Drive Test: Super-Stable Laser Shines in Minivan Experiment

The experiment shows how advanced lasers can be made both stable and transportable enough for field use in geodesy, hydrology, improved radar and space-based tests of fundamental physics.

The drive tests, limited to a short excursion of five meters across the grass at the NIST Boulder, Colo., campus, are described inOptics Express. Scientists evaluated the infrared fiber laser's performance with the vehicle stationary, with the motor alternately off and idling, and moving over uneven ground at speeds of less than 1 meter per second (i.e., 3.6 km/hr). The laser frequency remained stable enough with the car parked -- the most likely situation in the field -- to be used in some applications now, says David Leibrandt, a NIST post-doctoral researcher.

"Our group has been building and using ultra-stable lasers for more than 10 years, but they're large and delicate," Leibrandt explains."The ones we use for our optical atomic clocks occupy a small room and have to be very carefully isolated from seismic and acoustic vibrations. This paper presents a new design that is less sensitive to vibrations and could be made much smaller."

NIST scientists stabilized the test laser's frequency using a common technique -- locking it to the extremely consistent length of an optical glass cavity. This sphere, about the size of a small orange, hangs in a customized mount with just the right stiffness. The scientists also designed a system to correct the laser frequency when the vehicle moves. Six accelerometers surrounding the cavity measure its linear and rotational acceleration. The accelerometers' signals are routed to a programmable computer chip that predicts and corrects the laser frequency in less than 100 microseconds.

The new laser will make it easier to use advanced atomic clocks for geodesy (measurements of Earth), an application envisioned by the same NIST research group. The laser also might be used on moving platforms, perhaps in space-based physics experiments or on Earth generating low-noise signals for radar. Study results indicate the laser is roughly 10 times more resistant to undesirable effects from vibration or acceleration than the best radio frequency crystal oscillators. Improved mechanical design and higher-bandwidth accelerometers could make the laser even more stable in the future, the researchers say.

The research is supported by the Office of Naval Research, Air Force Office of Scientific Research, and Defense Advanced Research Projects Agency.

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Bats Lend an Ear to Sonar Engineering

Published on May 10, in IOP Publishing's journalBioinspiration& Biomimetics, the study provides key insights into the variability of the shapes of bat ears that exists between different species, and shows how this variability may affect the functionality of one of the most impressive navigational systems in nature.

Bats are one of a few animal groups that demonstrate biosonar -- the ability to generate and emit ultrasonic pulses and gauge the reflections to obtain detailed information on their surroundings.

Bats use biosonar as a way of navigating and hunting for food, however researchers have seen its potential to inspire new ways of engineering where manipulating outgoing or incoming waves with structures is a principal component.

Lead author Professor Rolf Müller, of Virginia Tech, said:"Using physical shapes to manipulate an outgoing or a received wave has application in many areas of engineering. Besides the obvious analogues of SONAR and RADAR, such principles could also find application in biomedical ultrasound, non-destructive testing, wireless communications, and sensory systems for autonomous robots and nodes in sensor networks."

The ear of a bat plays a crucial role in the overall sensing system by acting as a baffle to diffract the incoming waves therefore determining the ear's pattern of sensitivity to direction and frequency.

The researchers, working in a joint research laboratory of Shandong University and Virginia Tech, created 3D computer models of 100 bat pinnae -- the visible part of the ear that resides outside of the head -- from 59 different species, and transformed the models into cylindrical representations.

The representations were statistically analysed using principal component analysis -- a method that has previously been applied to analyse human faces, palms, and ears -- and were shown to vary in the opening angle of the pinna, breaks of symmetry between the right and left sides, and changes in width at both the top and bottom.

The researchers also demonstrated how this variability can affect the properties of beamforming -- the process by which the incoming signal is diffracted by the shape of the pinna to create a"beampattern" through which the bat sees it environment.

