Measurement of radio channels using an elastic convolver and spreadspectrum modulation. II. Results

A spread spectrum measurement system using a surface acoustic wave convolver has been used to measure radio wave propagation in steel works at 1.75 GHz with an echo delay resolution of ≈20 ns. Due to the high metal content of the factory halls, path loss is found to be small and its exponent to range between 1.1 and 2.3 only. We observed a delay spread between 82 and 548 ns depending on the size of the steel mill, its construction and machinery. Characterizing the radio channel by a stochastic delay line model the echo amplitude probability distribution is found to fit a Rician or log-normal distribution rather than a Rayleigh distribution. The fit of the amplitude distributions is determined by a χ² hypothesis test. From the channel impulse response the coherence bandwidth is deduced to range between 2.4 and 27.4 MHz     

Measurement of Young's modulus in an elastic material using 3D digital holographic interferometry

Digital holographic interferometry using three different illumination directions is applied to quantify in full field of view the deformation of an elastic membrane under a given vibration frequency. The technique allows the separation of the object microdisplacements components in the x, y, and z directions, and the resulting data is used to find the membrane Young's modulus. The latter was compared with the result obtained using the theory of thin plates for a clamped circular membrane under a uniformly distributed load, reaching a 95% agreement. Validation of the results between these methods shows the reliability of DHI to measure the mechanical properties of an elastic material.     

Frequency domain simulator for mobile radio channels and for IEEE 802.16-2004 standard using measured channels

Two radio channel simulators based on the time variant frequency transfer function have been implemented using digital signal processing techniques in SIMULINK. The first simulator uses a two ray channel model to determine the number of taps per coherent bandwidth of the channel by comparing the bit error rate (BER) with the tapped delay line model for differential quadrature phase shift keying. The results show that ten taps per coherent bandwidth are appropriate for a very close approximation of the channel. The second simulator utilises real channel measurements to estimate the BER for the IEEE 802.16 -2004 wireless metropolitan area network orthogonal frequency division-multiplexing standard with 256 carriers. Channel measurements at three frequencies in the 2-6-GHz frequency band in rural/semi rural environment demonstrate the simulator and relate the BER performance of the standard to the frequency selectivity of the channel.     

Measurement of radio-frequency temporal phase modulation using spectral interferometry

We present an optical method to measure radio-frequency electro-optic phase modulation profiles by employing spectrum-to-time mapping realized by highly chirped optical pulses. We directly characterize temporal phase modulation profiles of up to 12.5 GHz bandwidth, with temporal resolution comparable to high-end electronic oscilloscopes. The presented optical set-up is a valuable tool for direct characterization of complex temporal electro-optic phase modulation profiles, which is indispensable for practical realization of deterministic spectral-temporal reshaping of quantum light pulses     

Resonance scattering of elastic waves by an elastic inclusion in an elastic matrix. Numerical calculations

The scattering of an incident plane ultrasonic (longitudinal) wave by an elastic spherical inhomogeneity contained within an elastic matrix is studied. The emphasis is on the computation and analysis of basic multiple cases that result when different material behaviours are present in the matrix and in the inclusion. These calculations are useful in underwater acoustic applications. The behaviors are dominated by the soft or rigid backgrounds of the resonance scattering theory (RST). The first three multiple coefficients appearing in the expansions for the total elastodynamic fields developed around the inhomogeneity during the scattering process have been calculated in suitable frequency bands in all the cases considered. The examination of modulus, the real parts, and the imaginary parts of these (complex) coefficients under the RST approach allows the quantitative assessment of the conditions under which monopole or dipole resonances will occur and their relative magnitudes. The decomposition of the multiple coefficients into their resonance and background portions shows that it is the upward frequency shift of the background curves that controls the dominance of either radial (monopole) or translation (dipole) oscillations of the inclusion. This has an effect on the dispersion curves of the composite, which develop optical as well as acoustical branches. The real and imaginary parts of the multiple coefficients are respectively proportional to the attenuation and the effective wave speed in this simple inhomogeneous composite.     

Axisymmetric problems for an externally cracked elastic solid. I. Effect of a penny-shaped crack

The present paper examines the problem of a penny-shaped flaw which is located in the plane of an external crack in an isotropic elastic solid. The penny-shaped flaw is subjected to uniform internal pressure. The paper develops power series representations for the stress intensity factors at the boundary of the penny-shaped flaw and at the perimeter of the externally cracked region. These series representations are in terms of a non-dimensional parameter which is the ratio of the radius of the penny-shaped flaw to the radius of the externally cracked region.     

