A review: controlling the propagation of surface acoustic waves via waveguides for potential use in acoustofluidics

This paper presents a review of waveguides on lithium niobate for surface acoustic waves (SAWs), including in particular the classic literature on the topic with the intent of renewing interest in them in the context of potential applications in the burgeoning discipline of micro to nano-scale acoustofluidics. From the fundamentals of the piezoelectric effect we describe interdigital electrodes and how they generate acoustic waves, consider focusing interdigital electrodes as a simple means of laterally confining the acoustic energy propagating across a substrate, and then quickly move to waveguiding structures that provide confinement by defining either a region of slow wave velocity or a physically isolated structure. The ability to steer acoustic waves using these waveguides is considered. The many analytical, computational, and experimental tools devised by past investigators to design them are discussed in detail, as are the relative advantages and disadvantages of the waveguide designs considered over the years.