On the Design of Miniature MedRadio Implantable Antennas

A design frame for developing miniature implantable antennas at medical device radiocommunications band (401-406 MHz) is being sketched by addressing issues of resonance, efficiency, bandwidth (BW), and robustness. To that end, we visit fundamental design concepts of geometry, impedance matching, and quality factor Q and we show that a very small antenna insensitive to environmental variations and of optimum efficiency can be obtained. It is the first time, to our knowledge, that a Q calculation for miniature implanted antennas is conducted. In this paper, we consider a skin-tissue implantation scenario and planar dipoles with extremely thin profile and small aperture size. Notably, antennas' physical volume does not exceed 25 mm3. Results indicate a strong dependence of resonance frequency on the antenna geometry for fixed physical size. In addition, external impedance matching proves to be inferior to integral matching via metallization in relation with antenna radiation performance (gain, efficiency, and quality of communication link). Finally, the quality factor Q of small fixed-size antennas highlights the influence of the design on the exhibited resonance and sensitivity response (impedance BW, tolerance to detuning, and gain stability). Simulations are accompanied by measurements with very good agreement underlying the importance of our approach.