Characteristics of a thin film microtransformer with circularspiral coils

A thin-film 3.14-mm×3.88-mm microtransformer has been fabricated, using photolithography technology, to support high-frequency switching regulators. The microtransformer is composed of sputtered amorphous magnetic layers, electroplated copper windings with 20-μm width, and insulator layers. The coupling factor between the primary and secondary windings of the microtransformer is 0.97 for f=3 MHz. An input-output voltage ratio of 0.95 at 15 MHz is obtained at no-load. Observation of the domain images under high-frequency excitation indicates that the magnetic anisotropy of the microtransformer films is induced by rotating magnetic field annealing so as to increase the output voltage     

A new planar microtransformer for use in micro-switching converters

A planar microtransformer for use in microswitching converters of portable equipment is described. This microtransformer, consisting of planar coils and CoZrRe amorphous magnetic layers on a Si substrate, is fabricated by a dry process. It is about 0.3-mm thick, and 3×4 mm ². Its coils provide a relatively high inductance of 33 nH/mm ². This microtransformer is implemented in a forward converter, which operates well at 32 MHz     

Planar microtransformer with monolithically-integrated rectifierdiodes for micro-switching converters

A microtransformer that is monolithically integrated with rectifier diodes is developed as the first step towards developing a monolithic microswitching converter that can be integrated with semiconductor devices and magnetic components. This microtransformer consists of planar coils and CoZrRe amorphous magnetic layers on Si substrate. Two Schottky barrier diodes are formed on the Si substrate and directly connected to the secondary coil. This microtransformer chip is shown to perform both conversion and rectifying functions     

High-frequency operation of a planar-type microtransformer and itsapplication to multilayered switching regulators

The operation of a multilayered microtransformer composed of planar zig-zag coils and amorphous magnetic film is described. The transformer has a maximum efficiency of 77.5%. Its equivalent circuit is approximated by the parallel connection of the winding inductance and of the stray capacitance. Variable magnetic coupling is obtained between the primary and secondary windings by shifting the relative position of the two coils. The microtransformer is used in a magnetically controlled multilayered switching regulator. The regulator has an output of 1.4 W and an efficiency of 24%. The magnetization loss in the circuit is the same as that of the semiconductors. A two-output-type multilayered switching regulator is also proposed that has an acceptably good output characteristic at each port even though a common magnetic film is used     

Microfabricated Inductive Micropositioning Sensor for Measurement of a Linear Movement

An inductive device with a moving core will change its inductance as a function of the core position. By extending this principle to a microtransformer with multiple evenly spaced cores, a measurement system combining features of analog (variable reluctance) and incremental positioning may be devised. For detecting the direction of motion system (to know in which direction to count), an incremental length-measurement system not only requires one, but two output signals, which have to be offset by 90deg. This paper presents a microtransformer-based positioning system fulfilling these requirements. It presents the fabrication technology employed and discusses experimental test results     

Natural frequency spectrum of a flat superconducting cable

A matrix method is used to investigate the current damping process in a flat superconducting cable. A discrete spectrum of natural frequencies is obtained, each determining the rate of exponential damping of the corresponding induced current. Although the number of natural frequencies increases as the size of the cable increases, their spectrum remains finite because the maximum and minimum frequencies tend to finite limits. An analysis is made of the induced currents for the limiting frequencies. It is shown that in the range of minimum natural frequencies the induced currents are long-lived long current loops. At high frequencies the distribution of the induced currents in cable layers is sinusoidal. Pis’ma Zh. Tekh. Fiz. 25, 42–47 (July 12, 1999)     

Effect of frequency on fatigue crack growth behavior of magnesium alloy AZ61 under immersed 3.5 mass% NaCl environment

Fatigue crack growth test of AZ61 magnesium alloy was carried out under immersed NaCl environment at frequencies of 15, 5 and 0.5 Hz under a stress ratio of 0.1. In order to investigate the effect of frequency on fatigue crack growth behavior in detail, additional tests at frequencies ranged from 15 to 0.01 Hz were conducted under a constant ΔK of 3.25 MPa m^1/2. Effect of frequency was clearly observed in low ΔK region, where fatigue crack growth rate decreased with decreasing frequency. Crack closure would be a dominant factor for the frequency effect observed under immersed NaCl environment at frequencies ranged from 15 to 0.5 Hz. However, fatigue crack growth rates at frequencies lower than 0.05 Hz were higher than those at frequencies higher than 0.5 Hz. The accelerated fatigue crack growth rates at frequencies lower than 0.05 Hz would be attributed to the corrosion attack at the crack tip.     

