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Quarter‐Wave Plates to Improve Rotational Misalignment Robustness in Medical Telemetry
Author(s) -
Blauert John,
Kiourti Asimina
Publication year - 2021
Publication title -
bioelectromagnetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.435
H-Index - 81
eISSN - 1521-186X
pISSN - 0197-8462
DOI - 10.1002/bem.22365
Subject(s) - optics , transmission coefficient , bioelectromagnetics , materials science , physics , acoustics , transmission (telecommunications) , telecommunications , computer science , quantum mechanics , magnetic field
A major challenge in developing robust wireless links to implanted/ingestible antennas is the potential for rotational misalignment. In this paper, we present an artificially anisotropic quarter‐wave plate (QWP) capable of developing a circularly polarized wave from a linearly polarized wave. Without loss of generality, our QWP is composed of plastic and hydrogel, while the linearly polarized wave is developed by a bio‐matched antenna—a high gain, broadband antenna with a dielectric engineered to match to biological tissues. Using a basic implanted patch antenna, we demonstrate a 1.00 dB (1.26) variance in transmission coefficient over a 90° variance, with a remarkable average measured transmission coefficient of −34.4 dB (3.63 × 10 −4 ) at 2.4 GHz. Without the QWP, the rotational variance is 12.52 dB (17.9). Notably, the QWP increases the maximum input power to comply with specific absorption rate limitations. In our case, this allows for −15.0 dBm (31.6 µW) of power to be received by the implant, which is comparable to the −15.7 dBm (26.9 µW) received without the QWP. Additionally, we demonstrate that with the QWP, the standard deviation from the mean transmission for rotational misalignments remains below 3 dB (2.00) from 2 to 3.62 GHz, resulting in a simulated 57.7% fractional bandwidth. © 2021 Bioelectromagnetics Society.