I became addicted to metal detecting through this job of mine, writing for Caravan & Outdoor Life. In the July issue, I wrote about how I’d been given a Minelab Safari metal detector and told to ‘…fly up to PE and follow the Sunshine Coast looking for treasure.’ As you might have read, I found treasures galore, but no gold and silver. In my defence, it was my first treasure-hunt, so I was an absolute rookie. The treasures that I did discover were the memorable days out in the fresh air, getting suntanned and fitter as I dug like an aardvark in a termite mound. Added to that was a new interest in history, geography and archaeology… especially history, as I delved into the stories of the shipwrecks that have occurred along our coastline over the centuries.
Metal detecting is a stress-buster deluxe, too! You leave your worries at home as you wander along, hoping that the next squawk in your headphones is going to be the mother lode. Talking about home, my wife had dug out an engagement ring on her first try with the Safari – and at that moment I’d become completely hooked. So, here is a basic introduction to this fascinating hobby, thanks to a lot of help from the friendly people at Minelab South Africa.
How does a metal detector work?
Metal detectors create an electromagnetic (EM) field around the coil (normally the round bit that you sweep over the ground), and this field penetrates the ground. Because metal is conductive, it causes a change in the electromagnetic field. The detector senses this change through the coil and sends a signal to the control box, alerting the operator via the headphones. Metal detectors can determine the size, shape and composition of metallic objects beneath the coil.
Usually, the larger the object, the easier it is to detect. A metal detector’s EM frequencies are measured in kilohertz (kHz). Low frequency EM fields (e.g. 1.5 kHz) penetrate the ground deeply; but their sensitivity to smaller targets is low. High frequency EM fields (e.g. 65 kHz) have a shallower depth of penetration, but their sensitivity to small targets is high. The multi-frequency operation (used by the higher-end metal detectors) combines the advantages of both: good depth and high sensitivity. (I got this information from a Minelab information brochure; I feel it explains the technicalities better than I ever could.)
