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Proceedings Paper

Field dependence of FMR in ferrites and implications for microwave absorber design
Author(s): Stephen George Appleton
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Paper Abstract

There are numerous potential uses for a microwave absorbent material whose absorption can be modified by an applied stimulus. This paper presents work to exploit the dependence of the microwave properties of ferrites on applied magnetic fields, and to develop such an absorbent material. Ferromagnetic resonance (FMR) is known to result in absorption of incident microwave energy at a characteristic frequency for any given ferrite. The FMR frequency is dependent on the anisotropy field Han, which in turn can be modified by chemical doping. Therefore, ferrite RAMs can be produced to operate at required frequencies through judicious choice of the ferrite. Furthermore, if Han is supplemented by an applied magnetic field Happ, the FMR frequency will be increased by an amount dependent on the strength of Happ and on the sense of anisotropy. The microwave permeability and permittivity spectra of a range of ferrites were measured as functions of Happ, using a vector network analyzer. These were used as input to a computer model for calculating absorber performance, and the effects of bias fields on a variety of absorber designs were predicted. A novel system was developed to apply large fields in test panels, for validating performance predictions.

Paper Details

Date Published: 26 May 1995
PDF: 13 pages
Proc. SPIE 2448, Smart Structures and Materials 1995: Smart Electronics, (26 May 1995); doi: 10.1117/12.210469
Show Author Affiliations
Stephen George Appleton, Defence Research Agency (United Kingdom)

Published in SPIE Proceedings Vol. 2448:
Smart Structures and Materials 1995: Smart Electronics
Vijay K. Varadan, Editor(s)

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