| 摘要 |
A field disturbance sensor operates with a relatively low power, provides an adjustable operating range, is not hypersensitive at close range, allows co-location of multiple sensors, and is inexpensive to manufacture. The sensor includes a transmitter (11) that transmits a sequence of bursts (19) of electromagnetic energy. The transmitter frequency is modulated at an intermediate frequency. The sequence of bursts has a burst repetition rate and each burst has a burst width and comprises a number of cycles at a transmitter frequency. The sensor includes a receiver (21) which receives electromagnetic energy at the transmitter frequency, and includes a mixer (22) which mixes a transmitted burst with reflections of the same transmitted burst to produc e an intermediate frequency signal. Circuitry, responsive to the intermediate frequency signal indicates disturbances in the sensor field. Th e burst repetition rate is randomly or pseudo-randomly modulated so that bursts in the sequence of bursts have a phase which varies.
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