Build it and they will come, said the ghost to Kevin Costner in Field of Dreams. It may not be a baseball field, and it’s certainly not in a cornfield in Iowa, but John Bowerman’s Field of Beams, constructed in a horse paddock in Buckinghamshire, attracts visitors from around the world.
What are they coming to see? Simply one of the only (it’s possibly unique) test fields for some of the most advanced perimeter detection systems available on the market, including microwave and infrared beam detectors and a buried system called GPS.
Belying the sophistication of the equipment installed, Bowerman lets the field from a local publican and shares it with several horses, among them two racehorses which readers may have heard of: “Won’t cost a lot but...” and “Will cost a lot but...”, and a grey pony which has a fondness for headbutting expensive security equipment.
Equipment in the field includes some of the most sophisticated perimeter intrusion detection equipment available on the market today. Specifically, it comprises two buried GPS systems (one analogue and one digital), two microwave systems (one analogue and one digital), an infrared beam system and several fence-mounted microphonic systems, using various types of microphonic cable. All the systems use GPS signal analysers (except for the microwave detectors which are manufactured by Cias) to process the signals and relay the information to a secure hut fitted out with a test bench and an alarms panel.
Bowerman, who markets the equipment on behalf of the Italian manufacturer, GPS Perimeter Protection Systems, installed the equipment in the field two years ago for two reasons: real-life field testing and marketing.
For marketing purposes it’s imperative that he have a place to demonstrate installed equipment. As he explains, existing clients are not too keen to serve as his demonstration field: “It’s very difficult to persuade clients to allow other clients on their sites to have a look at their systems, primarily because they are not keen to show-off their security measures to everybody. Some clients will allow us to bring other clients to their sites, but you can’t keep going back to the same sites time after time, so we needed a place we could bring prospective customers to see the systems working.”
However, equally important was the need for a testing facility for his own purposes. Having come from a strong engineering background, he was not happy to sell systems without knowing how they would perform under real conditions.
“We wanted to have someplace where we could assess the performance of the systems under different conditions, typically conditions that you are likely to find in the field, to ensure that we could set the systems up properly and adjust them to get optimum performance,” he says.
The installation they have developed over the years is as real as it gets. The fences —chain link and pallisade — are good quality, but as Bowerman explains, “not perfect”. The chain-link fence has been allowed to go slack in places, so it flaps a bit in the wind. And the pallisade fence has a few loose palings and branches from a tree have been allowed to grow into it.
“You never get a perfect fence. This fence is typical of the fences we find in commercial sites,” he says. “What tends to happen is they are very nice when you first install them but six months later, without further maintenance, they tend to get loose. You need to know how the system is going to perform on a fence like that.”
The field itself isn’t perfectly level, it’s muddy and continually churned up by horses. “It’s okay for what we need it for because we can do tests in it. Again, it’s typical and not perfect,” Bowerman shrugs. A case of making a virtue of necessity, perhaps, but still it’s a good test bed for systems that, once installed, must tolerate a wide range of conditions.
Out, standing in their field
Bowerman showed SMT around the field, demonstrating the various systems which he has installed. We walked right over the most impressive, and most covert, of the systems, the GPS buried perimeter detectors. You don’t even notice the system until Bowerman points out the man-hole covers at either end of the field and the one in between.
Buried 20-25cm beneath the surface, GPS comprises two tubes which look like garden hoses, which are laid parallel to one another about a metre apart. These tubes are filled with a pressurised mix of water and anti-freeze. When someone walks across the ground, they create vibrations in the ground, typically in the range of 1 hertz to 16 hertz, very low frequencies indeed.
These vibrations affect the pressure in the hydraulic tubes, so that the tubes resonate directly in response to the vibrations in the ground. As we walked across the ground, each tube was resonating differently, depending on how far from each tube we were at the moment.
The two tubes run under the ground and pass into a sensor located under the man-hole cover. In each sensor is a detection chamber, which is split down the middle by a piezo-electric membrane. Each side of the chamber is filled with fluid which is free to flow in and out of one of the tubes.
As the vibrations cause the pressure in the tubes to change relative to each other, the pressure in either side of the sensor chamber changes and the piezo-electric membrane moves back and forth, generating a low-frequency electric signal. The signal is analysed by a microprocessor in the sensor, and the resulting information is sent via a cable to an alarm panel located in a nearby shed.
The detectors are sensitive enough, claims Bowerman, to detect a rabbit hopping over the surface and yet are virtually unaffected by nearby road and rail noise. This is possible not because of computing power but simply because of the mechanics of the system.
