SAW Based Passive Radio Sensor using Energy Gathering Method

Keywords:
SAW, passive radio sensor, energy gathering, RF

Abstract:
This paper represents the new passive radio sensors which need no external power sources and transmit sensor value to the aerial. The wireless sensors are emerging field of ubiquitous sensor network (USN) and structural health monitoring systems. Despite of the rapidly growing of wireless link technology, the power grid acts as an obstacle for USN. Our research focused on the method for the development of passive radio sensor which needs no batteries. In addition, our research focused on enhancing the passive sensor’s detection range, too. Since the FCC regulation strongly limits the transmitting power level and the operating frequency band, current SAW passive radio sensor cannot transmit sensor value over 4-5 meters long. We developed a novel SAW transponder as a transversal type with an energy gatherer for range expansion. The main operating principles are the SAW(Surface Acoustic Wave) excitation by the energy gatherer(sometimes these are called piezoelectric energy harvester) and the passive signal conditioning of sensor signal by the comb-like electrode formed on SAW passive transponder. The energy gatherer converts external vibration energy to electrical energy and can deliver enough electrical power to the SAW excitation circuit for proper operation. The gathered energy is about 20mJ for 10 (sec) mechanical vibration input. This energy level is enough to operate active circuit components, consuming 100mW, for 200 milliseconds and adequate for long range data transmission over 30 meters. The detection range over 30 meters is the current state of the art in passive radio sensor field and this target is feasible because our previous research reached 140 centimeters detection range without any receiver front-end circuitry. The developed sensor system can be effectively used such as embedded structural monitoring system, USN, or TPMS(Tire Pressure Monitoring Systems) and the use of energy gatherer to the passive radio sensor(transponder) for the purpose of range expansion is the new concept for USN and wireless sensors.

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Nanotech 2005 Conference Program Abstract