How Deep Can a Metal Detector Detect

by Michael Bernzweig

Metal detectors are useful for finding all kinds of things, from lost keys to a treasure buried in the ground. Depending on the target, metal detectorists may require a deep-seeking detector. But how deep can a normal detector and deep seeking detector actually go?

Most metal detectors can detect coins at an average maximum depth of 10 to 16 inches. Metal detectors transmit radio frequency signals from the search coil to locate the targets from the ground's surface to a depth of over 20 feet for large deep treasures.

To get the most out of your detector, develop a good swinging technique, target areas with a substantial opportunity to produce targets, and purchase a bigger coil if possible. This article will explore what determines the depth at which a metal detector can detect and how to get the most out of each type of metal detecting. As you learn to metal detect, you will constantly be gaining knowledge.

What Determines Metal Detector Detection Depth?

Metal detectors are designed with different search coils, which are the part of the detector that makes contact with the ground. Larger coils can cover more surface area and will detect targets at a greater depth than smaller coils. The same holds true for both land and underwater metal detector operation.

The main factors of metal detecting that affect a metal detector's detection depth are the target, coil size, settings, frequency, and ground conditions. 

The size of the coil is probably the most critical factor, with larger coils generally providing more depth. However, the problem with large coils is that they are more challenging to maneuver and lose a bit of sensitivity to smaller targets. When starting out, it's best to purchase a smaller coil and practice using it before moving on to a bigger one.

Your Target

Your metal detecting target also affects how deep your metal detector can go. Large, bulky pieces of metal will be detected at greater depths than smaller objects. This is because larger targets are easier to locate and, in some cases, produce a larger magnetic field or halo around the target for the detector to sense. Smaller targets can be located, just not as deeply.

The composition of a target, as well as its size, form, and orientation, affects how far down a metal detector can go. For example, a large, flat object made of iron will be easier to detect than a small, sub-gram gold nugget. Before using your metal detector on private land, be aware of metal detecting laws surrounding where you can use your device. 

When it comes to selecting a metal detector for gold prospecting, there are a few things to think about. Gold specific detectors have greater sensitivity than other types of detectors, allowing them to pick up even the tiniest pieces of gold or metal contaminant in a factory setting. 

Gold detectors are available in two varieties: 

These models have complicated electronics and special search coils that enable them to discover the tiniest gold nuggets in most cases.

VLF detectors are the most popular type of metal detection device. They operate at low frequencies, usually between three and 30 kHz. This makes them good at detecting large objects close to the surface but not so great at finding small, deep targets. 

Pulse induction (PI) metal detectors are designed for a treasure hunter to use in highly mineralized soils or saltwater. They emit short pulses of high-frequency energy into the ground and are very sensitive to metals. However, they're not as good at discriminating between different types of metals. 

Search Coils

At the bottom of a metal detector, there is a search coil. It consists of two sets of coiled wires, as the name implies. When metal detecting, the transmitter coil generates an electromagnetic field. Disturbances in the field are detected by the receive coil. These fluctuations suggest that a metallic object may be present in the ground. 

The diameter of a search coil determines its detection depth. A search coil's measurement is comparable to the coil's diameter. Typically the Deeper targets can be detected, the larger the search coil needs to be. Typically the depth range in the ground that you can expect from a search coil for a coin sized target is about 1.5 times the diameter of the coil.

There are many different types and models of metal detecting search coils available, including:

  • Small search coils - Small search coils are 4 to 8 inches in diameter and are best for finding jewelry, precious metals, coins, and other small objects or buried metal.
  • Medium search coils - Most metal detectors include standard medium search coils. They are usually 9 to 10 inches (22 to 25 cm) in diameter, and their search area is around 8 + inches (20 cm) wide and deep.
  • Large search coils - Large coils have diameters ranging from 10 to 15 inches and offer the greatest detection depth and coverage area. They're fantastic for searching out historical relics or prospecting.

Search Coil Types

There are three types of metal detector search coils that we're going to discuss in this article today which are the mono coil, the DD coil, and the concentric coil. By understanding the differences, a metal detectorist will gain the most advantage in the field.

Mono Coils

Monoloop coils are also effective at detecting small, deep nuggets that larger coils cannot. You can cover more ground by using larger coils. Mono search coils are suitable for shallow hunting in open areas. It's good to use mono coils when looking for gold nuggets. Their smaller footprint makes them good for detecting small targets in open areas. DD coils can detect gold nuggets with greater depth and sensitivity than mono loop coils, but they are louder. Mono coils work best in areas with little or no ground cover.

