How deep do metal detectors detect? As deep as the coil’s diameter. As a result, larger coil detectors will detect further. Most metal detectors can detect items 4-8 inches (10-20 cm) deep, while a mid-range metal detector can reach 12-18 (30-45 cm) underground in optimum conditions.
Some specialized detectors can reach depths of up to 65 feet (20 m). Of course, the depth you reach depends on your detector and what you’re looking for. Other factors, such as soil minerals, are also important.
Factors Affecting Detection Depth
1. Target Size
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Large targets are detected deeper by a metal detector than small targets. Larger items have a greater surface area, causing more disruption in the electromagnetic (EM) field produced by a metal detector.
2. Target Form
Because of the larger detectable surface area, round targets like coins or rings and flat rectangular objects like metal boxes or chests are simpler to detect at deeper depths. This is achievable using cheap metal detectors ranging from $100 t0 200 or $300 to $500.
On the other hand, long or thin structures like nails or cables are more difficult to detect deeper into the earth. They require higher-end models ranging from $1000 to $5000.
3. Target Orientation
A horizontal target is easier to detect deeper than a vertical target due to the larger surface area available to disrupt the detector’s EM field. Conversely, a vertical target has less surface area to work with, making detection more difficult.
4. Target Material
The type of metal you’re looking for impacts how far you can search. Highly conductive metals (such as silver) can be detected deeper than less conductive metals such as gold, lead, or stainless steel.
Metal Detectors Features
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1. Frequencies
The number of ground-penetrating electromagnetic (EM) waves a metal detector can broadcast per second is known as its operational frequency. These frequencies are measured in kilohertz (kHz). The majority of metal detectors operate at 7 to 25 kHz. Frequency technologies are divided into two categories:
a) Single-Frequency
Most entry-level metal detectors use the Very Low Frequency (VLF) technology. It sends a single frequency EM wave into the earth indefinitely. Low frequencies (sub 8 kHz) are best for targets that are deep, big, or extremely conductive, such as silver and copper.
Less conductive metals such as small gold nuggets are susceptible to high frequencies (about 40 kHz). However, they are unresponsive to more conductive metals, which are easily detected at lower frequencies. In addition, electronics and electricity cables can cause electromagnetic interference (EMI) at low frequencies.
b) Multi-Frequency
Multi-frequency transmission technology is used in higher-end metal detectors. Multi-frequency technology simultaneously transmits numerous frequencies across the spectrum. As a result, the metal detector can identify both small and large or deep targets simultaneously.
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2. Software Features
a) Ground Balance
Many metal detectors have a function called ground balance. It works to reduce interference from ground minerals. False signals can be produced by ground mineralization. When a metal detector beeps as if it’s detecting a target in the ground, it’s detecting iron or salt particles in the soil.
Ground Balancing features suppress the signals received from the minerals in the ground to mitigate this. As a result, only signals from actual targets are left behind.
b) Discrimination
The capacity of a metal detector to accurately discriminate metal items is referred to as discrimination. Their electrical or magnetic characteristics determine it. Some metals, such as silver, are extremely electrically conductive.
Their conductivity can distinguish these from less conductive metals such as gold or steel. Other metals, such as iron, can be identified by their magnetic properties.
3. Search Coils
A metal detector’s search coil is the round object at the end of the shaft. It is made up of two sets of coiled wires. The Transmit Coil produces an electromagnetic (EM) field while the Receive Coil detects disruptions in that field.
These tremors could suggest the presence of a metal object in the ground. Search coils come in a variety of sizes, shapes, and configurations. Each is tailored to specific goals, search locations, and mineralization levels.
The size of a metal detector’s search coil dictates how much ground it can cover. So what is the maximum depth a search coil can detect? The metal detecting depth of a search coil is usually equal to its diameter.
Consequently, the larger the coil, the greater the depth to which it can detect a target. However, there comes a limit where the EM field generated is too strong for the detector to identify small things. Small search coils produce concentrated electromagnetic fields and are ideal for finding small objects such as earrings or gold nuggets.
Small coils are also less vulnerable to EMI from power lines, cell phones, microwaves, and other electrical devices. Most metal detectors come with medium search coils as standard. They’re usually 9 – 10 (22 – 25 cm) in diameter and create an 8 – 20 cm wide and deep search field. Medium-sized search coils are useful in a wide range of applications. Coins, rings, and other jewelry are typical targets for them.
Large Search Coils have a diameter of 10 to 15 inches (25 to 38 centimeters) and provide the most detection depth and coverage area. They’re perfect for relic hunting and prospecting in distant locations. There are, however, trade-offs. They make it difficult to detect small targets.
What Causes Mineralization in the Ground?
Mineralization of the ground is a natural occurrence. For example, rainfall causes iron and other mineral particles in the soil to move to the surface over time—this build-up results in increased ground mineralization.
The makeup of soil varies substantially from one location to another. However, the soil color can be used to assess the level of ground mineralization where you live. The iron-rich ground is found worldwide, ranging in color from purple-red to reddish-brown.
It’s known as Red Clay soil in the southeast and southwest of the United States. South America, Southern and eastern India, Australia, and central and southern Africa are all home to this species.
