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Direct conversion crystalline silicon X-ray imagers are used for low-energy X-ray photon (4–20 keV) detection in scientific research applications such as protein crystallography. In this paper, we demonstrate a novel pixel architecture that integrates a crystalline silicon X-ray detector with a thin-film transistor amorphous silicon pixel readout circuit. We describe a simplified two-mask process to fabricate a complete imaging array and present preliminary results that show the fabricated pixel to be sensitive to 5.89-keV photons from a low activity Fe-55 gamma source. This paper presented can expedite the development of high spatial resolution, low cost, direct conversion imagers for X-ray diffraction and crystallography applications. [ABSTRACT FROM PUBLISHER]

In this paper, a 4H-SiC trench insulated gate bipolar transistor (IGBT) incorporating a Schottky contact in the collector side is proposed to reduce the turn-off energy loss. The proposed structure is explored and compared with the conventional IGBT using ATLAS. The simulation results have indicated that the reduction in turn-off energy loss is more than 88%, with a slight degradation in the I-V characteristics. Concurrently, with the same on-state voltage drop, the turn-off loss is reduced by a figure of 84%. [ABSTRACT FROM AUTHOR]

This paper presents a detailed theoretical analysis of the implications of nanoscale device structures on the average hole ballistic velocity calculated from quantum-mechanical strain-dependent 6\times 6~\text k \cdot \text p band-structure simulations. The simulations show that the crystallographic orientation of the uniaxial strain, channel, and surface affect the average ballistic velocity by modifying the energy–momentum (E − k) dispersion of the subbands (from which the ballistic velocity is calculated). Conversely, the analysis shows that semiconductor-body thickness and gate architecture influence the ballistic velocity by modifying the quantum confinement in the structure, which ultimately affects the relative hole occupation of k -states across different subbands. Key results of the work show that a 5-nm-body thickness yields a 6%–12% increase in the ballistic velocity compared to a 10-nm body. Likewise, a single-gate architecture gives up to an 11% increase over a double gate, but the improvement is dependent on the crystallographic surface orientation. Strained Ge shows a significantly enhanced ballistic velocity relative to strained Si for both {100}- and {110}-surface orientations with a predicted hole ballistic velocity exceeding 2 \times 10^7 cm/s at \textn_\texts^\textv+ = 5 \times 10^12 #/cm2. [ABSTRACT FROM PUBLISHER]

3-D integrations are unavoidable task for new emerging memories, including resistive switching random-access memory (RRAM), in order to overcome the market-leading nand flash. However, an RRAM crossbar array (CBA) suffers severe read margin degradation due to the sneak current, which becomes even more critical as the memory density increases with the 3-D integration. In this paper, we extend the two-port readout scheme for a 2-D CBA, proposed in our previous work, to the 3-D vertical structure. A closed-form expression of the operating principle is derived, and HSPICE simulation using a $32\times 32\times8$ vertical RRAM CBA considering practical circuit parameters verifies feasibility of the two-port scheme to the 3-D CBA. [ABSTRACT FROM AUTHOR]

Phase retrieval problems involve solving linear equations, but with missing sign (or phase, for complex numbers) information. More than four decades after it was first proposed, the seminal error reduction algorithm of Gerchberg and Saxton and Fienup is still the popular choice for solving many variants of this problem. The algorithm is based on alternating minimization; i.e., it alternates between estimating the missing phase information, and the candidate solution. Despite its wide usage in practice, no global convergence guarantees for this algorithm are known. In this paper, we show that a (resampling) variant of this approach converges geometrically to the solution of one such problem—finding a vector \bf x from \bf y, \bf A, where \bf y = \vert \bf A^T\bf x\vert and \vert\bf z\vert denotes a vector of element-wise magnitudes of \bf z—under the assumption that \bf A is Gaussian. Empirically, we demonstrate that alternating minimization performs similar to recently proposed convex techniques for this problem (which are based on “lifting” to a convex matrix problem) in sample complexity and robustness to noise. However, it is much more efficient and can scale to large problems. Analytically, for a resampling version of alternating minimization, we show geometric convergence to the solution, and sample complexity that is off by log factors from obvious lower bounds. We also establish close to optimal scaling for the case when the unknown vector is sparse. Our work represents the first theoretical guarantee for alternating minimization (albeit with resampling) for any variant of phase retrieval problems in the non-convex setting. [ABSTRACT FROM AUTHOR]

This paper focuses on studying the effect of increasing the ambient temperature up to 160 °C on the power harvested by an MEMS piezoelectric micro-cantilever manufactured using an aluminum nitride-on-silicon fabrication process. An experimental study shows that the peak output power decreases by 60% to 70% depending on the input acceleration. A theoretical study establishes the relationship of all important parameters with temperature and includes them into a temperature-dependent model. This model shows that around 50% of the power drop can be explained by a decreasing quality factor, and that thermal stresses account for around 30% of this decrease. [2017-0071] [ABSTRACT FROM PUBLISHER]

In a variety of fields, in particular those involving imaging and optics, we often measure signals whose phase is missing or has been irremediably distorted. Phase retrieval attempts to recover the phase information of a signal from the magnitude of its Fourier transform to enable the reconstruction of the original signal. Solving the phase retrieval problem is equivalent to recovering a signal from its auto-correlation function. In this paper, we assume the original signal to be sparse; this is a natural assumption in many applications, such as X-ray crystallography, speckle imaging and blind channel estimation. We propose an algorithm that resolves the phase retrieval problem in three stages, first, we leverage the finite rate of innovation sampling theory to super-resolve the auto-correlation function from a limited number of samples, second, we design a greedy algorithm that identifies the locations of a sparse solution given the super-resolved auto-correlation function, finally, we recover the amplitudes of the atoms given their locations and the measured auto-correlation function. Unlike traditional approaches that recover a discrete approximation of the underlying signal, our algorithm estimates the signal on a continuous domain, which makes it the first of its kind. Along with the algorithm, we derive its performance bound with a theoretical analysis and propose a set of enhancements to improve its computational complexity and noise resilience. Finally, we demonstrate the benefits of the proposed method via a comparison against Charge Flipping, a notable algorithm in crystallography. [ABSTRACT FROM AUTHOR]

