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Bitdrones: Interactive quadcopters allow for ‘programmable matter’ explorations

Could an interactive swarm of flying “3D pixels” (voxels) allow users to explore virtual 3D information by interacting with physical self-levitating building blocks? (credit: Roel Vertegaal)

We’ll find out Monday, Nov. 9, when Canadian Queen’s University’s Human Media Lab professor Roel Vertegaal and his students will unleash their “BitDrones” at the ACM Symposium on User Interface Software and Technology in Charlotte, North Carolina.

Programmable matter

Vertegaal believes his BitDrones invention is the first step towards creating interactive self-levitating programmable matter — materials capable of changing their 3D shape in a programmable fashion, using swarms of tiny quadcopters. Possible applications: real-reality 3D modeling, gaming, molecular modeling, medical imaging, robotics, and online information visualization.

“BitDrones brings flying programmable matter closer to reality,” says Vertegaal. “It is a first step towards allowing people to interact with virtual 3D objects as real physical objects.”

Vertegaal and his team at the Human Media Lab created three types of BitDrones, each representing self-levitating displays of distinct resolutions.

PixelDrones are equipped with one LED and a small dot matrix display. Users could physically explore a file folder by touching the folder’s associated PixelDrone, for example. When the folder opens, its contents are shown by other PixelDrones flying in a horizontal wheel below it. Files in this wheel are browsed by physically swiping drones to the left or right.

PixelDrone (credit: Roel Vertegaal)

ShapeDrones are augmented with a lightweight mesh and a 3D-printed geometric frame; they serve as building blocks for real-time, complex 3D models.

ShapeDrones (credit: Roel Vertegaal)

DisplayDrones are fitted with a curved flexible high-resolution touchscreen, a forward-facing video camera and Android smartphone board. Remote users could move around locally through a DisplayDrone with Skype for telepresence. A DisplayDrone can automatically track and replicate all of the remote user’s head movements, allowing a remote user to virtually inspect a location and making it easier for the local user to understand the remote user’s actions.

DisplayDrone (credit: Roel Vertegaal)

All three BitDrone types are equipped with reflective markers, allowing them to be individually tracked and positioned in real time via motion capture technology. The system also tracks the user’s hand motion and touch, allowing users to manipulate the voxels in space.

“We call this a ‘real reality’ interface rather than a virtual reality interface. This is what distinguishes it from technologies such as Microsoft HoloLens and the Oculus Rift: you can actually touch these pixels, and see them without a headset,” says Vertegaal.

The system currently only supports a dozen comparatively large 2.5 to 5 inch sized drones, but the team is working to scale up their system to support thousands of drones measuring under a half-inch in size, allowing users to render more seamless, high-resolution programmable matter.

Other forms of programmable matter

BitDrones are somewhat related to MIT Media Lab scientist Neil Gershenfeld’s “programmable pebbles” — reconfigurable robots that self-assemble into different configurations (see A reconfigurable miniature robot), MIT’s “swarmbots” — self-assembling swarming microbots that snap together into different shape (see MIT inventor unleashes hundreds of self-assembling cube swarmbots), J. Storrs Hall’s “utility fog” concept in which a swarm of nanobots, called “foglets,” can take the shape of virtually anything, and change shape on the fly (see Utility Fog: The Stuff that Dreams Are Made Of), and Autodesk Research’s Project Cyborg, a cloud-based meta-platform of design tools for programming matter across domains and scales.


Human Media Lab | BitDrones: Interactive Flying Microbots Show Future of Virtual Reality is Physical

Abstract of BitDrones: Towards Levitating Programmable Matter Using Interactive 3D Quadcopter Displays

In this paper, we present BitDrones, a platform for the construction of interactive 3D displays that utilize nano quadcopters as self-levitating tangible building blocks. Our prototype is a first step towards supporting interactive mid-air, tangible experiences with physical interaction techniques through multiple building blocks capable of physically representing interactive 3D data.

