Waveguide polarizer based on resonant tunneling

A novel and highly efficient waveguide polarizer which is based on the phenomenon of resonant tunneling is proposed. Designs for both transverse-electric (TE) and transverse-magnetic (TM) pass polarizers based on this principle are suggested, and it is shown that with such a device it is possible to achieve TM mode loss greater than 80 dB/mm and TE mode loss less than 0.5 dB/mm for the TE pass polarizer, and TE mode loss of 24 dB/mm with a TM mode loss less than 0.8 dB/mm for the TM pass polarizer     

Analytical approximations for the propagation characteristics of dual-mode fibers

In this paper we present accurate analytical approximations for the modal fields of dual-mode optical fibers with power law profiles based on a scalar variational analysis. We propose single parameter and two parameter trial functions and use these to study the dispersion characteristics and estimate the value of the normalized frequency corresponding to zero intermodal dispersion, which defines the operating point for such fibers. Our results show that the relatively simple single parameter field for the LP11mode gives a good fit to the field inside the core and estimates the propagation constant fairly well, but is inadequate to calculate the dispersion characteristics. On the other hand, the two parameter field estimates all these characteristics with a high degree of accuracy and enables one to accurately compute the normalized frequency for zero intermodal dispersion as well as dispersion tolerance around this value.     

Determination of Main Parameters Affecting Ozone Bleaching of Wheat Straw Pulp Using Plackett–Burman Design

Laboratory-scale studies were carried out on ozone bleaching of wheat straw soda pulp. Effects of five variables—pH, consistency, time, temperature, and ozone dose—on three pulp parameters— kappa number, brightness, and viscosity–were determined using Plackett–Burman experimental design. Results showed that for the parameter kappa number of pulp, ozone dose is the most important factor followed by pH and consistency. Pulp parameter viscosity is affected by factor pH, followed by consistency and ozone dose. Brightness of the wheat straw pulp mostly depends on factor ozone dose, followed by pH.     

Multiband BPF with wide upper stop band using asymmetrically positioned stub loaded open loop resonators

In this paper, asymmetrically positioned stub loaded open loop resonators with pseudo interdigital coupling are used to design compact multiband planar bandpass filters. The first design pertains to a dualband BPF that operates at 3.5 GHz and 5.7 GHz. The parameters like position of stub, which quantifies the asymmetry, and length of stub are further optimised using real coded genetic algorithm to evolve a triband BPF. The evolutionary design procedure is supported with an example of triband BPF having passband at 3.5 GHz, 5.5 GHz and 6.8 GHz, respectively. The transmission line models for both filters are developed as well as fabricated prototypes are realised and tested. There is a good agreement between the measured and simulated results. The measured insertion loss at first and second band centred around 3.5 GHz and 5.7 GHz of the dual band BPF are 1.5 dB and 1.25 dB, respectively. For the triband BPF the values are 1.24 dB, 1.6 dB and 1.8 dB at 3.5, 5.5 and 6.8 GHz, respectively. The dualband design covers the WiMAX and IEEE 802.11a bands where as the triband design also covers the 6.8 GHz RFID frequency.     

Measurement of dynamic surface tension using helical flow of a viscous liquid in a pool of another viscous liquid inside a micro-channel

Measurement of surface tension (s.t.) and critical micelle concentration (c.m.c.) of a surfactant in dynamic condition is important for several engineering applications, for which, the interface between two or more different phases does not remain constant but alters and replenishes continuously with flow of the fluids so that equilibrium may not be reached between the bulk and the interface. There are however not many methods for measuring these quantities in dynamic experiments which mimics the real dynamic situations. In this report, we present a novel two-phase flow pattern inside a triple-helical micro-channel using which, we show that it may be possible to measure the dynamic s.t. of a liquid. When two immiscible liquids such as oil and water are pumped into it, at a certain range of flow rates, oil flows as the continuous phase, whereas water remains in it as a wavy filament, the wavelength of which varies with the flow rates of oil and water but also on the interfacial tension between these two liquids. We show that wavelength decreases with increase in concentration of a solute attaining a minima at the c.m.c. A simple scaling analysis captures most experimental observations.