Greatly enhanced magneto-dielectric performance of the Ni 0.5 Zn 0.5 Fe 2 O 4 /polyvinylidene fluoride composites with a
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ries of Ni0.5Zn0.5Fe2O4 (NZO)/polyvinylidene fluoride (PVDF) composites were prepared and studied for their potential application as magneto-dielectric antenna substrate materials. The NZO ferrite powders were synthesized by the solid-state reaction method and then annealed at different temperatures of 700, 900 and 1100 °C. The influence of the annealing treatment on the grain size, crystallinity and magneto-dielectric properties were discussed. The magnetic and dielectric properties of the composites were measured in 1 MHz–1 GHz and 100 Hz–1 GHz, respectively. With the annealing temperature increase from 700 to 1100 °C, the initial permeability of the composites increases from 3.89 to 7.93, while the static permittivity changed regularly with the growing grain size. Almost equal values of l9 and e9 are obtained in the composite sample with the 1100 °C annealed NZO powders. Considering the relatively low magnetic and dielectric loss tangent, this material is the promising candidate for the design of miniaturized antennas.
I. INTRODUCTION
The rapid increasing demand for multifunctional and miniaturized communication devices results in a need for further integration and high density package of electronic components. This is especially true for antenna, since its size is an important factor, which determines the overall size of mobile devices.1 The length of the electromagnetic wave is influenced by the permittivity and perme0 ffi ability of the substrate materials (k ¼ pkffiffiffiffiffi , where k and 0 0 el
k0 are the wave length in the material and in vacuum, e9 and l9 are the relative permittivity and permeability of the material). Hence, the magneto-dielectric composite is desired as the substrate materials in the miniaturization design of antennas. Usually, the magnetic-dielectric composite possesses much higher permittivity than the permeability, which is not suitable to be used as the antenna substrate materials.2,3 That may lead to very high parasitic capacitance in device, as well as the mismatch of the antenna impedance to free space environment qffiffiffi 0
(Z ¼ Z0 le0 , where Z and Z0 are impedances of the materials and free space). This problem can be solved better by using the materials with almost equal values of relative permittivity and permeability, which are rarely found in nature. So the composite with the combination Contributing Editor: Michael E. McHenry a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.417
of high and almost equal permittivity and permeability as well as low-loss tangent is very necessary.4–6 Generally speaking, the ceramic-based composite always shows higher magnetic and dielectric loss than the polymerbased composite. And in most cases, composite with high permittivity is much easier to achieve than that with high permeability, which caused by the higher conductivity magnetic materials especially the metal alloys.7 Thus the ferrite-polymer composite is always selected for the preparation of this kind of composite. The physical and chemical properties
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