| 摘要 |
<p>PURPOSE:To substantially eliminate the place where electric waves are weak in an electric field distribution formed around a transmission cable by providing a transmitting portion with a means for varying a standing-wave generated in the transmission cable. CONSTITUTION:A transmitting portion 1A is provided with a standing-wave variation means 10A comprising high-frequency oscillators 111A-114A for producing different high frequencies and a switching means 12A for switching and driving the oscillators. The means 12A drives the high-frequency oscillators in sequence at every tmus, so that different high frequencies are transmitted to a transmission cable 2A at every tmus. The cable 2A releases leakage electromagnetic waves, around which an electric field is formed. Since the frequency varies, a standing-wave generated within the cable 2A also varies, so that the position at which the electric field is weak is varied at every tmus. That is, the place where the electric field is weak is substantially eliminated. Therefore, intruders can be detected throughout the cable 2A when passing above the cable 2A buried.</p> |
