Uniaxial Substrate Research Articles

Printed monopole antennas on uniaxial substrate: theory and simulation

The performance of printed monopole antennas (PMAs) on uniaxial substrate is studied and the same is theoretically analysed using spectral domain immittance approach. Using immittance approach, field components of unit current source is evaluated first and then directivity is also calculated. The theoretical values of the far-field radiation pattern and directivity of uniaxial substrate based rectangular PMAs are validated by high frequency structure simulator (HFSS), whereas return loss is calculated using HFSS.

Spectral Domain Analysis of Resonant Characteristics of High Tc Superconducting Rectangular Microstrip Patch Printed on Isotropic or Uniaxial Anisotropic Substrates

In this paper, radiation characteristics of the perfectly superconducting, or an imperfectly conducting rectangular microstrip, which is printed on isotropic or uniaxial anisotropic substrate are investigated using a Fourier transforms domain in conjunction with the stationary phase method. The effects of uniaxial anisotropy on the resonant frequency, half-power bandwidth, and radiation patterns are investigated as the function of anisotropy ratio values of substrate materials. It is found that the resonant frequency and the half-power bandwidth are affected significantly by the superconductivity property of the patch. Further results show that a thin superconductor patch has a significant effect on the radiation pattern. Results are compared with previously published data and are found to be in good agreement.

Arbitrary Beam Shaping Using 1-D Impedance Surfaces Supporting Leaky Waves

A technique for generating an arbitrary, prescribed radiation pattern from a 1-D leaky-wave antenna is presented. The technique is applied to leaky-wave impedance surfaces. A homogenized model for an impedance surface is used so that the work is not limited to particular geometries. The model consists of a grounded, uniaxial dielectric substrate topped by a reactance sheet. To synthesize prescribed aperture fields, the leakage constant α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> and phase constant β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> along the antenna are tailored. The aperture field is determined by adapting the Orchard-Elliott method used in array synthesis to continuous line sources. The aperture field is related to α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> and β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> using a well-known approach, then the transverse resonance technique is employed to analytically relate α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> and β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> to the electrical parameters of the impedance surface. Specifically, the extraordinary index and sheet reactance are used to control α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> and β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">||</sub> . The designs presented demonstrate the synthesis of a variety of far-field patterns. Full-wave simulations show an improvement over previous beam synthesis techniques based on geometrical optics. Moreover, the numerical techniques demonstrate an efficient, gradient search method as an alternative to the iterative FFT methods explored previously, which have not generated radiation patterns with such high accuracy.

Device-based in vitro techniques for mechanical stimulation of vascular cells: a review.

The most common cause of death in the developed world is cardiovascular disease. For decades, this has provided a powerful motivation to study the effects of mechanical forces on vascular cells in a controlled setting, since these cells have been implicated in the development of disease. Early efforts in the 1970 s included the first use of a parallel-plate flow system to apply shear stress to endothelial cells (ECs) and the development of uniaxial substrate stretching techniques (Krueger et al., 1971, "An in Vitro Study of Flow Response by Cells," J. Biomech., 4(1), pp. 31-36 and Meikle et al., 1979, "Rabbit Cranial Sutures in Vitro: A New Experimental Model for Studying the Response of Fibrous Joints to Mechanical Stress," Calcif. Tissue Int., 28(2), pp. 13-144). Since then, a multitude of in vitro devices have been designed and developed for mechanical stimulation of vascular cells and tissues in an effort to better understand their response to in vivo physiologic mechanical conditions. This article reviews the functional attributes of mechanical bioreactors developed in the 21st century, including their major advantages and disadvantages. Each of these systems has been categorized in terms of their primary loading modality: fluid shear stress (FSS), substrate distention, combined distention and fluid shear, or other applied forces. The goal of this article is to provide researchers with a survey of useful methodologies that can be adapted to studies in this area, and to clarify future possibilities for improved research methods.

