Virtual Lab for InteractivelyTeaching Phenomena of

Electromagnetics(http://www.ee.iitb.ac.in/course/~mapawar/website/btpportal/index.html)

B.sairamProject research intern,

Electrical Engineering Department,IIT-Bombay,Mumbai, India

Abstract- Electromagnetic theory presents adifficult task for the student. The essence ofthe problem is not the pretentiousmathematical treating of the field, but in thefield presentation and understanding of fieldinteraction with the material. To realize thisthere has been speculation for alternativemeans for propagating concepts to understandElectromagnetic theory. Such tools likeVirtual Labs enable the student to build inthe very simple way an arbitrary problem usingpreferred geometry and boundary conditions.This report ventures in the domain of Javabased applets for a Virtual Lab and differenttypes of applets have been developed andpresented.

I. INTRODUCTIONTeaching electromagnetics in graduate andundergraduate courses has beentraditionally a difficult task. Theinvolved physical and mathematicalconcepts, as curl, divergence andgradient, allied to the fielddetermination and representation are notonly difficult to understand but also leadoften to frustration and poor learningresults. Among the most serious problemsis the graphical representation ofelectric and magnetic fields, whoseanalytical expressions in the majority ofpractical cases cannot be expressed in ananalytical form.A correct understanding of the fielddistribution is essential for students to

understand how practical devices, aselectrical machines and transformers, workand how they can be designed andoptimized. The difficulties arise not onlyin understanding a given fielddistribution but also in how they can bedetermined correctly using classicalapproximated expressions or numericalprocedures. In general the fielddistribution should be determined solvinga set of non-linear partial differentialequations, whose solution is given only insome special cases and under somesimplifying assumptions.All these issues make the matter in somecases very complicated for studentsleading often to problems in otherdisciplines, which use the basic conceptsof electromagnetics as the starting point.Using the computer as support fordisciplines involving electrical andmagnetic fields can contribute to changethis situation, as many experiences inseveral universities have reported. Usingmodern numerical methods it is nowadayspossible to determine and representmagnetic and electrical fields in agraphical fashion, helping the students tounderstand their meaning, the underlyingconcepts and their practical applications.With the objective of improving theteaching and learning of disciplines likeelectromagnetics, transformers, electricmachines and others related to them

interactive programs have been developed[1].An interactive program tool designed toteach ElectromagneticField theory must fulfill tworequirements: (1) It must comprise a universalnumerical tool to ensure the solution ofgeneric problems(2) It must comprise a graphical interfaceto ensure easy and user-friendlypreparation of data used to solve aproblem and to visualize the results ofcomputation and provide a graphic analysisof the solution [2].

Many attempts have been made toincorporate these parameters forappropriate propagation of importantconcepts. There has an approach to thefinite element method applied to thesolution of stationary electromagneticproblems with axial symmetry. It is basedon the direct integration of the Maxwell’sequations and the use of first-ordertriangular elements, thereby avoiding thecomplex mathematical treatment of theory[3]. Also, use of FEM for help to teachapplied electrodynamics has beenimplemented in the form of tools adaptedfor tutorial designs of electricalmachines [4]. Furthermore, ACVEM – aCAT/CAL tool for numerical computation andvisualization of electromagnetic fields isdeveloped in which multiple numericalmethods have been modularized and builtinto which can be used to solveapplication problems. GUI features and themodularized computation systems aredeveloped for choosing numericalcomputation methods, the pre-process andadding more numerical computation featuresin ACVEM [5].

Virtual Labs is a project initiated by theMinistry of Human Resource Development,Government of India, under the NationalMission on Education through Information

and Communication Technology. The projectaims to provide remote-access toLaboratories in various disciplines ofscience and engineering for students atall levels from under-graduate toresearch. It also intends to develop acomplete Learning Management System wherethe students can avail the various toolsfor learning, including additional web-resources, video-lectures, animateddemonstrations and self- evaluation. IITBombay is also one of the institutionsparticipating in this project. On similarlines, this report demonstrates how aportal based on Java applets showcasingvarious phenomena of electromagneticstheory can be incorporated in such aVirtual Lab. The problem solutions arecomputed using the Finite Element Methodnumerical technique and thegeometry/meshing has been accomplishedusing the PDE toolbox in Matlab.

