Evaluation of the Laguerre-Gaussian mode purity produced by three-dimensional-printed microwave spiral phase plates

Computer-aided design software and additive manufacturing provide flexibility for the direct fabrication of multi-material devices. This design and fabrication versatility has been investigated for the manufacture of dielectric spiral phase plates (SPP) that generate electromagnetic waves with helical wavefronts. Three types of SPPs designed to produce an orbital angular momentum (OAM) mode number l = |1| were additively manufactured using material extrusion and polyjet fabrication methods. The OAM mode characteristics of the transformed helical microwaves as a function of the SPP geometrical features were investigated experimentally in the 12-18 GHz frequency range. The SPPs were further combined with an additively manufactured dielectric lens that provided a marked improvement in OAM mode purity. Finally, multiplexing and de-multiplexing of two OAM modes were demonstrated successfully using an optimum SPP geometry and arrangement.

Experimental evaluation of 3D printed spiral phase plates for enabling an orbital angular momentum multiplexed radio system

This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. The design and realization of the SPPs by means of additive manufacturing exploiting a high-permittivity material is described. Modes 1 and 2 SPPs are then evaluated at 15 GHz in terms of 3D complex radiation pattern, mode purity and beam collimation by means of a 3D printed dielectric lens. The results with the lens yield a crosstalk of -8 dB for between modes 1 and -1, and -11.4 dB for between modes 2 and -2. We suggest a mode multiplexer architecture that is expected to further reduce the crosstalk for each mode. An additional loss of 4.2 dB is incurred with the SPPs inserted into the communication link, which is undesirable for obtaining reliable LTE-based communications. Thus, we suggest: using lower loss materials, seeking ways to reduce material interface reflections or alternative ways of OAM multiplexing to realize a viable OAM multiplexed radio system.

Phase sequence in diisopropylammonium iodide: avoided ferroelectricity by the appearance of a reconstructed phase

Crystals of diisopropylammonium iodide are synthesized, grown and characterized.

Microwave dielectric characterisation of 3D-printed BaTiO3/ABS polymer composites

3D printing is used extensively in product prototyping and continues to emerge as a viable option for the direct manufacture of final parts. It is known that dielectric materials with relatively high real permittivity—which are required in important technology sectors such as electronics and communications—may be 3D printed using a variety of techniques. Among these, the fused deposition of polymer composites is particularly straightforward but the range of dielectric permittivities available through commercial feedstock materials is limited. Here we report on the fabrication of a series of composites composed of various loadings of BaTiO₃ microparticles in the polymer acrylonitrile butadiene styrene (ABS), which may be used with a commercial desktop 3D printer to produce printed parts containing user-defined regions with high permittivity. The microwave dielectric properties of printed parts with BaTiO₃ loadings up to 70 wt% were characterised using a 15 GHz split post dielectric resonator and had real relative permittivities in the range 2.6–8.7 and loss tangents in the range 0.005–0.027. Permittivities were reproducible over the entire process, and matched those of bulk unprinted materials, to within ~1%, suggesting that the technique may be employed as a viable manufacturing process for dielectric composites.

Manufacture of electrical and magnetic graded and anisotropic materials for novel manipulations of microwaves

Spatial transformations (ST) provide a design framework to generate a required spatial distribution of electrical and magnetic properties of materials to effect manipulations of electromagnetic waves. To obtain the electromagnetic properties required by these designs, the most common materials approach has involved periodic arrays of metal-containing subwavelength elements. While aspects of ST theory have been confirmed using these structures, they are often disadvantaged by narrowband operation, high losses and difficulties in implementation. An all-dielectric approach involves weaker interactions with applied fields, but may offer more flexibility for practical implementation. This paper investigates manufacturing approaches to produce composite materials that may be conveniently arranged spatially, according to ST-based designs. A key aim is to highlight the limitations and possibilities of various manufacturing approaches, to constrain designs to those that may be achievable. The article focuses on polymer-based nano- and microcomposites in which interactions with microwaves are achieved by loading the polymers with high-permittivity and high-permeability particles, and manufacturing approaches based on spray deposition, extrusion, casting and additive manufacture.

