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 H, 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 H is supplemented by an applied magnetic field Ha1,,, the FMR frequency will be increased by an amount dependent on the strength of Ha,,, fld on the sense of anisotropy.The microwave permeability and permittivity spectra of a range of ferrites were measured as functions of Han,, using a vector network analyser. 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.