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

Grant PS, Castles F, Lei Q, Wang Y, Janurudin JM, Isakov D, Speller S, Dancer C, Grovenor CR - Philos Trans A Math Phys Eng Sci (2015)

Bottom Line: While aspects of ST theory have been confirmed using these structures, they are often disadvantaged by narrowband operation, high losses and difficulties in implementation.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK patrick.grant@materials.ox.ac.uk.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Electromagnetic properties at 15 GHz of a superconducting composite composed of YBCO particles in an epoxy matrix. (a) Real part of the relative dielectric permittivity ε′ as a function of particle loading by area fraction A, at room temperature and in the superconducting state at a temperature of 77 K. (b) Real part of the relative permeability μ′. (c) The quantity . (d) Typical cross-sectional electron micrograph of the superconducting composites (scale bar, 500 μm).
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RSTA20140353F1: Electromagnetic properties at 15 GHz of a superconducting composite composed of YBCO particles in an epoxy matrix. (a) Real part of the relative dielectric permittivity ε′ as a function of particle loading by area fraction A, at room temperature and in the superconducting state at a temperature of 77 K. (b) Real part of the relative permeability μ′. (c) The quantity . (d) Typical cross-sectional electron micrograph of the superconducting composites (scale bar, 500 μm).

Mentions: Less-studied superconducting composites offer the potential for strongly temperature-dependent electromagnetic properties (as the material is cooled into, or heated out of, the superconducting state) with 0<μ′<1 in the superconducting state. For example, the variation of ε′ and μ′ for a series of cast epoxy-based composites containing different fractions of superconducting yttrium barium copper oxide (YBCO) particles at room temperature and 77 K (in liquid nitrogen) are shown in figure 1. The data at 77 K was obtained by submerging the waveguide measurement jig in liquid nitrogen. In accordance with previous studies [20,21], the quantity could be controlled by both the YBCO fraction and temperature, as shown in figure 1c, where n is related to the refractive index, but ignoring the imaginary components ε′′ and μ′′, which tend to be relatively lossy in these composites; for example, the acrylonitrile butadiene styrene (ABS)—YBCO composite had a loss tangent at 15 GHz of 0.025 at 0.2 vol% YBCO. The increase in n with YBCO filler fraction derived from the increase of ε′ with filler fraction shown in figure 1a, in accordance with the effective medium theory of Bruggeman [5], which provided a good fit to the effective permittivity data for YBCO volume fractions up to 50% using ε′=55 for the filler particles (note, considerably smaller than the bulk permittivity of BaTiO3 of at least several hundreds). As expected, the effective permittivity did not change significantly on cooling to 77 K. However, figure 1b shows there was a reduction in μ′ with temperature, in turn causing changes in n. The relative permeability at room temperature was 1 at all filler fractions, but the YBCO became diamagnetic below a transition temperature of 93 K owing to the Meissner effect, giving μ′<0.5 for the most heavily loaded composites, and the ability to tune n between 5 and 3.5 using temperature.Figure 1.


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

Grant PS, Castles F, Lei Q, Wang Y, Janurudin JM, Isakov D, Speller S, Dancer C, Grovenor CR - Philos Trans A Math Phys Eng Sci (2015)

Electromagnetic properties at 15 GHz of a superconducting composite composed of YBCO particles in an epoxy matrix. (a) Real part of the relative dielectric permittivity ε′ as a function of particle loading by area fraction A, at room temperature and in the superconducting state at a temperature of 77 K. (b) Real part of the relative permeability μ′. (c) The quantity . (d) Typical cross-sectional electron micrograph of the superconducting composites (scale bar, 500 μm).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4528831&req=5

RSTA20140353F1: Electromagnetic properties at 15 GHz of a superconducting composite composed of YBCO particles in an epoxy matrix. (a) Real part of the relative dielectric permittivity ε′ as a function of particle loading by area fraction A, at room temperature and in the superconducting state at a temperature of 77 K. (b) Real part of the relative permeability μ′. (c) The quantity . (d) Typical cross-sectional electron micrograph of the superconducting composites (scale bar, 500 μm).
Mentions: Less-studied superconducting composites offer the potential for strongly temperature-dependent electromagnetic properties (as the material is cooled into, or heated out of, the superconducting state) with 0<μ′<1 in the superconducting state. For example, the variation of ε′ and μ′ for a series of cast epoxy-based composites containing different fractions of superconducting yttrium barium copper oxide (YBCO) particles at room temperature and 77 K (in liquid nitrogen) are shown in figure 1. The data at 77 K was obtained by submerging the waveguide measurement jig in liquid nitrogen. In accordance with previous studies [20,21], the quantity could be controlled by both the YBCO fraction and temperature, as shown in figure 1c, where n is related to the refractive index, but ignoring the imaginary components ε′′ and μ′′, which tend to be relatively lossy in these composites; for example, the acrylonitrile butadiene styrene (ABS)—YBCO composite had a loss tangent at 15 GHz of 0.025 at 0.2 vol% YBCO. The increase in n with YBCO filler fraction derived from the increase of ε′ with filler fraction shown in figure 1a, in accordance with the effective medium theory of Bruggeman [5], which provided a good fit to the effective permittivity data for YBCO volume fractions up to 50% using ε′=55 for the filler particles (note, considerably smaller than the bulk permittivity of BaTiO3 of at least several hundreds). As expected, the effective permittivity did not change significantly on cooling to 77 K. However, figure 1b shows there was a reduction in μ′ with temperature, in turn causing changes in n. The relative permeability at room temperature was 1 at all filler fractions, but the YBCO became diamagnetic below a transition temperature of 93 K owing to the Meissner effect, giving μ′<0.5 for the most heavily loaded composites, and the ability to tune n between 5 and 3.5 using temperature.Figure 1.

Bottom Line: While aspects of ST theory have been confirmed using these structures, they are often disadvantaged by narrowband operation, high losses and difficulties in implementation.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK patrick.grant@materials.ox.ac.uk.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus