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The paper presents proof of concept of a viable multilayer technology to enhance the performance of multifilar helix, receive-only satellite antennas. Approximately, 30-μm layers of polyether ether ketone (PEEK) were deposited onto the Cu filars of a single layer dielectrically loaded multifilar helix antenna using aqueous electrophoretic deposition (EPD). The PEEK coating was densified at ~400-420 °C in flowing N to prevent oxidation of the Cu filars. A second Cu metallisation was deposited onto the surface of the PEEK and the resulting antenna characterised. The multilayer antenna revealed a dual band response with peak radiation efficiencies >25 % and ~50 % increase in bandwidth. Multilayered surface architectures fabricated from PEEK using EPD, therefore, show great potential for the development of a broad range of high-performance multiband dielectrically loaded antennas whose peak frequencies may, in principle, be tuned by modifying the thickness of the PEEK layer. [ABSTRACT FROM AUTHOR]

Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor ( Q) exhibited a correlation to the Gd content and the microstructures of Bi1− x Gd x NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. [ABSTRACT FROM AUTHOR]

The electrical discharge machining process is an effective way to machine hard alloys. A homogenized dual phase Fe-24.0%Mn-8.3%Al-5.0%Cr-0.38%Si-0.34%Mo-0.45%C (wt%) alloy casting piece was employed to study the phase transformation and microstructure phenomena of recast layers by means of electrical discharge machining. The wave-like recast layers appear with micro cracks. The thickness of the recast layer increases with pulse duration. When the pulse duration ranges from 200 to 300 μs, the discharge current has no influence on the thickness of the recast layer. The copper concentration is high in the recast layer caused by the melting of the copper electrode. The copper contents of the recast layer increase with the pulse duration and the discharge current. The novel solidification microstructures of the recast layer can be classified as (1) a dense and fine dendritic outermost sublayer, (2) a coarse dendritic intermediate sublayer and (3) an innermost γ recast zone. The average chemical composition of the recast sublayers is Fe-19.007%Mn-8.377%Al-2.981%C-4.505%Cr-0.627%Cu-0.377%Mo-0.376%Si (wt%). The novel structure of the recast sublayer is identified as (Fe,Mn)3AlCx, which was formed due to the re-melting of the matrix and the carburization of the cracked dielectric fluid. The precise lattice parameter, ao, of the (Fe,Mn)3AlCx phase measured by extrapolation against cos2θ/sinθ is 0.3801 nm. The microhardness of the recast layers is as high as Hmv574 due to the existence of (Fe,Mn)3AlCx carbide. [ABSTRACT FROM AUTHOR]

The electrical properties of CuxZn1−x(HCOO)2·2H2O have been studied over a temperature range of 78–400 K. Results of the electrical conductivity, σd.c., σa.c., thermoelectric power, θ, relative permittivity, ∈′r, and dielectric loss factor, ∈″r, were reported. Anomalies in the physical properties have been observed at 220 K and at the vicinity of the decomposition temperature, and the mechanism of decomposition of solids has been studied. A random nucleation process (A3) was found to be the predominant decomposition mechanism for the system investigated. The effects of chemical composition and crystal structure on the physical properties are discussed. [ABSTRACT FROM AUTHOR]