An Improved Theory for Reflection-Electrode-Grounded Single-Phase Unidirectional Transducers (SPUDTs) With Better Unidirectionality

This article presents an improved theory and design methodology for single-phase unidirectional transducers (SPUDTs), developed through systematic analysis of electrical reflections from multiple electrodes to significantly enhance unidirectionality. It is compatible with all reflection-electrode-grounded SPUDTs and supports diverse piezoelectric materials and acoustic modes. Leveraging the Lamb wave S0mode in LiNbO3thin films, the improved DART (IDART) demonstrates over five times the unidirectionality of conventional designs for 10-period transducers. Transmission line experiments with IDARTs achieve a 7.9% 3-dB bandwidth at 3 GHz, with insertion losses of 5.9 dB at room temperature and 4.9 dB at 50 K, reducing losses by up to 1.2 dB compared to conventional DART. Also, the improved EWC-SPUDT (IEWC-SPUDT) offers advantages over conventional designs. Both simulations and experiments confirm the superiority of our SPUDTs in terms of unidirectionality, bandwidth, and in-band ripple. This new discovery and innovation, stemming from a reexamination of the classical SPUDT theory, are expected to systematically enhance the performance of microwave acoustic devices that rely on SPUDTs, including filters, delay lines, and sensors.