Ultra-thin tunable microwave absorber using liquid crystals

A dynamically adaptive radar absorber is described which is based on a periodic array of microstrip patches that are printed on a 500 mu m-thick liquid crystal substrate. The measured reflectivity of the structure is less than -38 dB with a 200 MHz -10 dB bandwidth at 10.19 GHz when a +4 DC bias is applied. It is shown that a 34 dB reduction in signal loss occurs when the bias voltage is increased to 20 V.

Liquid crystal tunable mm wave frequency selective surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mu m thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.

Fabrication of Sub-micron Active Layer SSOI Substrates using Ion Splitting and Wafer Bonding Technologies

This paper reports the fabrication of SSOI (Silicon on Silicide On Insulator) substrates with active silicon regions only 0.5mum thick, incorporating LPCVD low resistivity tungsten silicide (WSix) as the buried layer. The substrates were produced using ion splitting and two stages of wafer bonding. Scanning acoustic microscope imaging confirmed that the bond interfaces are essentially void-free. These SSOI wafers are designed to be employed as substrates for mm-wave reflect-array diodes, and the required selective etch technology is described together with details of a suitable device.

Germanium on Sapphire By Wafer Bonding

This paper describes the creation of a germanium on sapphire platform, via wafer bonding technology, for system-on-a-chip applications. Similar thermal coefficients of expansion between germanium (5.8 x 10-6 K-1) and sapphire (5 x 10-6 K-1) make the bonding of germanium to sapphire a reality. Germanium directly bonded to sapphire results in microvoid generation during post bond annealing. Inclusion of an interface layer such as silicon dioxide layer by plasma enhanced chemical vapour deposition, prior to bonding, results in a microvoid free bond interface after annealing. Grinding and polishing of the subsequent germanium layer has been achieved leaving a thick germanium on sapphire (GeOS) substrate. Submicron GeOS layers have also been achieved with hydrogen/helium co-implantation and layer transfer. Circular geometry transistors exhibiting a field effect mobility of 890 cm2/V s have been fabricated onto the thick germanium on sapphire layer.

The masses of the cataclysmic variables AC Cancri and V363 Aurigae

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variables AC Cnc and V363 Aur (=Lanning 10). There is evidence of irradiation on the inner hemisphere of the secondary star in both systems, which we correct for using a model that reproduces the observations remarkably well. We find the radial velocity of the secondary star in AC Cnc to be K-R=176+/-3 km s(-1) and its rotational velocity to be v sin i=135+/-3 km s(-1). From these parameters we obtain masses of M-1=0.76+/-0.03 M-circle dot for the white-dwarf primary and M-2=0.77+/-0.05 M-circle dot for the K2+/-1 V secondary star, giving a mass ratio of q=1.02+/-0.04. We measure the radial and rotational velocities of the G7+/-2V secondary star in V363 Aur to be K-R=168+/-5 km s(-1) and v sin i=143+/-5 km s(-1), respectively. The component masses of V363 Aur are M-1=0.90+/-0.06M(circle dot) and M-2=1.06+/-0.11 M-circle dot giving a mass ratio of q=1.17+/-0.07. The mass ratios for AC Cnc and V363 Aur fall within the theoretical limits for dynamically and thermally stable mass transfer. Both systems are similar to the SW Sex stars, exhibiting single-peaked emission lines with transient absorption features, high-velocity S-wave components and phase-offsets in their radial-velocity curves. The Balmer lines in V363 Aur show a rapid increase in flux around phase 0 followed by a rapid decrease, which we attribute to the eclipse of an optically thick region at the centre of the disc. This model could also account for the behaviour of other SW Sex stars where the Balmer lines show only a shallow eclipse compared to the continuum.

