Acoustic tweezers

Acoustic tweezers (also known as acoustical tweezers) are a set of tools that use sound waves to manipulate the position and movement of very small objects with a diameter of 100 nanometers to 10 millimeters with the max density of any object levitated this way being 5.7 g/cm^3 the sound used to levitate objects is in the range of 20 kHz and higher normally 40 kHz is used for most consumer tweezers and levitators.

Strictly speaking, only a single-beam based configuration can be called acoustical tweezers. However, the broad concept of acoustical tweezers involves two configurations of beams: single beam of sound and a reflector of the sound to create standing waves or two beams of sound pointed directly at each other. The technology works by controlling the position and distance of acoustic pressure nodes and antinodes, this draws objects to the nodes which have an average lower pressure because of acoustic radiation pressure unless the object is 10% or less the size of the wavelength in that case the ponderomotive force will overcome the acoustic radiation and the object will move to the antinode. The target object must be considerably smaller than the wavelength of sound used unless specific circumstances are underplay that tailor distance between the nodes and the wavelength used for the object in question to levitate objects that are much larger than the wavelength in use though this takes some carful math and a lot of trial and error. The use of one-dimensional standing waves to manipulate small particles was first reported in the 1982 research article "Ultrasonic Inspection of Fiber Suspensions".

Acoustic waves have been proven safe for biological objects, making them ideal for biomedical applications. Recently, applications for acoustic tweezers have been found in manipulating sub-millimetre objects, such as flow cytometry, cell separation, cell trapping, single-cell manipulation, and nanomaterial manipulation.