Cambridge Consultants has launched a compact ‘through-wall’ radar sensing device which gives security forces a means of reducing the enormous risks involved in tactical entry, and siege or hostage situations.
The Prism 200 product, which is the size of a briefcase, uses sophisticated software to evaluate the position and movement of people in rooms and buildings. According to the company, it incorporates three advances that now make through-wall radar technology a highly practical proposition: a radar device that is battery-powered and highly portable; smart radar signal processing that senses human movement and position - even in difficult environments with lots of reflecting surfaces; and meaningful data presentation in forms to suit the user, including plan, elevation or 3D views.
Technical aspects
The Prism 200 is an 'impulse radar', which operates by transmitting a very short pulse and then listening for echoes from objects that the pulse bounces off. The system operates with a 100 Hz frequency (100 pulses/second), providing a fast update rate.
It uses ultra wide band (UWB) principles in a band around the 2 GHz region. This is a moderately low frequency that is a good compromise between being able to penetrate solid materials, but requiring antennas that are small enough to allow the system to be both compact and portable. This frequency means that the transmitted wavelength is physically short enough to allow it to penetrate some reinforced structures that have steel grids embedded in concrete.
The radar uses an array of antennas. These allow the system to accurately measure the angle of arrival of echo signal returns, yielding both horizontal and vertical information data so that 3D positions can be determined. The use of UWB technology also makes the system very good at resolving the distance of objects.
Fast digital signal processing is performed on the echo results to distinguish between objects that are static, such as furniture, and objects that move. The system achieves this by maintaining a memory of background signals and observing changes above and beyond that database.
Cambridge Consultants has also developed a sophisticated layer of signal processing that effectively enhances the contrast between real human subjects and secondary reflections that return via an indirect path. Much of the value of the system lies in this software layer, as a person or persons often need to be distinguished from a myriad of reflections - or clutter. Real-world environments such as offices can present major problems, due to their angular surfaces and use of strong reflecting materials such as metal.
The packaged system measures 210 x 300 x 450 mm and weighs 5,4 kg, including a li-ion battery pack. A video of the system in use can be seen at www.cambridgeconsultants.com/prism200.
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