Wide Range Of Incident Wavelengths Research Articles

Multifunctional composites for elastic and electromagnetic wave propagation

Composites are ideally suited to achieve desirable multifunctional effective properties since the best properties of different materials can be judiciously combined with designed microstructures. Here, we establish cross-property relations for two-phase composite media that link effective elastic and electromagnetic wave characteristics to one another, including the respective effective wave speeds and attenuation coefficients, which facilitate multifunctional material design. This is achieved by deriving accurate formulas for the effective electromagnetic and elastodynamic properties that depend on the wavelengths of the incident waves and the microstructure via the spectral density. Our formulas enable us to explore the wave characteristics of a broad class of disordered microstructures because they apply, unlike conventional formulas, to a wide range of incident wavelengths (i.e., well beyond the long-wavelength regime). This capability enables us to study the dynamic properties of exotic disordered "hyperuniform" composites that can have advantages over crystalline ones, such as nearly optimal, direction-independent properties and robustness against defects. We specifically show that disordered "stealthy" hyperuniform microstructures exhibit novel wave characteristics (e.g., low-pass filters that transmit waves "isotropically" up to a finite wavenumber). Our cross-property relations for the effective wave characteristics can be applied to design multifunctional composites via inverse techniques. Design examples include structural components that require high stiffness and electromagnetic absorption; heat sinks for central processing units and sound-absorbing housings for motors that have to efficiently emit thermal radiation and suppress mechanical vibrations; and nondestructive evaluation of the elastic moduli of materials from the effective dielectric response.

Aperiodic Vogel spirals for broadband optical wave focusing.

We demonstrate both experimentally and numerically a new type of hole array structure that exhibits optically diffractive focusing phenomenon. The hole arrays are designed based on the aperiodic Vogel spirals. In contrast to periodic and quasi-periodic hole arrays that contain discrete Bragg peaks in reciprocal space, the Vogel spiral hole arrays have particularly continuous Fourier components with circular symmetry, which enables optical wave focusing into a diffraction-limited hotspot for a wide range of incident wavelengths. We further demonstrate that the diffracted fields contain local orbital angular momentum (OAM) leading to rotations of the diffractive circular rings around the center, although the total OAM is zero.

Experimental study of the wave-dissipating performance of a four-layer horizontal porous-plate breakwater

This paper proposes a four-layer submerged horizontal porous plate breakwater to improve the wave-dissipation efficiency under a wide range of incident wave frequencies, especially long incident waves, and also discusses the design of the geometrical parameters, i.e., plate submergence and porosity. The breakwater performance was examined experimentally in a two-dimensional wave flume. The effects of the layer number, breakwater width, upper plate porosity, and incident wave height were compared. Increasing the layer number and breakwater width or reducing the upper plate porosity can be favorable to energy dissipation for long incident waves. A moderate alteration of the submerged depth of each layer shifts the proportion of energy reflected or transmitted but minimally affects the energy-dissipation performance. In addition, the incident wave height affects both energy dissipation and mass overtopping, and the combined effect is related to the incident wave frequency and steepness. Generally, the proposed four-layer breakwater demonstrates satisfactory performance under a wide range of incident wavelengths and has promising future applications in coastal engineering. An optimized design for the plate porosity and submergence can be expected to further improve the breakwater performance, and a detailed mechanism for non-linear wave interactions with the submerged horizontal porous plate warrants further study.

Interaction Between Two Perpendicular Fabry–Perot-Like Resonances of the Antenna–Dielectric–Slit Structure and Their Influences on the Transmission Enhancement

The interaction between the two perpendicular Fabry–Perot-like resonances of the antenna–dielectric–slit structure and their influences on the transmission enhancement are investigated with a finite-difference time-domain method. The transmission enhancement is found with the antenna width corresponding to a Fabry–Perot-like resonance condition in the antenna–dielectric–slit structure; otherwise, there is no such an enhancement even when the slit is positioned under the magnetic field maximum. On the other hand, the resonance characteristics of the vertical slit can also modify the field distribution in the horizontal cavity by changing the phase difference at the two antenna ends. It is shown that the enhanced transmission can be realized in a wide range of incident wavelengths from the visible to near-infrared regime for different slit geometries. The physical mechanism of extraordinary optical transmission is discussed with a theoretical dispersion relationship of surface plasmon polaritons based on a metal–insulator–metal cavity model.

Development of Visible Light Sensitive TiO<sub>2</sub> Photocatalysts and Their Sensitization Using Fe<sup>3+</sup> Ions

Titanium dioxide photocatalysts are promising substrates for photodegradation of pollutants in water and air, but show photocatalytic activities only under UV light. To utilize a wider range of incident wavelengths such as solar light, development of photocatalysts active under visible light is very important. Chemically modified titanium dioxide photocatalysts were prepared containing anatase phase with S (S4+) substituted for some lattice Ti atoms or N substituted for some lattice O atoms. These catalysts showed strong absorption of visible light and high activities for degradation of 2-propanol in aqueous solution and partial oxidation of adamantane under irradiation at wavelengths longer than 440 nm. The oxidation states of the S and N atoms incorporated into the TiO2 particles were determined to be mainly S4+ and N3− from XPS spectra, respectively. The photocatalytic activities of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions were markedly improved for oxidation of 2-propanol compared to those of S- or N-doped TiO2 without Fe3+ ions under a wide range of incident wavelengths, including UV light and visible light. The photocatalytic activity reached maximum with 0.90 wt% Fe3+ ions adsorbed on S-doped TiO2, and 0.36 wt% Fe3+ ions on N-doped TiO2. Furthermore, redox treatment of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions by reduction with NaBH4 followed by air oxidation resulted in further improvements in photocatalytic activities. In this case, the optimum amounts of Fe3+ were 2.81 and 0.88 wt% on the surfaces of S- and N-doped TiO2 photocatalysts, respectively.

Photothermal spectroscopy of Bacillus anthracis and Bacillus cereus with microcantilevers

Microcalorimetric optical and infrared spectroscopy is a method of determining the spectral absorption of small quantities of materials over a wide range of incident wavelengths. In this paper, the first spectroscopic results for microcantilevers coated with Bacillus anthracis (BA) are presented. These results, for B. anthracis from 2.5 to 14.5 μm, are compared with results from microcantilevers coated with Bacillus cereus (BC) and standard spectroscopic absorption data. The results demonstrate strong correlation between the deflection measurements and the reference spectroscopic absorption peaks. An advantage of this microcantilever-based method over traditional spectroscopy is that much smaller amounts of material (nanogram quantities) can be detected in comparison with the milligram amounts needed for standard methods. Another advantage is that the complete system can be relatively small without sacrificing spectral resolution.

Third-order nonlinear susceptibility of Mg II and Ca II ions

The nonlinear coefficientχ (3) (3ω) of the singly ionized atoms Mg II and Ca II has been calculated for a wide range of incident wavelengths from v.u.v. to i.r. In some parts of the spectrum the magnitude of the nonlinear susceptibility is comparable to that of the alkali metal vapours.

Some measurements of the resonance raman effects in β-carotene

The intensity of Raman scattering of β-carotene has been measured for a wide range of incident wave-lengths, and an approximate proportionality between this and the absorption coefficient has been observed.