Mar 5 2004
A team of physicists and engineers from the University of California, San Diego, the University of California, Los Angeles and Imperial College, London have developed a class of materials that respond magnetically to terahertz radiation, a fundamental finding relevant to many exciting applications in areas including guidance in zero visibility weather conditions, security and biomedical imaging and quality control.
The materials described in the study are metamaterials, artificially structured materials that extend the properties of existing naturally occurring materials and compounds. In 2000, UCSD researchers created and reported the first measurements of left-handed metamaterials, so-called because they reverse many of the physical properties that govern the behavior of ordinary materials. Left-handed materials were named one of the Top Ten scientific breakthroughs of the year by Science in December 2003 when these materials and their properties were independently confirmed by multiple groups. While not left-handed, the present metamaterials demonstrate that the magnetic response can be extended to much higher frequencies, namely the terahertz range, a set of frequencies that are intermediate between those of infrared rays and microwave rays.
The material designed by the researchers consists of a two-dimensional array of repeated patterned copper elements, called split ring resonators, deposited on a quartz plate. Each split ring resonator is made up of two concentric copper squares, both having a small gap. The gap in the larger square is on the opposite side as the gap in the smaller square. The width of one of the split ring resonators is roughly 50 microns, less than the thickness of a human hair.
The copper elements that compose these materials are analogous to the atoms in a regular material. While copper on its own is not magnetic, the geometry of the resonator leads to an effective magnetic response, so that the composite metamaterial can be characterized as magnetic. Therefore, these engineered metamaterials have properties that are not observed in their constituent materials.
According to the researchers, while terahertz scanners have great potential, up until now their uses have been limited because of the lack of inexpensive methods to generate and detect terahertz rays.