In this paper, we investigate sputtered physical vapor deposition (PVD) AlN nucleation layer effects on crystal quality and efficiency of GaN-based light-emitting diodes (LEDs) prepared on high-aspect ratio patterned sapphire substrate (HARPSS). The crystal quality of the GaN epitaxial layer prepared on HARPSS with a PVD AlN nucleation layer was significantly better than that with a conventional metal organic chemical vapor deposition (MOCVD)-grown AlN nucleation layer. In addition, the pure wurzite structure GaN prepared on HARPSS could be obtained using PVD AlN nucleation layer. With the PVD AlN nucleation layer, the 20-mA LED light output power of the LEDs can be enhanced by 47.7% compared with the LEDs with the conventional MOCVD-grown AlN nucleation layer. [ABSTRACT FROM AUTHOR]

Highly textured rolled sheets of Fe–Ga and Fe–Al alloys behave like single crystal, exhibiting magnetostriction values that are equal to ~ 80%–95% of those of single crystal along the $\langle 100\rangle $ axes. In this paper, we investigate the crystal orientation dependence of anisotropic magnetization and magnetostriction properties in highly textured disks of Fe–Ga and Fe–Al alloys. The highly textured samples are composed of a single (011) plane and small isolated grains, aside from the (011) grain, which exhibit three different cubic crystal orientations, such as $\langle 100\rangle $ , $\langle 110\rangle $ , and $\langle 111\rangle $ directions. Measured magnetostriction values strongly depend on a deviation angle of the $\langle 100\rangle $ direction from the rolling direction, well matched with the predicted values based on the anisotropic magnetostriction equation in the (011) plane. Of particular interest is the observation that measured values at the deviation angles over ~20° are higher than the predicted ones as much as the fraction of island grains with principal $\langle 100\rangle $ and $\langle 110\rangle $ directions along the strain measurement direction. In addition, it seems to be averaged out for magnetization behaviors along the three different directions in comparison with those of the single crystal Fe–Ga. [ABSTRACT FROM AUTHOR]

In III–nitride nanowire (NW)-based solar cells, efficient utilization of polarization charges is essential in order to achieve high performance. In this paper, the polarization behavior of a GaN/InxGa1–xN/GaN core/shell/shell triangular NW solar cell with {000-1} or {0001} as one of the facets is intensively studied through numerical simulations. An analysis of defect density, strain profile, and polarization charges at different facets of NWs with different “In” compositions is considered carefully. It is observed that an NW solar cell with a N-polar {000-1} facet is good enough to enhance carrier collection efficiency as compared with Ga-polar {0001} facet. This numerical study provides an innovative aspect of implementation of fundamental device physics with respect to recent growth techniques in order to realize the application of III–nitride NWs toward photovoltaic applications. The effect of an InxGa1–xN layer with different “In” compositions in all crystallographic orientations of NW solar cells is also discussed. It is interesting to observe that a maximum conversion efficiency of ~3.85% with the 93.38% fill factor is achieved from an n-GaN/i-InxGa1–xN/p-GaN nanowire solar cell considering 10% of “In” content under one Sun AM1.5 illumination. [ABSTRACT FROM PUBLISHER]

This paper proposes an observer for the sensorless control of doubly fed induction machines which is based on the effect of a natural signal injection in the stator windings due to the fifth harmonic of the line voltage. A method to extract the rotor position and speed only from the rotor current and stator voltage measurements is developed: As a novelty, the stator current measurement and the anisotropies in the machine design are not required. A phase-locked loop is used in order to track the harmonic current component which is induced in the rotor by the fifth line voltage harmonic and whose speed and position are directly related to the rotor speed and position. The tuning of the observer parameters is discussed together with the effect of the other line voltage harmonics. This paper is completed by the experimental validation of the observer performances. [ABSTRACT FROM PUBLISHER]

The robust and precise control of piezoelectric stages is quite challenging due to the existence of strong hysteresis nonlinearity. In this paper, the dynamics of a piezoelectric stage is identified as a second-order linear system preceded by an input hysteresis characterized by the Prandtl–Ishlinskii (PI) model. Then, a control strategy based on the uncertainty and disturbance estimator (UDE) is developed to mitigate the effect of hysteresis nonlinearity and improve the performance of the positioning control of the piezoelectric stage, without the detailed model of the hysteresis except the slope information of the PI hysteresis asymptotes. Moreover, the stability analysis of the closed-loop system with the UDE-based controller is provided. Extensive experimental studies are carried out on a Physik Instrumente P-753.31c piezoelectric stage to demonstrate that the UDE-based controller can achieve excellent performance in trajectory tracking and disturbance rejection, compared to the proportional–integral–derivative (PID) controller and a disturbance-observer-based controller. [ABSTRACT FROM PUBLISHER]

