PEA Space Charge Measurement System(Electrical & Electronics Seminar Topics

INTRODUCTION

The pulsed electro acoustic analysis (PEA) can be used for space charge measurements under dc or ac fields. The PEA method is a non-destructive technique for profiling space charge accumulation in polymeric materials. The method was first proposed by T.Takada et al. in 1985. The pulsed electro acoustic (PEA) method has been used for various applications. PEA systems can measure space charge profiles in the thickness direction of specimen, with a resolution of around 10 microns, and a repetition rate in the order of milliseconds. The experimental results contribute to the investigation of the charge transport in dielectrics, aging of insulating materials and the clarification of the effect of chemical properties on space charge formation. PEA method can measure only net charges and does not indicate the source of the charge.

Various space charge measurement techniques are thermal step, thermal pulse, piezoelectric pressure step, and laser induced pressure pulse, the pulse electro acoustic method. In the thermal step method, both electrodes are initially in contact with a heat sink at a temperature around -10 degrees Celsius. A heat source is then brought into contact with one electrode, and the temperature profile through the sample begins to evolve towards equilibrium consistent with the new boundary conditions.

The resulting thermal expansion of the sample causes a current to flow between the electrodes, and application of an appropriate deconvolution procedure using Fourier analysis allows extraction of the space charge distribution from the current flow data. This technique is particularly suited for thicker samples (between 2 and 20 mm). Next is the thermal pulse technique. The common characteristic is a temporary, non -destructive displacement of the space charge in the bulk of a sample created by a traveling disturbance, such as a thermal wave, leading to a time dependent change in charge induced on the electrodes by the space charge. Compression or expansion of the sample will also contribute to the change in induced charge on the electrodes, through a change in relative permittivity. The change in electrode charge is analyzed to yield the space charge distribution.

Thermal pulse technique yields only the first moment of the charge distribution and its first few Fourier coefficients. Next is laser induced pressure pulse. A temporary displacement of space charge can also be achieved using a pressure pulse in the form of a longitudinal sound wave. Such a wave is generated, through conservation of momentum, when a small volume of a target attached to the sample is ablated following absorption of energy delivered in the form of a short laser pulse. The pressure pulse duration in laser induced pressure pulse measurements depends on the laser pulse duration and it can be chosen to suite the sample thickness, ie, thinner the sample the shorter should be the laser pulse.

Space charge measurement has become a common method for investigating the dielectric properties of solid materials. Space charge observation is becoming the most widely used technique to evaluate polymeric materials for dc-insulation applications, particularly high-voltage cables. The presence of space charges is the main problem causing premature failure of high-voltage dc polymeric cables. It has been shown that insulation degradation under service stresses can be diagnosed by space charge measurements.

The term" space charge" means uncompensated real charge generated in the bulk of the sample as a result of (a) charge injection from electrodes, driven by a dc field not less than approximately 10 KV/mm, (b) application of mechanical/thermal stress, if the material is piezoelectric/ pyroelectric (c) field-assisted thermal ionization of impurities in the bulk of the dielectric.

Pebble-Bed Reactor(Electrical & Electronics Seminar Topics

INTROUCTION

The development of the nuclear power industry has been nearly stagnant in the past few decades. In fact there have been no new nuclear power plant construction in the United States since the late 1970s. What many thought was a promising technology during the "Cold War" days of this nation; they now frown upon, despite the fact that nuclear power currently provides the world with 17% of its energy needs. Nuclear technology's lack of popularity is not difficult to understand since the fear of it has been promoted by the entertainment industry, news media, and extremists. There is public fear because movies portray radiation as the cause of every biological mutation and now; terrorist threats against nuclear installations have been hypothesized. Also, the lack of understanding of nuclear science has kept news media and extremists on the offensive. The accidents at Three Mile Island (TMI) and Chernobyl were real and their effects were dangerous and, in the latter case, lethal. However, many prefer to give up the technology rather than learn from these mistakes.

