Prototyping airborne ultrasonic arrays

Focused ultrasound is the base mechanism for mid-air tactile feedback generation, acoustic levitation, wireless power transfer, directional audio and other emerging applications. The basic required set-up is an ultrasonic emitter with the capability of focusing its acoustic power at a target point. Ideally, a multi-emitter phased array is used since it is capable of steering and shaping the sound field with millimetre accuracy and a time response in the order of milliseconds. There are compelling commercial products and open designs for this kind of ultrasonic arrays. Here, we review the different elements that compose an ultrasonic array: from the emitters and the driving electronics to the signal generators or algorithms. We review some techniques to simulate the output of ultrasonic arrays or to determine the emission phases for target fields. Also, we provide some suggestions for future challenges related to cost, power and heat reduction.