Microstructural attributes such as grain size d and dislocation density ζ[subd] affect the hysteretic magnetic properties of steels because they affect domain wall movement and pinning. In an earlier paper, a model was proposed for computing hysteresis loops based on the effect of grain size and dislocation density. In that paper, hysteresis loops were compared that all had the same maximum field H[submax]. The result was that coercivity departed from linear relationships with inverse grain size (viz. 1/d) and &zeta[sup1/2][subd] for large values of 1/d and ζ[sup1/2][subd]. The same was true of hysteresis loss W[subH], except that hysteresis loss even showed a peak, first increasing and then decreasing with increasing 1/d and ζ[sup1/2][subd]. This kind of behavior had not been seen by experimenters, particularly core-loss people. It was learned that the core-loss experimenters compared hysteresis loops of the same maximum flux density B[submax] instead of the same H[submax]. In this paper, we use the model previously formulated to produce hysteresis loops with the same B[submax]. Indeed, the appropriate linear relationships are found. The paper also addresses effects of uniaxial anisotropy on these microstructural magnetic effects and why two hysteresis parameters are affected by microstructural variation. [ABSTRACT FROM AUTHOR]

The simplified ray-tracing technique reported in Part I of this paper is employed to compute the single-scattering properties of hexagonal columns with maximum dimensions ranging from 2 to 3500 μm with a size-bin resolution of 2 μm at wave-lengths of 0.86 and 2.13 μm. For small ice crystals, the current treatment of surface roughness may not be adequate because the applicability of the principles of geometric optics breaks down for small roughness scale. However, for ice crystals smaller than 40 μm, the aspect ratios of these particles are close to one, and the effect of surface roughness is quite small. In this paper, the diffraction is accounted for in the same way as in the case of smooth particles. It is essentially unfeasible to incorporate the effect of surface roughness into the numerical computation of the diffraction contribution. The scattering properties of individual ice crystals are then averaged over 18 particle size distributions whose effective particle radii (re) range from 5 to 90 μm. The single-scattering properties of ice clouds are strongly sensitive to surface roughness condition. Lookup tables that are built for the correlation between the bidirectional reflectances at wavelengths of 0.86 and 2.13 μm with different roughness conditions are used to retrieve ice cloud optical thickness and effective particle size over oceans. Pronounced differences are noticed for the retrieved cirrus cloud optical thickness and effective particle sizes in conjunction with different surface roughness conditions. The values of the retrieved cirrus cloud optical thickness in the case of the rough surface are generally smaller than their counterparts associated with smooth surface conditions. The effect of surface roughness on the retrieved effective particle radii is not pronounced for slight and moderate roughness conditions. However, when the surfaces of ice crystals are substantially rough, the retrieved effective radii associated with roughened particles are larger and smaller than their smooth surface counterparts for large (re > 50 μm) and small (re < 35 μm) ice crystals, respectively, whereas the effect of surface roughness on the retrieved effective radii shows a nonmonotonic feature for moderate particle sizes (35 μm < re < 50 μm). In general, the dominant effect of surface roughness on cloud property retrievals is to decrease the retrieved optical thickness and to increase the retrieved effective particle size in comparison with their counterparts in the case of smooth ice particles. [ABSTRACT FROM AUTHOR]

This paper presents a new semianalytical model for the energy dispersion of the holes in the inversion layer of pMOS transistors. The wave vector dependence of the energy inside the 2-D subbands is described with an analytical, nonparabolic, and anisotropic expression. The procedure to extract the parameters of the model is transparent and simple, and we have used the band structure obtained with the k ·p method to calibrate the model for silicon MOSFETs with different crystal orientations. The model is validated by calculating several transport-related quantities in the inversion layer of a heavily doped pMOSFET and by systematically comparing the results to the corresponding k · p calculations. Finally, we have used the newly developed band-structure model to calculate the effective mobility of pMOS transistors and compare the results with the experimental data. The overall computational complexity of our model is dramatically smaller compared to a fully numerical treatment (such as the k · p method); hence, our approach opens new possibilities for the physically based modeling of pMOS transistors. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of a new class of magnetic photonic crystals (MPCs) constructed from periodic arrangements of available (possibly anisotropic) homogeneous material layers. Earlier, analytical studies of semi-infinite versions of these crystals demonstrated that they exhibit the phenomena of minimal reflection at their interface, large amplitude growth of the harmonic wave within the crystal, and concurrent group velocity slow-down. These characteristics are associated with the so called frozen mode and occur at a specific frequency associated with a stationary inflection point within the Bloch diagram. In this paper, we present a characterization of these phenomena for a practical, finite thickness crystal slab and propose a realizable combination of materials consisting of available ferrite and dielectric media. The existence of significant wave amplitude growth and slow down are verified for materials with realistic losses. In addition, we identify and characterize the bandwidth of the magnetic photonic crystals and examine its relationship to the amplitude growth. [ABSTRACT FROM AUTHOR]

In this paper, the influence of the aspect ratio of Yee's unit cell on the numerical dispersion errors [in terms of the physical phase-velocity error (PVE) and the velocity-anisotropy error (VAE)] of two-dimensional (2-D) finite-difference time- domain (FDTD) and three-dimensional (3-D) FDTD methods is comprehensively investigated. Numerical results reveal that, for a fixed mesh resolution, the physical PVE and the VAE of both the 2-D and 3-D FDTD methods converge to certain limits for higher aspect ratio. Most importantly, it is found for the first time that for the 2-D and 3-D cases the converged dispersion errors (i.e., the limits) are, respectively, about 2.0 and 1.5 times of the corresponding square and cubic unit cells; and the validity of the above theoretical prediction is verified through numerical tests. The investigation carried out in this paper certainly confirms, from the numerical dispersion point of view, that very accurate numerical results can still be obtained even when the aspect ratio of the cells is higher. Consequently, it gives design engineers more freedom and confidence to use the FDTD methods, especially when the aspect ratio of the cells has to be greatly adjusted due to the special requirement of structures under study. [ABSTRACT FROM AUTHOR]

