Transmission and attenuation of the dominant mode in uniformly bentcircular hollow waveguides for the infrared: scalar analysis

A numerical evaluation is conducted of electric field distributions, phase constants, and attenuation constants of the lowest eigenmode in the general class of uniformly bent circular hollow waveguides. The analysis is based on a scalar equation, and numerical results are compared with those of existing approximate theories. Normalized forms of attenuation constants are presented for the parallel and perpendicular polarizations to the bending plane by using structural and material parameters. For sharply bent waveguides, useful and simple expressions are derived for the attenuation constants of the TE and TM modes in the corresponding slab geometry with suitable weighting parameters     

Topical Phenomena Observed in a Short-Gap Atmospheric Discharge Using Rotor and Post Electrodes

Correlation of light emission, discharge structure, waveform of the discharge current, electrode configuration, and electromagnetic radiation is examined with the intent of obtaining an effective means for preventing electromagnetic interference (EMI) due to a short-gap discharge. The electromagnetic radiation (EMR) level resulting from a current step which, in turn, was formed by a discrete movement of a cathode spot was clearly recognized. A combination of needle rotor and needle post gave the smallest electromagnetic radiation level in the experiments.     

Evaluation of the Parallel Conductor Theory for Measuring Human Limb Blood Flow by Electrical Admittance Plethysmography

We devised a compensation technique that measures the admittance change of a limb submerged in an electrolyte solution in a cylinder. Using this technique, we evaluated the accuracy of admittance plethysmography and the validity of the parallel-conductor model on which the theory of blood flow measurement by electrical admittance (or impedance) plethysmography is based. From a theoretical point of view, if a limb is regarded as a parallel-conductor model, the admittance change due to blood pooling following venous occlusion should disappear when the resistivity of the solution is equal to that of the blood.     

Polymerization of [2,5-bis(trifluoromethyl)phenyl]acetylene and polymer properties

Summary [2,5-Bis(trifluoromethyl)phenyl]acetylene [BTFPA; HCCC₆H₃-2, 5-(CF₃)₂]polymerized with W, Mo, and Nb catalysts to produce methanol-insoluble polymers in high yields. The poly(BTFPA) produced by the W(CO)₆-based catalyst at 30 °C was soluble in p-(CF₃)₂C₆H₄, and had relatively high molecular weight ([]=0.352 dL/g in p-(CF₃)₂C₆H₄). The main chain of the polymer was composed of alternating double bonds, and the polymer was a dark brown solid. The temperature at which the weight loss of the polymer started was higher than 300 °C. The polymerization behavior and polymer properties for BTFPA are compared with those for phenylacetylene and [o-(trifluoromethyl)phenyl]acetylene.     

Durable write-once optical disk memories for 800 nm using silverisland films

Durable write-once (WO) optical disk media have been demonstrated by using silver island films with a protection layer of fluorine-contained polymers. The reflectance of the silver island films is high at the wavelength of 800 nm and can be greatly lowered by laser irradiation, owing to the thermal deformation or the islands. Laser writing has been experimentally confirmed at almost the same line speed as that of compact discs (CDs). Therefore it is expected that a CD-compatible write-once optical disc can be realised     

Origin of electron mobility enhancement in (1 1 1)-oriented InGaAs channel metal-insulator-semiconductor field-effect-transistors

Electrical and physical characteristics of the Al₂O₃/InGaAs interfaces with (1 1 1)A and (1 0 0) orientations were investigated in an attempt to understand the origin of electron mobility enhancement in the (1 1 1)A-channel metal-insulator-semiconductor field-effect-transistor. The (1 1 1)A interface has less As atoms of high oxidation states as probed by X-ray photoelectron spectroscopy. The electrical measurements showed that energy distribution of the interface traps for the (1 1 1)A interface is shifted toward the conduction band as compared to that for the (1 0 0) interface. Laterally-compressed cross-section transmission electron microscopy images showed that the characteristic lengths of the interface roughness are different between the (1 1 1)A and (1 0 0) interfaces. The contributions of the Coulomb and roughness scattering mechanisms are discussed based on the experimental results.     

THz-wave absorption by field-induced carriers in pentacene thin-film transistors for THz imaging sensors

Innovative sensing systems based on THz electromagnetic waves have been attracting a great deal of attention. Although many THz detectors have been developed over the years, it is currently difficult to manufacture low-cost THz sensing/imaging devices. In the present study, we propose to use organic field-effect transistors (OFETs) and small potential fluctuation against the carriers within them (N. Ohashi, H. Tomii, R. Matsubara, M. Sakai, K. Kudo, M. Nakamura, Appl. Phys. Lett. 91 (2007) 162105). We use THz time-domain spectroscopy for OFETs in which the carrier density in the pentacene active layer is modulated by the gate bias. We found evidence that the accumulated free holes in pentacene films can be excited by THz photons to overcome the surrounding barriers in the fluctuating potential. The Drude–Lorentz model could not account for the shape of the absorption spectra, which suggests that the holes are weakly restricted by the potential fluctuation. The integrated absorption intensity was proportional to the transfer characteristics of the OFETs. The present findings represent an important step toward developing a new class of THz-wave sensors.     

Effect of off-orientation of seed crystal on silicon carbide (SiC) single-crystal growth on the (11 $$\bar 2$$ 0) surface0) surface

The effect of off-orientation growth has been investigated in terms of stacking fault formation during physical vapor transport (PVT) growth of silicon carbide (SiC) single crystals on the (11 0) seed crystal surface. Occurrence of stacking fault formation is largely dependent on the direction of off-orientation, and basal plane stacking fault density is significantly reduced by growing the crystals on a (11 0) seed crystal off-oriented toward 〈0001〉. The density of the basal plane stacking faults rapidly decreases from 100–150 cm⁻¹ to ∼10 cm⁻¹ as the degree of off-orientation is increased from 0 to 10 deg. The results are interpreted in the framework of microscopic facet formation during PVT growth, and the introduction of off-orientation of seed crystal is assumed to prevent (01 0) and (10 0) microfacet formation on the (11 0) growing surface through modification of the surface growth kinetics and to suppress the stacking fault formation. An erratum to this article is available at .     

Time division multiplexed OTDR system

A new technique to increase the effective sampling rate of an optical time-domain reflectometer using a time division multiplexing digital sampling averaging procedure is proposed. This permits an increase in distance measuring accuracy of an optical time-domain reflectometer.