How Does a Metal Detector Work?
The most common of detectors used in present days are Induction Balance (IB) type. In the basic version their search head consist of two loops (coils). One is for transmitting signals (TX) and the other is for receiving signals (RX).n Another very popular metal detector type is the Pulse Induction (PI). This type of detector utilises in most designs search coil consisting of only one loop used for both transmitting and receiving signals. There is some PI designs utilising search coils with more than one loop. This article does not comment on other basic topologies upon which metal detectors are build for a reason that the IB and PI detectors are the most efficient and powerful commonly used metal detectors to date. There is one most common believe that the receiving coils in the search head of all metal detectors are actually receiving signals reflected by the metal targets buried under the ground. The pure scientific fact how ever is this: IB Detectors In IB detectors the two loops fo
Although metal detectors incorporate many different technologies, features and characteristics, most metal detectors are basically the same. A metal detector detects metal objects through the transmission and reception of very low frequency (VLF) magnetic waves, referred to as VLF or motion detectors. A magnetic wave is transmitted through a section of the detector’s searchcoil, generating an invisible, magnetic field that expands outward into the immediate, surrounding area (air, earth, water, etc.). The effective size of the detection area depends upon both the size of the searchcoil and the resistance of the medium being searched. When this magnetic field encounters metal, the metal absorbs some of the field’s energy and the remaining energy creates a smaller, secondary magnetic field that is detected by the receiver coil. The receiver coil and detector’s circuitry measure both the field’s power loss and secondary field, effectively identifying metal by interpreting these effects, c
To understand how a metal detector works, we first need to understand a bit about magnetism and electricity. If we pass an electrical current through a wire, a magnetic field is formed around the wire. Conversely, if a magnet is passed over a piece of wire, it induces an electrical current into the wire. This is called an eddy current. In a straight piece of wire, the induced magnetic field is very short-lived as the eddy current has nowhere to go, dies out quickly, and consequently the magnetic field created is quite weak. If the same eddy current is magnetically induced into a piece of wire with both ends electrically joined (like a ring), these eddy currents effectively run round and round, creating a stronger, more concentrated magnetic field which lasts longer. The transmitter current of a metal detector is applied to the coil (of wire) and creates a large, concentrated magnetic field around the coil. This magnetic field will induce eddy currents into any metal targets in the grou
According to Lenz’s law of electromagnetism, when a conductor falls within a certain range of an oscillating (alternating) magnetic field, it generates an oscillating field of its own, which opposes the primary field. A magnetometer can pick up the resulting changes in the overall field, signaling the nearby presence of a conductive object, typically a piece of metal. The range of metal detectors varies from a few feet for the smallest coils, to 10 feet (3 m) for 12 to 15-inch (30.5 to 38.1 cm) coils. The key to a functioning metal detector is the presence of eddy currents generated by conductive objects in the environment. Just like pushing a paddle through a lake of water can cause little vortices to appear on the surface, producing an oscillating field in the environment causes electromagnetic vortices when the electrons in metal generate their own oscillating field. Frequencies of 3 to 20 kHz are known to produce the best results, and some more modern metal detectors even allow the
