Since Sept. 11, increasing security has been a main priority of U.S. officials, and Penn State scientists believe they have found a way to assist in that endeavor by developing a fence that detects, locates and determines intruders.

David Swanson, associate professor of acoustics and senior research associate for the Applied Research Lab, Nicholas C. Nicholas, ARL senior research associate, along with David Rigsby, a private consultant, created this defense mechanism.

Swanson said, "We were forced with 'How do you protect a large area?' You have to come up with low-cost solutions."

The large areas could be airports, ranches or military bases, for example.

The trio came up with the idea of using a tensioned wire to detect disturbances. This plan was taken to L. Raymond Hettche, director of ARL, who gave some funding to the project.

"He deserves a lot of credit for his foresight," Nicholas said.

Some other similar devices could cost between $120 to $180 a linear foot, Nicholas said, "which makes them prohibitively expensive. There are facilities that have fences a mile long."

Their fence costs are considerably less than other systems that use microwaves or co-axial cables.

For the hardware, the cost of the fence is about $1 a linear foot, but Nicholas said, "It is not accurate to say it costs $1 a linear foot. You have the processors, the (personal computer), the radio frequency links, and the labor to set it up. Even with all of this, it is a fraction of the costs of the alternatives."

There is an inconspicuous wire that runs along the fence. The wire is held steady by a pulley. Whenever the fence is disturbed, the waves are transmitted along the wire to a sensor, which then sends the information to an outdoor computer. The computer signals the main station, which can evaluate the situation.

"It was an inexpensive little experiment, and it worked," Swanson said.

An experimental fence was installed at the ARL's engine test facility.

Disruptions along the fence's wire could be localized within 20 feet, Nicholas said.

Also, if there is a camera on the fence, it can be steered toward the disturbance to see what is causing it.

"One of the strengths of this is the only things you need to carry out there are the sensors, the PC and the software," Nicholas said.

The pulleys, wires, clamps and other materials can be bought at a local hardware store, he said.

"Each installation needs to have a certain amount of tailoring," Nicholas said.

The scientists were concerned natural elements could also disturb the fence, which could make detection difficult, but the test alleviated these fears.

"The wind will excite the fence differently than somebody climbing the fence," Swanson said.

A person could damage the system by cutting the wire or attempting to damage the computer.

But Swanson said that it would be possible to detect such an intrusion, because, "You know somebody is messing with the fence."

Penn State has filed a provisional patent for the invention.

"The next stage will be an engineering development model, so that we can fully evaluate the considered potential of this," Nicholas said.

The computer location process also will be further developed.

"We have to do some algorithm development," Rigsby said.

"We have to (complete) software that manages multi-sensor input," Rigsby added.

The final version of the fence is not too far from completion, the researchers said.

"A couple of months -- that's literally the kind of time scale," Swanson said.

"We're pretty far along now," Swanson added.