The use of Vibration in Microfluidics for Particle Handling and Sorting Seminar

This seminar will cover two methods of actuation of microfluidic devices which can achieve particle collection in microfluidic systems. The first is based on low frequency vibration, the second on ultrasonic vibration.

Acoustic radiation forces can be used to collect particles in predictable locations by use of ultrasonic standing waves; however the force amplitudes which can be obtained are related to the particle radius cubed, consequently handing particle below 2 µm is problematic. The use of low frequency vibration (in the order of 200Hz) will be shown as a mechanism by which particles as small as 0.2 µm can be collected in regular structures. This is achieved in small droplets deposited on a vibrating substrate.

Secondly the use of ultrasound in microfluidic chambers will be shown to be capable of particle separation. Two examples will be examined, firstly, a vibrating bubble can cause strong streaming patterns the drag from which causes nearby particles to move in swirling trajectories, however there is a second force mechanism arising from the proximity of the particles to the bubble, which gives rise to Bjerknes forces. With two force types generated it is possible to tune the system such that particles either swirl near the bubble or are attracted and held on the bubbles surface the behaviour being dependant on particle size or density, hence a tuneable sorting mechanism is achievable. Secondly, an open fluidic chamber excited to standing wave vibration by actuation at a resonant frequency is shown to cause particle separation by the mixed generation of acoustic radiation force and acoustic streaming.