Dual-Band 3-D Implantable MIMO Antenna for IoT-Enabled Wireless Capsule Endoscopy

This article proposes an implantable antenna using a 3-D multiple-input-multiple-output (MIMO) configuration, which operates at 915 and 2450-MHz bands. Both frequency bands are wider enough to cover the important industrial, scientific, and medical (ISM) bands at 915 and 2450 MHz. Using a meandered geometry, introducing capacitive regions between meandered arms and partially slotted ground keeps the antenna dimensions small. Consequently, it consumes an overall volume of
$5\times 5\times 4.75{=}118.75$
mm3 (
$0.0001\lambda _{g} {^{{3}}}$
, where
$\lambda _{g}$
is the guided wavelength at 915 MHz). All elements of the antenna radiate in diversified directions, enabling radiation pattern diversity, resulting in a lower envelope correlation coefficient (ECC) value. Moreover, it provides good gains at both frequency bands (−28.85 dBi at 915 MHz and −20.68 dBi at 2450 MHz). The MIMO channel parameters, and user safety analysis are performed, indicating satisfactory results. Each element of the proposed antenna has a peak SAR value of 306.19 and 252.36 W/Kg at 915 MHz and 2.45 GHz, respectively. The radiation efficiency of the MIMO antenna system is noted to be 0.15 and 0.19% at 915 and 2450 MHz, respectively. When the implant has
$B_{r}{=}120$
Mb/s (high-speed connectivity), the proposed antenna can cover an area up to 8 and 5.2 m at 915 and 2450 MHz, respectively. The practical validation of the proposed design is performed considering two software-defined radios (SDRs). To the best of the authors’ knowledge, this is the most compact 3-D implantable MIMO antenna that has been designed to date.