Uniaxial Substrate Research Articles

Theoretical investigation of HTS compact microstrip antennas printed on anisotropic substrates using hybrid cavity model

This work explores the effects of a compact, superconducting C-shaped patch printed on uniaxial anisotropic substrate, utilizing two uniaxial substrate materials: boron nitride and magnesium fluoride. This study employed the superconducting material BSCCO (2212 BSCCO crystal), with a critical temperature of 95 K. Using the hybrid cavity model, we identified and extracted two key parameters: the resonance frequency of conductive elements and the superconducting resonance frequency. We analyzed the impact of the operating temperature on the resonant frequency of a C-shaped superconductivity microstrip antenna, as well as the effect of the uniaxial substrate material and its thickness on the surface resistance and surface reactance. The results showed that temperature significantly affects the resonant frequency of the compact antenna. Our research highlighted the importance of selecting the correct operating temperature for a superconducting microstrip antenna to ensure optimal performance in compact microstrip antenna designs.

Large spatial shifts of reflected light beam off biaxial hyperbolic materials

Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–Hänchen (GH) shift and Imbert–Fedorov (IF) shift in a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically calculates and analyzes the GH shift and IF shift for the natural biaxial hyperbolic material (NBHM). We select the surface with the strongest anisotropy within the NBHM and obtain the complex beam-shift spectrum. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface increases significantly compared with that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86λ 0 at about 841 cm−1 when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7λ 0 for a circularly-polarized beam incident on a 1700-nm-thick NBHM. It is found that the spatial-shift increases when a highly anisotropic hyperbolic polariton is excited in hyperbolic material, where the shift spectrum exhibits an oscillating behaviour accompanied with sharp shift peak (steep slope). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors.

Tip-scan high-speed atomic force microscopy with a uniaxial substrate stretching device for studying dynamics of biomolecules under mechanical stress.

High-speed atomic force microscopy (HS-AFM) is a powerful tool for studying the dynamics of biomolecules in vitro because of its high temporal and spatial resolution. However, multi-functionalization, such as combination with complementary measurement methods, environment control, and large-scale mechanical manipulation of samples, is still a complex endeavor due to the inherent design and the compact sample scanning stage. Emerging tip-scan HS-AFM overcame this design hindrance and opened a door for additional functionalities. In this study, we designed a motor-driven stretching device to manipulate elastic substrates for HS-AFM imaging of biomolecules under controllable mechanical stimulation. To demonstrate the applicability of the substrate stretching device, we observed a microtubule buckling by straining the substrate and actin filaments linked by α-actinin on a curved surface. In addition, a BAR domain protein BIN1 that senses substrate curvature was observed while dynamically controlling the surface curvature. Our results clearly prove that large-scale mechanical manipulation can be coupled with nanometer-scale imaging to observe biophysical effects otherwise obscured.

Enhancement and Manipulation of Near-Field Thermal Radiation Using Hybrid Hyperbolic Polaritons

Owing to a high electromagnetic confinement and a strong photonic density of states, hyperbolic surface plasmon polaritons (HSPPs) provide a fascinating promise for applications in thermal photonics. In this work, we theoretically predict a possibility for the improvement of the near-field radiative heat transfer on the basis of tailoring the electromagnetic state of hyperbolic metasurfaces by the uniaxial hyperbolic substrate. By using the photonic tunneling coefficient and the polaritons dispersion, we present a comprehensive study of the hybrid effect of the hyperbolic substrate on HSPPs. We find that due to the hybrid effect of the hyperbolic substrate, the anisotropy surface state of hyperbolic metasurfaces would undergo significant deformations and even topological transition. Moreover, we systematically exhibit the evolution of such hybrid hyperbolic mode with different thicknesses of the hyperbolic substrate and analyze the thickness effect on radiative properties of the hybrid system. It is shown that the resulting heat transfer with the assistance of the hybrid hyperbolic mode by optimizing the substrate parameters is many times stronger than that of monolayer hyperbolic metasurface at the same vacuum gap. Taken together, our results provide a platform to tailor 2D hyperbolic plasmons as a potential strategy toward passive or active control of the near-field heat transfer, and the hybrid hyperbolic mode presented here may facilitate the system design for near-field energy harvesting, thermal imaging, and radiative cooling applications.

