A self-contained electromagnetic impact sensor includes a frame, a fixed permanent magnet, a fixed coil, and a metallic body elastically mounted for movement within the frame. An impact received by the sensor imparts motion to the metallic body, thereby altering the pattern of magnetic flux extending...http://www.google.fr/patents/US5623248?utm_source=gb-gplus-shareBrevet US5623248 - Miniature electromagnetic impact sensor
