Liquid based tunable lenses – from concept to application

Quasi-planar stepped lenses (QSLs) based on phasing have proven to perform closely to conventional refractive lenses for the generation of both focused and limited diffraction beams. These types of lenses have enabled applications, such as droplet extraction, trapping, and manipulation, as well as limited diffraction wavepacket generation. Ultrasonic beams formed in this manner have proven to closely match with simulations. These lenses function similarly to phased arrays but lack tunability and are restricted to a single frequency, which is inherent to their design. More recently, an approach using liquid based phasing has been developed that can be tuned to generate different beam types and focal depths while also enabling multi-frequency operation. In addition, it has a planar surface which can facilitate improved coupling to surfaces in relation to QSLs. The liquid lens generates the required phase modulation through the variation in speeds of sound in saltwater solutions. This talk traces the development of the liquid lens approach starting from the QSLs to the current designs. In addition to describing the current progress, we look ahead to the future prospects of these devices, including applications that may be of practical interest.