Interrogator for stacked passive inductive transponders

In logistics and other applications there is a huge demand for passive inductive transponder systems that are for "tagging" various objects. The capability to read multiple transponders quasi simultaneously is one of the main advantages when compared with other solutions. However, if the objects and thus the transponders as well are arranged in a stack - i.e. the mutual inductances of the transponder coils become very high - common transponder systems fail to operate since supply voltages induced in the passive transponders are not sufficient. In this communication a system consisting of an interrogator and a stack of passive inductive transponders is analyzed employing network theory and computer simulations. A novel interrogator capable of reading a transponder stack is proposed and its operation varified by simulation results.