Patent ID: 8727129

Claim:
An ultrasonic microfluidic apparatus for separating small particles from large particles contained in a sample fluid, comprising: a sample input channel for channeling the sample fluid containing the small particles and the large particles; a recovery fluid input channel containing recovery fluid, routing said recovery fluid to flow substantially parallel and adjacent to the sample fluid, wherein said recovery fluid contacts the sample fluid; an acoustic transducer that produces an acoustic standing wave, that generates a pressure field having at least one node of minimum sound pressure amplitude; and an acoustic extension structure located proximate the sample fluid and said recovery fluid that positions said at least one acoustic node in said recovery fluid concentrating the large particles in said recovery fluid wherein said acoustic extension structure includes a bypass fluid channel containing bypass fluid, said bypass fluid channel located substantially parallel and adjacent the sample fluid and said recovery fluid; and an acoustically transparent wall between said bypass channel and the sample fluid and said recovery fluid.