Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Flexing fingers for micro-robotics: Berkeley Lab scientists create a powerful, microscale actuator

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley, have developed an elegant and powerful new microscale actuator that can flex like a tiny beckoning finger.

Based on an oxide material that expands and contracts dramatically in response to a small temperature variation, the actuators are smaller than the width of a human hair and are promising for microfluidics, drug delivery, and artificial muscles.

"We believe our microactuator is more efficient and powerful than any current microscale actuation technology, including human muscle cells," says Berkeley Lab and UC Berkeley scientist Junqiao Wu. "What's more, it uses this very interesting material—vanadium dioxide—and tells us more about the fundamental materials science of phase transitions."

Wu is corresponding author of a paper appearing in Nano Letters this month that reports these findings, titled "Giant-Amplitude, High-Work Density Microactuators with Phase Transition Activated Nanolayer Bimorphs." As often happens in science, Wu and his colleagues arrived at the microactuator idea by accident, while studying a different problem.

Vanadium dioxide is a textbook example of a strongly correlated material, meaning the behavior of each electron is inextricably tied to its neighboring electrons. The resulting exotic electronic behaviors have made vanadium dioxide an object of scientific scrutiny for decades, much of it focused on an unusual pair of phase transitions.

When heated past 67 degrees Celsius, vanadium dioxide transforms from an insulator to a metal, accompanied by a structural phase transition that shrinks the material in one dimension while expanding in the other two. For decades, researchers have debated whether one of these phase transitions drives the other or if they are separate phenomena that coincidentally occur at the same temperature.

Wu shed light on this question in earlier work published in Physical Review Letters, in which he and his colleagues isolated the two phase transitions in single-crystal nanowires of vanadium dioxide and demonstrated that they are separable and can be driven independently. The team ran into difficulty with the experiments, however, when the nanowires broke away from their electrode contacts during the structural phase transition.

"At the transition, a 100-micron long wire shrinks by about 1 micron, which can easily break the contact," says Wu, who has a dual appointment as a professor in UC Berkeley's department of Materials Sciences and Engineering. "So we started to ask the question: this is bad, but can we make a good thing out of it? And actuation is the natural application."

To take advantage of the shrinkage, the researchers fabricated a free-standing strip of vanadium dioxide with a chromium metal layer on top. When the strip is heated via a small electrical current or a flash of laser light, the vanadium dioxide contracts and the whole strip bends like a finger.

"The displacement of our microactuator is huge," says Wu, "tens of microns for an actuator length on the same order of magnitude—much bigger than you can get with a piezoelectric device—and simultaneously with very large force. I am very optimistic that this technology will become competitive to piezoelectric technology, and may even replace it."

Piezoelectric actuators are the industry-standard for mechanical actuation on micro scales, but they're complicated to grow, need large voltages for small displacements, and typically involve toxic materials such as lead. "But our device is very simple, the material is non-toxic, and the displacement is much bigger at a much lower driving voltage," says Wu. "You can see it move with an optical microscope! And it works equally well in water, making it suitable for biological and microfluidic applications."

The researchers envision using the microactuators as tiny pumps for drug delivery or as mechanical muscles in micro-scale robots. In those applications, the actuator's exceptionally high work density—the power it can deliver per unit volume—offers a great advantage. Ounce for ounce, the vanadium-dioxide actuators deliver a force three orders of magnitude greater than human muscle. Wu and his colleagues are already partnering with the Berkeley Sensing and Actuation Center to integrate their actuators into devices for applications such as radiation-detection robots for hazardous environments.

The team's next goal is to create a torsion actuator, which is a much more challenging prospect. Wu explains: "Torsion actuators typically involve a complicated design of gears, shafts and/or belts, and so miniaturization is a challenge. But here we see that with just a layer of thin-film we could also make a very simple torsional actuator."

The Nano Letters paper was coauthored by Kai Liu, Chun Cheng, Zhenting Cheng, Kevin Wang, and Ramamoorthy Ramesh. Wu's earlier work on separating phase transitions in vanadium dioxide appears in Physical Review Letters, titled "Decoupling of Structural and Electronic Phase Transitions in VO2," and is coauthored by Zhensheng Tao, Tzong-Ru T. Han, Subhendra D. Mahanti, Phillip M. Duxbury, Fei Yuan, and Chong-Yu Ruan, and Kevin Wang.

For a video of this work:

"Giant-Amplitude, High-Work Density Microactuators with Phase Transition Activated Nanolayer Bimorphs"

"Decoupling of Structural and Electronic Phase Transitions in VO2"
This research was supported in part by the DOE Office of Science; theory and synthesis research was supported by the National Science Foundation.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at .

More information about Junqiao Wu's research can be found at

Alison Hatt | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR

nachricht Taming chaos: Calculating probability in complex systems
21.03.2018 | American Institute of Physics

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Modular safety concept increases flexibility in plant conversion

22.03.2018 | Trade Fair News

New interactive map shows climate change everywhere in world

22.03.2018 | Earth Sciences

New technologies and computing power to help strengthen population data

22.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>