Shake, rattle and ... power up? A new MEMS device generates energy from small vibrations

Sep 14, 2011 by Jennifer Chu
A new energy harvesting device converts low-frequency vibrations into electricity. The device, the size of a U.S. quarter, is shown mounted on a stand. Photo: Arman Hajati

Today's wireless-sensor networks can do everything from supervising factory machinery to tracking environmental pollution to measuring the movement of buildings and bridges. Working together, distributed sensors can monitor activity along an oil pipeline or throughout a forest, keeping track of multiple variables at a time.

While uses for wireless sensors are seemingly endless, there is one limiting factor to the technology — power. Even though improvements have brought their energy consumption down, wireless sensors’ batteries still need changing periodically. Especially for networks in remote locales, replacing batteries in thousands of sensors is a staggering task.

To get around the power constraint, researchers are harnessing electricity from low-power sources in the environment, such as vibrations from swaying bridges, humming machinery and rumbling foot traffic. Such natural energy sources could do away with the need for batteries, powering wireless sensors indefinitely.

Now researchers at MIT have designed a device the size of a U.S. quarter that harvests energy from low-frequency vibrations, such as those that might be felt along a pipeline or bridge. The tiny energy harvester — known technically as a microelectromechanical system, or — picks up a wider range of vibrations than current designs, and is able to generate 100 times the power of devices of similar size. The team published its results in the Aug. 23 online edition of Applied Physics Letters.

“There are wireless sensors widely available, but there is no supportive power package,” says Sang-Gook Kim, a professor of mechanical engineering at MIT and co-author of the paper. “I think our vibrational-energy harvesters are a solution for that.”

Putting the squeeze on

To harvest electricity from environmental vibrations, researchers have typically looked to piezoelectric materials such as quartz and other crystals. Such materials naturally accumulate electric charge in response to mechanical stress (piezo, in Greek, means to squeeze or press). In the past few years, researchers have exploited piezoelectric material, or PZT, at the microscale, engineering MEMS devices that generate small amounts of power.

Various groups have gravitated toward a common energy-harvesting design: a small microchip with layers of PZT glued to the top of a tiny cantilever beam. As the chip is exposed to vibrations, the beam moves up and down like a wobbly diving board, bending and stressing the PZT layers. The stressed material builds up an electric charge, which can be picked up by arrays of tiny electrodes.

However, the cantilever-based approach comes with a significant limitation. The beam itself has a resonant frequency — a specific frequency at which it wobbles the most. Outside of this frequency, the beam’s wobbling response drops off, along with the amount of power that can be generated.

“In the lab, you can move and shake the devices at the frequencies you want, and it works,” says co-author Arman Hajati, who conducted the work as a PhD student at MIT. “But in reality, the source of vibration is not constant, and you get very little power if the frequency is not what you were expecting.”

To address the problem, some researchers have taken a “power in numbers” approach, simply increasing the number of cantilever beams and PZT layers occupying a chip. However, Kim and Hajati say this tactic can be wasteful, and expensive.

“In order to deploy millions of sensors, if the energy harvesting device is $10, it may be too costly,” says Kim, who is a member of MIT’s Microsystems Technology Laboratories. “But if it is a single-layer MEMS device, then we can fabricate [the device for] less than $1.”

Bridging the power divide

Kim and Hajati came up with a design that increases the device’s frequency range, or bandwidth, while maximizing the power density, or energy generated per square centimeter of the chip. Instead of taking a cantilever-based approach, the team went a slightly different route, engineering a microchip with a small bridge-like structure that’s anchored to the chip at both ends. The researchers deposited a single layer of PZT to the bridge, placing a small weight in the middle of it.

The team then put the device through a series of vibration tests, and found it was able to respond not just at one specific frequency, but also at a wide range of other low frequencies. The researchers calculated that the device was able to generate 45 microwatts of power with just a single layer of PZT — an improvement of two orders of magnitude compared to current designs.

“If the ambient vibration is always at a single frequency and does not vary, [current designs] work fine,” says Daniel Inman, professor of aerospace engineering at the University of Michigan. “But as soon as the frequency varies or shifts a little, the power decreases drastically. This design allows the bandwidth to be larger, meaning the problem is, in principle, solved.” Inman adds that going forward, the MIT group will have to aim lower in the frequencies they pick up, since few vibrations in nature occur at the relatively high frequency ranges captured by the device.

Hajati says the team plans to do just that, optimizing the design to respond to lower frequencies and generate more power.

“Our target is at least 100 microwatts, and that’s what all the electronics guys are asking us to get to,” says Hajati, now a MEMS development engineer at FujiFilm Dimatix in Santa Clara, Calif. “For monitoring a pipeline, if you generate 100 microwatts, you can a network of smart sensors that can talk forever with each other, using this system.”


This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Explore further: New approach to form non-equilibrium structures

More information: Paper: "Ultra-wide bandwidth piezoelectric energy harvesting"

Related Stories

Saving crops and people with bug sensors

Apr 29, 2014

University of California, Riverside researchers have created a method that can classify different species of insects with up to 99 percent accuracy, a development that could help farmers protect their crops ...

Precise control of optical frequency on a chip

Apr 23, 2014

In the 1940s, researchers learned how to precisely control the frequency of microwaves, which enabled radio transmission to transition from relatively low-fidelity amplitude modulation (AM) to high-fidelity ...

Detecting infection with a microchip

Apr 10, 2014

(Phys.org) —Alexander Star places a lapel pin on a table in his Eberly Hall office. Affixed to it is a microchip that he and his team have developed that may save joint implants before they're ruined by ...

Big, fast, weird data

Apr 08, 2014

The "Big Data" research that continues to dominate IT agendas has traditionally focused on making sense of the growing volumes of computer data. Yet in recent years, the volume question has given way to the other V's of Big ...

Recommended for you

New approach to form non-equilibrium structures

3 hours ago

Although most natural and synthetic processes prefer to settle into equilibrium—a state of unchanging balance without potential or energy—it is within the realm of non-equilibrium conditions where new possibilities lie. ...

Nike krypton laser achieves spot in Guinness World Records

5 hours ago

A set of experiments conducted on the Nike krypton fluoride (KrF) laser at the U.S. Naval Research Laboratory (NRL) nearly five years ago has, at long last, earned the coveted Guinness World Records title for achieving "Highest ...

Chemist develops X-ray vision for quality assurance

9 hours ago

It is seldom sufficient to read the declaration of contents if you need to know precisely what substances a product contains. In fact, to do this you need to be a highly skilled chemist or to have genuine ...

The future of ultrashort laser pulses

10 hours ago

Rapid advances in techniques for the creation of ultra-short laser pulses promise to boost our knowledge of electron motions to an unprecedented level.

IHEP in China has ambitions for Higgs factory

Jul 23, 2014

Who will lay claim to having the world's largest particle smasher?. Could China become the collider capital of the world? Questions tease answers, following a news story in Nature on Tuesday. Proposals for ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Isaacsname
not rated yet Sep 14, 2011
Sounds like they'd be good at harvesting energy from turbulant flows. I'm surprised with the advances in PZT manufacture we haven't seen more applications.
Nederlander
not rated yet Sep 15, 2011
Maybe, for inspiration, this research team could contact scientists studying violins (complex objects, but still just 'curved boxes', that resonate at a wide range of frequencies).