Passive sensors using RF backscatter

An application of RF backscatter to monitor passive (zero DC power) sensors is presented. The technique uses an RF signal, from a probing platform, to probe a passive sensor. The passive sensor contains a transducer that acts like an impedance to RF signals, and therefore produces a quantifiable backscatter depending on the value of that impedance. This RF impedance is also a function of the physical parameter under observation. The heterodyned signal from the incident and backscattered RF signals, as in a frequency modulated continuous wave (FMCW) radar, is a low frequency signal containing information on the impedance that can be extracted by digital signal processing (DSP). There are a number of transducers, especially ones that are MEMS-based, which can thus be characterized at RF, and the physical parameter information extracted. The technique has the potential for the development of a class of very economic, reliable, accurate and self-calibrating sensors with no DC power requirement and without the use of any chips in the sensors.