Ten Year Performance Evaluation of a Field-Scale Zero-Valent Iron Permeable Reactive Barrier Installed to Remediate Trichloroethene Contaminated Groundwater

The Monkstown Fe0 PRB, Europe’s oldest commercially installed PRB, had been treating trichloroethene (TCE) contaminated groundwater for about 10 years on the Nortel Network site in Northern Ireland when cores were collected in December, 2006. Groundwater data from 2001-2006 indicated that TCE is being remediated to below detection limits as the contaminated groundwater flows through the PRB, Ca and Fe carbonates, crystalline and amorphous FeS, and Fe (oxy)hydroxides precipitates are present in the Fe0 filing material within the PRB. A greater variety of minerals are associated with a 1 cm thick slightly cemented crust at the entrance of the Fe0 section of the reactive vessel and the discontinuous cemented Fe0 material directly below it. Also, a greater presence of microbial communities occurred in the upper portion of the PRB compared to the lower section which might be due to less favourable conditions (i.e. high pH, low oxygen) for microbial growth in the lower section of the PRB. Visual estimation suggests that the Fe0 filings in the effluent section of the PRB have life-span of 10+ years compared to the Fe0 filings in the thin influent section of the PRB which may have a life span of only ~2-5 more years. Multi-tracer tests indicated that preferential pathways have formed in this PRB over the 10 years of operation.

Biological influence on the morphology and micromorphology of selected Podzols (Spodosols) and Cambisols (Inceptisols) from the Eastern United States and Northeast Scotland

Biological activities greatly influence the formation of many soils, especially forest soils under cool humid climates. The objective of this study was to investigate the effects of vegetation and soil biota on the formation of selected soils. Field morphology, micromorphology, and carbon and organic matter analysis were determined on six Podzols (Spodosols) and two Cambisols (Inceptisols) from the eastern United States and north-east Scotland. Humification of plant material by soil fauna and fungi occurs in all organic horizons. Thick organic coatings are observed on soil peds and rock fragments from the E1 to the Bs horizon in a Haplic Podzol from Clingmans Dome Mt., TN. Thin sections reveal large accumulations of root material in different stages of decomposition in the spodic horizons of a Haplic Podzol from Whiteface Mt., NY. Organic carbon ranges from 5.4 to 8.5% in the spodic B horizons of the Whiteface Mt. Podzol. Earthworms and enchytraeids have a great effect on the structure of the surface and subsurface horizons in the Dystric Cambisols from Huntly and Clashindarroch Forests, Scotland and a Cambic Podzol from the Corrie Burn Basin, Scotland. Podzols from Speymouth Forest, Scotland (Gleyic Podzol), Cling-mans Dome Mt., and Whiteface Mt. have thick organic horizons. The Podzols from the Flatwoods in Georgia, the Pine Barrens in New Jersey, the Corrie Burn Basin, and the Cambisol from Huntly Forest have only A horizons at the surface. The Clashindarroch Forest soil has a very thin organic horizon. Warm and humid climates and sandy parent material are responsible for thick E horizons and lack of thick organic horizons in the Flatwoods (Carbic Podzol) and Pine Barrens (Ferric Podzol) soils. Earthworms and enchytraeids thrive in the Corrie Burn Basin and Huntly Forest soils due to the vegetation and the highly weathered basic parent material. The site at Clashindarroch once carried oak, and then birch forest, both of which produce a mild litter and also encourage earthworm and enchytraeids. This fauna is responsible for much mixing of the topsoil. The present conifer vegetation will eventually produce a deep litter and cause podzolization.

Performance evaluation of a zerovalent iron reactive barrier: Mineralogical characteristics

