At the end of the past 19th century, a lot of scientists and engineers used their increasing knowledge concerning electrical theory in attempts to devise a special machine which could pinpoint metal. The real use of such devices was aimed at finding ore bearing rocks which would give very huge advantages to any miner.
One German physicist known as Heinrich Dove (lived from 1803 to 1879) actually invented the system of induction balance, which got incorporated into walk through metal detectors hundreds of years later. Early machines, however, were crude and used too much battery power. They worked only to very limited degrees. Alexander Bell did use such a machine to attempt locating a bullet that was lodged in the torso of the American President called James Garfield (this was done in the year19 18). The metal detecting device worked well, but the attempt has proven unsuccessful since the spring bed made of metal coils that Garfield laid on confused the signal.
Modern developments of metal detectors began in earnest during the 1920s. Gerhard Fisher developed a radio direction and finding system that was to be applied for precise and accurate navigation. The system did work extremely well, but were noticed anomalies in various areas where geographical terrain contained some ore bearing type of rock. He then reasoned that if the radio beam was distorted by the metal, then it must be very possible to design a type of machine which can detect metal using resonating of a search coil at radio frequency. This is the humble beginning of the walk through metal detectors.
In the year 1925, Gerhard Fisher requested for and was granted a first of its kind patent for a device that acts as a metal detector. Although he was the very first person who was granted a legal patent for a metal detecting device, the very first to apply was actually Shirl Herr who was a businessman coming from Crawfordsville in Indiana. His original application for a type of hand held and hidden metal detecting contraption was filed in the month of February in 1924. This actually bears the hidden attributes of the modern walk through metal detectors. However, it was not patented before July, 1928.
Herr assisted the Italian leader known as Benito Mussolini in the recovery of items that remained from the galleys of the Emperor Caligula at the very bottom of the Lake known as Nemi in Italy. This was in the month of August in 1929. The invention by Herr was also used by Richard Byrd, an Admiral in the Second Expedition of the Antarctic in the year 1933. It was effectively used to locate certain objects left behind during earlier explorations. It was very effective up to depths of only eight inches.
However, one Polish officer that was attached to a particular unit stationed in Scotland in the early years during the Second World War refined the original design into a very practical mine detector. They were very heavy and ran on the old vacuum tubes. They also needed separate large battery packs. However, this spelt the beginning of the development of the now commonly used walk through metal detectors.
Modern walk through metal detectors are top models which are fully computerized and use state of the art technology in integrated circuitry. This allows the user to even set sensitivity, discrimination of metals detected, track speed and even threshold volume, not to mention notch filters, among others. They have the capacity to hold these parameters in the inbuilt memory for any future use. Compared to a decade past, detectors are very light, intensively deep seeking, use much less battery power with the ability to discriminate even better.