Induction-type metal detector with increased scanning area capability

Abstract

A metal detector includes a detector head having a primary or transmit coil for the transmission of electromagnetic radiation therefrom, and having a plurality of secondary or receiving coils associated therewith for having voltages induced therein by transmissions from said primary coil. The presence of metallic objects within the detector head affects the voltage level induced in the secondary coils, a condition which may be detected as indicative of such presence of metallic objects. Each detector head preferably includes a primary coil about the periphery thereof, with a plurality of secondary coils, all in the same plane with the primary coil, situated axially in from the periphery of the detector head in a mutually non-overlapping configuration, preferably about the center of such detector head. A plurality of such detector heads may be supported in co-planar alignment by a common non-metallic support structure for scanning relatively larger areas at a time. The primary coil of each respective detector head may be sequentially pulsed and selectively spaced to avoid interference with adjacent detector heads, thereby avoiding certain inherent disadvantages in applying conventional single detector head frequency-dependent tuned coil technology to multiple head use in an integral metal detector system.