Metal detectors are instruments built to detect the presence of metals, mostly buried in the ground. Nowadays, they are widely used in the field of defense to detect enemy land mines. Other than military personnel, they are also used by security personnel, geophysicists, and archaeologists.
Metal Detectors History
During the last decade of the 19th century, scientists from all over the world explored the prospect of constructing a device which could detect metals. It was believed that introducing such a device would help to detect rocks with ore content beneath the surface of the Earth, thus making mining easier. In 1881, when President James Garfield was hit by a bullet, a device working on a similar concept was used by eminent scientist, Alexander Graham Bell to try to locate the bullet. The attempt though, was unsuccessful as the detection tool was baffled by the metal bed on which the President was lying.
A radio direction finding system used for accurate navigation was developed by Gerard Fisher in the 1930s. While testing this system, Fisher realized that there was some deviation from the normal trend of the machine when it closed in on an area that was believed to have ore-bearing rocks. He realized that it was possible to design a tool to detect the presence of metals by utilizing search coil resonator at a radio frequency. By 1937, he was granted a patent for the detection device, thus becoming the first person to get a patent for a metal detector.
A Polish lieutenant, Josef Stanislaw Kosacki refined the design to come up with a practical detector during the World War II. This heavy detector, which operated on vacuum tubes, required separate batteries for functioning. One of the most useful equipment in the war, it was widely used to clear the minefields laid by the retreating German forces.
Being an armed forces research operation, the modification of the device into a full-fledged metal detector was kept a secret for about five decades. Once the concept was out, many firms came up with their innovative versions of the same. Amongst the early manufacturers was Oregon-based Whites Electronics, which introduced a detection machine called the 'Oremaster Geiger Counter'.
Induction Balance System
The induction balance system which worked on the theory of magnetism was invented by German physicist, Heinrich Wilhelm Dove, many years before the invention of the metal detector. The system was made up of two electrically balanced coils, which would get unbalanced when closed in on any metal. The use of the induction balance system in these detectors made these crude devices more powerful.
The development of the metal detector also received a major boost with the development of Beat Frequency Oscillator (BFO) by Charles Garrett. Later, the introduction of the transistor supported the idea of coming up with smaller and lighter detectors, which would operate on relatively smaller batteries. Though small, these machines were much more powerful than their older counterparts. In the years to follow, the growing demand for this device was tapped by many companies.
Today, metal detectors have become compact and sophisticated devices. These fully-computerized gadgets use integrated circuit technology, which allows the user to set fundamentals like sensitivity to a particular metal, tracking speed, notch filters, etc. The in-built memory chip also stores the collected data for further use. From bulky machines, the detectors have gone through many tests and modifications to become the hand-held devices that we use presently. They have definitely come a long way to become power-optimized tracking devices.