A differential measurement SAW device for passive remote sensoring

The application of differential measurement to suppress unwanted dependencies is a well known method in SAW sensoring. Usually these applications exploit a Two-Delay-Line- or Two-Resonator-Circuitry where the difference of two frequencies ideally depends only on the variable to be measured. This approach can be used to greatly reduce temperature dependence of certain sensors. However this circuitry cannot be operated passively, which is a clear demand for remote sensor systems. For an application in wireless remote sensor systems, a new conception of SAW sensor device has been developed to reduce the disturbing influences of the radio channel. The device consists of two SAW resonators with different center frequencies. The difference of the two center frequencies is almost independent of influences in the radio channel