Development Of Modern Metal Detectors

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early metal detectorsIt is believed that the first metal detector was discovered accidentally in 1925 when a radio engineer in the United States noticed a metal water tank was causing interference with his field experiments. Since the making of the first clumsy giants, detectors have been advanced to the stage where they do almost everything except dig.

From 1927 to the Second World War metal detectors were transmitter-receiver sets which had to be carried with straps on the shoulders. These had large and heavy batteries and were capable of finding only cricket ball or bigger sized targets. Mineralized ground interference was a major problem.

Miraculously one of these pre-war early detectors is still in existence in northern Victoria, Australia. In 1942 three people, Barnes, Muldoon and Kate Campbell formed a syndicate to try their luck on the Kingower gold fields with a huge detector developed by Barnes, who had been working on the problem of demagnetizing or degaussing ships traveling in waters laid with magnetic floating mines.

He achieved this by devising a series of cables wrapped around the ships hull. The cables were energized with DC current which neutralized the ships magnetic field. It was the ships magnetic field which triggered the floating mines and stopped the subsequent explosions which had sunk numerous ships up to that time.

The detector consisted of a large wooden wheelbarrow, with solid wooden wheels and long shaft handles. A long cable was wound onto a coil on the barrow; this led to a square frame standing upright on a beam which was carried out front by two strong men. The barrow also carried a car battery. It was wheeled into position and the area reached by the extended cable was scanned. The operator listened for signals transmitted back through head-phones.

The contraption apparently worked well enough to discover the farm’s water pipes and a lot of scrap metal. The effort required to move the device and the fact that it only detected large objects meant that it had limited use on the gold fields.

The Metal Detector In WW II

During World War II the metal detector became invaluable for locating the shallow land mines. After the war these ex-service machines were often bought by North American treasure hunters. United States manufacturers did not see the potential of developing this machine for the hobbyist until 1960-1961.

Transistorized circuits had been developed in 1957 and by the 1960s their use was commonplace. The development of the silicon transistor meant that metal detectors could be built which were light-weight and had little battery drain.

From the 1960s to 1973 most metal detectors were of the transmitter-receiver or BFO type. These machines were limited in scope in areas with ground mineralization, and they could not penetrate to any great depth. In 1974 the VLF (very low frequency) detectors were developed and so ushered in a new era of treasure hunting and prospecting. These recently developed machines still fail to cancel out the effect of salt water in beach sands and many still react to magnetic rocks, however with experienced operators these interferences can be overcome.

 

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