Measurement uncertainty and temporal resolution of Doppler global velocimetry using laser frequency modulation

A Doppler global velocimetry (DGV) measurement technique with a sinusoidal laser frequency modulation is presented for measuring velocity fields in fluid flows. A cesium absorption cell is used for the conversion of the Doppler shift frequency into a change in light intensity, which can be measured by a fiber coupled avalanche photo diode array. Because of a harmonic analysis of the detector element signals, no errors due to detector offset drifts occur and no reference detector array is necessary for measuring the scattered light power. Hence, large errors such as image misalignment errors and beam split errors are eliminated. Furthermore, the measurement system is also capable of achieving high measurement rates up to the modulation frequency (100 kHz) and thus opens new perspectives to multiple point investigations of instationary flows, e.g., for turbulence analysis. A fundamental measurement uncertainty analysis based on the theory of Cramér and Rao is given and validated by experimental results. The current relation between time resolution and measurement uncertainty, as well as further optimization strategies, are discussed.     

Measurement of elastic constants using vibrating wire strain gauges on disc and ring specimens

Useful methods of determining elastic constants employing diametrically–loaded disc and ring specimens have been proposed and applied by Durelli and Ferrer. Young's modulus may be measured from tests on a suitably dimensioned ring specimen. Subsequently Poisson's ratio may be found using a disc. The application of the methods described by the authors does not suit the case where the specimens are small and of stiff materials such as metals. In such a case sensitive means are required for measuring change in diameter with light loading. The paper indicates how this can be carried out for an aluminium alloy. The theory relating to the use of the disc for determining Poisson's ratio has been generalised to allow for measurement of change in length over part or all of a diameter. Poisson's ratio of the aluminium alloy was determined with a disc specimen 0.874 in (22.2 mm) diameter, vibrating wire strain gauges on either side of the specimen indicating change in diameter with loading. A ring was subsequently machined from the disc and similarly tested to confirm Young's modulus.     

Harmonic generation at an unbonded interface—I. Planar interface between semi-infinite elastic media

An analysis is made of the nonlinear dynamics of a system composed of an unbonded planar interface separating two semi-infinite linear elastic media. The unbonded interface, by definition, cannot support tension and hence opens up in the tension phase of a propagating disturbance, if it is not already open. The opening and closing of the interface is the origin of the nonlinearity. This is perhaps the simplest nonlinear problem involving continuous media, since the problem reduces to the consideration of a pair of independent first order ordinary differential equations involving the center of gravity and width of the gap. In the case of an incident sinusoidal wave the second harmonic generation efficiency is determined as a function of the ratio of the ambient hydrostatic pressure to the stress amplitude of the incident wave.     

A partially debonded ellipsoidal inclusion in an elastic medium. Part I: Stress and displacement fields

The paper calculates the elastic field of an ellipsoidal inclusion which has undergone an internal deformation and has debonded over a part of its boundary from the surrounding medium. The problem is reduced to the solution of a (singular) integral equation for the displacement discontinuity across the debond. The essential steps of a method of solving this equation are outlined. The elastic field is used in the companion paper (Part II) to calculate the stress intensity factors along the edge of debond.     

Measurement of the trapping efficiency of an elliptical optical trap with rigid and elastic objects

Optical tweezers and their various modifications offer a sophisticated way to perform noncontact cell manipulation. In this paper, we quantify forces existing in an elliptical trap formed by two cylindrical lenses and compare the results with a point optical trap case. The trapping efficiency of point and elliptical traps was analyzed by measuring the Q values of both traps. Polystyrene microspheres and red blood cells (RBCs) were used as samples. Stretching of the RBC was taken into account in the Q value measurements. Although the Q value of a point optical trap is larger than that of an elliptical trap when measured for a single RBC, we can manipulate the orientation of an RBC in a point trap with the elliptical trap and can also trap several RBCs simultaneously in the elliptical trap far from the cuvette surfaces by using a long-working-distance water immersion objective. This opens new possibilities for studying light-matter interactions at the cellular level.     

Debond dynamics of an elastic strip,I: Timoshenko-beam properties and steady motion

The paper considers debond of a Timoshenko-beam from a substrate which is rigid during the event. Essential relations expressing support conditions, continuity conditions, conservation of momentum and energy balance are discussed. Details relating to steady motion are exemplified.

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Résumé Le mémoire considère le cas du décollement d'une poutre de Timoshenko d'un substrat considéré comme rigide au cours de ce décollement. Les relations essentielles exprimant les conditions de support, les conditions de continuité, la conservation des moments et l'équilibre énergétique sont discutées. Des détails concernant le mouvement lent sont illustrés à titre d'exemple.

