Characteristics Of Plane Waves Research Articles

Mathematical study on reflection and transmission of plane waves in a rotating piezo-thermo-elastic composite structure

The present investigation is concerned with the study of reflection and transmission characteristics of plane waves in two distinct rotating piezo-thermo-elastic substrates under the purview of dual-phase-lag (DPL) model and Lord–Shulman (LS) theory of thermo-elasticity. Mathematical expressions for electric displacements, stresses, amplitudes and energy ratios are derived. The influence of rotation on the amplitude ratios is extensively studied and comparative analyses are performed graphically among DPL and LS theories. Energy conservation law holds in the entire process of reflection and transmission phenomena. This study may be useful in the construction and design of temperature sensors and other piezoelectric surface-acoustic-wave devices.

Instabilities in internal gravity waves

<abstract><p>Internal gravity waves are propagating disturbances in stably stratified fluids, and can transport momentum and energy over large spatial extents. From a fundamental viewpoint, internal waves are interesting due to the nature of their dispersion relation, and their linear dynamics are reasonably well-understood. From an oceanographic viewpoint, a qualitative and quantitative understanding of significant internal wave generation in the ocean is emerging, while their dissipation mechanisms are being debated. This paper reviews the current knowledge on instabilities in internal gravity waves, primarily focusing on the growth of small-amplitude disturbances. Historically, wave-wave interactions based on weakly nonlinear expansions have driven progress in this field, to investigate spontaneous energy transfer to various temporal and spatial scales. Recent advances in numerical/experimental modeling and field observations have further revealed noticeable differences between various internal wave spatial forms in terms of their instability characteristics; this in turn has motivated theoretical calculations on appropriately chosen internal wave fields in various settings. After a brief introduction, we present a pedagogical discussion on linear internal waves and their different two-dimensional spatial forms. The general ideas concerning triadic resonance in internal waves are then introduced, before proceeding towards instability characteristics of plane waves, wave beams and modes. Results from various theoretical, experimental and numerical studies are summarized to provide an overall picture of the gaps in our understanding. An ocean perspective is then given, both in terms of the relevant outstanding questions and the various additional factors at play. While the applications in this review are focused on the ocean, several ideas are relevant to atmospheric and astrophysical systems too.</p></abstract>

All dielectric terahertz carpet cloaking by phase compensation metasurfaces

Metasurfaces can control the phase, amplitude and polarization of electromagnetic waves, providing a new method for the design of cloaking devices. At present, most of the metasurface carpet cloaking devices are based on metal structure with larger ohmic loss, which severely limits the efficiency of the devices. Here, we propose to use all dielectric unit structure to construct metasurface layer. By using local phase compensation principle, all dielectric metasurface carpet cloaking can be designed in terahertz region. Based on the numerically simulation of near field and far field characteristics, the cloaking effect can be confirmed. The incident wavefront is reflected by the cloaking device and the plane wave characteristics can be recovered well. The cloaking effect can be effective in a broadband range from 0.3 to 0.58 THz. Moreover, the proposed all dielectric metasurface cloaking technology can be extended to the visible light and microwave range.

Plane wave in non-local semiconducting rotating media with Hall effect and three-phase lag fractional order heat transfer

This paper deals with the propagation of the plane wave in a nonlocal magneto-thermoelastic semiconductor solid with rotation. The fractional-order three-phase lag theory of thermoelasticity with two temperatures has been applied. When a longitudinal wave is incident on the surface z = 0, four types of reflected coupled longitudinal waves (the coupled longitudinal displacement wave, the coupled thermal wave, coupled carrier density wave, and coupled transverse displacement wave) are identified. The plane wave characteristics such as phase velocities, specific loss, attenuation coefficient, and penetration depth of various reflected waves are computed. The effects of two temperatures, non-local parameter, fractional order parameter, and Hall current on these wave characteristics are illustrated graphically with the use of MATLAB software.

Effects of rotation, voids and diffusion on characteristics of plane waves in a thermoelastic material

PurposeThe purpose of this paper is to study the effects of rotation, voids and diffusion on characteristics of plane waves in a thermoelastic material.Design/methodology/approachLord and Shulman generalization of linear thermoelasticity is used to study the plane waves in a rotating thermoelastic material with voids and diffusion. The thermoelastic solid is rotating with a uniform angular velocity. The problem is specialized in two dimensions to study wave propagation. The plane harmonic solutions of governing field equations in a plane are obtained.FindingsA velocity equation is obtained which indicates the propagation of five coupled plane waves in the medium. Reflection of an incident plane wave from stress-free surface of a half-space is also considered to obtain the amplitude ratios of various reflected waves. A numerical example is considered to illustrate graphically the effects of rotation, frequency, void and diffusion parameters on speeds and amplitude ratios of plane waves.Originality/valueThe present problem covers the combined effects of rotation, voids and diffusion on characteristics of plane waves in linear thermoelastic material in the context of Lord and Shulman (1967) and Aouadi (2010) theories, which are not studied in literature yet.

