Physics

Transducer

Optics

Magnet

French horn

Acoustics

Programming language

Computer science

Quantum mechanics

Acoustic levitation

Levitation

Stack (abstract data type)

Physics of Fluids

The acoustic levitation of liquid drops has been a key phenomenon for more than 40 years, driven partly by the ability to mimic a microgravity environment. It has seen more than 700 research articles published in this time and has seen a recent resurgence in the past 5 years, thanks to low cost developments. As well as investigating the basic physics of levitated drops, acoustic levitation has been touted for container free delivery of samples to a variety of measurements systems, most notably in various spectroscopy techniques including Raman and Fourier transform infrared in addition to numerous X-ray techniques. For 30 years, the workhorse of the acoustic levitation apparatus was a stack comprising a piezoelectric transducer coupled to a horn shaped radiative element often referred to as the Langevin horn. Decades of effort have been dedicated to such devices, paired with a matching and opposing device or a reflector, but they have a significant dependence on temperature and require precision alignment. The last decade has seen a significant shift away from these in favor of arrays of digitally driven, inexpensive transducers, giving a new dynamic to the topic which we review herein.

Beyond the Langevin horn: Transducer arrays for the acoustic levitation of liquid drops