Cost-Effective 3-D-Printable Water-Based MIMO and SISO Antennas for High-Data-Rate Biomedical Implantable Devices

In this article, a water-based implantable antenna (WBIA), easily convertible into multiple-input multiple-output (MIMO) is introduced for medical implantable applications. The MIMO version of the WBIA is composed of two circular radiators apart by a small edge-to-edge gap of
$0.018\lambda $
. The MIMO WBIA has a compact radius of 5 mm and a height of 4 mm which exhibits one of the miniaturized sizes previously reported for medical applications. This miniaturization is made possible by the very high permittivity of water and the capacitive effect between the WBIA ground plane and corresponding radiators. Both antennas provide complete control over the operating frequency by adjusting the height and radius of the water (antenna), allowing for customization to suit other desired frequencies. The radiators of both the MIMO antennas are radiating in opposite directions, thus also enabling radiation diversity. In a homogeneous phantom, the MIMO antenna exhibits a wider -10 dB bandwidth of 500 MHz, a higher gain of -18 dBi, and an isolation of 17 dB at 2.45 GHz. Because of the use of water and minimal metal without slots or vias, the proposed antennas exhibit significantly lower specific absorption rate (SAR) values compared to previously reported implantable antennas; therefore, the proposed antennas offer enhanced user safety benefits. Due to electrical properties comparable to human tissue, the proposed WBIAs smoothly transform the radiated energy; therefore, they provide very high radiation efficiencies compared to previously designed antennas. Apart from the aforementioned benefits, the proposed antennas are 3-D printable, thus offering much lower fabrication costs. To validate the performance of a complete system capable of performing biotelemetry, the antennas are integrated with capsule circuitry. The results measured in minced pork are found to be in close agreement with the simulation results. Due to frequency control, flexible functionality, high efficiency, lower SAR, pattern diversity (PD), and lower fabrication costs, the proposed antennas could be more beneficial for MIDs, especially for capsule endoscopes.