Authors : A.M.O. Obiazi, F.I. Anyasi, O. Jacdonmi, P.A. Otubu and I. Abhulimen
Abstract: Metal detectors are effective and useful security tools employed in strategic places such as airports, banks, stadiums, government houses and major hotels to detect the presence of ferro, para and dis-magnetic metals on persons, luggages and consignments. The study presents a metal detector comprising an RF oscillator, a detector/smoothing unit, comparator and a switching/signaling unit. A transistor colpitt oscillator is used with its inductor being a toroidal coil, thus acting as a transducer converting magnetic variations to voltage level changes through direct feedback mechanism. The tank circuit is set such that the feedback voltage is just sufficient to maintain oscillation. Magnetic variations caused by materials distort the initial set position, automatically cutting off oscillation and hence the transistor due to the biasing techniques employed. The comparator is set to switch to a negative voltage whenever the potential at its positive impact falls below 0.5 V and vice-versa. The performance of the detector was satisfactory, particularly for short-range applications. It detected both ferrous and non-ferrous metals like steel and aluminum at a range determined by the type of material and its relative size.
A.M.O. Obiazi, F.I. Anyasi, O. Jacdonmi, P.A. Otubu and I. Abhulimen, 2010. Implementing a Robust Metal Detector Utilizing the Colpitts Oscillator with Toroidal Coil. Journal of Engineering and Applied Sciences, 5: 56-63.