The variability occurs as a result of the evolution of bats whose habitats range from environments with virtually no structures, to those with simple structures (calm water surfaces), to habitats with very complicated structures (dense forests).

The researchers found, for example, that a group of bats that hunts for prey in dense vegetation with trains of long, closely-spaced objects are separated from other bats by the widths of their pinna openings, demonstrating how biodiversity can provide a useful insight into how a general principal can be customised to fit different needs.

Professor Müller continued,"In order for this to happen, the ears of bats must be studied further. An example would be to expand the sample to include more diversity and find more specific relationships between pinna shape and beamforming across different species. Small local shape features that are hard to capture by the present analysis can also have a big impact on the function."

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Robotics: A Tiltable Head Could Improve the Ability of Undulating Robots to Navigate Disaster Debris

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and"swim" through granular material. In a new study, they show that varying the shape or adjusting the inclination of the robot's head affects the robot's movement in complex environments.

"We discovered that by changing the shape of the sand-swimming robot's head or by tilting its head up and down slightly, we could control the robot's vertical motion as it swam forward within a granular medium," said Daniel Goldman, an assistant professor in the Georgia Tech School of Physics.

Results of the study will be presented on May 10 at the 2011 IEEE International Conference on Robotics and Automation in Shanghai. Funding for this research was provided by the Burroughs Wellcome Fund, National Science Foundation and Army Research Laboratory.

The study was conducted by Goldman, bioengineering doctoral graduate Ryan Maladen, physics graduate student Yang Ding and physics undergraduate student Andrew Masse, all from Georgia Tech, and Northwestern University mechanical engineering adjunct professor Paul Umbanhowar.

"The biological inspiration for our sand-swimming robot is the sandfish lizard, which inhabits the Sahara desert in Africa and rapidly buries into and swims within sand," explained Goldman."We were intrigued by the sandfish lizard's wedge-shaped head that forms an angle of 140 degrees with the horizontal plane, and we thought its head might be responsible for or be contributing to the animal's ability to maneuver in complex environments."

For their experiments, the researchers attached a wedge-shaped block of wood to the head of their robot, which was built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit. The doorstop-shaped head -- which resembled the sandfish's head -- had a fixed lower length of approximately 4 inches, height of 2 inches and a tapered snout. The researchers examined whether the robot's vertical motion could be controlled simply by varying the inclination of the robot's head.

Before each experimental run in a test chamber filled with quarter-inch-diameter plastic spheres, the researchers submerged the robot a couple inches into the granular medium and leveled the surface. Then they tracked the robot's position until it reached the end of the container or swam to the surface.

The researchers investigated the vertical movement of the robot when its head was placed at five different degrees of inclination. They found that when the sandfish-inspired head with a leading edge that formed an angle of 155 degrees with the horizontal plane was set flat, negative lift force was generated and the robot moved downward into the media. As the tip of the head was raised from zero to 7 degrees relative to the horizontal, the lift force increased until it became zero. At inclines above 7 degrees, the robot rose out of the medium.

"The ability to control the vertical position of the robot by modulating its head inclination opens up avenues for further research into developing robots more capable of maneuvering in complex environments, like debris-filled areas produced by an earthquake or landslide," noted Goldman.

The robotics results matched the research team's findings from physics experiments and computational models designed to explore how head shape affects lift in granular media.

"While the lift forces of objects in air, such as airplanes, are well understood, our investigations into the lift forces of objects in granular media are some of the first ever," added Goldman.

For the physics experiments, the researchers dragged wedge-shaped blocks through a granular medium. Blocks with leading edges that formed angles with the horizontal plane of less than 90 degrees resembled upside-down doorstops, the block with a leading edge equal to 90 degrees was a square, and blocks with leading edges greater than 90 degrees resembled regular doorstops.

They found that blocks with leading edges that formed angles with the horizontal plane less than 80 degrees generated positive lift forces and wedges with leading edges greater than 120 degrees created negative lift. With leading edges between 80 and 120 degrees, the wedges did not generate vertical forces in the positive or negative direction.

