Inter-Wall Fire Detection by Low-Cost Microwave Radiometric Sensors

This paper addresses the possibility to detect a fire behind a concrete or brick wall exploiting a microwave radiometric sensor. The sensor operates at 12 GHz in such a way as to balance a good wall penetration capability with a reasonable antenna size. To keep low the radiometer cost, commercial Satellite Television (SAT-TV) components along with a noise-adding calibration architecture have been adopted. First, a simple system model is presented in order to estimate the radiometric contrast due to the presence of fire as a function of the wall properties and fire size. Then the sensor is described, underlining both key technologies and achieved performances. Thanks to the continuous gain calibration, the antenna noise temperature can be retrieved with an error of plusmn3 K, without thermally stabilizing the instrument electronics. Finally, real fire detection experiments in indoor environments have been carried-out. A 15 dBi standard-gain horn antenna is used to sense the scene. As a result, a 0.06 m² wooden fire placed at a distance of about 2.4 m from the sensor is visible even behind a 0.12 m thick concrete wall. The obtained radiometric contrast in this case is of about 1.4 K.