Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy

In this study, demonstration of simultaneous prediction of solid wood density and moisture content, both of which are critical in manufacturing operations, of 4 species (Aspen, Birch, Hemlock and Maple) was accomplished using terahertz time-domain spectroscopy (THz-TDS). THz measurements of wood at various moisture contents were taken for two orientations of the THz field (parallel and perpendicular) with respect to the visible grain. The real and imaginary parts of the dielectric function averaged over the frequency range of 0.1 to 0.2 THz had strong correlation with density and moisture content of the wood. We extend a model that has been applied previously to oven-dry wood to include the effects of moisture below the fiber saturation point by combining two effective medium models, which allows the dielectric function of water, air and oven-dry cell wall material to be modeled to give an effective dielectric function for the wood. A strong correlation between measured and predicted values for density and moisture content were observed.     

Charge transport in Si-SiO2 and Si-TiO2 nanocomposite structures

The experimental data on dispersed Si-SiO₂ and Si-TiO₂ nanocomposite structures different in terms of physical, chemical, and insulator properties of oxide components are reported. The parameters of the nanocomposite structures are studied by FTIR spectroscopy and impedance spectroscopy. It is shown that, in such structures, the mechanisms of charge-carrier transport are defined by the properties of Si nanocrystallites and the corresponding oxide as well as by interaction processes at interfaces between grains.     

Characterization of in-situ terahertz detection by optical interaction in a periodically poled stoichiometric lithium tantalate nonlinear crystal

Terahertz waves are generated using a femtosecond laser pulse in a periodically poled stoichiometric lithium tantalate crystal and simultaneously detected via a non-collinear optical parametric interaction inside the same crystal. Real time up-conversion signal between the generated THz and an optic probe pulses is measured depending on the beam overlapped conditions using a general silicon-photodiode for the THz detection. The non-collinear geometry is to facilitate manipulated property of the position-dependent bandwidth at narrow and broad bandwidths of 45 GHz and 3.3 THz, respectively at the one crystal. Furthermore, an aperture effect at the detection part is characterized as the function of size and position owing to the spatial distribution of the frequency conversion signal and it is applied in optimization of the in-situ detection scheme.     

Terahertz polarization beam splitter based on photonic crystal and multimode interference

We design a compact terahertz （THz） polarization beam splitter. Both plane wave expansion method and fi- nite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The designed polarization beam splitter can split TE-polarized and TM-polarized THz waves into different propagation di- rections. The simulation results show that the extinction ratios are larger than 18.36 dB for TE polarization and 13.35 dB for TM polarization in the frequency range from 1.86 THz to 1.91 THz, respectively. The designed polarization beam splitter has the advantages of small size and compact structure with a total size of 4.825 mm×0.400 mm.     

A practical RFID authentication mechanism for digital television

As information technology continuously progresses, more applied technologies are developed, such as radio frequency identification (RFID). In this paper, we propose a novel digital television (DTV) structure that uses RFID for encryption. RFID is widely used for various applications because of its advantages such as an extended lifetime and security, and it is less affected by environmental constraints. The proposed protocol uses RFID for encryption to withstand many attacks that the traditional system is vulnerable to, such as impersonation attack, replay attack and smart card cloning. Compared with other protocols, the proposed protocol is more secure and efficient. Thus, our proposed protocol makes the DTV framework more complete and secure.     

Improved Hydrogen Capping Effect in n-Type Crystalline Silicon Solar Cells by SiN(Si-Rich)/SiN(N-Rich) Stacked Passivation

The effect of hydrogen capping of SiN(Si-rich)/SiN(N-rich) stacks for n-type c-Si solar cells was investigated. Use of a passivation layer consisting of Si-rich SiN with a refractive index (n) of 2.7 and N-rich SiN with a refractive index of 2.1 improved the thermal stability. A single SiN passivation layer with a refractive index of 2.05 resulted in an initial lifetime of 200 μs whereas the layer with a refractive index of 2.7 resulted in a high initial lifetime of 2 ms, but the layer degraded rapidly after firing. A stacked passivation layer with refractive indices of 2.1 and 2.7 had a stable lifetime of 1.5 ms with an implied open-circuit voltage (iV _oc) of 720 mV after firing. The thermally stable passivation mechanism with changing amounts of Si–N and Si–H bonding was analyzed by Fourier-transform infrared (FTIR) spectroscopy. Incorporation of the SiN _x stack layer (2.7 + 2.1) into the passivated rear of n-type Cz silicon screen-printed solar cells resulted in energy conversion efficiency of 19.69%. Improved internal quantum efficiency in the long-wavelength range above 900 nm, with V _oc of 630 mV, is mainly because of superior passivation of the rear surface compared with conventional solar cells.     

