Optical and Mechanical Metamaterials
JENNIFER DIONNE
Stanford University
LUKE SWEATLOCK
Northrop Grumman Aerospace Systems
The ability to engineer the properties of high-performance materials is critical for applications ranging from high-efficiency energy production and storage to advanced medical imaging and therapeutics. The principle of “metamaterials” refers to the design of composites whose properties derive as much from their structure as from their composition.
Metamaterials have energized many materials engineering disciplines, leading not only to the discovery of a powerful “toolbox” of new design methods but also to an expansion in fundamental understanding of the physics of materials. Metamaterials have been particularly impactful in the fields of mechanics and photonics, where they have prompted reevaluation of a number of conventionally accepted bounds on material performance and the discovery of an array of surprising, and often useful, properties.
Optical metamaterials, for example, have enabled control over both electric and magnetic fields of light, so that permittivities and permeabilities can be precisely tuned throughout positive, negative, and near-zero values. Through careful design of subwavelength “meta-atoms,” optical metamaterials have enabled negative refraction, optical lensing below the diffraction limit of light, and invisibility cloaking. In addition, mechanical metamaterials, thanks to their micron-to-submicron structure, exhibit extraordinary responses to applied forces, including negative bulk moduli, negative Poisson’s ratios, and negative mass densities. Such effects have been used to create solids that behave like liquids and ultralight, low-density materials with unprecedented strength.
This session highlighted recent scientific advances in metamaterials—fundamental breakthroughs, technological relevance, and impacts. Speakers discussed metallic and ceramic mechanical metamaterials, compliant mechanisms,
new plasmonic and resonant dielectric optical metamaterials and metasurfaces, acoustic metamaterials, microelectromechanical devices, and advanced nano- and microscale manufacturing of large-area metamaterials.
The session began with a talk by Julia Greer (California Institute of Technology), who creates and studies advanced materials that derive extraordinary strength from 3D architecture and microstructure. She also studies recoverable mechanical deformation in compliant nanomaterials. By constructing nanolattices of a wide variety of constituents—from ceramics to metals, semiconductors, and glasses—her research enables new applications in thermomechanics and affects such disparate fields as ultralightweight batteries and biomedical devices. The second speaker, Chris Spadaccini (Lawrence Livermore National Laboratory), described the development of engineering materials with remarkably light weight and ultrahigh stiffness, as well as the relationship between nanostructure and designer properties such as negative thermal expansion and negative stiffness. Next, Andrea Alù (University of Texas, Austin) discussed metamaterial-based design engineering. His research highlights the connection between metamaterials’ microscopic structural properties (e.g., symmetry and shape) and their macroscopic response, focusing on the creation of new useful devices that would not be possible with conventional materials. Examples of such devices are one-way antennas, “invisibility cloaks” that work over a wide spectral bandwidth, and acoustic circulators. The final speaker, Alexandra Boltasseva (Purdue University), talked about optical and infrared metamaterials and about metamaterial-enabled devices that could revolutionize optical technologies in communications, photovoltaics, and thermal radiation management. One of her research focus areas is the incorporation of high-temperature and functional materials as constituents of metamaterials. This is a critical frontier as optical metamaterials transition from the laboratory to specific real-world applications with challenging requirements.
