Investigation and Analysis of EM Pulse Propagation Inside Human Head for High-Resolution UWB Elliptical SAR Imaging

In this paper, an ultra-wideband (UWB) microwave imaging system based on an elliptical synthetic aperture radar (ESAR) is proposed as a possible solution for human head imaging. The system along with the image reconstruction method operates in the time domain. We have adopted the global back-projection technique to an elliptical trajectory of data acquisition, to shape around the head. A miniaturized, low profile custom-designed, UWB patch antenna capable of operating in the proximity of the head tissues is used as a sensor. The antenna aperture impedance is matched to the head tissues to enable pumping radiating electromagnetic waves into the human head needles of any coupling liquid. The impact of operational bandwidth and radiated power on system key performance factors i.e., penetration depth, range-resolution, and safety aspects are fully investigated based on calculations as well as full-wave simulations. It is observed that by increasing the bandwidth of radiated pulse from 0.8∼2.8 GHz (which was used in most of the previous works) to 1.0∼5.2 GHz, the range resolution can be improved remarkably from 23.0 mm to 16.0 mm deep inside the head. However, further increase in operational bandwidth will not improve the resolution of the system and a significant fraction of the radiated power will be dissipated in the brain tissues. To demonstrate the system performance, a constellation of 12 antenna elements is placed in an elliptical shape directly attached to the 3D phantom to acquire the raw data using full-wave simulations. Finally, an image from a 3D MRI-derived phantom is reconstructed to validate the imaging capability of the designed system. The proposed system can be used as a tool for early diagnosis as well as for treatment monitoring while getting therapy like chemo or radiotherapies.