A novel multilayered planar coil based on biocompatible liquid crystal polymer for chronic implantation

Abstract

Reliable power and data transmission is essential for chronic operation of implantable devices such as neuroprosthetics. Despite a number of advantages of planar coils based on polymer substrate over conventional wire-wound coil such as flexibility, miniaturization, batch-fabrication and easy integration with circuitries, they suffered from relatively low inductance and quality factor due to limited space for placing conductor lines. One way to avoid this problem is to use multilayered approach to secure enough surface area, but this has not been done due to lack of proper materials and processing technologies. Long term reliability is another issue that has not been satisfied with conventional polymer materials. Here we developed a new multilayered planar coil based on biocompatible liquid crystal polymer (LCP) substrate to overcome the limitations of conventional planar coils. We adopted a method of laminating multiple layers of LCP films through thermal bonding. This method allowed easy construction of multilayered structure, and design flexibility provided by extended space. The latter was utilized by interconnecting each layer in either series or parallel configuration to improve quality factor and wireless performance. Multilayered coils were designed and properties were estimated using FEM simulation considering parasitic interlayer capacitance. Electrical properties of fabricated coils were measured, and their power and data transmission capability was tested in laboratory condition as well as in vivo experiments. Finally we show that the coil can be deformed into spherical shape to fit curvature of the eye for retinal prosthesis application without degradation of electrical properties and link performance.