Compact Dual-Band MIMO Implantable Antenna System for High-Data-Rate Cortical Visual Prostheses Applications

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 x 7 x 0.3 mm(3), 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.