Markers of bone turnover for the prediction of fracture risk and monitoring of osteoporosis treatment: a need for international reference standards

A method of manipulating microparticles in a liquid using ultrasound is proposed and demonstrated. An ultrasonic standing wave with nodal planes whose positions are controllable by varying the relative phase of two applied sinusoidal signals is generated using a pair of acoustically matched piezoelectric transducers. The resulting acoustic radiation force is used to trap micron scale particles at a series of arbitrary positions (determined by the relative phase) and then move them in a controlled manner. This method is demonstrated experimentally and 5 ?m polystyrene particles are trapped and moved in one dimension through 140 ?