Using a numerical simulation of object drag and building on the group's previous studies of lift and drag on flat plates in granular media, the researchers were able to describe the mechanism of force generation in detail.

"When the leading edge of the robot head was less than 90 degrees, the robot's head experienced a lift force as it moved forward, which resulted in a torque imbalance that caused the robot to pitch and rise to the surface," explained Goldman.

Since this study, the researchers have attached a wedge-shaped head on the robot that can be dynamically modulated to specific angles. With this improvement, the researchers found that the direction of movement of the robot is sensitive to slight changes in orientation of the head, further validating the results from their physics experiments and computational models.

Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot's ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.

This material is based on research sponsored by the Burroughs Wellcome Fund, the National Science Foundation (NSF) under Award Number PHY-0749991, and the Army Research Laboratory (ARL) under Cooperative Agreement Number W911NF-08-2-0004.

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Engineers Patch a Heart: Tissue-Engineering Platform Enables Heart Tissue to Repair Itself

Led by Gordana Vunjak-Novakovic, Professor of Biomedical Engineering at Columbia University's Fu Foundation School of Engineering and Applied Science, the researchers developed a novel cell therapy to treat myocardial infarction (heart damage that follows a heart attack). They were able, for the first time, to combine the use of human repair cells that were conditioned during in-vitro culture to maximize their ability to revascularize and improve blood flow to the infarcted tissue with a fully biological composite scaffold designed to deliver these cells to the damaged heart. With this platform, they could both keep the cells within the infarct bed (in contrast to the massive cell loss associated with infusion of cells alone) and enhance cell survival and function in the infarct bed, where most of the cells would have died because of the obstruction of their blood supply.

"We are very excited about this new technique," said Dr. Vunjak-Novakovic."This platform is very adaptable and we believe it could be readily extended to the delivery of other types of human stem cells we are interested in to rebuild the heart muscle and further our research of the mechanisms underlying heart repair."

In effect, the Columbia Engineering team (with Amandine Godier-Fournemont and Timothy Martens as lead authors) removed the cells of a human heart muscle -- the myocardium -- leaving a protein scaffold with intact architecture and mechanical properties. They filled the scaffold with human mesenchymal progenitors (stem cells that can differentiate into many cell types) and then applied the patches to damaged heart tissue. The patches promoted the growth of new blood vessels and released proteins that stimulated the native tissue to repair itself. Moreover, the team also used this controllable platform to identify the signaling mechanisms involved in the repair process, and expand our knowledge about the role of cells and scaffold design on heart repair.

"It really is encouraging to make progress with 'instructing' cells to form human tissues by providing them with the right environments," noted Dr. Vunjak-Novakovic."The cells are the real 'tissue engineers' -- we only design the environments so they can do their work. Because these environments need to mimic the native developmental milieu, the progress in the field is really driven by the interdisciplinary work of bioengineers, stem cell biologists, and clinicians. By enabling regeneration and replacement of our damaged tissues, we can help people live longer and better."

Dr. Vunjak-Novakovic and her team already have several active research projects that continue this line of work. They are now investigating the formation of a contractile cardiac patch using human stem cells that can give rise to both the muscle and vascular compartments of the heart muscle. They are also studying how the cells within such a cardiac patch, when implanted on infarcted heart tissue, develop their ability to generate mechanical force and electrical conduction, and how these functions can be modulated by in-vitro culture.

"Ultimately, we envision this system as a possible point of care approach," said Dr. Vunjak-Novakovic,"with components actually produced and assembled in the operating room to most effectively target-signaling mechanisms involved in the repair process of someone's damaged heart."

The Columbia Engineering study has been supported by the NIH (National Institutes of Health).

