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ANNA UNIVERSITY NOV/DEC 2012 RESULTS | AU NOV/DEC 2012 RESULTS ANNOUNCING DATE(TENTATIVE) | ANNA UNIVERSITY THIRD/FIFTH/SEVENTH SEMESTER NOV/DEC 2012 RESULTS | WHEN WILL THE ANNA UNIVERSITY NOV/DEC 2012 RESULTS WILL BE ANNOUNCED

Anna University, Chennai

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Information Anna University Nov/Dec 2012 Results
(Common To All Anna Univ Affiliated Colleges In TN)

Welcome Students,

Anna University Nov/Dec 2012 Examination has end with 29th December 2012 For Second,third,fourth,fifth,sixth,seventh,eighth Semester (Includes Arrears)

 Anna University, Chennai is started Paper Valuation All around Tamilnadu Various Zones from 22rd December 2012(by Saturday) and same has been completed on 6th January 2013 This time anna university, Chennai is very intense about the publications of November/December 2012 results on time because they face so many difficulties during May/June 2012 Examination Session

Announcing Anna University Nov/Dec 2012 results earlier will definitely helps students to plan their preparations for April/May 2013 Examination accordingly, schedule for anna university april/may 2013 will be announced by march 2013 month  

This Time Anna University, Chennai Has Taken certain Steps to do the things better and efficient way, the main hurdles for any university is getting information  from various affiliated colleges on Time, that too our anna university take over more than 550 Engineering colleges in tamilnadu,

“A web portal http://coe1.annauniv.edu has been developed to acquire the non-confidential data pertaining to the colleges and their faculty and the students for the smooth and effective  conduct of examinations and publication of results on time”

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REJINPAUL.COM RESULT INFO. UPDATES ON Nov/Dec 2012
(2nd,3rd,4th,5th,6th,7th,8th Semester Results)

(Common To All Affiliated Colleges)

18/02/2013 | 7:11 Pm | - Rejinpaul.com Updates

Anna University Nov/Dec 2012 Results Has Been Delayed due to pending work and Same is likely to be Announced Shortly and Today Meeting Got Over . Latest Official Information Reveals That, People Need Another Minimum Of 3-4 Days To Complete The Pending Work and Results are Likely To Be Announced by This Week

Next Result Info. Update : Coming Soon

Piezoelectric Transducers

The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing. The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa. The active element is basically a piece of polarized material (i.e. some parts of the molecule are positively charged, while other parts of the molecule are negatively charged) with electrodes attached to two of its opposite faces. When an electric field is applied across the material, the polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material. This alignment of molecules will cause the material to change dimensions. This phenomenon is known as electrostriction. In addition, a permanently-polarized material such as quartz (SiO2) or barium titanate (BaTiO3) will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the piezoelectric effect. Additional information on why certain materials produce this effect can be found in the linked presentation material, which was produced by the Valpey Fisher Corporation.

Piezoelectric Effect (PPT, 89kb)   Piezoelectric Elements (PPT, 178kb)

The active element of most acoustic transducers used today is a piezoelectric ceramic, which can be cut in various ways to produce different wave modes. A large piezoelectric ceramic element can be seen in the image of a sectioned low frequency transducer. Preceding the advent of piezoelectric ceramics in the early 1950's, piezoelectric crystals made from quartz crystals and magnetostrictive materials were primarily used. The active element is still sometimes referred to as the crystal by old timers in the NDT field. When piezoelectric ceramics were introduced, they soon became the dominant material for transducers due to their good piezoelectric properties and their ease of manufacture into a variety of shapes and sizes. They also operate at low voltage and are usable up to about 300^oC. The first piezoceramic in general use was barium titanate, and that was followed during the 1960's by lead zirconate titanate compositions, which are now the most commonly employed ceramic for making transducers. New materials such as piezo-polymers and composites are also being used in some applications.

The thickness of the active element is determined by the desired frequency of the transducer. A thin wafer element vibrates with a wavelength that is twice its thickness. Therefore, piezoelectric crystals are cut to a thickness that is 1/2 the desired radiated wavelength. The higher the frequency of the transducer, the thinner the active element. The primary reason that high frequency contact transducers are not produced is because the element is very thin and too fragile.

Characteristics of Piezoelectric Transducers

The transducer is a very important part of the ultrasonic instrumentation system. As discussed on the previous page, the transducer incorporates a piezoelectric element, which converts electrical signals into mechanical vibrations (transmit mode) and mechanical vibrations into electrical signals (receive mode). Many factors, including material, mechanical and electrical construction, and the external mechanical and electrical load conditions, influence the behavior of a transducer. Mechanical construction includes parameters such as the radiation surface area, mechanical damping, housing, connector type and other variables of physical construction. As of this writing, transducer manufacturers are hard pressed when constructing two transducers that have identical performance characteristics. 

A cut away of a typical contact transducer is shown above. It was previously learned that the piezoelectric element is cut to 1/2 the desired wavelength. To get as much energy out of the transducer as possible, an impedance matching is placed between the active element and the face of the transducer. Optimal impedance matching is achieved by sizing the matching layer so that its thickness is 1/4 of the desired wavelength. This keeps waves that were reflected within the matching layer in phase when they exit the layer (as illustrated in the image to the right). For contact transducers, the matching layer is made from a material that has an acoustical impedance between the active element and steel. Immersion transducers have a matching layer with an acoustical impedance between the active element and water. Contact transducers also incorporate a wear plate to protect the matching layer and active element from scratching.

The backing material supporting the crystal has a great influence on the damping characteristics of a transducer. Using a backing material with an impedance similar to that of the active element will produce the most effective damping. Such a transducer will have a wider bandwidth resulting in higher sensitivity. As the mismatch in impedance between the active element and the backing material increases, material penetration increases but transducer sensitivity is reduced.

Transducer Efficiency, Bandwidth and Frequency
Some transducers are specially fabricated to be more efficient transmitters and others to be more efficient receivers. A transducer that performs well in one application will not always produce the desired results in a different application. For example, sensitivity to small defects is proportional to the product of the efficiency of the transducer as a transmitter and a receiver. Resolution, the ability to locate defects near the surface or in close proximity in the material, requires a highly damped transducer.
It is also important to understand the concept of bandwidth, or range of frequencies, associated with a transducer. The frequency noted on a transducer is the central or center frequency and depends primarily on the backing material. Highly damped transducers

6th sem

http://www.mediafire.com/?qunczbye8es83an
solid state drives
http://www.mediafire.com/error.php?errno=320
HVE

solid state drives notes

http://www.mediafire.com/?qunczbye8es83an

6th sem notes for EEE

http://www.iannauniversity.com/2012/08/anna-university-notes-6th-semester-eee.html

How Windshield Wipers Work

http://auto.howstuffworks.com/wiper.htm

http://www.ece.tamu.edu/~huang/files/ClassNotes/129.pdf