Wireless passive surface acoustic wave (SAW) sensing system.

摘要

Due to their small size and ruggedness, Surface Acoustic Wave (SAW) devices have been widely used as part of wireless sensing or identification system especially in inaccessible and inhospitable environments. In addition, SAW devices find widespread applications as filters in communication systems and also as physical, chemical and bio-sensors and ID tags. The passive wireless SAW sensing system mainly consists of a passive SAW sensor and an interrogation unit which sends a burst signal to the SAW sensor and processes the sensor response. The main objectives of this work were designing, prototyping and fabricating the interrogation unit on a PCB and also designing modeling, simulating and fabricating SAW devices. Significant results obtained from the burst transceiver and simulation as well as measurement results of SAW devices will be presented together with some of the challenges faced.; The interrogation unit is a burst transceiver operating in the Industrial, Scientific and Medical (ISM) band at 433 MHz. The prototype was built using connectorized modules and manufacturer demonstration boards. Once the prototype burst transceiver was tested for its functionality, a miniaturized version was designed and fabricated on a PCB, The PCB layout was prepared using FreePCB(TM) software and manufactured at Cirexx International, CA. Both the prototype and the PCB burst transceiver is characterized using a cascaded gain and noise figure analysis performed for both the transmit and the receive sections.; SAW delay lines and resonators operating at 100 MHz were first designed and then fabricated at the University of Michigan's Micro/Nano fabrication facility in Ann Arbor, MI. Simulation of the frequency response of SAW devices were performed in MATLAB(TM), PSpice Capture(TM) and CoventorWare(TM). The design aspects of SAW devices and details of modeling the SAW devices in each of the above software packages are presented. Simulation results obtained from all the three software packages are compared with measured responses and the relative merits and demerits of each method will be presented.