Metal detectors operate using electromagnetism. They emit intermittent electromagnetic fields and receive signals sent back by conductive items. Therefore, the machine must be able to detect the magnetic field of a metal object for it to function. The most basic and inexpensive device will find an object fairly close to the ground surface, preferably within a foot. More advanced deep search metal detectors can pick up signals from objects buried deeper within the ground.
Stainless steel is one of the most difficult metals to detect because steel has poor electrical conductivity and low magnetic permeability. Therefore, the metal does not produce a signal strong enough for the detector to notice and recognise.
Other elements that a metal detector cannot easily detect include:
● Diamonds
● Glass
● Liquid
● Paper
● Pearls
● Plastic
● Stone figurines
Gemstones Detection:
Detecting precious and semi-precious stones like diamonds is difficult unless they are set in a metal fitting such as a jewellery fitting. The detector will not identify them directly as they are non-metallic.
Moreover, sometimes the mineral indicator for gold turns out to be a diamond indicator. Such indicators include chromium garnets, green olivine, and magnetite. Often upon striking gold, there is likely a diamond rock nearby. Additionally, sometimes the pure garnet crystals are also very valuable.
Many gold-hunting detectors have a higher operating frequency that increases their sensitivity. These frequencies begin at 20kHz and extend to 70kHz and greater.
Ultimately, the odds of finding gemstones attached to jewellery are greater than finding them in their natural state in the ground. Places likely to hide lost jewellery that may have precious gemstones include golf courses, beaches, and outdoor concert spaces where trinkets easily get lost.
Conditions Where the Detector won’t Find Metals:
Even though a metal detector cannot identify some metals, it will also be ineffective in certain circumstances.
Ferromagnetic material in sand
Many areas of sand and types of soil have an amount of iron and conductive properties. Moreover, sometimes salts in dissolved underground water also lend the sand or soil these conductive properties. The low-frequency detectors, then, can pick up strong signals from the ferromagnetic elements in the sand.
Crowded spaces
Managing security has become a real concern today. With a great influx of people, such as in an airport or shopping mall, you might have a hard time detecting anything metallic. Additionally, with so many conductive and semi-conductive materials available, some machines have a hard time detecting small metal elements.
Weather conditions
The prevailing weather conditions determine a detector’s efficiency. For example, treasure hunts in areas covered by a thick layer of snow will make detecting a signal from a buried item difficult.
Detectors have various applications beyond finding nuggets of treasure. For example, an explosive vapor detector determines the presence of any explosive material in a space. The best frequency will depend on the detector’s job. Consequently, a simple, affordable device is sufficient for treasure hunting as a hobby. More critical endeavours will then benefit from a higher-level detector.
