How does a metal detector find metal ?
Essentially, a metal detector detects metal through the transmission and reception of very low frequency (VLF) magnetic waves. Most of today’s detectors operate on a VLF and are referred to as VLF or motion detectors.
A magnetic wave is transmitted through the transmitter portion of the detector’s searchcoil, which subsequently generates an invisible, intangible magnetic field that balloons outward into the surrounding medium, such as air, earth, clothing, water, etc.. The field size varies depending upon the size of the searchcoil and the resistance of the medium into which the signal is transmitted.
When metal enters this magnetic field, it absorbs some of the field’s energy. The remaining energy causes eddy currents to flow over the surface of the metal, creating a smaller, secondary magnetic field that also flows into the surrounding medium.
The receiver coil in conjunction with the detector’s circuitry measures the field’s power loss and detects the presence of the secondary field. Essentially, a metal detector “finds” metal by simultaneously interpreting these two effects and conveys the results via an audio and/or visual alarm.
All metals are classified according to their ability to conduct electricity. A metal is typically referred to as a good conductor (e.g., aluminum, gold, and silver) or a poor conductor (e.g., iron and stainless steel).