Kazuo Sato

Metamaterials are a new class of ordered composites that exhibit exceptional electromagnetic properties not readily observed in nature. In particular, artificial materials with both negative permittivity and permeability have attracted widespread interest in recent years. These composites are constructed from an array of metallic in dielectric and magnetic substrates and exhibit unusual electromagnetic properties such as inverted Snell's law and Doppler shift behavior within a particular frequency range. Recent research activities in the field of metamaterials have not only demonstrated interesting physical phenomena but also lead to the development of design procedures and the realization of promising new microwave and millimeter-wave components and devices. A promising technique for the creation of new electromagnetic materials is topology design optimization. Significant research efforts have led to the development of microwave and millimeter-wave applications of metamaterials such as couplers, resonators, negative refractive index lenses, small antennas, backfire-to-endfire leaky-wave antennas, and absorbers. These new metamaterials should open up a new field of future automotive applications, such as beam steering antenna systems for radar and mobile communication, novel magnetic materials for electric motors, and high-performance absorbing and shielding materials for electromagnetic compatibility. In this review, we survey metamaterials in microwave and millimeter-wave applications. In addition, we present recent R&D activities of our laboratory in the field of metamaterials.

Yoshitsugu Kojima

The storage and generation of hydrogen is a basic problem for its use in fuel cells. Chemical hydrides such as NaBH₄, LiH and NaH are known as high hydrogen containing materials. NaBH₄, in particular, is stable compared with other chemical hydrides, easy to handle and can be synthesized from common natural resources. However, with mixing of NaBH₄ and H₂O at room temperature, only a small amount of the theoretical yield of hydrogen is liberated. In this work, we show that Pt-LiCoO₂ is an excellent catalyst for releasing hydrogen by hydrolysis of NaBH₄ solution. Using the catalyst with a stoichiometric amount of water (H₂O/NaBH₄: 2 mol/mol) at a high H₂ pressure above 0.6 MPa produced nearly the theoretical H₂ yield. The 10-kW-scale hydrogen generator comprised a storage vessel of NaBH₄ solution, a solution pump, a byproduct storage tank for the NaBO₂ solution, a separator and a hydride reactor. The reactor contained a honeycomb monolith coated with the Pt-LiCoO₂ catalyst. NaBH₄ was synthesized by annealing NaBO₂ with MgH₂ under high H₂ pressure.