MAGNETIC FIELD SENSOR AND METHOD

摘要

A sensor for sensing magnetizable and magnetized areas on or in an authenticatable item such as a security document during relative lateral movement between the sensor and the item described. A sensor, which is typically hand-held, comprises a sensing device including a magnet (8) and a microcoil (6) arranged such that the microcoil is under the influence of the magnetic flux from the magnet thus defining a magnetic circuit, the magnet (8) generating a steady magnetic field in use. The microcoil (6) is connected in an electrical circuit with an indicator, such as a buzzer (31), for indicating induced voltage in the circuit caused by a change in magnetic flux influencing the turns of the coil. A change in magnetic flux takes place during the passage of a magnetizable or magnetized area of an authenticatable item past the sensor by perturbing the magnetic field created by the magnet across the coil.