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.

  • [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
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel synthesis technique to integrate high- Q 3-D filters with highly efficient slot antennas is presented in this paper. This technique allows for compact integration of 3-D filters and antennas with very high antenna efficiency and significantly reduced form factor of integrated RF front ends. Prototype four-pole Chebyshev cavity filters integrated with slot antennas are demonstrated at X -band using both coaxial and coplanar waveguide feeding. The center frequency and fractional bandwidth of the filter/antenna system with coaxial feeding are 9.96 GHz and 6.0%, respectively. Due to the high- Q factor (~850) of the cavity resonator, the efficiency of this filter/antenna system is measured to be 89%, compared with the measured S <sub>21</sub> of -0.5 dB (89%) for an identical filter. This means a near 100% efficient slot antenna is achieved within this integrated filter/antenna system. The measured impedance matching, efficiency, gain, and radiation pattern closely agree with simulation results. Equivalent-circuit models of the integrated filter/antenna system are developed and verified with full-wave simulations. This technique can be applied for filter/antenna integration in all microwave, millimeter-wave, and submillimeter-wave frequency regions.
    IEEE Transactions on Microwave Theory and Techniques 05/2011; · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel method is presented in this paper to precisely characterize the dielectric properties of silicon carbon nitride (SiCN) ceramic materials at high temperatures for wireless passive sensing applications. This technique is based on a high quality factor (Q) dielectrically loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent. The dielectric properties of SiCN ceramics are characterized from 25 °C to 1000 °C. Two different metallization processes are implemented for the measurements with the highest temperatures of 500 °C and 1000 °C, respectively. A custom-made thru-reflect-line calibration kit is used to maximize the measurement accuracy at every temperature point. It is observed that the dielectric constant and loss tangent of the SiCN sample without Boron doping increase from 3.707 to 3.883 and from 0.0038 to 0.0213, respectively, when the temperature is raised from 25 °C to 500 °C, and for the SiCN with Boron doping (SiBCN), the dielectric constant and loss tangent increase from 4.817 to 5.132 and from 0.0020 to 0.0186, respectively, corresponding to the temperature ranging from 25 °C to 1000 °C. Experimental uncertainties for extracted εr and tanδ are no more than 0.0004 and 0.0001, respectively. The temperature dependency of Si(B)CN dielectric properties, as well as the dielectrically loaded cavity resonator structure, provides the basis for the development of wireless passive temperature sensors for high-temperature applications.
    IEEE Transactions on Microwave Theory and Techniques 01/2013; 61(2):960-971. · 2.23 Impact Factor