Wave Ratio Impedance Research Articles

Application of fractional order theory of thermoelasticity to a bilayered structure with interfacial conditions

ABSTRACTIn this work, fractional order theory of thermoelasticity is applied to a bilayered structure being in imperfect thermal and mechanical contact. The model is subjected to a sudden heating at the traction-free end, assumed to be undisturbed at infinity. The heat conduction in each medium is described by the time-fractional heat conduction equations with two fractional order parameters, respectively. An analytical technique based on Laplace transform is adopted. Numerical results are computed and represented graphically, from which the effects of fractional derivative parameters of both media, thermal contact resistance, elastic wave impedance ratio on the responses are discussed.

Non-linear 2-D FE analysis for the assessment of isolation performance of wave impeding barrier in reduction of railway-induced surface waves

The establishment of wave impeding barriers (WIBs) beneath the railway track or below the protected residential buildings resting on soft soil can be commonly used to reduce the ground borne vibrations caused by high-speed train traffic. This paper deals with the non-linear 2D finite element modeling for the prediction of shielding performance of WIB on the dynamic response of vibrating coupled soil–structure system. Energy absorbing boundaries along the truncated interfaces of the unbounded nature of the underlying soil media are implemented in the time domain along with Newmark’s integration. This numerical model and its computational work were adapted with simulation of the passing train load completely account for plastic deformations of the underlying soil medium under Mohr–Coulomb failure criterion and directly predicting the reduction effect on the structural response. Extensive parametric investigations for both passive and active isolation cases under different train speeds have been performed to reveal the influence of its wave impedance ratio on the shielding efficiency. The important findings based on obtained numerical results are presented.

Different kinds of band-pass filters based on one-dimensional photonic crystal heterostructures

Three kinds of band-pass filters (BPFs), termed a TE BPF, a TM BPF and a BPF at oblique incidence, are designed by crossing the band edges of two different one-dimensional (1D) photonic crystals (PCs). The TE BPF, fulfilling the function of high reflectivity for p-polarization and high transmittance in a narrow pass-band for s-polarization, is constructed by two subPCs, one of which is obtained by decreasing the lattice constant of the other one while the other parameters keep the same. The TM BPF also comprises two subPCs, but the materials of one subPC are quite different with those of the other one. Similarly, the BPF at oblique incidence, from which both polarization waves can transmit in a narrow pass-band at oblique incidence, is composed of two different subPCs. Note that, the distribution of the wave impedance of material in each BPF should be periodic to prevent unexpected defect modes. The new filters not only provide narrow pass-bands and wide non-transmission bands, but also have simple structures. This is a result of the fact that the wave impedance ratio between composites is enlarged by introducing magnetic materials. The new designs have potential applications in optical filters and optical integrated circuits.

Analysis of enlargement of the omnidirectional total reflection band in a special kind of photonic crystal based on the incident angle domain

A special kind of one-dimensional (1D) magnetic photonic crystal (MPC) is investigated. The refractive indices of the alternating layers in such a MPC are equal. As a result, the stop-band edges of TE mode coincide with those of TM mode, and the stop-bands for both modes expand as the incident angle increases. Based on the incident angle domain method, the omnidirectional total reflection (ODTR) band determined by the wave impedance ratio between the composites can be enlarged substantially using a heterostructure in which the stop-band edges of the sub-PCs can be completely adjacent at any incident angle. Moreover, the requirement of ODTR of each sub-PC is unnecessary, which extends the range of materials; that is, the wave impedance ratio between the composites and the refractive index ratio between the composites and the incident media can be much lower than that required in a single periodic structure.

ENLARGED PHOTONIC BAND GAPS IN ONE-DIMENSIONAL MAGNETIC STAR WAVE GUIDE STRUCTURE

Photonic band structure and re∞ection properties of one- dimensional magnetic star wave-guide (MSWG) structure composed of a backbone (or substrate) waveguide along which a flnite side branches grafted periodically have been investigated. The dispersion relation and hence the photonic band gaps (PBGs) of the magnetic SWG structure have been obtained by applying the Interface Response Theory (IRT). Investigation of dispersion characteristics shows that the existence of band gaps in magnetic SWG structures does not require the contrast in the wave impedance of the constituent materials, which is unlike the usual magnetic photonic crystal structure, where there must be the contrast in the wave impedance for the existence of the band gaps. Moreover, magnetic SWG structures have wider re∞ection bands in comparison to normal magnetic photonic crystal (MPC) structure for the same contrast in the wave impedance. Analysis shows that the width of forbidden bands for MSWG structure changes with the change in permittivity and permeability of the backbone, and side branches materials even the ratio of wave impedance is the same, but it remains the same in case of MPC structure. In addition to this, we have studied the efiects of variation of number of grafted branches and substrates, i.e., number of nodes on the re∞ection bands of magnetic SWG structure.

Shock Wave Structure in Polyurethane Foam.

Shock wave propagation in polyurethane (PU(R)) foam was experimentally studied. The experiment was conducted in a shock tube by measuring pressure along the PU(R) foam in a shock tube, by means of holographic interferometry and streak camera recording. It was found that the stress-strain curve of PU(R) has an inflection point. When the pressure behind the incident shock wave was below the inflection-point pressure Pc, the wave impedance ratio of the incident shock wave and transmitted pressure wave Zi/Zt increased sharply. This indicates that only a small amount of energy is transmitted into the foam if the pressure is below Pc. For pressures larger than Pc, Zi/Zt decreases asymptotically to a small finite value.

Shock Wave Structure in Polyurethane Foam.

An experimental study was made of shock wave propagation in polyurethane (PUR) foam. The experiment was conducted in a shock tube by measuring pressure along the PUR foam by means of holographic interferometry and streak camera recording. It was found that the stress-strain curve of PUR have an inflection point. When the pressure behind the incident shock wave was below the inflection point pressure PC, the wave impedance ratio of the incident shock wave and transmitted pressure wave Zi./Zt increased sharply. This indicates that only a small amount of energy is transmitted into the foam if the pressure is below Pc. For pressure larger than Pc, Zi, /Zt decreases asymptotically to a small finite value.

CHARACTERISTICS OF LOVE WAVE GENERATED AROUND A DIPPING BASEMENT

Source mechanism and characteristics of the horizontally propagating waves generated around a dipping basement due to the incident SH wave are investigated. A new analitical method which combines boundary elements, finite elements and energy transmitting boundary is proposed. Two layered media, the upper layer of which has semi-infinite boundary in one side and a dipping interface in the other side, is used in the analysis. It is found that the incident SH wave is mostly transformed into Love wave whose period is close to Airy phase at the horizontal part of the surface layer in the case that both the ratio of wave impedance and the inclination of basement are small; all reflected SH wave is predominant in the other case.