  Acoustic tweezers can manipulate microscopic objects and cells independently
of the optical, magnetic and electrical properties of the objects or their
medium. However, because ultrasonic waves are attenuated within few
millimeters, existing devices must synthesize intricate and powerful acoustic
fields in a very narrow footprint immediately close to the manipulated object.
Here we show that the design of microscale acoustic tweezers can be
considerably simplified by taking advantage of the nonlinear nature of the
acoustic trapping force. In our experiment, a featureless piezoelectric crystal
coated with a photoacoustic conversion layer is hit by an electric pulse and a
spatially modulated laser pulse to generate synchronized electro- and photo-
acoustic waves. Interference between these waves creates a hybrid acoustic
trapping force 30 times stronger than the laser pulse alone but with the same
spatial information. By disentangling the tradeoff between spatial resolution
and trapping force that has long held back the development of acoustic
tweezers, this field hybridization strategy opens new avenues for cell
manipulation in organ on chip and organ printing.
