Design, modeling and characterization of microfluidic devices for ultrasonic manipulation

An ultrasonic micropositioning system which is capable of separating particles into distinct and observable lines has been modeled using a finite element approach. The use of such a contactless manipulation method is believed to have many applications in the fields of microtechnology, life-sciences and lab-on-a-chip devices, one example would be in cell assays. The device consists of an etched silicon wafer which is bonded to a piece of glass the etched area can thus be filled with a fluid containing suspended particles. When the system is excited to vibration by the macro-piezoelectric plate attached on the underside of the silicon wafer, a pressure field is established throughout the fluid volume. When an inhomogeneity in a fluid is exposed to an ultrasonic field the acoustic radiation force results, this is found by integrating the pressure, retaining second order terms, over the surface of the field and taking the time average. Consequently, due to the presence of a pressure field in the fluid in which the particles are suspended, a force field is created. The finite element model is shown to be able to predict the frequencies at which resonance occurs, and the resulting modal shapes.