A passive RFID transponder sensor system includes a sensor assembly having a focused field transponder antenna with a highly magnetically permeable transponder antenna stem, and a reader antenna with an electrical reader coil generating a magnetic field having magnetic flux extending between the reader antenna and a sensor assembly. The electrical transponder coil and the electrical reader coil are coupled by the magnetic field, so that information can be transferred to and from the sensor assembly through the magnetic field by which the electrical transponder coil and the electrical reader coil are coupled.