Transparent Reflectors Research Articles

Reduction of solar infrared heating by using highly transparent thin films based on organic chiral nematic liquid crystal polymer.

This paper demonstrates a thin and transparent reflector film for the near infrared, based on chiral nematic liquid crystal (CLC) polymers. Two films reflect almost 50% of unpolarized incident light from 730 to 820 nm and from 880 to 1030 nm, while remaining completely transparent in the visible region with transmittance >90%. An efficient window uses the combination of two reflectors. After exposing two window-cubes for 2 h to direct sunlight, the temperature inside the cube with reflector windows was 4°C lower than in cube with plain windows. This reveals that the infrared (IR) reflectors can effectively control the indoor temperature. These films, which are 8 µm in thickness, can be detached from the glass substrates and used as a free-standing film, or be attached to a flexible optical foil or a solid window. The foils can be applied in buildings, offices, and automobiles to statically reduce the energy consumption required for air conditioning or lighting. The free-standing foils show acceptable resistance to polar protic solvents and are thermally stable up to 100°C.

Efficient mm-wave photomodulation via coupled Fabry–Perot cavities

An efficient mm-wave photomodulator is designed based on coupled Fabry–Perot modes in a low-lifetime silicon wafer and an adjacent cavity formed from a transparent reflector, such as indium tin oxide. The modulation of a reflected beam using this coupled-cavity design is increased by a factor of 7 compared with that from an isolated silicon wafer, while also introducing a degree of tunability and maintaining low angular dispersion. For the particular design built and tested, a modulation of 32% is achieved for an extremely low optical illumination of just 0.006W/cm2 and with a maximum operation rate of more than 3 kHz. The large increase in modulation, coupled with the flexibility of the design and the fact that all components can be industrially manufactured, makes this photomodulator a promising candidate for many communication, imaging, and sensing applications.

Transparent Wideband Circularly Polarized GNSS Antenna for Vehicular Applications

In this paper, a single-layer one-sided wideband coplanar waveguide (CPW)-fed transparent circularly polarized (CP) rectangular slot antenna with tilted beam is proposed. The antenna is designed on a glass substrate with a mesh grid in the conductive layer in order to increase the transparency. Since most of the vehicles’ windshields are inclined for about 30 degrees, the beam of the antenna is designed to be tilted for about 30 degrees in elevation. For measurement verification, an inclined stage is fabricated to resemble the inclined surfaces (such as the windshields). The 10-dB impedance bandwidth of the antenna is 40.8% (1.13 - 1.71 GHz) with a 3-dB axial ratio bandwidth of 47.4% (1.06 - 1.72 GHz) and a 3-dB gain bandwidth of about 54% (1.02 - 1.78 GHz) with a maximum right handed circular polarization (RHCP) gain of 5.3 dBic. Also, the transparency of the antenna is about 95%. Therefore, the antenna is a good candidate for vehicular applications such as location tracking, using global navigation satellite system (GNSS) and specifically global positioning systems (GPS). Furthermore, a small-size transparent reflector is designed to be used below the proposed antenna in order to increase the front to back ratio (FBR).

A Method to Develop Flexible Robust Optically Transparent Unidirectional Antennas Utilizing Pure Water, PDMS, and Transparent Conductive Mesh

A method to realize low-cost, optically transparent, flexible, and unidirectional antennas is presented in this article. The key to the method is making a flexible transparent reflector made using a new method—injection of pure water into a flexible transparent cavity that is made out of polydimethylsiloxane (PDMS) polymer and integrating the flexible reflector with a flexible dipole made of transparent conducting mesh. This method is simple and inexpensive. Hence, it is useful for large-scale production of transparent, flexible, robust, and low-cost antennas as well as RF/microwave components for wearable body-area networks and other such systems that require flexible and transparent components. To validate the method, an antenna operating in the 2.45 GHz band was designed, fabricated, and tested under various conditions. Its measured gain is 3.2 dBi and efficiency is 51%. To the best of our knowledge, this is the first water-based transparent flexible antenna. Due to the shielding effect of the water-based reflector, it produces a low specific absorption rate (SAR) in the human body when it is worn, as expected from a unidirectional antenna. Furthermore, it is investigated and confirmed that the use of pure water in the reflector makes the antenna significantly more efficient as opposed to salt water.

