Specific Power Level Research Articles

Integrated FTTH and In-Building Fiber-Coax OFDM Field Trial

The performance of multi-service provisioning employing orthogonal frequency division multiplexed (OFDM) signals in fiber-to-the-home (FTTH) networks integrating hybrid fiber-coax in-building distribution is evaluated with a field trial in Towercom FTTH network in operation in Bratislava, Slovakia. The optical link budget performance is evaluated on an FTTH link of 35.8 km of standard single-mode fiber including hybrid 100-m fiber and 20-m coax in-building distribution transmitting a five-in-one multi-service bundle. The multi-service OFDM bundle includes LTE for phone service provision, WiMAX for wireless data and home security, DVB-T and UWB for TV and HD video broadcasting, and a custom OFDM signal providing wired gigabit Ethernet (GbE) connectivity. The specific optical power level requirements for both downstream and upstream directions to achieve successful bi-directional communication are evaluated in a WDM-PON configuration. The experimental results indicate that multi-service downstream provision with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 5}\hbox{-}{\rm dBm}$</tex></formula> optical power arriving to customer premises is required. In the upstream, the optical power power requirement at the central office is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 9}~{\rm dBm}$</tex></formula> for return communication. The optical attenuation level that can be supported by the network is investigated to evaluate the splitting ratio and the maximum capacity (number of users) of the network. Final application was confirmed experimentally with the transmission of multi-service OFDM signals in Towercom FTTH network including a 1:8 passive splitter.

Experimental investigation of a liquid cooled high temperature proton exchange membrane (HT-PEM) fuel cell coupled to a sodium alanate tank

In high temperature proton exchange membrane (HT-PEM) fuel cells, waste heat at approximately 160 °C is produced, which can be used for thermal integration of solid state hydrogen storage systems. In the present study, an HT-PEM fuel cell stack (400 W) with direct liquid cooling is characterized and coupled to a separately characterized sodium alanate storage tank (300 g material). The coupled system is studied in steady state for 20 min operation and all relevant heat flows are determined. Even though heat losses at that specific power and temperature level cannot be completely avoided, it is demonstrated that the amount of heat transferred from the fuel cell stack to the cooling liquid circuit is sufficient to desorb the necessary amount of hydrogen from the storage tank. Furthermore, it is shown that the reaction rate of the sodium alanate at 160 °C and 1.7 bar is adequate to provide the hydrogen to the fuel cell stack. Based on these experimental investigations, a set of recommendations is given for the future design and layout of similar coupled systems.

Excitation of relaxation oscillations in a semiconductor superlattice by incident waves: efficient terahertz harmonics generation

Generation of terahertz harmonics by frequency multiplication with a semiconductor superlattice due to an excitation of relaxation oscillations by incident waves is investigated theoretically. It is shown that the relaxation oscillation excitation becomes feasible if the superlattice dc resistance is low enough in comparison with a characteristic radiation impedance of the external waveguide system. The power of the generated harmonics as a function of the incident wave power demonstrates a threshold-like behavior at a specific input power level dependent on the superlattice peak current. We demonstrate that for typical superlattice parameters the roll-of frequency of the generated harmonics is mostly specified by the plasma frequency of electrons in a superlattice miniband. We argue that an increase of the superlattice miniband widths could essentially enhance both the efficiency and the spectral range of the generated terahertz harmonics.

Calibrated non-linear vector network measurement without using a multi-harmonic generator

The current generation of non-linear vector network analysers (NVNA) relies on a multi-harmonic generator to establish an absolute phase reference. Such a reference may not be readily available or, more importantly, may impose limitations on tone spacing in multi-tone testing for one type of NVNA based on a four-port VNA. The latter is a severe limitation when characterising memory behaviour in RF non-linear circuits. Here a hybrid NVNA is proposed that combines a sampling oscilloscope, a four-port VNA and phase-locked signal generators. A signal generator, phase locked to generators that are combined as the multi-tone excitation, provides the relative phase reference during swept power measurements using the VNA. The high dynamic range VNA-based measurements are corrected in absolute phase using the oscilloscope-based NVNA measurement at a specific power level. The hybrid NVNA has high dynamic range and the lower bound on tone spacing is determined by the memory depth of the oscilloscope, the windowing effect of the VNA receivers and the phase noise of the multi-tone sources. At 2 GHz, the hybrid NVNA has a dynamic range of 40 dB at 200 Hz tone spacing for a two-tone signal, increasing to more than 80 dB for tone spacings of 200 kHz and greater.

Enhancing of Biodegradability of Sewage Sludge by Microwave Irradiation

In our work we focused on the effect of the microwave energy at the aerobic and anaerobic biological degradability of sewage sludge. The sewage sludge is a multiphase system with high water content. Because of the presence of water molecules sludge is able to absorb the microwave energy efficiently. Because of the variable dielectric properties the different component of sludge heat differently, these effects cause „thermal shock”. During the microwave treatment the configuration of macromolecules are varied and the cell walls of the microorganisms are opened by the thermal shock, it means the organic compounds are accessible for further biological degradable. In our experiments digested municipal sewage sludge and undigested dairy-sludge were used. Labotron 500 professional microwave equipment was used for the microwave treatment at 2450 MHz frequency. The specific microwave power level was changed between 1 to 5 W/g. Oxitop PM barometrical measurement system was used for determination of the biogas production at 40 °C, the measurement of the chemical oxygen demand (COD) of sludge was based on a potassinium-bichromate method, and a respirometric BOD meter was used for the biochemical oxygen demand (BOD) measurement (20 °C). Our results showed that, the microwave energy could be a practical and effective alternative technique to enhance the biodegradability of sludge, because after microwave treatment increases the biodegradability from 7 up to 40% by diary sludge and from 12 up to 48% by municipal sludge. It was found, that the originally resistant sludge after a microwave pre-treatment became more degradable, and its biogas production increased from 20-30 ml/g dry weight up to 500 ml/ gdry weight. The highest microwave power level effects the highest biogas yield, but the energy balance at lower specific power level (1-2 W/g) and longer treatment time gave just notable net energy production compared to the control sample.

A Versatile Video-Waveform Corrector for TV Transmitter and Studio Applications

The basis of a TV system is that the video signal is assigned a specific power level (amplitude) at a specific point in time. Of prime significance, then, are the time-domain characteristics of the video signal waveform.

Theoretical Performace of a Crossed Field MHD Accelerator

A theoretical analysis of a crossed-field MHD plasma accelerator based on the radial-source flow model is presented in which any propellant that is a mixture of seed and inert gas can be treated, and allowance is made for the flow of Hall currents. Provision is made for investigation of both a shifting equilibrium and a frozen equilibrium expansion in the accelerator. Calculations are carried out for a number of potentially practical designs. The results are reported in terms of specific impulse, thrust, efficiency, and electrical power level. (auth)