Design and System Verification of Reconfigurable Matching Circuits for Implantable Antennas in Tissues With Broad Permittivity Range

In this communication, we present an effective solution for reconfigurable matching circuits for tuning medical implant communications service (MICS) band implantable antennas in various tissues. We use only two lumped components, a shunt inductor and a series varactor with bias in the proposed circuits, to match a spiral antenna on the neurostimulator platforms. By properly tuning the bias voltage of the varactor, impedance matching of the same antenna is achieved in different tissues with a broad relative permittivity range from 5 to 60, which indicates superior antenna performance in the dramatically changeable biological environments. With the merits of simple configuration and easy voltage programming, the proposed circuits are accurately designed on impedance trace of the Smith Charts. In clinical applications, we integrate the reconfigurable matching circuit with the neurostimulator platform. The proposed circuits with implantable antenna are numerically analyzed and experimentally validated at the system level. We achieve good antenna impedance matching performance in various types of tissues, i.e., the reflection coefficients are less than -20 dB, and a 6-12 dB benefit of link budget is achieved in different tissues.