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In this study, a compact dual-band multiple-input multiple-output (MIMO) implantable antenna system is proposed for cortical visual prostheses (CVP) devices. The antenna has dimensions of $7\times 7\times 0.3$ mm3, which is the smallest size in the literature with dual-band characteristics, operating at industrial, scientific, and medical (ISM) bands of 915 and 2450 MHz. To achieve a high data rate, the proposed antenna employs MIMO technology comprising two probe-fed elements with the same ground plane and an edge-to-edge separation of 0.4 mm. This configuration with an integrated inductor minimizes multipath distortion and enables smooth communication with high data rates, as demonstrated by conducted MIMO channel studies and link budget analysis. Ex vivo measurements of S-parameters, gain, and radiation patterns are performed on the antenna-integrated CVP device in a saline-filled head phantom. The antenna exhibits a measured -10-dB bandwidth of 16.3% and 8.7% with high isolation of 31 and 29 dB, alongside directional radiation patterns that feature a peak realized gain of -30.47 and -24.71 dBi at 915 and 2450 MHz, respectively. Moreover, the system exhibits satisfactory MIMO characteristics with an envelope correlation coefficient (ECC) of less than 0.1, diversity gains (DGs) greater than 9.95 dB, and a channel capacity (CC) of 9.97 b/s/Hz at an SNR of 20 dB. Specific absorption rate (SAR) and magnetic resonance imaging (MRI) compatibility analysis are conducted to ensure the system’s safety. Owing to its excellent performance, the proposed MIMO antenna system emerges as a promising candidate for compact CVP applications, offering high-data-rate communication capabilities.

Compact implantable medical devices (IMDs) require miniaturized and multiband antennas to efficiently navigate space limitations and diverse frequency demands in biomedical applications. This article proposes an ultra-miniaturized implantable antenna featuring the smallest footprint with a volume of 0.7 mm3 and exhibits quad-band characteristics: telemetry at 915 MHz, wireless power transfer at midfield bands of 1450 and 1900 MHz, and control signaling at 2450 MHz. Extensive simulation analyses were conducted for the antenna alone and integrated antenna systems to realize the versatility of the proposed antenna. For validation, measurements were performed in saline-filled realistic head and American Society for Testing and Materials (ASTMs) phantoms. Good agreement between the simulation and measured results was observed. The antenna showed stable performance in all scenarios with a measured −10 dB bandwidth of 136, 122, 108, and 134 MHz at 915, 1450, 1900, and 2450 MHz, respectively. Moreover, the antenna exhibited satisfactory measured gain values of −27.45, −23.25, −23.14, and −22.48 dBi at the respective frequency bands. Finally, the implementation of the wireless biotelemetry feature of the proposed antenna system was achieved and demonstrated through the utilization of a pair of software-defined radios (SDRs). Sustainable and stable wireless data transmission characteristics were shown at transmission distances of up to 2.5 m. With its remarkable features, the proposed antenna addresses the critical need for efficient communication in the Industrial Internet of Medical Things (IIoMT) devices, enabling telemetry, wireless power transfer, and control signaling in biomedical applications with limited space and diverse frequency demands.