Simulation of Terahertz Generation from Lateral Diffusion Currents in Semiconductor Devices

In this paper we model the carrier dynamics and resulting THz emission from lateral diffusion currents within a semiconductor device which has been partially masked by a metallic mask. We present a numerical 1D model and a 1D Monte Carlo simulation which both demonstrate that regardless of the excitation laser spot shape we do not expect to see measurable THz emission in the direction of the optical pump propagation from lateral diffusion currents. Experimentally such devices do produce strong THz emission. We analytically investigate the role of the metal mask and we found that it suppresses the emission of dipoles that are in a region that is less than a wavelength away from the interface. The results from the numerical model are also included in a finite element analysis model of the geometry which predicts THz emission if and only if the metal mask is present.     

Photoelectric and photovoltaic properties of structures based on mesoporous silicon passivated with iron

The photoelectric and photovoltaic properties of structures based on mesoporous silicon passivated with iron (SiMP:Fe) are studied. It is shown that these properties ambiguously depend on the iron concentration. In the case of a sample with space-charge-limited currents (SCLCs), the charge-transport mechanism in the Al-SiMP:Fe-p-Si-Al heterostructure changes under illumination from the SCLC type to the barrier type. Passivation with 0.1–0.2 at % iron stabilizes not only the electrical, but also the photoelectric and photovoltaic properties of the structures. A further increase in the Fe concentration gives rise to new traps caused by the appearance of iron and silicon oxides, which leads to instability of the properties. The structures exhibit high sensitivity under low-level illumination. The open-circuit voltage is 16 mV under AM-1 irradiation (～2 mW/cm²).     

Channel Estimation in Long Term Evolution Uplink Using Minimum Mean Square Error-Support Vector Regression

In this paper, minimum mean square error-support vector regression (MMSE-SVR) is proposed, which is shown to be adequate for the estimation of the long term evolution (LTE) uplink channel with nonlinear features. MMSE-SVR was applied to estimate real channel environments such as the vehicular A channels defined by the International Telecommunication Union (ITU). The simulation results show that the proposed method has a better performance than the least squares support vector machine (LS-SVM) and the standard MMSE with linear and spline interpolation.     

Electrical Characteristics of Al/Poly(methyl methacrylate)/p-Si Schottky Device

Al/Poly(methyl methacrylate)(PMMA)/p-Si organic Schottky devices were fabricated on a p-Si semiconductor wafer by spin coating of PMMA solution. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of Al/PMMA/p-Si structures have been investigated in the frequency range of 1 kHz–10 MHz at room temperature. The diode parameters such as ideality factor, series resistance and barrier height were calculated from the forward bias current–voltage (I–V) characteristics. In order to explain the electrical characteristics of metal–polymer–semiconductor (MPS) with a PMMA interface, the investigation of interface states density and series resistance from C–V and G–V characteristics in the MPS structures with thin interfacial insulator layer have been reported. The measurements of capacitance (C) and conductance (G) were found to be strongly dependent on bias voltage and frequency for Al/PMMA/p-Si structures. The values of interface state density (D _it) were calculated. These values of D _it and series resistance (R _s) were responsible for the non-ideal behavior of I–V and C–V characteristics.     

On the kinetics of electron processes in 60Co γ-irradiated n-Ge single crystals

Variations in the main electrical parameters of n-Ge single crystals with different doping levels under the effect of 60Co γ-irradiation are investigated. A noticeable increase in the carrier mobility in the irradiated samples is observed in some dopant concentration range and the nature of this effect is explained. It is demonstrated that the electron-mobility variation under the action of γ-irradiation in the initial n-Ge crystals with an oxygen impurity and in the annealed crystals have opposite signs. It is established that the oxygen complexes formed in the samples during annealing and the local lattice stresses near these complexes play a key role in the radiation-induced mobility increase. It is clarified that the radiation resistance of the electron mobility significantly depends on the crystallographic orientation of the investigated samples.     

Fir laser stabilization using stark effect: Data on CH3Br and CH3Cl

Data on the influence of the Stark Effect on an optically pumped FIR laser with CH₃Cl or CH₃Br as active medium are given for various wavelengths. A very simple method for an effective FIR power stabilisation based on the Stark Effect is described. Its working is illustrated with the EPR signal of a 10% diluted DAG sphere.     

