Abstract: A method and apparatus for detecting the presence of an object, such as a biological organism, particularly that of a human. Changes occuring upon occupation of a unoccupied spacial location are sensed and analyzed to produce a display, or otherwise used to control other devices. The apparatus includes an antennae to detect electromagnetic radiation changes caused by an organism coming into contact with the antennae or in a spacial area in proximity of the antennae. The changes detected by the antennae are coupled through a receiver to a bridge network for analysis. The circuitry of the bridge network compares the changes caused by the detected object to a zero reference. An output from the bridge is applied to a process which compares all signals with a vector preset in the process. Amplitude and phase are compared with known characteristics for the presence of a human body.

Abstract: An electromagnetic lock for doors includes a large electromagnet mounted on the door frame, and a strike plate or armature secured to the door. A double-throw, double-pole type of relay or other switching circuit serves to selectively connect the electromagnet to receive rectified current when it is energized, and to receive a reverse pulse from a large capacitor when the door circuitry is de-energized. The large capacitor is charged to the same voltage as the electromagnet to insure full reversal of the magnetic domains to prevent residual magnetism. The double-throw, double-pole switch may be actuated by a high speed relay to insure timely switching of the contacts to apply reverse current from the capacitor to the electromagnet. The relay coil may be a latching relay which is selectively actuated in one direction while the circuit is energized, and is reversed as the electromagnet is discharged, so that it draws no current except when it is being switched on.