Large Static Displacements Research Articles

Dynamics of thin-film piezoelectric microactuators with large vertical stroke subject to multi-axis coupling and fabrication asymmetries

The high performance and small size of MEMS based scanners has allowed various optical imaging techniques to be realized in a small form factor. Many such devices are resonant scanners, and thus their linear and nonlinear dynamic behaviors have been studied in the past. Thin-film piezoelectric materials, in contrast, provide sufficient energy density to achieve both large static displacements and high-frequency resonance, but large deformation can in turn influence dynamic scanner behavior. This paper reports on the influence of very large stroke translation of a piezoelectric vertical actuator on its resonant behavior, which may not be otherwise explained fully by common causes of resonance shift such as beam stiffening or nonlinear forcing. To examine the change of structural compliance over the course of scanner motion, a model has been developed that includes internal forces from residual stress and the resultant additional multi-axis coupling among actuator leg structures. Like some preceding vertical scanning micro-actuators, the scanner of this work has four legs, with each leg featuring four serially connected thin-film PZT unimorphs that allow the scanner to generate larger than 400 µm of vertical displacement at 14 VDC. Using an excitation near one or more resonances, the input voltage can be lowered, and complementary multi-axis rotations can be also generated, but change of the resonant frequencies with scanner height needs to be understood to maximize scanner performance. The presented model well predicts the experimental observation of the decrease of the resonant frequencies of the scanner with the increase of a dc bias voltage. Also, the effects of the magnitude and uniformity of residual stress across the scanner structure on the natural frequencies have been studied.

The Utility of GNSS for Earthquake Early Warning in Regions with Sparse Seismic Networks

Abstract Real‐time Global Navigation Satellite Systems (GNSS) data are on their way to being well integrated into earthquake early warning (EEW) systems. The strength of GNSS data lies in the resolution of large dynamic and static displacements. Because of the limits in precision, GNSS data alone cannot resolve small ground displacements due to, for instance, P waves. Therefore, their use is currently limited to refining early warnings with more precise earthquake characteristics, such as magnitudes or ground‐motion predictions. Here, we analyze 1‐Hz Global Positioning System (GPS) data from the 24 January 2016 M w 7.1 Iniskin earthquake, which ruptured 125 km under Cook Inlet in Alaska, to motivate the inclusion of GNSS‐derived S ‐wave measurements into the trigger algorithms of EEW systems in regions lacking dense early‐warning instrumentation networks. We derive a relationship between earthquake depth and distance to help determine whether GNSS S ‐wave observations could expedite warnings to specific locations. Because the Iniskin earthquake was deep, by the time the S wave reached the surface, the P wave had already been observed over a wide region, limiting the potential for unique contributions from GNSS data to this event. For the same earthquake occurring near the surface, however, S waves derived from GNSS data have the potential to increase the warning time. Regardless of the depth, the Iniskin earthquake is an excellent example of the utility of GNSS in rapidly assessing the magnitude, improving predictions of ground shaking, and estimating the area of impact for the earthquake.

Aerodynamic stability of long span suspension bridges with low torsional natural frequencies

Classical flutter of suspended bridge decks can be avoided if the torsional frequencies are lower than the vertical. Wind tunnel tests of single boxes and twin box section models with torsional natural frequencies above and below the vertical frequency has been conducted. Flutter was avoided in all tests where the torsional frequency was lower than the vertical. But too low torsional stiffness caused large static displacements of the girder at medium–high wind speeds and steady state oscillations driven by a combination of torsional divergence and stalling behavior at the critical wind seed. In order to design aerodynamically stable suspension bridges with low torsional natural frequencies it is suggested to increase the mass moment of inertia and provide adequate torsional stiffness by the main cables spacing.

Direct mapping of microscopic polarization in ferroelectricx(BiScO3)−(1−x)(PbTiO3)throughout its morphotropic phase boundary

Pair distribution functions of ferroelectric $x{\mathrm{BiScO}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x){\mathrm{PbTiO}}_{3}$, obtained from neutron total scattering data, were examined and modeled utilizing the reverse Monte Carlo technique to depict exclusively the local structure of this compound throughout its reported morphotropic phase boundary (MPB). Microscopic polarizations due to the cation shifts have been mapped out from the refined crystal structure as a function of composition in order to reveal individual cation behavior driven by the composition. Direct evidences are provided for large static displacements of the cations $(\ensuremath{\sim}0.2\ensuremath{-}0.5\phantom{\rule{0.28em}{0ex}}\AA{})$, local cation ordering between Ti and Sc, and a categorical change of favored polarization directions of the cations at the conjuncture of the MPB. Apart from Sc, all cations have demonstrated an apparent transition from a relatively defined directional distribution to a broad and random distribution at $x={x}_{\mathrm{MPB}}$, suggesting a flattening of the local potential function for them. These features can further be correlated with the general concept of structural instability of a ferroelectric system at the MPB, which is often linked to the manifestation of enhanced physical properties.

