Power/Performance Bits: Aug. 27

The sound of typing
Cybersecurity researchers at the Southern Methodist University found a way to detect what a user is typing based on sensor data collected from a nearby smartphone. The team found that acoustic signals produced by typing on a computer keyboard can successfully be picked up by a smartphone, which can then be processed to determine which keys were struck – even in noisy conference rooms.

“We were able to pick up what people are typing at a 41 percent word accuracy rate. And we can extend that out – above 41 percent – if we look at, say, the top 10 words of what we think it might be,” said Eric C. Larson, an assistant professor in SMU Lyle School’s Department of Computer Science.

“We were looking at security holes that might exist when you have these ‘always-on’ sensing devices – that being your smartphone,” Larson added. “We wanted to understand if what you’re typing on your laptop, or any keyboard for that matter, could be sensed by just those mobile phones that are sitting on the same table. The answer was a definite ‘Yes.'”

To mimic real scenarios, the team arranged several people in a conference room, talking to each other and taking notes on a laptop. Placed on the same table as their laptop or computer, were as many as eight mobile phones, kept anywhere from three inches to several feet away from the computer, according to Mitch Thornton, director of SMU’s Deason Institute and professor of electrical and computer engineering. Study participants were not given a script of what to say when they were talking, and were allowed to use shorthand or full sentences when typing. They were also allowed to either correct typewritten errors or leave them, as they saw fit.

Thornton noted that it might take only a couple of seconds to obtain information on what you’re typing, and that there would be no way to know if you were a victim.

“There are many kinds of sensors in smartphones that cause the phone to know its orientation and to detect when it is sitting still on a table or being carried in someone’s pocket. Some sensors require the user to give permission to turn them on, but many of them are always turned on,” Thornton explained. “We used sensors that are always turned on, so all we had to do was develop a new app that processed the sensor output to predict the key that was pressed by a typist.”

“Based on what we found, I think smartphone makers are going to have to go back to the drawing board and make sure they are enhancing the privacy with which people have access to these sensors in a smartphone,” Larson said.

Some specific knowledge of the environment is needed for this attack, such as the material of the table, as metal and wooden tables create different sound waves when typed upon. Larson notes that “An attacker would also need a way of knowing there are multiple phones on the table and how to sample from them.”

Folding soft robots
Two recent studies took different approaches to making soft robots softer. Currently, soft robots must be tethered to external power and control systems or require hard components to pump fluids, limiting their applications.

At Harvard University and Caltech, researchers created origami-inspired soft robotic systems that can move and change shape in response to external stimuli.

Through sequential folds, origami can encode multiple shapes and functionalities in a single structure. Using liquid crystal elastomers that change shape when exposed to heat, the research team 3D-printed two types of soft hinges that fold at different temperatures and thus can be programmed to fold in a specific order.

“With our method of 3D printing active hinges, we have full programmability over temperature response, the amount of torque the hinges can exert, their bending angle, and fold orientation. Our fabrication method facilitates integrating these active components with other materials,” said Arda Kotikian, a graduate student at Harvard SEAS and the Graduate School of Arts and Sciences.

To demonstrate the principle, the team built several devices including an untethered soft robot nicknamed the “Rollbot.” The Rollbot begins as a flat sheet, about 8 centimeters long and 4 centimeters wide. When placed on a hot surface, about 200°C, one set of hinges folds and the robot curls into a pentagonal wheel.

Another set of hinges is embedded on each of the five sides of the wheel. A hinge folds when in contact with the hot surface, propelling the wheel to turn to the next side, where the next hinge folds. As they roll off the hot surface, the hinges unfold and are ready for the next cycle.

The self-propelling Rollbot begins as a flat sheet, about 8 centimeters long and 4 centimeters wide, and curls into a pentagonal wheel when placed on a hot surface. Hinges embedded on each of the five sides of the wheel folds when in contact with the surface, propelling the wheel to turn to the next side. As the hinges roll off the hot surface, they unfold and are ready for the next cycle. (Video courtesy of Lori K. Sanders/Harvard SEAS)

“Using hinges makes it easier to program robotic functions and control how a robot will change shape. Instead of having the entire body of a soft robot deform in ways that can be difficult to predict, you only need to program how a few small regions of your structure will respond to changes in temperature,” said Connor McMahan, a graduate student at Caltech.

“Many existing soft robots require a tether to external power and control systems or are limited by the amount of force they can exert. These active hinges are useful because they allow soft robots to operate in environments where tethers are impractical and to lift objects many times heavier than the hinges,” said McMahan.

Another device, when placed in a hot environment, can fold into a compact folded shape resembling a paper clip and unfold itself when cooled.

“These untethered structures can be passively controlled,” said Kotikian. “In other words, all we need to do is expose the structures to specific temperature environments and they will respond according to how we programmed the hinges.”

While this research only focused on temperature responses, liquid crystal elastomers can also be programmed to respond to light, pH, humidity and other external stimuli.

“This works demonstrates how the combination of responsive polymers in an architected composite can lead to materials with self-actuation in response to different stimuli,” said Chiara Daraio, Professor of Mechanical Engineering and Applied Physics at Caltech. “In the future, such materials can be programmed to perform ever more complex tasks, blurring the boundaries between materials and robots.”

Soft pump
Researchers at École Polytechnique Fédérale de Lausanne (EPFL) and Shibaura Institute of Technology built a soft pump complete with flexible electrodes.

The pump weighs one gram, is completely silent and consumes very little power, which it gets from a 2cm by 2cm circuit that includes a rechargeable battery. “If we want to actuate larger robots, we connect several pumps together,” said Herbert Shea, director of EPFL’s Soft Transducers Laboratory. “We consider this a paradigm shift in the field of soft robotics.”

The pump bending over a finger. (Source: © Vito Cacucciolo / 2019 EPFL)

The soft and stretchable pump is based on the physical mechanism used today to circulate the cooling liquid in systems like supercomputers. The pump has a tube-shaped channel, 1mm in diameter, inside of which rows of electrodes are printed. The pump is filled with a dielectric liquid. When a voltage is applied, electrons jump from the electrodes to the liquid, giving some of the molecules an electrical charge. These molecules are subsequently attracted to other electrodes, pulling along the rest of the fluid through the tube with them. “We can speed up the flow by adjusting the electric field, yet it remains completely silent,” said Vito Cacucciolo, a post-doc at EPFL’s Soft Transducers Laboratory.

The researchers successfully implanted their pump in a type of robotic finger widely used in soft robotics labs and are working with a team to develop fluid-driven artificial muscles and flexible exoskeletons.