On the modes and loss mechanisms of a high Q mechanical oscillator

We have performed laser-Doppler vibrometry measurements of the vibration of a double-paddle oscillator. Seven modes with principally out-of-plane moti on have been identified. Their resonance frequencies and mode shapes are in excellent agreement with three-dimensional finite element simulations. We have found that the second antisymmetric torsional mode has exceptionally g ood vibration isolation of its mode shape. This explains its extremely smal l low temperature internal friction below 10 K (2x10(-8)). By correlating t he internal friction of each mode with features of their mode shapes, a cri terion has been established to develop high Q oscillators. (C) 2001 America n Institute of Physics.