Figure 1：(a) Toroidal structure in a single unit lattice. (b) Metamaterial formed by multiple toroidal structures and conductor array.

A five-member research team, including Din-Ping Tsai, director general of the NARL’s Instrument Technology Research Center (ITRC) cum professor at National Taiwan University, and Nikolay I. Zheludev, professor at the University of Southampton, UK, has published their findings on toroidal dipolar response in an artificially engineered medium or metamaterial in Science, a leading scientific joual, on November 4, 2010, which attracted attention in the international scientific community. 

With an innovative idea coupled with precision manufacturing and measurement technologies, the team successfully developed “toroidal metamaterial” (Figure 1) and pROVided direct experimental evidence that the toroidal artificially engineered structure can be made into metamaterials with many potential applications, thus creating opportunities for the design and manufacturing of metamaterials (Figure2).

Materials in nature are made of atoms and molecules, to which the atomic oscillations patte determines the properties of materials. Metamaterials, on the other hand, are artificially structured media with unique and exotic properties not observed in natural materials. They possess resonant electromagnetic waves and amplification effects with toroidal or donut-shaped coil, and frequently gain their properties from structure or microscopic resonances rather than composition. 

Metamaterials with artificial-atom like toroidal coil have controllable electro-optical properties. Potential applications of metamaterials are growing and include: 1) superlenses or perfect lenses that go beyond the diffraction limit; 2) smart solar cells that absorb light completely to create energy; 3) electromagnetic and acoustic cloaks that hide objects and leave incoming waves unscattered; 4) high-gain antennas; 5) laser electro-optical sensors; etc. The NARL-ITRC is currently employing toroidal metamaterials to develop scientific devices in energy technology, environment protection and biomedical engineering.