How is it that GPS is unaffected by distant vibrations? This is where the dual-tube construction comes into its own. Should a train pass by, even just 20 metres away, the vibrations will cause the pressure in both tubes to change in harmony because the source of the noise is relatively far away. The pressure inside the sensor, on both sides of the piezo-electric membrane, also changes in harmony, resulting in a minimal amount of movement in the membrane, generating a very weak electrical signal which can be ignored.
Bowerman explains: “The tubes are relatively close together compared to the noise source, so you are getting an increasing pressure on both sides of the membrane which balances out the signal. You haven’t done any signal processing yet, but you have eliminated the background noise. You can concentrate your electronic processing on the sounds of people walking across the perimeter.”
After the mechanical technique has eliminated background noise, advanced electronic signal processing (called Fourier analysis) takes over.
And with advanced signal processing under development,
users will even be able to train the system to tell the difference between animals and people and how to differentiate between a person crawling, rolling or tiptoeing over the perimeter. It will also be possible to pick out even lower level signals from the background noise, says Bowerman.
Competing systems
Other types of buried perimeter detection systems on the market include radio-frequency and microphonic. With radio frequency systems, two coaxial cables are buried close together. One is charged and designed to leak energy, the other is not charged and absorbs the energy, thus creating a field between them. A body passing through the field disrupts it, thus generating an alarm signal.
Microphonic systems work by “listening” for the low frequency noises generated under the ground by bodies passing over it. It works, but advanced signal processing is necessary to eliminate background interference and pick out the desired signals from the noise.
Bowerman claims that GPS has advantages over both of these systems. Because of the construction of the sensor, background noise is eliminated even before signal processing begins, meaning you have a better quality signal and can throw more processing power at analysing the signal rather than picking it out of the noise.
And with GPS no one can ever be sure exactly where the perimeter is. Because it is hydraulic, there are no RF signals to detect. The tubes are made of non-ferrous materials and are virtually undetectable.
When installing them around a perimeter, they don’t even have to be laid in a straight line, which has two advantages: firstly no one can ever be certain where the perimeter begins and ends, and secondly, you can follow the terrain — over hills, into ditches, around trees and other obstacles.
More than one string
However, GPS isn’t the answer to all perimeter protection problems, and Bowerman is the first to admit it. He believes in having more than one string in his bow, which is why he will also recommend fence-mounted microphonic systems (using similar signal analysis techniques to GPS but at higher frequencies), infrared beam detectors and microwave beam detectors. Each has their purpose, and the biggest mistake that anyone can make, he says, is trying to make one system suit all needs.
Bowerman explains his approach to securing a perimeter: “If you have flat ground, with relatively long, straight lines of sight, then infrared beams and microwaves are good forms of security. Microwave gives you slightly higher security because it gives you this complete cone of coverage whereas an infrared beam is this thick.” He holds out his clenched fist to demonstrate. “You need a few of those to give you complete protection.”
Infrared beams are good but have their drawbacks, too, in that they can be affected by heavy rain, fog, mist and snow. “Microwave beams are not affected by these things, but both are cost-effective for long straight runs.”
A ballpark figure for installed cost (and Bowerman cautions that this is a rough estimate only) is about £10 per metre, for infrared beam and microwave. For GPS you are looking at £30-£40 a metre. GPS comes into its own when you don’t have a long, straight perimeter.
The problem with IR and microwave is that they need line of sight to work. “The number of sites you go to where you get long, straight lines of sight are relatively small,” says Bowerman. Most perimeters tend to go up and down hills, zig-zag between obstacles and change direction entirely. Under those conditions, microwave and infrared beam becomes prohibitively expensive because everytime you change direction, you have to install a new detector.
And as mentioned earlier this is where buried systems come into their own. “With buried detectors, because the tubes are flexible, the shape of the perimeter isn’t an issue. It doesn’t cost you anything more to go in a straight line than to go in curves and zig-zags.”
World-wide demand
A look at the range of projects that Bowerman has worked on in the past six months shows the range of sites he gets involved with, and the world-wide demand for this type of security technology.
Bread and butter for Bowerman is prison work, where microwave detectors are often specified. He has also been involved with projects for NATO in Holland, in Malaysia for the Singapore-Malaysia expressway, and a residential project in Bermuda in the past six months. “We supply systems for everything from scrapyards to residential homes, from nuclear powers stations to prisons,” he says. “One of our latest projects is a house in London that needed just 20 metres of perimeter protection.”
The vast range of projects which Bowerman has worked on is, perhaps, indicative of the extent to which the security industry gets involved with all facets of life. His field of beams, in a horse paddock in Buckinghamshire, may not be glamorous but it certainly proves the adage: if you build a better mousetrap, the world will beat a path to your door, even if it’s a cold and muddy path.
Source
SMT
