Chip-sized, high-speed terahertz modulator raises possibility of faster data transmission

Confined terahertz waves interact with tunable, two-dimensional electron gas in a novel slot waveguide. Credit: Nano Lab, Tufts University School of Engineering.

MEDFORD/SOMERVILLE, Mass. (January 19, 2017) – Tufts University engineers have invented a chip-sized, high-speed modulator that operates at terahertz (THz) frequencies and at room temperature at low voltages without consuming DC power. The discovery could help fill the “THz gap” that is limiting development of new and more powerful wireless devices that could transmit data at significantly higher speeds than currently possible.

Measurements show the modulation cutoff frequency of the new device exceeded 14 gigahertz and has the potential to work above 1 THz, according to a paper published online today in Scientific Reports. By contrast, cellular networks occupy bands that are much lower on the spectrum where the amount of data that can be transmitted is limited.

The device works through the interaction of confined THz waves in a novel slot waveguide with tunable, two-dimensional electron gas. The prototype device operated within the frequency band of 0.22-0.325 THz, which was chosen because it corresponded to available experimental facilities. The researchers say the device would work within other bands as well.

Although there is significant interest in using the THz band of the electromagnetic spectrum, which would enable the wireless transmission of data at speeds significantly faster than conventional technology, the band has been underutilized in part because of a lack of compact, on-chip components, such as modulators, transmitters, and receivers.

“This is a very promising device that can operate at terahertz frequencies, is miniaturized using mainstream semiconductor foundry, and is in the same form factor as current communication devices. It’s only one building block, but it could help to start filling the THz gap,” said Sameer Sonkusale, Ph.D., of Nano Lab, Department of Electrical and Computer Engineering, Tufts University, and the paper’s corresponding author.

The work was supported by the Office of Naval Research under award N00014-09-1-1075 and Defense University Research Instrumentation Program grant N00014-12-1-0888.

P.K. Sing and S. Sonkusale, “High Speed Terahertz Modulator on the Chip Based on Tunable Terahertz Slot Waveguide,” Scientific Reports, published online Jan. 19, 2017. DOI: 10.1038/SREP40933.

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About Tufts University’s School of Engineering

Located on Tufts' Medford/Somerville campus, the School of Engineering offers a rigorous engineering education in a unique environment that blends the intellectual and technological resources of a world-class research university with the strengths of a top-ranked liberal arts college. Close partnerships with Tufts' excellent undergraduate, graduate and professional schools, coupled with a long tradition of collaboration, provide a strong platform for interdisciplinary education and scholarship. The School of Engineering’s mission is to educate engineers committed to the innovative and ethical application of science and technology in addressing the most pressing societal needs, to develop and nurture twenty-first century leadership qualities in its students, faculty, and alumni, and to create and disseminate transformational new knowledge and technologies that further the well-being and sustainability of society in such cross-cutting areas as human health, environmental sustainability, alternative energy, and the human-technology interface.

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Department of Defense funds terahertz-range metamaterials research

http://phys.org/wire-news/161698553/department-of-defense-funds-terahertz-range-metamaterials-resear.html

Metamaterials research having potential applications in high-speed data transmission, medical imaging and other kinds of imaging and remote sensing is the focus of a U.S. Department of Defense project funded for five years at $7.5 million.

Penn State is part of this six-member Multi-University Research Initiative by the Air Force Office of Scientific Research. The project is led by Mark Cappelli, professor of mechanical engineering, Stanford University. Also collaborating with Stanford are the University of Texas at Austin, Tufts University, UCLA and the University of Washington.

Penn State researchers will focus on the fundamental science necessary to develop plasma photonic crystals and plasma-embedded metamaterials that operate in the terahertz range. Terahertz is the region of the electromagnetic spectrum that lies between far infrared and microwave, and is a nonionizing frequency invisible to the human eye. This regime is already being used in airport surveillance and astronomy.

The researchers will generate the plasmas inside holes in the metamaterial arrays using radio frequency excitation with the entire device encapsulated in an inert gas. Using micro-lens arrays, focused lasers will generate very dense, highly ionized plasma arrays. Unlike the metal structures of typical metamaterials, researchers can control a plasma's dielectric properties by varying the plasma density. Plasmas afford the possibility of controlling metamaterials at high bandwidth. This will enable such applications as antennas with beam steering, filter devices, multiplexers, phase shifters and electro-optical modulators.

Researchers at Penn State will be the primary team charged to develop a new class of low-loss dielectric resonators and multilayer low temperature co-fired ceramics to replace the usual metallic split-ring resonators found in traditional metamaterial structures. Metamaterials are artificial structures with sub-wavelength features that can interact with electromagnetic waves in a manner unlike that of natural materials. Long-term goals of metamaterials research include invisibility cloaking devices and perfect lenses to capture short-range light waves for fine detail light microscopy.

