Simulation Study On The Electromagnetic Field Distribution Of Microwave Sintering/welding Cavity For Structural Ceramics

Structural ceramics have tremendous market potential profit for the highstability and good mechanical properties in very harsh environment or engineeringapplication conditions, such as high-temperature resistance, oxidation resistance,corrosion resistance and wear resistance. Microwave sintering/welding technologyis achieved by using the microwave absorption property of the materials. The heatgenerated to high temperature by coupling of the special band of the microwaveand the basical material microstructure. The materials can be overall heated forsintering/weldingdensification.This technologyis important for preparingthe newhigh performance materials and products of structural ceramics.By using the simulation software to simulate the electromagnetic fielddistribution inside the specimen and the cavities, the research work of this thesisprovides the technical support in improving the microwave sintering/weldingprocess and design the new advanced R&D microwave heating equipment, Thetechnique is also can be used to analyze the influence of the microwave parametersand sample dimension on electromagnetic field distribution.The accurate graphic display and color contrast were used to characterizemicrowave electromagnetic field distribution rule of the geometric size of samples.The simulation is achieved by using high frequency structure simulator(HFSS) based on the finite element method. The accuracy and reliability of HFSSapplications to model and simulate the microwave sintering are proved by thenumerical simulation and experimental results of field contour distribution. Theimproved cavity design with an extended distribution range of homogenous fieldbased on the simulation is also studied, which can be used for sintering larger sizesamples.Three uniform region of the electromagnetic field decreases to different levels when the cylindrical samples are loaded on single-mode sintering cavity.The smaller reduction can be obtained on the evenly area of both-side. The largerreduction can be obtained on the middle uniformity region due to the largermicrowave energy absorption. The uniform field density and stability of thisregion is greatly reduced. Improved single-mode sintering cavity can furtherextendthe uniform field space range, uniform field volume is doubled.The electricfield distribution of the sinteringcavityand the effects of the sample geometrysizeand microwave parameters are studied as follow: firstly, the electric field of thesample increases graduallyfrom inside to outside when the surface radius R is verysmall; secondly, the higher electric field appears in the center and both sides of thesample with increases of the radius R. The completely opposite electric fielddistribution is obtained when the axial height (H) and the relative dielectricconstantεr is different. The internal electric field of the sample becomes uniformwhen the axial height (H) and the relative dielectric constantεr at the point of thechanging boundary. The reduction scale of the radial surfacedepolarization field islarger than the increased scale of the axial surface depolarization field when theaxial height H is increased. The stability of the middle uniform region inner thecavity increases gradually. The depolarization field of the sample is increased dueto the increases of the relative dielectric constantεr..The stability of the middleuniform region inner the cavity decreases gradually. The inner electric field of thesample is increased gradually from inside to outside while the inner electric fieldof the cavity is not be changed when the tangent of dielectric lose angle (tgδ) isdifferent. The depolarization field increases with the increasing of the tangent ofdielectric lose angle (tgδ)The electric field distributions of the single-mode microwave welded cavityand the loaded sample are simulated. The influences orientation of the sample onthe inner electric field of the cavityand the loaded samples are also discussed. Theresults show that the contact surface electromagnetic field intensity is muchstronger and relatively uniform when the orientation of the sample is along the Zaxis. The uniformity of the inner electric field distribution of the different sizedsintered sample in the microwave multimode resonant cavity is also simulated anddiscussed. If the height is not changed, the inner electric field intensity anduniformity in the microwave multimode resonant cavity increase with thedecreasing of the diameter. The inner electric field distributions of the sample isuniform with the sample size of d = 80mm, h = 100mm. If the diameter is notchanged, the inner electric field uniformity increases while the electric fieldintensity decreased in the microwave multimode resonant cavity with thedecreasing of the height. The inner electric field distributions of the sample isuniform with the sample size of d = 40mm, h = 80mm. The internal electricintensityof the latter sample is much stronger than that of the former one.For the multi-mold cavity welding sample, the influence of the loadingdirection on the electromagnetic field distribution is small, while the influence ofthe sample dimension on sample contact surface electromagnetic fields distributionin the welding process is much higher. The results show that the uniformelectromagneticfields distribution area is in theregion of radius R less than 40mmand height less than 50 mm.In conclusion, the technical is very important to improve the microwavesintering/welding process and design the new advanced R&D microwave heatingequipment by simulating the electromagnetic field specimen and distributionsimulation in the single and multi mode sintering/welding cavities and the loadedsamples. The sample dimension and loading direcution can be controlled in thesintering/weding process to improve the success ratio of the microwavesintering/weding. The larger size and complex structural ceramics can be easilyfabricated.