The effect of topological bumpy surface underlayer on compositionally modulated atomic layer stacking in high uniaxial magnetocrystalline anisotropy ( $K_u$ ) hcp Co80Pt20 film with (00.2) crystallographic texture orientation was investigated. In this paper, the following has been discussed. Concerning preparation of underlayer with various morphologies, an annealing process prior to the deposition of Co80Pt20 film, and introduction of a metal-oxide buffer layer are effective to obtain underlayers with surface roughness ranging from \sim 0.4$ to 2 nm and grain size ranging from \sim 6.7$ to 12.5 nm. To realize a compositionally modulated atomic layer stacking structure, which is confirmed by the high angle annular dark field detector scanning transmission electron microscopy observation, an underlayer with surface roughness less than \sim 1$ nm and/or grain size larger than \sim 8 erg/cm $^3$ , surface roughness reduction to $ \sim 0.5$ nm and grain size increase to $ \sim 12$ nm are needed. [ABSTRACT FROM AUTHOR]

Phase retrieval is an inverse problem which consists in recovering an unknown signal from a set of absolute squared projections. Recently, gradient descent algorithms have been developed to solve this problem. However, their optimization cost functions are non-convex and non-smooth. To address the non-smoothness of the cost function, some of these methods use truncation thresholds to calculate a truncated step gradient direction. But, the truncation requires designing parameters to obtain a desired performance in the phase recovery, which drastically modifies the search direction update, increasing the sampling complexity. Therefore, this paper develops the Phase Retrieval Smoothing Conjugate Gradient method (PR-SCG) which uses a smoothing function to retrieve the signal. PR-SCG is based on the smooth-ing projected gradient method which is useful for non-convex optimization problems. PR-SCG uses a nonlinear conjugate gradient of the smoothing function as the search direction to accelerate the convergence. Furthermore, the incremental Stochastic Smoothing Phase Retrieval algorithm (SSPR) is developed. SSPR involves a single equation per iteration which results in a simple, scalable, and fast approach useful when the size of the signal is large. Also, it is shown that SSPR converges linearly to the true signal, up to a global unimodular constant. Additionally, the proposed methods do not require truncation parameters. Simulation results are provided to validate the efficiency of PR-SCG and SSPR compared to existing phase retrieval algorithms. It is shown that PR-SCG and SSPR are able to reduce the number of measurements and iterations to recover the phase, compared with recently developed algorithms. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3-based ferroelectric single crystals have recently undergone a substantial development, resulting in improved crystal quality and large piezoelectric coefficients, exceeding 700 pC/N, over a broad temperature range. However, further development necessitates a detailed understanding of the mechanisms defining the domain structure and its temperature evolution. This paper presents the investigation into the crystallographic structure and domain configurations of a (K,Na,Li)(Ta,Nb)O3 single crystal over a broad temperature range. The crystal was grown by the submerged-seed solution growth technique and investigated using in situ transmission electron microscopy, X-ray diffraction, dielectric measurements, and polarized light microscopy. The lattice distortion, structural phase transitions, and domain configurations are reported. A transition from the lamellar orthorhombic to the rectangular tetragonal domain structure is observed upon heating. Moreover, the milky optical appearance of the crystal was investigated and found to result from the presence of regions with different domain configurations and domain sizes. The formation of these regions is related to the growth defects, which govern the domain formation when cooling below the Curie temperature. [ABSTRACT FROM AUTHOR]

Electrodeposited thin films in MEMS devices often show fiber texture resulting in transverse isotropic, effective elastic properties. It is of interest to predict these elastic properties since they play a role in device performance. In addition to predicting effective material properties of the devices, we quantify the uncertainty in our predictions of these material properties for use in downstream simulations aimed at studies of performance, lifetime, or reliability. In this paper, we estimate the numerical value of the effective in-plane Young's modulus of thin nickel polycrystalline films using numerical simulation. We also examine the variability and sensitivity of the in-plane Young's modulus due to uncertainties in microstructure geometry, crystallographic texture, and numerical values of single-crystal elastic constants. The importance of accurate characterization of the texture is shown, as is the sensitivity of the effective in-plane Young's modulus to single-crystal elastic moduli. [ABSTRACT FROM AUTHOR]

This paper presents a method to estimate the magnetic properties and width of a damaged area which is the result of the carried out punching process. Both a finite-element method (FEM) numerical model and a method for estimating the damaged area width are proposed based on data obtained from the noninvasive measurements as well as on an experimental study of the crystallographic structure. In addition, the authors propose an algorithm, using the FEM numerical model, to identify the equivalent magnetic properties of the material in the damaged area. The results obtained from the FEM model were compared with those obtained by the analytical formula proposed earlier. [ABSTRACT FROM AUTHOR]

