Abstract: Metal detector and method in which soil mineralization effects and responses to other undesired materials are eliminated. A periodic excitation signal is transmitted into an area where a target is to be detected, and signals returned by the target are processed to provide an output signal corresponding to the target. A plurality of signals are extracted from the output signal during different phase intervals in the period of the excitation signal and processed to provide signals which are free from ferrite response and/or response to other undesired materials. The signals which are free from response to ferrite and/or other undesired materials are then compared to identify the target.

Abstract: Walk-through ferrous metal detector and method in which potential carriers of weapons and other ferrous metal objects pass through a surveillance area in which the earth's magnetic field is monitored, and disturbances in the field due to movement of ferrous metal objects are detected.

Abstract: Metal detector for locating and classifying metal objects of different types in the ground or other surroundings. Automatic compensation is provided for signals produced by magnetic materials in the soil and by misalignment of the coils in the sensing head.

Abstract: Eddy current type metal detector for locating and distinguishing between metal objects of different types in the ground or other surroundings. Differentiation is employed to eliminate signals from the ground soil or other material in which the object is located, and objects of a particular type are detected from the phases of signals which they produce.