II. VIRTUAL ELECTROMAGNETICS LABThe objective of the VirtualElectromagnetics Lab is to provide remote-access to lab simulations and growenthusiasm in students to conductexperiments by arousing their curiosity.This would help them in learning basic andadvanced concepts through remoteexperimentation. The students can availthe various tools for learning which areotherwise available to limited number ofusers due to constraints on time andgeographical distances. It is a vision toinclude simulations for all the essentialphenomena in Electromagnetics under onedomain for common benefit andunderstanding of interested students. Itis being accomplished by embedding Javaapplets in a regular HTML script. Thecomputational data is imported from Matlabwhich is where we actually solve theproblem using a numerical technique.Finite Element Method is the techniqueused in this implementation and the

geometry & mesh is constructed using PDEtoolbox.

III. OVERVIEW OF FEMFinite Element Method is a numericaltechnique for finding the approximatesolution for the boundary valued problemsfor differential equations. In order toproduce a stable solution it uses thecalculus variations to minimize the errorfunction qualitatively like joining smalllines to produce an approximate circle.The steps followed in solving the boundaryvalued problem by using FEM are:(1)Meshing of the domain.(2)Approximation of solution(3)Assembly of the system(4)Applying boundary condition

IV. OVERVIEW OF JAVA APPLETSJava Applets are used to provideinteractive features to web applicationsthat cannot be provided by HTML alone.They can capture mouse input and also havecontrols like buttons or check boxes. Inresponse to the user action an applet canchange the provided graphic content. Thismakes applets well suitable fordemonstration, visualization and teaching.There are online applet collections forstudying various subjects, from physics toheart physiology. We have attempted toinclude electromagnetic field theory asone of the subjects being studied throughthis medium.

V. APPLETS DEVELOPEDA. Curl free static electric field:

This applet demonstrates theConservation Law which states that thework done by the electric field in movinga charged particle around a closed loopcomes out to be zero due to no effectivechange in potential. For this purpose wehave produced the electric field byimporting field plot data from matlab and

for drawing the contour we use mousemotion listener and mouse action listenermethods. After releasing the mouse, themethod for calculating the integral isinvoked and the result is displayed in thejava console.

Fig1. Field distribution and contourinput.

Fig2. Result of the integral calculation.

B. Proximity effect:This applet demonstrates how the ACresistances of a conductor will changeswith the variation in frequency and thedirection of current in a proximalconductor. For this purpose we haveimported the current distribution plotsform matlab and used java graphics andaction listener to display the variationsin current distributions according to theuser’s choice of current direction andfrequency of the conductors.

Fig3. Current distribution (10A, 50Hz,same direction)

Fig4.Current distribution (10A, 100Hz,same direction)

Fig5. Current distribution (10A, 50Hz,opposite direction)

C. Magnetic vector and scalar potential based field computation

This applet demonstrates how smoothly thefield distribution plot will vary with thevariation of number of nodes in FEManalysis. For this purpose we haveimported the field distribution plots ofan L-section for different number of nodesfrom matlab and used java graphics andaction listener to display the variationof the field distribution according to theuser’s choice of number of nodes.

Fig6. Field distribution for 65 nodes

Fig7.Field distribution for 821 nodes

Fig8.Field distribution for 70 nodes

Fig9.Field distribution for 240 nodes

D. Grading of cables:This applet demonstrates the analysis ofthe grading of a two layer insulationunderground cable. For obtaining theuniform stress along the insulation of thecable, the permittivity of the insulationshould decrease as we go away from core ofthe cable because the value of stressdecreases as the distance from coreincreases. For this purpose we haveimported the stress distribution variationfor different values of permittivity ofthe two insulations and used java graphicsand action listener to display thevariation of the stress distributionaccording to the user’s choice ofpermittivity of the respectiveinsulations.

