A very simple benchtop technique that uses the force of acoustical waves to create a variety of 3-D structures will benefit the rapidly expanding field of metamaterials and its myriad applications. Metamaterials are artificial materials engineered to have properties not found in nature. They usually gain their unusual properties — such as negative refraction that enables subwavelength focusing and negative bulk modulus – from structure rather than from composition. The new technique, developed by Los Alamos National Laboratory (LANL) researchers, is expected to make highly desirable metamaterials more accessible. It harnesses an acoustical wave force that causes nanometer-scale particles to cluster in periodic patterns in a host fluid that is later solidified, said Farid Mitri of LANL. These images show microcomputed x-ray tomography renderings of an acoustically engineered nanocomposite metamaterial based on ~5-nm-diameter diamond nanoparticles. (Images: Farid G. Mitri, Los Alamos National Lab) “The periodicity of the pattern formed is tunable, and almost any kind of particle material can be used, including metal, insulator, semiconductor, piezoelectric, hollow or gas-filled sphere, nanotubes and nanowires,” he said. The entire process of structure formation is very fast and takes anywhere from 10 s to 5 min. Mitri and his colleagues believe that this technique can be adapted easily for large-scale manufacturing and that it holds the potential to become a platform technology for the creation of a new class of materials with extensive flexibility in terms of periodicity (millimeter to nanometer) and the variety of materials that can be used. “This new class of acoustically engineered materials can lead to the discovery of many emergent phenomena, understanding novel mechanisms for the control of material properties, and hybrid metamaterials,” Mitri said. Applications of the technology, to name only a few, include invisibility cloaks to hide objects from radar and sonar detection, subwavelength focusing for production of high-resolution lenses for microscopes and medical ultrasound/optical imaging probes, miniature directional antennas, biological scaffolding for tissue engineering, lightguides and a variety of sensors. The LANL work is described in the March 2011 issue of Review of Scientific Instruments. For more information, visit: www.lanl.gov