You will find the most objects at a shallow depth (0 – 10 inches) during metal detecting. This is no coincidence because this is the average depth of metal objects in the bottom. However, there are also metal objects that are located deeper in the ground.
You might wonder if you are able to find these deeper located objects with your metal detector. This depends on the maximum depth range of your metal detector. How deep can a metal detector actually go?
The average metal detector can detect small objects to a depth of 10 inches (25 cm) and larger objects to a depth of 14 inches (35 cm). There are several things that will influence the maximum depth range of a metal detector.
Chiefly, the target size, the bottom structure, the conductivity of an object, the coil size and the settings of the metal detector will influence the maximum detection depth of the metal detector.
Of course, there are many more factors that determine the maximum detection depth of your metal detector. In this article I will mention all the factors that affect the maximum depth of your metal detector. I will also tell you what kind of metal detectors are suitable for detecting deep located objects.
Furthermore, I will tell you how you can increase the maximum detection depth of your metal detector. Enjoy Reading!
What does affect the maximum depth of a metal detector?
As mentioned earlier, the average metal detector can detect small objects up to a depth of 10 inches and larger objects up to 14 inches. The maximum detection depths may vary among different metal detectors, with modern models often having greater depth capabilities compared to older ones.
In the upcoming sections of this article, I will provide a detailed explanation of how multi-frequency metal detectors and pulse induction metal detectors can detect objects at even greater depths than single-frequency ones. But first, let’s explore the various factors that influence the maximum depth of your metal detector
1. Target Size
The metal detector can detect larger objects at greater depths compared to smaller objects. This is because larger objects emit a larger electromagnetic field, making them easier to detect.
As a result, items such as horseshoes and iron pieces are more likely to be found at greater depths, while smaller objects like coins, rings, and buttons may be detected at shallower depths
2. Target Position
The target position is very decisive for the maximum depth range of the metal detector. A horizontally placed coin is more likely to be found than a vertically placed coin. This is because the horizontally placed coin has a larger surface area that can receive and emit a magnetic field.
3. Target shape
Thin materials are much more difficult to detect than materials with a large surface area. Thin nails are therefore more difficult to detect than shrapnel, buttons or coins. This is because flat objects can better receive and emit electromagnetic fields.
4. Target Conductivity
Some materials are better conductors than other materials. Good conductors can better and faster receive and emit a stronger electromagnetic field compared to bad conductors. This means that you are able to detect the metals with a high conductivity deeper than the metals with a low conductivity.
In the table below you can see different metals with a different conductivity.
| Metal | Conductivity (S/m) | Maximum detection depth |
|---|---|---|
| Silver | 6.3 x 107 | Deep |
| Copper | 5.96 x 107 | Deep |
| Aluminum | 3.5 x 107 | Deep |
| Mercury | 1.02 x 106 | Medium |
| Nichrome | 9.09 x 105 | Shallow |
6. Soil structure
Mineralization
When a soil has been under the influence of rain for a long period of time, some little iron particles will arise. These little metal particles disturb the electromagnetic field of the metal detector.
This means that the electromagnetic field of the metal detector can’t reach a metal object at a great depth without getting disturbed. Therefore, a metal detector will not be able to detect deep objects in soils with a lot of soil mineralization.
Water
Wet soils will better conduct electricity than dry soils. The deeper located metal objects will be detected sooner because water provides better conductivity. It is therefore a good idea to go metal detecting after a heavy rain shower.
Hence, permeable soils are good for detecting deep located objects. In permeable soils is much space between the pores of the bottom. Water can easily flow in these pores. Therefore, the conductivity of the soil will be improved.
Type of soil
Bottoms with heavy-clay layers and rocks cause more little disturbances in the electromagnetic fields compared to loose sand grounds. Therefore, it is more difficult to locate deep objects in these heavy-clay soils.
7. Coil size
The coil of a metal detector is the round shape at the lowest part of the metal detector. The coil has an inner and outer ring; also known as the transmitter and receiver. The transmitter sends out an electromagnetic field and the receiver receives the reflected electromagnetic field.
This electromagnetic field is created by copper wires in combination with electricity in the metal detector’s coil. The size of the coil of a metal detector determines the depth up to where the metal detector receives the signals.
The wider and larger the metal detector’s coil, the deeper the metal detector can detect. This is because a wider coil can send out a larger electromagnetic field. The time until the magnetic field fades is longer here.
But you have to be careful with this; larger coils won’t be very useful for finding small objects. The large coils will detect a lot of metals because of the large electromagnetic field. This is not useful when you want to find little objects.
Large coils will also be more sensitive for EMI (Electromagnetic Interference). This means that the electromagnetic field transmitted from the coil will be disturbed by electromagnetic fields of other devices. Large coils are also not useful in mineralized bottoms because the metal detector will detect too much metals.
Always consider which coil size you will need in your situation! In my other blog I will tell you all the differences between the coils.
8. Metal detector settings
Discrimination function
The maximum depth of the metal detector will be decreased when using the discrimination function of the metal detector. The discrimination function gives you the option to ignore certain materials. This could be very useful in high mineralized bottoms.
When the metal detector has to ignore some metals, it can’t operate to its full potential. The sensitivity will be less when using this option. Unfortunately, there is not much that you can do about this because you will often need this function…
Sensitivity function
Almost all metal detectors have a sensitivity function, which allows you to adjust how your metal detector reacts to metal objects. A higher sensitivity level increases the size of the electromagnetic field generated by the metal detector.