This paper introduces a novel way of building transformer cores using consolidated stacks of electrical steel to reduce construction times without causing an increase in the core losses. The novel core design introduced in this paper can exhibit lower power loss than the conventional cores by taking advantage of the high anisotropy of grain-oriented electrical steels and reducing the flux along the transverse direction of the steel. Open circuit tests and thermal imaging techniques were used to assess the performance of the cores. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of the transient (short-term) and stable (long-term) cross-sectional profiles of elongated trenches formed by anisotropic wet etching on Z-cut quartz. Because all quartz planes parallel (and near-parallel) to the [0001] direction display very low (and dissimilar) etch rates, dramatically different profiles are observed depending on the particular mask alignment of the trench edges with respect to the substrate. Nevertheless, the profiles can be easily predicted by identifying the location of a few key orientations for each trench profile. This is done by measuring the etch rate distribution on a hemispherical specimen of quartz and locating the local maxima of the (signed) curvature of the etch rate for all planes parallel to the trench edges. We show that this generalizes the traditional method based on locating the local minima of the etch rate. Furthermore, our approach enables capturing accurately the etch front by applying the traditional Wulff–Jaccodine construction on just a few key orientations, thus greatly simplifying the use of that method and highlighting the simplicity and importance of the proposed key orientations. A maximum positive curvature recognition method is developed based on applying the moving average filter to the calculation of the first, second, and third order derivatives of the etch rate. This allows quick locating of all orientations that will appear on the short-term and long-term profiles, even for the complete etch rate distribution, thus helping the design of desired profiles with vertical (or nearly vertical) side walls. Furthermore, the proposed maximum positive curvature recognition method accurately explains the formation of complex facets on square cavities, as well as on the top, middle, and bottom regions of micro-needle arrays etched on quartz Z-cuts. [2017-0025] [ABSTRACT FROM AUTHOR]

Ray-tracing techniques are commonly used for calculating the paths taken by electromagnetic waves in a medium that has an associated refractive index, such as the earth's ionospheric plasma. Ray equations derived from Hamilton's equation are usually used to determine ray paths and ray tubes defined by tracing adjacent rays separately. There are advantages in describing ray tubes in terms of a main ray and variational rays. In this paper, equations for variational rays are derived for anisotropic inhomogeneous media such as the earth's ionosphere. The ray-tracing technique is ideal for simulating ionospheric propagation experiments, and examples are given of ground illumination as a function of ground range and frequency. [ABSTRACT FROM PUBLISHER]

In this paper, the negative-bias temperature instability (NBTI) in p-type gate-all-around silicon nanowire MOSFETs (SNWTs) is investigated for circuit aging analysis. Several important features of NBTI in SNWTs are discussed, including the impacts of 2-D hydrogen diffusion, the nonuniform temperature profile caused by self-heating effects, the multiple crystallographic orientations of nanowire channel surface, the gate-trimming process-induced additional trapping effects, and the impacts of oxide hole trapping. A predictive NBTI model for SNWTs is proposed and adopted in circuit simulation to evaluate the performance degradations of typical logic and analog circuits, such as inverter, static random access memory cell, ring oscillator, and current mirror. Without considering other indirect factors, the results indicate that the performance degradation directly due to NBTI alone is relatively small, i.e., within the range of less than 8% degradation for the typical circuits simulated. However, the NBTI behavior in SNWTs is sensitive to process variations, which cause enhanced variability problem by inducing time-dependent threshold voltage fluctuations. [ABSTRACT FROM AUTHOR]

Three 3D isotropic dispersion-finite-difference timedomain (ID-FDTD) algorithms are formulated based on two new spatial difference equations. The difference equations approximate the spatial derivatives in Maxwell's equation using more spatial sampling points distributed in an isotropic manner. The final spatial difference equation is a weighted summation of the two new difference and the conventional central difference equations. Therefore, based on the proposed spatial difference equation and choices of the weighting factors, seven different FDTD schemes can be formulated, which include the Yee scheme. Among the seven schemes, three methods can show isotropy of the dispersion superior to that of the Yee scheme. The weighting factors for the three schemes are numerically determined to minimize the anisotropy of the dispersion by using an optimization technique. In this paper, the dispersion& stability characteristics and the numerical complexity of the three ID-FDTD schemes are addressed. Also, the upper bound of the Courant number of the three ID-FDTD schemes is heuristically proposed and numerically verified. One scattering problem is considered to show the improved accuracy of the proposed ID-FDTD scheme. [ABSTRACT FROM AUTHOR]

This paper presents the full characterization of the reversible magneto-mechanical behavior of iron-silicon single crystals. Magnetostriction and magnetization measurements under tensile mechanical loading have been performed on specimen collected along the (100), (110) and (111) crystallographic axes. A theoretical interpretation of the results is attempted. [ABSTRACT FROM AUTHOR]

We demonstrate a new class of low-profile frequency selective surfaces (FSS) with an overall thickness of λ/24 and a third-order bandpass frequency response. The proposed FSS is a three layer structure composed of three metal layers, separated by two electrically thin dielectric substrates. Each layer is a two-dimensional periodic structure with sub-wavelength unit cell dimensions and periodicity. The unit cell of the proposed FSS is composed of a combination of resonant and non-resonant elements. It is shown that this arrangement acts as a spatial bandpass filter with a third-order bandpass response. However, unlike traditional third-order bandpass FSSs, which are usually obtained by cascading three identical first-order bandpass FSSs a quarter wavelength apart from one another and have thicknesses in the order of λ/2, the proposed structure has an extremely low profile and an overall thickness of about λ/24, making it an attractive choice for conformal FSS applications. As a result of the miniaturized unit cells and the extremely small overall thickness of the structure, the proposed FSS has a reduced sensitivity to the angle of incidence of the EM wave compared to traditional third-order frequency selective surfaces. The principles of operation along with guidelines for the design of the proposed FSS are presented in this paper. A prototype of the proposed third-order bandpass FSS is also fabricated and tested using a free space measurement system at C band. [ABSTRACT FROM AUTHOR]

