Impedance Matching at Skin–Air Interface for Transmission-Range Improvement of Implantable Antennas

This article presents a novel impedance matching layer (IML) placed on skin tissue to enhance the transmission ability for implantable antenna. The IML is designed with a particular dielectric constant to mitigate the reflection occurred at skin–air interface at 2.45 GHz Industrial Scientific and Medical (ISM) band. To obtain this targeted effective dielectric constant, periodic posts are inserted into a 3-D printed substrate to increase its shunt capacitance, forming an IML with a height of 17 mm for enhancement of transmission ability. Furthermore, a slow wave structure is adopted to lower the profile of IML further to 7 mm, making it more comfortable for routine wearing. To testify the property of the proposed IML, a slot implantable antenna is designed, and its gains with and without IML are comparatively studied. The simulated results exhibit a gain enhancement of over 5 dB with IML loaded, providing a promising solution for a typical communication link for implantable application.