A data transmission technique for passive sensor-transponders in medicine

The use of sensor-transponder technologies particularly in medical applications opens valuable possibilities in therapy of human cardiovascular system diseases, e.g. cardiac insufficiency. The application presented here is representative for future applications, where the use of miniaturized passively-powered sensor-transponder systems with high read range is relevant. In the past, load-modulation was developed as a simple technique to transmit data from low-cost ID-transponders to a reader. This technique can be considered as suboptimal for the given challenges in the presented medical and other possible high-demanding applications. Higher read ranges and small antenna dimensions are necessary. In consequence new techniques, especially for data transmission, have to be developed. First of all, the limitations of the load-modulation technique are analyzed. Conventional solutions are then discussed. It is shown that existing solutions could not be used for this specific and future applications. A new data transmission technique called "frequency conversion" is presented. This technique allows data transmission over a greater distance. Measurements in a practical implementation verifiy the performance of this technique.