A free space frequency‐time‐domain technique for electromagnetic characterization of materials using reflection‐based measurement

In this report, a free space frequency‐time‐domain technique is presented for characterizing the electrical properties and thickness of the sample using multiple reflections and fabry‐perot resonance phenomenon. The retrieval of constitutive electromagnetic parameters of the sample has been carried out by comparing the measured reflection coefficient data from the sample at two different incident angles. The relative permittivity as well as relative permeability along with the thickness of different samples viz., beryllia, silicon, and plexiglass have been evaluated with high accuracy in the frequency range 1 to 15 GHz. The method is also experimentally validated by successfully reconstructing the unknown material properties of two different samples. The unique advantage of this method lies in non‐requirement of any prior knowledge of the sample's thickness for measuring the complex relative dielectric constant as well as relative permeability of the sample. To determine the electromagnetic properties of the sample, the sole knowledge of reflection coefficient data are needed. Moreover, the method does not involve any additional measurement for the reference calibration. The simple, cost‐effective proposed scheme is quite useful in many applications like accurate determination of signal strength in indoor wireless communication, through wall imaging, food industry, and so on.     

Exact piezothermoelastic axisymmetric solution of a finite transversely isotropic cylindrical shell

This work presents an exact piezothermoelastic solution of a finite transversely isotropic piezoelectric cylindrical shell under axisymmetric thermal, pressure and electrostatic excitation. The general solution of the governing equations is obtained in terms of potential functions which satisfy the boundary conditions at the ends. The axisymmetric loadings are expanded as a Fourier series in the axial coordinate. The coefficients in the infinite set of potential functions are obtained by solving sets of six algebraic equations resulting from the satisfaction of boundary conditions at the inner and outer surfaces of the shell for each Fourier component. The inverse problem of inferring the applied temperature and pressure fields from the given measured distribution of electrical potential difference between the inner and outer surfaces of the shell has also been solved. Numerical results are presented for typical pressure, thermal and electrostatic loadings.     

Self-assembly through hydrogen-bonding and C–Hπ interactions in metal complexes of N-functionalised glycine

The complex [Ni(L1)₂(py)₂]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas co-crystals having composition 2[Ni(L1)₂(py)₃(H₂O)] · [Ni(L1)₂(py)₂(H₂O)₂] · 2py · 2H₂O was obtained from solution state reaction.     

Coupled Efficient Zigzag Finite Element Analysis of Piezoelectric Hybrid Beams under Thermal Loads

A new one-dimensional beam finite element is developed for hybrid piezoelectric beams under thermal load, using a coupled efficient layerwise (zigzag) theory developed recently by the authors. The theory accounts for the layerwise variations of the axial and the transverse displacements while keeping the number of displacement variables independent of the number layers. The beam element has two nodes with four mechanical and a variable number of electric potential degrees of freedom at each node. In the thickness direction, the thermal and the electric fields are approximated as piecewise linear across an arbitrary number of sublayers in a layer. Cubic Hermite interpolation is used for the deflection and electric potentials at the sublayers and linear interpolation is used for the axial displacement and the shear rotation. The thermal field is computed using a consistent six-noded thermal finite element with a quadratic interpolation along longitudinal direction and a linear interpolation along thickness direction. The formulation is validated by comparing the results with the Navier-type solution of the zigzag theory for simply-supported hybrid beams. The element is free from shear locking. The accuracy of the zigzag theory is established by comparing the results of hybrid composite and sandwich beams with the two-dimensional finite element results using ABAQUS for cantilever and clamped-clamped end conditions under different thermal loads. The control of thermal deflection by the application of actuation potential is illustrated. The effects of electric boundary conditions and the pyroelectric effect on the response are discussed.     

Three-dimensional piezoelasticity solution for dynamics of cross-ply cylindrical shells integrated with piezoelectric fiber reinforced composite actuators and sensors

A benchmark three-dimensional (3D) exact piezoelasticity solution is presented for free vibration and steady state forced response of simply supported smart cross-ply circular cylindrical shells of revolutions and panels integrated with surface-bonded or embedded monolithic piezoelectric or piezoelectric fiber reinforced composite (PFRC) layers. The effective properties of PFRC laminas for the 3D case are obtained based on a fully coupled iso-field model. The governing partial differential equations are reduced to ordinary differential equations in the thickness coordinate by expanding all entities for each layer in double Fourier series in span coordinates, which identically satisfy the boundary conditions at the simply-supported ends. These equations with variable coefficients are solved using the modified Frobenius method, wherein the solution is constructed as a product of an exponential function and a power series. The unknown constants of the general solution are finally obtained by employing the transfer matrix method across the layers. Results for natural frequencies and the forced response are presented for single layer piezoelectric and multilayered hybrid composite and sandwich shells of revolution and shell panels integrated with monolithic piezoelectric and PFRC actuator/sensor layers. The present benchmark solution would help assess 2D shell theories for dynamic response of hybrid cylindrical shells.     

