Monday, November 12, 2012

Line-Reflect-Reflect Technique Download Seminars

              LRR- LINE REFLECT REFLECT is a new self-calibration procedure for the calibration of vector network analyzers (VNA). VNA measure the complex transmission and reflection characteristics of microwave devices. The analyzers have to be calibrated in order to eliminate systematic errors from the measurement results.

              The LRR calibration circuits consist of partly unknown standards, where L symbolizes a line element and R represents a symmetrical reflection standard. The calibration circuits are all of equal mechanical length. The obstacle, a symmetrical-reciprocal network is placed at three consecutive positions. The network consists of reflections, which might show a transmission. The calibration structures can be realized very easily as etched structures in microstrip technology.

              During the calibration [G], [H], which represents the systematic errors of the VNA is eliminated in order to determine the unknown line and obstacle parameters.




     


MICROWAVE DEVICES

              Microwave devices are devices operating with a signal frequency range of 1-300GHz. A microwave circuit ordinarily consists of several microwave devices connected in some way to achieve the desired transmission of a microwave signal.

The various microwave solid state devices are,

* Tunnel diodes
              These are also known as Esaki diodes. It is a specially made PN junction device which exhibits negative resistance over part of the forward bias characteristic. Both the P and the N regions are heavily doped. The tunneling effect is a majority carrier effect and is very fast. It is useful for oscillation and amplification purposes. Because of the thin junction and shot transit time, it is useful for microwave applications in fast switching circuits.

* Transferred electron devices
              These are all two terminal negative resistance solid state devices which has no PN junction. Gunn diode is one of the transferred electron devices and which works with the principle that there will be periodic fluctuations in the current passing through an n-type GaAs substrate when the applied voltage increases a critical value i.e. 2-4Kv/cm.


*Avalanche transit-time devices
              These are used for amplification purposes. And the basic principle is the voltage breakdown at the reverse biased PN junction with the supply of electrons and holes.

          These microwave solid state devices are used for generation and amplification of microwave signals by means of velocity-modulation theory. The interconnection of two or more microwave devices is regarded as a microwave junction. From the network theory a two-port device can be described by a number of parameter sets, such as the H, Y, Z and ABCD. All these network parameters relate total voltages and total currents at each of the two ports. If the frequencies are in the microwave range, the two port network representation is as shown in FIG: 1.
              The logical variables are traveling waves rather than total voltages and total currents. These are S-parameters, which are expressed as

b1=   S11a1+S12a2
b2=   S21a1+S22a2



Light emiting polymers Download Seminars

Light emitting polymers or polymer based light emitting diodes discovered by Friend et al in 1990 has been found superior than other displays like, liquid crystal displays (LCDs) vacuum fluorescence displays and electro luminescence displays.  Though not commercialised yet, these have proved to be a mile stone in the filed of flat panel displays.  Research in LEP is underway in Cambridge Display Technology Ltd (CDT), the UK.

             In the last decade, several other display contenders such as plasma and field emission displays  were hailed as the solution to the pervasive display.  Like LCD they suited certain niche applications, but failed to meet broad demands of the computer industry.

             Today the trend is towards the non_crt flat panel displays.  As LEDs are inexpensive devices these can be extremely handy in constructing flat panel displays.  The idea was to combine the characteristics of a CRT with the performance of an LCD and added design benefits of formability and low power.  Cambridge Display Technology Ltd is developing a display medium with exactly these characteristics.

             The technology uses a light-emitting polymer (LEP) that costs much less to manufacture and run than CRTs because the active material used is plastic.

WHAT IS LEP ?

             LEP is a polymer that emits light when a voltage is applied to it.  The structure comprises a thin film semi conducting polymer sandwiched between two electrodes namely anode and cathode.  When electrons and holes are injected from the electrodes, the recombination of these charge carriers takes place, which leads to emission of light that escape through glass substrate.

             The ban gap, that is energy difference between valence band and conduction band of the semi conducting polymer determines the wave length, that  is colour of the emitted light.

             The first polymer LEPs used poly phinylene vinylene (PPV) as the emitting layer.  Since 1990, a number of polymers have been shown to emit light  under the application of an electric field; the property is called the electro luminescence(EL)

             PPV and its derivatives, including poly thiophenes, poly pyridines, poly phenylenes and copolymers are still the most commonly used materials.

             Efforts are on to improve stability, lifetime and efficiency of polymer d3evices by modifying their configuration.

 

CHEMISTRY BEHIND LEP


             LEPs are constructed from a special class of polymers called conjugated polymers.  Plastic materials with metallic and semiconductor characteristics are called conjugated polymers.  These polymers posses delocalised pi electrons along the backbone, whose mobility shows properties of semiconductors.  Also this gives it the ability to support positive and negative charge carriers with high mobility along the polymer chain.

             The charge transport mechanism in conjugated polymers is different from traditional inorganic semiconductors.  The amorphous chain morphology results in inhomogeneous broadening of the energies of the chain segments and leads to hopping type transport.

                 Conjugated polymers have already found application as conductor in battery electrodes, transparent conductive coatings, capacitor electrolytes and through hole platting in PCB’s. There are fast displaying traditional materials such as natural polymers etc owing to better physical and mechanical properties and amenability to various processes.

Interactive Voice Response System Download Seminars



                   IVRS is an important development in the field of interactive communication which makes use of the most modern technology available today. IVRS is a unique blend of both the communication field and the software field, incorporating the best features of both these streams of technology. IVRS is an electronic device through which information is available related to any topic about a particular organization with the help of telephone lines anywhere in the world.

                   IVRS provides a friendly and faster self service alternative to speaking with customer service agents. It finds a large scale use in enquiry systems of railways, banks, universities, tourism, industry etc. It is the easiest and most flexible mode of  interactive communication because pressing a few numbers on the telephone set provides the user with a wide range of information on the topic desired. IVRS reduces the cost of servicing customers.
 

IVRS-    INTERACTIVE VOICE RESPONSE SYSTEM

                   The IVRS on the whole consists of the user telephone, the telephone connection between the user and the IVRS and the personal computer which stores the data base. The interactive voice response system consists of the following parts.

HARDWARE SECTION

1.      Relay: For switching between the ring detector and the DTMF decoder.
2.      Ring detector: To detect the presence of incoming calls.
3.      DTMF decoder: To convert the DTMF tones  to 4 bit BCD codes.
4.      Micro controller: To accept the BCD calls, process them and transmit them serially to the PC.
5.      Level Translator: To provide the interface between PC and micro controller.
6.      Personal Computer: To store the data base and to carry out the text to speech conversion.
7.      Audio Amplifier: To provide audio amplification to standard output and to act as a buffer between the telephone line and sound card.