Design of acoustic lenses for ultrasonic human-computer interaction

A novel Twisted Acoustic Lens (TAL) design to spread the radiated acoustic energy of a flat transducer is proposed. The lens is comprised of many perforations deployed uniformly, with trajectories that are circular helices of different radii. We have fabricated and characterized a disc-shaped TAL of thickness 7 mm and twist angle of 45° and demonstrated that the energy radiated by a directive ultrasonic transducer can be significantly dispersed. It is possible to almost triple the -6 dB directivity of a circular transducer of 20 mm of diameter at frequencies between 60 kHz and 80 kHz. The proposed lens design has great potential in certain ultrasonic touchless applications in which a commercially available ultrasonic transducer needs to be turned into field-of-view maximizing acoustic component while maintaining a flat front end.