Artificial surfaces of intertwined square spirals:A CPW model

Intertwining planar spirals arranged in doubly periodic arrays enables a substantially subwavelength response of the unit cell smaller than 1/40 of wavelength with large fractional bandwidths. These properties are important for application at low frequencies, conformal curved surfaces, or with compact radiators. It is shown that interleaving counter-wound spiral arms extended into adjacent unit cells dramatically increase the array equivalent capacitance while reducing the inductance. A coplanar waveguide (CPW) model has been developed to analytically estimate the equivalent capacitance and inductance of intertwined spiral array elements in terms of their geometrical parameters. The proposed CPW model is shown to provide an accurate prediction of the fundamental resonance frequency and can be instrumental in the design of the arrays for a specified frequency response. © 2012 IEEE.

Periodic Arrays of Interwoven Quadrifilar Spirals on Ferrite Substrates

The properties of metasurfaces composed of doubly periodic arrays of interwoven quadrifilar spiral conductors on magnetized ferrite substrates have been investigated with the aid of the full-wave electromagnetic simulator. The effects of incident wave polarization and ferrite magnetization on the scattering characteristics have been analysed at both normal and in-plane dc magnetic bias. The features of the fundamental topological resonances in the interwoven spiral arrays on ferrite substrates are illustrated by the simulation results and the effects of ferrite gyrotropy and dispersion on the array resonance response and fractional bandwidth are discussed.

ARTIFICIAL SURFACES WITH INTERWOVEN AND TESSELLATED PATTERNED CONDUCTORS: PROPERTIES AND PHENOMENOLOGY

The features of artificial surfaces composed of doubly periodic patterns of interwoven planar conductors are discussed. The free-standing intertwined quadrifilar spirals and modified Brigid's crosses are presented as illustrative examples to demonstrate the highly stable angular reflection and transmittance response with low cross-polarisation and a broad fractional bandwidth. The main mechanisms contributing to the substantially sub-wavelength response of these arrays are discussed showing that interweaving their conductor patterns provides concurrent control of both the equivalent capacitance and inductance of the unit cell. The effects of dielectric substrate and conductor thickness on the properties of intertwined spiral and modified Brigid's cross arrays are discussed to provide insight in the effect of the structure parameters on array performance.

Entwined spiral arrays on ferrite substrates

The properties of metasurfaces formed by the entwined spiral arrays on normally magnetised fer-rite substrates have been explored. It is shown that the coupling between the array fundamental topological resonance and the ferromagnetic resonance of the ferrite substrate leads to significant increase of the fractional bandwidth (FBW). The features of resonance transmittance assisted by the volume spin waves excited by the entwined spirals in the ferrite substrate are discussed.

Metasurfaces with interwoven conductor patterns on dielectric substrates

The properties of metasurfaces comprised of interwoven conductor patterns on dielectric substrates have been examined. The significant reduction of the fundamental resonance frequency fr and expanded fractional bandwidths (FBWs) offered by the intertwined spirals and Brigid’s crosses extended beyond a single unit cell has been achieved with the aid of thin dielectric substrates. A qualitative model has been proposed and proved to adequately predict the main properties of entwined spiral arrays on dielectric substrates.

Interwoven spiral arrays on ferrite-dielectric substrates for high-impedance metasurfaces

A high impedance metasurface (HIMS) composed of the arrays of intertwined planar spirals on thin (~0.1λ) ferrite-dielectric substrate is proposed. The HIMS exhibits fractional bandwidth in excess of 10% and excellent angular and polarisation stability of the circular polarised waves at oblique incidence.

An endophilin-dynamin complex promotes budding of clathrin-coated vesicles during synaptic vesicle recycling

Clathrin-mediated vesicle recycling in synapses is maintained by a unique set of endocytic proteins and interactions. We show that endophilin localizes in the vesicle pool at rest and in spirals at the necks of clathrin-coated pits (CCPs) during activity in lamprey synapses. Endophilin and dynamin colocalize at the base of the clathrin coat. Protein spirals composed of these proteins on lipid tubes in vitro have a pitch similar to the one observed at necks of CCPs in living synapses, and lipid tubules are thinner than those formed by dynamin alone. Tubulation efficiency and the amount of dynamin recruited to lipid tubes are dramatically increased in the presence of endophilin. Blocking the interactions of the endophilin SH3 domain in situ reduces dynamin accumulation at the neck and prevents the formation of elongated necks observed in the presence of GTPγS. Therefore, endophilin recruits dynamin to a restricted part of the CCP neck, forming a complex, which promotes budding of new synaptic vesicles.