| 摘要 |
An intrusion detection system for detecting objects entering a particular region is comprised of a transmitter, receiver and cable assembly, wherein the transmitter and receiver are connected at opposite ends of the cable assembly. In a first embodiment, the cable assembly is comprised of a transmit and receive cable pair that are aligned at each end and positioned at a constant distance from each other along the length. The transmitter is connected to the transmit cable at one end of the cable assembly, and the receiver is connected to the receive cable at the opposite end of the assembly, with a uniform electromagnetic field established between the cables. An intrusion perturbs the field, which causes a change in the magnitude and/or phase of the received signal. In a second embodiment, the cable assembly is comprised of a single detection cable with the transmitter and receiver connected to opposite ends. An electromagnetic field of propagation extends beyond the unshielded, or partially shielded detection cable and an intrusion causes a change in the effective dielectric constant of the cable. The change in the dielectric constant causes either a positive or negative phase shift depending on whether the intruding object is entering or departing the electromagnetic field. In either embodiment, the phase, or magnitude or both of the received signal are detected to produce a comparison signal which may be filtered to remove environmental effects. A response signal monotonically related to the magnitude of the changes may be produced and then compared to one or more thresholds. An alarm is indicated when the response signal exceeds a threshold.
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