Communications of the ACM
Frequency Filter Could Advance Terahertz Data Transmission
University of Utah Professor Ajay Nahata (left) and graduate student Andrew Paulsen (right) examine a terahertz frequency filter fabricated using a recently developed inkjet printing technique.
Credit: Dan Hixson / University of Utah
University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that could allow cellphone users and Internet surfers to download data a thousand times faster than today. Once the filter is designed, it can be fabricated using an off-the-shelf inkjet printer.
Filtering out different frequencies will be important in the development of the terahertz spectrum for communications. By filtering out unwanted frequencies users can download information from the Internet or talk on a cellphone, for example, with less noise or interfering signals.
The terahertz range refers to the band of frequencies between infrared light and radio waves. Engineers consider it the next frontier in communications because of the enormous potential for boosting data transmission rates. The technology also is being studied for next-generation medical imaging and airport scanners. Terahertz rays, or T-rays, can pass through many materials without using ionizing radiation, which makes them attractive for use in medical imaging and security screening devices.
This new methodology for creating filters is described in "K-space Design of Terahertz Plasmonic Filters," published in The Optical Society's online journal, Optica.
"Your cellphone operates at a frequency of 2.4 gigahertz. A terahertz is a thousand gigahertz," says graduate student Andrew Paulsen, who co-authored the paper with Ajay Nahata, an electrical and computer engineering professor at the University of Utah. "If we could effectively use the terahertz spectrum for communications, we could have a thousand times more bandwidth than we currently do."
Paulsen and Nahata discovered that by creating certain computer-generated designs using engineering software called MATLAB and printing them on a plastic sheet via a regular inkjet printer, they could create a filter that allows certain terahertz frequencies to pass through while blocking others out. The printer uses silver-metal ink similar to what is used for the production of circuit boards and tiny antennas.
By using a terahertz generator, which shoots out an invisible beam of light, researchers can measure the frequencies as the beam passes through the filter. The dimensions and geometry of the printed designs, which can look like a wavy bull's-eye for example, determine which frequencies get through and to what extent.
This method is an important step in utilizing the terahertz spectrum for commercial use, possibly as the basis for the next "5G" network for cellphones. If cellphones on a current "4G" network can download data at 10 to 15 megabits per second, terahertz technology can potentially send data back and forth at terabits per second (or millions of megabits per second). Using filters in such a network will be a vital component because it will be necessary to separate frequencies in order to create multiple communication channels. Many wireless devices use filters to single out frequencies, including Wi-Fi routers, televisions, and cellphones.
It might be another 10 years before consumers are using Wi-Fi routers or cellphones with terahertz technology, but communications companies could use it for their network backbones much sooner. A current limitation of terahertz frequencies is that they require line of sight and can transmit only over short distances. But some researchers have already achieved lightning download speeds with wireless terahertz chips, and others are interested in broadcasting super-high-definition 4K television signals over the air with cameras that use the terahertz spectrum.
"Terahertz technology is something there is a lot of interest in," Nahata says. "I guarantee that people will come up with new ideas that can use all of that available bandwidth."
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