**Acknowledgement**

The author wish to express a grateful acknowledgement to Universiti Sains Malaysia for financial support through Short Term and Research University (Individual) Grants awarded for the accomplishment of related works quoted in this paper.

### **7. References**

24 Dielectric Material

increase in dielectric constant.

**6. Conclusion** 

constant.

**Author details** 

**Acknowledgement** 

*University Sains Malaysia, Malaysia*

Zulkifli Ahmad

dipole polarization occurring at very low frequency region.

At K = 0, there is no interaction between phases while a high K values showed a strong interaction. This interaction also dependent on the filler sizes. For a given volume fraction filler, a smaller particle size has a larger fraction of interphase volume in the region between the filler and the matrix granting more polarization to operate. Thus they lead to a relative

A major concern with polymer/ceramic composites is the heterogeneity in phase which lead to formation of cracks and voids. This effect is known as Maxwell-Wagner effect which reduce the dielectric constant. A more serious type of heterogeneity is that the composite comprised of conductive inorganic fillers which could lead to a mistaken interpretation of

Polymers offer an alternative to the traditionally inorganic and ceramic material as dielectric amterials. This is due to their highly flexible, tractable processing, good chemical stability and readily tunable properties. The main drawback is they have lower thermal stability which limit their wider applications. Generally their dielectric constant is lower than non-polymeric materials. The mechanism which contribute to the dielectric properties are the interaction of electric field with electronic, atomic and dipole poalarization. These are dependent on polarizabity of constituents structure and the free volume as formulated in Clausius-Mossotti equation. The electronic and to some extent the atomic polarization are instantaneous throughout the measureable range of frequencies. However in dipole polarization there is relaxation time allowing an exponential decay of motion to return to equilibrium state. This different behavior contribute significantly to the values of dielectric constant and dielectric loss. These properties can be utilized to detect for any local or segmental motion during change in frequency and temperature treatment. Dielectric properties can be design by introducing polarizable groups into polymer chains, increasing free volume by inducing porosity as well as copolymerization. Increasing dielectric constant can be effectively made by producing nanocomposites with inorganic fillers possessing high dielectric

The author wish to express a grateful acknowledgement to Universiti Sains Malaysia for financial support through Short Term and Research University (Individual) Grants awarded

for the accomplishment of related works quoted in this paper.


[21] Simpson J O and St.Clair A K, Fundamental insight on developing low dielectric constant polyimides, Thin Solid Films,Volumes 1997, 308-309, 480-485

**Chapter 2** 

© 2012 Huitema and Monediere, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

**Dielectric Materials for Compact** 

L. Huitema and T. Monediere

http://dx.doi.org/10.5772/50612

**1. Introduction** 

Additional information is available at the end of the chapter

**Dielectric Resonator Antenna Applications** 

Dielectric resonators using high-permittivity materials were originally developed for microwave circuits, such as filters or oscillators as tuning element [1]. Indeed, in the late nineteen sixties, the development of low-loss ceramic materials opened the way for their use as high-Q elements [2-4]. Then, making use of dielectric materials to create the dielectric resonator antenna (DRA) illustrates the ingenuity of Professor S. A. Long [5], who was the first to propose such a procedure in the early nineteen eighties. Indeed, it introduced the use of a dielectric resonator as an antenna by exciting different modes using multiple feeding mechanisms. During the nineties, emphasis was placed on applying analytical or numerical techniques for determining input impedance, fields inside the resonator and Q-factor [6]. Kishk, Junker, Glisson, Luk, Leung, Mongia, Bhartia, Petosa and so on, have described a significant amount of DRAs' analyses and characterizations [7-18]. Petosa and al. proposed

Current DRA literatures focus on compact designs to address portable wireless applications. Among them, new DRA shapes or hybrid antennas are developed to enhance the antenna

The first part will address a brief overview of the most common used DRA shapes and structures including both rectangular and cylindrical DRAs. The emphasis will be placed on better understanding what DRAs exactly are and how to develop such an antenna. This part will detail fundamental modes of DRAs, their resonant frequencies, fields inside the

A second part will focus on the relevant dielectric material properties having a significant contribution to achieve better antenna performances. It will detail the kind of materials

and reproduction in any medium, provided the original work is properly cited.

both in literatures and book [6,12] many of the recent advances on DRAs.

impedance bandwidth [13-19] or for multiband antenna applications [20-22].

resonator and radiation patterns corresponding to these modes.

DRAs can use, which is closely linked to the targeted application.