Mechanical Amplifier for Translational Kinetic Energy Harvesters

This paper reports the design, optimization, and test results of a mechanical amplifier coupled to an electromagnetic energy harvester to generate power from low- amplitude (±1 mm) and low-frequency (<5 Hz) vibrations in the presence of large static displacements. When coupled to a translational kinetic energy harvester, the amplifier boosts small vibration amplitudes by as much as 4x while accommodating translational displacements of more than 10x of vibration amplitudes. A complete electromagnetic energy harvester using this mechanical amplifier produces 16x improvement in output power (30 mW vs 1.9 mW without amplifier at 5 Hz), and a high power density of 170 μW/cm3.

Phonon scattering rates and atomic ordering inAg1−xSb1+xTe2+x(x=0,0.1,0.2)investigated with inelastic neutron scattering and synchrotron diffraction

The phonon dispersions and scattering rates of the thermoelectric material ${\mathrm{Ag}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{1+x}{\mathrm{Te}}_{2+x}\phantom{\rule{0.28em}{0ex}}(x=0,0.1,0.2)$ were measured with inelastic neutron scattering, as function of both temperature $T$ and off stoichiometry $x$. In addition, detailed measurements of diffuse scattering were performed with both neutron and synchrotron x-ray diffraction. The results show that phonon scattering rates are large and weakly dependent on $T$ or $x$, and the lattice thermal conductivity calculated from these scattering rates and group velocities is in good agreement with bulk transport measurements. We also find that the scattering rates and their temperature dependence cannot be accounted for with common models of phonon scattering by anharmonicity or point defects. The diffuse scattering measurements show a pervasive, complex signal, with several distinct components. In particular, broad superstructure reflections indicate a short-range ordering of the Ag and Sb cations on their sublattice. Single-crystal Bragg peak intensities also reveal large static atomic displacements, compatible with results from Rietveld refinement of neutron powder diffraction data. Our results indicate that a complex nanostructure, arising from multiple variants of nanoscale anisotropic superstructures of cations, and large atomic displacements, is likely responsible for the strong phonon scattering.

Strike-slip earthquakes can also be detected in the ionosphere

It is generally assumed that co-seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake. Consequently, it is expected that co-seismic ionospheric disturbances are only observable after earthquakes with a significant dip–slip component. Therefore, earthquakes dominated by strike-slip motion, i.e. with very little vertical co-seismic component, are not expected to generate ionospheric perturbations. In this work, we use total electron content (TEC) measurements from ground-based GNSS-receivers to study ionospheric response to six recent largest strike-slip earthquakes: the Mw7.8 Kunlun earthquake of 14 November 2001, the Mw8.1 Macquarie earthquake of 23 December 2004, the Sumatra earthquake doublet, Mw8.6 and Mw8.2, of 11 April 2012, the Mw7.7 Balochistan earthquake of 24 September 2013 and the Mw 7.7 Scotia Sea earthquake of 17 November 2013. We show that large strike-slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip–slip earthquakes of equivalent magnitude. We consider that in the absence of significant vertical static co-seismic displacements of the ground, other seismological parameters (primarily the magnitude of co-seismic horizontal displacements, seismic fault dimensions, seismic slip) may contribute in generation of large-amplitude ionospheric perturbations.

