Dynamic Modulation Yields One-Way Beam Splitting

This article demonstrates the realization of an extraordinary beam splitter based on nonreciprocal and synchronized photonic transitions in obliquely illuminated space-time-modulated (STM) slabs which impart the coherent temporal frequency and spatial frequency shifts. As a consequence of such unusual photonic transitions, a one-way beam splitting and amplification is exhibited by the STM slab. Beam splitting is a vital operation for various optical and photonic systems, ranging from quantum computation to fluorescence spectroscopy and microscopy. Despite the beam splitting is conceptually a simple operation, the performance characteristics of beam splitters significantly influence the repeatability and accuracy of the entire optical system. As of today, there has been no approach exhibiting a nonreciprocal beam splitting accompanied with transmission gain and an arbitrary splitting angle. Here, we show that oblique illumination of a periodic and semi-coherent dynamically-modulated slab results in coherent photonic transitions between the incident light beam and its counterpart space-time harmonic (STH). Such photonic transitions introduce a unidirectional synchronization and momentum exchange between two STHs with same temporal frequencies, but opposite spatial frequencies. Such a beam splitting technique offers high isolation, transmission gain and zero beam tilting, and is expected to drastically decrease the resource and isolation requirements in optical and photonic systems. In addition to the analytical solution, we provide a closed-form solution for the electromagnetic fields in STM structures, and accordingly, investigate the properties of the wave isolation and amplification in subluminal, superluminal and luminal ST modulations

Study of chemical and physical behavior cotton fabrics treated by corona discharge after several laundering

Cotton fabric because of finishing process has shrinkage behavior after laundering and for improving this problem, chemical agents utilize for anti-shrinkage. This temporary finishing can reduce shrinkagebut has many environmental problems. Corona discharge treatment has been used for cotton fabric, other fibers and polymers. This treatment can reduce costs and environmental impacts. In this study, cotton fabric was treated by corona discharge instrument at 2 - 40 passages and fabrics were washed with laundering method. After four times laundering, shrinkage behavior of corona discharge treated fabric as compared with un-treated fabric decrease. After 10 passages of corona discharge treatment,water, dye absorption and shrinkage are modified but after 14 passages, despite of shrinkage improvement, dyeing properties decrease

A new three-dimensional conical ground-plane cloak with homogeneous materials

A new three dimensional conical ground plane electromag- netic cloak is proposed and designed based on the coordinate transfor- mation of Maxwell's equations. Material parameters of the conical invisible cloak are derived which have simple form and lesser inhomo- geneity compared with other 3-dimensional cloaks. Because of conve- nient form of the constitutive tensors of the conical cloak, we propose a new strategy for homogeneous approximation of the materials of the cloaks. Numerical simulations confirm that approximation with eight slices, is more than enough and this cloak can hide any object on the ground as well as inhomogeneous ones.</p

Space-time modulation: Principles and applications

The ever-increasing demand for high-datarate wireless systems has led to a crowded electromagnetic (EM) spectrum. This demand has successively spurred the development of versatile microwave and millimeter-wave integrated components possessing high selectivity, multifunctionalities, and enhanced efficiency. These components require a class of nonreciprocal structures endowed with extra functionalities, e.g., frequency generation, wave amplification, and full-duplex communication. Space-time (ST) modulation has been shown to be a perfect candidate for high-data-rate transmission given its extraordinary capability for EM-wave engineering. ST-modulated (STM) media are dynamic, directional EM structures whose constitutive parameters vary in both space and time.</p

Space-Time-Varying Surface-Wave Antenna

As of today, the application of space-time modulated media has been limited to parametric amplification, nonreciprocity, and frequency mixing. This article exhibits the functionality of the space-time modulated medium as a surface-wave antenna and demonstrates that a space-time modulated medium makes a perfect antenna. We first present the analytical solution for electromagnetic fields inside a space-time modulated medium. The analytical solution reveals the existence of surface-waves in such a medium as well as their temporal and spatial frequencies. We next introduce the concept of space-time surface-wave antenna system, where the transition of space-wave to surface-wave is utilized for a pure signal receive. The analytical solution is supported by FDTD numerical simulation of the medium, which gives a more in-depth insight into the analysis of the structure. The study is expected to pave the way for further study on the application of space-time media in antenna systems.</p

