Creating a nanocomposite metamaterial structure using the radiation force of ultrasound standing waves

We propose to use the method based on the acoustic radiation force of counter-propagating (or standing) waves (at 1 MHz) generated inside a resonator cavity to direct the organization of nanoparticle clusters in a host fluid and create periodic arrays that are solidified in a bulk matrix. Gradually, the periodic pattern becomes permanent with full cure of the epoxy matrix so as to form a 3D periodic structure. We also show particle assembly by superimposing two ultrasound waves propagating in perpendicular directions. Furthermore, x-ray micro-computed tomography is used as a quality control tool to map the internal structure and characterize each nanocomposite. The fabrication method is a fast, cost-effective, versatile tool and not limited to a particular frequency so as to create metamaterials with different periodicities. The particles may consist of any material (metal, insulator, semiconductor, superconductor, nanowires, or tubes, CNTs, etc.), and other geometries (cylindrical, hexagonal, and other symmetries) may be also possible. Though not investigated here, the ultimate aim is to use the present results as a base for the development of finite-element models which take into account all the structural features to explore the various metamaterial functionalities in optical, acoustical, thermal, or even gravitational applications.