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New dimension to high-temperature superconductivity discovered

In this artistic rendering, a magnetic pulse (right) and X-ray laser light (left) converge on a high-temperature superconductor to study the behavior of its electrons (credit: SLAC National Accelerator Laboratory)

The dream to push the operating temperature for superconductors to room temperature — leading to future advances in computing, electronics and power grid technologies — has just become more real.

A team led by scientists at the Department of Energy’s SLAC National Accelerator Laboratory has combined powerful magnetic pulses with some of the brightest X-rays on the planet, discovering a surprising 3-D arrangement of a material’s electrons that appears closely linked to high-temperature superconductivity.

The scientists say this unexpected twist marks an important milestone in the 30-year journey to better understand how materials known as high-temperature superconductors conduct electricity with no resistance at temperatures hundreds of degrees Fahrenheit above those of conventional metal superconductors (but still hundreds of degrees below freezing). The study was published today (Nov. 5) in Science.

There are already many uses for standard low-temperature superconducting technology, from MRI machines that diagnose brain tumors to a prototype levitating train, the CERN particle collider that enabled the Nobel Prize-winning discovery of the Higgs boson, and ultrasensitive detectors used to hunt for dark matter — the invisible constituent believed to make up most of the mass of the universe.

‘Totally unexpected’ physics

“This was totally unexpected, and also very exciting. This experiment has identified a new ingredient to consider in this field of study. Nobody had seen this 3-D picture before,” said Jun-Sik Lee, a SLAC staff scientist and one of the leaders of the experiment conducted at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser.  (A planned upgrade to the LCLS, known as LCLS-II, will include a superconducting particle accelerator.) “This is an important step in understanding the physics of high-temperature superconductors.”

The 3-D effect that scientists observed in the LCLS experiment, which occurs in a superconducting material known as YBCO (yttrium barium copper oxide), is a newly discovered type of “charge density wave.” This wave does not have the oscillating motion of a light wave or a sound wave; it describes a static, ordered arrangement of clumps of electrons in a superconducting material. Its coexistence with superconductivity is perplexing to researchers because it seems to conflict with the freely moving electron pairs that define superconductivity.

The 2-D version of this wave was first seen in 2012 and has been studied extensively. The LCLS experiment revealed a separate 3-D version that appears stronger than the 2-D form and closely tied to both the 2-D behavior and the material’s superconductivity.

The experiment was several years in the making and required international expertise to prepare the specialized samples and construct a powerful customized magnet that produced magnetic pulses compressed to thousandths of a second. Each pulse was 10-20 times stronger than those from the magnets in a typical medical MRI machine.

A powerful blend of magnetism and light

This custom-made magnet was used in an experiment at SLAC’s Linac Coherent Light Source X-ray laser to study an effect known as a charge density wave. (credit: Jun-Sik Lee)

Those short but intense magnetic pulses suppressed the superconductivity of the YBCO samples and provided a clearer view of the charge density wave effects. They were immediately followed at precisely timed intervals by ultra-bright LCLS X-ray laser pulses, which allowed scientists to measure the wave effects.

“This experiment is a completely new way of using LCLS that opens up the door for a whole new class of future experiments,” said Mike Dunne, LCLS director.*

“I’ve been excited about this experiment for a long time,” said Steven Kivelson, a Stanford University physics professor who contributed to the study and has researched high-temperature superconductors since 1987.

Kivelson said the experiment sets very clear boundaries on the temperature and strength of the magnetic field at which the newly observed 3-D effect emerges. “There is nothing vague about this,” he said. “You can now make a definitive statement: In this material, a new phase exists.”

The experiment also adds weight to the growing evidence that charge density waves and superconductivity “can be thought of as two sides of the same coin,” he added.

A view of the X-ray Correlation Spectroscopy experimental station at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. This station was used for an experiment studying an effect in a superconducting material. (credit: SLAC National Accelerator Laboratory)

A more complete map

But it is also clear that YBCO is incredibly complex, and a more complete map of all of its properties is required to reach any conclusions about what matters most to its superconductivity, said Simon Gerber of SIMES and Hoyoung Jang of SSRL, the lead authors of the study.