Recent advances in theory, concepts and applications of space-time modulated media

We report on our latest results concerning the theory, concepts and applications of space-time modulated media. This includes a collection of theoretical, numerical and experimental demonstration of classes of space-time varying structures and their unique functionalities.</p

Advanced Wave Manipulation through Oblique Illumination of Space-Time Modulated Media

We present a theoretical and numerical framework for the wave spectrum manipulation and control of electromagnetic waves using time-periodic space-time modulated slabs. We show that such slabs provide peculiar and unique control over electromagnetic fields as well as wave spectrum alteration. Interesting features include new frequency generation, unidirectional wave manipulation and space-scanning.</p

Advanced Wave Engineering via Obliquely Illuminated Space-Time-Modulated Slab

This paper introduces an advanced wave engineering technique based on unidirectional frequency generation and spatial decomposition in general space-time-modulated (STM) slabs. The extraordinary wave engineering provided by such slabs is comprised of unidirectional wavefront shaping, nonreciprocal frequency generation, and spatial decomposition of ST harmonics (STHs). We first derive a rigorous analytical solution for the wave scattering from general ST permittivity-and permeability-modulated (STPPM) slabs. The analytical solution considers the most general form of spatiotemporal variation and wave incidence, i.e., oblique incidence and scattering from time-periodic spatially aperiodic/periodic STPPM slabs. The spatial aperiodicity may be utilized for further spectrum engineering and suppression of undesired STHs. Next, it will be shown that an equilibrated ST refractive-index-modulated slab with equal permittivity and permeability modulation strengths exhibits highly enhanced nonreciprocity. The FDTD numerical simulation of general STM slabs is presented, providing extra leverage for the analyses of wave propagation and scattering in such media. We show that oblique incidence to an STM slab yields nonreciprocal spatial decomposition of generated STHs. The explored peculiar properties of STM slabs under oblique incidence is expected to pave the way for the realization of new class of subharmonic generators, radars, illusion cloaks, and spatial mixers and isolators.</p

Antioxidant activity, total flavonoid and total phenolic contents of extracts taken from aerial parts of Ballota platyloma using three different methods: percolation, ultrasonic and polyphenolic fraction

Background: The genus Ballota L. (BL) belongs to the Labiateae family spread throughout the world. Plants of this genus possess anti oxidant, anti cancer, anti microbial and anti inflammatory properties. This study aimed to investigate the antioxidant activities of extract taken from aerial parts of Ballota platyloma Rech. f. using percolation, ultrasonic and polyphenol fraction methods. Materials and Methods: In this experimental study, aerial parts of Ballota platyloma were collected from Veresk (Mazandaran, Iran). Dried aerial parts of Ballota platyloma were extracted by percolation, and polyphenol fraction. The antioxidant activity of extracts was investigated using different methods: 1, 1-diphenyl- 2-picryl hydrazyl (DPPH), &rlm;iron ion chelating activity and reducing power. Data were analyzed using ANOVA and Duncan test at a significant level of P&lt;0.05. Results: The total phenolic and total flavonoid contents were in order of polyphenol&gt; ultrasonic &gt; percolation, The IC50 for polyphenol, percolation and ultrasonic extracts were 7.52&plusmn;1.07, 6.64&plusmn;0.87 and 2.58&plusmn;0.06, respectively. The IC50 for iron chelating ability were in order of polyphenol &lt; ultrasonic &lt; percolation. Polyphenol fraction showed better reducing power than the ultrasonic and percolation extracts (P&lt;0.001) which was comparable to that of Vitamin C (P&lt;0.05). Conclusion: The results showed that polyphenol fraction was rich in total phenolic and total flavonoid contents. Polyphenol fraction showed the best activity in reducing power but ultrasonic extracts was the most potent one in DPPH radical-scavenging activity. Thus, antioxidant activity may be attributed to the presence of phenols and flavonoids in the extracts