Superplasticity by internal frictional heat under biased cyclic loading

A new damping method was developed not only as a testing tool to investigate in situ deformation under stress, but also as a processing method to superplastically deform ceramics. The specific damping capacity (SDC) at low frequencies (<0.2 Hz) decreased with increasing frequencies, which matched previous internal friction results. However, at higher frequencies (0.2–5 Hz) SDC increased with frequencies, which was explained by a new internal frictional heat mechanism. Three different ceramics: a non-superplastic one and two superplastic ones with different activation energies, showed the same behavior at the high frequency damping tests (1–5 Hz). From these results, it was deduced that a cyclic load at high frequencies, superimposed on a static one, has a great potential to enhance superplasticity by specifically heating up grain boundaries from internal frictional heat.     

Frequency multiplier with a feedback

Conclusions A multiplier with a feedback has the unique combination of the following properties: a wide range of multiplied frequencies (10:1 and wider); a large and easily variable scaling factor; it is independent of the input signal voltage shape or amplitude; it can operate with a variable input frequency; it is insensitive to stray frequency modulation of the input signal at frequencies above the effective modulating range; a possibility of direct multiplication of the difference of two frequencies, or even a linear combination of several frequencies; and a possibility of correcting the nonlinearity of transducers, if this nonlinearity is not too large.Thus, it meets virtually all the requirements which can be specified for a frequency multiplier intended for working in a frequency-digital measuring system.     

On the modal behavior of a three-dimensional functionally graded cantilever beam: Poisson’s ratio and material sampling effects

Modal behavior of a three-dimensional (3D) homogeneous and functionally graded (FG) cantilever beam is studied using the Rayleigh–Ritz (RR) method and the finite element method (FEM). The effect of Poisson’s ratio and material sampling point on the natural frequencies is further addressed using the FEM. The natural frequencies (first three) obtained using the RR method converge as the number of admissible shape functions increase. The natural frequencies (first 15) obtained using the FEM vary considerably with the material gradation, more so for the lower modes than for the higher modes. Poisson’s ratio significantly changes the torsional natural frequencies of the homogeneous and graded beams. Considerable change in the natural frequencies is seen for the linear graded beams whose material properties are sampled at the element centroid rather than at Gaussian integration points. This difference is easily observed for beams modeled using a coarse mesh rather than a fine mesh. The natural frequencies of the y   direction hyperbolic tangent beam with material nonhomogeneity parameter β=100$\beta =100$ matches well with those of the y direction bi-material beam. The natural frequencies of the power-law graded 3D cantilever beam obtained using the FEM matches closely with the 2D reference (Qian and Ching, 2004 [1]) solution obtained using the meshless local Petrov–Galerkin method.     

