Another improvement over conventional smoke and flame detection technology has been demonstrated at the Universität Duisburg Essen, Germany, this one using microwaves to detect fire. The goal of the microwave project was to investigate the thermal radiation emissions of fires to detect fires by their thermal radiation in the microwave region.

“The main advantage of the microwave region compared to infrared is that the attenuation of microwaves due to smoke is negligible,” said research scientist Thorsten Kempka. Conventional detectors are based on thermal radiation in the infrared region; however, attenuation of this radiation due to smoke is high.

“Microwave radiation offers some distinct advantages in comparison with conventional IR radiation,” Kempka said. For example, microwave radiation penetrates thick smoke with only slight attenuation, and it has the ability to penetrate practically all materials except metals.

Moreover, unlike infrared methods and semiconductor sensors, microwave radiometers are mostly insensitive to environmental conditions, such as water vapor, dust and high temperatures.

Kempka has developed and tested a device that has the ability to detect smoldering fires earlier than conventional detectors.

“Data taken from the test fires confirm the basic functionality of this approach,” Kempka said. Test measurements indicate that in some cases it's possible to detected fires earlier than with optical or gas sensors. A major advantage is the ability of microwave radiation to penetrate non-metallic material, which means that fires can be detected even behind walls.

Kempka reported the microwave receiver device is able to measure thermal radiation from 2GHz to 4GHz. Kempka said the receiver is controlled by a conventional PC, making measurement setup easier. “One can choose any combination from the 380- by 100MHz frequency bands for a single measurement,” he said. A graphical tool can then be used to configure and control the measurement.