New Wireless Bridge Sensors Powered By Passing Traffic

Source:

http://www.sciencedaily.com/releases/2007/10/071019175317.htm

ScienceDaily (Oct. 22, 2007) — Clarkson University researchers have developed technology that uses the vibrations caused by passing traffic to power wireless bridge monitoring sensors.

Wireless battery-powered sensors that monitor bridges and report changes that may lead to failure are easy to install, but it is unwieldy to provide power for the sensors. Each bridge needs at least several sensors, many installed in hard-to-access locations. Replacing millions of batteries could become a problem, adding to the expense of maintaining the bridges. The Clarkson researchers have found a way around this problem.
"We have completely eliminated the battery from the equation," says Assistant Professor Edward S. Sazonov, who developed the technology along with Professor Pragasen Pillay. "Hermetically sealed wireless sensors powered by bridge vibration can remain on the bridge without need of maintenance for decades, providing continuous monitoring of such parameters as ice conditions, traffic flows and health status."
The two electrical and computer engineering professors, along with graduate students Darrell Curry and Haodong Li, used the New York State Route 11 bridge, a steel girder structure, which runs over the Raquette River in Potsdam, N.Y., as a case study.
Energy was harvested by locating an electromagnetic generator on a girder. The harvester responded to one of the natural vibration frequencies of the bridge. Each time a car or a truck passed over the bridge, even in a different lane from the sensor installation, the whole structure vibrated and excited the mover in the generator, producing electrical energy. Harvested electrical energy powered unique wireless sensors that increased energy output of the harvester and consumed only microwatts of power while performing useful tasks.
Sazonov and Pillay have been invited to present their work at the Transportation Research Board of the National Academies Meeting in Washington, D.C., in January. The board provides support for their research.
They are also working on using the energy harvesting technology to power the various sensors in passenger cars.
Wireless monitoring of bridges and overpasses has gained much attention in the past few years. Bridge collapses happen suddenly and unpredictably, often leading to tragic loss of human life. In 2006, the Federal Highway Administration listed 25.8 percent of the nation\'s 596,842 bridges as either structurally deficient or functionally obsolete. While many of these bridges will remain in service for years, they need monitoring and rehabilitation. Currently, bridge monitoring is performed through periodic visual inspections. In the tragic example of I-35W Mississippi River bridge collapse, the bridge passed a visual inspection a year prior to failure.
Adapted from materials provided by Clarkson University.

Fausto Intilla

www.oloscience.com

Hydrogen Storage Model Speeds Development Of Alternative Fuel Vehicles

Source:

http://www.sciencedaily.com/releases/2007/10/071003100601.htm

Science Daily — Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have developed a model that could help engineers and scientists speed up the development of hydrogen-fueled vehicles by identifying promising hydrogen-storage materials and predicting favored thermodynamic chemical reactions through which hydrogen can be reversibly stored and extracted.
Because of global environmental changes associated with man-made carbon dioxide emissions and the limited resources of fossil fuels, developing alternate and renewable energy sources is important for a sustainable future. Hydrogen is a potential source of clean energy for future use in passenger vehicles powered by cheap and energy-efficient fuel cells, but its widespread adoption has been hindered by the need to store it on-board at very high densities.
A promising solution to this problem involves storing hydrogen within a material in the form of a chemically bound hydride, for example lithium hydride (LiH). Unfortunately, simple binary hydrides, in which hydrogen combines with light elements such as lithium, sodium, magnesium or others, do not adequately satisfy the requirements for on-board storage, as the hydrogen-yielding reaction requires heating the material to impractically high temperatures.
Because of this, researchers have turned to multicomponent hydride mixtures with higher volumetric and gravimetric densities, better operating temperatures and improved reaction rates for practical hydrogen storage. However, this flexibility comes at the price of drastically increased complexity associated with the large number of competing reactions and possible end-products other than hydrogen.
Thus, predicting desirable hydrogen storage with multicomponent mixtures has proved difficult. For example, the recently studied lithium hydride compound Li4BN3H10 was found to have as many as 17 hydrogen-release reactions, of which only three were found to be feasible — and none were in the desired range of temperatures and hydrogen pressures for practical on-board storage in hydrogen-powered vehicles.
The research team used modern quantum mechanical theories and high-powered computers to develop an algorithm that can automatically and systematically pinpoint phases and reactions that have the most favored thermodynamic properties — that is, those that can release hydrogen at ambient temperatures using the waste heat from a proton exchange membrane (PEM) fuel cell. The team tested the method on the well-studied Lithium-Magnesium-Nitrogen-Hydrogen system, predicting all experimentally observed pathways in the system. The researchers say this method can also be applied to other multicomponent hydrogen systems.
The new method, published in Advanced Materials, was developed by Alireza Akbarzadeh, a UCLA postdoctoral researcher in the department of materials science and engineering; Vidvuds Ozolins, UCLA associate professor of materials science and engineering; and Christopher Wolverton, professor of materials science and engineering at Northwestern University in Illinois.
"The development of an algorithm that goes beyond chemical intuition and finds all hydrogen storage reactions 'in silico' is crucial and will help the scientific and engineering community to develop revolutionary new hydrogen-storage materials," Akbarzadeh said. "This is a major achievement in the field, which can boost up the search for the best reversible solid-state hydrogen storage."
"We are steadily approaching the moment when we will be able to theoretically design materials with desired properties, just like a tailor makes a suit to fit the customer's needs," Ozolins said. "This will bring in a qualitatively new era of collaboration between theory and computation, experiment and technology development."
The research was funded by grants from the U.S. Department of Energy.
Note: This story has been adapted from material provided by University of California, Los Angeles.

