Additive Manufactured Matching Medium Design for Implant Communications

The design of matching media with different dielectric constants for the use in implant communications is presented in this paper. Each medium consists of a three-dimensional printed honeycomb structure filled with a high dielectric lossless semi-liquid. The dielectric constant of the media is determined by the infill percentage of the honeycomb structure as well as the dielectric constant of both the semi-liquid and the material of the structure. An algorithm is developed that can specify values for the infill percentage to reach a target dielectric constant value from a given material and semi-liquid. For the measurements, several honeycomb structures with different infill percentages are fabricated with polylactic acid using additive manufacturing. Water-based semi-liquids are developed to fill the structures. The dielectric constants of the fabricated media are measured with a half-filled rectangular resonant cavity. The practical results indicate that target dielectric constants ranging from 8 to 34 are reached by using semi-liquids with dielectric constants ranging from 20 to 65 between 2.2 GHz-3.2 GHz. The practical results are also shown to be in good agreement with the numerical ones with an error of less than 9% for all different cases.