Reconfigurable Pico-cell Antenna Array for Indoor Coverage in GSM 900 Band

This paper proposes a simple antenna array based on three stacked shorted patches aimed to be used as GSM (900 MHz) indoor base station antenna. Three same linearly polarized stacked patches are set in three orthogonal planes in space forming pyramid-like structure. The antenna array can be used for nearly omnidirectional coverage as well as for covering three 120º sectors. The proposed array also offers the possibility of polarization diversity

Free volume, molecular grains, self-organisation, and anisotropic entropy : machining materials

In this article, the relationship between molecular architecture and the formation of twist-bend phases is reviewed under the context of shape dependency. We conclude that the twist-bend phase is a universal phenomenon, which occurs in a wide variety of materials, for dimers through to main chain polymers. In the process, the chemical information on molecular design is effectively lost or irrelevant, and molecular topology takes precedence over electrostatic interactions in mesophase formation. As a consequence of this macro-scale material, engineering by shape alone becomes a possibility, potentially more phases may be realised, and entropy is anisotropic

The Shape of Things to Come: : The Formation of Modulated Nematic Mesophases at Various Length Scales

The twist-bend nematic phase is a recently discovered liquid-crystalline phase that exhibits macroscopic chirality even when formed from achiral materials, and as such presents a unique testbed for studies concerning the spontaneous breaking of mirror symmetry in soft matter. It is primarily exhibited by materials whose molecular structure is composed of two rigid aromatic units (such as biphenyl connected by a flexible spacer). The local structure of the NTB phase is nematic-like - with molecules having an average orientational order but no positional order - with a nanoscale helix where the pitch is of the order of several nanometres. A helix is chiral, and so the bulk NTB phase - in the absence of a biasing chiral environment - spontaneously separates into macroscopic domains of opposite handedness. After discussing the structure of this mesophase and its elucidation this concept article presents the molecular factors that determine its incidence. The apparent dependency primarily on molecular shape and bend-angle rather than particular functional group combinations manifests in this mesophase being exhibited on length scales far beyond those of simple liquid-crystalline dimers, not only in oligomers and polymers but in aqueous suspensions of micron sized helical particles

Optically Active Bimesogens Incorporating Branched Central Spacers

In the current fascination with liquid crystalline dimers, bimesogens and oligomers the role of the central spacer in these systems has perhaps been somewhat neglected. In compound 1, a phenyl 4-cyanobenzoate bimesogen, the central spacer incorporates a methyl group at the 2- position and is therefore chiral. The helical twisting power of 1, measured in both 5CB and E7, was found to be 0.36 and 0.35 μm-1 wt%-1 respectively. Compound 1 exhibited a monotropic chiral nematic phase, however no twist-bend modulated phase was observed. We prepared a number of analogues of 1 incorporating different mesogenic units and observe that those with a small aspect ratio are non mesogenic, whereas those with larger aspect ratios variously exhibit chiral nematic, TB, SmC and SmB phases

Nanohelicoidal Nematic Liquid Crystal Formed by a Non‐Linear Duplexed Hexamer

The twist‐bend modulated nematic liquid crystal phase exhibits phenomena of fundamental importance to science; the formation of a helical pitch of nanometre scale in a fluid and the spontaneous breaking of mirror symmetry leading to a quasi‐fluid state composed of chiral domains despite being composed of an achiral material. We note that this phase has only been observed for materials with two or more mesogenic units, the manner of attachment between which is always linear. In this communication we report on non‐linear oligomers, with a H‐shaped hexamesogen found to exhibit both nematic and twist‐bend modulated nematic phases. This shatters the widely held assumption that a linear sequence of mesogenic units is a prerequisite for this phase, and points to this state of matter being exhibited by a much wider range of self‐assembling structures than was previously envisaged. The present results support the double helix model of the TB phase as opposed to the simple heliconical model. This new class of materials has the potential to act as low molecular weight surrogates for cross linked liquid‐crystalline elastomers

An Insight into Creeping Electromagnetic Waves around the Human Body

The electromagnetic wave propagation around human body torso is modelled by considering elementary electric and magnetic dipoles over an infinite muscle-equivalent cylinder. The poles in the spectral domain Green’s function with smallest imaginary part are found to correspond to creeping wave propagation coefficients which predict the general trend in propagation around human body. In addition, it was found that axial magnetic field component is crucial for communication via creeping waves since it generates modes with smaller field decay compared to axial electric field. The developed model may thus serve as a practical guideline in design of on-body wearable antennas. The theoretical considerations are verified with simulations and measurements on the prototype of PIFA antenna placed on the human body

New refinement of the crystal structure of Zn(NH3)(2)Cl-2 at 100 K

The crystal structure of [ZnCl2(NH3)(2)], diamminedichloridozinc, was reinvestigated at low temperature, revealing the positions of the hydrogen atoms and thus a deeper insight into the hydrogen-bonding scheme in the crystal packing. In comparison with previous crystal structure determinations [MacGillavry & Bijvoet (1936). Z. Kristallogr. 94, 249-255; Yamaguchi & Lindqvist (1981). Acta Chem. Scand. 35, 727-728], an improved precision of the structural parameters was achieved. In the crystal, tetrahedral [Zn(NH3)(2)Cl-2] units (point-group symmetry mm2) are linked through N-H center dot center dot center dot Cl hydrogen bonds into a three-dimensional network

An Adiabatic Coaxial Line for Microcalorimeter Power Measurements in Wireless Communication for Smart Grid

This paper presents the extended results and prototype of the adiabatic copper conductor constructed with two interruption points in the external conductor layer, for use as a microcalorimeter power standard in wireless communication for a smart grid frequency range. Gaps are intended to drive down the thermal transfer from the outer environment into microcalorimeter and to reduce measurement inaccuracies in the microcalorimeter. The proposed design method is based on the combination of thermal and electromagnetic finite-element method simulations by which the desired line performance has been tailored. A prototype of the proposed adiabatic line has been manufactured and measurements on the prototype are presented along with the design procedure. Measured results are in line with the ones predicted by numerical calculations

High-Pressure Synthesis of Rare-Earth Borate-Nitrate Crystals for Second Harmonic Generation

The crystals of a novel family of rare-earth borate-nitrate compounds, Ln(7)(BO3)(3) (NO3)N3O (Ln = Pr, Nd), were grown at high-pressure in KAs flux and their crystal structure was determined. The new type of the crystalline structure consists of parallel chains of Ln(6) octahedra connected by common faces and forming the channels with the NO3 triangular planar motifs in the center, and isolated OLn(4) tetrahedra separated from each other by N-3 triangular motifs. Each NO3 triangle is in fact a part of rather unusual (NB3O12) block consisting of 3 distorted BO4 tetrahedra around central nitrogen atom. Under near-infrared (NIR) (lambda(em) = 1064 nm excitation, both compounds revealed a strong signal of second harmonic generation (SHG) at half the excitation wavelength (lambda(em) = 532 nm), which is in agreement with their noncentrosymmetric structure. In addition, a photon up-conversion (UC) emission at lambda(em) = 880 nm was observed for microcrystals of Nd-7(BO3)(3)(NO3)N3O, which was assigned to the UC process occurring within the 4f electronic manifold of Nd3+ ions. The dual-emission (SHG/UC) properties of Nd-7(BO3)(3)(NO3)N3O microcrystals, concomitant with the absence of photobleaching, makes them prospective candidates for microscopic probes in biological studies