Domain wall depinning from FM/AFM interface defects by spin-polarized current

We report a theoretical investigation of the impact of spin-transfer torque on magnetic head-to-head domain walls of Fe and Ni80Fe20 (Permalloy PyTM) nanowires exchange coupled to a two-sublattice uniaxial antiferromagnetic substrate. Our results indicate that provided the interface exchange interaction is large enough, the domain walls pin to interface defects consisting of steps perpendicular to the easy antiferromagnetic axis, separating terraces with opposite effective interface exchange fields. We also found that the dipolar and interface energies lead to narrow V-shaped domain walls and that the spin-transfer torque effects are restricted to the domain wall. Depinning walls from the step defect at the interface require polarized spin current densities of the order of 107 A/cm2 for both materials.

In silico stress fibre content affects peak strain in cytoplasm and nucleus but not in the membrane for uniaxial substrate stretch.

Existing in silico models for single cell mechanics feature limited representations of cytoskeletal structures that contribute substantially to the mechanics of a cell. We propose a micromechanical hierarchical approach to capture the mechanical contribution of actin stress fibres. For a cell-specific fibroblast geometry with membrane, cytoplasm and nucleus, the Mori-Tanaka homogenization method was employed to describe cytoplasmic inhomogeneities and constitutive contribution of actin stress fibres. The homogenization was implemented in a finite element model of the fibroblast attached to a substrate through focal adhesions. Strain in cell membrane, cytoplasm and nucleus due to uniaxial substrate stretch was assessed for different stress fibre volume fractions and different elastic modulus of the substrate. A considerable decrease of the peak strain with increasing stress fibre content was observed in cytoplasm and nucleus but not the membrane, whereas the peak strain in cytoplasm, nucleus and membrane increased for increasing elastic modulus of the substrate. Finite element mesh of reconstructed human fibroblast and intracellular strain distribution in cell subjected to substrate stretch.

Analysis of the Combinatory Effect of Uniaxial Electrical and Magnetic Anisotropy on the Input Impedance and Mutual Coupling of a Printed Dipole Antenna

The main objective of this work is to investigate the combinatory effects of both uniaxial magnetic and electrical anisotropies on the input impedance, resonant length and the mutual coupling between two dipoles printed on an anisotropic grounded substrate. Three different configurations: broadside, collinear and echelon are considered for the coupling investigation. The study is based on the numerical solution of the integral equation using the method of moments through the mathematical derivation of the appropriate Green’s functions in the spectral domain. In order to validate the computing method and evaluated MatlabⓇ calculation code, numerical results are compared with available literature treating particular cases of uniaxial electrical anisotropy; good agreements are observed. New results of dipole structures printed on uniaxial magnetic anisotropic substrates are presented and discussed, with the investigation of the combined electrical and magnetic anisotropies effect on the input impedance and mutual coupling for different geometrical configurations. The combined uniaxial (electric and magnetic) anisotropies provide additional degrees of freedom for the input impedance control and coupling reduction.

2 × 2 anisotropic transfer matrix approach for optical propagation in uniaxial transmission filter structures.

Multi-layered metamaterial structures show promise in a wide variety of optical applications such as superlenses, electromagnetic cloaking, tunable filters, sensors, and spatial light modulators. Optical transmission analysis of multilayer metallo-dielectric stacks with overall thickness less than the wavelength of light can be modeled using effective medium theory and the Berreman matrix method. For multilayer anisotropic stacks of arbitrary thickness, a rigorous 4 × 4 transfer matrix embodiment is typically used. In this work, a 2 × 2 anisotropic transfer matrix method is developed to analyze optical propagation through multilayer uniaxial stacks of arbitrary thicknesses. Optical transmission of a multilayer silver-zinc oxide stack deposited on a quartz substrate is modeled with this 2 × 2 anisotropic transfer matrix method and reconciled with experimental observations. Results indicate that this numerical approach is applicable to in situ assessment of the complex refractive indices of constituent metal and dielectric layers. Additionally, the anisotropic 2 × 2 transfer matrix method enables the possibility of modeling the transmission of the same metallo-dielectric structure deposited on an electro-optic, uniaxial substrate. Simulation results predict that adjusting the bias field across the substrate results in an electrically tunable transmission filter.