High temperature fatigue crack growth in Inconel 718

Abstract

The nickel base superalloys are extensively used in high temperature applications, so it is important to know their behaviour under conditions of high-temperature fatigue. This paper studies the influence of ΔK, loading frequency, stress ratio and temperature on the high temperature fatigue crack growth rate of nickel base superalloys. This study is based on fatigue tests carried out in corner crack specimens of Inconel 718 at 600°C and at room temperature. Three stress ratios (R = 0.05, 0.5 and 0.8) and loading frequencies ranging from 0.0017 to 15 Hz were considered in the tests. For frequencies below 0.25 Hz, the load wave shape was trapezoidal with different dwell times at maximum load. At relatively high frequencies the propagation is cycle dependent, while for lower frequencies it is time dependent. At intermediate frequencies a mixed crack growth occurs. The transition frequencies from cycle dependent to mixed regime and from mixed to time dependent regime were obtained for each R. The increase of R increases the transition frequencies, i.e., extends the time dependent crack growth to higher frequencies. The increase of R also produces an increase of cyclic crack growth rate for all regimes of crack growth. In the time dependent regime, a higher variation is observed, that can be explained by an acceleration of oxidation damage promoted by the increase of maximum stress. An approach for modelling the high-temperature fatigue crack growth in nickel base superalloys is presented. A good agreement was observed between time dependent fatigue results and mathematical models based on static load results.     

Theoretical andFTi.r. spectroscopic studies of platinum carbonyl clusters encapsulated in the zeolite cage

A suitable theoretical model makes possible to calculate the atomic, bond, and mean polarizabilities of the platinum carbonyl clusters encapsulated in zeolites. It has been found that the CO stretching frequencies depend on the charge on platinum and there exists a correlation between the CO vibrational frequencies and the mean polarizabilities of platinum carbonyl clusters. The CO stretching frequencies shifts toward higher frequencies with increasing polarizabilities of the clusters. Using the results of the mean polarizability calculation, from the infrared spectra of the CO molecules interacting with the Pt²⁺ ions exchanged into NaY zeolites, formation of the Chini cluster involving 12 Pt atoms can be established.     

Viscous oscillations in a circular cylinder with an elastic cover on the free surface

The effects of an elastic membrane on the viscous oscillations of liquid filling a circular cylindrical container are studied by using the natural viscous complex eigenfunctions of the problem. The free surface of the liquid is assumed to be fully covered by the membrane. By projecting the governing equations onto an appropriate basis, a nonlinear eigenvalue problem for the complex frequencies is obtained. This is then solved to obtain the modal frequencies as a function of the Reynolds number Re, the tension parameter τ, the mass parameter ζ and the liquid depth h. The zero velocity conditions on both the side and bottom walls are satisfied unlike in earlier studies where either only the sidewall or only the bottom wall conditions were met. Results are presented for the four lowest non-axisymmetric modes as a function of Re, h, τ and ζ. The elastic cover increases the slosh frequencies but only in comparison with an uncovered free surface with a contact line that is free to move; the frequencies are lower when compared with those of a free surface with pinned contact line. There are ranges of Re, h, τ and ζ for which the oscillations are overdamped and the sloshing is aperiodic. Though the frequencies and damping rates decrease for an increasing mass of the elastic cover, there exist ranges of Re, h and τ for which the heavier cover produces higher slosh frequencies.     

Free vibrations of spherical belts with circular and longitudinal ribs

We propose a procedure for the numerical evaluation of the frequencies of free vibrations of spherical belts with circular and longitudinal ribs, determine those frequencies, and study the influence of the parameters of the ribs on the natural frequencies of free vibrations of shell structures reinforced by ribs. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 124–127, May–June, 1998.     

High temperature fatigue crack growth in a cobalt base superalloy

The rates of fatigue crack propagation of a cobalt base superalloy (HS 188) were measured at 75, 1112, 1400 and 1600°F as a function of the range of the stress intensity factor ΔK. Test frequencies were 0.01, 0.1, 1 and 10 Hz. At each elevated temperature there is a critical frequency below which the crack growth rate is oxidation and creep dependent, increasing with decreasing frequency. The mode of fracture changes from transgranular at high frequencies to intergranular at low frequencies.     

Some problems in providing the unit of measurement of signal power ratios in the microwave band

The main problems in drawing up standard documentation and developing promising methods of checking the working standards of attenuation at high frequencies and microwave frequencies by analyzing the functioning of systems for providing the unit of measurement in the area of attenuation at high frequencies and microwave frequencies and the technical characteristics of the working standards are formulated. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 45–48, October, 1999.     

