Tailored and anisotropic dielectric constants through porosity in ceramic components

Electr. & Comput. Eng. Dept., Univ. of Central Florida, Orlando, FL, USA
IEEE Transactions on Microwave Theory and Techniques (Impact Factor: 2.23). 12/2005; DOI: 10.1109/TMTT.2005.859039
Source: IEEE Xplore

ABSTRACT In this paper, different densities within a ceramic are used to provide a wide continuous range of dielectric constants for high-frequency applications. Cofiring different ceramic materials together to make a single unified structure to obtain different dielectric constant combinations is quite difficult due to phase stability issues and shrinkage mismatches. However, using various levels of porosity in order to alter the effective dielectric constant in the same material allows patterning different dielectric constants into a single unit. Since the structure is made from a single material, the varying porosity regions can be made compatible. Glassy-carbon-assisted and microcellular-structure-based porous titania allow for an extremely wide range of dielectric constants, ranging from 12 to 90, while maintaining a low loss tangent. Highly anisotropic materials are demonstrated herein to achieve a dielectric constant contrast of 90/9.6 using large-range aligned microcellular structure. Dielectric-resonator antennas are shown as an application of adjusting the bandwidth between 0.5% and 2.5% by tailoring the ceramic dielectric constant. A stratified-medium-loaded cavity resonator and a buried dielectric ring resonator internal to a microcellular substrate are used to demonstrate both the cofiring and variable dielectric constant capabilities of structured porosity.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In porous media, the porosity introduces inhomogeneity in the bulk, which alters the mechanisms of leakage and breakdown exhibited by the dense analog. The presence of pores in solid dielectrics significantly degrades the electrical characteristics and breakdown strength of the material. Lanthanum doped BaTi0.6Zr0.4O3 composition in Ba1-xLaxTi0.6[1¿5x/12]Zr0.4O3 were prepared by modified chemical route. (COOH)2.2H2O, Ba(NO3)2, ZrOCl2.8H2O and La2O3 are used to precipitate barium oxalate hydrate, lanthanum oxalate hydrate and zirconium oxyhydroxide from its water solution onto the surface of suspended TiO2 particles. The lanthanum doped BaTi0.6Zr0.4O3 composition was found to be cubic by XRD analysis. A gradual shift of 2¿ angles to the higher angle with increasing lanthanum percentage in the BTZ reveals the contraction of perovskite lattice. The frequency dependence of dielectric permittivity and loss tan ¿ of the ceramics has been investigated. It is found that dielectric permittivity (¿r) decreases and loss tan ¿ decreases with increase in lanthanum percentage. Loss tan ¿ increases and dielectric permittivity (¿r) decreases with increase in porosity. Resistivity decreases and current density increases with increase in porosity. Neither of the samples shows semiconductivity, which is believed to be because of titanium vacancy compensation.
    Solid Dielectrics, 2007. ICSD '07. IEEE International Conference on; 08/2007
  • [Show abstract] [Hide abstract]
    ABSTRACT: Dielectric materials with high dielectric constant contrast (68.7/6.37) are cofired inside low temperature cofired ceramics (LTCC) to demonstrate the capability of this processing technique for various metamaterial applications. Optical measurement shows good compatibility between the two different LTCC materials. By creating stratified-medium-loaded resonators inside electromagnetic bandgap (EBG) structures, bulk material properties of the high/low-dielectric-constant materials are characterized and verified at microwave frequencies to further prove the cofirability. This cofirability of different materials into one entity is the enabling technique for realizing artificial metamaterial substrates and vertically integrated RF front ends
  • [Show abstract] [Hide abstract]
    ABSTRACT: Microwave electromagnetic bandgap (EBG) structures have potential applications in improving the radiating features of antennas and the transmission properties of waveguides. Extrusion freeforming is a rapid prototyping technique for assembling ceramic dielectric lattice structures directly from a computer design file. It is without heating, cooling or polymerization processes to contend with at the construction stage. Various limitations on overall build thickness prompted us to explore lamination by welding to produce larger three-dimensional quasi-crystals. Microwave transmission through normal and side incidence showed that the bandgap frequency was in the 90–110 GHz region in all directions, matching the design that was informed by computer modelling. In order to image the EBG internal crystal structure, micro-computed tomography was used for scanning and reconstruction. Finally, the effect of structural defects including roundness and sagging of filaments and deviation of inter-filament spacing caused by fabrication errors on bandgap frequency was investigated.
    Journal of Physics D Applied Physics 06/2009; 42(14):145107. · 2.53 Impact Factor


Available from
Oct 23, 2014