Utilization of SAW Resonators to Enable Identification Capabilities in Subharmonic Tags

We report on the design and performance of the first prototypes of a new class of ultrahigh-frequency (UHF) subharmonic tags (SubHTs) featuring identification capabilities. Our SubHTs rely on a set of surface acoustic wave (SAW) resonators to implement a remote identification functionality. In order to do so, it requires narrowband interrogation signals even when targeting
$\geq16$
-bits encoding data capacities (EDCs). The reported SubHT prototypes leverage the dynamics of high-quality factor
$(Q)$
SAW resonators, combined with those of time-modulated solid-state components, to enable a far-field passive identification without requiring any batteries, any active components, or any ad-hoc memory devices. The wireless performance of a reported SubHT has been characterized in an uncontrolled electromagnetic setting, showing a 2.5-m read range and a read rate of 537 interrogations per second when relying on a transmitter using an effective isotropic radiated power (EIRP) level of 23 dBm. Moreover, the SubHTs discussed in this work provide their electronic readers with immunity to electromagnetic clutter, multipath, and self-interference, even in indoor and uncontrolled electromagnetic environments. Through the demonstration of the SubHT prototypes reported here, we have unveiled a new path toward the adoption of SubHTs in large deployments of wireless sensor nodes (WSNs).