Harvesting Energy from Swaying Buildings

Researchers already have come up with a number of creative ways to harvest energy from uncommon means, such as ambient energy in the air, motion, and even people’s footsteps. Now a researcher from The Ohio State University has designed tiny, tree-like objects that can harness vibrations from the movement of swaying buildings or bridges to provide energy for structural sensors and other applications.

Ryan Harne, assistant professor of mechanical and aerospace engineering at Ohio State, who directs the university’s Laboratory of Sound and Vibration Research, is the leader of the research. He and his team are working on the design of tiny objects that look somewhat like trees with only a few branches that can generate renewable power when they are shaken by the wind. They also can convert into energy the structural vibrations of bridges or buildings when they sway, he said.

“Buildings sway ever so slightly in the wind, bridges oscillate when we drive on them, and car suspensions absorb bumps in the road,” Harne said in an article on The Ohio State website. "In fact, there’s a massive amount of kinetic energy associated with those motions that is otherwise lost. We want to recover and recycle some of that energy.”

A mechanical engineer at The Ohio State University is exploring how to tap the vibration created when objects such as buildings or trees sway or are shaken to harvest energy for structural sensors.
(Source: Wikipedia)

Harne declined to be interviewed by Design News.

The initial goal of Harne’s work is to power sensors that monitor the structural integrity of buildings, bridges, and the like, without having to use batteries or plug sensors directly into power lines, which is how it’s typically done. Energy harvesting would be a better and less expensive solution, especially for sensors in remote or hard-to-reach locations, he said.

While capturing wind or vibration energies from movement to generate energy has been explored in other research, most projects have tested similar energy harvesting objects using idealized vibrational patterns, and not the random ones found in real-world scenarios.

Harne set about trying to capture realistic ambient vibrations with tree-shape electromechanical devices, first determining through mathematical modeling that it is possible for tree-like structures to maintain vibrations at a consistent frequency despite large, random inputs. Called internal resonance, this allows energy to be captured and stored effectively through power circuitry.

Harne found a way to use this internal resonance to make an electromechanical tree vibrate with large amplitudes at a consistent low frequency even when experiencing only high-frequency forces. He and his team then tested this mathematical model in an experiment, for which they built a device out of two small steel beams connected by a strip of polyvinylidene fluoride, which was used as the electromechanical material.

The team tested the device -- which converted the structural movements into electrical energy, on an object that shook it back and forth at high frequencies. The result of the experiment was the production of a small voltage -- about 0.8V -- from the motion.

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Another experiment added noise to the project -- which acted to randomly nudge the tree-like device slightly more in one direction. This produced something called “saturation phenomenon” that channeled the high-frequency energy into a low-frequency oscillation, more than doubling the voltage of the previous experiment to about 2V, Harne said.

These voltages are extremely low, he noted, but Harne plans to continue his work -- which he began as a postdoctoral researcher at the University of Michigan before moving to Ohio State -- to improve on the amount of energy generated.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.