What are the different types of metal detecting search coils and how do they work? Search coils are one of the vital parts of a metal detector, and can come in various shapes and sizes, depending on your specific need. Generally flat in construction, a search coils for metal detectors will consist of a transmit coil, and a receive coil, though it is possible to have a mono-coil, in which a single coil works as both the transmitter and receiver coil.
When powered, the transmit coil will generate a magnetic field in the surrounding area, and if a metallic item is located within the field, the magnetic field will become distorted. The receive coil then senses the distortion and will send a signal to the control housing, which alerts the user to the presence of a metallic object.
While not all detectors have the capability, some special models have a tertiary coil, which is generally just a second receive coil, that can further pinpoint the location of the object detected. Some metal detector coils can go even further, are able to determine the approximate depth of the object as well; though this technology is currently limited to one company.
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Metal Detector Coils, How They Work And Classification
This is a simple beginners guide to metal detecting search coils to take the complexity out of the equation.
a) By Size
What are the different types of search coils for metal detectors available when it comes to sizes and styles? Search coils are quite varied, with each design offering better performance in specific areas, as well as the various sizes offering not only more ground coverage, but deeper detection rates. It is generally known and accepted that the diameter of a search coil is an approximation of its detection depth for a coin sized object, though not always a guarantee.
Metal detector coils, how do they work and what about coil size? When it comes to coil size, larger diameter search coils, larger coils offer a larger scanning area as well as a deeper detection. However, due to the larger, and less concentrated field, they are not always able to detect smaller items such as coins. This can also pose an issue when used in areas with large quantities of metal items such as trash, as it can be detecting several targets at once; making pinpointing one item more laborious and less fun.
On the other hand, a smaller sized coil is able to locate smaller objects, as its magnetic field is concentrated over a smaller area. Smaller coils are considered to be best used in areas with larger amounts of metal debris, though due to the smaller diameter, more scans will need to be done to scan the area. However, this can possibly be beneficial, as the chances for detecting multiple targets at once are smaller, which helps to pinpoint the location easier.
b) By Shape And Configuration
Just as search coils come in various sizes, they can also be found in a few different shapes and configurations that offer different benefits for the environments they’re used in; with an elliptical coil being more maneuverable than circular coils, and with its narrow width, it allows for greater coverage of an area. On the other hand, a circular coil offers more sensitivity in non-mineralized soil, as well as detection depth; this makes it the most commonly used shape on the market. Search coils can also come in a 2-box shape, which is best used for detecting deep buried items, due to the larger distance between the transmit and receive coils.
What Are The 5 Different Types of Metal Detecting Search Coils
Metal detector search coil designs are quite varied, so to remove the mystery of them, let’s take a look shall we….
a) Concentric Search Coils
Concentric search coils consist of a transmit coil on the outside with a receive coil on the inside, giving the advantage of the coils being wound as large as possible in the search diameter; thus providing the best detection depth, as well as largest detection field.
Concentric coils also provide the most symmetrical field, which makes it easier to pinpoint objects, and has more consistency in target identification, which makes it the most common and versatile search coil.
However, this design is not flawless, and is the most susceptible to interference from minerals in the ground, which makes it much less effective in heavily mineralized grounds.
b) Imaging Coil
There is also an advanced version of the concentric coil, called an imaging coil. This version is virtually the same as concentric, but features a second receive coil, which provides the detector with additional target information, for true target-sizing, as well as target depth capabilities.
By using the additional information, the detector is able to more fully characterize the target, and even differentiate trash from treasure of the same conductivity. However, this capability is limited to only one type of detector, exclusive to one company.
c) Mono Coils
Mono coils are available only for Pule Induction detectors, and are a varied form of the concentric coils. The difference between these two coils is that the mono coil has the transmit and receive coils located together, or one coil which acts as both the transmit and receive.
The performance of a mono coil is basically the same as a concentric; providing maximum sensitivity, but still suffering performance in mineralized grounds.
d) Double D Coils
The Double D design is intended to reduce ground interference, recovering performance lost by the concentric coil in mineralized soil. The design is named by the shape of both the coils, which are, of course, in the shape of a “D”. With this configuration, the coils generate a canceling effect of the ground signals.
The positive detection field runs beneath the center section of the design, from front to back; the other portion of the coil produces the negative, or canceling, detection field, which is what helps to maintain performance over mineralized ground.
However, due to the small positive field, this design is less sensitive than the concentric coil of the same size over normal, non-mineralized grounds. Over mineralized grounds, on the other hand, this design will provide much better performance, which is why the Double D is recommended for areas where the ground is more mineralized than normal. Such as areas where people often go when they are prospecting or hunting for relics.
e) 2-Box Coils
Another design of coils is referred to as a 2-box. In this configuration, the transmit and receive coils are actually separated by several feet. This gives the detector a lightweight and more manageable design, and giving the performance of a 3 to 4 foot diameter search coil.
Due to its size, a 2-box model is perfect, and most often used for locating deeply buried items such as caches or relics. While it can easily detect larger objects deeper underground, it often ignores smaller items, around 3” in diameter.
Conclusion on the Beginners Guide To What are the Different Types of Metal Detecting Search Coils
Use The Right Type Of Search Coil For Optimized Performance
The various types of metal detector search coil designs are designed to work more optimally in certain environments. While some may still work sufficiently in other environments, they may not provide the desired performance. For example, a Pulse Induction detector would be best for beach detecting, as they ignore minerals in the sand, allowing you to focus on actual objects, rather than the surrounding “noise” created by minerals, which can be quite frustrating. Some entry level detectors come with presets to minimize, or even negate, the coil from picking up minerals in the ground, potentially causing either false positives, or for some, making it difficult to discern when an item is discovered.
While for beginners many of the coil types and sizes will not be used, it is helpful, as well as important, to at least be familiar with them for future use. For the most part, the default search coil included with a metal detector is at least sufficient for anything from simple hobby detecting or beach searching. However, not all coils are created equal, and not all are designed for every purpose, and can potentially either ignore metallic objects in their field, or become triggered by mineralized sand or dirt.
Keep Search Coils In Best Shape And Avoid Damage
Since the search coil is a vital piece of metal detecting, it is important to keep it in the best shape possible, to avoid damaging the coil, which can result in negative impacts of performance, or the coil no longer working. While many hunters have personal preferences regarding search coil covers, it is usually left up to the individual whether or not to use a cover. Though some have noticed slight increases in depth detection without a cover, others choose to take the safe route and potentially sacrifice deeper detection for a longer lasting and better shape coil.
Use Search Coil Covers
In our beginners guide to metal detecting search coils, choosing the right coil covers both protects and keeps your coil clean. By using a cover, it will also keep dirt and rock fragments from getting inside and disrupt the magnetic field, especially if the dirt that gets inside is mineralized, which can result in your detector receiving false positives, even when not held over any metallic objects. To protect against this, it is recommended to use a sealant to not only keep your cover from falling off, but to also protect your search coil from the water, dirt, and other contaminants as you hunt for your treasures.