Hobbies And Interests
History
The first crude form of metal detector was invented by Alexander Graham Bell in 1881 in order to try to locate a bullet in President James Garfield's body. Gerhard Fischar made metal detectors portable in 1925. Metal detectors first became available to general consumers in 1931.
Effects
Some metal detectors are designed to remain in a stationary position. Metallic objects that pass over them set off an alarm. There are also portable metal detectors that can be placed over surfaces. These metal detectors light up or make a noise when metal is present.
Types
The three types of metal detectors are VLF, PI and BFO. VLF creates a consistent electromagnetic field. This field is pulled toward metal. When the VLF detects this pull, the metal detector triggers an alarm. PI detectors use an electromagnetic pulse. These pulses last a persistent amount of time, except when metal is present. The metal pulls at the pulse, drawing it out. The BFO, which is the cheapest type of metal detector, creates radio signals. The electromagnetic field that is created by the metal interferes with the radio signal and a signal is triggered.
Parts
Regardless of how the device detects metal, metal detectors all have three parts. A control box turns on the metal detector and determines the volume of the alarm. The shaft connects the control box to the search coil. The search coil is where the metal is detected.
Uses
Metal detectors are used both for security and recreational uses. Commercial metal detectors are often used to detect metal objects that might be collected by the user. Security metal detectors are designed to detect bombs, knives and firearms that are being smuggled into areas where they are not allowed such as airports and schools. The military also uses metal detectors to detect land mines.