Comparison of Passive 2-D and 3-D Ring Arrays for Medical Telemetry Focusing

In this letter, we investigate the performance of subdermal ring designs for focusing electromagnetic fields inside the body for next-generation implantablemedical devices. We will concentrate on the Medical Implant Communications Service band (402-405 MHz), but prepare our design at 433 MHz, the nearest Industrial, Scientific, Medical band. The designs include two-dimensional (2-D or coplanar) and 3-D arrays of circular rings and 3-D arrays of ellipses. The 3-D ring and ellipse arrays focus the fields more effectively than 2-D designs, through constructive coupling between the rings. Compared to the case where no rings are used, the power available from the focused field 20 mm below the skin is 2.24 times and 3.12 times larger if 3-D rings and 3-D ellipses are utilized, respectively. Rings can be used for circular polarization applications, and ellipses are more optimal for linear polarization applications.