Body-Matched Gradient Index Lens Antenna for Electromagnetic Torso Scanner

A lens antenna that performs both as a matching medium and as a spherical-to-planar wave transformer for near-field electromagnetic medical scanning is presented. By achieving those two main targets, the antenna, which can be classified as body-matched gradient index (GRIN) lens, maximizes signal penetration and forms a focused plane wave incident field distribution inside the torso. Consequently, it improves image quality in electromagnetic imaging (EMI) applications. A design process is proposed based on the theory of multilayer medium with different dielectric properties. To realize the obtained dielectric values, the structure is 3-D printed in a planar structure comprising multiple sets of holes forming four layers. Each row has eleven holes with different radii that are filled with freshwater to create four distinct permittivity layers. The fabricated lens is illuminated using an H-shaped slot antenna. It is tested on a torso phantom that is comprised of skin and fat layers and torso tissue-mimicking mixture. The GRIN lens antenna achieves a wide fractional bandwidth of 53% at 0.78–1.34 GHz with a size of
$130\times 130\times53.6$
mm
³
(
$0.3\lambda _{0}\times 0.3\lambda _{0}\times 0.14\lambda _{0}$
, where
$\lambda _{0}$
is the wavelength at the lowest operating frequency). The lens structure improves the signal penetration at the center of the torso by 6 dB compared to a standard slot antenna. Moreover, the electric field intensity can be steered inside the torso phantom by controlling water level in the created holes.