A High Data Rate Implantable MIMO Antenna for Deep Implanted Biomedical Devices

In this article, a compact multiple-input multiple-output (MIMO) implantable antenna based on meandered resonators is proposed for use in medical implantable devices. Such devices require compactness and high data rates. Regarding compactness, the antenna has a size of $5.35\times 6.2 \times 0.12$ mm³ (operating frequency of 2.45 GHz) which is one of the smallest sizes reported in the literature for this class of antennas. This compactness is achieved using the meandered resonators and slots in the ground plane. For high data rates, the proposed antenna is of MIMO configuration and consists of two probe-fed elements that share the same ground plane and are placed at a distance (edge-to-edge) of 0.4 mm from each other. This configuration reduces multipath distortion and achieves seamless communications with high data rates as evident from conducted link budget analysis and MIMO channel studies. The ex vivo measurements (S-parameters, gain, and radiation patterns) are performed on the proposed antenna when placed inside a capsule and implanted in minced meat. A bandwidth of 320 MHz and isolation of 28 dB are achieved at the design frequency along with omni-directional radiation patterns with a peak realized gain of −20.5 dBi. Specific absorption rate (SAR) analysis and input power studies are performed to ensure patient’s safety. The result shows that the antenna has a safe 10 g SAR of 402.8 W/kg at an input power of 1 W. Also, the capsule device can be operated at a safe power level of 3.97 mW, which is far greater than the maximum allowable power limit ( $25~\mu \text{W}$ ).