Frequency tuning is a concept used in telecommunications as a way of matching the frequencies of transmitters and receivers. In practice, this is achieved when both ends of the communication link tune into the same frequency channel.
In today’s colossal communications networks, the ability to reliably synthesize as many frequencies as possible and to rapidly switch from one to another is paramount for seamless connectivity. However, say the researchers, a century after the invention of the radio, the quest for the ideal electronic tuner is still ongoing.
In their work, the researchers found that phase-change nanowires could serve as the ultimate tunable frequency synthesizers and filters for the future of IoT and 5G networks. Owing to extremely-low power requirements (less than a picowatt) and ultra-high quality (Q) factors in nanoelectromechanical systems (NEMS) resonators, tunable NEMS have the potential to be the ultimate building blocks in communication electronics and signal processors, say the researchers.
Phase-change materials (PCMs) can switch between amorphous and crystalline states permanently yet reversibly, however, the change in their mechanical properties has largely gone unexploited. While the most practical configuration using suspended thin-films suffers from limitations, the researchers overcame these limitations using nanowires as active NEMS.
They fabricated vibrating nanostrings of a chalcogenide glass (germanium telluride) that resonate at predetermined frequencies, just like guitar strings. To tune the frequency of these resonators, the researchers switch the atomic structure of the material, which in turn changes the mechanical stiffness of the material itself.
This differs from existing approaches that apply mechanical stress on the nanostrings similar to tuning a guitar using the tuning pegs. These approaches directly translate into higher power consumption because the pegs are not permanent and require a voltage to hold the tension.
“By changing how atoms bond with each other in these glasses, we are able to change the Young’s modulus within a few nanoseconds,” says Utku Emre Ali, at the University of Oxford who completed the research as part of his doctoral work. “Young’s modulus is a measure of stiffness, and it directly affects the frequency at which the nanostrings vibrate.”
Professor Ritesh Agarwal, School of Engineering and Applied Science, University of Pennsylvania who collaborated on the study first discovered a unique mechanism that changed the atomic structure of novel nanomaterials back in 2012.
“The idea that our fundamental work could have consequences in such an interesting demonstration more than 10 years down the line is humbling,” says Agarwal. “It’s fascinating to see how this concept extends to mechanical properties and how well it works.”
Professor Harish Bhaskaran, Department of Materials, University of Oxford who led the work says, “This study creates a new framework that uses functional materials whose fundamental mechanical property can be changed using an electrical pulse. This is exciting and our hope is that it inspires further development of new materials that are optimized for such applications.”
The researchers further estimate that their approach could operate a million times more efficiently than commercial frequency synthesizers while offering 10-100 times faster tuning. Although improving the cyclability rates and the readout techniques is a necessity for commercialization, these initial results might mean higher data rates with longer-lasting batteries in the future.