Follow-up experiments are needed to provide a detailed visualization of the 3-D effect, and to learn whether the effect is universal across all types of high-temperature superconductors, said SLAC staff scientist and SIMES investigator Wei-Sheng Lee, who co-led the study with Jun-Sik Lee of SSRL and Diling Zhu of LCLS. “The properties of this material are much richer than we thought,” Lee said.

“We continue to make new and surprising observations as we develop new experimental tools,” Zhu added.

* Researchers conducted many preparatory experiments at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), which also produces X-rays for research. LCLS and SSRL are DOE Office of Science User Facilities. Scientists from SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC, and SSRL and LCLS were a part of the study.

Abstract of Three-Dimensional Charge Density Wave Order in YBa2Cu3O6.67 at High Magnetic Fields

Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.

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Graphene could take night-vision thermal imagers beyond ‘Predator’

Alien’s view of soldiers in the movie Predator (credit: 20th Century Fox, altered by icyone)

In the 1987 movie “Predator,” an alien who sees in the far thermal infrared region of the spectrum hunts down Arnold Schwarzenegger and his team — introducing a generation of science-fiction fans to thermal imaging.

The ability of humans (or aliens) to see in the infrared allows military, police, firefighters, and others to do their jobs successfully at night and in smoky conditions. It also helps manufacturers and building inspectors identify overheating equipment or circuits. But currently, many of these systems require cryogenic cooling to filter out background radiation, or “noise,” to create a reliable image. That complicates the design and adds to the cost and the unit’s bulkiness and rigidity.

Schematic of graphene thermopile (credit: Allen L. Hsu et al./Nano Letters)

To find a more practical solution, researchers at MIT, Harvard, Army Research Laboratory, and University of California, Riverside, have developed an advanced device by integrating graphene with silicon microelectromechanical systems (MEMS) to make a flexible, transparent, and low-cost device for the mid-infrared range.

Testing showed it could be used to detect a person’s heat signature at room temperature (300 K or 27 degrees C/80 degrees F) without cryogenic cooling.

Future advances could make the device even more versatile. The researchers say that a thermal sensor could be based on a single layer of graphene, which would make it both transparent and flexible. Also, manufacturing could be simplified, which would bring costs down.

This work was reported in ACS journal Nano Letters. It has been supported in part by MIT/Army Institute for Soldier Nanotechnologies, Army Research Laboratories, Office of Naval Research GATE-MURI program, Solid State Solar Energy Conversion Center (S3TEC), MIT Center for Integrated Circuits and Systems, and Air Force Office of Scientific Research.

UPDATE Nov. 6, 2015: corrected wording to clarify that the device operates in the mid-infrared, not far-infrared range.

Abstract of Graphene-Based Thermopile for Thermal Imaging Applications

In this work, we leverage graphene’s unique tunable Seebeck coefficient for the demonstration of a graphene-based thermal imaging system. By integrating graphene based photothermo-electric detectors with micromachined silicon nitride membranes, we are able to achieve room temperature responsivities on the order of ∼7–9 V/W (at λ = 10.6 μm), with a time constant of ∼23 ms. The large responsivities, due to the combination of thermal isolation and broadband infrared absorption from the underlying SiN membrane, have enabled detection as well as stand-off imaging of an incoherent blackbody target (300–500 K). By comparing the fundamental achievable performance of these graphene-based thermopiles with standard thermocouple materials, we extrapolate that graphene’s high carrier mobility can enable improved performances with respect to two main figures of merit for infrared detectors: detectivity (>8 × 108 cm Hz1/2 W–1) and noise equivalent temperature difference (<100 mK). Furthermore, even average graphene carrier mobility (<1000 cm2 V–1 s–1) is still sufficient to detect the emitted thermal radiation from a human target.

