Surveillance technique for natural or artificial structures - uses detection of acoustic stress pulses in structure, converted to electric signals

摘要

A surveillance technique is described for natural or artificial structures such as sites or works of art. Acoustic stress pulses are sensed and detected on or in one or more structural elements. These acoustic pulses are transformed into electrical signals which are filtered so that only those pulse components lying within a know frequency band are transmitted. These components are converted into peaks whose level crosses the mean level of the corresponding components. Only those peaks whose levels are greater than a predetermined threshold are transmitted. The transmitted peaks are counted periodically to determine their rate.