Design and implementation of a volume conduction based RFID system for smart implants

As the population ages, knee and hip replacement surgeries are more and more popular, and embedding an RFID (radio frequency identification) tag on these implants for identification becomes an important issue. Traditional operation of an RFID tag by wireless means will not work on the implantable knees or hips which are made of metal because of the interference caused by metallic objects degrading the field strength near the RFID tag. This paper proposes a method of operating an RFID tag using volume conduction while avoiding the RF interference in a metallic environment. To increase the efficiency of power transmission, electrodes in this paper are designed and optimized for a real knee implant. Experiments using saline have been conducted and the results have shown that volume conduction has a better performance than wireless methods in that signal attenuation is far less in metallic environments. Finally, the experiment on reading an implanted RFID tag through pig skin shows that volume conduction is an effective method to operate an RFID tag embedded on a metallic implant.