New speakers developed partly at Virginia Tech promise big and energy-efficient sound

Of all the energy used to power the speakers of your Bluetooth device, your iPhone, or your 70-inch flatscreen TV, 95 percent of it gets wasted as heat.

While these technologies feature increasingly powerful computer chips and state-of-the-art design, the sound systems found inside incorporate the same electrodynamic speakers first developed by General Electric in the 1920s.

Guoliang “Greg” Liu is working to revolutionize that.

Working with a team from Israel, the Virginia Tech chemist has designed a prototype “electrostatic” speaker that boasts: the thinnest and lightest-weight speaker membrane with the highest aspect ratio ever; 10 to 100 times more energy efficient; the first bilayer structure of a single layer graphene (one atom thick of carbon) and high-performance polymers; polymers recycled from the likes of cars or bullet-proof vests; and graphene made of any carbon source, from anything from dinner leftovers to dog waste, according to Liu, an assistant professor in the Department of Chemistry and the Blackwood Junior Faculty Fellow in the College of Science. 

(For all you Spinal Tap fans out there, that’s turning it up to 11.)

“I do my best to be a big champion for energy efficiency so that we are good citizens of the Earth,” said Liu, who is an affiliated member of the Virginia Tech Macromolecules Innovation Institute and the Academy of Integrated Science's nanoscience program. “We want to develop a type of speaker that meets the needs of our energy-savvy customers. For example, cellphone users today really want to save energy and have a long battery life.”

Single layer graphene is the ultimate ultra-thin material, just about one-third of a nanometer (a sheet of paper is about 100,000 nanometers thick), yet extremely strong and highly conductive. Because the membrane is so thin, it doesn’t take a lot of force, or energy, to vibrate and produce sound — hence, it potentially offers high energy efficiency.

But for two years the daunting task of integrating single layer graphene membranes into the architecture and electronics of an acoustic speaker had thwarted Gabriel Zeltzer, manager at Waves Audio in Israel. Or in technical terms, according to Zeltzer, “I was trying to understand if graphene based heterostructures could be made as free-standing membranes, capable of displacing air at amplitudes and frequencies compatible with small form factor audio devices.” 

Around 2016, Zeltzer reconnected with Liu at a American Physical Society conference in Baltimore. The two had briefly worked together six years earlier at the Hitachi Global Storage Technologies Research Center in San Jose, California.

They met for lunch, swapped stories about the projects they were working on, discovered common interests, and literally grabbed napkin paper to write down ideas on which to collaborate. Chief among them was the graphene membrane problem.

“Greg expressed confidence and was certain he would find the proper polymer to create a polymer/graphene heterostructure which could do the job,” Zeltzer would later write.

Working out of the Bar Ilan University engineering department run by colleague Doron Naveh, Zeltzer began sending single layer graphene to Liu’s lab at Virginia Tech. Liu’s team experimented with different polymers and in 2017 developed a process that, combined with the graphene substrate, produced a 300-nanometer thin membrane that “delivered sound at comparable levels to the same form factor electrodynamic ‘classical’ speakers,” Zeltzer wrote. “This represented not only a breakthrough in the material science realm … but also provided one of the highest energy efficiency devices to produce sound.”

The potential of this membrane is immense, according to Naveh. “Audio applications are the tip of a huge iceberg including advanced optics and even quantum mechanical devices having the ability of extreme sensitivity in sensing low electrical and optical signals.”

Zeltzer likens the energy savings of their innovation to that of a LED light versus the incandescent bulb. “In the not-so-distant future, we can envision the majority of the acoustic devices to replace the electrodynamic speakers in applications where the energy consumption is of paramount importance, such as portable and mobile acoustic applications.”

But acoustic speakers are just the opening act of this energy-efficient Lollapalooza. “Opto-mechanical devices, macroscopic quantum mechanical devices, extremely sensitive detectors of physical processes and novel phenomena — further developments will without a doubt have a broader impact and show the true potential of this nanoscale thick ‘David' while overtaking the existing ‘Goliath,’” Zeltzer said.

The team is now working to scale up and mass manufacture these highly technical membrane structures to accommodate the millions of devices that potentially would incorporate the technology — a stage dubbed “from the lab to the fab,” Doron quipped. They are ramping up research and development facilities at the Virginia Tech Corporate Research Center and in Israel. Despite the challenges, he adds, with partners like Liu and Virginia Tech, “I have very little doubts.”

As for Liu, he’s grateful not only for the chemistry that has gone into the project, but the one that reunited him with Zeltzer.

“Chemistry connected us and our enthusiasm for science,” Liu said, “and we’ve worked together ever since. I’m so lucky to have a great friend like Gabriel.”

-Written by Michael Hemphill

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