External Plane Wave Research Articles

The far-field diffraction of a plane wave on a system of randomly and in average periodically located point scatterers: the Debye-Waller factor

The description of the superposition field of a system of point sources with a random and, on average, periodic structure is considered. The description is given in the far field and the point sources are considered as centers of secondary sphere waves generated by an external plane wave. In contrast to the traditional approach, where description of the diffraction pattern is given on the base of wave field averaging, here the intensity is averaged.In the framework of the suggested approach the analytic formula of dependence of the average intensity on the direction observation is found. The influence of disorder on the values of intensity of main maximums of a periodic structure is investigated. It is shown that this influence depends on the ordinal numbers of the maximum and in the case of central main maximum this influence vanishes. The question of applicability of the Debye-Weller factor for describing of the statistic of diffracted field is discussed.

A Simulation of Air Lasing Seeded by an External Wave in a Femtosecond Laser Filament.

Air lasers induced by femtosecond laser filaments play an important role in remote sensing applications. Few studies have been dedicated to the spatial distribution of external-seeded air laser radiation in the laser filament based on the numerical simulation method, which can pave the way to understanding the mechanism of the external-seeded air lasing process during filamentation. In this study, numerical simulations of the propagation of an air laser seeded by an external plane wave with a wavelength of 391 nm during femtosecond laser filamentation were performed. The results indicated that the air laser's beam intensity distribution varies from a ring pattern to a donut pattern when the filament length and nitrogen ion density are raised as a result of the defocusing and lasing effects of the filament plasma. Here, the ring pattern is formed by several thin rings, while the donut pattern refers to a notably thicker, ring-like structure. In addition, it has been demonstrated that the air laser's beam power would increase exponentially versus the filament length and the nitrogen ion density. The knowledge about the angular distribution of air lasing could be important for optimizing the detection geometry of the LIDAR setup, including the view angle and the size of the collecting optical component.

Numerical study on THz radiation of two-dimensional plasmon resonance of GaN HEMT array

The GaN high electron mobility transistor (HEMT) has been considered as a potential terahertz (THz) radiation source, yet the low radiation power level restricts their applications. The HEMT array is thought to improve the coupling efficiency between two-dimensional (2D) plasmons and THz radiation. In this work, we investigate the plasma oscillation, electromagnetic radiation, and the integration characteristics of GaN HEMT targeting at a high THz radiation power source. The quantitative radiation power and directivity are obtained for integrated GaN HEMT array with different array periods and element numbers. With the same initial plasma oscillation phase among the HEMT units, the radiation power of the two-element HEMT array can achieve 4 times as the single HEMT radiation power when the array period is shorter than 1/8 electromagnetic wavelength. In addition, the radiation power of the HEMT array varies almost linearly with the element number, the smaller array period can lead to the greater radiation power. It shows that increasing the array period could narrow the main radiated lobe width while weaken the radiation power. Increasing the element number can improve both the radiation directivity and power. We also synchronize the plasma wave phases in the HEMT array by adopting an external Gaussian plane wave with central frequency the same as the plasmon resonant frequency, which solves the problem of the radiation power reduction caused by the asynchronous plasma oscillation phases among the elements. The study of the radiation power amplification of the one-dimensional (1D) GaN HEMT array provides useful guidance for the research of compact high-power solid-state terahertz sources.

Automated adaptive TFSF method for solving time domain Maxwell's equations

AbstractThe total field–scattered field (TFSF) formulation is quite popular for solving Maxwell's equations in finite difference time domain (FDTD) and finite volume time domain (FVTD) methods. Here a fixed TFSF interface around the scattering body is employed to separate the total field (TF) cells and scattered field (SF) cells. This interface is selected based on experience as it is assigned prior to the solution, and, therefore, the solution accuracy may not be optimal. In the present work, a novel automated adaptive total field–scattered field (ATFSF) method is proposed for accurately computing the electromagnetic scattering by complex‐shaped metal objects excited by an external plane wave. In the proposed method, an algorithm is devised to dynamically identify the TF cells and the SF cells, to be solved using TF and SF methods, respectively, using intensity of electromagnetic (EM) wave. The algorithm is tested in a 2‐D spectral volume time domain (SVTD) framework for solving electromagnetic scattering, and the predicted surface current/radar cross section is compared against the SF, TF, and the conventional TFSF methods. It is seen that the present method improves the solution accuracy significantly.

