Dr. David C. Swanson, associate professor of acoustics and senior research associate at the University's Applied Research Laboratory (ARL), led the team that developed the approach at ARL's Institute for Emerging Defense Technologies. He says the approach is particularly appropriate for use in large fenced areas, for example, around airports, cattle ranches, military bases, high schools or embassies.

The new fence security system uses an inconspicuous tensioned wire as an extended sensor. The wire can be attached to any new or existing fence and is used to monitor the vibrations in the fence.

Swanson says, "The approach uses geophones – inexpensive, rugged, off-the-shelf ground sensor technology hooked up to the tensioned wire – and a low-cost embedded PC and software." The software, developed at ARL, enables the user to suppress background or environmental vibrations, sort through the signal carried by the wire and pinpoint information that indicates intrusion.

"Using the new approach, you can have the fence call you when there is an intrusion. You can also manage how sensitive you want the response," Swanson adds. "For example, you can have the fence call whenever a squirrel goes by or only when a larger animal gets through the fence." In addition to being sensitive, rugged and inconspicuous, the new system is cost effective. Competing systems equipped, for example, with microwave or co-axial cable technology, are much more expensive. A high tech prison fence, for example, can cost about $165 per foot. The researchers estimate that their approach would cost less than $1 per foot, plus about $5,000 for the central processor to retrofit a typical existing fence.

The new approach locates the site of intrusion by monitoring the vibrations in the fence and precisely detecting the time of arrival of signals from two or more locations. Measured differences between the signal's arrival times indicate the point at which the intrusion occurs. In addition, the system can classify the type of disturbance as well as locate the point of contact along the fence. Even careful climbing by an intruder, for example, would change the loading on the fence and signal that a human intruder was present rather than a squirrel. This information can be used by security personnel to plan a response or even to deploy less-than-lethal weapons or deterrents, automatically, to dissuade intruders from further invasion.

A prototype of the fence has been installed around ARL's engine test facility at Penn State's auto test track at the Pennsylvania Transportation Institute. The University has also applied for a provisional patent application on the invention. Besides Swanson, the inventors include Dr. Nicholas C. Nicholas, ARL senior research associate, and David A. Rigsby, a consultant. The research was supported by the Applied Research Laboratory.