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We have explored the use of printed spiral coils (PSC's) for neuroprosthetic transcranial telemetry applications. We fabricated two-dimensional PSC's on a thin (25 μm) polyimide substrate using copper (35 μm) as a conducting material. All the coils had a fixed inner diameter of 1.0 cm. We fabricated two sets of coils. One set of coils consisted of 2- to 5-turn circular and square spiral coils and had different trace widths (W), different spacings (S) between adjacent traces, and different outer diameters. The other set of coils consisted of 5-turn circular spiral coils and had fixed inner and outer diameters but different W to S ratios. We measured loss resistances (R s and R p) and quality factors (Q) of these coils at different resonating frequencies in the range of 5-40 MHz. Over this frequency range, we observed that for fixed inner and outer diameters, the coil with the largest W achieved the lowest R s and the highest R, and Q. These electrical properties and the fact that these coils can conform to the complex convoluted cortical surface suggest that a PSC can provide a viable alternative to a conventional wire-wound coil for neuroprosthetic transcranial telemetry applications.
Date of Publication: July 1998