This report deals with the study and design of interrogation electronics for probing surface acoustic wave (SAW) transducers used as passive wireless sensors of physical quantities. The basic principle is to develop hardware aimed at probing the response of SAW resonators through a radiofrequency wireless link in order to extract a temperature information. Resonators whose operating frequency is centered on the 433.92 MHz ISM band are developed as part of the SAWHOT project aimed at measuring high (650 oC) temperatures. SAW resonators load energy when stimulated at resonance frequency. Upon stopping emission, this power is returned as a radiofrequency signal. The presented electronic systems operate on the analysis of the power returned by the sensor, based on a frequency-sweep network analyzer architecture. Two interrogation units are presented. The former is based on a Direct Digital Synthesis frequency source : the flexibility of this digital approach allows for probing resonating sensors following several algorithms meeting various constraints including measurement speed and resolution. Sub-millisecond interrogation resonance frequency identification is compatible with probing the response of sensors located on mobile targets such as a rotating motor axis. The achieved resolution lies in the 0.1 oC range. The latter approach aims at designing a compact reader with a reduced number of components, including all the elements of the interrogation chain, and hence a lower power consumption. This approach is based around integrated, single chip, radiomodems : this components combines radiofrequency and digital functionalities and is diverted from its original digital communication purpose for probing SAW sensors. Timing and isolation constraints as well as accessing the analog receiver stage require a dedicated analysis of the functionalities of the various available chips. The algorithm developed for using such a component require the use of the signal processing techniques well known in the field of RADAR target detection in order to measure the temperature following the probing of a dual resonator for a differential measurement. The resulting temperature accuracy is 1 oC and the recorded data are transmitted through a digital wireless link.
