The Design and Functionality of Metal Detectors
The metal detector was invented in 1881 by Alexander Graham Bell following the shooting of President James Garfield. The President had survived the shooting and was rushed to the hospital where doctors were unable to locate the lodged bullet in his body. in an attempt to save the President; Alexander Graham Bell developed a crude electromagnetic metal detector known as the: induction balance. However, this attempt was unsuccessful since the metal springs on the bed interfered with the device's precision. The induction balance was then used to detect explosives during World War I and II and became the medal for the development of modern metal detectors as more research and investment was put into the technology. In 1925, Gerhard R. Fisher developed a portable metal detector. He got a patent for his device and began industrial production, making it available for sale in 1931 through his company Fisher Research Labs. Fisher's device has since been improved on over the years by several other people, increasing the metal detector's usability and precision.
Modern metal detectors use either of these technologies: Very low frequency (VLF), Pulse induction (PI) or Beat-frequency oscillation (BFO):
I. Very low frequency (VLF) or induction balance metal detectors use two coils; the transmitter coil which is a coil loop with a coil wire within it, where an electric current is passed to one direction in the wire and to the opposite direction in alternating loops; the second coil is the receiver coil which is an inner coil loop with an inner coil of wires. The receiver coil picks up and amplifies frequencies from objects Electricity moving in in the transmitter coil creates an electromagnetic field which pushes down and forth to the ground each time the current changes direction. When this magnetic field interacts with a metallic object emitting a magnetic field: a small current pass through the receiver coil which then produces a signal, the strength of the signal is determined by how close the object is to the ground whereby; close objects emit stronger currents and stronger signals while objects which are deeper on the ground emit weaker currents and weaker signal. Objects which are deeper on the ground emit weak electromagnetic fields which cannot be detected by the VLF.
II. Pulse induction (PI) metal detectors have one coil which acts as both a transmitter and receiver and may have two or three coils working together. The Pulse induction metal detectors work by sending short electric pulses which generate an electromagnetic field. At the end of the pulse, the magnetic field collapses and reverses polarity, causing a brief and sharp electric spike (of approximately 30 microseconds long) which triggers the next pulse. This electric spike is known as the reflected pulse. The number of pulses varies from a dozen to thousands per second, depending on the device. If a PI metal detector identifies a metal object, the pulse; the reflected pulse lasts longer than normal, signaling the presence of the object.
All Beat-frequency oscillation (BFO) metal detectors have two coils: the larger coil is located in the search box while the smaller one is at the control box. The coils are each connected to an oscillator which produces electric currents at different speeds for each coil. The electric current in turn produces radio waves which are picked by a receiver the control box that produces audible tones to note the difference between the frequencies of a BFO metal detector notices a metallic object, the magnetic field of the object interferes with the frequency of the radio waves causing the receiver to produce longer or louder audible tones.
Tips and techniques for using metal detectors
You can use the metal detector to detect metal objects of any kind; either for security (detective) purposes at events, buildings or other installations; and/or for fun activities such as treasure hunting and coin shooting. Regardless of the use, proper handling of metal detectors results in higher effective, especially when you are using. Here are some tips and techniques for using metal detectors:
1.The most basic way of using a portal metal detector is sweeping - this is moving the device from side to side across the target area. While doing this slightly overlap each area as you gain ground to avoid missing a spot and keep the metal detector parallel to the search area.
2.Always move the metal detector slowly and as close to the surface as possible and be keen to listen to the faintest noise. Moving so fast may make you miss the signal as; the detector may not respond in time as compared to your movements.
3.Always ensure that you protect your metal detector with covers such as plastics (which will not interfere with their effective. if and when you are going to use them in salty water or send.
4.Ensure that you clean your metal detectors before storing them. This is important because foreign objects on the device such as insects, leaves, sand, and water among others may corrode it over time. Use a mild detergent, hot water l (of not more than 40 degrees centigrade} and a piece of cloth to clean and dry the device.
5.Ensure that you store your metal detector appropriately when not in use and that you abide by the instructions parodied by the manufacturer in the user manual. Finality, you should also note that there are several factors which could interfere with the precision of your metal detector. These include; mineral composition of the soil as certain minerals interfere with the metal detector: size of the object smaller objects are harder to detect? type of metals ferrous and now- ferrous metals are easy to detect while stainless steel is a bit difficult to detect: orientation effect this is related to the position of the object in relation to the metal detector, for instance; a non-sphere object such as a wire may be easy to detect on one side and harder on the other: and interference from other objects such as metal pipes, cables, and furniture among st others.
