Magneto-dieletric properties of bismuth substituted barium hexaferrite

Ridgway, Leah M. (2011) Magneto-dieletric properties of bismuth substituted barium hexaferrite. PhD thesis, University of Nottingham.

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The work contained within this thesis seeks to address the dielectric and magnetic properties of bismuth substituted barium hexaferrite (composition BaBixFe12-xO19 where x = 0.0, 0.2, 0.5, 0.8, 1.0 and 1.5) across a broad frequency spectrum. This material is potentially of interest in antenna applications (specifically a dielectric resonator antenna) where high permittivity and permeability materials can be exploited to physically minimize the size of antenna devices.

At low frequencies (20Hz - 3MHz) LCR meter based analysis was used to investigate the capacitance and inductance of the materials. The highest measured permittivity at 1MHz was Er = 86.18 - 9.910j, tanδ = 0.11. High frequency (45MHz - 20GHz) permittivity was investigated using a vector network analyser (VNA) and coaxial probe. The highest recorded permittivity at 2.45GHz was Er = 14.69 - 1.664j, tanδ = 0:08. A link between substitution level and permittivity and substitution level and inductance was made at either 1MHz or 2.45GHz. The homogeneity of the samples was explored using a near- field permittivity sensor. This showed small localized variations of permittivity across the surface but not significant enough to adversely effect bulk measurements. A dielectric resonator antenna was fabricated using a bismuth substituted barium hexaferrite sample. Resonant frequencies were identified at 6.6, 9.55 and 13.6GHz and radiation patterns for the system showed agreement with published theoretical results. This confirmed the suitability of the material in this application as a high permittivity material with relatively low loss.

This thesis contributes to scientific knowledge by characterising a broad range of bismuth composition materials across a wide frequency range, investigating the link between permittivity/inductance and doping level and presenting full results. The material has also been characterised using a near-field permittivity technique and used to fabricated a dielectric resonator antenna which have not previously been undertaken.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Harrison, I.
Keywords: Dielectric magnetic permittivity, Hexaferrite, Ferrite antenna, DRA
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Electrical and Electronic Engineering
Item ID: 12183
Depositing User: EP, Services
Date Deposited: 30 May 2012 13:23
Last Modified: 15 Dec 2017 19:20

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