Throughput Evaluation of Oversampled Receiver: An Example of WiMAX System

In this paper, we propose an oversampled WiMAX receiver as an attempt to improve throughput of WiMAX system. In communication, oversampling is a technique that a signal is sampled with a higher sampling frequency than its original bandwidth at the receiver side. Thus more signal sequences, which is received through different paths, may be obtained compare to system with conventional sampling. These additional sequences generate diversity. This study theoretically analyzes an oversampled wireless communication system in case of capacity with outage over Rayleigh distributed flat fading channel and presents throughput of the oversampled WiMAX receiver that obtained by simulation over a realistic channel model and by experimental tests. Since the performance of an oversampled system very much depends on the channel conditions, realistic channel model and experimental study are essential to exhibit realistic performance benchmarks. Theoretical analyzes, simulations and experimental results clearly show that the oversampled receiver significantly outperforms the spectrum efficiency of the communication system.     

A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.     

Effective Permittivity and Refractive Index of TiO2/Ge and SiO2/Ge Nanostructures at High Frequencies

We have calculated the effective permittivity and refractive index of TiO₂/Ge and SiO₂/Ge nanostructures for a broad range of terahertz frequencies. The structures are composites of two different kinds of nanosphere, one made from high-refractive-index dielectric materials of different radius and the other from n-type germanium.     

Wavelet Based Identification of Substances in Terahertz Tomography Measurements

In comparison to the X-ray computed tomography Terahertz technique significantly enhances the amount of the information acquired during the sample measurement. Not only amplitude, but also phase, time and spectral characteristics can be determined in THz time-domain spectroscopy. Thus, Terahertz tomography allows localization and identification of substances within the objects due to the characteristic fingerprints in this frequency range. Certainly, an appropriate data processing and comparison algorithms are crucial for the accurate identification of the substances in the measured sample. Therefore, we present a new wavelet-based identification method which is suitable even for the substances with broad absorption curves and small or no absorption peaks. The performance of this algorithm was evaluated with the help of a tomographic sample filled with four substances, which were previously characterized for the external database. The continuous wavelet transform was applied to every data cell of the tomographic measurement and compared to the database. Received sinograms were reconstructed into images which depict estimated similarity between the measured and database substances. Furthermore, we suggest a method for the reduction of spectral data after the continuous wavelet transform. This method is based on the extraction of the distinctive features in the form of ridge lines.     

Effects of Propagation Models on AODV in Mobile Ad-hoc Networks

Mobile ad-hoc networks (MANET) operate like self organizing entity. The mobile nodes are operate in a host as well as in a router and dynamic topology. In MANET every network node operates autonomously. It has limited resources like power, bandwidth and storage capacity. Selection of a propagation model plays the vital role of application possibilities in MANET. In this paper, calculations have been performed for three propagation models: Two-ray ground, COST 231 and Okumura–Hata model. The paper shows the impact of these propagation models based on Ad-hoc on-demand distance vector (AODV) protocol at 1.5 GHz frequency, varying transmitted power and number of nodes. This paper also studies effects of the propagation models with the conclusion of choosing the most accurate propagation model. Okumura–Hata propagation model shows better results at 1.5 GHz frequency as compared to COST 231 and Two-ray ground model in open space using Network Simulator (NS 2.35). Two-ray ground propagation model shows better results with varying transmitted power and number of nodes as compared to COST 231 and Okumura–Hata model.     

Liquid crystal alignment films produced by the R.F. Plasma beam technique

An rf plasma system is described suitable for deposition of anisotropic SiO(in2) films capable of aligning liquid crystal cells parallel to the substrate surface at approximately zero tilt and perpendicular to the plane of incidence. The electrooptical response of twisted cells made by this technique and their ε(H) curves are discussed.     

Implementation of AES Key Schedule Using Look-Ahead Technique

The commencement of decryption process of Advanced Encryption Standard (AES) algorithm is dependent on availability of the last round key. In this paper, we propose a look-ahead technique for increasing the speed of implementation of AES key schedule using which the last round key can be made available fast. The other round keys can also be computed in a parallel path using the proposed technique. Applications such as key search engines need to be agile to key changes for decrypting given encrypted messages using all the keys in the available key space so that fast decryption is possible. The FPGA implementation results using Xilinx XC5VLX85 are also provided.     

p +-Si/nano-SiO2/n +-Si capacitor-based tunnel diode with negative differential resistance and a quartz resonator

To demonstrate the extending functionality of the simplest MOS (metal-oxide-semiconductor) capacitor, a structure with a p ⁺-Si/nano-SiO₂ heterojunction in which strongly degenerate n ⁺-Si is used instead of a metal electrode is considered. As a result, a tunnel diode with negative differential resistance and a quartz resonator is obtained. Its electrical characteristics are superior to those of the corresponding Esaki diode and are controlled not only by the Silicon doping level, but also by the SiO₂ thickness.