Magnetic detectors

A security screening apparatus for differentiating between ferromagnetic objects having different magnetisation, comprising:

• at least one magnetic sensor arranged to produce a signal indicative of an ambient magnetic field or gradient over a zone of sensitivity around the sensor;
• a signal processing circuit configured to receive as an input the signal from the magnetic sensor;
• a detection circuit configured to determine whether a signal is above a detection threshold, and, in response to a detection, emit an alert signal;
• and
• a detection zone defining module configured to define a detection zone within the zone of sensitivity, the detection zone including an inner bound at a predetermined distance from the magnetic sensor,
• wherein the detection zone defining module is configured such that objects with a large magnetization, such as rifles, shotguns, or shrapnel suicide vests, are detectable within the detection zone to the extent that they cause an alert signal to be emitted, whilst objects with a smaller magnetization do not cause an alert to be emitted, and
• wherein the predetermined limit is between 30 and 500 mA/m2, or more preferably between 70 and 300 mA/m2, or most preferably is substantially 100 mA/m2.