Acoustic waveguides for actuators

Using a 3 × 4 × 5 mm torsional microtransducer attached to a 30-cm long, 0.3-mm diameter flexible stainless steel wire, torsional vibration and coupled torsional-flexural vibration is transmitted to a remotely-placed rotor. The torsional microtransducer uses flat, thickness-poled lead zirconate titanate (PZT) elements attached to the surface of a square-sided prism with a tapered horn and tip; the elements twist the structure and generate torsional vibration amplified by the horn and tip at 150-260 kHz. Swaged to the wire - the 'acoustic waveguide' - torsional vibration is transmitted into the wire, and flexural vibration is developed in the wire due to strong torsional-flexural coupling, demonstrated by measurement of the vibration velocity. Standing wave vibration was generated (standing wave ratio, SWR≈7.5) in the waveguide with nothing on the waveguide tip, but upon using a rotor, traveling wave vibration transmitted energy to the rotor (SWR≈4), which acted essentially as a loss; by placing a damping material on the tip instead of a rotor, very similar traveling wave motion was obtained (SWR≈1.5). The few torsional resonances of the transducer were found to be greatly increased in number by the waveguide, and rotors, with a contact radius of 300 ̈m, were found to rotate for most of these resonances in either direction at up to 11,500 rpm and 3.5 μN-m.