Abstract
The paper describes the complex permittivity measurements of textiles and leathers in a free space at 330 GHz. The destructive role of the Rayleigh scattering effect is considered and the angular-invariant limit for an incidence angle has been found out experimentally within 25–30 degrees. If incidence angle exceeds this critical parameter, the uncertainty caused by the Rayleigh scattering is drastically increased preventing accurate measurements of the real and imaginary parts of a bulky material. The phenomenon must be taken into consideration in predicting shielding effectiveness of materials covering hidden object in concealed threat detection with millimeter-wave radar systems.
Highlights
Submillimeter and THz waves demonstrate a reasonable penetration depth in certain common materials, such as fabric, plastic, and wood
Knowledge of the dielectric properties of these materials is important in predicting overall performance of mm-wave imagers because a penetration depth is governed by these characteristics
There are a lot of microwave methods suggested for measuring complex permittivity [4], but free-space approach is more suitable in submm range since the sample size has reasonable dimensions in order to avoid undesirable edge diffraction effect
Summary
Submillimeter and THz waves demonstrate a reasonable penetration depth in certain common materials, such as fabric, plastic, and wood They are good candidates for detecting various hidden objects such as concealed weapons, drags, and explosives. The deviations of real and imaginary parts of the dielectric constant can be considered as a measure of a nonuniformity of the thickness and International Journal of Microwave Science and Technology surface’s shape of the dielectric slab approximating a real sample. This parameter has statistical nature and should be characterized by standard deviation of the measured material characteristics in angular domain. High directivity Gaussian beam hornlens antenna was employed in order to suppress undesirable spillover effect during variations of the sample’s position
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