An Analytical Evaluation of the Shielding Effectiveness of Enclosures Containing Complex Apertures

Analytical methods are significantly useful tools for engineers in computational modeling. These methods provide fast simulations, while preserving physical meaning. In this paper, a full analytical formulation is developed based on the circuit approach, also known as Intermediate Level Circuit Model (ILCM), to evaluate the shielding effectiveness (SE) of metallic structures. The proposal focuses on rectangular enclosures containing apertures of complex geometrical shape, illuminated by an external plane wave. The enclosure is taken as a short-circuited waveguide. The aperture is treated as a transmission line with an intrinsic impedance that depends on the aperture polarizability, according to Bethe’s theory of small holes. The formulation easily takes into account high-order resonant modes and different apertures, such as circular, elliptical, round-ended and cross-shaped apertures. The ILCM technique reveals good agreement with a numerical full-wave method for various configurations of enclosures, covering a large range of frequencies from 0.5 GHz to 2.5 GHz, thus offering perspectives for parametric and/or optimization SE studies.

Multi-particle assembling patterning by acoustic forces and scattering dissipation

There has been growing interest in exerting the radiation forces to trap and cluster the randomly distributed cells in body fluid, the micro-particles in water, or the microorganism in the fluid-like culture medium. The standing wave is extensively utilized as a patterning tool, and micro-particles assemble at the nodes or antinodes. For the frequencies above megahertz, the distances among nodes or antinodes are below millimeters, too close for cluster separation or detection. We create a scenario where traveling waves dominate instead of standing waves by way of scattering dissipation, and particles assemble at a central location. We first provide a theoretical prediction model based on the translational addition theorem and the partial-wave expansion method. We evaluate the attenuation exerted by an external plane wave on a set of particles immersed in the host-fluid medium, and the bulk acoustic wave (BAW) device is used to verify the prediction. It is found that, for the high concentration medium with particles, the scattering dissipation is significant and the forces are directed towards a central space instead of the nodes or antinodes of the standing waves, leading to meaningful separation of micro-particles from their host-fluid medium.

Efficient analytical method for the shielding effectiveness of an apertured enclosure based on the BLT equation

An efficient analytical method based on the Baum–Liu–Tesche (BLT) equation has been developed for predicting the shielding effectiveness (SE) of an apertured enclosure excited by an external plane wave. First, the equivalent circuit and the signal flow graph are constructed, which helps understand the energy transmission of the enclosure. Then, the SE is obtained by using the generalised BLT equation, and the proposed analytical method is employed to analyse the effect of various parameters on the SE. Finally, the analytical method is extended to handle the enclosure with an aperture array, an enclosure with apertures at the opposing walls and two cascaded enclosures. The analytical method has been successfully verified by the CST over a wide frequency band of 0–3.0 GHz, which consumes less time than conventional numerical methods. Besides, whatever the condition of the enclosure or the aperture is, the analytical method can predict the SE and higher-order modes at higher frequencies accurately.

An efficient method for predicting the shielding effectiveness of an enclosure with multiple apertures

ABSTRACT An efficient analytical method has been proposed for predicting the shielding effectiveness (SE) and resonances of a metallic enclosure with multiple apertures against an external incident plane wave. First, the electromagnetic (EM) field distribution within the enclosure through multiple apertures is represented by the equivalent electric and magnetic dipole moments based on the Bethe’s theory for small aperture coupling. Then, the EM fields in the enclosure can be obtained by using the scalar wave functions, where the unknown coefficients in the functions are related to the equivalent dipole moments. Finally, the analytical method is applied to handle the enclosure with multiple apertures, and corresponding inclusions about the SE and resonances can be obtained. Compared with the full-wave simulation software CST over the frequency range of 0–2.5 GHz, the analytical method is proved to be accurate and effective, which consumes less time than the conventional numerical methods.

