"Noncontact Modal Excitation of Small Structures Using Ultrasound Radiation Force" July 17, 2007 3:30-4:30 PM BRK 1001 Dr. Thomas M. Huber Gustavus Adolphus College, Department of Physics Abstract: Modal analysis of MEMS and other small structures is important for many applications. However, conventional excitation techniques normally require contact, which may not be feasible for small objects. We will describe a method that utilizes the radiation force at the difference frequency generated by two intersecting ultrasound beams. The resulting low-frequency excitations were measured using a scanning vibrometer. This excitation technique has been demonstrated for hard drive suspensions, MEMS and other small devices. There are several unique advantages of the ultrasound radiation force relative to mechanical shakers. The technique is relatively insensitive to distracting resonances of fixtures and support structures. Another advantage is broadband excitation; a 550-kHz confocal ultrasound transducer can be used to excite resonance frequencies from 100 Hz to at least 50 kHz. Other advantages include the ability to selectively excite different modes. For example, the amplitude of a hard drive suspension's 5.0-kHz torsional mode was suppressed by an order of magnitude by shifting the modulation phase between the two ultrasound beams by 90 degrees. Similarly, for a MEMS mirror, the relative amplitude of a torsional mode could be enhanced by a factor of 10 by changing the ultrasound focus spot position. Short Bio: Bachelors in Physics and Computer Science, St. John's University, Collegeville, MN, 1983 Ph.D. in Physics, University of Wyoming, 1989. Thesis topic: Search for Mixing of Muonium and Antimuonium at the TRIUMF accelerator in Vancouver, British Columbia Current: Physics Department at Gustavus Adolphus College since 1989. Current Research areas: Musical acoustics and ultrasound excitation.