Ultrasound standing wave device for particle manipulation

Using ultrasonic standing waves for noncontact manipulation of microparticles or cells has raised many possible applications in life sciences and medicine. This paper introduces the basic concept and methods of applying ultrasound to manipulate the microparticles in fluids, and also gives two practical examples of trapping and manipulating microparticles with ultrasound standing waves. The design, simulation, fabrication and testing of these two resonant-mode ultrasonic manipulation devices are presented, and some practical issues are discussed, such as temperature changes and streaming. The first device uses a bespoke high frequency (up to 25 MHz) lithium niobate transducer coupled to a fabricated precision reflector and spacers to form a multiple of half-wavelength ultrasound standing waves (30 µm) across a macroscale fluid chamber (2 × 5 mm2) in which the microparticles are distributed and trapped by ultrasonic radiation forces. The second device has a 12-element kerfless ultrasonic linear array (2.5 MHz) coupled to a disposable rectangular capillary to trap and manipulate microparticles along the capillary by controlling the active elements of the array. The experimental results of both devices with 10 µm polystyrene beads show correspondence with pressure distributions simulated with the finite element method and demonstrate the feasibility for potential applications in life sciences