Diffuse field transmission through multilayered cylinders using a Transfer Matrix Method

Abstract This paper discusses the use of a Transfer Matrix (TM) method for predicting the acoustic behavior of infinite cylinders consisting of a generic arrangement of homogeneous and heterogeneous periodic layers of various nature (fluid, solid, poroelastic). A through-radius TM is derived for a layer characterized by cylindrical periodicity by manipulating the dynamic stiffness matrix related to a finite element model of a unit cell. The proposed technique is equally appealing for homogeneous layers since few elements are needed in this case. In such a framework, different layers can be combined to form multilayered systems and the related acoustic radiation or transmission due to an external plane wave or a diffuse acoustic field can be assessed. The proposed approach is validated in case of cylinders consisting of homogeneous layers by comparison with alternative approaches. In order to demonstrate the usefulness of the approach, the sound transmission through a cylindrical structure with resonators is presented.

Analytical method for electromagnetic coupling to a penetrated transmission line in cascaded multiple enclosures with hybrid apertures

An efficient analytical model has been developed for predicting the electromagnetic (EM) field coupling to a lossless transmission line (TL) penetrating through cascaded multiple rectangular enclosure with hybrid apertures (apertures with and without conductive sheets coexist) excited by an external plane wave of oblique incidence. First, The EM field in the enclosure through apertures covered by conductive sheets is derived using the dyadic Green’s function and the transfer impedance of the sheet. Then, the EM field in the enclosure through apertures without sheets is derived based on the Bethe’s small holes theory and the mirror procedure. Finally, the electric current induced at the TL terminals is obtained combining the equivalent lumped-pi circuit model of the TL and the Agrawal’s model. The analytical model has been successfully verified by the finite-difference time-domain (FDTD) method over the frequency range of 0.1 ~ 3 GHz, which consumes less time than numerical methods.

Photonic band engineering in absorbing media for spectrally selective optoelectronic films.

Spectrally selective materials are of great interest for optoelectronic devices in which wavelength-selectivity of the photoactive material is necessary for applications such as multi-junction solar cells, narrow-band photodetectors, transparent photovoltaics, and tailored emission sources. Achieving controlled transparency or opacity within multiple wavelength bands in the absorption, reflection, and transmission spectra are difficult to achieve in traditional semiconductors that typically absorb at all energies above their electronic band gap and is generally realized by the use of external bandpass filters. Here, we propose an alternate method for achieving spectral selectivity in optoelectronic thin films: the use of photonic band engineering within the absorbing region of a semiconductor in which resonant photonic bands are strongly coupled to the external reflectivity and transmission spectra. As a first step, we use optical simulations to systematically study the effect of material absorption on the properties of the photonic bands in a photonic crystal slab structure. We find that adding a weak loss to the materials model does not appreciably change the frequencies of the photonic bands but does reduce the quality factor of the associated photonic modes. Critically, the radiating photonic bands induce strong Fano resonance features in the transmission and reflection spectra, even in the presence of material absorption, due to coupling between the bands and external electromagnetic plane waves. These resonances can be tuned by adjusting the photonic crystal structural properties to induce spectral selectivity in the absorbing region of semiconductors. Lastly, we demonstrate this tuning method experimentally by fabricating a proof-of-principle photonic structure consisting of a self-assembled polystyrene bead monolayer infiltrated with PbS CQDs that displays both near-infrared absorption enhancement and visible transparency enhancement over a homogeneous control film, qualitatively matching predictions and showing promise for optoelectronic applications.

Phases of driven two-level systems with nonlocal dissipation

We study an array of two-level systems arranged on a lattice and illuminated by an external plane wave which drives a dipolar transition between the two energy levels. In this set up, the two-level systems are coupled by dipolar interactions and subject to nonlocal dissipation, so behave as an open many-body quantum system. We investigate the long-time dynamics of the system at the mean-field level, and use this to determine a phase diagram as a function of external drive and detuning. We find a multitude of phases including antiferromagnetism, spin density waves, oscillations and phase bistabilities. We investigate these phases in more detail and explain how nonlocal dissipation plays a role in the long-time dynamics. Furthermore, we discuss what features would survive in the full quantum description.