Optical eigenmodes of a cylindrical microcavity

Abstract

The optical mode structure of a cylindrical microcavity has been investigated using a transfer matrix approach. We derive exact algebraic equations from which the frequencies of the optical eigenmodes of the two polarizations can be obtained, as well as approximate explicit algebraic expressions for those frequencies.     

Methodological quality in clinical trials and bibliometric indicators: no evidence of correlations

Citation frequencies and journal impact factors (JIFs) are being used more and more to assess the quality of research and allocate research resources. If these bibliometric indicators are not an adequate predictor of research quality, there could be severe negative consequences for research. To analyse to which extent citation frequencies and journal impact factors correlate with the methodological quality of clinical research articles included in an SBU systematic review of antibiotic prophylaxis in surgery. All 212 eligible original articles were extracted from the SBU systematic review “Antibiotic Prophylaxis in Surgery” and categorized according to their methodological rigourness as high, moderate or low quality articles. Median of citation frequencies and JIFs were compared between the methodological quality groups using Kruskal–Wallis non-parametric test. An in-depth study of low-quality studies with higher citation frequencies/JIFs was also conducted. No significant differences were found in median citation frequencies (p = 0.453) or JIFs (p = 0.185) between the three quality groups. Studies that had high citation frequencies/JIFs but were assessed as low-quality lacked control groups, had high dropout rates or low internal validity. This study of antibiotic prophylaxis in surgery does not support the hypothesis that bibliometric indicators are a valid instrument for assessing methodological quality in clinical trials. This is a worrying observation, since bibliometric indicators have a major influence on research funding. However, further studies in other areas are needed.     

Free vibration analysis of adhesively bonded single lap joints with wide and narrow functionally graded plates

This study investigates the three-dimensional free vibration behaviour of an adhesively bonded functionally graded single lap joint. The functionally graded plates of the adhesive joint are composed of ceramic (Al₂O₃) and metal (Ni) phases varying through the plate thickness. The effects of geometrical parameters, such as plate width, plate thickness and overlap length, especially the effect of the similar and dissimilar material composition variations through-the-thicknesses of both upper and lower plates on the natural frequencies and corresponding mode shapes of the adhesive joint were also investigated using both the finite element method and the back-propagation artificial neural network (ANN) method. A series of the free vibration analyses were carried out for various random values of the geometrical parameters and the through-the-thickness material composition so that a suitable ANN model could be trained successfully. The proposed ANN models indicated that increasing plate thickness and compositional gradient exponent resulted in increases in the first 10 frequencies whereas the overlap length has negligible effect. In contrast, the natural frequencies decrease suddenly with increasing the plate width. For the plate width >50 mm, the natural frequencies become very low and the effect of the other design parameters on the natural frequencies becomes minor. In case the upper and lower plates have similar or dissimilar material composition variations the mode shapes were affected considerably, but the natural frequencies.     

Structural dynamics of real and modelled Solanum stamens: implications for pollen ejection by buzzing bees

An estimated 10% of flowering plant species conceal their pollen within tube-like anthers that dehisce through small apical pores (poricidal anthers). Bees extract pollen from poricidal anthers through a complex motor routine called floral buzzing, whereby the bee applies vibratory forces to the flower stamen by rapidly contracting its flight muscles. The resulting deformation depends on the stamen''s natural frequencies and vibration mode shapes, yet for most poricidal species, these properties have not been sufficiently characterized. We performed experimental modal analysis on Solanum elaeagnifolium stamens to quantify their natural frequencies and vibration modes. Based on morphometric and dynamic measurements, we developed a finite-element model of the stamen to identify how variable material properties, geometry and bee weight could affect its dynamics. In general, stamen natural frequencies fell outside the reported floral buzzing range, and variations in stamen geometry and material properties were unlikely to bring natural frequencies within this range. However, inclusion of bee mass reduced natural frequencies to within the floral buzzing frequency range and gave rise to an axial-bending vibration mode. We hypothesize that floral buzzing bees exploit the large vibration amplification factor of this mode to increase anther deformation, which may facilitate pollen ejection.