Effect of annealing temperature on the structural, morphological and optical properties of ThO2 thin films grown by photochemical metal–organic deposition

In this work, we report the influence of annealing temperature on the structural, morphological and optical properties of ThO2 thin films deposited on fused quartz and (100) silicon substrates by photochemical metal–organic deposition (PMOD) using hinokitiolate thorium (IV) complex as the precursor. X-ray photoelectron spectroscopy (XPS) confirmed the deposition of the ThO2 films. The effect of thermal annealing (from 300 °C to 1100 °C) on the structural properties of the ThO2 films was evaluated with X-ray diffraction (XRD), UV–Vis transmittance spectroscopy, spectroscopic ellipsometry and atomic force microscopy (AFM). XRD patterns of the films annealed above 300 °C revealed that all diffraction peaks belong to a cubic ThO2 structure without preferential orientation. The average crystallite size increased from 2.3 nm to 3.7 nm as the annealing temperature increased from 300 °C to 750 °C. Annealing at 1100 °C promoted the formation of huttonite (β-ThSiO4) in the ThO2 layer. Films deposited on fused quartz showed 80% transmittance in the visible range, and the annealing temperature did not impact the band gap energy. The AFM studies revealed that as the annealing temperature increased, the film surface roughness decreased. Between 750 °C and 950 °C, the film surface was relatively smooth with an of RMS surface roughness in the range 2.3–5.0 nm. The values of the refractive index of the films were in the range of n = 1.6 for the as-deposited film to n = 2.1 for the films annealed at 750 °C. This result suggests the potential use of ThO2 films as a transparent reflector material for short wavelengths.

Gloria Knolls Slide: A prominent submarine landslide complex on the Great Barrier Reef margin of north-eastern Australia

We investigate the Gloria Knolls Slide (GKS) complex on the Great Barrier Reef margin of north-eastern Australia, the largest extant mixed carbonate-siliciclastic province in the world. Based on the most complete bathymetric and sub-bottom profile datasets available for the region, we describe the main surface and subsurface geomorphologic characteristics of this landslide complex. The GKS forms a 20km along-slope and 8km across-slope indentation in the margin, extending from 250 to 1350m depth, and involves a volume of 32km3 of sediment remobilized during three events. Three main seafloor terrains can be distinguished based on seafloor morphology: a source area, a proximal depositional area and a distal depositional area. The source area includes a main headwall scarp with a maximum height of 830m and a secondary scarp at 670m depth. The proximal depositional area is flat and smooth, and lacks debris exposed on the seafloor. The distal depositional area has a hummocky surface showing a distinctive cluster of eight knolls and over 70 small debris blocks. A dredge sample from the top of the largest knoll at a depth of 1170m reveals the presence of a cold-water coral community. In the sub-bottom profiles, the mass-transport deposits in the GKS are identified below the background sediment drape as partially confined, wedge-shaped bodies of mostly weak amplitude, transparent reflectors in the proximal depositional area; and more discontinuous and chaotic in the distal depositional area. The failed sediment slabs of the GKS were evacuated, transported and disintegrated downslope in three events following a sequential failure process spreading successively from the lower slope to the upper slope. The first event initiated at the lower slope at the depth of the secondary scarp, moved downslope and disintegrated over the basin floor leaving coherent blocks. The subsequent second and third events were responsible for the formation upslope of the main scarp in the GKS. The timing of emplacement of the first GKS event, constrained by radiometric age of fossil biota from the surface of the largest slide block, was at least before 302±19ka. The presence of alternating mixed carbonate and siliciclastic lithologies that build the slope might have played an important role as a preconditioning factor in this region. Preliminary estimations suggest that unusually large seismic events were the most likely triggering mechanism for the GKS. This work contributes to the understanding of large mass-movement deposits in mixed carbonate-siliciclastic margins and provides a useful morphologic characterization and evolutionary model for assessing its tsunamigenic potential with further numerical simulations. In addition, the discovery of a cold-water coral community on top of the largest knoll has implications for identifying similar landslide-origin cold-water coral communities on the GBR margin.

Micromirror based virtual image automotive head-up display

A micromirror based virtual image head-up Display (HUD) system for automobile is presented. This auto-HUD includes a micromirror laser vector scanning display module, a projection screen, a reflective mirror and a transparent reflector for generating the virtual image. The display module integrates a micromirror driven by four repulsive-force actuators, a laser, the driving and control circuits and a double concave lens. The prototype of the micromirror HUD is fabricated and installed in a car model. Its performance is tested. The micromirror HUD is superior over the conventional HUD in terms of viewing angle, cost and size.

