London, England, September 4, 2001 – Safety in places like nightclubs and football grounds could be improved by a new generation of people-counting thermal imagers. Speaking at the Institute of Physics conference on sensors and their applications, which ran this week in London, Steve Hollock from IRISYS described a sensor developed by the firm that could bridge the gap between accurate but expensive thermal imagers with 50,000 pixels and the simple, cheap infrared-beam sensors that are too primitive for many desired applications.
Close-circuit television is often used to monitor people going into and out of shops, stations, and other public places, but there are many problems in using this kind of system if an accurate count of people is needed, notes Hollock. Another kind of sensor, an active infrared beam, is also problematic, as two people cutting the beam at the same time will only register as one. Sophisticated thermal imagers are normally only used in areas such as defense, as their cost is prohibitive for other markets.
The detector developed by Hollock and colleagues at IRISYS, which is similar in some ways to such higher-end thermal imagers, provides a counting system at a cost well within reach for many retailers and small businesses. This detector counts the number of people in the field of view irrespective of the lighting conditions and can even find out the speed and direction that someone is moving, as well as their size and the length of time they have been in the field of view. By linking a number of such devices, it is also possible to get an overall picture of the motion of people, without counting the same individual twice.
The new sensor has a detector array made up of 256 (16 X 16) elements formed by a pattern of electrodes on the surface of a ceramic chip. It is connected to a silicon chip that controls the output of the detector elements and allows the data to be processed. A viewing window is attached to the detector and has a filter to select the wavelength of radiation that falls on the detector elements. Human bodies radiate most intensely around 10 microns, so to detect people, a filter is chosen to let this radiation through.
According to Hollock, the key to making this detector simple is that the detector only responds to changes in temperature, so it does not see individual static objects in the scene known as scene clutter. By only giving a signal when an object moves within the scene, this detector saves a lot of computing power compared with video-based systems. The accuracy of the detector is extremely accurate, as it can resolve up to a 0.5-degree-centigrade change in temperature.
“Bringing high-performance sensing technology within reach of commercial applications will allow access to situation data previously unavailable or too expensive to gather” notes Hollock. “The most recent interest in this system has come from the automotive industry. They are looking for a way of telling where in a car a person is when an airbag goes off. Our detector gives information on the position of the person more accurately than any visual system as it is unaffected by shadows or night driving, so it could be incorporated into cars to make airbags safer,” he added.
For more information on this research please contact Hollock at IRISYS Ltd, Phone: +44 (0)1327 357824, Fax: +44 (0)1327 357825, Email: [email protected].