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Search Coils for Metal Detecting

A typical metal detector has four basic parts:

  • A stabilizer that maintains stability during sweeping
  • A control box
  • A shaftbetween the control box and the coil
  • The aforementioned search coil

The metal detector coil is the part that detects metal. It's also known as a search coil, and it comes in two primary types, each with its own particular strengths and weaknesses. But before we examine those, here's a quick lesson on how metal detectors work.

How Detectors Find Metal
A metal detector creates a current in its search coil that results in an electromagnetic field. This field extends to a depth that is about equal to the coil's diameter. When the field pulses back and forth in the ground, it is affected by conductive objects, i.e. metals. The magnetic field of the metal object travels as a small electric current through the coil, which amplifies its frequency and signals the control box. This frequency shift is audible to the detectorist, and the strength of the magnetic field reveals how deeply the object is buried.

GMD051

Types of Metal Detector Coils
Metal detectors generally feature one of three coil types: concentric, elliptical, or double D.

Concentric coils are the ones most commonly found in metal detectors. They're round and of varying thickness. Some concentric coils have a single hole in the center or a series of holes in a spider's web shape (thus the name "spider coils").

In general, concentric coils are considered better than elliptical coils at picking out which objects are worth investigating and pinpointing the location of those objects.

Because they're longer and narrower than their concentric counterparts, elliptical metal detector coils cover more ground in a single sweep. Their shape also gives elliptical coils greater detection depth.

Double D detector coils are so named because their transmitting and receiving coils are shaped like back-to-back Ds. Double Ds are round like concentric coils, and though they're not as capable of deep detection, they do cover more ground per sweep, which is why they're sometimes called widescan detector coils.

Concentric vs. Elliptical vs. Double D
So which coil type is best? The answer depends on what you're looking for. Separating the signals of small objects at relatively shallow depths is likely a job for a concentric coil. However, detectorists who have learned how to effectively use an elliptical coil may find it convenient for covering a lot of ground or uncovering treasures that were too deep for other detectors. Widescan detector coils, on the other hand, are very good at ignoring ground mineralization.


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