Deep-marine seabed erosion and gravel lags in the northwestern Rockall Trough, North Atlantic Ocean

A zone of active seabed erosion has been identified in the northwestern Rockall Trough using seismic reflection profiles and cores. The region from George Bligh Bank to Rockall Bank has been subject to vigorous bottom-current activity, for at least the last 35 Ma. Bottom currents originate from southward flowing North Atlantic Deep Water, in water depths of 500–2000 m. Acoustic character mapping reveals a zone of erosion extending over 8500 km 2 along the northwestern margins of the trough. The erosion surface is characterized by an acoustically reflective seabed, with occasional parallel to transparent reflectors. These are the result of strong bottom-currents exposing the underlying volcanic basement, drift sequences and fan sediments. The erosion surface is covered by a <10 m veneer of Quaternary sediment. The majority of the basin consists of well-stratified, parallel Quaternary drift and hemipelagite sequences. Along the western margin of the trough, these sediments form broad-sheeted drifts. Eocene sediments adjacent to George Bligh Bank have been exposed by strong bottom-currents for the last 35 Ma, compared with the flanks of Rockall Bank, where sedimentation was intermittent. Core sampling from George Bligh Bank and Rockall Bank recovered Quaternary gravelly–sandy muds interpreted as gravel lags, and muddy sandy contourites, overlying early–mid-Eocene aged sediments. The gravels represent the influence of a strongest North Atlantic Deep Water flow, winnowing coarse sediment into ‘lags’, commonly preserved within sandy contourite sequences.

HINDOO cruise deep-sea channel survey in the Bay of Bengal

During Leg 4 of KH-00-5 (Hakuho-maru INDian Ocean Observation Cruise: HINDOO Cruise), we conducted swath bathymetry survey using the SeaBeam 2120 system (20 kHz) together with a 3.5 kHz sub-bottom profiler to map the bathymetric features of the submarine channels of the Bengal Fan (Emmel and Curray, 1985), and to calculate the inflow sediment volume from the Indian subcontinent since the Last Glacial Maximum (LGM). Piston and multiple cores were taken for various analyses to understand more on the history of Himalaya- Karakoram mountain ranges under continent-continent collision and its consequent climatic changes.Swath bathymetric profiles are not distinct due to the smooth slopes, however it is useful to trace submarine channels. Two channel types, active and old channels, are identified both on swath bathymetry and sub-bottom profiles. Active channels are characterized by V-shaped deep and narrow structures inside the channel (Figs.3, 5). High channel levees show parallel strong reflectors, and has slumping down channel walls with stepping features at some places. Differ from the active channels, old channels are characterized by U-shaped wide and shallow structures (Figs.4, 6). Strong and transparent reflectors which are identified inside channel levees, might be overbank fine-grained sediments paralleling the subbottom (Damuth, 1980).

Narrow-band far-infrared interference filters with high-T c, superconducting reflectors

We report on experiments showing that high-T c , superconductors are well suitable for constructing of high-quality far-infrared Fabry-Perot interference filters in the terahertz frequency range. In an interference filter we use two plane-parallel MgO plates with YBa 2 Cu 3 O 7 thin films as partly transparent reflectors on adjacent surfaces. For the first-order main resonances adjusted to frequencies around 2 THz a quality factor of ≅200 and a peak-transmissivity of 0̃.5 have been reached. Study of the filters with YBa 2 Cu 3 O 7 films of different thickness indicate the possibility of reaching still higher selectivity. An analysis of the filter characteristics delivered the dynamical conductivity of the high-T c films.

Quasi-optical Fourier method of spatial structure analysis of electromagnetic fields

Wide use of computing engineering and radiolocation and communication systems has promoted development of new methods and means of receiving and processing signals based on discrete transformations in orthogonal function classes. A technical realization of the devices which use basic function systems to describe two-dimensional signals in quasi-optics becomes a simpler one when using orthogonality properties of Gaussian wave beams. A multimode two-mirror open resonator (OR) (of Fabry-Perot type) with an input partially transparent reflector is an ideal tool for orthogonal transformation of fields in the millimeter- wave region. The paper reveals the concept, gives assessments to the spectral methods of recording and analyzing an electromagnetic SHF-field amplitude-phase structure and describes possible application methods.