The principal investigators at Penn State are Clive Randall, professor of materials science and engineering, and Michael Lanagan, professor of engineering science and mechanics. The Penn State team members are pioneers in the development of dielectric materials and leaders in the long-running Center for Dielectric Studies, an industry supported research center that recently was renewed with technical new opportunities with North Carolina State University as the NSF I/UCRC Center for Dielectrics and Piezoelectrics.

Provided by Pennsylvania State University

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Paper-based metamaterial biosensor

http://www.nanowerk.com/spotlight/spotid=21789.php

(Nanowerk Spotlight) Paper has emerged as a focus area for researchers developing innovative techniques for printed basic electronics components. Electronic paper displays are already a commercial reality and prototypes of things like paper batteries are under development. In these applications, researchers transfer thin-films, nanoparticles or other nanostructures onto the desired substrate via various processes (see "Direct-growth fabrication for paper-based electronics").

Another area where paper could lead to low-cost innovative devices and applications is lab-on-a-chip technology. Currently, these microfluidic devices are fairly expensive due to their lithography-based fabrication process with channels patterned in glass or plastic and tiny pumps and valves directing the flow of fluids.

Inexpensive paper-based sensing kits already play an important role in ready-to-use diagnostics. Researchers have even managed to create an inexpensive microfluidic platform on hydrophobic paper with laser treatments (see "New lab-on-chip advance uses low-cost, disposable paper strips").

In a further advance, scientists have now fabricated a paper-based metamaterial device which can be potentially utilized for quantitative analysis in biochemical sensing applications.

"When compared with lab-on-a-chip fabricated on conventional substrates, paper-based biosensors still need to improve in sensitivity and accuracy, in part due to the difficulty in obtaining high-resolution, small feature sizes – e.g., micrometers or less with sharp edges – on paper substrates where conventional photolithography techniques are difficult to apply," Fiorenzo Omenetto, professor of biomedical engineering at Tufts University School of Engineering, explains to Nanowerk.

In new work led by Hu (Tiger) Tao, a postdoctoral reseach associate in Omenetto's group, together with collaborators from Tufts and Boston University, have successfully interfaced metallic resonators with high resolution with paper. The team has reported their findings in a paper ("Metamaterials on Paper as a Sensing Platform") in the June 3, 2011, online edition of Advanced Materials.

This ability to simply pattern resonators on paper substrates brings together the versatility and potential sophistication of electromagnetic transduction with an abundantly available substrate such as a paper.

"Our device adds functionality to an approach that exists in practical diagnostics and has been reinvented, notably by Whitesides et al. ("Patterned Paper as a Platform for Inexpensive, Low-Volume, Portable Bioassays" and "Low-Cost Printing of Poly(dimethylsiloxane) Barriers To Define Microchannels in Paper") as a widely available lab-on-a-chip platform" says Omenetto.

While most paper-based biosensors – usually a strip of paper doped with an antibody specific to an antigen of interest – use colorimetric readout and detect the color or intensity change in the visible range, metamaterials offer a broader operating range, covering from radio frequency to optical wavelengths. These patterned papers offer more opportunities for multiplexed and quantitative analysis.

"In our device, paper acts as the dielectric substrate providing both support and a material to sample and embed analytes which then modulate the resonance of the split-ring resonators that compose the metamaterials," explains Omenetto. "This offers additional utility in the signal transduction capabilities and provides the possibility to explore label-free sensing strategies based on electromagnetic modulation."

In their work, the team led by Omenetto patterned paper substrates through selective deposition of a target material (gold) through a 500-nm-thick silicon nitride film microstencil-based shadow mask.

a) Schematic of the micrometer-sized metamaterial resonators sprayed on paper substrates with a predefined microstencil. b) Photograph of a paper-based terahertz metamaterial sample. c) Optical microscopy image of one portion of an as-fabricated paper metamaterial sample. (Reprinted with permission from Wiley-VCH Verlag)

After fabrication of the stencils, using surface micromachining technology, the entire patterning and deposition process on paper was conducted in a dry, chemical-free environment.

Tao describes the process: "Similarly to what we had previously done for silk ("Metamaterial Silk Composites at Terahertz Frequencies"), the microstencils were carefully attached to the paper substrates in contact mode. A thin layer of 150-nm-thick gold was then sprayed on the paper substrates using electron beam evaporation. Since the surface roughness of the paper substrate affects the pattern quality (including both the minimum transferable line width and sharpness), the researchers used photo paper with a surface roughness of less than 18 nm."

After fabricating their paper metamaterial, the team undertook a proof-of-concept demonstration that they would work as biosensors by coating the paper with glucose solutions of various concentrations. The solution was allowed to dry in air and the transmission spectra were then measured by THz-TDS as a function of frequency.

