A method for detection of powder materials in metallic hollow structures using microwaves

This paper presents a method for detection of the presence of small amounts of solids (powders, granules, etc.) inside metallic structures such as process vessels and containers. The method is based on propagation of microwave electromagnetic (EM) energy inside the structures and analysing the complex reflection coefficient Γ represented by the scattering parameter S11. 3D EM simulations were used to predict the behaviour of S11 for structures of rectangular, circular, and conical shapes, contaminated with materials with weak dielectric properties. The suggested method sensitivity and the effects of the material size and its distribution were assessed and results presented of comparisons of simulations and measurements. This paper demonstrates the ability to detect very low levels of contamination, e.g. of the order of 0.01-0.03 parts of a reference vessel's volume of one (e.g. length = 1 cm, width = 0.5 cm, and height = 2 cm) for materials with weak dielectric properties. This sensitivity is even better in terms of volume ratio (contamination/vessel's volume) for structures with bigger volumes and contaminants with stronger dielectric properties e.g. wet powders. The method is fully scalable for vessels with different sizes. Therefore industrial application of the method to physical processing of pharmaceutics, food, agriculture and others is envisioned.