New MEMS Device Turns Vibrations into Energy

September 26th, 2011 by EnergyRefuge.com
Posted in Category Energy, Category North America

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 MEMS — picks up a wider range of vibrations than current designs, and is able to generate 100 times the power of devices of similar size.

“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.”
The motivation behind the research is to overcome one limit that wireless sensors, which are ubiquitous across several industries, face: power. Their batteries need regular changes. In order to do away with them, researchers are trying to tap electricity from low-power sources such as vibrations from swaying bridges, humming machinery and rumbling foot traffic. These could replace batteries, MIT says.

How to do that is the question. MIT says the most common way to go about it is to use piezoelectric materials such as quartz and other types of crystals. Piezo means in Greek to squeeze or press and these materials naturally accumulate electric charge in response to mechanical stress. So far these materials have been exploited with tiny MEMS devices that generate small amounts of power.

One approach that has been tried is to use a small microchip with layers of PZT glued to the top of a tiny cantilever beam, which will move up and down like a wobbly diving board when exposed to vibrations. The beam bends and stresses the PZT layers, and the stressed material builds up an electric charge, which can be picked up by arrays of tiny electrodes. The problem with this approach is that the beam has its own resonant frequency and its wobbling response drops off outside of this frequency. As a consequence, so does 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.”

Researchers have dealt with the problem by taking a “power in numbers” approach. They simply increased the number of cantilever beams and PZT layers occupying a chip. But it’s expensive and wasteful.

“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.”

Kim and Hajati’s solution is 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, they engineered 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.

During several tests carried out, the researchers found the device was able to respond not just at one specific frequency, but also at a wide range of other low frequencies. They calculated that the device was able to generate 45 microwatts of power with just a single layer of PZT, which represents an improvement of two orders of magnitude compared to current designs.

The results of the research appeared in the Aug. 23 online edition of Applied Physics Letters.

Article by Antonio Pasolini.

Integrated Hydropyrolysis and Hydroconversion (IH2) Technology

The IH2 technology is an advanced pyrolysis technology that uses low-pressure hydrogen together with a proprietary catalyst supplied by CRI to remove virtually all of the oxygen present in the starting biomass and produce finished hydrocarbon fuel products. No external hydrogen is required because it’s produced from within the process.

IH2 is designed to have low environmental impact. Since the process produces its own hydrogen and a surplus of water to be self-sufficient, it can operate in a stand-alone configuration anywhere there is sufficient biomass feed for conversion. A broad range of non-food source feedstocks can be used with the process, which mitigates concerns about seasonality, regionality, availability, and cost and does not interfere with the food chain. Work is also underway to determine the suitability of municipal waste as a potential feedstock.

The process is unique in that it directly produces either blending stocks or finished liquid hydrocarbon fuels like gasoline, diesel and jet fuel, known as drop-in products. This is unlike many other biofuels technologies that produce a crude intermediate that requires substantial further upgrading.

The process is based on mature components that are integrated and operated in the IH2 mode. IH2 technology is highly flexible and is economical for both small- and large-scale applications. It is based upon integrating existing process equipment, which would be engineered and made available through traditional routes, so no new manufacturing channels need to be established.

Therefore, the technology risks have been minimized, and the scaleup requirements are well understood.

The cost of product from IH2 as determined by an independent government laboratory is significantly lower than what has been reported for other advanced biofuels processes.

Yields of product fuels have ranged from 26% to 46% depending on feedstock. This is over 70% efficient energy conversion, and the production of exportable steam can raise the overall process efficiency even higher.

Produced fuels have been analyzed by GTI's technology licensee, CRI. First generation products have had excellent traits: oxygen content is less than 1%, it contains the same molecules as refined petroleum products, and the gasoline octane number is around 85. Second generation products using improved catalysts have demonstrated that product quality can be managed effectively.

The overall greenhouse gas reduction for the products, relative to petroleum counterparts, has been calculated to be over 94%.

GTI has received funding support for R&D and preliminary engineering for this novel process from the U.S. Department of Energy (EERE Office of Biomass Program) under the integrated biorefinery initiative. Participants in GTI's project include Cargill, Johnson Timber, Aquaflow, Blue Marble Energy, National Renewable Energy Laboratory and Michigan Technological University.

The timeline to market is short, and commercial introduction is expected in 2014.

GTI is continuing to conduct pilot testing, and a new second-generation facility capable of continually processing 50 kilograms of dry biomass per day, will demonstrate biomass handling and conveyance for multiple feedstocks and produce product in sufficient quantities for fuels certification and engine testing. It will serve as the platform for process optimization and detailed characterization through continuous operations, allowing the IH2 team to validate the economics, including catalyst consumption, and provide product valuation. CRI provided much of the funding for the new pilot plant.

Switchgrass offers up even more ethanol

Brian Wallheimer, Purdue University
Aug. 31, 2011 11:45am

Adding a pretreatment step would allow producers to get more ethanol from switchgrass harvested in the fall, according to a Purdue University study.

Michael Ladisch, a distinguished professor of agricultural and biological engineering, and Youngmi Kim, a research scientist, compared switchgrass based on growing location, harvest time and whether it was given a pretreatment step. They found that location wasn't important, but the other two factors could significantly increase the amount of ethanol obtained from the feedstock.

"Switchgrass harvested in the spring had more cellulose, but also more lignin," said Kim, whose findings were published in the early online version of the journal Bioresource Technology. "You do not get the advantage of the increased cellulose content because it's more difficult to extract those sugars because of the lignin."

Lignin, a rigid substance found in plant cell walls, is one of the most significant problems with cellulosic ethanol production. Besides the harvest time, a pretreatment step - cooking switchgrass in hot water under pressure for about 10 minutes - would also help work around lignin.

Before pretreatment, Kim said about 10 percent of cellulose was converted to glucose, the yeast-fermentable sugar that produces ethanol. After pretreatment, that number jumped to as much as 90 percent. The pretreatment dissolves hemicellulose, which bonds cellulose and lignin in the plant. Once it is gone, there is more access to the sugars contained in the cellulose.

"There is more surface area for the enzymes to digest cellulose," Kim said.

Ladisch said advancements in techniques to work around lignin could make spring switchgrass more attractive. But he said that fall switchgrass given a pretreatment and fermentation with special yeast shows potential to give as much as 800-1,000 gallons of ethanol per acre per year, compared with 150-250 gallons per year without pretreatment. Ladisch said corn ethanol from grain produces about 500-600 gallons per acre per year.

"This shows that we can improve the processes and increase the amount of ethanol we get from switchgrass," Ladisch said.

Ladisch is chief technology officer at Mascoma, a renewable fuels company based in New Hampshire. He received no funding from the company for this research, which was supported by the U.S. Department of Energy.

The work is part of a concerted research effort on pretreatments by a consortium made up of the University of California Riverside, Auburn University, Texas A&M University, Michigan State University, Genencor and the National Renewable Energy Laboratory together with Purdue University.