A study of printed spiral coils for neuroprosthetic transcranial telemetry applications

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.