VI. Future Options/Avenues of Exploration
Metamaterials can be considered generalized composite materials. The potential impact of MMs can be understood by considering glass or carbon fiber composites—artificially structured media that are often stronger and lighter weight than conventional materials—which have revolutionized structural and mechanical engineering. MMs have the potential to likewise impact waves such as electromagnetic and acoustic waves. MMs have an emerging suite of tools and techniques that provide guidance and precise design methods for electromagnetic, acoustic, and other types of materials that control wave phenomena. MMs are also currently demonstrating highly graded index of refraction materials. The impact and relevance to DoD and national security is not yet realized, but could be transformational. Areas to watch include:
Metamaterial Design – Design techniques for arriving at a homogenized description of an otherwise inhomogeneous collection of objects. The techniques for metamaterial design have been refined over the past decade, but techniques continue to evolve and should be monitored for emerging capabilities that will drive innovation and realization of practical structures.
Metamaterials Fabrication – Once designed, physical metamaterial implementations must be found that enable the conceived designs. Not all metamaterial theoretical designs translate to practical implementation. There is a necessary step of coordinating theory and simulation of metamaterials with available dielectrics and metals, as well as fabrication and manufacturing techniques; realization of structures often requires innovation, experimentation, and iteration.
Metamaterial Integration into Devices – The successful development of devices requires an in-depth evaluation of existing technology. Entry points for metamaterial structures and components into existing technologies can be subtle, and require the fusion of traditional engineering methods with emerging metamaterial designs and structures. MMs face a number of technical challenges, including narrow band operation and polarization sensitivity (more complex designs may address these), as well as losses and small feature sizes (both particularly at optical and shorter wavelengths).
MMs also face a number of more non-technical issues: (1) A broadened definition of MMs by those in related fields who seek funding (e.g., photonic crystals and frequency selective surfaces); (2) Unrealistic short term expectations; (3) The potential to impair U.S. innovation and research through classification of MM research in the U.S.A.; (4) Highly competitive worldwide research, with heavy funding levels abroad.
At microwave and radio frequencies, MM manufacturing technologies are better understood, and the transition to applications is critical. The teaming of MM experts with industrial and DoD system designers is crucial, as the latter have knowledge of system needs and can help to identify areas where MM structures and devices can have an impact. In the THz, radar, infrared, and optical regimes, basic research is necessary into dielectric materials, conductors, structures, and manufacturing methods. Innovations in materials and structures will optimally be led by interactions between MM theorists, materials engineers, and fabrication researchers. Early interaction of these researchers with the component and systems communities will identify the critical aspects for MMs for each application (e.g., does loss matter?).