Optical surface plasmons at a metal-crystal interface with the Drude-Lorentz model for material permittivity

The theory of surface electromagnetic waves (SEMWs) propagating at optical frequencies along the interface of an isotropic metallic plasma [e.g., gold (Au)] and a uniaxial crystal [e.g., Rutile (TiO2)] is revisited with the Drude-Lorentz (DL) model for the complex dielectric material permittivity (ϵp). The latter accounts for the contributions of both the intraband transitions of the free electrons and the multiple interband transitions of the bound electrons in metals. The propagation characteristics of the wave vectors and wave frequency of SEMWs, the hybridization factors, i.e., the amplitude ratios between the transverse-electric (TE) and transverse-magnetic (TM) modes in the isotropic metal, and between the ordinary and extraordinary modes in the uniaxial substrate are studied numerically. It is found that the results are significantly modified from those with the Drude model for ϵp, especially in the short-wavelength spectra (λ ≲ 500 nm) and with a small deviation of the orientation of the optical axis. The excitation of such SEMWs can have novel applications in transportation of EM signals in a specified direction at optical frequencies (∼PHz).

Development and validation of a device for in vitro uniaxial cell substrate deformation with real-time strain control

Substrate deformation affects the behaviour of many cell types, including bone, skeletal muscle and endothelial cells. Nowadays, in vitro tests are widely employed to study the mechanotransduction induced by substrate deformation. The aim of in vitro systems is to properly reproduce the mechanical stimuli sensed by the tissue in the cellular microenvironment. Accurate strain measurement and control is therefore necessary to ensure the cell senses the proper strain for the entire treatment. Different types of in vitro systems are commercially available or can be custom-designed; however, none of these devices performs a real-time measurement of the induced strains. In this study, we proposed a uniaxial strain device for in vitro cell stimulation with an innovative real-time strain control. The system was designed to induce sinusoidal waveform stimulation in a huge range of amplitude and frequency, to three silicone chambers stretched by a linear actuator. The real-time strain measurement and control algorithm is based on an optical tracking method implemented in LabVIEW 2015, and it is able to adapt the input amplitude to the linear motor, if necessary, hanging the stimulation signal for about 120 ms. Validation of the strain values measured during the real-time tracking algorithm was carried out through a comparison with the digital image correlation (DIC) technique. We investigated the influence of number of reference points and image size on the algorithm accuracy. Experimental results showed that the tracking algorithm allowed for a real-time measurement of membrane longitudinal strains with a relative error of 0.3%, on average, in comparison to the strains measured with DIC in post-processing analysis. We showed a high homogeneity of the strain pattern on the entire chamber base for different stimulation conditions. Finally, as proof of concept, we employed the uniaxial strain device to induce substrate deformation in a human osteosarcoma cell line (SaOS-2). The experimental results showed a consistent change in cell shape in response to the mechanical strain.

Discrete element simulation of damage evolution in coatings

This paper aims to use discrete element method (DEM) to investigate the cracking and interfacial delamination in ceramic coatings under uniaxial substrate tension. In DEM, the domain of the problem is discretized with a set of dense packing random arrangement of particles bonded together with springs or beam elements. In this method, partial damages can be well described which gives new insights into the qualitative description of damages in ceramic coating/substrate structures. A DEM solver code and dense particle packing generator has been developed by the authors. Yttria-stabilized zirconia is considered as an example of ceramic coatings which is usually used as a thermal insulator for superalloy substrates. A unit cell of ceramic coating/substrate structure was considered with three coating thicknesses and the effect of coating thickness was investigated on damage initiation and propagation. The results showed that the coating thickness affects the damage initiation mechanism. In addition, the structures with thick coatings are more susceptible to interfacial delamination.

Qualitative description on channel cracking in ceramic type coatings due to substrate tension using 3D discrete element method

The objective of this work is to simulate qualitatively the initiation and propagation mechanism of channeling cracks in ceramic coatings due to uniaxial and biaxial substrate tension. Most of the previous simulations on damage evolution in coating/substrate structures were performed in 2D; however, in the current study, to demonstrate the damage evolution both in coating thickness and surface, several numerical simulation was performed in the 3D space frame. To this end, a FORTRAN code of Discrete Element Method (DEM) with Euler-Bernoulli beam bond elements and the random spherical arrangement was developed. Furthermore, the brittle fracture criterion was assigned for the coating while the substrate was considered to have linear elastic and isotropic behavior and to remain intact during loading. Three unit cells with the same dimensions and different coating thicknesses were considered. It was found that the coating thickness affects the damage initiation mechanism. In both uniaxial and biaxial tension, the increase of the coating thickness resulted in damage initiation near the interface and propagation to the top surface. At the surface view, the results showed that the free surfaces and edges could be susceptible to damage initiation in thin coatings.