Recently, there has been a resurgence of interest in nuclear power development by several governments, despite the resistance. The value of nuclear power as an alternative fuel source is still present and public fears have only served to make the process of obtaining approval more difficult. This resurgence is due to the real threat that global warming, caused by the burning of fossil fuels, is destroying the environment. Moreover, these limited resources are quickly being depleted because of their increased usage from a growing population.

The estimation is that developing countries will expand their energy consumption to 3.9 times that of today by the mid-21st century and global consumption is expected to grow by 2.2 times. Development has been slow since deregulation of the power industry has forced companies to look for short term return, inexpensive solutions to our energy needs rather than investment in long term return, expensive solutions. Short-term solutions, such as the burning of natural gas in combined cycle gas turbines (CCGT), have been the most cost effective but remain resource limited. Therefore, a few companies and universities, subsidized by governments, are examining new ways to provide nuclear power.

An acceptable nuclear power solution for energy producers and consumers would depend upon safety and cost effectiveness. Many solutions have been proposed including the retrofit of the current light water reactors (LWR). At present, it seems the most popular solution is a High Temperature Gas Cooled Reactor (HTGR) called the Pebble Bed Modular Reactor (PBMR).

HISTORY OF PBMR

The history of gas-cooled reactors (GCR) began in November of 1943 with the graphite-moderated, air-cooled, 3.5-MW, X-10 reactor in Oak Ridge, Tennessee. Gas-cooled reactors use graphite as a moderator and a circulation of gas as a coolant. A moderator like graphite is used to slow the prompt neutrons created from the reaction such that a nuclear reaction can be sustained. Reactors used commercially in the United States are generally LWRs, which use light water as a moderator and coolant.

Development of the more advanced HTGRs began in the 1950s to improve upon the performance of the GCRs. HTGRs use helium as a gas coolant to increase operating temperatures. Initial HTGRs were the Dragon reactor in the U.K., developed in 1959 and almost simultaneously, the Arbeitsgemeinshaft Versuchsreaktor (AVR) reactor in Germany.

Dr Rudolf Schulten (considered "father" of the pebble bed concept) decided to do something different for the AVR reactor. His idea was to compact silicon carbide coated uranium granules into hard billiard-ball-like graphite spheres (pebbles) and use them as fuel for the helium cooled reactor.

The first HTGR prototype in the United States was the Peach Bottom Unit 1 in the late 1960s. Following the success of these reactors included construction of the Fort S. Vrain (FSV) in Colorado and the Thorium High Temperature Reactor (THTR-300) in Germany. These reactors used primary systems enclosed in prestressed concrete reactor vessels rather than steel vessels of previous designs. The FSV incorporated ceramic-coated fuel particles imbedded within rods placed in large hexagonal shaped graphite elements and the THTR-300 used spherical fuel elements (pebble bed). These test reactors provided valuable information for future design

Low - k Dielectrics

INTROUCTION

In this fast moving world time delay is one of the most dreaded situations in the field of data communication. A delay in the communication is as bad as loosing the information, whether it is on the internet or on television or talking over a telephone. We need to find out different ways to improve the communication speed. The various methods adopted by the communication industry are the wireless technology, optical communications, ultra wide band communication networks etc. But all these methods need an initial capital amount which makes all these methods cost ineffective. So improving the existing network is very important especially in a country like INDIA.

The communication systems mainly consist of a transeiver and a channel. The tranceiver is the core of all data communications. It has a very vast variety of electronic components mostly integrated into different forms of IC chips. These ICs provide the various signal modifications like amplification, modulation etc. The delay caused in these circuits will definitely affect the speed of data communication.

This is where this topic LOW-k DIELCTRICS becomes relevant. It is one of the most recent developments in the field of integrated electronics. Mostly the IC s are manufactured using the CMOS technology. This technology has an embedded coupling capacitance that reduces the speed of operation. There are many other logics available like the RTL,DTL,ECL,TTL etc . But all these other logics have higher power consumption than the CMOS technology. So the industry prefer CMOS over other logics .