This provides you with the ability to detect objects at greater depths. Conversely, a lower sensitivity level produces smaller electromagnetic fields, limiting your detection range to shallower depths.
Therefore, it is important to set your sensitivity level appropriately if you want to locate objects that are buried deep.
9. Frequency of the metal detector
The frequency of a metal detector refers to the number of electromagnetic signals it emits per second. Most metal detectors operate within a frequency range of 5 to 30 kHz.
A metal detector with a frequency of 5 kHz emits 5,000 signals per second, while a 30 kHz metal detector emits 30,000 signals per second. The frequency of the metal detector plays a role in determining its detection depth.
Low Frequency metal detector
Metal detectors with a low frequency range, typically between 5 to 10 kHz, emit long wavelengths that can penetrate the ground effectively. This allows low frequency metal detectors to reach greater depths during detection.
Low frequency metal detectors are particularly suitable for searching for highly conductive metals like silver. However, one limitation of low frequency detectors is their reduced ability to detect small objects.
Additionally, low frequency metal detectors may be less effective in detecting low conductive metals compared to higher frequency detectors. It’s important to consider the specific application and target materials when choosing the appropriate frequency range for metal detecting.
High Frequency metal detector
Metal detectors with a high frequency range, typically between 10 to 30 kHz, emit shorter wavelengths that have more difficulty penetrating the ground. As a result, high frequency metal detectors generally have a shallower depth capability compared to low frequency detectors.
However, high frequency metal detectors excel at detecting small metal objects that may be missed by low frequency detectors. They are particularly effective for detecting low conductive materials.
It’s worth noting that high frequency metal detectors are more sensitive to mineralized soil conditions, which can cause increased electromagnetic interference. On the other hand, they offer greater accuracy when it comes to detecting small objects at shallower depths.
Multi-Frequency metal detector
To take advantage of the benefits of both a low frequency metal detector and high frequency metal detector, multi-frequency metal detectors have been made. These multi-frequency metal detectors emit all kind of frequencies.
As a result of this, the metal detector is able to detect at different depths. Moreover, the multi-frequency metal detector can detect both low conductivity and high conductivity materials.
The multi-frequency metal detector can also detect both large and small objects. It is possible to adjust the frequencies with the most multi-frequency metal detectors depending on a specific situation.
So it is smart to use low frequencies in high mineralized bottoms and to find deep located objects that are high conductive. Conversely, it is smart to use high frequencies for finding shallow located small objects that are low conductive in bottoms with less bottom mineralization.
| Metal Detector | Advantages | Disadvantages |
|---|---|---|
| Low frequency | – Can detect deep objects. – Good for finding high conductive materials. – Good in finding large objects. – Less sensitive for high mineralized bottoms. | – Bad in detecting low conductive materials. – Not good in finding small objects. |
| High frequency | – Good for detecting shallow located objects. – Good for finding low conductive materials. – Very accurate for finding small objects. | – Can detect less deep than a low frequency metal detector. – Very sensitive for high mineralized bottoms. – Less suitable for finding high conductive materials. |
| Multi-frequency | – Can detect both small and large objects. – Can detect both low conductive and high conductive materials. | – Proper ground balancing is needed. |
10. Other Factors
Vegetation on the surface
Some fields have vegetation on the surface; for example roots and weeds. As a result of this, the distance between the soil surface and your coil increases. Hence, the maximum depth of your metal will be reduced.
Distance coil and surface
You should always keep your coil as close as possible to the surface without touching the ground. Otherwise, your metal detector won’t be able to detect at the maximum depth. This could lead to missing deeper located metal objects.
The angle of your coil
It is really important to keep your coil 180 degrees horizontal. Otherwise, the electromagnetic field of your metal detector will be sent into the ground with an angle. This could lead to a lower detection depth range of the metal detector.
EMI (Electromagnetic Interference)
In some areas there is a lot of Electromagnetic Interference. This means that there are some other devices that send out a weak electromagnetic field. This electromagnetic field disturbs the electromagnetic field of the metal detector.
This means that your metal detector can’t operate to its full potential. As a result of the electromagnetic interference, the maximum depth of your metal detector will decrease.
Devices like radio’s, power lines and radars could cause electromagnetic interference. EMI could also lead to the fact that your metal detector will constantly beep.
Smooth movement with your metal detector
Another thing that can reduce the maximum depth of your metal detector is a wrong movement with the metal detector. Some people swing too hard with the metal detector.
Consequently, the metal detector won’t be able to properly receive the electromagnetic fields of the metal objects beneath the surface. Always make sure to detect slow and steady with your metal detector!
The wrong movement with a metal detector can also lead to the constantly beeping of the metal detector!
Pulse Induction metal detector
The average pulse induction metal detector is able to detect deeper than a VLF metal detector. This is because a pulse induction sends out pulses.
These pulses can reach a greater depth. However, this could lead to some problems because a pulse induction metal detector does not have a proper discrimination function.
Frequently Asked Questions
To increase the maximum depth of your metal detector, you should use a larger coil, a low frequency metal detector, a high sensitivity and you should keep the coil as close as possible to the surface.
The maximum detection depth of the metal detector depends on the size, the shape, the position and the conductivity of the target.
Moist soils are more conductive than dry soils. This is why the maximum detection depth in moist soils is deeper than in dry soils. The maximum detection depth in bottoms with a high mineralization is less deep than bottoms without mineralization. Also bottoms with heavy-clay and rocks decrease the maximum detection depth.