Easy generation of airborne ultrasonic helical wavefronts

In this work, the feasibility to easily generate airborne ultrasonic helical wavefronts is demonstrated. We have experimentally obtained airborne ultrasonic Helical Wavefronts (HW) of great quality by gluing a ferroelectret film on a helicoid surface. A comparison between measured and theoretical results of the pressure and phase distributions of this type of wavefront is accomplished. The simple fabrication procedure, which results inexpensive and reliable, opens up a new alternative to explore the special features of wavefronts with screw-type dislocations.