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The authors report a study on microwave properties of a ferrimagnetic ceramic composite (Gd 3 Fe 5 O 12 )GdIG X -(Y 3 Fe 5 O 12 )YIG 12X . The magnetic and dielectric measurements at microwave frequency were made through the Hakki -Coleman's procedure and through the excitation of a cylindrical ferrite resonator antenna (FRA). The hysteresis loops of the GdIG X YIG 12X ferrimagnetic composite were obtained. The numerical simulation study was performed using Ansoft's High Frequency Structure Simulator (HFSS TM ) software. The agreement between the experimental data and the simulated results is very good. These results demonstrated that, by varying the material composition of the resonator, ferrimagnetic composite GdIG X YIG 12X could operate as a magneto-dielectric antenna with bandwidth in the range of 7.5 -11% and in the frequency range of 4.4 -5.3 GHz. Additionally, all FRAs presented a low negative value of t f , which indicates suitability for microwave applications such as mobile communication systems or satellite broadcast systems.

We study the effects of a dc external magnetic field on the polaritons propagating in hollow dielectric cylinders, taking into account the retardation effects. In solving Maxwell's equations we show that only the TM modes can propagate in these systems, and we obtain the dispersion relation of the confined-surface-polariton modes. The effects of geometric parameters and the external magnetic field on the propagation of surface-polariton modes are also analyzed and show significant influence on the behavior of the modes. Numerical results are presented for the dispersion relation of surface polaritons with GaAs as the optically active medium.

In this study, the dielectric properties of the GdIGXYIG1–X ferrite composite material at radio frequency (RF) and microwave frequency bands were studied. These measurements were carried out in different sample geometries: thick films and cylindrical ceramic bulk ferrite resonator. In the RF range, we observed that the material is rather stable because of its short changes as a function of temperature and frequency range. The temperature capacitance coefficient values for all the samples (thick films and cylindrical ceramic bulk samples) presented short positive values at the RF range. The GdIG0.5YIG0.5 thick film was used as a substrate for the microstrip antenna device, where the upper Ag electrode served as a circular patch antenna and a microstrip line was used as a feed line. The microstrip antenna operates in this configuration at 8.185 GHz. In the study of the dielectric properties of the composites antenna geometry, with the same ferrite composite, a bulk cylindrical geometry was investigated. A numerical study, together with the experimental, was done, and the dielectric characteristics of the composite like ϵr, tgδE, and μr were obtained. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1595–1602, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24395

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