The Role of Shielding Effects in Operating Non-Imaging Sensors
The role of coating materials in shielding the target varies widely depending on the nature of the coating materials. These effects can be accurately predicted with knowledge of the complex permittivity of the covering layer and its physical structure. The free space approach is most suitable in the mm-wave range since the sample size has reasonable dimensions in order to avoid undesirable edge effects. However, the drawback of most of the free space measuring systems is the presence of ripples in the measured data caused by multiple reflections from sample surfaces and antennae. Passive millimetre and microwave sensors are based on the analysis of incoherent signals like the thermal emission of the human body in the mm-wave range. Evaluation of scattering effects inherent to wide band signals is also becoming an important issue in the design of ultra-wide band sensors operating in complex, real-world environments.