Near-Field Circular Array for the Transcutaneous Telemetry of UHF RFID-Based Implantable Medical Devices

Wireless communication with Implantable Medical Devices (IMDs) based on Radiofrequency Identification in the UHF band suffers from the constraints on the maximum power absorbed by the body tissues. Accordingly, an interrogating antenna placed onto the skin is capable to monitor only a limited region just below its footprint. In some applications like the hand prosthesis controlled by Electromyographic signals emitted by muscle contractions, multiple IMDs have to be used to increase the degrees of freedom in driving the actuators. An array of interrogators, working in the near-field can mitigate this bottleneck by greatly extend the read region inside the body. Sequentially- and simultaneously-fed arrays by a same reader are here investigated to optimize the multi-sensor backscattering modulated links. The conditions (feeding scheme and alignment) to guarantee a robust interrogation of a relevant number of implanted sensors with no battery onboard are identified also accounting for the safety constraints related to the SAR. Numerical simulations and experimentation with a cylindrical phantom resembling human limbs, hosting reference antennas, demonstrate that the simultaneous feed permits to interact with eight IMDs by using nearly all the available power from typical readers (30 dBm, 22 dBm as a minimum) without exceeding the SAR limit with a power margin (w.r.t. sensor-oriented ICs with −10 dBm power sensitivity) of more than 5 dB for any angular alignment between the array and the sensors.