Surface roughness of ice crystals is a morphological parameter important to the scattering characteristics of these particles. The intent of this paper, reported in two parts (hereafter, Parts I and II), is to investigate the accuracy associated with some simplifications in calculating the single-scattering properties of roughened ice crystals and to quantify the effect of surface roughness on the retrieval of the optical and microphysical properties of ice clouds from satellite observations. In Part I, two ray-tracing schemes, a rigorous algorithm and an approximate algorithm with a simplified treatment of surface roughness, are employed to calculate the single-scattering properties of randomly oriented hexagonal ice crystals with size parameters in the geometric optics regime. With the rigorous approach, it requires substantial computational effort to accurately account for the multiple external reflections between various roughness facets and the reentries of outgoing rays into the particles in the ray-tracing computation. With the simplified ray-tracing scheme, the ray-tracing calculation for roughened particles is similar to that for smooth particles except that, in the former case, the normal of the particle surface is statistically perturbed for each reflection-refraction event. The simplified ray-tracing scheme can account for most the effects of surface roughness on particle single-scattering properties without incurring substantial demand on computational resources and, thus, provides an efficient way to compute the single-scattering properties of roughened particles. The effect of ice-crystal surface roughness on the retrieval of the optical thicknesses and effective particle sizes of cirrus clouds is reported in Part II. [ABSTRACT FROM AUTHOR]

In switched-mode power supplies—the predominant type of power converter in contemporary electronic equipment—ferrite magnetic components under dc bias conditions are typically large and have relatively high losses. The nature of these losses is not widely understood, and research in this area has been hampered by the difficulty of obtaining accurate core loss measurements. This paper reviews previous studies on the nature of core losses under dc bias, and presents new results, measured by a technique that has not previously been utilized for the measurement of core losses under dc bias conditions. The results show that ferrite core losses increase significantly with an increasing dc bias, and highlight the need for further research over a wider range of conditions to fully characterize the phenomenon. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel mechanism for recording at a head field significantly below the medium coercivity in a perpendicular recording geometry. By applying a localized ac field at adequate frequency to the perpendicular recording medium, saturation recording can be achieved with recording field amplitudes significantly below the medium coercivity, or the medium perpendicular anisotropy field. A scheme utilizing spin torque to generate a localized ac field at high frequency (tens of gigahertz) with kilo-oersted field amplitude in the medium is proposed along with a systematic modeling analysis. Recording simulations at high linear densities are presented. [ABSTRACT FROM AUTHOR]

To implement a high-stability and high-frequency overtone temperature-compensated crystal oscillator (TCXO) conveniently, an improved design of the novel overtone TCXO is described in this paper. A 120-MHz TCXO based on mixing of dual crystal oscillators is implemented. It utilizes a 100-MHz AT-cut 5th-overtone crystal oscillator mixed with a 20-MHz AT-cut voltage-controlled crystal oscillator (VCXO). The 120-MHz mixed product is filtered to produce the output signal. The total frequency deviation of 20-MHz and 100-MHz crystal oscillators is compensated by adjusting the output frequency of the 20-MHz oscillator to produce the stable 120-MHz output frequency. In this work, verifying experimental results of the compensation are presented. The stability of the experimental 120-MHz overtone TCXO with microprocessor temperature compensation achieves ±2 × 10-7 over the temperature range from -30°C to +70°C. A phase noise level of -133 dBc/Hz at 1 kHz offset has been initially measured for the prototype TCXO. The experimental result demonstrates this approach can conveniently implement the high-frequency overtone temperature compensation with a relatively high stability, and it is available for a wider frequency range as well. [ABSTRACT FROM AUTHOR]

In this paper, optical propagation in a 3-D photonic crystal optical waveguide is simulated numerically using the finite-diffence time-domain (FDTD) method. Since the division number of the analysis domain increases to model the structure of the photonic crystal precisely, huge memory is required, and it takes much time to solve the problem. Furthermore, using the micron-order wavelength needs a much larger division number. Therefore, we apply to this problem parallel processing using a PC cluster not only to speed up but also to gather memories in each node. We simulated the optical waveguide made of the 3-D photonic crystal using a parallelized FDTD method, and our results show that parallel processing is an effective approach for reducing the calculation time and expanding the analysis domain. [ABSTRACT FROM AUTHOR]

This paper uses the solutions of the linearized Landau-Lifshitz equation to establish the limitations of coherent precession models. Contrary to traditional argument, such models are valid only in the limit of vanishing surface anisotropy. The paper examines the theoretical basis for this conclusion in the context of an idealized magnetic surface. It considers several practical examples in which the response of bilayer composites is explained in terms of a unidirectional surface anisotropy. [ABSTRACT FROM AUTHOR]

In this paper, the two-dimensional vector magnetic properties depending on the exciting frequency are made clear by using the finite element method (FEM) and the Enokizono, Soda, and Shimoji (E&SS) modeling as an anisotropic material modeling. In the investigations, a 3-phase 3-leg transformer model is analyzed under some exciting frequency conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel microcomputer temperature-compensating method for an overtone crystal oscillator (MCOXO) is presented. In this method, a ceramic oscillator is chosen, and its output frequency is mixed with the output frequency of an overtone crystal oscillator. A crystal filter is used to suppress the spurious mixing products. A microcomputer is used to control the switch capacitance array that is connected to the ceramic oscillator circuit. The frequency deviation of the crystal oscillator is directly compensated by the output frequency of the ceramic oscillator. As a result, the method is able to overcome the disadvantages of frequency stability degradation and phase noise deterioration that are provoked by adding inductance or frequency multiplication in traditional compensating approaches. At the same time, this method is able to compensate a quite wide frequency range and many types of oscillators, not just crystal oscillators. The experimental compensating results show that, using this method, the frequency-temperature stability of a 100 MHz 5th overtone temperature-compensated crystal oscillator can achieve ⩽ ±2 × 10-6 for 0-70°C. [ABSTRACT FROM AUTHOR]