Structural Properties in Incommensurately Modulated Spinel Compound CuV2S4

We have studied the incommensurate crystal structure of the spinel compound CuV2S4 at low temperatures using the synchrotron powder diffraction technique. The powder diffraction pattern at 70 K shows that the splitting of the fundamental 800 reflection peak and the weak superlattice reflections with a modulation vector \(\mathbf{q}\sim 3/4[110]\) due to the structural phase transition at 90 K were observed. It is found that the crystal structure at 70 K has an orthorhombic unit cell with the superspace-group \(Imm2(0\)β\(0)\) with a modulation vector \(\mathbf{q}= 0.7391(5)\mathbf{b}^{*}\). By Rietveld analysis including the incommensurate modulation along the \(b\)-axis, large static atomic displacements were found at the positions of V atoms, suggesting that V atoms play an important role in a charge-density wave (CDW) transition. The atomic displacements indicate that V1 atoms at the \(4c\) site form dimers along the \(a\)-axis, suggesting that a commensurate CDW forms along the \(a\)-axis. Furthermore...

非整合な構造をもつスピネル化合物CuV&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;4&lt;/sub&gt;の結晶構造解析

We have investigated the incommensurate crystal structure of the spinel CuV2S4, which exhibits incommensurate charge-density wave at 90 K, using the synchrotron powder diffraction technique. It is found that the crystal structure at 70 K has an orthorhombic unit cell with the superspace-group Imm2（0β0）with a modulation vector q＝0.7391（5）b*. By Rietveld analysis including the incommensurate modulation along the b-axis, large static atomic displacements were found at the positions of V atoms, suggesting that V atoms play an important role in a charge-density wave transition. We have found the formation of V clusters, and arrangements of the clusters form a gradation pattern along the b-axis.

New Total Ossicular Replacement Prostheses With a Resilient Joint

New flexible total ossicular prostheses with an integrated microjoint can compensate for large static displacements in the reconstructed ossicular chain. When properly designed, they can mimic the function of the joints of the intact chain and ensure good vibration transfer in both straight and bent conditions. Prosthesis dislocations and extrusions are frequently observed after middle ear surgery. They are mainly related to the altered distance between the coupling points because of large static eardrum displacements. The new prostheses consist of 2 titanium shafts, which are incorporated into a silicone body. The sound transfer function and stapes footplate displacement at static loads were evaluated in human temporal bones after ossicular reconstruction using prostheses with 2 different silicones with different hardness values. The stiffness and bending characteristics of the prostheses were investigated with a quasi-static load. The sound transfer properties of the middle ears with the prostheses inserted under uncompressed conditions were comparable with those of ears with intact ossicular chains. The implant with the soft silicone had improved acoustic transfer characteristics over the implant with the hard silicone in a compressed state. In the quasi-static experiments, the minimum medial footplate displacement was found with the same implant. The bending characteristics depended on the silicone stiffness and correlated closely with the point and angle of the load incidence. The titanium prostheses with a resilient joint that were investigated in this study had good sound transfer characteristics under optimal conditions as well as in a compressed state. As a result of joint bending, the implants compensate for the small changes in length of the ossicular chain that occur under varying middle ear pressure. The implants require a stable support at the stapes footplate to function properly.

A low-voltage three-axis electromagnetically actuated micromirror for fine alignment among optical devices

In this paper, a new three-axis electromagnetically actuated micromirror structure has been proposed and fabricated. It is electromagnetically actuated at low voltage using an external magnetic field. The main purpose of this work was to obtain a three-axis actuated micromirror in a mechanically robust structure with large static angular and vertical displacement at low actuation voltage for fine alignment among optical components in an active alignment module as well as conventional optical systems. The mirror plate and torsion bars are made of bulk silicon using a SOI wafer, and the actuation coils are made of electroplated Au. The maximum static deflection angles were measured as ±4.2° for x-axis actuation and ±9.2° for y-axis actuation, respectively. The maximum static vertical displacement was measured as ±42 µm for z-axis actuation. The actuation voltages were below 3 V for all actuation. The simulated resonant frequencies are several kHz, and these imply that the fabricated micromirror can be operated in sub-millisecond order. The measured radius of curvature (ROC) of the fabricated micromirror is 7.72 cm, and the surface roughness of the reflector is below 1.29 nm which ensure high optical performance such as high directionality and reflectivity. The fabricated micromirror has demonstrated large actuated displacement at low actuation voltage, and it enables us to compensate a larger misalignment value when it is used in an active alignment module. The robust torsion bar and lifting bar structure formed by bulk silicon allowed the proposed micromirror to have greater operating stability. The additional degree of freedom with z-axis actuation can decrease the difficulty in the assembly of optical components and increase the coupling efficiency between optical components.