Spectroscopic, nonlinear optical and quantum chemical studies on Pyrrolidinium p-Hydroxybenzoate--a phase matchable organic NLO crystal

Good quality and bulk single crystals of Pyrrolidinium p-Hydroxybenzoate (PYPHB), a newly identified nonlinear optical material, were grown for the first time. It crystallizes in monoclinic system with an acentric space group Cc. The molecular structure including carbon, proton positions and functional groups has been confirmed through nuclear magnetic resonance and Fourier transform infrared spectra. Its transmission window has been observed for UV-VIS-NIR region along with its theoretical limit. The photoluminescence behavior has been observed by exciting the crystal at 310 nm. The principal refractive indices and second order NLO coefficient of PYPHB are determined by Mach-Zehnder interferometer and Maker-Fringe experiments respectively. The coherence length and phase-matchablility of PYPHB crystals are measured to explore its efficacy towards device fabrications. The dipole moment, polarizability and molecular orbital energy of an isolated PYPHB molecule have also been calculated theoretically and the results are found to corroborate the experimental values.

Non-equilibrium and differential function between intraepithelial and lamina propria virus-specific TCRalphabeta(+) CD8alphabeta(+) T cells in the small intestinal mucosa

The gastrointestinal mucosa regularly encounters commensal and pathogenic microbiota. Gut mucosal lymphocytes consist of two phenotypically different populations residing in the intestinal intraepithelial (IEL) compartment and lamina propria (LP). Little is known about compositional and functional differences of antigen-specific T cells from these mucosal compartments after mucosal infection, or the degree of trafficking between them. We here studied the B8R(20-27)-specific CD8 T-cell response in LP and IEL compartments after intrarectal immunization with modified vaccinia virus Ankara (MVA). CD8(+) T cells in the IEL compartment had much lower avidity than in the LP or spleen during acute and memory phases. Surprisingly, the TCR Vbeta-chain distribution of antigen-specific T cells and the length of the CDR3 region of the dominant Vbeta genes showed substantial dissimilarities between IEL and LP antigen-specific CD8alphabeta T cells in individual mice, increasing with time. We show functional and compositional differences between these mucosal compartments during the effector and memory phases of the immune response, indicating limited crosstalk and microenvironmental differences between the IEL, LP, and spleen. The restricted migration of cells from each of these mucosal compartments could partly account for a founder effect we observed in the IEL TCRalphabeta CD8alphabeta epitope-specific repertoire that might impact protective efficacy.

The infrared dielectric tensor and axial dispersion in caesium L-malate monohydrate

Caesium hydrogen L-malate monohydrate (CsH(C(4)H(4)O(5))·H(2)O) is a novel coordination compound of L-malic acid and caesium that crystallizes into a monoclinic structure and shows promising properties for application as a piezoelectric, pyroelectric and electro-optic material. In the present work we use polarized infrared reflectivity measurements to investigate the dielectric tensor of the material in the spectral range of 40-4000 cm(-1). The use of a three-polarization technique allows us to obtain from the reflectivity data the parameters that characterize the B phonons with wavevectors varying in the plane perpendicular to the monoclinic axis. Consequently, we are able to monitor the frequency dependence of the orientation of the principal dielectric axes in this plane. Using these results we can evaluate the role of polar phonons in the low frequency dielectric response, characterize the dielectric tensor in the terahertz frequency range and describe the axial optical and dielectric dispersion over the frequency range investigated.

Diagnostic pitfalls of ultrasonographic uterine screening in women treated with tamoxifen

Recent reports of an association between tamoxifen treatment for breast cancer and endometrial pathology prompted a screening program for women receiving tamoxifen. Twenty-two women were examined; 15 were asymptomatic, and 7 were referred because of abnormal vaginal bleeding. All underwent vaginal ultrasonography followed by endometrial sampling. The sonographic studies showed endometrial abnormalities in all 22 women--typically, irregular thickening of the endometrium. Some had cystic formations, and three had fluid in the endometrial cavity. No pathology or inadequate material was found in the endometrial samples from the 15 asymptomatic women. Endometrial polyps were suspected sonographically and removed from two of the five women with vaginal bleeding. The discrepancy between the sonographic findings and histology in the asymptomatic women could have been due to stromal edema from tamoxifen treatment. Abnormal ultrasonographic findings in asymptomatic women treated with tamoxifen probably represent insignificant changes in the endometrial architecture and not a true abnormality. The need for routine endometrial sampling or hysteroscopy in every case is therefore questionable.