A Way to Improve the Efficiency of High Frame Rate Imaging Algorithm with Limited Diffraction Beams

Jian-yu Lu has studied a high frame rate (HFR) ultrasound imaging system since 1997. In the system, weighting echo signal by limited diffraction beam spends most of the computing time of imaging algorithm. In the paper the spectrum of HFR ultrasound imaging is analyzed. Combining limited bandwidth properties of image spectrum and the plane wave characteristics of limited diffraction wave, a method, which can improve the efficiency of weighted processing algorithms, is put forward. Simulation results show that it effectively reduces the calculation amount of weighting, meanwhile maintaining image quality.

Plane waves at an imperfectly bonded interface of two orthotropic generalized thermoelastic rotating half-spaces with two relaxation times

The present paper concentrates on the study of reflection and refraction characteristics of plane waves at an imperfectly bonded interface of two orthotropic generalized thermoelastic rotating half-spaces with different elastic and thermal properties. In this type of problem of orthotropic thermoelastic rotating medium, there are three types of plane waves quasi longitudinal (QL-) wave, quasi thermal (T-mode) wave and quasi transverse (QT-) wave, whose velocities depend on the angle of incidence, imperfection and rotation. The amplitude ratios of reflected waves to that of incident one in each case have been derived. Some special cases of boundaries, i.e. normal stiffness, transverse stiffness, thermal contact conductance, slip boundary and welded contact boundary have been deduced from an imperfect one. Effect of rotation on the amplitude ratios of different reflected and refracted waves with respect to incident QL-wave at different boundaries have been studied graphically. It is observed that thermal properties, imperfect boundary and rotation have significant effect on the propagation of waves.

无限长非均匀圆柱对平面波散射的彩虹特性研究

无限长非均匀圆柱对平面波散射的彩虹特性研究

Propagation characteristics of plane waves of defects in a viscoplastic medium

It is shown that dispersion is not observed in the propagation of a weakly damped wave, and dissipation is frequency-dependent. For strongly damped waves, dispersion and dissipation are observed. However, a wave in a viscoplastic medium decays over very short distances and the penetration depth of strongly damped waves of defects is bounded by the skinlayer thickness.

Total reflection characteristics of plane waves at the interface including a chiral medium

The total reflection characteristics of plane waves from the interface including a chiral medium have been studied with complex chiral material parameters. The possible values of chirality admittance ζc are determined for left-circularly polarized (LCP) and right-circularly polarized (RCP) total reflections at fixed incident angles from an interface between free space and a chiral medium. It is found that there exists a region of parameter ζc, in which neither LCP nor RCP modes can be totally reflected for any incident angle θ. It is demonstrated that for ζ1 = Re(ζc) > 0, total reflection is preferred for LCP mode whereas RCP total reflection is favored for ζ1 < 0.

Reflection and transmission characteristics of plane waves at the interface including chiral media

The reflection from and transmission characteristic of the plane waves are studied at the interface between media including chiral media. The co-polarized and cross-polarized reflection and transmission coefficients are derived from the chiral constitutive relations. Possible values of chirality admittance ζc are determined for fixed Brewster angles. In addition, the features of reflection and transmission in some typical cases including the normal incidence case and that containing a mirror-conjugated medium are discussed in detail. For example, complex chiral parameters for minimal reflection coefficient in the case of normal incidence are optimized.

Transient analysis of electromagnetic fields in a magnetic medium with hysteresis in a three-dimensional space

A fundamental application of the spatial network method to a magnetic medium with hysteresis is presented. Results for the propagation characteristics of plane waves show that complicated distortion occurs in instantaneous and spatial variations of the field components. It is also shown that the rate of power attenuation agrees well with the theoretical rate of hysteresis loss. >

Microwave power absorption differences between normal and malignant tissue

An open-ended coaxial probe that produced a fringing field in the termination tissue was used to measure the fractional power absorption for malignant tumors and normal adjacent tissue in female W/Fu isogeneic rats over the 30 to 2000 MHz range. The fractional power absorption was determined as the difference in measured incident and reflected power divided by the incident power for SMT-2A tumors, and for normal adjacent muscle and mammary tissue. For the coaxial probe, the ratio of power absorbed in málignant to that in normal adjacent tissue peaked at 180 MHz with values of 4.28 and 1.40 for malignant/mammary and malignant/ muscle, respectively. By fitting the measured data to an equation for power absorption because of the fringing-field probe, tissue conductivity and dielectric constant versus frequency were determined. These tissue properties were used to determine the ratio of power absorbed in malignant to normal tissue versus frequency for a propagating plane wave. For plane waves, peak differential absorption occurs at 300 MHz; 4.81 and 1.46 for malignant/ mammary and malignant/muscle, respectively. Since direct-contact applicators for microwave hyperthermia have both fringing-field and plane-wave characteristics, our results indicate that any operating frequency from 180 to 300 MHz would provide a near optimum differential power absorption between malignant and normal tissue.