Properties of elastic waves in quasiregular structures with planar defects

We have studied the elastic waves in quasiregular structures following the Fibonacci and Rudin–Shapiro sequences, and having planar defects, that is breaks of the quasiregular structure in different parts of the system. It is seen that the different kinds of defects produce effects on different ranges of the frequency spectrum, and can introduce more localized states in the gaps, or modify the frequencies of the states in the gaps. We have also studied the phase time and transmission coefficients, thus seeing how these localized modes can be used as frequency filters.     

Electromechanical impedance measurement from large structures using a dual piezoelectric transducer

This study develops a new electromechanical (EM) impedance measurement technique specifically for continuous monitoring of large structures. Conventionally, a single surface-mounted lead zirconate titanate (PZT) transducer is often used to measure the EM impedance of a coupled PZT-structure system for damage diagnosis. However, when the target structure is massive, the impedance measurement becomes challenging. In this study, a dual piezoelectric transducer, composed of two separate but concentric PZT segments, is used for effective measurement of the EM impedance from large-scale structures. The impedance measurement using the dual PZT is theoretically formulated and numerically verified. Then, a series of experiments are carried out on a laboratory-size specimen and full-scale bridge and building structures. The experimental results reveal that the proposed technique successfully measures the EM impedance signals from massive structures with a high signal-to-noise ratio (SNR) and good repeatability even when the conventional techniques fail to do so. At the same time, the proposed technique allows low-cost and fast measurement of impedance signals.     

Thermal fields in laser–multi-layer structures interaction

In the present paper, we are dealing with the thermal fields for laser–periodic multilayer structures interaction. Our point of view is originally that we consider any order transverse laser beams, like heating sources. We consider that the laser beam acts in IR (Nd:YAG or CO₂ laser beam) and it is in one transverse mode or in only a few decoupled modes. In order to solve this problem, we will use the Green function method. Specific results are presented for a laser beam (Nd:YAG laser) operating in the mode TEM₀₁ and a two-layer structure.     

Nonlinearity of magnetoacoustic excitations in planar structures

This paper reports on the results of experimental investigations into the threshold power of the onset of nonlinearity of magnetoacoustic vibrations in planar structures (such as a ferrite film-dielectric substrate structure) in the range of phase matching of the higher bulk magnetostatic and acoustic modes. Under the experimental conditions, the wavelength of the higher bulk magnetostatic modes is of the order of 1 μm and shorter. On this basis, the energy of these vibrations with respect to the origin of the magnetostatic wave spectrum is determined by the energy of the inhomogeneous exchange interaction. The standing magnetoacoustic waves are examined in conventional yttrium iron garnet films with free surface spins in which, under standard conditions, only dipole magnetostatic vibrations are excited in planar resonators. Consideration is given to the threshold power of the onset of precession instability of the dipole exchange acoustic modes which, as was shown earlier by the authors, are excited in the range of the phase matching of the exchange and acoustic modes. A comparative analysis is performed for the threshold powers of dipole magnetostatic, exchange acoustic, and dipole exchange acoustic modes. It is demonstrated that the threshold power of the instability of magnetostatic modes decreases significantly when the natural frequencies of the dipole modes coincide with those of the exchange acoustic modes. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 7, 2002, pp. 1285–1289. Original Russian Text Copyright ? 2002 by Bugaev, Gorsky.     

Functionally graded materials for impedance matching in elastic media

When functionally graded material layers are inserted between two impedance mismatching media, passbands with extremely large bandwidths can appear in these layered systems. An accurate and effective iterative method is developed to deal with these layered systems with extremely large layer number.     