In this paper, different densities within a ceramic are used to provide a wide continuous range of dielectric constants for high-frequency applications. Cofiring different ceramic materials together to make a single unified structure to obtain different dielectric constant combinations is quite difficult due to phase stability issues and shrinkage mismatches. However, using various levels of porosity in order to alter the effective dielectric constant in the same material allows patterning different dielectric constants into a single unit. Since the structure is made from a single material, the varying porosity regions can be made compatible. Glassy-carbon-assisted and microcellular-structure-based porous titania allow for an extremely wide range of dielectric constants, ranging from 12 to 90, while maintaining a low loss tangent. Highly anisotropic materials are demonstrated herein to achieve a dielectric constant contrast of 90/9.6 using large-range aligned microcellular structure. Dielectric-resonator antennas are shown as an application of adjusting the bandwidth between 0.5% and 2.5 % by tailoring the ceramic dielectric constant. A stratified-medium-loaded cavity resonator and a buried dielectric ring resonator internal to a microcellular substrate are used to demonstrate both the cofiring and variable dielectric constant capabilities of structured porosity. [ABSTRACT FROM AUTHOR]

In a previous paper, the three-dimensional equations of linear piezoelectricity with quasielectrostatic approximation were extended to include losses attributed to the mechanical damping in solid and the resistance in current conduction. These equations were used to investigate the plane wave propagation in an unbounded solid and forced thickness vibration of an infinite piezoelectric plate. In the present paper, these equations are used to obtain solutions of plane harmonic wave of arbitrary direction in an infinite and dissipative piezoelectric plate with general crystal symmetry. Dispersion curves are computed and plotted for real frequencies and complex wave numbers. All frequency branches are complex for dissipative plate. There are no longer any pure real or pure imaginary or complex conjugate frequency branches as those existing for nondissipative plates. Effects of dissipation on the wave propagation are examined in detail for AT-cut of quartz as well as barium titanate ceramic plate. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a novel temperature compensated crystal oscillator—analog memory compensated crystal oscillator (AMCXO), a microcomputer compensated crystal oscillator (MCXO) based on an analogue approach, and we compare the performance between MCXO and AMCXO, and analyze the necessity of developing AMCXO. Both AMCXO and MCXO, combined with their test systems, use computers to generate the control signals used for the compensated crystal oscillators according to temperature variation. However, the execution devices are much different from each other in the practical temperature compensated crystal oscillators. A MCXO uses a set of digital units, including a microprocessor, to realize the compensation. For it, equations or tables are used to express the relationship between the control signal and temperature. An AMCXO uses an analogue memory, which has the same functions as the digital units of MCXO. For AMCXO, a curve or figure based on the equations or tables is used to express the same relationship. Their test systems have obvious distinctions in temperature experiment, data acquisition, and processing. A better performance will be obtained by using a more complicated AMCXO test system, and the cost can be reduced at the same time. [ABSTRACT FROM AUTHOR]

In this paper, we present the design of measurements for single crystals by using the general results in Part I of this paper. The selection of impedance measurement or admittance measurement for both bar and plate type resonators is dependent on whether the cutting orientation 1 is parallel to or perpendicular to the electric field direction n. Two matrices A and B, which are defined in part I of this paper, are major tools used for the measurement design. For different cutting orientations, the elements in matrix A are associated with different elastic and piezoelectric constants. Matrix B reveals what vibration modes can be excited electrically and how to excite them. With the aid of matrices A and B, the design of measurement becomes straightforward. The measurement for a rhombohedral class (3m) LiNbO3 single crystal is used as an example to demonstrate the experiment and calculation procedures. It is found that by using either three thin bars and one plate or three plates and one thin bar we can completely characterize the complex materials constants of a LiNbO3 single crystal. [ABSTRACT FROM AUTHOR]

This paper reports on the recent breakthrough of achieving high orientation ratio (OR) on directly textured glass substrates. The authors show the necessary structural conditions to obtain OR on glass substrates. They present a unique design of a medium structure including a seedlayer, an underlayer, and an antiferromagnetically coupled magnetic structure. Such a structure gives rise to a high OR and leads to improved recording performance. In particular, the authors show the significant low-noise benefit of the oriented media with narrow recording heads. This technology has enabled the extension of glass disk media to ultrahigh density longitudinal recording. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) gas sensors with unique oxide semiconductor thin-film transistor (TFT) configuration using ZnO nanoparticles (NPs) as gas-sensing element were fabricated and their gas-sensing responses were evaluated. The ZnO NPs composing the sensing elements were synthesized using atomic layer deposition (ALD). The optimum ALD conditions for the particle-like island-growth of ZnO were established by systematically investigating the ALD temperature and cycle conditions from 140 °C to 160 °C and from 5 to 30, respectively. Controlled devices of the sensor TFTs were prepared with different ALD conditions, in which sensing and read-out elements were designed to be physically separated. This unique device configuration provided us both benefits of improvement in gas-sensing property and stability of the device characteristics. The device showed instant gas responses as well as stable device behaviors at different operating temperature even with repeated gas measurements. Sufficiently good response to NH3 were obtained at 150 °C, which was significantly lower than the operating temperature of previously reported NH3 gas sensors. Based on the results the combination of novel TFT configuration and ALD-prepared ZnO NPs could be an effective method for the improvement in device characteristics of the gas sensors. [ABSTRACT FROM PUBLISHER]