On the performance of microstrip antenna embedded in composite laminated substrates

AbstractFiber‐reinforced composite structures can be tailored to desire mechanical properties and to embed microstrip antenna in aerospace applications. The electromagnetic characteristics of a microstrip antenna on isotropic and uniaxial substrates have been known, but that embedded in composite laminated substrates remain unavailable to date. This work aims at analyzing the performance of microstrip antenna embedded in composite laminated substrates by spectral domain analysis. Parameter studies are conducted to investigate the effects of the substrate's dielectric constants, the fiber directions (the orientation between the antenna and the laminate layers), and the stacking sequence on antenna's resonant frequency and radiation pattern. The antenna size when embedded in composite laminated substrates is larger than that when attached on isotropic substrates, or conversely, the resonant frequency will deviate lower if assuming the substrate as isotropic. The far‐field pattern in composite laminated substrates is more ‘directional’ than that in isotropic substrates. The antenna gain in the substrates of symmetric stacking with ±45° fiber direction is 20 dB better than that in isotropic substrates in some elevations. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Analysis of Annular Ring Microstrip Antenna with Air Gap and Uniaxial Substrate Superstrate Layers

Analysis of superstrate loaded, air gap tuned annular ring microstrip antenna is performed and effects of air gap tuning on the resonant frequency are investigated. Results obtained indicate that due to air gap tuning, resonant frequency can be incrementally or decrementally changed depending on the adjustment of anisotropy ratio of substrate and superstrate layers. Results can be used to obtain tunable, wideband antenna operation.

Characteristics of a high Tc superconducting rectangular microstrip patch on uniaxially anisotropic substrate

Resonant characteristics of a high Tc superconducting rectangular microstrip patch printed on uniaxially anisotropic substrate are investigated using a full-wave spectral analysis in conjunction with the complex resistive boundary condition. The uniaxial medium shows anisotropy of an electric type as well as anisotropy of a magnetic type. Both permittivity and permeability tensors of the substrate are included in the formulation of the dyadic Green’s function of the problem. The accuracy of the analysis is tested by comparing the computed results with previously published data for several anisotropic substrate materials. Numerical data of the resonant frequency and bandwidth as a function of electric anisotropy ratio are presented. Variations of the resonant frequency and bandwidth with the magnetic anisotropy ratio are also given. Finally, results showing the influence of the temperature on the resonant frequency and quality factor of the high Tc superconducting rectangular microstrip patch on a uniaxial substrate are also given.

Characterization of Superstrate-Loaded Resistive Rectangular Patch Antenna

The scattering radar cross section (RCS) of a superstrate loaded resistive rectangular microstrip patch which is printed on isotropic or uniaxial anisotropic substrate are investigated, where an accurate design based on the moment method technique in the spectral domain is developed. Entire domain sinusoid basis functions without edge condition and roof top sub-domain basis functions are introduced to expand the unknown current on the metal patches. The integral equation includes a superstrate resistive boundary condition on the surface of the patch and the effects of anisotropic substrate are developed. The necessary terms for representing the surface resistance on the patch were derived and were included in the equation in the form of a resistance matrix. Comparative study between our results and those available in the literature is done and showed a very good agreement.

Plasmons in graphene on uniaxial substrates

Placing graphene on uniaxial substrates may have interesting application potential for graphene-based photonic and optoelectronic devices. Here, we analytically derive the dispersion relation for graphene plasmons on uniaxial substrates and discuss their momentum, propagation length, and polarization as a function of frequency, propagation direction, and both ordinary and extraordinary dielectric permittivities of the substrate. We find that the plasmons exhibit an anisotropic propagation, yielding radially asymmetric field patterns when a point emitter launches plasmons in the graphene layer.

FULL-WAVE ANALYSIS OF ANISOTROPIC CIRCULAR MICROSTRIP ANTENNA WITH AIR GAP LAYER

In this paper, the efiect of both uniaxial anisotropy in the substrate and air gap layer on the resonant frequency and bandwidth of circular microstrip patch are investigated. The problem is rigorously formulated based on the spectral domain technic in conjunction with Galerkin approach for computing the resonant frequency, half-power bandwidth, and radiation fleld of a tunable circular patch antenna which is printed on isotropic or uniaxial anisotropic substrate. The TM set of modes issued from the magnetic wall cavity model theory are used to expand the unknown currents on the patch. Resonant frequency shift due to uniaxial anisotropy is flrstly investigated for difierent anisotropy ratio values of substrate. Then, the efiect of inclusion of air gap layer inserted between anisotropic substrate and ground plane on the resonance characteristics is also investigated. The results obtained from this approach are in very good agreement with the experimental results available in the literature.

