Projects / Programmes
Models for characterisation of composites with ferrite and other ferromagnetic inclusions in microwave frequency range
| Code |
Science |
Field |
Subfield |
| 2.04.01 |
Engineering sciences and technologies |
Materials science and technology |
Inorganic nonmetallic materials |
| Code |
Science |
Field |
| P260 |
Natural sciences and mathematics |
Condensed matter: electronic structure, electrical, magnetic and optical properties, supraconductors, magnetic resonance, relaxation, spectroscopy |
effective medium theory, composite, ferromagnetic material, microwaves, permeability and permittivity measurements
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
19411 |
PhD Vladimir Boštjan Bregar |
Materials science and technology |
Head |
2007 - 2008 |
105 |
Abstract
Use of the composite materials is already well established, yet, fast advance of electronics further increased the need for new homogeneous and composite materials for application in microwave frequency range. For an efficient research and development and a successful implementation of composite materials it is important to be able to measure the effective properties of the composite and to understand the relation between intrinsic properties of inclusions and effective properties of the composite. In order to connect intrinsic properties of inclusions and effective properties of composites several analytical models were derived.
The main objective of our project is an extension of these models for the description of composites with ferrite and ferromagnetic inclusions that will be able to connect intrinsic and effective parameters also in the microwave frequency range. Within this work we will derive appropriate forms of models and theoretically analyze them to obtain basic limits of application. We will also experimentally examine several composite materials of significant technological interest and compare theoretical results of the models with the measured properties of real composites. This will allow further analysis of the application possibility of various models, most importantly the application of models for calculation of intrinsic properties from measured effective properties and predicting of effective properties on basis of reference composite or known intrinsic properties.
In order to experimentally examine or verify models' calculations we are going to assemble a set-up for measurement of complex permeability and permittivity in microwave frequency range and establish appropriate measurement protocols. This will allow characterization of magnetized or unmagnetized composite materials or nanocomposites with arbitrary volume fraction of inclusions. Further, we will develop several procedures for preparation of various composite samples, like composites with nanosized inclusions (nanocomposites) or composites with inclusions in the form of flakes.
Significance for science
Within the project we adapted, analyzed and validated few standard analytical models for specific description of composites with ferromagnetic inclusions, but can be applied also for other similar systems like dielectric composites in range of large dielectric losses. Analytical models are adapted for application on ferromagnetic composites with different states (magnetized, single-domain or demagnetized), but imporatntly also include imaginary component of electromagnetic properties, that are important in the microwave frequency range. Together we also analyzed the importance and effect of the inclusion agglomeration and conductivity of the inclusions, which is relevant for realistic composites. For this we used both experimental results and results of the numerical modeling, which allows very specific analysis of microstructure or individual parameters. We established relatively large difference between predictions of the analytical models and measurements on the real composites. The difference was largest in frequency range where the imaginary part of the permeability or permittivity is significant compared with real part. Further also the microstructure is very important since agglomeration or percolation significantly changes the effective properties of the composite with nonconductive inclusions. In the case of conductive inclusions we determined that eddy-currents have important effect, especially in combination with microstructure effects. All these conclusions are valid beyond ferromagnetic composites for similar systems with electromagnetic parameters. In parallel we also analyzed the ability of the analyitical models for predictions of the effective properties of the composites that have ferromagnetic inclusions, based on the known intrinsic properties of the inclusions or measured effective properties of a test composite. Results show that the prediction accuracy of the models varies with imput parameters and it is important to select the appropriate model for specific case in order to obtain applicable results. Therefore, with our study we established limited applicability of the analytical models for description of composites without incorporation of specific microstructure of the composite under study, and determined the range of application for specific models.
Significance for the country
Within the project we upgraded the measurement system for characterisation of electromagnetic parameters of materials in the microwave frequency range, which is unique in Slovenia and one of a few in Europe. Additionally, the project activities were connected with development of other measurement methods and lead also to the acquirement of new specific knowledge in the field of soft-magnetic composites and magnetism in the microwave frequency range. Better understanding of ferromagnetic (soft-magnetic) composite materials allowed further work, on higher technological level, with research and development of new products and applications with these materials. This opened new business opportunities in foreign markets and allowed more targeted development of products. Further, development of the field of ferromagnetic composites and accompanying measurement systems was connected to education and training of undergraduate and graduate students and transfer of knowledge as two diploma theses and training of two young researchers.
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