Circuit for detecting the presence of a permanent magnet near to an active medical device

摘要

A resonant circuit (10) employs a coil (12) and capacitor (14). The presence of a permanent magnet (16) near the coil reduces the coil inductance and this is detected by analysing the response to impulses from an excitation circuit (18). The excitation circuit is able to deliver a burst of N pulses and the analytical means determines the presence of a magnet when a preset number of responses M show diminished inductance.