| 摘要 |
Intrusion detection apparatus for detecting an intrusion within a space, comprising: transmitter apparatus 20 for transmitting into the space a first acoustic signal at a first frequency and a second acoustic signal at a second frequency; receiver apparatus 22 for receiving and demodulating a first reflected acoustic signal produced by reflection of the first acoustic signal within the space and a second reflected acoustic signal produced by reflection of the second acoustic signal within the space to generate a first in-phase data component and a first quadrature data component for the first received signal and a second in-phase data component and a second quadrature data component for the second received signal; processing apparatus 32 for receiving the first in-phase and first quadrature data components and generating a first deviation value in dependence thereon, receiving the second in-phase and second quadrature data components and generating a second deviation value in dependence thereon, and comparing the first deviation value and the second deviation value and generating an intrusion signal in dependence on that comparison. |