There is a limited amount of information about the effects of mineral precipitates and corrosion on the lifespan and long-term performance of in situ Fe° reactive barriers. The objectives of this paper are (1) to investigate mineral precipitates through an in situ permeable Fe° reactive barrier and (2) to examine the cementation and corrosion of Fe° filings in order to estimate the lifespan of this barrier. This field scale barrier (225' long x 2' wide x 31' deep) has been installed in order to remove uranium from contaminated groundwater at the Y-12 plant site, Oak Ridge, TN. According to XRD and SEM-EDX analysis of core samples recovered from the Fe° portion of the barrier, iron oxyhydroxides were found throughout, while aragonite, siderite, and FeS occurred predominantly in the shallow portion. Additionally, aragonite and FeS were present in up-gradient deeper zone where groundwater first enters the Fe° section of the barrier. After 15 months in the barrier, most of the Fe° filings in the core samples were loose, and a little corrosion of Fe° filings was observed in most of the barrier. However, larger amounts of corrosion (~10-150 µm thick corrosion rinds) occurred on cemented iron particles where groundwater first enters the barrier. Bicarbonate/ carbonate concentrations were high in this section of the barrier. Byproducts of this corrosion, iron oxyhydroxides, were the primary binding material in the cementation. Also, aragonite acted as a binding material to a lesser extent, while amorphous FeS occurred as coatings and infilings. Thin corrosion rinds (2-50 µm thick) were also found on the uncemented individual Fe° filings in the same area of the cementation. If corrosion continues, the estimated lifespan of Fe° filings in the more corroded sections is 5 to 10 years, while the Fe° filings in the rest of the barrier perhaps would last longer than 15 years. The mineral precipitates on the Fe° filing surfaces may hinder this corrosion but they may also decrease reactive surfaces. This research shows that precipitation will vary across a single reactive barrier and that greater corrosion and subsequent cementation of the filings may occur where groundwater first enters the Fe° section of the barrier.

Physicochemical Characterization of Poly(ethylene glycol) Plasticized Poly(methyl vinyl ether-co-maleic acid) Films

The influence of the poly(ethylene glycol) (PEG) plasticizer content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) was investigated with tensile mechanical testing, thermal analysis, and attenuated total reflectance/Fourier transform infrared spectroscopy. Unplasticized films and those containing high copolymer contents were very difficult to handle and proved difficult to test. PEG with a molecular weight of 200 Da was the most efficient plasticizer. However, films cast from aqueous blends containing 10% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 4 : 3 and those cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 2 : 1 possessed mechanical properties most closely mimicking those of a formulation we have used clinically in photodynamic therapy. Importantly, we found previously that films cast from aqueous blends containing 10% (w/w) PMVE/MA performed rather poorly in the clinical setting, where uptake of moisture from patients' skin led to reversion of the formulation to a thick gel. Consequently, we are now investigating films cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000, where the copolymer/plasticizer ratio is 2 : 1, as possible Food and Drug Administration approved replacements for our current formulation, which must currently be used only on a named patient basis as its plasticizer, tripropylene glycol methyl ether, is not currently available in pharmaceutical grade

Submillimeter wave frequency selective surface with polarisation independent spectral responses

This paper reports the design, construction and electromagnetic performance of a new freestanding frequency selective surface (FSS) structure which generates coincident spectral responses for dual polarisation excitation at oblique angles of incidence. The FSS is required to allow transmission of 316.5 - 325.5 GHz radiation with a loss = 0.6 dB and to achieve = 30 dB rejection from 349.5 - 358.5 GHz. It should also exhibit crosspolarisation levels below -25 dB, all criteria being satisfied simultaneously for TE and TM polarisations at 45° incidence. The filter consists of two identical, 30 mm diameter, 12.5 ?m thick, optically flat, perforated metal screens separated by 450 ?m. Each of the ˜5000 unit cells contains two nested, short circuited, rectangular loop slots and a rectangular dipole slot. The nested elements provide a passband spectral response centred at 320 GHz in the TE and TM planes; the dipole slot increases the filter roll-off above resonance. The FSS was fabricated from silicon-on-insulator wafers using precision micromachining and plating processes including the use of Deep Reactive Ion Etching (DRIE) to pattern the individual slots and remove the substrate under the periodic arrays. Quasi–optical transmission measurements in the 250 – 360 GHz range yielded virtually identical copolarised spectral responses, with the performance meeting or exceeding the above specifications. Experimental results are in excellent agreement with numerical predictions.

Design and measurement of reconfigurable millileter wave reflectarray cells with nematic liquid crystal

Numerical simulations are used to study the electromagnetic scattering from phase agile microstrip reflectarray cells which exploit the voltage controlled dielectric anisotropy property of nematic state liquid crystals (LC). In the computer model two arrays of equal size elements constructed on a 15?m thick tuneable LC layer were designed to operate at centre frequencies of 102 GHz and 130 GHz. Micromachining processes based on the metallization of quartz/silicon wafers and an industry compatible LCD packaging technique were employed to fabricate the grounded periodic structures. The loss and phase of the reflected signals were measured using a quasi-optical test bench with the reflectarray cells inserted at the beam waist of the imaged Gaussian beam, thus eliminating some of the major problems associated with traditional free-space characterisation at these frequencies. By applying a low frequency AC bias voltage of 10 V, a 165o phase shift with a loss 4.5 dB-6.4 dB at 102 GHz and 130o phase shift with a loss variation between 4.3 dB – 7 dB at 130 GHz was obtained. The experimental results are shown to be in close agreement with the computer model.

