| 摘要 |
<p>A method for detecting abnormal situations in ultrasonic antitheft systems in which an emitter transducer generates ultrasound the return signals of which are received by a receiver transducer consists of interrupting the ultrasound emission at predetermined intervals for a predetermined period, and emitting an ultrasonic pulse of duration less than said predetermined period. The response or return signal from said pulse is received and analyzed, after which a signal is emitted for the purpose of restoring normal ultrasound emission if the value of said response signal is other than zero, or a signal for the purpose of activating an alarm device if the value of said response signal is zero.</p> |