Strong fields and neutral particle magnetic moment dynamics

Interaction of magnetic moment of point particles with external electromagnetic fields experiences unresolved theoretical and experimental discrepancies. In this work we point out several issues within relativistic quantum mechanics and QED and we describe effects related to a new covariant classical model of magnetic moment dynamics. Using this framework we explore the invariant acceleration experienced by neutral particles coupled to an external plane wave field through the magnetic moment: we study the case of ultrarelativistic Dirac neutrinos with magnetic moment in the range of 10−11 to 10−20 μB; and we address the case of slowly moving neutrons. We explore how critical accelerations for neutrinos can be experimentally achieved in laser pulse interactions. The radiation of accelerated neutrinos can serve as an important test distinguishing between Majorana and Dirac nature of neutrinos.

Efficient analytical method for the coupling to penetrated transmission line in multiple enclosures based on electromagnetic topology

An efficient analytical model based on electromagnetic (EM) topology has been developed for predicting the EM field coupling with a lossless penetrated transmission line (TL) of which the termination loads are located in two enclosures, respectively, excited by an internal vertical monopole and an external plane wave of oblique incidence. Firstly, the electric fields generated by the plane wave are calculated based on Bethe's aperture coupling theory and scalar wave function method. Then, the topology network of the EM interaction is established according to the analysis of the interference paths and the coupling mechanism from sources to the TL. Finally, the electric current induced at the line terminations is obtained by combining the generalised Baum-Liu-Tesche equation and the Agrawal's model. The analytical model has been successfully verified by the finite difference time domain method over a broad frequency range, and costs less time and fewer computational resources than numerical methods, which provides guidance for the field-to-line coupling in complex multiple enclosures against different sources.

Electromagnetic coupling to an apertured enclosure via a penetrated transmission line based on electromagnetic topology

An efficient analytical model based on electromagnetic topology (EMT) has been developed for predicting the electromagnetic (EM) field coupling to a rectangular enclosure with an electrically large aperture via a penetrated transmission line (TL), excited by an external plane wave of oblique incidence. First, the electric field in the enclosure is calculated based on the modified Bethe’s small holes theory and mirror procedure. Then, the topology networks of the EM interaction are constructed by analyzing the coupling paths and mechanism, and the electric current induced at the termination loads of the TL is obtained using the generalized Baum–Liu–Tesche equation combined with the Agrawal’s model. The analytical model has been successfully verified by the finite difference time domain method over a wide frequency band of 0.5~3 GHz, which consumes less time than numerical methods. Finally, the analytical model is employed to analyze the effect of various parameters on the induced current, including the length, the height, and the direction of the line.

Study of imperfect bonding effects on sound transmission loss through functionally graded laminated sandwich cylindrical shells

Effects of imperfect bonding on sound transmission across a double-walled cylinder with FGM-core are studied by using the three-dimensional theory of elasticity. Aluminum and zirconia are inner and outer shells respectively, whereas the FGM-core is sandwiched between these layers. A very thin adhesive epoxy interlayer was applied in order to bond the adjacent layers. The imperfect bonding (adhesive epoxy interlayer) is modeled by a linear spring model. Infinite values of stiffness of linear spring reveal that there are no interfaces between the adjacent layers. However, the interface tractions do not exist and the layers are completely deboned from each other due to zero values of these parameters. The linear spring model is incorporated into the global transfer matrix with the aid of suitable transfer matrices. The proposed model is used to calculate the effects of imperfect bonding on TL of multi-layered cylinder which excited by an external plane wave. The obtained results are compared with those of other researches recently published in the literature. Excellent agreement is observed for high stiffness of adhesive bond. The results have also illustrated the fact that the existence of imperfect interfaces leads to the enhancement of the TL of sandwich cylindrical shell. Moreover, low stiffness of interlaminar adhesive bonding has more positive effect on the TL enhancement, particularly in high frequency range. Finally, it can be concluded that at high frequencies the spring layer model with low stiffness cannot transmit the waves because of more fluctuations.

