Design of Highly Directive GRIN MS Lens Integrated DFHA for Deep Tissue Biomedical Imaging

A novel highly directive gradient refractive index (GRIN) metasurface (MS) lens integrated dielectric-filled horn antenna (DFHA), with an enhanced signal penetration and spatial focusing, is developed for the effective monitoring and detection of tumors deep inside the body. For this purpose, two novel GRIN MS lens topologies are proposed, where an optimized refractive index distribution along with the lens aperture is generated using an improved analytical formulation. In the first lens configuration, the core layer (CL) is sandwiched between two similar impedance matching layers (IMLs) on each side. In the second configuration, the CL is still surrounded by two IMLs on both sides, but one of the IMLs, in this case, is improved to avoid the requirement of an additional dielectric layer between the lens and the biological tissue. All the layers of the MS lens are based on an array of especially designed square ring-shaped unit cells. The proposed MS lens-based DFHA enhances the signal penetration by a maximum of 12 dB at 100 mm penetration inside the torso compared to the case without a lens. It also facilitates better spatial resolution due to the presence of an MS lens, which shrinks threefold the 3 dB beamwidth at 100 mm inside the torso than that of the DFHA without an MS lens. The proposed GRIN MS lens integrated DFHA is fabricated and tested on a realistic torso phantom to evaluate the tumor detection capability deep inside the torso. The simulation and experimental results show that the proposed GRIN MS lens-based DFHA can effectively be employed for tumor detection with high resolution deep inside the body.