Embedded absorbers for helicopter rotor lag damping

Radial and chordwise damped vibration absorbers embedded in the rotor blade are compared for rotor lag damping augmentation. Results show that the radial absorber is more effective in transferring damping to the rotor blade lag mode. The chordwise absorber needs to be at a more outboard location and have a larger mass to introduce levels of lag damping comparable to that introduced by the radial absorber. The 1/rev amplitude of a chordwise absorber at the blade tip, per degree of blade lead-lag motion in forward flight, is of the order of 35% of the blade chord, and such a stroke might be difficult to accommodate. The 1/rev amplitude of a radial absorber at 70% span (having significantly lower mass than the chordwise absorber and producing comparable lag damping) is of the order of 4% of the rotor blade span. The static displacement of the radial absorber under centrifugal load needs to be limited using a frequency-dependent (high static stiffness, low dynamic stiffness) or nonlinear spring. The chordwise absorber can also undergo a large static displacement under the chordwise component of the centrifugal load if there is an offset from the feather axis, and this would again have to be limited using a strategy such as a frequency-dependent spring. Significant advantages of the radial absorber are—higher lag damping, lower absorber mass, space for absorber mass travel, and no chordwise travel of blade center of gravity reducing susceptibility to aeroelastic instability and dynamic pitch-link loads.

Low energy electron diffraction and low energy electron microscopy microspot I∕V analysis of the (4×4)O structure on Ag(111): Surface oxide or reconstruction?

A low energy electron diffraction (LEED) I/V analysis was performed of the (4 x 4) oxygen structure on Ag(111). Two data sets were used, one recorded with a conventional LEED system and a second with a low energy electron microscope (LEEM). The data sets agree well with each other, demonstrating that I/V structure analyses can be performed with the same quality with LEEM as with conventional LEED. The structure obtained confirms the recently proposed model that involves a reconstruction of the Ag(111) surface. Previous models based on a thin layer of Ag(2)O that had been accepted for more than 30 years are disproved. The reconstruction model contains two units of six triangularly arranged Ag atoms and a stacking fault in one half of the unit cell. The six O atoms per unit cell occupy sites in the trenches between the Ag(6) triangles. Small lateral displacements of the Ag atoms lift the mirror symmetry of the structure, leading to two nonequivalent groups of O atoms. The atoms of both groups are located approximately 0.5 Angstrom below the top Ag layer, on fourfold positions with respect to the top layer Ag atoms. Ag-O distances between 2.05 and 2.3 Angstrom are found. The oxygen atoms exhibit large static or dynamic displacements of up to 0.3 Angstrom at 300 K.

Investigation of the structural features of high-temperature superconducting crystals by the method of channelization and resonant nuclear reactions

The structural features of the oxygen sublattice in the YBa2Cu3O7 crystals are analyzed based on a comparison of the calculated angular dependence of the yield of resonant nuclear reaction 16O(α, α)16O with the available experimental results obtained for ions with energies of 3.055, 3.06, and 7.6 MeV. It is established that in crystal films there are vacancies in oxygen chains at room temperature, and oxygen atoms are considerably displaced from the equilibrium positions in directions perpendicular to the axis. In thick crystals at temperatures close to the temperature of phase transition into the superconducting state, no large thermal and/or static displacements of oxygen atoms from the equilibrium positions are observed.

Displacive ordering in the hydrogen sublattice of yttrium trihydride

Powder samples of YH3 and YD3 have been studied by neutron diffraction (ND) with a much higher statistical accuracy thanobtained previously. The profile analysis of the obtained ND patterns confirmed the high-symmetryHoH3-typestructure of YH3 and ruled out the ‘broken symmetry’ structures proposed recently to explain the insulatingproperties and lattice dynamics of this compound. At the same time, it was demonstrated that theHoH3-type structure is only the structure of the mean lattice ofYH3. Large static displacements of H atoms from the symmetrical positions in thisstructure do occur, and ordering of these displacements on a short-range scale cansettle the controversies between the crystal structure and physical properties ofYH3.

