Low-loss SAW RFID using the reflective multistrip coupler as reflectors

Surface acoustic wave radio frequency identification (SAW RFID) has gained widespread adoption in remote sensing and identification. However, conventional SAW RFID tags suffer from significant energy loss due to the inherently low reflectance of standard reflectors, fundamentally limiting their wireless interrogation range. To address this limitation, this paper proposes a novel SAW RFID architecture employing reflective multistrip couplers (RMSCs), which exploit the velocity difference between symmetric and antisymmetric wave modes to achieve coherent reflection, thereby circumventing conventional electrical or mechanical reflection mechanisms. Numerical simulations were conducted to analyze performance deterioration induced by parasitic resistances and capacitance and to identify the optimal strip number for peak reflectance. The fabricated RMSC reflector achieves a low loss of 1 dB, with a reflectance difference of merely 0.33 dB compared to the simulation results. A 433 MHz SAW RFID prototype implementing RMSC reflectors on a 128°YX-LiNbO₃ single-crystal substrate demonstrated a -10.63 dB peak time-domain amplitude at room temperature, representing a substantial improvement over conventional designs. Temperature characterization from -20 °C to 90 °C revealed linear functions in time delay and phase responses, with coefficients of determination (R²) exceeding 0.9999. These results validate the RMSC reflector as a high-reflectance solution for enhancing SAW RFID performance, suggesting significant potential for long-range wireless sensing applications.