Microwave heating of multiphase materials : modelling and measurement

[摘要] ENGLISH ABSTRACT: Both coaxial probe and waveguide (WG) measurement systems for electric and magneticmaterial property extraction were investigated. These measurement techniques were usedto determine electrical properties of an inhomogeneous rock sample in its solid andcrushed states. A lumped element model of the probe was used and permittivity wasdetermined by the inversion algorithm developed by Stuchly and Stuchly. To support thistechnique it was compared to a full wave inversion algorithm and referenced to propertiesof the same samples but determined by a resonant cavity technique. The Nicholson, Rossand Weir inversion algorithm was used to determine material properties from WGmeasurements. As a reference, the same techniques were applied to a well definedmaterial. It was found that neither of the measurement techniques could measure low lossfactors or conductive materials and literature values were used in these cases. Varioussimulation models of the multiphase ore in both its solid and crushed states are presented.These models were utilised in finite-difference time-domain (FDTD) simulations ofdifferent microwave (MW) cavities. Simulation and experimental S-parametercomparisons are presented. The level of accuracy achieved varies as a function of thegeometrical representation and material properties. After an S-parameter comparison withsimulation results it was concluded that the electrical properties of both the solid andcrushed rocks have been well determined for MW cavity design. Predicted and measuredfield distributions in cavities were also compared and it is shown that accurate models ofmultiphase materials become especially important in the determination of fielddistributions in and around different rock phases. Recommendations for the suggestedmaterial property determination and verification processes are presented. A specificapplication of this work is in the field of microwave assisted comminution.

[发布机构] Stellenbosch University