Coils (Probes) for metal detectors
Coils (probes) for metal detectors are key components used to detect metal objects in the ground. These coils can come in a variety of shapes, sizes and types that affect the depth and accuracy of detection. Below is a detailed description of the different types of coils and their use in different types of metal detectors:
A concentric coil for metal detectors is a specific type of coil that consists of two circular coils placed one above the other. The outer coil is used to transmit the electromagnetic signal, while the inner coil is responsible for receiving the signal. This arrangement allows concentric coils to produce a very well defined and narrow detection field, which is ideal for accurately locating metal objects in the ground.
Advantages of concentric coils:
- Better Discrimination: concentric coils are better able to discriminate between different types of metals and ignore unwanted metals or minerals in the soil.
- More Accurate Localization.
- Less Interference: The coil design minimizes interference from minerals in the soil, which is especially useful in mineralized areas.
Disadvantages:
- Limited Depth Capability: Concentric coils generally do not have as great a depth range as some other types of coils, such as Double-D coils.
Concentric coils are suitable for areas with less scrap metal and where high detection accuracy and good discrimination capability are needed. This type of coil is popular among metal detectorists looking for specific targets, such as coins or jewelry, in less contaminated locations.
Double-D (2D) metal detectorcoils have a specific shape that resembles two overlapping "D" letters, hence their name. This design allows the transmitting and receiving coils to be arranged in the shape of two semicircles, which are arranged so that their straight edges overlap. As a result, Double-D coils are able to generate a wide and flat detection field, which is particularly useful for searching large areas.
Advantages of Double-D coils:
- Wide Detection Field: This coil provides a wider detection field, which is useful for effectively searching large areas.
- Deeper Penetration: Double-D coils can penetrate deeper into the ground, allowing detection of larger objects or objects located in deeper layers.
- Better Performance in Mineralized Soils: Due to their design, these coils are less susceptible to interference caused by high soil mineralization, improving their performance in challenging conditions.
Disadvantages:
- Lower Locational Accuracy: Although Double-D coils excel at searching large areas, they may have difficulty accurately locating smaller or closely spaced objects due to their wider detection field.
Double-D coils are ideal for prospectors who need to explore large areas such as beaches, fields and forests where depth and resistance to mineralization is key. This type of coil is popular among advanced metal detector users who need a robust and effective tool for their search. Nowadays, 2D coils are already more advanced than concentric coils in all respects and in the sub-satellite all manufacturers have switched to this technology only.
Mono coils for Pulse Induction (PI) metal detectors are simple designs that combine transmitting and receiving functions into a single coil. This design is typical of PI detectors, which are known for their ability to operate in deep and highly mineralized soils.
Advantages of mono coils:
- Depth capability.
- Strong signal: Since the coil combines both functions, it can generate a very strong electromagnetic field, increasing the chances of detecting deeply buried metals.
- Resistance to mineralisation: mono coils are less sensitive to interference from mineralised soils, making them suitable for use in difficult terrain.
Disadvantages:
- Lower Discrimination Capabilities: Because PI detectors with mono coils primarily emit strong pulses and measure return signals, they may have difficulty discriminating between different types of metals.
- In areas with a high incidence of scrap metal, it may be more difficult to discriminate between closely spaced objects.
Mono coils are excellent for use in extreme conditions and are particularlyparticularly useful when searching in deep water or on beaches with high salt levels. They are also popular with prospectors looking for gold and other precious metals where depth of search is a priority.
Reel design
A metal detector coil consists of several coils of conductive wire, which are usually mounted on a plastic or composite frame. This frame is designed to be resistant to external influences and not to conduct electromagnetic signals. The coil itself is protected by a waterproof cover, allowing it to be used in a variety of environments, including water and mud. Advanced coils for the multi-frequency detector range already have part of the detector electronics in them.
Coil functions
The main function of the coil is to transmit and receive electromagnetic signals. When the detector coil passes over a metal object, the electromagnetic field is disturbed and the detector records this as a finding. Different types of coils and their specific characteristics are designed to maximize the search efficiency in different conditions and for different types of metals.
Different coil sizes for metal detectors serve different purposes, which affects the effectiveness of the search depending on the terrain and type of target. Here is a detailed description of the purpose of small separation and large depth coils:
Small separation coils
These coils are typically lightweight and smaller in diameter, making them ideal for use in areas with high levels of metallic debris. Because of their smaller size, they can better separate nearby targets and are more effective at locating smaller objects. They are suitable for use in difficult terrain such as forests, old houses and other areas with many potential targets.
Large depth coils
Large coils typically have a larger diameter, allowing them to penetrate deeper into the ground and detect larger objects that are deeper below the surface. These coils are ideal for use in open areas such as beaches, fields and large undeveloped areas where metallic debris is less likely to be found and greater search depths are desirable.