A frequency-agile metamaterial that for the first time can be
tuned over a range of frequencies in the so-called “terahertz
gap” has been engineered by a team of researchers from Boston
College, Los Alamos National Laboratory and Boston
The team incorporated semiconducting materials in critical
regions of tiny elements – in this case metallic split-ring
resonators – that interact with light in order to tune
metamaterials beyond their fixed point on the electromagnetic spectrum,
an advance that opens these novel devices to a broader array of uses,
according to findings published in the online version of the journal
“Metamaterials no longer need to be constructed only
out of metallic components,” said Boston College Physicist
Willie J. Padilla, the project leader. “What we’ve
shown is that one can take the exotic properties of metamaterials and
combine them with the unique prosperities of natural materials to form
a hybrid that yields superior performance.”
Padilla and BC graduate student David Shrekenhamer, along with
Hou-Tong Chen, John F. O’Hara, Abul K Azad and Antoinette J.
Tayler of Los Alamos National Laboratory, and Boston
University’s Richard D. Averitt formed a single layer of
metamaterial and semiconductor that allowed the team to tune terahertz
resonance across a range of frequencies in the far-infrared spectrum.
The team’s first-generation device achieved 20
percent tuning of the terahertz resonance to lower frequencies
– those in the far-infrared region –addressing the
critical issue of narrow band response typical of all metamaterial
designs to date.
Constructed on the micron-scale, metamaterials are composites
that use unique metallic contours in order to produce responses to
light waves, giving each metamaterial its own unique properties beyond
the elements of the actual materials in use.
Within the past decade, researchers have sought ways to
significantly expand the range of material responses to waves of
electromagnetic radiation – classified by increasing
frequency as radio waves, microwaves, terahertz radiation, infrared
radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Numerous novel effects have been demonstrated that defy accepted
“Metamaterials demonstrated negative refractive
index and up until that point the commonly held belief was that only a
positive index was possible,” said Padilla.
“Metamaterials gave us access to new regimes of
electromagnetic response that you could not get from normal
Prior research has shown that because they rely on
light-driven resonance, metamaterials experience frequency dispersion
and narrow bandwidth operation where the centre frequency is fixed
based on the geometry and dimensions of the elements comprising the
metamaterial composite. The team believes that the creation of a
material that addresses the narrow bandwidth limitations can advance
the use of metamaterials.
Enormous efforts have focused on the search for materials that
could respond to terahertz radiation, a scientific quest to find the
building blocks for devices that could take advantage of the frequency
for imaging and other applications.
Potential applications could lie in medical imaging or
security screening, said Padilla. Materials undetectable through x-ray
scans – such as chemicals, biological agents, and certain
explosives – can provide a unique
“fingerprint” when struck by radiation in the
far-infrared spectrum. Metamaterials like the one developed by the
research team will facilitate future devices operating at the terahertz
frequency of the electromagnetic spectrum.
In addition to imaging and screening, researchers and
high-tech companies are probing the use of terahertz in switches,
modulators, lenses, detectors, high bit-rate communications, secure
communications, the detection of chemical and biological agents and
characterization of explosives, according to Los Alamos National