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Solar-Thermal Flat-Panels That Generate Electric Power: Researchers See Broad Residential and Industrial Applications

Two technologies have dominated efforts to harness the power of the sun's energy. Photovoltaics convert sunlight into electric current, while solar-thermal power generation uses sunlight to heat water and produce thermal energy. Photovoltaic cells have been deployed widely as flat panels, while solar-thermal power generation employs sunlight-absorbing surfaces feasible in residential and large-scale industrial settings.

Because of limited material properties, solar thermal devices have heretofore failed to economically generate enough electric power. The team's introduced two innovations: a better light-absorbing surface through enhanced nanostructured thermoelectric materials, which was then placed within an energy-trapping, vacuum-sealed flat panel. Combined, both measures added enhanced electricity-generating capacity to solar-thermal power technology, said Boston College Professor of Physics Zhifeng Ren, a co-author of the paper.

"We have developed a flat panel that is a hybrid capable of generating hot water and electricity in the same system," said Ren."The ability to generate electricity by improving existing technology at minimal cost makes this type of power generation self-sustaining from a cost standpoint."

Using nanotechnology engineering methods, the team combined high-performance thermoelectric materials and spectrally-selective solar absorbers in a vacuum-sealed chamber to boost conversion efficiency, according to the co-authors, which include MIT's Soderberg Professor of Power Engineering Gang Chen, Boston College and MIT graduate students and researchers at GMZ Energy, a Massachusetts clean energy research company co-founded by Ren and Chen.

The findings open up a promising new approach that has the potential to achieve cost-effective conversion of solar energy into electricity, an advance that should impact the rapidly expanding residential and industrial clean energy markets, according to Ren.

"Existing solar-thermal technologies do a good job generating hot water. For the new product, this will produce both hot water and electricity," said Ren."Because of the new ability to generate valuable electricity, the system promises to give users a quicker payback on their investment. This new technology can shorten the payback time by one third."

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New Way to Control Conductivity: Reversible Control of Electrical and Thermal Properties Could Find Uses in Storage Systems

"It's a new way of changing and controlling the properties" of materials -- in this case a class called percolated composite materials -- by controlling their temperature, says Gang Chen, MIT's Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories. Chen is the senior author of a paper describing the process that was published online on April 19 and will appear in a forthcoming issue ofNature Communications. The paper's lead authors are former MIT visiting scholars Ruiting Zheng of Beijing Normal University and Jinwei Gao of South China Normal University, along with current MIT graduate student Jianjian Wang. The research was partly supported by grants from the National Science Foundation.

The system Chen and his colleagues developed could be applied to many different materials for either thermal or electrical applications. The finding is so novel, Chen says, that the researchers hope some of their peers will respond with an immediate,"I have a use for that!"

One potential use of the new system, Chen explains, is for a fuse to protect electronic circuitry. In that application, the material would conduct electricity with little resistance under normal, room-temperature conditions. But if the circuit begins to heat up, that heat would increase the material's resistance, until at some threshold temperature it essentially blocks the flow, acting like a blown fuse. But then, instead of needing to be reset, as the circuit cools down the resistance decreases and the circuit automatically resumes its function.

Another possible application is for storing heat, such as from a solar thermal collector system, later using it to heat water or homes or to generate electricity. The system's much-improved thermal conductivity in the solid state helps it transfer heat.

Essentially, what the researchers did was suspend tiny flakes of one material in a liquid that, like water, forms crystals as it solidifies. For their initial experiments, they used flakes of graphite suspended in liquid hexadecane, but they showed the generality of their process by demonstrating the control of conductivity in other combinations of materials as well. The liquid used in this research has a melting point close to room temperature -- advantageous for operations near ambient conditions -- but the principle should be applicable for high-temperature use as well.

The process works because when the liquid freezes, the pressure of its forming crystal structure pushes the floating particles into closer contact, increasing their electrical and thermal conductance. When it melts, that pressure is relieved and the conductivity goes down. In their experiments, the researchers used a suspension that contained just 0.2 percent graphite flakes by volume. Such suspensions are remarkably stable: Particles remain suspended indefinitely in the liquid, as was shown by examining a container of the mixture three months after mixing.

