FERROMAGNETIC FOREIGN BODY SCREENING METHOD AND APPARATUS

摘要

A method and an apparatus are disclosed for applying a low strength, time varying magnetic field (26) to a selected screening region of a host, and for sensing a responsive magnetic field (28) from a retained ferrous body within the screening region. The excitation field coil is designed to create a region of finite magnetic field within the screening region, and a region of near zero magnetic field. The sensors (24) are placed within the region of near zero magnetic field to minimize the effect of the applied field. The effects of the applied field are further reduced by use of a reference sensor, field compensation coils, and a feedback loop. The magnetic gradient by the sensors (24) is processed to locate and characterize the ferrous body.