Analytical method for load response of a transmission line in a double-enclosure with multiple covered apertures

An efficient analytical model has been developed for predicting the load response of a lossless transmission line (TL) in a rectangular double-enclosure with multiple apertures covered by conductive sheets, excited by an external plane wave of oblique incidence. First, the electromagnetic field in the enclosure is calculated using the enclosure dyadic Green’s function and the transfer impedance of the sheets against the plane wave. Then, the electric current induced at the termination loads of the TL is computed in combination of the equivalent lumped-pi circuit model of the line and the Agrawal’s model. The analytical model has been successfully verified by the full-wave software CST (Computer Simulation Technology) over a wide frequency band, and it is employed to analyze the effect of various parameters on the induced current, including the sheet conductivity, the load impedance, and the position of the line. This model consumes less time compared with numerical methods, and it can also deal with covered aperture arrays on multiple sides of the enclosure.

Efficient Reciprocity-Based Hybrid Approach for Analyzing Radiated Susceptibility Responses of Multilayer PCBs

An efficient reciprocity-based hybrid approach is proposed to analyze the radiated susceptibility problems of external incident electromagnetic interference coupling to multilayer printed circuit boards (PCBs) through board edges. The proposed approach constructs a multiport Thevenin equivalent circuit that includes the coupling of an external incident plane wave to a multilayer PCB, concatenates the circuit devices mounted on the PCB to the equivalent circuit, and then solves the induced voltages or currents across the circuit devices. Both numerical simulation and experimental verification are carried out to validate the proposed approach, and good agreement between them is observed. The proposed approach is computationally efficient, especially for the parameter analysis. Moreover, it can also be applied to analyze the multilayer PCBs with linear or nonlinear circuit devices.

An exact solution of three-dimensional elasticity for sound transmission loss through FG cylinder in presence of subsonic external flow

An exact elasticity solution is presented to study sound transmission loss through functionally graded cylinder in presence of subsonic external flow. This structure cylindrical is excited by an external plane wave with two angles of incidenceψ andγ. The mechanical properties of the functionally graded material are assumed to vary uniformly and continuously with the change of volume fractions of the constituting materials across the thickness of the cylinder according to the power-law distribution. The functionally graded cylinder is approximated by a laminate model, whereas the solution is expected to gradually approach the exact one as the number of layers increases. The governing equations of motion for each layer are derived, based on 3-D elasticity theory. Then, the transfer matrix method is employed, which includes a global transfer matrix that composed as the product of the local transfer matrices by applying continuity of the displacement and stress components at the interfaces of neighboring layers. The transmission loss of the multi-layered functionally graded cylinder are presented for different incidence angles, Mach numbers, thicknesses, radii and distribution functions over a wide frequency range. Comparing the results of present study with those of previous models, particularly for thin shells, leads into good agreements as a result of ignoring the effects of shear and rotation terms on TL. The numerical results of positive Mach number show that TL decreases at the stiffness and coincidence controlled regions with increasing the Mach number but it behaves in opposite manner just in mass-controlled region. In addition, the results indicate that the TL is improved as consequences of decreasing the volume fractions through the thickness of FG cylindrical shells.

Excited and enhanced twinborn acoustic-induced mutual forces in oblique grating structures

We propose a water-immersed geometrically oblique grating structure patterned with a 1D periodic array of oblique rhombuses. Twin acoustic-induced mutual forces (both repulsive and attractive) between coupled steel plates were realized in this system when the external plane wave normally impacted the plates. Calculations showed that the emerging forces are more than an order of magnitude larger than the corresponding induced force of a conventional grating structure. We also found that the strong acoustic-induced mutual forces stem from the resonant excitation of nonleaky flexural Lamb modes in the coupled plates, and that these forces couple more strongly with the external incident acoustic waves. Furthermore, the amplitudes and resonant wavelengths of these forces can be coarsely controlled by changing the symmetry of the system and finely adjusted by varying the slant angle and the edge-length of the oblique rhombus. The proposed acoustic system could potentially be applied in sensors and in the ultrasonic detection of weak signals in water.