Modeling three-dimensional elastic wave propagation in circular cylindrical structures using a finite-difference approach

Wave propagation along circular cylindrical structures is important for nondestructive-testing applications and shocks in tubes. To simulate elastic wave propagation phenomena in such structures the governing equations in cylindrical coordinates are solved numerically. To reduce the required amount of computer memory and the computational time, the stress components are eliminated in the equilibrium equations. In the resulting coupled partial differential equations, in which only the three displacement components are involved, the derivatives with respect to spatial coordinates and time are approximated using second order central differences. This leads to the present new approach, which is both accurate and efficient. In order to obtain a stable scheme the displacements must be allocated on a staggered grid. The von Neumann stability analysis is performed and the result is compared with an existing empirical criterion. Mechanical energies are observed in order to validate the finite-difference code. Since no material damping or energy dissipation is taken into account in the equations of motion, the total energy must remain constant over time. Only negligible variations are observed during long-term simulations. Dispersion relations are used to check the physical behavior of the waves calculated with the proposed finite-difference method: Theoretically calculated curves are compared with values obtained by a spectrum estimation method, applied to the results of a simulation.     

Surface polaritons and transmission in multi-layer structures containing anisotropic left-handed materials

We study the surface polaritons and optical transmission in multi-layer structures containing alternate anisotropic left-handed materials and isotropic right-handed materials. By means of the transfer matrix method, the dispersive relations of the surface polaritons are derived. In contrast to the single left-handed slab, the multi-layer structure is capable of supporting more surface polaritons due to the existence of more interfaces between the left-handed and right-handed layers. We further make detailed investigations of the optical transmission associated with the surface polaritons. Numerical results show that the variance of the thickness of each layer will obviously affect the positions of the transmission peaks, corresponding to the surface polariton branches. Moreover, the presence of the absorption in the anisotropic left-handed materials plays a crucial role in the optical transmission spectra. PACS 41.20.Jb; 73.20.Mf; 78.20.Bh; 42.70.Qs     

Magnetoelectric effect in amorphous FeNiSiC ferromagnet-piezoelectric planar structures

The magnetoelectric (ME) effect is studied in composite two- and three-layer disk structures containing magnetostriction layers of an amorphous FeNiSiC ferromagnet and a lead zirconate titanate piezoelectric layer. Due to a high magnetostriction (∼33 × 10⁻⁶) and a low saturation field (∼200 Oe), an FeNiSiC layer has a high piezomagentic coefficient, which results in an effective ME coupling in low fields (∼25 Oe). The ME effect is ∼0.2 V cm⁻¹ Oe⁻¹ at a low frequency and increases to 11.9 and 13.2 V cm⁻¹ Oe⁻¹ when bending and in-plane mechanical vibrations are excited in a resonance manner in the structures at frequencies of ∼8.2 and ∼170.0 kHz, respectively. Structures containing amorphous FeNiSiC layers are promising for magnetic field transducers and electric energy generators and converters.     

Field emission rate in planar powder electroluminescent structures

The intensity of electroluminescence from an electroluminescent phosphor (electrophosphor) excited by unipolar voltage pulses with a linear front is studied. Based on experimental data, an expression for the free carrier emission rate in a planar electroluminescent capacitor with the polarization mechanism of luminescence is derived.     

Diagnostics of elastic properties of a planar interface between two rough media using surface acoustic waves

The results of experimental studies on the nonlinear elastic properties of a planar interface between two media are presented—an optically polished glass substrate and flat samples with different degrees of roughness. The nonlinear elastic properties of the interfaces between two media were investigated by the spectral method using surface acoustic waves (SAWs). The effect of external pressure applied to the interface on the efficiency of the generation of the second SAW harmonic was studied. Using the measured amplitudes of the first and second harmonics of the SAW that passes along the interface, the second-order nonlinear acoustic parameter was calculated as a function of the external pressure applied to the sample at a fixed amplitude of a probing wave. It was revealed that the nonlinear parameter of the SAW is a nonmonotonic function of the pressure at the boundary. The results were analyzed on the basis of an elastic contact nonlinearity, and it is concluded that these results can be used in nondestructive testing for roughness and waviness of surfaces of flat solids.     

Conversion of waveguide modes in nonuniformly magnetized planar structures

An analysis is made of a planar structure with a nonuniform distribution of magnetization throughout the thickness of a waveguide layer that corresponds to the rotation of magnetic momentum in the plane of the layer. The results of the study show the feasibility of efficiently controlling the conversion of orthogonally polarized modes due to the change of thickness of the transition layer and the angle of magnetization rotation across the waveguide layer.     