Fig10.Stress distribution for e1=4 ande2=4

Fig11.Stress distribution for e1=4 ande2=3.1

Fig12.Stress distribution for e1=4 ande2=1.5

E. Amperes law:This applet demonstrates Ampere’s lawwhich states that magnetic field loopintegral is proportional to currentenclosed in the loop. For this purpose wehave imported the field plot data frommatlab and used mouse motion listener andmouse listener methods to draw the contourof user’s choice. After user releases themouse, method for calculating the integralwill be called and the result will bedisplayed in java console proving thehypothesis. The technical mechanism issimilar to the one used for conservationlaw.

Fig12. Magnetic field distribution andthe contour

Fig13. Result of the integral calculation.

VI. CONCLUSION & WEB PORTALTo summarize, an approach to teachingelectromagnetics phenomena using Javabased applets embedded in Virtual Labs hasbeen comprehensively discussed and severalapplets have been developed andintegrated. The advantage of such animplementation is that we can havedifferent scenarios based on the data we

import from Matlab and therefore adjustselective parameters and understand thechanges that it brings to the fieldbehavior in the actual display. The samealso implies that for similarapplications, there need not be verycontrasting codes, easing theincorporation of many similar problems inthe portal. The unintelligible work ofcreating the geometry and meshing iseliminated and the implementation is time-efficient in all possible ways. Acollection of Java Applets fordemonstrating various phenomena ofElectromagnetics developed by me and isuploaded on a web portal for common accessvia webpage for Field Computational Lab,Electrical Engineering, I.I.T Bombay. (URL:http://www.ee.iitb.ac.in/course/~mapawar/website/btpportal/index.html)

VII. ACKNOWLEDGEMENT

I would like to thank my guide Prof. S.V Kulkarni for giving me tremendous support,warmth and invaluable insights while I implemented this project. I would like to express extreme gratitude to M.A.Pawar forhis immense help in the development of theJava Applets. Special thanks to Sarang Pendharkar, Vyshak Baburajan and Aditi Kamat for being there when I got stuck or needed help. Lastly, I am grateful towardsPrathamesh Joshi ,Vamsi for helping me learn and comprehend Java.

VIII. REFERENCES

[1] Luis Alberto Pereira, Dr.-Ing, “Software forTeaching Electrical Machines andElectromagnetics for Graduate and UndergraduateCourses” 0-7803-709-10 /01/$10@2001 IEEE.

[2] M. Trlep, A. Hamler, M. Jesenik, and B.˘Stumberger, “Interactive Teaching ofElectromagnetic Field by Simultaneous FEM

Analysis” IEEE TRANSACTIONS ON MAGNETICS, VOL.42, NO. 4, APRIL 2006.

[3] JOSE´ ROBERTO CARDOSO,1 VIVIANE CRISTINE SILVA,1NANCY MIEKO ABE,2 LUIZ NATAL ROSSI1, “Approachto Teaching the Finite Element Method Applied toElectromagnetic Problems with Axial Symmetry toElectrical Engineering Students” © 1999 JohnWiley & Sons, Inc. CCC 1061-3773/99/030133-13.

[4] Yvan Lefévre, Julien Fontchastagner, andFrédéric Messine, “Buildinga CAD System for Educational Purpose Based Onlyon a Mesh Tool and a Finite Elements Solver” IEEETRANSACTIONS ON MAGNETICS, VOL. 42, NO. 4, APRIL 2006.

[5] Junwei Lu, “Numerical Computation andVisualization of Electromagnetic Fields UsingMATLAB based Integrated Programming Language”10.1109/ICCEA.1999.825242@1999 IEEE.