Noise Exposure Measured By The Millimeter-wave Radiation Experimental Research

Millimeter wave (MMW) radiometric imaging technology plays an important role in area of the detection of contraband concealed on personnel, due to the fact that MMW can penetrate smoke, dust and certain thickness of clothing. When the imaging is carried out in an indoor situation, the radiometric temperature contrast between different objects in imaging scene is so small and it leads to the problems of inferior image quality and low detection accuracy. The temperature difference of objects indoors can be improved by means of noise illumination. Taking this as the background, this paper investigates the MMW radiometric measurement under noise illumination in the aspects of theory analysis and engineering experiment.The effect to the radiometric temperature contrast produced by the noise illumination is analyzed with methods of combining the simulation modeling and experiment. According to the theory of MMW radiometric measurement, the model for radiometric temperature of concealed objects has been analyzed, and both the mathematic expression of radiometric temperature of concealed objects under noise illumination and the effects of noise illumination to radiometric temperature and radiometric temperature contrast are discussed in detail. The ways of illumination and choice of noise source are also presented, and the model of radiometric temperature increment of the objects under illumination is derived based on the idea of the Noise Radar. In addition, the increments of both radiometric temperature and radiometric temperature contrast between objects are calculated based on the illumination model.The operation principle and calibration of W-band K-factor total power radiometer are also discussed; moreover, the sources of the measurements and analysis errors are also analyzed. A series of measurements to typical objects are carried out outdoors, and some experimental data of radiometric temperature of the objects before and after illumination by single-frequency MMW signal source is obtained. The radiometric temperature of the ground gets an increment of 21.69K and that of the concealed metal target is 111.27K. The experiments demonstrate that the models of concealed objects detection with noise illumination are feasible.