Wireless wideband SAW sensor - antenna design

Wireless SAW RFID sensors offer several advantages over similar silicon technology that include passive operation, radiation hardness, and the ability to operate in extreme temperatures. Due to these unique material and device properties, NASA has shown considerable interest in passive, wireless SAW sensors for ground and space flight operations. Several embodiments of SAW sensors have been well established in literature, but often the limiting factor on device size and performance is the tag antenna. Therefore, in order to develop a unified sensor target, a discussion of design principles and tradeoffs for both the SAW device and antenna will be presented in this paper. Antennas designed and fabricated will be presented, including a simple disk monopole, a planar open-sleeve dipole, and an on-wafer meandered dipole, with a discussion on gain, size, and bandwidth. The evolution of the antenna design is toward smaller antennas that minimize tradeoffs. The eventual wafer level integration of the antenna allows the sensor application to exploit some of the known SAW substrate advantages and has application in high temperature or strain sensors. Example orthogonal frequency coded (OFC) temperature sensors on YZ-LiNbO₃ for use at 250 and 915MHz will be used as device examples. By properly designing the combined antenna/SAW target matching, insertion loss can be minimized and range increased. Experimental results on the integration of several sensor targets will be presented. Work presented is a foundation for a realizable wireless, multi-sensor platform.