Design and modeling for comb drive actuator with enlarged static displacement

New comb drives using high stiffness ratio springs are designed and modeled to provide capabilities of large static displacement and continuous motion for applications, such as micro XY stage, two dimensional lens scanner, variable optical attenuator, and optical switch, etc. The maximum static displacement of conventional comb drive is constrained by the side sticking effect of comb finger electrodes. Since the side sticking effect will become obvious and exhibit strong impact on actuator behavior in the case that the spring lateral stiffness is decreased when the static displacement is increased, and the rotation moment caused by unbalanced force between electrode fingers resulted from the environment disturbance and/or fabrication deviation will enhance the side pulling phenomena. The aforementioned sticking effect occurs at the static displacement smaller than the analytical results estimated by conventional stability criteria. Thus, a new stability criterion is proposed for providing more accurate predicted maximum static displacement. A new hybrid spring with an n-shaped joint for comb drive is developed and proposed in this paper as well. This new spring is capable of not only enhancing the lateral stiffness against to the lateral mechanical disturbance and shock, but also efficiently eliminating the rotation moment caused by the disturbance over the large displacement range. The design scheme is verified by the simulation results.

Large-deformation tests and total-Lagrangian finite-element analyses of flexible beams

Presented here is a total-Lagrangian displacement-based finite-element formulation for general anisotropic beams undergoing large displacements and rotations. The theory fully accounts for geometric nonlinearities (large rotations), general initial curvatures, and extensionality by using Jaumann stress and strain measures, an exact coordinate transformation, and a new concept of orthogonal virtual rotations. Moreover, transverse shear deformations are accounted for by using a first-order shear-deformation theory. To verify the accuracy of the finite-element model, two test fixtures have been built for bending and twisting experiments. Large static deformation tests of beams with different loading conditions have been performed. The finite-element results agree closely with the experimental results and numerically exact solutions obtained by using a multiple shooting method to solve for post-buckling deformations of highly flexible beams undergoing large static rotations and displacements in three-dimensional space.

A Displacive Structural Transformation in theCuO2Planes ofYBa2Cu3Oxat the Underdoped-Overdoped Phase Separation Line

A structural phase transformation in the CuO_2 planes of YBa_2Cu_3O_x has been observed at the onset of the overdoped regime, x=6.95. We have measured as a function of x the dimpling in the CuO_2 planes by EXAFS, and the O2,3 in-phase (A_1g) mode by Raman scattering. The data show for x>6.95 anomalously large static displacements of the Cu2 atoms off the O2,3 layer, and a gap in the distribution of the O2,3 in-phase Raman shifts. We conclude the structure of overdoped YBa_2Cu_3O_x to be a martensitic form of the structure most favourable for the superconductivity, and possibly at the origin of the split superconducting transition in the overdoped regime.

A model of local atomic structure in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3

We have developed a model of local atomic structure in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) by pair-density function analysis of neutron and x-ray powder diffraction data. We find large static displacements of all atomic species from their ideal cubic perovskite sites producing a long-range average structure consistent with a crystallographic disorder model, however local correlations of these displacements are significant. Two distinctly different B cation environments are found, as are two unique environments for Pb. The model suggests the formation of structurally ordered regions in which the two types of B cation environments are 1:1 ordered. Details of this model for the local atomic structure of PMN and how it was obtained are described.

Small Vibrations of Flexible Bars by Using the Finite Element Method with Equivalent Uniform Stiffness and Mass Methodology

The object of this research is to calculate natural frequencies and mode shapes of a small oscillation vibration, superimposed on large static displacement, by using the finite element method in conjunction with the equivalent uniform stiffness and mass method. The equivalent uniform stiffness and mass matrices are determined from the differential equation by using Galerkin's method. The analysis herein is three-fold. Firstly, the large static equilibrium configuration of the deformed flexible beam is established. This is achieved by using the Euler-Bernoulli equation in conjunction with equivalent pseudo-linear and/or equivalent non-linear systems of constant stiffness. This concept and methodology were used quite extensively by the authors to study large deformation characteristics of various flexible beam problems of uniform and variable stiffness and of arbitrary loading conditions (see, for example, the work of Fertis and Afonta [1, 2], and Fertis and Lee [3, 4]). Secondly, the differential equation of motion for small amplitude vibrations from the large static equilibrium configuration is derived. Galerkin's technique is used to approximate the differential equation of motion. Finally, the natural frequencies of vibration and the associated mode shapes are determined by solving the resulting eigenvalue problem. A canned eigensolver from the University of Akron IMSL is used to extract the eigenvalues and eigenvectors. The concept of equivalent pseudo-linear systems of constant stiffness is used extensively in this research, in order to simplify the solution of these complex non-linear problems.