A Mechanical Beam Resonator Engineered at Nanoscale for Ultralow Thermoelastic Damping

ABSTRACTA mechanical beam resonator engineered at nanoscale for suppressing thermoelastic damping to obtain ultrahigh quality factor is reported. The resonator employs the torsion mode of a spring beam to excite the rotation oscillation of a nanoscale resonant beam. The ultralow thermoelastic damping in the resonator is obtained by employing torsion oscillation. Optimal study of thermoelastic damping is carried out by varying the dimensional parameters of the resonator. The resonator operating in the MHz regime with the quality factor over one million is obtainable by the proposed oscillation exciting method and appropriate design of dimensional parameters of the beams. In order to obtain such overall intrinsic quality factor, virtual supports are employed to eliminate attachment loss in the resonator.

Dynamic Unstructured Grids Method with Applications to Unsteady Flows Involving Moving Boundaries

Spring analogy method for dynamic unstructured grids is studied. The stiffness of the springs in the vertex spring method is analyzed. Improvements considering squashing spring effect and boundary effect are developed to the standard method. Applications of the improved spring analogy method to dynamic grids generation show that the new method greatly improves the deforming ability and the quality of the grids. This improved unstructured dynamic mesh method, coupled with ALE Euler solver, is then applied to simulate unsteady transonic flow about harmonious oscillation of rigid wing and bend-torsion oscillation of high-aspect ratio sweepback wing of High-Altitude-Long-Endurance Unmanned Aerial Vehicles; computational results are in good agreement with those of other literatures and experiments

Design of a New Spacer Damper for Bundle Power Transmission Lines Dynamic Behavior Monitoring Based on Fiber Bragg Grating Sensor

Galloping and ice shedding, two of significant dynamic damages to bundle conductors, are both typical three-degree-of-freedom vibrations, while few technique is studied on monitoring the torsion oscillation of the whole bundles and the sub-conductors. For the monitoring of the vertical, horizontal, and especially torsional oscillations, a novel type of spacer damper is developed, which can also detect the torsion motion of each sub-conductor, with consideration of the special configurations of bundle cables and integrated with fiber bragg grating sensors. Then, a distributed FBG network is introduced.

Oscillatory Indirect Coupling Between Perpendicularly Magnetized Co Monolayers Through Cu (111)

ABSTRACTCo-Monolayers, prepared by MBE on Cu (111) -surfaces at room temperature and covered by Cu, are ferromagnetic with a Curie-temperature of about 430 K. They are magnetized perpendicularly because of a strong perpendicular magnetic surface anisotropy of the Cu/Co (111) -interface. They provide a remarkably good representation of the 2-dimensional Ising Model. The indirect coupling between these perpendicularly magnetized ferromagnetic monolayers was investigated using samples of type Cu (111) /lCo/DçuCu/lCo/Cu, containing Co/Cu/Co-trilayers composed of Co-Monolayers and a spacer consisting of DCu atomic layers of Cu (111). Torsion oscillation magnetometry of these samples showed clearly a coupling between the monolayers with an oscillatory dependence on DCu. The amplitude of the oscillation is strongly reduced if the coupled Co-films consist of 5 ML instead of 1 M.L. The present controversy on the presence or absence of antiferromagnetic and oscillatory indirect coupling in the Co/Cu (111) -system is discussed in the light of these experiments. The discussion shows that the oscillatory coupling is an intrinsic property of ideal (111)-structures, and can be understood by the RKKY-type theory of indirect coupling between ferromagnetic Monolayers. The usual application of this theory to the coupling between thicker films is justified. However, in the fcc (111) -system there is apparently a specific barrier against complete coalescence, resulting in a tendency to retain holes and channels in the Cu-spacer. This tendency is stronger in flat single-crystal samples than in sputtered films with high densities of atomic steps. Apparently, this results in competing ferromagnetic hole coupling which may more or less completely obscure the intrinsic oscillatory coupling, preferentially in samples grown on extremely flat single crystal surfaces.