"With higher glucose concentration, the analyte-induced resonance should shift more since the shift is mainly due to alterations in the split ring resonator capacitance" says Tao (split ring resonators are the most commonly used elements to build MM structures and devices). "We were able to verify this by the experimental results. A resonance at 908 GHz was observed for the paper metamaterial sample without coating and this value shifted continuously to lower frequencies as the concentration of the glucose solution increased."

Potential applications of this work are label free sensors that can be widely manufactured or additional transducers to be interfaced on paper-based assays.

The team would now like to develop multifunctional devices, with multiple antennas and split-ring resonators of different kinds that can provide a multi-channel analysis of analytes that are deposited on the paper sheet and develop RF-based assays that are cheap, disposable and that minimize the use of chemicals for transduction.

By Michael Berger. Copyright © Nanowerk

Implantible Antenna investigating protein signatures with Terahertz

MY NOTE: I HAD ASKED THIS QUESTION SOMETIME BACK ON A CONFERENCE CALL REGARDING ADVANCED PHOTONIX: CAN T-RAY DETECT BIOLOGICAL/DNA SIGNATURES? LOOKS LIKE IT CAN, IS MY READ OF THIS STORY, OR IT WILL BE ABLE TO.
IF YOU READ THE NEWS THIS WEEK, ABOUT EGG CONTAMINATION, YOU CAN IMAGINE HOW TERAHERTZ MAY BE USED FOR THE SAFE TESTING OF FOOD, IN THE NOT TOO DISTANT FUTURE.


Implantable Antenna Could Someday Alert Doctors To Signs Of Disease
August 23, 2010

Silk and gold, usually a pairing for the runways of Milan, are now the main ingredients for a new kind of implantable biosensor. Researchers at Tufts University have crafted a small antenna from liquid silk and micropatterned gold. The antenna is designed to spot specific proteins and chemicals in the body, and alert doctors wirelessly to signs of disease. Scientists say the implant could someday help patients with diabetes track their glucose levels without having to test themselves daily.

According to Fiorenzo Omenetto, professor of biomedical engineering at Tufts University, silk is a natural platform for medical implants--it's biocompatible, and while it's delicate and pliable, it's also tougher than Kevlar. Implanted in the body, silk can conform to any tissue surface, and, unlike conventional polymer-based implants, it could stay in place over a long period of time without adverse effects. Omenetto has previously taken advantage of these properties to mold silk into tiny chips and flexible meshes, pairing the material with transistors to track molecules, and with electrodes to monitor brain activity.

Now Omenetto is exploring the combination of silk and metamaterials--metals like gold, copper, and silver manipulated at the micro- and nanoscale to exhibit electromagnetic characteristics not normally found in nature. For example, scientists have created metamaterials that act as "invisibility cloaks" by manipulating metals to bend light all the way around an object, rendering it invisible.

Omenetto and his colleague Richard Averitt, associate professor of physics at Boston University, used similar principles to create a metamaterial that's responsive not to visible light, but rather to frequencies further down the electromagnetic spectrum, within the terahertz range. Not coincidentally, proteins, enzymes, and chemicals in the body are naturally resonant at terahertz frequencies, and, according to Averitt, each biological agent has its own terahertz "signature."

Terahertz science is a new and growing field, and several research groups are investigating specific protein "T-ray" signatures. A silk metamaterial antenna could someday pick up these specific signals and then send a wireless signal to a computer, to report on chemical levels and monitor disease.

To engineer the responsive end of such an antenna, the team first created a biocompatible base by boiling down silk and pouring the liquid solution into a centimeter-square film. The researchers then sprayed gold onto the silk film, using tiny stencils to create different patterns all along the film. Each area of the film responds to a different terahertz frequency depending on the shape of the gold pattern. The team then wrapped the patterned film around a capsule to form an antenna.

To test its performance, Omenetto and Averitt subjected the antenna to terahertz radiation and found that the antenna was resonant at specific frequencies. Going a step further, the researchers implanted the antenna in several layers of muscle tissue from a pig, and still detected a terahertz signal.

"We'll try to sense something next and maybe put the antenna in contact with something we'd like to detect, like glucose," says Omenetto. "We'll see if we can replicate a proof of principle, and try to add some meaning to the resonance."

Rajesh Naik, a materials science expert at the Air Force Research Laboratory at Wright-Patterson Air Force Base, says the research has great practical potential.

"Proteins and other molecules can be entrapped within silk films, allowing one to monitor in-vivo chemical reactions," says Naik. "Similar resonating structures can be patterned onto other polymeric materials, but silk has an added advantage of being biocompatible."

SOURCE: Massachusetts Institute of Technology