Radiofrequency acoustic passive wireless sensors - Interrogations strategies

Passive wireless interrogation devices meet a need that no other technology can address: providing a signal representative of a physical quantity by means of a passive transducer (without a local power source) whose characteristics are probed via a radio-frequency link. These sensors are deployed in hostile environments in which a power source would be unavailable, or in environments where the sensor's longevity could not be guaranteed by a local power source. The principle behind the design of passive wireless interrogation sensors is to consider them as a cooperative target of a short-range RADAR system: the RADAR behaves as a signal source designed to probe the response of the target, whose RADAR section ("response") is affected by its environment, and in particular the physical quantity to be measured. The signal back-propagated by the target contains the information of interest to us – the measured quantity – extracted after reception by the RADAR through signal processing. We are also striving to follow two principles which, while not intrinsically linked to passive wireless interrogation sensors, guarantee the robustness of the measurement: we are focusing on information linked to the phase or frequency of the signals rather than their amplitude, for the sake of robustness and immunity of the response to the environment. In addition, we are looking for linear mechanisms for target interaction with the electromagnetic field radiated by RADAR, in order to guarantee a sensor response whatever the incident power, the range then being limited by the noise floor of the receiving stage, which determines the lowest detectable power.