     

Implementation of an ANCF beam finite element for dynamic response optimization of elastic manipulators

Theoretical and practical aspects of an absolute nodal coordinate formulation (ANCF) beam finite element implementation are considered in the context of dynamic transient response optimization of elastic manipulators. The proposed implementation is based on the introduction of new nodal degrees of freedom, which is achieved by an adequate nonlinear mapping between the original and new degrees of freedom. This approach preserves the mechanical properties of the ANCF beam, but converts it into a conventional finite element so that its nodal degrees of freedom are initially always equal to zero and never depend explicitly on the design variables. Consequently, the sensitivity analysis formulas can be derived in the usual manner, except that the introduced nonlinear mapping has to be taken into account. Moreover, the adjusted element can also be incorporated into general finite element analysis and optimization software in the conventional way. The introduced design variables are related to the cross-section of the beam, to the shape of the (possibly) skeletal structure of the manipulator and to the drive functions. The layered cross-section approach and the design element technique are utilized to parameterize the shape of individual elements and the whole structure. A family of implicit time integration methods is adopted for the response and sensitivity analysis. Based on this assumption, the corresponding sensitivity formulas are derived. Two numerical examples illustrate the performance of the proposed element implementation.     

On the overall elastic moduli of polymer-clay nanocomposite materials using a self-consistent approach. Part I: Theory

Although few investigations recently proposed to describe the overall elastic response of polymer-clay nanocomposite materials using micromechanical-based models, the applicability of such models for nanocomposites is far from being fully established. The main point of criticism to mention is the shelving of crucial physical phenomena, such as interactions and length scale effects, generally associated by material scientists, in addition to the nanofiller aspect ratio, to the remarkable mechanical property enhancement of polymer-clay nanocomposites. In this Part I of two-part paper, we present a micromechanical approach for the prediction of the overall moduli of polymer-clay nanocomposites using a self-consistent scheme based on the double-inclusion model. This approach is used to account for the inter-inclusion and inclusion-matrix interactions. Although neglected in the models presented in the literature, the active interaction between the nanofillers should play a key role in the reinforcing effect of nano-objects dispersed in a polymer matrix. The present micromechanical model incorporates the nanostructure of clay stacks, modeled as transversely isotropic spheroids, and the so-called constrained region, modeled as an interphase around reinforcements. This latter is linked to the interfacial interaction between matrix and reinforcements that forms a region where the polymer chain mobility is reduced. To account for length scale effects, interphase thickness and particle dimensions are taken as explicit model parameters. Instead of solving iteratively the basic homogenization equation of the self-consistent scheme, our formulation yields to a pair of equations that can be solved simultaneously for the overall elastic moduli of composite materials. When the interphase is disregarded for spheroids with zero aspect ratio, our formulation coincides with the Walpole solution (J Mech Phys Solids 1969;17:235-251). Using the proposed general form, a parametric study is presented to analyze the respective influence of aspect ratio, number of silicate layers, interlayer spacing and nanoscopic size of the transversely isotropic spheroids on the overall elastic moduli of nanocomposite materials.     

Measurement of low-frequency ultrasonic wave in water using an acoustic fiber sensor.

An acoustic fiber sensor for measurement of ultrasonic waves, which used the approximate Raman-Nath diffraction effect where light diffraction waves were generated in an optical fiber by strain due to the ultrasonic waves, was proposed and examined. In order to characterize the acoustic fiber sensor as a basic study, measurements of low-frequency ultrasonic waves in water were examined using a step index fiber operating as a detection sensor. The results showed that characteristics of detected signals agreed with the theoretical prediction based on Fraunhofer diffraction. This indicates that our proposed fiber sensor can be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.     

Measurement of the thermal parameters of semiconductor products using pulse-amplitude modulation of the heating power

Estimates of the systematic error in measuring a temperature-sensitive parameter of a semiconductor article are obtained. These errors are due to transient electrical and thermal processes which occur when the article is switched from the heating mode to the measurement mode. It is shown that the use of pulse-amplitude modulation of the heating power enables these errors to be reduced considerably.     

Measurement of steep aspheric surfaces using an anamorphic probe

Synthetic aperture interferometry has been previously proposed as a possible in-process method to measure aspheric form (R. Tomlinson, Appl. Opt.42, 701, 2003.). Preliminary demonstration utilized a scanning probe consisting of a pair of bare single mode fibers to perform source and receive functions. It was found that this probe did not have sufficient numerical aperture (NA) to measure steep surfaces and that simply increasing the NA decreases the light gathering efficiency substantially. In this paper, we introduce supplementary optics to increase the NA, and the light gathering efficiency has been increased by adopting an anamorphic design. A spherical test optic of known form is measured to demonstrate the capability of the new probe design.