Dual-Band 3-D Implantable MIMO Antenna for IoT-Enabled Wireless Capsule Endoscopy
Amjad Iqbal, Penchala Reddy Sura, Amor Smida, Muath Al‐Hasan, Ismail Ben Mabrouk, Tayeb A. Denidni
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 5\times 4.75{=}118.75$ </tex-math></inline-formula> mm3 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0001\lambda _{g} {^{{3}}}$ </tex-math></inline-formula>, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{g}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{r}{=}120$ </tex-math></inline-formula> 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.