Study of acoustic emission (AE) caused by high voltage insulators

Acoustic emission (AE) study based on the acoustic signal ranges from 30MHz to 300MHz has been performed to diagnose the deterioration of insulation level in outdoor ceramic insulator. Different weather conditions combining with artificially created pollution were produced in laboratory and measurements were recorded over a fixed period of time. Pollution due to fine dust particles has been created according to IEC standard under wet and dry conditions. Samples that exhibit internal cracks and fracture were used in this study. The collected AE signals were sampled and analysed using fractal theory. The results of this study have clearly demonstrated the prospect of using AE technique to monitor the working condition of outdoor insulator.

Al- Jazeera : a broadcaster creating ripples in a stagnant pool

Al-Jazeera is unique in the Arab world. In an environment of state-controlled or compliant media, this Arab-language news channel thinks of itself as a breath of fresh air or a source of fresh water. It broadcasts controversial subjects and, in doing so, it has attracted an audience of 35 million households glued to its programming - and criticism.

Al-Jazeera : a broadcaster creating ripples in a stagnant pool

Al-Jazeera is unique in the Arab world. In an environment of state-controlled or stale media, this Arab-language news channel sees itself as a source of fresh water in a parched region bereft of freedom of expression. It broadcasts controversial subjects and, in doing so, has attracted an audience of 35 million households - and plenty of criticism. Most notable controversies have been the airing of tapes of Osama bin Laden. and the broadcasting of images of captured Coalition soldiers and bloodied corpses during the Iraq war. Before those events, Al-Jazeera had criticised Arab heads of state, blatantly ignoring the Arab States Broadcasting Union's code of honour. Some companies have avoided the channel because advertising in the Middle East is based on political, not commercial, interests. Yet along the way, AI-Jazeera has put Qatar. a tiny Gulf nation of perhaps 600,000 people, on the world map. Based on the last-known interviews before the station went on a war footing, this paper looks at why and how AI-Jazeera does what it does. Among the things covered are how the station defines freedom of expression through its own eyes. the role that the station and its employees believe they are serving in the marketplace. and why they do what they do. The paper also considers the station s role in the war in Iraq in March and April of 2003.

Donor-п-acceptor conjugated copolymers for photovoltaic applications : tuning the open-circuit voltage by adjusting the donor/acceptor ratio

A class of new conjugated copolymers containing a donor (thiophene)−acceptor (2-pyran-4-ylidene-malononitrile) was synthesized via Stille coupling polymerization. The resulting copolymers were characterized by 1H NMR, elemental analysis, GPC, TGA, and DSC. UV−vis spectra indicated that the increase in the content of the thiophene units increased the interaction between the polymer main chains to cause a red-shift in the optical absorbance. Cyclic voltammetry was used to estimate the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) and the band gap (Eg) of the copolymers. The basic electronic structures of the copolymers were also studied by DFT calculations with the GGA/B3LYP function. Both the experimental and the calculated results indicated an increase in the HOMO energy level with increasing the content of thiophene units, whereas the corresponding change in the LUMO energy level was much smaller. Polymer photovoltaic cells of a bulk heterojunction were fabricated with the structure of ITO/PEDOT/PSS (30 nm)/copolymer−PCBM blend (70 nm)/Ca (8 nm)/Al (140 nm). It was found that the open-circuit voltage (Voc) increased (up to 0.93 V) with a decrease in the content of thiophene units. Although the observed power convention efficiency is still relatively low (up to 0.9%), the corresponding low fill factor (0.29) indicates considerable room for further improvement in the device performance. These results provided a novel concept for developing high Voc photovoltaic cells based on donor-π-acceptor conjugated copolymers by adjusting the donor/acceptor ratio.

Pi-shaped MEMS architecture for lowering actuation voltage of RF switching

A wide band low actuation capacitive coupling electrostatic RF MEMS switching device is presented in this paper. The device includes a pi-shaped matching architecture containing two switches connected by a high impedance short transmission line. The device can act as a switch for any desired frequency whilst requiring only 12volts for actuation. By optimizing the length and the characteristic impedance of the transmission line, the switch can be tailored for desired frequency bands. The switch is calculated and simulated for Ka to V frequency bands demonstrating excellent improvements of RF characteristics.

Design and simulation of a low voltage wide band RF MEMS switch

This paper presents design of an electrostatic wide band shunt capacitive coupling RF MEMS switch with low actuation voltage. The key factors of the RF MEMS switch design are the proper scattering parameters, low actuation voltage, and the cost of the fabrication process. An overview of the recent low actuation voltage RFMEMS switches has been presented. These designs still suffer from the complexity of process, lack of reliability, limitation of frequency band, and process cost. RF characteristics of a shunt RF MEMS switches are specified mostly by coupling capacitor in upstate position of the membrane Cu. This capacitor is in trade-off with actuation voltage. In this work, the capacitor is eliminated by using two short high impedance transmission lines, at the input and output of the switch. The simulation results demonstrate an improvement in the RF characteristic of the switch.

Low actuation-voltage shift in MEMS switch using ramp dual-pulse

This paper proposes a ramp dual-pulse actuation-voltage waveform that reduces actuation-voltage shift in capacitive microelectromechanical system (MEMS) switches. The proposed waveform as well as two reported waveforms (dual pulse, and novel dual-pulse) are analyzed using equivalent-circuit and equation models. Based on the analysis outcome, the paper provides a clear understanding of trapped charge density in the dielectric. The results show that the proposed actuation-voltage waveform successfully reduces trapped charge and increases lifetime due to lowering of actuation-voltage shift. Using the proposed actuation-voltage waveform, the membrane reaches a steady state on the electrode faster.

Accurate modeling of low actuation voltage RFMEMS switches using artificial neural networks

This paper presents a fast and accurate method for extracting the scattering parameters of a RF MEMS switch by using its essential parameters. A neural network is developed for parametric modeling of the switch. The essential parameters of the switch are analyzed in terms of its return loss and isolation with variation of its geometrical component values. Simulation results show that the proposed approach can be used to accurately model the RF characteristics of RF-MEMS switches. The results show good agreement between the neural network prediction and electromagnetic simulations.