The searchcoil is a vital part of your metal detector. It is the fl at, typically circular disk, which generates a magnetic fi eld and senses metallic targets in the surrounding environment. It is located at the end of the stem and is connected to the control housing via a cable normally wound around the stem. The size and depth of the magnetic fi eld is determined by the shape and size of the searchcoil. Understanding the purposes behind the various sizes and shapes of searchcoils will empower you with the ability to choose the best searchcoil for each application
Searchcoils generally consist of two internal sets of coiled wires, a Transmit Coil (TX) and a Receive Coil (RX). Mono coils can be diff erent in that one coil acts as both the TX and the RX. When the detector is turned on, the TX coil generates a magnetic fi eld in the surrounding space. When a metallic object is within this generated magnetic fi eld, it will create a distortion in the magnetic fi eld. The RX coil will sense this distortion and send a signal to the control housing. A searchcoil’s detection pattern is determined by the combination of the TX’s generated fi eld pattern and the RX’s sensing fi eld pattern.
Because the magnetic fi eld of a small searchcoil is concentrated within a small volume, it is the best choice for hunting in areas with a lot of metal debris. This allows you to maneuver through and around trash to locate good targets, especially when searching in tight places where large searchcoils cannot go. In addition, because of their concentrated detection fi eld, small searchcoils are the best for detecting very small objects. However, a small searchcoil provides less coverage per sweep; more scans will be required to cover a search area.
For general-purpose hunting, which typically includes coins and coin-sized targets, a medium sized searchcoil (8 – 9″) is the best choice. Because a medium sized searchcoil provides the best combination of magnetic fi eld concentration, detection depth and capability to detect the greatest range of target sizes within the detection area, it is standard with most detectors. In addition, it’s lightweight and easy to maneuver.
Large searchcoils generate wider and deeper magnetic fi elds than small coils and consequently provide greater depth and coverage. This means that scanning a search area requires fewer sweeps with a large searchcoil than with a smaller coil. This larger scan area, however, can become a problem in trashy areas where the searchcoil is detecting several targets at once.
In addition to searchcoil sizes and shapes, there are also a variety of searchcoil confi gurations available, with each proving to be the best choice depending on hunting applications and ground conditions. The confi guration of
a searchcoil refers to the arrangement of the TX and RX coils within the searchcoil shell. There are basically fi ve confi gurations: Concentric, Mono, Imaging, Double-D and 2-box.
Concentric The concentric confi guration consists of a TX coil and RX coil which are usually circular and arranged as shown at left. The advantage of this confi guration is that both the TX and RX coils are wound as large as possible within a given searchcoil diameter. This provides the largest possible detection fi eld and greatest detection depth, making the concentric coil potentially the most sensitive confi guration available.
A mono-coil is available only on Pulse Induction detectors and is a variation of the concentric confi guration. The mono-coil can be manufactured with the TX and RX coils located together or as a single coil acting as both TX and RX. The detection and performance characteristics of the mono are essentially the same as the concentric in that it provides the maximum possible sensitivity, but suff ers some performance in mineralized ground.
An Imaging searchcoil is an enhanced version of the concentric confi guration that features an additional RX coil. This extra coil provides the detector with additional target information necessary for true target-depth perception and true target-sizing capabilities. With this additional sizing information, the detector can more fully characterize a target and for the fi rst time distinguish between trash and good targets of the same conductivity (e.g. a quarter vs. a soda can). Only Garrett’s GTI series off ers this technology; no other detector in the world has this capability.