DD Coils

Double D coils have two loops of wiring (like reversed capital letters D) that overlap in the middle. One coil transmits signals, and the other receives them. For deep and shallow hunting, the double-D search coil is a good choice. Despite having more depth than mono coils, they are still sensitive enough to detect small targets and fine gold. They can also find gold nuggets at greater depths. While nugget detecting, prospectors often use small gold pans.

Concentric Coils

Round coils with a single loop of wire transmit and receive signals in the same plane. Your gold metal detector's success depends on selecting the right coil for your application. Concentric coils offer good depth and sensitivity but aren't as versatile as DD and mono coils. In mildly mineralized soil, they detect small targets near one another more effectively than other coils. A variety of coil shapes are available, including elliptical and semi-elliptical coils. A narrow and precise path is cut by the elliptical design. Minimal mineralization is ideal for concentric coils. In areas with heavy mineral saturation, a double d coil may be the best choice.

Settings and Frequency

The settings on your metal detector also affect how deeply it can detect metals. This includes both ferrous metal and nonferrous metal as well. The higher the sensitivity setting, the deeper the detector will reach. However, increasing the sensitivity also increases the chances of false signals, even if you are using the best metal detector, so increase this setting with caution! If you are looking for a precious metal object like a gold nugget, a gold detector set in the all-metal mode will be the best choice. Different metals will require more or less sensitivity to be detected based on their frequency and conductivity of detection. A single frequency model such as a Bounty Hunter metal detector will locate targets in one specific frequency range. A multi-frequency model like the XP Deus 2 can locate targets in a wide range of frequencies. Unwanted targets like stainless steel have a very low conductivity. Precious metal targets like gold have a very high frequency.

The frequency of your metal detector also affects its detection depth. Higher frequencies are better at detecting small targets at great depths, while lower frequencies are better at detecting large objects closer to the surface. 

Popular Coin Jewelry Relic and Gold Prospecting VLF Detector models

  • Garrett Ace
  • Bounty Hunter Platinum Pro
  • Nokta Makro Legend
  • Fisher Gold Bug Pro
  • XP DEUS 2

Deep Seeking Metal Detectors

Some specialized metal detectors are designed to operate at depths of 20 feet or greater, but these are not cheap metal detectors, some costing $2,000 or more. These detectors are used by treasure hunters to locate objects buried deep in the ground. Some of the best metal detectors for deep seeking and underwater metal detecting include:

  • Fisher Gemini 
  • Groundtech Discovery SMR
  • Conrad GR-3 Plus
  • Detech 5100 Pro
  • Garrett GTI 2500

Environmental Conditions and Ground Balance

Ground mineralization and conditions are also a factor in how deeply your metal detector can detect. Soil with a high mineral content will interfere more with the electromagnetic field and block the signal from reaching the target than soil with low mineral content. 

To combat this interference, most metal detectors have a ground balance feature that allows you to adjust the machine's settings so it is optimized for the type of soil you're detecting in. This ensures that the greatest possible amount of signal strength is directed towards the target, resulting in better detection depth.

Several trace minerals, such as zinc, magnesium, and iron, are present in the soil in trace amounts. Ground mineralization is a condition in which high levels of these trace minerals exist in the soil. When the receiving chip in a metal detector search coil receives a signal from the eddy current of metals detected underground, the chip will emit an audio signal in the detector control box as a result of the signal it receives.

Increasing mineralization levels can be countered by setting your ground balance properly and adjusting your discrimination settings. In highly mineralized areas, you may have difficulty detecting deep targets. It is unlikely that metal detectors without ground balancing or discrimination features will work well in highly mineralized ground.

Now that you know what factors influence detection depth, here are some tips on how to take advantage of each condition:

  • Use a large search coil and increase the detector's sensitivity if you want to find large objects buried deep in the ground.
  • Use a small search coil and a moderate sensitivity setting if you are searching for small objects buried deep in the ground.
  • The most accurate results will be obtained if you adjust your ground balancing feature precisely when detecting heavily mineralized soil. It is also possible to compensate with a bit of discrimination.

Metal detectors are not one-size-fits-all machines; each person will have to experiment with their own settings to find what works best in different environments. With a little practice and some trial and error, you'll be able to detect metals at greater depths than ever before!

A metal detector can detect targets buried deep in the ground. In addition to coil size and type, machine settings and environmental conditions all affect the depth at which a metal detector can detect. You can find underground treasures with a little practice and experimentation!

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