Fausto Intilla
www.oloscience.com

Nanotubes Can Detect And Repair Cracks In Aircraft Wings, Other Structures

Source:

http://www.sciencedaily.com/releases/2007/09/070927132550.htm

Science Daily — Adding even a small amount of carbon nanotubes can go a long way toward enhancing the strength, integrity, and safety of plastic materials widely used in engineering applications, according to a new study.

Researchers at Rensselaer Polytechnic Institute have developed a simple new technique for identifying and repairing small, potentially dangerous cracks in high-performance aircraft wings and many other structures made from polymer composites.
By infusing a polymer with electrically conductive carbon nanotubes, and then monitoring the structure’s electrical resistance, the researchers were able to pinpoint the location and length of a stress-induced crack in a composite structure. Once a crack is located, engineers can then send a short electrical charge to the area in order to heat up the carbon nanotubes and in turn melt an embedded healing agent that will flow into and seal the crack with a 70 percent recovery in strength.
Real-time detection and repair of fatigue-induced damage will greatly enhance the performance, reliability, and safety of structural components in a variety of engineering systems, according to principal investigator Nikhil A. Koratkar, an associate professor in Rensselaer’s Department of Mechanical, Aerospace and Nuclear Engineering.
Details of the project are outlined in the paper “In situ health monitoring and repair in composites using carbon nanotube additives,” which was published online this week by Applied Physics Letters. Rensselaer graduate students Wei Zhang and Varun Sakalkar were co-authors of the paper. The team has been working on the project for more than 18 months.
The majority of failures in any engineered structure are generally due to fatigue-induced microcracks that spread to dangerous proportions and eventually jeopardize the structure’s integrity, Koratkar said. His research is looking to solve this problem with an elegant solution that allows for real-time diagnostics and no additional or expensive equipment.
Koratkar’s team made a structure from common epoxy, the kind used to make everything from the lightweight frames of fighter jet wings to countless devices and components used in manufacturing and industry, but added enough multi-walled carbon nanotubes to comprise 1 percent of the structure’s total weight. The team mechanically mixed the liquid epoxy to ensure the carbon nanotubes were properly dispersed throughout the structure as it dried in a mold.
The researchers also introduced into the structure a series of wires in the form of a grid, which can be used to measure electrical resistance and also apply control voltages to the structure.
By sending a small amount of electricity through the carbon nanotubes, the research team was able to measure the electrical resistance between any two points on the wire grid. They then created a tiny crack in the structure, and measured the electrical resistance between the two nearest grid points. Because the electrical current now had to travel around the crack to get from one point to another, the electrical resistance – the difficulty electricity faces when moving from one place to the next – increased. The longer the crack grew, the higher the electrical resistance between the two points increased.
Koratkar is confident this method will be just as effective with much larger structures. Since the nanotubes are ubiquitous through the structure, this technique can be used to monitor any portion of the structure by performing simple resistance measurements without the need to mount external sensors or sophisticated electronics.
“The beauty of this method is that the carbon nanotubes are everywhere. The sensors are actually an integral part of the structure, which allows you to monitor any part of the structure,” Koratkar said. “We’ve shown that nanoscale science, if applied creatively, can really make a difference in large-scale engineering and structures.”
Koratkar said the new crack detection method should eventually be more cost effective and more convenient than ultrasonic sensors commonly used today. His sensor system can also be used in real time as a device or component is in use, whereas the sonic sensors are external units that require a great deal of time to scan the entire surface area of a stationary structure.
Plus, Koratkar’s system features a built-in repair kit.
When a crack is detected, Koratkar can increase the voltage going through the carbon nanotubes at a particular point in the grid. This extra voltage creates heat, which in turn melts a commercially available healing agent that was mixed into the epoxy. The melted healing agent flows into the crack and cools down, effectively curing the crack. Koratkar shows that these mended structures are about 70 percent as strong as the original, uncracked structure – strong enough to prevent a complete, or catastrophic, structural failure. This method is an effective way to combat both microcracks, as well as a less-common form of structural damage called delamination.
“What’s novel about this application is that we’re using carbon nanotubes not just to detect the crack, but also to heal the crack,” he said. “We use the nanotubes to create localized heat, which melts the healing agent, and that’s what cures the crack.”
Koratkar said he envisions the new system for detecting cracks to eventually be integrated into the built-in computer system of a fighter jet or large piece of equipment. The system will allow the operator to monitor a structure’s integrity in real time, and any microcracks or delamination will become obvious by provoking a change in electrical resistance at some point in the structure.
The system should help increase the lifetime, safety, and cost effectiveness of polymer structures, which are commonly used in place of metal when weight is a factor, Koratkar said. There is also evidence that carbon nanotubes play a passive role in suppressing the rate at which microcracks grow in polymeric structures, which is the subject of a paper Koratkar expects to publish in the near future.
The research is team is now working to optimize the system, scale it up to larger structures, and develop new information technology to better collect and analyze the electrical resistance data created from the embedded grid and embedded carbon nanotubes.
The ongoing research project is funded in part by the National Science Foundation and the U.S. Army.
Note: This story has been adapted from material provided by Rensselaer Polytechnic Institute.

Fausto Intilla

www.oloscience.com