Tag Archives: SEAS

Harvard University researcher Chirarattananom’s Flight of the RoboBee

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The flight of  Chirarattananom’s RoboBee took place last summer but the research has only now been published. There’s a May 2, 2013 news release on EurekAlert heralding this robotic first from 2012,

In the very early hours of the morning, in a Harvard robotics laboratory last summer, an insect took flight. Half the size of a paperclip, weighing less than a tenth of a gram, it leapt a few inches, hovered for a moment on fragile, flapping wings, and then sped along a preset route through the air.

Like a proud parent watching a child take its first steps, graduate student Pakpong Chirarattananon immediately captured a video of the fledgling and emailed it to his adviser and colleagues at 3 a.m.—subject line, “Flight of the RoboBee.”

“I was so excited, I couldn’t sleep,” recalls Chirarattananon, co-lead author of a paper published this week in Science.

The demonstration of the first controlled flight of an insect-sized robot is the culmination of more than a decade’s work, led by researchers at the Harvard School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard.

Here’s what it looks like,

The tiny robot flaps its wings 120 times per second using piezoelectric actuators -- strips of ceramic that expand and contract when an electric field is applied. Thin hinges of plastic embedded within the carbon fiber body frame serve as joints, and a delicately balanced control system commands the rotational motions in the flapping-wing robot, with each wing controlled independently in real-time. Credit: Kevin Ma and Pakpong Chirarattananon, Harvard University.

The tiny robot flaps its wings 120 times per second using piezoelectric actuators — strips of ceramic that expand and contract when an electric field is applied. Thin hinges of plastic embedded within the carbon fiber body frame serve as joints, and a delicately balanced control system commands the rotational motions in the flapping-wing robot, with each wing controlled independently in real-time.
Credit: Kevin Ma and Pakpong Chirarattananon, Harvard University.

The Harvard [University] Gazette May 2, 2013 article by Caroline Perry, which originated the news release, provides more detail about what makes this particular robotic work unique,

“We had to develop solutions from scratch, for everything,” explains Wood [Robert J. Wood, Charles River Professor of Engineering and Applied Sciences at SEAS, Wyss core faculty member, and principal investigator of the National Science Foundation-supported RoboBee project]. “We would get one component working, but when we moved onto the next, five new problems would arise. It was a moving target.”

Flight muscles, for instance, don’t come prepackaged for robots the size of a fingertip.

“Large robots can run on electromagnetic motors, but at this small scale you have to come up with an alternative, and there wasn’t one,” says co-lead author Kevin Y. Ma, a graduate student at SEAS.

The tiny robot flaps its wings with piezoelectric actuators — strips of ceramic that expand and contract when an electric field is applied. Thin hinges of plastic embedded within the carbon fiber body frame serve as joints, and a delicately balanced control system commands the rotational motions in the flapping-wing robot, with each wing controlled independently in real time.

At tiny scales, small changes in airflow can have an outsized effect on flight dynamics, and the control system has to react that much faster to remain stable.

While it’s called the RoboBee project, the researchers’ inspiration for this prototype is a fly. Unlike most flies, this one is tethered, at least for now (from Perry’s article),

The prototypes are still tethered by a very thin power cable because there are no off-the-shelf solutions for energy storage that are small enough to be mounted on the robot’s body. High-energy-density fuel cells must be developed before the RoboBees will be able to fly with much independence.

Future research plans include (from Perry’s article),

… integrating the parallel work of many different research teams that are working on the brain, the colony coordination behavior, the power source, and so on, until the robotic insects are fully autonomous and wireless.

Here’s a citation for and a link to the research paper,

Controlled Flight of a Biologically Inspired, Insect-Scale Robot by Kevin Y. Ma,  Pakpong Chirarattananon,  Sawyer B. Fuller, and Robert J. Wood. Science 3 May 2013: Vol. 340 no. 6132 pp. 603-607 DOI: 10.1126/science.1231806

The paper is behind a paywall.

On reading about the RoboBee project I was reminded of Michael Crichton’s 2002 cautionary tale, Prey, which focuses on a possible future where small, swarming bots that fly threaten to take over the world. More happily, I was also inspired musically and found this rendition of the Flight of the Bumblebee,

Have a nice Friday, May 3, 2013!

Harvard researchers look deeply into oily puddles as they rethink thin films and optical loss

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For centuries it was thought that thin-film interference effects, such as those that cause oily pavements to reflect a rainbow of swirling colors, could not occur in opaque materials. Harvard physicists have now discovered that even very “lossy” thin films, if atomically thin, can be tailored to reflect a particular range of dramatic and vivid colors.

from the Oct. 14, 2012 news release on EurekAlert (also available on the Harvard School of Engineering and Applied Sciences [SEAS] news page),

The discovery is the latest to emerge from the laboratory of Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS, whose research group most recently produced ultrathin flat lenses and needle light beams that skim the surface of metals. The common thread in Capasso’s recent work is the manipulation of light at the interface of materials that are engineered at the nano- scale, a field referred to as nanophotonics. Graduate student and lead author Mikhail A. Kats carried that theme into the realm of color.

“In my group, we frequently reexamine old phenomena, where you think everything’s already known,” Capasso says. “If you have perceptive eyes, as many of my students do, you can discover exciting things that have been overlooked. In this particular case there was almost a bias among engineers that if you’re using interference, the waves have to bounce many times, so the material had better be transparent. What Mikhail’s done—and it’s admittedly simple to calculate—is to show that if you use a light-absorbing film like germanium, much thinner than the wavelength of light, then you can still see large interference effects.”

The result is a structure made of only two elements, gold and germanium (or many other possible pairings), that shines in whatever color one chooses.

These are gold films colored with nanometer-thick layers of germanium. Credit: Photo courtesy of Mikhail Kats, Romain Blanchard, and Patrice Genevet

The Oct. 14, 2012 news item on ScienceDaily notes,

“We are all familiar with the phenomenon that you see when there’s a thin film of gasoline on the road on a wet day, and you see all these different colors,” explains Capasso.

Those colors appear because the crests and troughs in the light waves interfere with each other as they pass through the oil into the water below and reflect back up into the air. Some colors (wavelengths) get a boost in brightness (amplitude), while other colors are lost.

That’s essentially the same effect that Capasso and Kats are exploiting, with coauthors Romain Blanchard and Patrice Genevet. The absorbing germanium coating traps certain colors of light while flipping the phase of others so that the crests and troughs of the waves line up closely and reflect one pure, vivid color.

“Instead of trying to minimize optical losses, we use them as an integral part of the design of thin-film coatings,” notes Kats. “In our design, reflection and absorption cooperate to give the maximum effect.”

Most astonishingly, though, a difference of only a few atoms’ thickness across the coating is sufficient to produce the dramatic color shifts. The germanium film is applied through standard manufacturing techniques — lithography and physical vapor deposition, which the researchers compare to stenciling and spray-painting — so with only a minimal amount of material (a thickness between 5 and 20 nanometers), elaborate colored designs can easily be patterned onto any surface, large or small.

“Just by changing the thickness of that film by about 15 atoms, you can change the color,” says Capasso. “It’s remarkable.”

I will never look at another oily puddle the same way again.