When purchasing a metal detector, it is common to receive a round-shaped coil, as it is the most commonly used and cost-effective option for manufacturers. This round coil is versatile and suitable for various detecting conditions.
However, there are numerous other types of coils available, each with its own size, shape, and properties. These different coils are designed to cater to specific types of terrains and targets. It’s important to understand the differences between metal detector coils and determine which one is suitable for your needs.
In general, large coils are capable of detecting deeper targets compared to small coils. Large coils are better suited for detecting larger targets, while small coils are more effective at detecting smaller targets.
When it comes to detecting in areas with high trash or ground mineralization, using a smaller coil is often recommended. This is because small coils provide better target separation and are less affected by interference from surrounding objects or minerals.
The three most common types of coils are the concentric coil, the double-D (DD) coil, and the monoloop coil. Each coil type has its own set of characteristics and advantages.
This sounds of course a little bit bluntly, but don’t worry. In this article I will explain you everything about the different coil sizes and shapes. After reading this article you know exactly what kind of coil size you need in your situation.
You will also find out what the differences are between the coil shapes. Last but not least, you will find out which coil shape is the best for your situation. Enjoy reading this blog!
What is a metal detector coil and how does it work?
The metal detector coil, located at the lowest part of the metal detector, typically has a round shape. Inside the coil, there are copper wires. When the electrical current from the batteries flows through these copper wires, it generates an electromagnetic field.
The transmitter, which is the outer ring of the coil, sends this electromagnetic field into the ground. When the electromagnetic field encounters a metal object buried in the ground, it is reflected or “bounced back.”
The receiver, which is the inner ring of the coil, detects this returned electromagnetic field. The receiver then converts the received electromagnetic field into an electrical signal, which is interpreted by the metal detector to indicate the presence of a metal object.
This electrical signal will be used in the control box. In the control box, the electrical signal will be converted into the beeping sound of the metal detector.
All in all, the coil compares the incoming and outgoing electromagnetic field. When the detector notices differences, it starts beeping.
What is the difference between the sizes of a coil?
Metal detector coils are produced in different sizes. This means that you can use both small and large sizes. Each size has their own properties and advantages. Lets start with the large coils.
Large coils
Large coils are indeed suitable for detecting in clean grounds without ground mineralization and trash. Their ability to emit a large electromagnetic field enables them to cover a larger surface area, allowing the detection of multiple metal objects simultaneously. However, when detecting in areas with a lot of trash, valuable objects may be missed as the metal detector may primarily detect the trash.
Large coils are advantageous for reaching greater depths compared to smaller coils. This is particularly useful for detecting objects buried at significant depths. It’s important to note that this deeper detection capability applies mainly to bottoms with minimal trash and ground mineralization.
Locating small objects precisely can be more challenging with a large coil due to the size of the electromagnetic field it generates. The broad field makes it difficult to pinpoint the exact location of small objects.
One consideration with large coils is their weight. They tend to be heavier than smaller coils, which can lead to fatigue in the arms during prolonged use. However, the advantage of covering a larger surface area in a relatively short time can save you valuable detecting time.
Small coils
The smaller coils are more suitable for grounds with a lot of trash and ground mineralization. This is because the small coil sends out a small electromagnetic field. This makes it much easier to accurately locate a valuable small object that is located between trash.
The small electromagnetic field doesn’t reach a great depth. Hence, the small coil is not suitable for finding deep located objects.
On the other hand, the small coil is suitable for finding shallow located small objects. This means that this kind of metal detector is also more suitable for prospectors. It gives prospectors the possibility to find gold(nuggets). Furthermore, the small coil is also more suitable for finding coins, bullets and thimbles.
Small coils are less heavier than large coils. This means that you have to carry less weight than with a large coil. This can help you to avoid tired arms. However, it takes more time to detect a large surface because it basically sends out a smaller electromagnetic field.
Maybe you are a little bit overwhelmed by all the information. I can completely understand this. To make everything clear for you, I made a little summary table with all the advantages and disadvantages of small and large coils.
| Advantages | Disadvantages | |
|---|---|---|
| Small coil | – Light weight. – Good to maneuver between obstacles. – Suitable for accurately locating small objects. – Relatively suitable for detecting in bottoms with a lot of ground mineralization and trash. | – Can’t reach great depths. – Less suitable for detecting large objects. – Can’t cover a lot of ground. |
| Large coil | – Can reach great depths. – Covers a lot of ground. – Suitable for locating large targets. | – Heavy weight. – Not suitable for grounds with bottom mineralization and a lot of trash. – Less suitable for locating small targets. |
What kind of metal detector coils are there?
As said before, there are different sizes and shapes of metal detector coils. Each shape has its own properties and advantages. The most common coil shapes are:
- The Concentric Coil
- The Double-D Coil
- The Monoloop Coil
Actually, there are some more unknown coil shapes. The other coils are the imaging coil, the 2-box coil and the anti-interference coil. Let’s take a look at all the advantages and disadvantages of each shape.
The Concentric Coil
The most common coil is the concentric coil. This coil has an inner and outer ring. The inner ring is the receiver and the outer ring is the transmitter. These two rings are separated from each other.
The concentric coil is relatively cheap compared to other coils. This is because the concentric coil is cheap to produce for manufacturers. This is the reason why most of the affordable metal detectors have a concentric coil.
The concentric coil sends out an electromagnetic field in the shape of valley parabola. This is useful for bottoms without ground mineralization because you can detect deep in these bottoms.
