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Low-frequency dielectric spectroscopy and distinct relaxation modes in smectic phases of liquid crystal dimers
摘要： Low-Frequency (LF~20Hz–10MHz) ac field response and relaxation modes are investigated in layered liquid crystalline (LC) smectic phases exhibited by Hydrogen bonded dimers, viz., nOnBA:MA:nOBA’s with sort spacer moiety and long flexible end chains for n=10,11 and 12. Permittivity (ε') and loss (ε'') determined from capacitance and loss factor. Phase transition temperatures (Tc) are determined. Intra-molecular aromatic interaction and storage capacity are evinced by hysteresis behavior. Data of loss ε''(ω) and permittivity ε'r(ω) recorded in smectic phases infers non-Debye type of asymmetric dispersion. Multiple loss peaks in ε''(ω) is argued to involve distinct time scaled relaxations. Relaxation analyzed by Cole-Davidson method. Re-orientation of longitudinal dipole moment μ to the field analyzed. μ is resolved by rigid core, intra-molecular repulsive and flexible end-chain components. Observed distinct time scale response confirms dipolar components. Trends of relaxation frequency, activation energy, loss maxima, dielectric strength and distribution parameter are analyzed in device perspective. Relaxation and order director fluctuations analyzed. ODF suggest the device utility in high temperature smectic phases far away from critical fluctuations.
关键词： Order Director Fluctuations,Relaxation,Permittivity,Resolved dipole moment,Activation energy,Reorientation,Loss
更新于2025-09-23 15:23:52
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An enhanced circular polarization near-field focused antenna array by director patches
摘要： This paper presents an enhanced circular polarization (CP) near-field focused (NFF) antenna array. There exist three advantages for the CP NFF antenna. First, this study provides an effective way to realize the CP and NFF simultaneously and do not need to design a specific patch shape for CP, which provides more freedom to change the patch shape for improving other performances. The effective way is arranging the element excitation according to maximum power transmission efficiency theory under the condition of a CP testing antenna. Second, the array element consists of a driven and director patches, and the director patches tilt the element beam from broadside direction to focal point, and then obviously enhance the electric field focusing gain. Third, the proposed array antenna achieves much less size of focal point by using much less element number than published papers. The curves for the impedance and axial ratio (AR) as function of frequency, focus width and depth are analyzed. The simulated and measured results basically agree.
关键词： antenna array,circular polarization (CP),near-field focused (NFF) antenna,director patch
更新于2025-09-23 15:21:01
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Piezoelastic response of smart functionally graded structure with integrated piezoelectric layers using discrete double directors shell element
摘要： The purpose of the paper is to predict the electromechanical behavior of composite shell structures with embedded piezoelectric layers using 3D-shell model based on a discrete double directors shell element. The implementation is applicable to the analysis of isotropic and functionally graded shells with integrated piezoelectric layers. The third-order shear deformation theory is introduced in the present method to remove the shear correction factor and improve the accuracy of transverse shear stresses. The present results were compared with reference solutions from literature in order to verify the accuracy of the present formulation and excellent agreement was found. A parametric study is carried out to highlight the in?uence of material composition and curvature radius on the de?ection and axial stress along the thickness.
关键词： Active functionally graded shells,Finite element analysis,Double director shell,Piezoelectric sensors/actuators,Smart structures
更新于2025-09-10 09:29:36
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Cylindrical nematic liquid crystal shell: effect of saddle-splay elasticity
摘要： This study introduces cylindrical nematic liquid crystal (LC) shells. Shells as confinement can provide soft matter with intriguing topology and geometry. Indeed, in spherical shells of LCs, rich defect structures have been reported. Avoiding the inherent Plateau–Rayleigh instability of cylindrical liquid–liquid interfaces, we realize the cylindrical nematic LC shell by two different methods: the phase separation in the nematic–isotropic coexistence phase and a cylindrical cavity with a glass rod suspended in the middle. Specifically, the director configurations of lyotropic chromonic LCs (LCLCs) in the cylindrical shell and their energetics are investigated theoretically and experimentally. Unusual elastic properties of LCLCs, i.e., a large saddle-splay modulus, and a shell geometry with both concave and convex curvatures, result in a double-twist director configuration.
关键词： cylindrical nematic liquid crystal shells,lyotropic chromonic LCs,double-twist director configuration,saddle-splay elasticity
更新于2025-09-10 09:29:36
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Numerical Modeling of the Static Electric Field Effect on the Director of the Nematic Liquid Crystal Director
摘要： A two-dimensional model of the Frederiks effect is used to investigate the static electric field effect on the orientation of the nematic liquid crystal (LC) director in a side-electrode cell. The solutions are obtained by the standard finite-difference methods. The programs for the numerical solution of a two-dimensional parabolic partial differential equation are developed both in FORTRAN and C/C++. The Frederiks transition threshold for the central part of the cell and the dependences of the director’s orientation distribution on a high electric field are obtained. The results of the calculation are compared with the experimental data.
关键词： nematic liquid crystal,two-dimensional model of the Fredericks effect,finite-difference methods,electric field,director,numerical solution
更新于2025-09-09 09:28:46
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A Novel Deployable Quasi-Yagi Monopole Antenna using Three Origami Magic Spiral Cubes
摘要： We propose a deployable quasi-Yagi monopole antenna using origami magic spiral cubes, constructed from low cost paper substrate. The proposed quasi-Yagi antenna consists of an L-shaped driven monopole, an L-shaped reflector, and two L-shaped directors. These driven monopole, reflector and directors are designed in L-shaped geometries to achieve maximum gain in a limited cube size. The driven element and reflector are realized on the origami magic cube #1, while the two directors are designed on the magic cubes #2 and #3, respectively. The cubes are stacked together using a thin adhesive film. The presented geometry of the origami magic spiral cube antenna can be easily folded and unfolded. The dimensions in the unfolded state are 44 mm × 44 mm × 132 mm while the dimensions in the folded state are 44 mm × 44 mm × 8 mm. Therefore, in the folded state, the antenna occupies only 6% of the unfolded volume. We have numerically analyzed the antenna performance and verified the outcomes experimentally. The L-shaped reflector has increased the monopole antenna gain from 1.9 to 5.7 dBi. With the addition of two directors, the gain is further increased to 7.3 dBi at 1.9 GHz.
关键词： Origami magic cube,director,reflector,driven element,deployable Yagi antenna
更新于2025-09-09 09:28:46