Intruder alarm less prone to false alarms - activated IR emissions and ultrasonic reflection pref. includes polymer etc. components

摘要

An intruder alarm consists of a detector contg. polarised material with both piezoelectric and pyroelectric properties for sewing acoustic vibrations and electromagnetic waves in the infra-red range. A significant variation of either of these emissions in the area surveyed by the detector causes an electric signal in at least one separate circuit. Signals occurring simultaneously in circuits corresponding to acoustic and i.r. waves trigger an alarm. The material used in the detector is pref. an inorganic oxide, esp. BaTiO3 or LiNbO3 type structures, e.g. titanium lead zirconate ceramics or LiTaO3 or a vinylidene fluoride (co)-polymer. These materials are treated in an intense electric field to acquire piezoelectric and pyroelectric properties.