Resonant Frequency of Tunable Microstrip Ring Antenna Printed on Isotropic or Uniaxially Anisotropic Substrate

In this study, the resonant frequency of annular ring microstrip resonator with uniaxial anisotropic substrate and air gap layer is analyzed. The cavity model for simple ring microstrip antenna is extended with some modifications for the tunable geometry taking into account the anisotropy in the layer. The theoretical resonant frequency results are in very good agreement with the experimental results reported elsewhere. The air gap tuning effect on the resonant characteristics is also investigated for fundamental and higher order modes.

The extended magneto optic method to explore the Longitude Magneto Optic Kerr effect of the ultrathin magnetic film grown on optic uniaxial substrate

A general method to solve the Magneto optic effect of the multilayer ultrathin films grown on the optic uniaxial crystal substrate has been developed by using a new boundary matrix. Based on this method, we can apply the magneto optic to any magnetic ultrathin film grown on uniaxial substrate as long as we choose a proper coordinate system. The formula for longitude Magneto Optical Kerr effect is derived to find out the influence of the optic properties of the uniaxial crystal on the magneto optic characteristics of multilayer system. A numerical simulation was carried out to find out the relation between Kerr rotation and optic properties of substrate. The result can be used to select the best suitable substrate on which the sample grown.

Surface plasmon propagation in a metal strip waveguide with biaxial substrate

Surface plasmon propagation in a nano metal strip waveguide with a biaxial substrate material was studied. The dispersion of the four fundamental modes propagating in the strip waveguide structure was analysed using a formalism based on the method of lines. The propagation properties of these modes with respect to the thickness of the metal film was studied, with two different biaxial materials as substrate for the waveguide. The results were then compared with the asymmetric strip waveguide structures with isotropic substrate and a uniaxial anisotropic substrate. Propagation characteristics as a function of longitudinal and transverse anisotropic components of the substrate material were also studied. The characteristics of the fundamental modes are observed to vary depending on the anisotropy of the biaxial material used.

The RCS of a Resistive Rectangular Patch Antenna in a Substrate-Superstrate Geometry

The scattering radar cross section (RCS) and the resonant frequency problem of a superstrate loaded resistive rectangular microstrip patch which is printed on isotropic or uniaxial anisotropic substrate are investigated, where an accurate design based on the moment method technique is developed. The choice of two types of basis functions (entire domain and roof top functions) is illustrated to develop the unknown currents on the patch. The accuracy of the computed technique is presented and compared with other computed results.

Phase modulator birefringence effect on multibound soliton formation in an active mode-locked fiber laser

Multibound solitons generated in an active mode-locked fiber ring resonator can be considered to offer some significant applications in the coding for optical packet transmission. Optical phase modulators (PMs) incorporated in such fiber ring resonators are fabricated in uniaxial birefringent crystal substrate and thus influence both polarized modes of a coupled linearly polarized mode from a weakly guiding fiber forming the ring. Thus there are two polarized rings in such a structure of the active mode-locked fiber ring resonators. They are coupled and interact with each other in the generation of multibound solitons. This paper thus studies the influence of two types of electrodes for phase modulation, lumped and traveling wave, in such birefringent fiber active ring resonators, and hence the transitional formation of multibound solitons. It is shown that there exist comblike spectral components in the ring cavity due to the birefringence property of the PM. Furthermore, the narrow free spectral range of the ring resonator limits the pulse shortening and hence the formation of the multibinding of solitons.

