Low-Loss Magneto-Dielectric Materials: Approaches and Developments

Abstract

Magneto-dielectric materials with matching permeability and permittivity have significant advantages for miniaturization and efficiency improvement of antennas. The main requirements for this kind of magneto-dielectric material include a high refractive index, matched permeability and permittivity, and low magnetic and dielectric losses at the application frequency. However, it is very difficult to meet these requirements simultaneously. This review presents the approaches and developments of magneto-dielectric materials of three types: spinel-based, hexagonal-based, and composite magneto-dielectric materials. It is proved that choosing the proper type of magneto-dielectric material is very important to obtain a higher refractive index and matched permeability and permittivity in the application frequency band. When the application frequency is low (less than 30 MHz), adopting composites of spinel ferrite and high-dielectric material is the best choice to improve the refractive index. When the application frequency is between 30 MHz and 100 MHz, it is better to choose spinel-based magneto-dielectric materials in consideration of both their relatively high refractive index and low losses. When the application frequency increases to 100 MHz to 500 MHz, hexagonal-based magneto-dielectric materials offer better performance. Finally, when the application frequency is beyond 500 MHz, to obtain matched permeability and permittivity, choosing composites of hexaferrite and an organic medium is recommended. Solutions for how to decrease magnetic and dielectric losses and expand the application frequency range are also discussed.