Optimized matching of an implantable medical device antenna in different tissue medium using load pull measurements

RF communication with implantable medical devices (IMD) such as a pacemaker experience unique challenges due to the operating conditions within a human body. This includes added body losses caused by the different tissue compositions where material properties range from ε_r=58 (muscle) to ε_r=5.58 (fat). In order to achieve maximum throughput for a 402MHz RF signal, it is important to have minimum mismatch losses between the RF front end of a device and the embedded antenna. This paper presents a method to optimize the matching with various tissues using load pull analysis with a prototype implantable medical device as an example. By using automated impedance tuners, an optimum impedance point was found, improving the mismatch loss by as much as 3dB compared to a design with no consideration given to tissue variation.