A micro-particle positioning technique combining an ultrasonic manipulator and a microgripper

The acoustic radiation force acts on particles suspended in a fluid in which acoustic waves are present. It can be used to establish a force field throughout the fluid volume capable of positioning the particles in predictable locations. Here, a device is developed which positions the particles in a single line by the sequential use of two excitation frequencies which have been identified by a finite element model of the system. The device is designed such that at one end there is an opening which allows the fingers of a microgripper to enter the fluid chamber. Hence the gripper can be used to remove the last particle in the line. The high accuracy of the positioning of the particles prior to gripping means that the microgripper needs just to return to a fixed position in order to remove subsequent particles. Furthermore, the effects of the microgripper fingers entering the fluid volume whilst the ultrasound field is excited are examined. One result being the release of a particle stuck to a gripper finger. It is believed that this combination of techniques allows for considerable scope in the automation of microgripping procedures.