THEORY AND DESIGN OF A TUNABLE QUASI-LUMPED QUADRATURE COUPLER

In this article, we present the theory and a design methodology for a unable Quasi-Lumped Quadrature Coupler (QLQC). Because of its topology, the coupler is simply reconfigured by switching the bias of two varactor diodes via a very simple DC bias circuitry. No additional capacitors or inductors are required. A prototype at 3.5 GHz is etched on a 0.130-mm-thick layer substrate with a dielectric material of relative permittivity of 2.22. The simulated and measured scattering parameters are, presented. (c) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2219-2222 2009: Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24526

SiO in G34.26: Outflows and shocks in a high mass star forming region

We have looked for SiO emission as evidence of shocks in the high mass star formation region G34.26+0.15. JCMT, VLA and FCRAO observations show that SiO emission is widespread across the region. The SiO emission highlights a massive, collimated out ow and other regions where stellar winds are interacting with molecular clumps. As in other star forming regions, there is also SiO at ambient velocities which is related to the out ow activity. No strong SiO abundance enhancement was measured in either the out ow or the low velocity gas, though abundances up to 10(-8) are possible if the SiO is locally enhanced in clumps and optically thick. SiO emission is not detected from the hot core itself, indicating either that SiO is not strongly enhanced in the hot core or that column densities in the region where grain mantle evaporation has taken place are low. In line of sight spiral arm clouds, we measure a SiO abundance of 0.4-2 x 10(-10), consistent with previous estimates for quiescent clouds.

A Novel Quad-Polarization Agile Patch Antenna

In this communication we present a novel polarization-agile microstrip antenna design. To dynamically change the polarization state, the radiating patch is fed by a tunable quasi-lumped coupler. The whole structure can be dynamically altered to radiate electromagnetic waves with vertical linear, horizontal linear, right-handed circular or left-handed circular polarization simply by changing the operating mode of the quasi-lumped coupler. Due to its topology the coupler is simply reconfigured by switching the bias of two varactor diodes via a very simple DC bias circuitry: no additional capacitors or inductors are required. A prototype is fabricated with a 0.762-mm-thick upper layer substrate for the radiating element and a 0.130-mm-thick layer substrate for the coupler circuit, both with the same dielectric material relative permittivity of 2.22. The simulated and measured scattering parameters, the axial ratio in circular radiation-mode and the cross-polarization level in linear mode, the gain and the radiation patterns are presented. The agile polarization capabilities of this new antenna, as demonstrated in this communication, underscore its suitability for modern wireless communications in a multi-path propagation environment.

94 GHz dual-reflector antenna with reflectarray subreflector

The design, construction and measured performance is described of an offset parabolic reflector antenna which employs a reflectarray subreflector to tilt the focused beam from the boresight direction at 94 GHz. An analysis technique based on the method of moments (MoM) is used to design the dual-reflector antenna. Numerical simulations were employed to demonstrate that the high gain pattern of the antenna can be tilted to a predetermined angle by introducing a progressive phase shift across the aperture of the reflectarray. Experimental validation of the approach was made by constructing a 28 × 28 element patch reflectarray which was designed to deflect the beam 5° from the boresight direction in the azimuth plane. The array was printed on a 115 µm thick metal backed quartz wafer and the radiation patterns of the dual reflector antenna were measured from 92.6-95.5 GHz. The experimental results are used to validate the analysis technique by comparing the radiation patterns and the reduction in the peak gain due to beam deflection from the boresight direction. Moreover the results demonstrate that this design concept can be developed further to create an electronically scanned dual reflector antenna by using a tunable reflectarray subreflector.