Dispersion of plasmon polaritons guided by a metal film of finite width deposited on a uniaxial substrate

We discuss the propagation characteristics of surface plasmon modes supported by a thin lossy metal film of finite width deposited on a uniaxially anisotropic substrate, numerically evaluated using the method of lines. The metal film with finite width (strip waveguide) has been a subject of intensive study, both theoretically and experimentally, since it is the platform of choice for constructing plasmon circuits for optoelectronic integration, over the past few years. Plasmon waveguides with anisotropic dielectric environment have gained importance in research recently. Specifically, artificial substrate materials with strong anisotropy have been proposed as a means of improving the propagation range of plasmon polaritons in wide metal films. In our investigation, it is observed that the anisotropic nature of the substrate removes the degeneracy of the fundamental pair modes which are degenerate in an asymmetric strip waveguide with isotropic substrates.

A Model for Stress Fiber Realignment Caused by Cytoskeletal Fluidization During Cyclic Stretching

Uniaxial cyclic substrate stretching results in a concerted change of cytoskeletal organization such that stress fibers (SFs) realign away from the direction of stretching. Recent experiments revealed that brief transient stretch promptly ablates cellular contractile stress by means of cytoskeletal fluidization, followed by a slow stress recovery by means of resolidification. This, in turn, suggests that fluidization, resolidification and SF realignment may be linked together during stretching. We propose a mathematical model that simulates the effects of fluidization and resolidification on cytoskeletal contractile stress in order to investigate how these phenomena affect cytoskeletal realignment in response to pure uniaxial stretching of the substrate. The model comprises of individual elastic SFs anchored at the endpoints to an elastic substrate. Employing the global stability convention, the model predicts that in response to repeated stretch-unstretch cycles, SFs tend to realign in the direction perpendicular to stretching, consistent with data from the literature. The model is used to develop a computational scheme for predicting changes in cell orientation and polarity during stretching and how they relate to the underlying alterations in the cytoskeletal organization. We conclude that depletion of cytoskeletal contractile stress by means of fluidization and subsequent stress recovery by means of resolidification may play a key role in reorganization of cytoskeletal SFs in response to uniaxial stretching of the substrate.

Transmission of electromagnetic waves through sub-wavelength channels

We propose a method of tunneling electromagnetic (EM) waves through a channel with sub-wavelength cross section. By filling the channel with high-epsilon isotropic material and implementing two matching layers with uniaxial metamterial substrates, the guided waves can go through the narrow channel without being cut off, as if it has just passed through the original empty waveguide. Both the magnitude and phase information of the EM fields can be effectively restored after passing this channel, regardless of the polarization of the incoming wave. The performance of this sub-wavelength channel, which is designed with coordinate transformation methodology, is studied theoretically and numerically.

SYNTHESIS OF SUPERCONDUCTING CIRCULAR ANTENNAS PLACED ON CIRCULAR ARRAY USING A PARTICLE SWARM OPTIMISATION AND THE FULL-WAVE METHOD

In this paper, synthesis of superconducting circular antennas mounted on circular array is designed by the combination of a method based on particle swarm and a full-wave method. Full- wave method is used for computing the resonant frequency, bandwidth, radiation pattern and the e-ciency of a perfectly superconducting, or an imperfectly conducting circular microstrip, which is printed on isotropic or uniaxial anisotropic substrate. Particle Swarm Optimization (PSO) has been used to obtain the minimum side lobe level (SLL) of circular array, by varying elements excitations and/or positions. Numerical results concerning the efiect of the parameters of substrate and superconducting patch on the antenna performance are presented and discussed. It is found that superconducting circular antenna could give high e-ciency. Also, results show the e-ciency of PSO in producing desired radiation characteristics and are in good agreement with previously published data.

Optimization of superconducting antenna arrays using RBF neural network

In this work, RBF neural network is used to optimize the radiation pattern of non-uniform linear arrays of High superconducting rectangular microstrip antennas, on uniaxial anisotropic substrate. Using superconductors can reduce the insertion loss, and obtain a rather high gain. The full-wave method is used to computing the resonant frequency, and radiation pattern of superconducting rectangular antennas. Galerkin method is used in the resolution of the electric field integral equation. The radial basis function neural network is able to obtain feasible solutions, for the array by matching the desired Di and actual array patterns Fi. The results obtained from the simulation show that we reached our goals by a great degree of validity.