Power Flow Angles of GHz Propagating Acoustic Waves in Thin-Film Lithium Niobate

This paper presents a framework for investigating the power flow angle (PFA) of acoustic waves in thin-film lithium niobate (LiNbO
3
). Four-port acoustic delay line testbeds are implemented with different gap lengths and in-plane orientations for accurately extracting PFA of fundamental symmetric (S0) mode in X-cut LiNbO
3
. The PFA extraction method is readily extendable to other acoustic modes and materials. The proposed testbeds can also be used as miniature radio frequency (RF) directional couplers. It also offers the possibility of implementing novel acoustic elements in thin-film LiNbO
3
.