Development of a flexible large-area array based on printed polymer transducers for mid-air haptic feedback

Ultrasound based mid-air haptic feedback devices can produce tactile sensations at any time and position without restricting human motion. This is useful for augmented and virtual reality, feedback buttons and virtual user interfaces. The haptic feedback mechanism is caused by acoustic radiation force and streaming. Typical solutions to induce haptic feedback reported in literature use arrays made up of 'standard' single element transducers and are heavy, rigid and bulky. A novel alternative uses printed polymer transducers (PPTs), which consist of piezomembranes created using a printing process. PPTs are light, fully flexible, have a thickness < 0.25 mm and can easily be integrated in curved surfaces. However, as the piezoelectric charge coefficients of P(VDF-TrFE) are lower than those of regular PZT5A/H, higher excitation Voltages are needed to achieve the sound pressures required for haptic feedback. In this work we report on the development of flexible large-area arrays based on PPTs for mid-air haptic feedback. Simulations and experimental results of test membranes and a 300+ membrane annular array prototype are presented. Extrapolating the results of the aforementioned array, the full size array is expected to produce radiation forces an order of magnitude above the tactile threshold reported in literature.