Potential of hollow Al₂O₃ nanoparticles for reducing dielectric properties of Al₂O₃‐epoxy matrix composites in microwave frequency range

Abstract

In this article, a transmission line circuit model for an HMSIW Wilkinson power divider is presented. The scattering parameters of the power divider are derived using the power-current relation for waveguide impedance and even-and odd-mode analysis. Derived formulations indicate that the value of the shunt resistor can be adjusted to achieve an optimum isolation performance across a wide bandwidth. This method, which is applicable to any type of interconnect, serves as a rapid means to determine the initial design parameters of the power divider and its subsequent optimization. The S-parameters of an HMSIW power divider calculated using the presented approach are validated with full-wave simulations and measurements. Measured results show the maximum isolation of 40.9 dB at 10.44 GHz and the achievement of 71% 10-dB isolation bandwidth by choosing a 110-X branch resistor. . Possible approach to reduce dielectric constant is to introduce air or vacuum pores inside the composite. However, incorporation of pores to a matrix is undesirable, because the existence of pores leads to poor mechanical properties [4]. Another approach for low dielectric constant is the use of nanoparticle: Al 2 O 3 nanoparticle compact shows lower dielectric constant at GHz frequencies compared with Al 2 O 3 particle compact of micrometer order diameter (Matsumura and Kagawa, manuscript in preparation). Therefore, use of hollow Al 2 O 3 nanoparticle seems effective solution to overcome this problem. However, dielectric property of hollow Al 2 O 3 nanoparticle-dispersed polymer matrix composite has not yet examined.The attention of this article is to examine the potential for obtaining low dielectric constant hollow Al 2 O 3 nanoparticle-dispersed polymer matrix composites. Solid a-Al 2 O 3 nanoparticle was also used as dispersion materials for comparison purpose. The merit of using hollow Al 2 O 3 nanoparticle on effective dielectric constant of composite is discussed. X-ray diffraction results confirmed that the crystalline structure of the hollow Al 2 O 3 shell depends on the total oxidation time and temperature, respectively. In the present particle, the dominant crystalline structure is determined to be a-Al 2 O 3 . For comparison purpose, commercially available solid a-Al 2 O 3 nanoparticles (TM-D, Taimei Chemical, Nagano, Japan) were also used. The particle had an average diameter of 130 nm. EXPERIMENTAL PROCEDUREThe hollow Al 2 O 3 nanoparticles were mixed with a mixture of low viscous liquid epoxy resin (Epicoat, Japan Epoxy Resins, Tokyo, Japan), curing agent (DBU, San-apro, Kyoto), and accelerator (MH-700, New Japan Chemical,, Osaka). This process was done at room temperature in ambient air. Then, they were mixed by rotating mixing container for 6 min using hybrid deforming mixer (AR-250, Thinky, Tokyo). Thereafter, the mixture was degassed for 4 min, then cast into a cylindrical mold (inner diameter: 50 mm), and postcured in ambient air in an oven at 373 K for 2 h followed by 383 K for 5 h. After curing, the material was cooled ...