Investigation of Oxygen-Adsorbed Iron Pnictide Crystals

In this present study, we synthesized a new compound of YbFe₂As₂ crystals by using a melt growth technique. The YbFe₂As₂ crystals had been characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The presence of oxygen was found by EDAX on the surfaces of grown YbFe₂As₂ crystals which had been kept in air ambience for few months. The measurement of magnetization (M) versus temperature (T) using a superconducting quantum interference device (SQUID) at constant magnetic field (H = 100 Oe) for oxygen-adsorbed YbFe₂As₂ (YbFe₂As₂:O₂) had revealed an occurrence of sharp slope change around 140 K. An additional slope change had been observed around 40 K. We had carried out magnetization and transport measurements for oxygen-adsorbed YbFe₂As₂ (YbFe₂As₂:O₂) and oxygen-adsorbed BaFe₂As₂ (BaFe₂As₂:O₂) for comparative study also. M versus T data at H = 10,000 Oe had exhibited a paramagnetic behavior for both YbFe₂As₂:O₂ and BaFe₂As₂:O₂. The result of M versus H measurements at 2 K had shown that the saturation had not been achieved for YbFe₂As₂:O₂ at H = 80,000 Oe. There was a slope change observed in transport measurement for YbFe₂As₂:O₂ at 15 K which was not noticed for BaFe₂As₂:O₂.     

Generative model based robotic grasp pose prediction with limited dataset

Applied Intelligence - In the present investigation, we propose an architecture which we name as Generative Inception Neural Network (GI-NNet), capable of predicting antipodal robotic grasps...     

A metasurface‐based broadband quasi nondispersive cross polarization converter for far infrared region

A broadband nondispersive cross polarization converter (CPC) structure using metasurface for far infrared region has been proposed in this article. The structure is transmittive in nature, which converts a linearly polarized incident wave to its mutually orthogonal linearly polarized wave over a band of frequency ranging from 10.25 to 22.7 THz maintaining a high polarization conversion ratio (PCR) of more than 0.95. The fractional bandwidth of 75.6% corresponding to the center frequency of PCR bandwidth having more than 0.9 PCR value has been realized. The structure is also studied for oblique incidences where it shows wide band polarization conversion up to 45° for both TE and TM polarized oblique incident waves. The electric field distributions at the top and bottom surfaces of the structure close to the center frequency of polarization conversion bandwidth indicate the orthogonal rotation of incident linearly polarized wave at the frequency of interest. For the given set of media interface a separate study on polarization conversion through Brewster angle concept has been carried out simultaneously. The structure exhibits high PCR by maintaining the compactness in thickness (~ λ/5) as well as periodicity (~ λ/3) compared to the existing reported ones.     

Coupled efficient layerwise and smeared third order theories for vibration of smart piezolaminated cylindrical shells

The improved third order zigzag theory and its smeared counterpart (without the zigzag effect), recently developed by the authors for static analysis of piezoelectric laminated cylindrical shells, are extended to dynamics. The piezoelectric layers are considered as radially polarized to make use of the extension actuation mechanism that is best suited for effective actuation and sensing. The zigzag theory accounts for the layerwise variation of inplane displacements and includes the transverse normal extensibility under electric field, and also satisfies the conditions on transverse shear stresses at the layer interfaces and at the inner and outer surfaces of the shell. Yet, the number of primary displacement variables is only five, same as its smeared counterpart. The two theories are critically assessed for their accuracy by direct comparison with the three dimensional piezoelasticity solutions for free and forced vibration response of simply supported smart angle-ply infinite-length and cross-ply finite-length shells, with a variety of heterogeneous composite and sandwich laminates. It is shown that the zigzag theory, in spite of being computationally efficient, is very accurate even for shells with highly inhomogeneous laminates. In contrast, the smeared third order theory is grossly inadequate for smart shells made of inhomogeneous composite and sandwich substrates.