Industrial applications of ultrasonic flexural waves: Object transport and cooling of microelectronic components

As conventional actuators such as DC and AC motors are becoming less and less adequate in high precision manufacturing environment, actuators operated on drastically different principles such as piezoelectric actuation need to be developed. Investigation of ultrasonic flexural waves (UFW) created by piezoelectric actuators as a new actuation source is conducted. Two novel applications of UFW are studied: object transport and cooling. An object transport system, which consists of an aluminum beam and modules containing piezoelectric actuators and a horn, was built to investigate the transport characteristics of UFW. The transport system makes use of the fact that when a traveling wave propagates along the length of the beam a point on the surface of the beam traverses an elliptic path. Two modes of operation are studied: frictional drive and acoustic levitation. With a power input of 20 Watt, a transport speed of 10 cm/s was obtained by frictional drive for an object weighing 30 grams and a transport speed of 26 cm/s was achieved by acoustic levitation for a planar object weighing 2 grams. The transition from acoustic levitation to frictional drive was observed during the experiment. Experimental threshold ratios of mass/area for the transition are presented. The tests indicate that not only the phase difference but also the excitation frequency were the dominant factors in determining the transport speed and direction. Another novel application of UFW is cooling. Ultrasonic vibrations induce bulk circular airflow called acoustic streaming that enhances heat transfer rate through forced convection. Feasibility of using UFW as an alternative to conventional fan-based cooling is investigated. A temperature drop of 40°C was achieved with a vibration amplitude of 25 μm at an excitation frequency of 28 kHz. Computational fluid dynamics simulation was performed to investigate the cooling performances of UFW. The advantages of cooling using UFW are silent operation, simple structure, and slim profiles which make this promising technology ideal candidate for cooling microelectronic components.