Numerical evaluation of the acoustic radiation from planar structures with general baffle conditions using wavelets

A method is presented for computing the acoustic radiation from baffled, unbaffled, or partially baffled planar structures. The surface displacement and the surface pressure are expressed in terms of wavelets, and the acoustic dynamic stiffness (baffled case) or the acoustic receptance (unbaffled case) between any two wavelets is derived in closed form. The wavelets are employed with translation only (i.e., no dilation), and the jinc function is used; the Hankel transform of this function is the Heavyside step function, and this feature greatly simplifies the analysis. There is a trivial mapping between the wavelet amplitudes and the physical motion of the structure, and hence the dynamic stiffness and receptance results can readily be used to derive the acoustic dynamic stiffness matrix (by inverting the receptance matrix in the unbaffled case) in any set of generalized coordinates. Partially baffled systems can then be studied by substructuring the dynamic stiffness matrix. A set of example problems is considered in which the method is used to compute the resistive and reactive radiation efficiency of a range of benchmark systems.     

Reduction of elastic strains in directly-bonded silicon structures

The elastically strained state of the interface in directly-bonded silicon structures has been studied by x-ray diffraction topography and IR spectrometry. The pattern of the contrast observed in the x-ray topographs and the intensity oscillations in the IR spectra indicate a periodic strain distribution caused by the long-period surface microroughness on the plates to be bonded. The local microroughness did not exceed 2 Å, and it did not noticeably affect the interface structure. Two types of the structure were subjected to a comparative analysis, (i) with a smooth interface prepared by standard direct-bonding technology, and (ii) with an interface displaying a regular relief. The strain level in type-II structures was found to be lower by more than an order of magnitude. A model is proposed to account for the observed reduction of elastic strains at the bonded sections of the interface in terms of elastic relaxation of the free surfaces in the relief voids through their deflection and displacement.     

Proximity effect and spontaneous vortex phase in planar SF structures

The proximity effect in SF structures is examined. It is shown that, due to the oscillations of the induced superconducting order parameter in a ferromagnet, the critical temperature of an SF bilayer becomes minimal when the thickness of the ferromagnetic layer is close to a quarter of the period of spatial oscillations. It is found that the spontaneous vortex state arising in the superconductor due to the proximity of the magnetic domain structure of a ferromagnet brings about noticeable magnetoresistive effects.     

Finite-dimensional model for defect-trapped light in planar periodic nonlinear structures

We study the dynamics of 2D gap solitons (GSs) in Bragg resonant nonlinear (photonic) gratings in the presence of localized defects. Previous work [Stud. Appl. Math.115, 209 (2005)] explains the mechanism of trapping the GS-carried energy at a defect via a resonant energy transfer from the GS into defect modes. We derive a finite-dimensional model that describes the evolution of the defect-trapped state as an interaction of linear defect modes and show that this model approximates the full dynamics very well in the regime when moderate amounts of GS energy are trapped.     

Remanent domain structures in magnetic garnet epilayers after planar saturation

Garnet epilayers with a 〈111〉 axis tilted from the film normal have been subjected to a planar saturating field and their remanent domain structures studied with the Faraday effect. For certain directions of applied field, it is possible to produce a mixed polarity state. The creation of the mixed state is discussed in terms of homogeneous nucleation. The possibility of utilising the mixed state for characterising garnet properties is mentioned.     

Negative luminescence and thermal radiation in semiconductor planar resonator structures

We present the results of theoretical and experimental investigation of interference effects of negative luminescence (NL) in planar resonator structures with an optically thin active semiconductor layer, as well as association of those effects with thermal radiation (TR) from such structures. The conditions are studied at which one can determine the NL characteristics of a structure with equilibrium electrons and holes by measuring its TR. We investigated the spectra and angular dependence of NL in the planar structures where active element is a Pb_0.8Sn_0.2Te film on a transparent BaF₂ substrate coated with aluminium. It is shown that, for such structures, NL efficiency in the interference peaks may be close to unity, and the antenna effect appears in the radiation pattern at some fixed wavelength. Both radiation intensity and the near-field energy in the vicinity of NL source energy are studied.