Evolutionary optimization of Haferman carpet fractal patterned antenna array

This article investigates radiation characteristics of a new type of fractal shaped antenna array based on Haferman carpet geometry. An iterative feed matrix eases the complexity of array factor calculation that makes the array factor suitable for the application of any evolutionary optimization techniques. It is seen that Haferman carpet array produces peak side lobe level (PSLL) better than Sierpinski carpet that produces ?10 dB PSLL at every stage of growth. Optimization techniques have been applied for array element reduction and PSLL minimization at different stages of growth. Here, PSLL is minimized by turning off array elements and also by varying inter element spacing between the array elements. The optimized version of Haferman carpet array produces better characteristics (49.38% thinning with ?20.5 dB PSLL for stage‐2, 46.3% thinning with ?22 dB PSLL for stage‐3 and 42.3% thinning with ?21dB PSLL for stage‐4) than its original counterpart in terms of reduced element count and PSLL. Numerical results for obtaining optimized array performance exploit both DE as well as PSO. A comparative study on the performance is also presented. As a whole, Haferman carpet is seen to be more effective approach than Sierpinski carpet in fractal antenna paradigm. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:719–729, 2015.     

Novel method for characterisation of single-mode fibres and prediction of crossover wavelength and bandpass in nonidentical fibre directional couplers

We present here a novel and accurate method for the characterisation of single-mode fibres from a measurement of the wavelength dependence of the Petermann spot size. We also show its applicability in the prediction of the crossover wave length and bandpass in wavelength filters using nonidentical fibre directional couplers.     

Numerical analysis of optical fibers using matrix approach

The authors conduct a numerical analysis of optical fibers characterized by arbitrarily graded, cylindrically symmetric refractive index profiles by transforming them into equivalent planar profiles and using a matrix approach developed earlier for the analysis of planar optical waveguides (see ibid., vol.5, p.660-7, 1987). The method, which involves only straightforward multiplication of 2×2 matrices, can be used to calculate the propagation constant, modal field profiles, leakage/absorption loss, etc. of fibres with arbitrarily graded profiles. The applicability of the method has been shown through calculations of propagation constant and modal fields of single-clad and coaxial step-index fibers. Calculations of leakage loss of LP₀₁ and LP₁₁ modes in depressed inner clad fibers have also been presented. The method was also used to determine the coupling length in a coaxial optical-fiber coupler, which has potential applications in optical-fiber sensing     

Fiber spot size: a simple method of calculation

The ability to integrate the Laguerre-Gauss functions in closed form is exploited to allow a simple but accurate evaluation of single-mode fiber spot size using Galerkin's method. The method avoids the need for numerical integration in a broad class of refractive-index profiles. Its simplicity depends on the use of a pattern-matching algorithm to avoid the numerical integration normally called for. The algorithm is very fast and gives exact results. The development of symbolic computer languages makes this approach especially easy. A symbolic program was used to predict the spot size and the far-field radiation pattern, and the results are compared with the exact values, getting excellent results     

Compact UWB bandpass filter with dual‐notch bands using asymmetric tri‐section stepped impedance resonator

In this study, a novel high selective UWB band pass filter (BPF) with dual notch band is presented. UWB BPF is realized using stub‐loaded multiple‐mode resonator (MMR). The MMR is constructed by loading a quintuple mode open stub at the centre in an asymmetric tri‐section stepped impedance resonator (ATSSIR). Five modes, including two odd modes and three even modes, placed within UWB band. Two transmission zeros generated by the fractal stub improve the passband selectivity greatly. Two half wavelength long fractal Hilbert resonators are embedded near I/O line to achieve notch bands at 5.1 and 5.9 GHz. Aperture‐backed interdigital coupled‐lines are implemented to improve the coupling. The proposed prototype is fabricated and tested. The measured insertion loss is observed to be within 1.5 dB over the passband. By virtue of two transmission zeros (TZs), on either side of the passband, at 5.1 and 5.9 GHz, respectively, the passband selectivity is achieved with measured roll‐off factor at around 34 dB/octave. The out‐of‐band rejection of the filter is greater than 22 dB up to 18 GHz. The simulated results are in good agreement with the measured responses.     

Differential evolution to synthesize low sidelobe thinned isophoric time‐modulated planar array with increased directivity

In this article, a novel method for synthesizing rectangular planar array through thinning and time‐modulation is proposed. A new differential evolution based approach that generates a rank based population is adopted to find out the optimum element off position for thinning and ontime duration to modulate the antenna elements in time domain. The proposed synthesis method defines a preservative boundary at the array center where the antenna elements are not thinned and time‐modulated rather uniformly excited. It is shown that this proposed thinning and time‐modulation strategy with an optimum preservative boundary helps to realize low side lobe radiation pattern with increased directivity by controlling less number of optimization variables as compared to traditional approach. It also reduces the feed network complexity specifically for large antenna arrays.     

Peptide Induced Crystallization of Calcium Carbonate on Wrinkle Patterned Substrate: Implications for Chitin Formation in Molluscs

We here present the nucleation and growth of calcium carbonate under the influence of synthetic peptides on topographically patterned poly(dimethylsiloxane) (PDMS) substrates, which have a controlled density of defects between the wrinkles. Experiments with two lysine-rich peptides derived from the extracellular conserved domain E22 of the mollusc chitin synthase Ar-CS1, AKKKKKAS (AS8) and EEKKKKKES (ES9) on these substrates showed their influence on the calcium carbonate morphology. A transition from polycrystalline composites to single crystalline phases was achieved with the peptide AS8 by changing the pH of the buffer solution. We analyzed three different pH values as previous experiments showed that E22 interacts with aragonite biominerals more strongly at pH 7.75 than at pH 9.0. At any given pH, crystals appeared in characteristic morphologies only on wrinkled substrates, and did not occur on the flat, wrinkle-free PDMS substrate. These results suggest that these wrinkled substrates could be useful for controlling the morphologies of other mineral/peptide and mineral/protein composites. In nature, these templates are formed enzymatically by glycosyltransferases containing pH-sensitive epitopes, similar to the peptides investigated here. Our in vitro test systems may be useful to gain understanding of the formation of distinct 3D morphologies in mollusc shells in response to local pH shifts during the mineralization of organic templates.     

Einstein relation in carbon nanotubes and quantum wires of nonlinear optical and optoelectronic materials

We study the Einstein relation for the diffusivity-to-mobility ratio (DMR) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical and optoelectronic materials. The respective DMR in QWs exhibits increasing quantum steps with increasing electron statistics. In CNTs, the DMR exhibits periodic oscillations with increasing carrier degeneracy and the nature is radically different as compared with the corresponding DMR of QWs since they emphasize the different signatures of the two entirely different one dimensional nanostructured systems. In addition, we have suggested an experimental method of determining the DMR for CNTs and QWs having arbitrary dispersion laws.