RECENTLY, A group of researchers decided to analyze the influence of insulation on implanted antennas for biotelemetry applications in the Medical Device Radiocommunications Service band. Together with Benjamin Fuchs from France's University of Rennes, Francesco Merli, Juan R. Mosig, and Anja K. Skrivervik from Switzerland's Ecole Polytechnique Fdrale de Lausanne worked to find the insulation properties that facilitate power transmission. In doing so, they hoped to enhance communication between an implanted antenna and an external receiver.
The researchers found that a simplified model of human tissuesbased on spherical geometries that are excited by ideal sources, such as electric dipole, magnetic dipole, and Huygens sourceprovides reasonable accuracy. Due to its analytical formulation, it also remains very tractable. They succeeded in showing that the proper choice of biocompatible insulation material can improve an implanted antenna's radiation efficiency (in their investigated cases, by up to six times). External insulation simplifies the electromagnetic (EM) transition from the biological tissue to the outer free space. In doing so, it reduces the power absorbed by the human body.
Thanks to the structure's geometry, the team could analytically compute the EM field with a mode-matching technique (MMT) based on spherical-wave expansion. In addition, a convergence criterion was defined to compute the power radiated at any radial distanceincluding the near-field rangewith controlled accuracy. Through their work, the researchers gained insight into the enhancement of power transmission via internal, bio-compatible and external, flexible insulations. The results obtained for the internal insulation provide guidelines for the selection of biocompatible material and the implanted antenna design. See "The Effect of Insulating Layers on the Performance of Implanted Antennas," IEEE Transactions On Antennas And Propagation, Jan. 2011, p. 21.