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In this study, we propose a miniaturized triple-band multiple-input-multiple-output (MIMO) implantable antenna having four ports designed for the real-time transmission of high-quality images and videos for wireless capsule endoscopy (WCE) and deep tissue applications. The proposed antenna operates in the industrial, scientific, and medical (ISM) bands of 0.902–0.928 GHz for data telemetry and 2.400–2.4835 GHz for power-saving applications and midfield band (1.704–1.833 GHz) for seamless wireless power transfer (WPT). The antenna has a compact size of $7.5\times 10.5\times 0.127$ mm3, achieved through the utilization of meandered resonators. The use of meandered resonators also resulted in reduced coupling between the MIMO elements due to opposite flowing current cancellation. The presented MIMO antenna, optimized inside a realistic capsule with batteries, sensors, and electronic components, was fabricated and tested. Simulated and measured results in terms of S-parameters and radiation patterns correlated well with measured bandwidths of 90, 129, and 200 MHz and measured gains of −37.3, −30.3, and −27.9 dBi at 0.915, 1.780, and 2.450 GHz, respectively. Verification of the specific absorption rate (SAR) affirms that the suggested antenna is suitable for utilization within the human body. In addition, based on the link-budget analysis, it can be confirmed that the presented implantable MIMO antenna can establish a reliable communication link up to distances of 14, 9, and 6 m at 0.915, 1.780, and 2.450 GHz, respectively, for transferring high data rate (78 Mb/s) information. Moreover, an assessment of MIMO and diversity performance, specifically with regard to envelope correlation coefficient (ECC) and diversity gain (DG), was conducted, revealing results that fell within acceptable limits. To the authors’ best understanding, this marks the first four-port triple-band implantable MIMO antenna specifically designed for applications in WCE and deep tissue scenarios.

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.

Remote patient monitoring can improve healthcare outcomes by enabling patients to receive continuous care at home. However, a reliable and convenient means of wireless communication and power transfer is needed to drive implantable biomedical devices. In this study, a complete wireless power transfer (WPT) system and data transmission for remote patient health monitoring is proposed, comprising an implantable receiver (Rx) antenna, an efficient rectifier integrated with the Rx, and a transmitter (Tx) antenna. The implantable Rx antenna has small footprints with dimensions $\pi \times 5^{2}\,\,\times0.75$ (58.9 mm3) and exhibits dual-band characteristics: 915 and 2450 MHz for simultaneous wireless power reception and data transmission, respectively. The rectifier of a similar size to the antenna was optimized to operate at 915 MHz with an RF–dc conversion efficiency of 82%. The individual components of the WPT system were simulated, optimized, fabricated, and measured for scattering parameters and gain in a saline-filled 3-D head phantom and minced pork. The implantable antenna and rectifier were then integrated to form a compact rectenna system. A demonstration is performed in the realistic scenario to determine the power reception capability of the proposed implantable rectenna system. For safety purposes, specific absorption rate (SAR) and temperature analysis were conducted and found to be within acceptable limits. Finally, to verify the reliability of the communication link with an external unit, the received power was measured, and the implantable Rx element was found to be capable of effectively communicating over distances of up to 2 m. Our results suggest that this technology has the potential to greatly improve the adoption and effectiveness of remote patient health monitoring, by providing a convenient and reliable means of wireless communication and power transfer.