An ultrasonic microcutter is an alternative approach to conventional ultrasonic instruments actuated by sandwich piezoelectric transducers for surgery. This paper reports high-power behavior of a microcutter actuated by the piezocrystal lead magnesium niobate?lead titanate (PMN-PT), defining its practical performance and the feasibility of PMNPT actuation for surgical applications. The microcutter was driven at resonance with constant current amplitudes, either unloaded or loaded by poultry breast tissue, until its behavior achieved a steady state. During this driving process, its electric impedance, resonant frequency, and vibration velocity, along with the temperature increase of the PMN-PT, were recorded in real time. The microcutter produced a maximum vibration velocity >2.8 m/s with an excitation current of 0.11 Arms. The mechanical loss increased significantly with current amplitude, resulting in a maximum temperature increase approaching 50°C around the interface between the PMN-PT and the blade, where they were bonded together with epoxy. Because of the low phase-transition temperature of PMN-PT, this temperature rise prevented the microcutter from working at higher current amplitudes. Along with the high vibration velocity, it also caused a frequency shift downward by 3 kHz at the same current amplitude. During tests with poultry breast tissue, radiation reactance increased the resonant frequency and the radiation resistance increased the loss of the microcutter. However, the loss did not further increase the temperature of the piezoelectric material. The maximum force and the overall work required to penetrate the microcutter into poultry breast tissue were reduced by 47.1 ? 8% and 53.5 ? 6%, respectively, when the microcutter was actuated at a current of 0.07 Arms. [ABSTRACT FROM AUTHOR]

Giant magnetoelectric (ME) effects have been investigated recently in composites of magnetostrictive and piezoelectric materials. The usage of highly strictive piezoelectric and magnetostrictive materials as well as an increased understanding of their elastic coupling leads to magnetoelectric (ME) responses that are much higher than those published in the 1970s. Magnetic field sensors based on the ME effect promise sensitivities approaching those of low-temperature SQUID sensors. This paper concentrates on ME devices that were fabricated by sputtering magnetostrictive Fe-Co/Tb-Fe multilayers on piezoelectric PMN-PT single crystals. Intrinsic and induced magnetic anisotropies lead to a pronounced directional dependence of the ME effect. Thin magnetic films display anisotropies that are induced by the demagnetization field that can reduce the "out of plane" ME effects. "In-plane" ME effects can be enhanced by annealing and field-cooling leading to a pronounced easy and hard direction. In Fe-Co/Tb-Fe multilayers the magnetostriction along the easy axis vanishes and the ME effect is maximized along the hard axis. Therefore, a combination of three individual sensors realizes a magnetic vector field sensor. [ABSTRACT FROM AUTHOR]

This paper analyzes the write field profiles for perpendicular head designs that have been proposed for reaching 1 Tb/in². Designs considered include side shielded poles and high anisotropy poles. A vector Stoner-Wohifarth writing criteria is used to find the maximum medium anisotropy each head can write on, subject to the constraints that transition curvature and transition jitter do not exceed the bit cell length. Vector fields are also used to assess thermal switching on adjacent tracks. For optimal writing consistent with these assumptions, the number of grains under the read head is 5 for the shielded design (Hk = 1380 kA/m) with a 20 nm thick medium and a stability coefficient of 40, and is 3.6-4 (Hk = 930 kA/m) for the high anisotropy designs. The improved downtrack gradient of the shielded design accounts for much of this difference, and suggests that a downtrack shield may improve the high anisotropy design. In all cases, transition curvature suggests the read head width will be limited to around 30% of the track pitch, which is substantially less than current values. [ABSTRACT FROM AUTHOR]

The paper studies the difference between the reflection coefficients of a surface acoustic wave incident on a groove or strip along the inverse directions. This difference occurs because of the crystallographic anisotropy of the substrate and/or the asymmetry of the shape of the obstacle. The numerical computations are carried out by the finite element method. A perfectly matched layer is implemented to truncate the computational domain. Some general properties of the transmission and reflection coefficients of surface acoustic waves are also discussed. [ABSTRACT FROM PUBLISHER]

This paper reports on the formation mechanism, structure, crystallographic anisotropy, magnetic properties and postannealing of single-crystal and [001] textured poly-nanocrystalline Nd2Fe14B flakes with a micron, submicron or nanosize thickness prepared by a non-surfactant-assisted high energy ball milling (HEBM) technique. Nd15.5Fe78.5B6 ingot micro-powders were the precursor while ethanol was the only milling medium. Similar to the structural evolution process in the surfactant-assisted HEBM, single-crystal flakes with a micron then submicron thickness were first formed. With further milling, [001] textured poly-nanocrystalline flakes with a submicron then nanosize thickness were formed. The formation of anisotropic flakes was mainly related to the polar nature of ethanol which would form a thin coating layer on the flakes through carboxylate bonds to prevent cold welding and agglomeration during the HEBM. The Nd2Fe14B flakes prepared by the HEBM in ethanol for 5 h have a [001]-in-plane texture, a thickness in the range of 100–450 nm and a width in the range of 0.7–18 \mum, a coercivity iHc of 2.3 kOe, and a I006/I105 value of Nd2Fe14B phase of 5.3. Postannealing at 400–550^\circC for 0.5 h had little effect on the flake dimensions while resulting in a reduced [001] texture and reduced remanence values besides coarser grain sizes. With increasing annealing temperature, iHc first increased, reached its maximum value of 2.8 kOe at 450^\circC, then decreased. An anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. [ABSTRACT FROM PUBLISHER]