Variation in phase diagrams of strained (011) epitaxial BaTiO3 thin films

Phenomenological theory based on sixth-order and eighth-order potentials are used to investigate the effect of variation in free energy coefficients and material constants on phase stability of single-domain (011)-oriented epitaxial BaTiO3 subject to both biaxial and uniaxial substrate constraints. Relative size of a variety of ferroelectric regions in the computed misfit strain phase diagrams is systematically examined. The computed Curie phase transition and subsequent polarization rotation and formation of low-symmetry monoclinic structures are dependent on the selection of potentials and variation in electrostrictive and elastic constants, and such dependence is found to be closely associated with in-plane strain anisotropy.

A study on failure of double-layer thermal barrier coatings subjected to uniaxial compression tests using acoustic emission analysis and digital image correlation

The failure behavior and fracture process of double-layer thermal barrier coatings under uniaxial compressive substrate loading has been investigated. Coating systems containing GZO with low and high porosity (LP, HP) were fabricated to examine the influence of microstructure on failure behavior and strain energy. An YSZ-HP single-layer system serves as a reference. All ceramic coatings were deposited via atmospheric plasma spraying (APS) on cylindrical rods and turbine blade-shaped specimens made from CoNiCrAlY (LCO-22) coated, nickel-based, single crystal superalloy (PWA 1483). Prior to compression tests, isothermal pre-oxidation at 1050 °C and dwell-times of 100, 500 and 1.500 hours, as well as cyclic annealing tests between 50 and 1050 °C up to 500 cycles were performed, to study the effects of thermal ageing on strain energy to failure. In-situ acoustic emission (AE) measurements provides quantitative information about the failure processes under compressive substrate loading. A stereo camera system monitors the three-dimensional displacements and the surface fracture processes. For as-sprayed coatings, strain to failure of the investigated GZO/YSZ systems is comparable to the referenced single-layer TBC. AE analysis indicates coating failure at earlier stages and less substrate loads after thermal ageing with increasing dwell-time. Consequently, the pre-oxidation leads to reduced strain to failure values in all investigated coating systems. Digital image correlations (DIC) suggests that the failure behavior of as-sprayed GZO/YSZ coatings is similar to the referenced YSZ system. However, a different behavior was observed for pre-oxidized coatings, where cracking and spallation of GZO occurs predominantly.

A Comprehensive Method for Accurate Strain Distribution Measurement of Cell Substrate Subjected to Large Deformation.

Cell mechanical stretching in vitro is a fundamental technique commonly used in cardiovascular mechanobiology research. Accordingly, it is crucial to measure the accurate strain field of cell substrate under different strains. Digital image correlation (DIC) is a widely used measurement technique, which is able to obtain the accurate displacement and strain distribution. However, the traditional DIC algorithm used in digital image correlation engine (DICe) cannot obtain accurate result when utilized in large strain measurement. In this paper, an improved method aiming to acquire accurate strain distribution of substrate in large deformation was proposed, to evaluate the effect and accuracy, based on numerical experiments. The results showed that this method was effective and highly accurate. Then, we carried out uniaxial substrate stretching experiments and applied our method to measure strain distribution of the substrate. The proposed method could obtain accurate strain distribution of substrate film during large stretching, which would allow researchers to adequately describe the response of cells to different strains of substrate.

A new efficient and proper modeling of isotropic/uniaxial anisotropic substrate specifications in design procedures of metasurfaces

Specifications of the substrates are among the most important and problematic parameters that still do not have proper models in the design procedures of metasurfaces. In this paper, a new fast and exact algorithm based on artificial neural networks (ANNs) is presented, which makes it possible to design frequency-selective surfaces (FSSs) on various kinds of standard substrates. Also for the first time, designing FSSs on uniaxial anisotropic substrates can be easily done in short time and without any optimization algorithms. During this paper, first equivalent geometry approach (EGA) is demonstrated as a new method of preparation the ANNs. Then EGA is used to train geometry transformation ANNs. The advantage of this approach is to reduce the size of training datasets by about 98% and prevent from superfluous simulations. Hence, the time needed for training of the networks is much less than before. Numerical results are used to show that the required time for developing FSSs is <200 ms on average, and errors are <2%. For the final validation, a prototype sample of FSS is fabricated on the RO4003 substrate with 20 mil thickness. Both analytical and experimental results confirm the correctness of the predicted values.

