Preliminary Results of Near Field Microwave Imaging System for Dielectric Material

Abstract

Microwave imaging (MWI) method refers to applications and technology that using electromagnetic radiation of frequencies anywhere between several hundred mega-hertz (MHz) and several hundred giga-hertz (GHz). Depending on the frequency, this radiation penetrates many objects. So, microwave imaging provides a wealth of target information and its imaging. Radar based MWI has been using in such areas land resource survey, disaster monitoring, growth observation, ocean observation, terrain mapping, oceanographic research, glacier research, etc. Nowadays, MWI is emerged as a new imaging technique apart from conventional imaging. It is used in literature for breast tumor and lung lesion detection. Because MWI is using non-ionizing electromagnetic waves which is not harmful effects on living tissues and cells on medical imaging purposes. In literature image reconstruction is done by back-projection algorithm, delay and sum technique and iterative born method. Mentioned methods are contain excessive mathematical calculations and time consuming. This study intends to enlarge MWI concept and includes microwave imaging based on radar basics. Near field measurements is done with 2D scanning system, 2 port vector network analyzer (VNA) and computer. Only complex $S_{21}$ scattering parameters are obtained. Coherent signal measurements contain both amplitude and phase information. By using only complex $S_{21}$ transmission parameters microwave images are constructed. Data visualization and image reconstruction algorithms are applied to raw data. Finally, image processing techniques are performed and meaningful microwave raw images obtained. In this preliminary study, a 30 cm length 5 cm diameter dielectric target is discussed. The position and dimension of the dielectric target were determined within the %1 error on the $x$ and $y$ axis compared with real measurements. As a result, dielectric target distinguishes from background. The next stage of this study is to image embedded bone-like dielectric materials including determining the orientation while it has an irregular shape.