Theoretical and experimental analysis of high Q SAW resonator transient response in a wireless sensor interrogation application

Wireless sensing using SAW resonators calls for an accurate modeling and simulation of the charging and discharging of a resonator, connected to a resonant antenna (monopole/dipole) as a source/load. It is well known that a resonator takes about Q/π time periods of the natural resonant frequency to charge/discharge appreciably. The charging and discharging is critically affected by the static capacitance and the antenna impedance. The present work describes the theoretical modeling and experimental validation of the charging and discharging steps of a high Q SAW resonator in a wireless protocol and loading/unloading transients under variable load conditions are estimated. Furthermore, interrogation range using a monostatic RADAR-like reader (+10 dBm emitted power in the 434 MHz ISM band, -60 dBm detection limit) is estimated in air, dielectric media with or without conducting term, consistent with experimental measurements at 3 m in air when using a monopole antenna, 1! 2 m when using directive Yagi-Uda antenna on the interrogation unit (monopole on the sensor side), 40 cm in tap water, negligible distance in sea water.