Acoustic tweezers

Acoustic tweezers use sound waves to trap, move, or manipulate microscopic objects without physical contact. They typically act through acoustic radiation forces in a fluid or on a surface.

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Acoustic radiation force: The time-averaged force exerted by an acoustic field on an object or medium. It supplies the main force that traps particles against competing fluid motion.
Ultrasound: Sound waves with frequencies above the upper limit of human hearing, approximately 20 kilohertz. Many acoustic tweezers use ultrasound to create controllable forces at small scales.
Cell sorting: The separation of cells into groups based on properties such as size, density, or biological markers. Acoustic forces can separate cells without labels or direct mechanical contact.
Optical tweezers: A technique that uses tightly focused light to trap and manipulate microscopic particles. Both methods trap objects remotely, but optical tweezers use light rather than sound.
Acoustic heating: The increase in temperature caused by absorption of acoustic energy in a material or fluid. Heating constrains exposure conditions, especially when manipulating living cells.
Acoustic standing wave: A wave pattern with stationary nodes and antinodes, formed by overlapping waves traveling in opposite directions. Its pressure pattern creates preferred trapping positions for particles.
Piezoelectric transducer: A device that converts electrical signals into mechanical vibrations, or vibrations into electrical signals, using piezoelectric materials. It generates the sound waves that form acoustic traps.
Cell manipulation: The controlled positioning or movement of individual cells or cell groups. Acoustic traps can reposition cells while limiting direct contact with tools.
Magnetic tweezers: A technique that uses magnetic fields to apply forces to magnetic particles or attached probes. Magnetic tweezers require magnetic susceptibility or labels, unlike many acoustic traps.
Acoustic cavitation: The formation, oscillation, or collapse of bubbles in a liquid under acoustic pressure. Cavitation can damage samples and limit the intensity of usable acoustic fields.