Cartesian Decomposition of Infrared Spectra Reveals the Structure of Solution-Deposited, Self-Assembled Benzoate and Alkanoate Monolayers on Rutile (110)

Cartesian polarization analysis transforms a set of surface infrared spectra obtained in different geometries into their Cartesian components using a mathematical transform, providing direct insight into the bonding geometry of adsorbed molecules. This technique was extended to uniaxial substrates and used to analyze solution-deposited, self-assembled benzoate and alkanoate monolayers on rutile (110). This analysis resolved a long-standing controversy regarding the existence of paired molecules in benzoate monolayers, showing that two distinct isomers exist within the monolayer: a tilted tetramer, which is paired, and a twisted monomer, which is not. The two isomers are nearly isoenergetic, as shown by analysis of STM images and complementary DFT simulations. Infrared and XPS spectra as well as STM images of heptanoate and octanoate monolayers showed the formation of complete monolayers (as opposed to sparse layers or multilayers); however, the alkyl chains in the monolayer are disordered and loosely pack...

Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism

Optical whispering gallery mode (WGM) resonators are a powerful and versatile tool used in many branches of science. Fine tuning of the central frequency and line width of individual resonances is however desirable in a number of applications including frequency conversion, optical communications and efficient light-matter coupling. To this end we present a detailed theoretical analysis of dielectric tuning of WGMs supported in axisymmetric resonators. Using the Bethe-Schwinger equation and adopting an angular spectrum field representation we study the resonance shift and mode broadening of high $Q$ WGMs when a planar dielectric substrate is brought close to the resonator. Particular focus is given to use of a uniaxial substrate with an arbitrarily aligned optic axis. Competing red and blue resonance shifts ($\sim 30$ MHz), deriving from generation of a near field material polarisation and back action from the radiation continuum respectively, are found. Anomalous resonance shifts can hence be observed depending on the substrate material, whereas mode broadening on the order of $\sim 50$ MHz can also be simply realised. Furthermore, polarisation selective coupling with extinction ratios of $> 10^4$ can be achieved when the resonator and substrate are of the same composition and their optic axes are chosen correctly. Double refraction and properties of out-coupled beams are also discussed.

Design of Heterogeneous Nuclei for Lateral Crystallization via Uniaxial Assembly of Cellulose Nanocrystals

Semicrystalline polymers (SCPs) represent a group of cheap heterogeneous nuclei for crystallization. Nevertheless, cellulose, the most abundant biogenic SCP, is notorious for its poor processability. This limits its application as the orientational guiding agent in crystallization of functional compounds. Different from current polymer engineering approaches to uniaxial SCP thin films, we explored a novel approach to the uniaxial cellulose thin film via the oriented assembly of cellulose nanocrystals (CNCs) by means of a simple dip-coating technique. This thin film successfully guides the lateral crystallization of two drug compounds, which in turn reflects the uniformity of the uniaxial CNC alignment on the macroscopic scale. Furthermore, unlike traditional SCP thin films, the assembly route driven by different external forces can lead to CNC thin films with distinct orientational characters for fabrication of patterned drug thin films. The emerging colloidal assembly route to a uniaxial SCP substrate le...

Spectral Solution for Scattering Analysis of Periodic Plasmonic Nano-antennas on Iso/Anisotropic Substrate

A fast solution for the scattering analysis of periodic plasmonic nano-antennas (PPNAs) on iso/anisotropic substrates is presented. This method is based on derivation of the spectral dyadic Green's function with taking into account the plasmonic effects. The obtained dyadic Green's function is then used in an integral equation formulated for computing the induced surface current densities on the PPNAs. The resultant integral equation is solved by means of Galerkin's Method of Moments with entire-domain basis and test functions. With the help of this computational technique, the scattering characteristics of several examples are analyzed. The computed results are validated by means of a full-wave EM solver based on finite element method. For showing the efficiency of this method, the convergence rate and computation time in terms of space harmonic orders are calculated. It is shown that the developed method is an efficient and speedy technique for the analysis of such periodic plasmonic structures. In addition, we study an array of PPNAs on a uniaxial anisotropic substrate where the scattering characteristics are calculated as a function of the optic-axis direction. It is found that using anisotropic materials as the substrate of PPNAs allows additional degrees of freedom for controlling the scattering information.