| 摘要 |
A vehicle presence detection system for detecting the presence of vehicles preceding along a roadway. A transmitter produces periodic pulses of sonic frequency. A transducer emits the sonic energy pulses, receives reflected sonic energy from the vehicles and generates electrical signals corresponding to such received energy. A wave guide is interposed at the output of the transducer for setting up substantially a line source of sonic energy providing an operating elliptical pattern of a minimum intensity over the roadway. Detection circuitry is actuated to manifest the distinctive indication of vehicle presence.
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