The electromagnetic field of the concentric coil starts wide and the deeper it goes, the smaller the area gets. The concentric has a good consistency in target identification.
The Double-D Coil
The double-d coil has an ellipse shape instead of a circle shape. The double-d coil has two sides that look like a D. This is why it is called a double-d coil. The higher part of the double-d coil is the transmitter and the lower part is the receiver.
The ellipse shape makes it easier to maneuver between obstacles. Very useful if you are searching on a surface with a lot of vegetation.
The double-d coil sends out an electromagnetic field in a thin line shape. This is the middle part of the coil where the right D intersects with the left D.
The thin detection area of the double-D coil indeed makes it suitable for highly mineralized bottoms and areas with a lot of trash. Its narrow detection width allows for precise targeting of small objects that may be located amidst the trash. The double-D metal detector is particularly useful for discriminating certain objects.
However, it’s important to note that the double-D coil may not achieve the same depth as the concentric coil when used in clean bottoms without much trash or mineralization.
The double-D coil typically comes at a higher price compared to the concentric coil. This is because the double-D coil incorporates more complex technology and design features.
The Monoloop coil
The monoloop coil differs from other coils in that it consists of a single coil that acts as both the transmitter and receiver. It is specifically designed for use with pulse induction metal detectors.
The pulses emitted by the monoloop coil penetrate into the ground in a cone shape, allowing for greater depth penetration in areas without significant ground mineralization.
Prospectors often prefer using the monoloop coil because it is well-suited for detecting gold nuggets and small objects. Its design and capabilities make it effective for this particular type of metal detecting.
The Imaging coil
This coil is pretty similar to the concentric coil. However, the imaging coil has one more receiver ring than the concentric coil. The function of this second receiver is that the imaging coil can better and more accurately determine what kind of object there is beneath.
Because of this accurate detecting ability, the imaging coil can reach greater depths than the concentric coil. The problem with imaging coils is that these coils are quit expensive compared to a concentric coil.
The 2-Box coil
This is one of the least common metal detector coils. They are not suitable for the average hobbyist. The 2-box coil does have a receiver and a transmitter. However, these two are far from each other.
The 2-box coil is suitable for covering much ground in a short time. The 2-box coil can detect really deep. The disadvantage about this is that the 2-box coil is not really sensitive. Therefore, this coil is not suitable for finding small objects.
You can’t use the 2-box coil in bottoms with a lot of trash because the electromagnetic field is way too large.
Anti-interference coil
The anti-interference coil, also known as the “salt coil,” is specifically designed to detect in challenging environments where there is a high level of interference. It is particularly effective in reducing interference from power lines and other devices that emit electromagnetic fields.
One of the notable benefits of the anti-interference coil is its ability to remain quiet even when operating near power lines. This allows metal detector users to explore areas that are typically less visited or overlooked due to the presence of power lines.
Additionally, the anti-interference coil is well-suited for detecting in saltwater environments. It can effectively handle the unique challenges posed by saltwater conditions, making it a valuable tool for beachcombing and underwater metal detecting.
Overview
Summary table
| Concentric coil | Double-D coil | Monoloop coil | Imaging coil | 2-Box coil | Anti-Interference coil |
|---|---|---|---|---|---|
| Circle shape with inner and outer ring | Ellipse shape with separated transmitter and receiver | Circle shape and the single coil is both the transmitter and receiver | Circle shape with a transmitter and an extra receiver | Rectangular shape with separated transmitter and receiver | Circle shape without space between transmitter and receiver |
| Separated transmitter and receiver | Upper D is transmitter, bottom D is receiver | Only for pulse induction metal detectors because it uses pulses | The two receivers lead to a better target identification | The transmitter and receiver are far from each other | Separated transmitter and receiver |
| Relatively cheap | Relatively expensive | Relatively expensive | Very expensive | Very expensive | Relatively expensive |
| Wide and deep detection | Very thin detection area. Hence, suitable for bottoms with a lot of trash and bottom mineralization | Wide and deep detection | Wide and deep detection | Really wide and deep detection. Hence, the sensitivity is very low | Wide and deep detection. It is not sensitive for EMI |
| Suitable for variety of targets | Especially suitable for small objects | Used for finding gold nuggets and small targets | Suitable for variety of targets | Especially used for really large targets. Therefore, not really useful for the average hobbyist | Suitable for detecting close to power lines and other devices that send out an electromagnetic field |
What kind of metal detector coil do I need?
Each situation needs a different coil size and different coil shape. When you want to find deep located large objects. You should go for a large coil with an imaging or concentric shape. When you want to find little objects like coins you should go for a smaller coil with a double-d shape.
Not only your purpose is important for choosing the right coil, but also the environmental factors like bottom structure. Large coils are not suitable for highly mineralized bottoms or bottoms with a lot of trash.
When you want to detect in bottoms with a lot of trash and bottom mineralization you should go for a smaller coil or a double-d coil. If you want to know whether you should need a coil protector/cover, you should definitely read my blog about coil covers.
Frequently Asked Questions
The average size of a metal detector coil is around the 9 to 12 inches. A small coil is about 5 inches and the large coil is about 12 inches.
The best coil for detecting in highly mineralized bottoms is a small coil or a double-d coil. With these coils you can detect small objects very accurately. Furthermore, you can easier discriminate metals that you don’t want to find.
Yes, you can easily replace the coil of the metal detector if it is needed. You can choose different sizes and different shapes dependent on your purpose. Large coils are used for detecting at a great depth for large objects, while small coils are used for detecting at a shallow depth for small objects.