Translocation of microparticles in a fluid-flow by adjusting the operating frequency of ultrasonic standing wave (USW)

Recently, many studies have been reported on the non-contact manipulation of microparticles in a fluid-flow using ultrasound since ultrasonic standing wave enables particles to align to its pressure nodal or anti-nodal plane depending on their density and compressibility due to the acoustic radiation force. This phenomenon can be applied usefully to noncontact and rapid manipulation such as trapping and translocation of organic or inorganic microparticles like cells and ceramic powder in many technological fields. The objective of this work is to find an efficient way to translocate microparitcles to one side of a flow channel in the aim of several applications like filtration & separation of particles & cells etc. A modularized microchannel comprising steel and acrylic with a width of 1.5 mm was manufactured for this purpose. An ultrasound transducer installed at one side of the microchannel module generates ultrasonic standing wave field inside the channel. Ultrasound within the frequency range of 1.81 MHz ~ 3.14 MHz was applied to concentrate particles at the pressure nodal lines. The aligned particles at pressure nodal lines can be moved in a certain degree as varying the operating frequency of the ultrasound since the location of the pressure nodes depends on the frequency. The total range of the particle movement by changing only frequency is somewhat limited, but it is possible to shift all particles nearly to the channel wall when using periodical increasing sweep as an actuation signal. The experimental results confirm that the sweeping of the operational frequency can be one of efficient methods to translocate microparticles in fluid-flow using ultrasound. This method can be successfully utilized in the field of filtration and separation techniques as well.