Space surveillance apparatus with sound source and method of short-range space surveillance

摘要

A space surveillance apparatus includes at least one source of sonic radiation driven by a driver circuit as well as a processing or evaluation circuit. Upon movement of an object, or presence of a foreign object within a monitored space, the processing circuit triggers an alarm signal. Each sonic source defines the volume of its own monitored space, according to the equation: ##EQU1## wherein: L=Length of main direction of radiation of the monitored space;PPD=Diameter of diaphragm of sonic source; andPP&lgr;=Wavelength of acoustic wave.PPThe driver circuit drives the sonic source either in continuous mode, or in pulsed mode, and either at a constant wavelength or at a variable wavelength, i.e. in frequency modulation.