off the metal detector. I guess it is a similar system, but it works a little differently than I thought.

I was also unaware that you could set the thing to pick up different types of metals. It seems like that would be helpful for some people.

I have always thought about buying a metal detector, and this article makes me more interested in it. Does anyone know how much a decent metal detector costs and what some good brands are?

JimmyT
Post 3

@jmc88 - I'm with you. I've never really found much from my metal detector. It can still be fun hunting around for stuff, though. I remember when I first got mine that I searched around my yard and found a big chunk of steel underground. I still don't have any idea what it was or why it was there. I ended up taking it down to the scrap yard with a bunch of other stuff one time and got a couple dollars for it, so that was good.

I have an uncle that lives in Virginia near the site of an old Civil War skirmish. Since the site isn't protected, he is able to take anything there that he finds

. He says has gone out several times and found old musket balls. I think he's found a few other small metal things that he guesses probably came from the people during the war. Nothing is really worth that much money, but it makes and interesting collection and a good story.
jmc88
Post 2

This was very interesting, especially for someone who has done metal detecting before and has always wondered how one worked.

I have never had very much success with metal detectors, though. My friend has one, and we used to go down on the shores by the river near where we live and look for stuff in the sandy areas. We always figured there would be some interesting things that would wash up there, but we never found anything.

I think about the only thing we found worth any money was an antique glass pop bottle with a metal cap. Everything else we found were just either old tin cans or pieces of scrap metal.

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