By selecting different fluids and different materials suspended within that liquid, the critical temperature at which the change takes place can be adjusted at will, Chen says.

"Using phase change to control the conductivity of nanocomposites is a very clever idea," says Li Shi, a professor of mechanical engineering at the University of Texas at Austin. Shi adds that as far as he knows"this is the first report of this novel approach" to producing such a reversible system.

"I think this is a very crucial result," says Joseph Heremans, professor of physics and of mechanical and aerospace engineering at Ohio State University."Heat switches exist," but involve separate parts made of different materials, whereas"here we have a system with no macroscopic moving parts," he says."This is excellent work."

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Pier Review: Comparing Ultra High-Resolution Photographs from the Past and the Present Could Hold the Key to Restoring Hastings' Fire-Damaged Pier

Prior to the fire, NPL, the UK's National Measurement Institute, had been surveying the pier to support redevelopment plans and to monitor long-term changes in the pier. The project was part of the development of a world leading low-cost technique to assess long-term degradation of structures.

The technique is called Digital Image Correlation. It has been used in the laboratory for some time but NPL have recently been pioneering its use for looking at civil engineering structures. It involves taking ultra high-resolution panoramic photos -- images up to 1.4 Giga Pixels in size -- at two different times to identify structural changes. Advanced mathematical programs then analyse the pair of images to identify changes in the structure pixel by pixel. Using this information, engineers can understand how large structures change over time.

Following the devastating fire, NPL scientists returned to Hastings to take their second set of photos. They were then required to develop more advanced analysis techniques, which could deal with the much larger than anticipated changes to the Pier, and produce meaningful information about the structure. This work is proving more valuable than expected as considerable change has now taken place. In addition, the large panoramic images provide a snapshot of the structure in time, which is useful for archival purposes.

Up to 45 images were stitched together to produce an ultra high-resolution final image 80,000 pixels wide -- 300-400 times more detailed than a typical camera-phone photograph. Processing a pair of these images, one before the fire and one after, can help highlight where the structure has apparently changed because of the fire.

Results have been very positive. Whilst the super-structure has been severely damaged and there are large visual changes, the cast iron framework -- or sub-structure -- seems much less affected. The sub-structure on the west side of the Pier appears to be remarkably similar pre and post fire. On the East side there are small areas where there are some changes, and one localised area of the sub-structure about half way along showing significant distortion. But the vast majority of the sub-structure seems largely unchanged. The area showing the most distortion -- presumably caused by the extreme heat -- was at a downwind point where anecdotally the fire was seen to be fiercest.

Digital Image Correlation allows the computer to effectively carry out the laborious checking of the whole structure. This means quicker and cheaper identification of areas which have been deformed or damaged, and hence may need closer inspection. This is important on large structures such as piers as it allows civil engineers to focus their efforts on the parts that most need attention, dramatically speeding the inspection process and reducing the cost of repair.

The project has also helped prove the concept of Digital Image Correlation for the measurement of changes in large structures, by providing NPL with a real-life case study enabling development of key analysis software.

Nick McCormick, Principle Research Scientist at NPL, said:"It was fortunate that we began the project before the fire, as the results will be invaluable in regenerating the pier when restoration funding is secured. From a scientific point of view, the scale of the changes actually proved very interesting, although challenging, and required us to develop far more advanced analysis techniques than originally intended. These will be hugely important in our work to develop low cost monitoring solutions for other structures. Obviously we hope the next one won't be so badly damaged part way through our study. For most applications we work on we would expect to monitor much less significant changes over time -- for example small cracks appearing in bridges or building subsidence -- so that problems can be remedied before they escalate to cause such serious damage."

Digital Image Correlation is one of a number of techniques that NPL is developing for low-cost examination of large civil engineering structures such as bridges, buildings, tunnels and piers.

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