Compact Microstrip Antennas With Enhanced Bandwidth for the Implanted and External Subsystems of a Wireless Retinal Prosthesi

In this communication, two pairs of compact microstrip antennas were introduced for a dual-unit retinal prosthesis operating at two frequencies of 1.45 and 2.45 GHz. For the 2.45 GHz frequency band, a triangular microstrip antenna with shorting pin and 7 mm x 6.93 mm x 0.63 mm dimensions is explored to enhance the intraocular element bandwidth. Also, a modified rectangular patch (26 mm x 24 mm x 1.43 mm) with parasitic radiators is employed for the extraocular element. In the 1.45 GHz frequency band, another triangular microstrip intraocular element (6.25 mm x 6 mm x 0.63 mm) is proposed by etching a series of slots, which results in lower resonance frequency. For the extraocular element at 1.45 GHz, a planar inverted-f antenna (PIFA) (28 mm x 24 mm x 1.43 mm) with parasitic radiators is introduced. The effectiveness of intraocular and extraocular antennas was evaluated through simulation and further examined by fabricating to characterize the performance in a wireless system inside eye phantom. Specific absorption rate (SAR) analysis of the proposed antennas, results of the simulation, and experimental coupling measurements are presented. Compared with others' work in this problem, with this proposed structure, we could enhance the impedance bandwidth up to 36% without compromising the coupling, which is advantageous for high-resolution retinal prosthesis.