Multipurpose use of radiofrequency sources for probing passive wireless sensors and routing digital messages in a wireless sensor network

As the interest for sensor networks is growing, the demand for integrating both measurement algorithm and data transmission pushes to develop adapted electronic platforms to address this challenge. The use of radiofrequency (RF) passive surface acoustic wave sensors probed by radiomodem interfaces commonly found on wireless sensor node platforms is therefore investigated in this work. This approach allows for providing sensors with virtually infinite life expectancy since no local power source is needed on the sensing site. Rather than harvesting energy from the environment, the passive sensor is loaded by an incoming RF source provided by the same RF interface than the one used for digital communication of the gathered data. Implementing such a scheme in an adhoc wireless sensor network configuration is demonstrated using a novel platform based on the XE1203F radiomodem which provides the specific interfaces mandatory to such an application. Furthermore, a measurement demonstration locating the sensing element in an oven heated to 550 degrees C emphasizes environmental conditions in which no energy storage or battery would withstand such harsh conditions, while the wireless interrogation between the interrogation unit (reader) and the sensor removes the need for high temperature-compatible connector and electrical cable. Implementing the sensor probing algorithm as well as the radiomodem control interface in the TinyOS executive environment then provides access to all the functionalities of this portable development tool, including multi-hop data routing and dynamic ad-hoc network construction, while complying with a clear software hierarchy ranging from low level drivers accessing the hardware to user applications implemented as tasks.