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(Color online) (a) Top view of SAW micromotor, a 1 mm solid steel sphere placed atop a retaining hole in PZT patterned with orthogonally placed IDTs. Upon generation of a Rayleigh SAW from an IDT, the SAW propagates (b) past the hole and (c) the contact line formed with the rotor placed upon it. The particle motion is everywhere retrograde with respect to the propagation direction of the SAW, including all points (d) along the contact line. This motion acts against the ball’s inertia and generates rotation through stick-slip motion.
(Color online) (a) SAW propagates left-to-right in the substrate, passing through the hole without substantial change as indicated by LDV measurement of the instantaneous z-polarized displacement, particularly in (b) comparison of the displacements along lines A–A and B–B, and (c) progressive images of the displacement, separated in time by 39 ns intervals (representing 1/8 of the wave period for 3.2 MHz) (enhanced online, along with demonstration of motor operation). [URL: http://dx.doi.org/10.1063/1.3662931.1]10.1063/1.3662931.1
(Color online) Angular velocity of the rotor with respect to (a) time and (b) torque of the motor obtained during operation with magnetic preload. The maximum speed achieved was approximately 1900 rpm, and the maximum torque achieved was 5.37 μN–mm using the weight of the rotor, approximately 41.1 μN, as the loading on the contact interface. Note the coefficient of determination, R 2, values is well above 0.5, permitting the use of Nakamura’s method for estimating the torque-speed behaviour in (b). (c) Maximum model-predicted and experimentally measured rotor speeds in the system. The relatively poor comparison at low and high voltages is due to the complete absence of friction or stick-slip modelling in the very simple contact model, but the model does give an indication of the motor’s output rotor speed without requiring substantial computations.
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