Inside the IC there are lots of interconnections between points in the CMOS substrate. These refer to the connection between the different transistors in the IC. For example , in the case of NAND LOGICS there are lots of connections between the transistors and their feedbacks. These connections are made by the INTERCONNECT inside the IC . Aluminum has been the material of choice for the circuit lines used to connect transistors and other chip components. These thin aluminum lines must be isolated from each other with an insulating material, usually silicon dioxide (SiO2).

This basic circuit construction technique has worked well through the many generations of computer chip advances predicted by Moore's Law1. However, as aluminum circuit lines approach 0.18 mm in width, the limiting factor in computer processor speed shifts from the transistors' gate delay to interconnect delay caused by the aluminum lines and the SiO2 insulation material. With the introduction of copper lines, part of the "speed limit" has been removed. However, the properties of the dielectric material between the layers and lines must now be addressed. Although integration of low-k will occur at the 0.13mm technology node, industry opinion is that the 0.10mm generation, set for commercialization in 2003 or 2004, will be the true proving ground for low-k dielectrics because the whole industry will need to use low-k at that line width.

The YouTube (R)evolution Turns 5

Founded five years ago, YouTube is now a full-fledged grown-up by Internet standards. Its days as an impulsive startup--replete with a cluttered office located between a pizza parlor and a Japanese restaurant--are long gone; and is incredible growth over the past half-decade has changed how we live, play, and do business

Opera 10.5 lags in my speed tests

Opera, which was bumped down to fifth place in browser usage after Google Chrome burst on the scene, has embraced a super-fast JavaScript engine as part of its bid to stay relevant.

Unfortunately for Opera, my tests show more work is needed.

The beta version of Opera 10.5 arrived Thursday morning, and I thought it a good time to compare how some of the cutting-edge versions of the browsers were shaping up in performance--especially because Mozilla has released a preview version of the next version of Firefox.

VoCable Electronics Seminar Topics

Voice (and fax) service over cable networks is known as cable-based Internet Protocol (IP) telephony. Cable based IP telephony holds the promise of simplified and consolidated communication services provided by a single carrier at a lower cost than consumers currently to pay to separate Internet, television and telephony service providers. Cable operators have already worked through the technical challenges of providing Internet service and optimizing the existing bandwidth in their cable plants to deliver high speed Internet access. Now, cable operators have turned their efforts to the delivery of integrated Internet and voice service using that same cable spectrum.Cable based IP telephony falls under the broad umbrella of voice over IP (VoIP), meaning that many of the challenges that telecom carriers facing cable operators are the same challenges that telecom carriers face as they work to deliver voice over ATM (VoATM) and frame-relay networks. However, ATM and frame-relay services are targeted primarily at the enterprise, a decision driven by economics and the need for service providers to recoup their initial investments in a reasonable amount of time. Cable, on the other hand, is targeted primarily at home. Unlike most businesses, the overwhelming majority of homes in the United States is passed by cable, reducing the required up-front infrastructure investment significantly. Cable is not without competition in the consumer market, for digital subscriber line (xDSL) has emerged as the leading alternative to broadband cable.

Optic Fibre Cable

Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber. Transmission on optical fiber wire requires repeaters at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company's branch office to local customers (known as local loops). Optical fiber consists of a core, cladding, and a protective outer coating, which guide light along the core by total internal reflection. The core, and the higher-refractive-index cladding, are typically made of high-quality silica glass, though they can both be made of plastic as well. An optical fiber can break if bent too sharply. Due to the microscopic precision required to align the fiber cores, connecting two optical fibers, whether done by fusion splicing or mechanical splicing, requires special skills and interconnection technology.Two main categories of optical fiber used in fiber optic communications are multi-mode optical fiber and single-mode optical fiber. Multimode fiber has a larger core allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors