| 摘要 |
<p>Volumetric alarm system based on ultrasonic waves wherein the signal picked up by the receiving station is returned in an amplified form and, on reaching the receiving station, is retransmitted after further amplification, and so on, the phenomenon being continuous and repeated in each cycle, there being created, due to the fact that, while crossing the protected area, the various frequencies composing the signal undergo varying attenuation in relation to a prevailing frequency, a resonance of the entire system on said prevailing frequency which is automatically selected from among the other frequencies, thus further creating a broad signal which is always present, reliability of the system being thereby considerably improved.</p> |