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Fastest brain-computer-interface speller developed

System diagram of the advanced SSVEP-based BCI speller. It consists of four main procedures: visual stimulation, EEG recording, real-time data processing, and feedback presentation. The 5 × 8 stimulation matrix includes the 26 letters of the English alphabet, 10 numbers, and 4 symbols (space, comma, period, and backspace). The image of the screen stimulation matrix shown here is only for illustration. (credit: Xiaogang Chen et al./PNAS)

Brain–computer interface (BCI) spellers allow a paralyzed patient to spell out words by looking at letters on a screen. Paralyzed patients can communicate by gazing at different letters to spell out a word.

Currently, the most advanced systems for doing this use “steady state visually evoked potential” (SSVEP). This method tags different characters on a screen by flashing each character at a different frequency (from 3.5 Hz to 75 Hz in one system). When a patient looks at a specific flashing character, the brain generates evoked electrical activity at the same (or multiples of) the specific frequency of the visual stimulus. This video demonstrates how that works:


Nikolay Chumerin |SSVEP-based mindspeller

However, the low communication rate (low number of characters per minute) for existing SSVEP systems is a remaining obstacle to improving BCI-based communication. That’s because the tagged visual evoked potentials are difficult to detect due to interference from spontaneous EEG signals.

A new world record for BCI spellers claimed

Researchers at Tsinghua University in China and State Key Laboratory Integrated Optoelectronics, Institute of Semiconductors (IOS), Chinese Academy of Sciences have now developed a significantly improved SSVEP system. It can achieve rates of about 60 characters (∼12 words) per minute (5.32 bits per second) — a claimed new world record for BCI spellers, using either non-invasive or invasive methods.

To achieve that, the 40 characters in the stimulation matrix (used on the display) are tagged with a more sophisticated flickering frequency and phase coding scheme similar to that used in telecommunications systems, along with user-specific decoding. Real-time data analysis recognizes the target character through pre-processing, feature extraction, and classification.

The researchers suggest that the spelling speed achieved with this system (~1 character per second) seems close to the speed limit of human gaze control.

The research was published in Proceedings of the National Academy of Sciences. It was supported by the Chinese National Basic Research Program, the National High-Tech R&D Program, the National Natural Science Foundation, and the Recruitment Program for Young Professionals.

Abstract of High-speed spelling with a noninvasive brain–computer interface

The past 20 years have witnessed unprecedented progress in brain–computer interfaces (BCIs). However, low communication rates remain key obstacles to BCI-based communication in humans. This study presents an electroencephalogram-based BCI speller that can achieve information transfer rates (ITRs) up to 5.32 bits per second, the highest ITRs reported in BCI spellers using either noninvasive or invasive methods. Based on extremely high consistency of frequency and phase observed between visual flickering signals and the elicited single-trial steady-state visual evoked potentials, this study developed a synchronous modulation and demodulation paradigm to implement the speller. Specifically, this study proposed a new joint frequency-phase modulation method to tag 40 characters with 0.5-s-long flickering signals and developed a user-specific target identification algorithm using individual calibration data. The speller achieved high ITRs in online spelling tasks. This study demonstrates that BCIs can provide a truly naturalistic high-speed communication channel using noninvasively recorded brain activities.

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A new 3-​​D printing method for creating patient-​​specific medical devices

The 3D magnetic printing process systematically aligns and selectively polymerizes groupings of voxels (volume “pixels”) programmed to have specific reinforcement orientation within each layer of printed material based upon a shifting field. The 3-D printer build plate peels after a layer is complete to print additional layers. (credit: Joshua J. Martin et al./Nature Communications)

Northeastern University engineers have devel­oped a 3-D printing process that uses mag­netic fields to shape com­posite materials (mixes of plas­tics and ceramics) into patient-specific biomedical devices, such as catheters.

The devices are intended to be stronger and lighter than cur­rent models and the cus­tomized design could ensure an appro­priate fit, said Ran­dall Erb, assis­tant pro­fessor in the Depart­ment of Mechan­ical and Indus­trial Engi­neering.

The magnetic field enables the engineers to con­trol how the ceramic fibers are arranged, allowing for con­trol of the mechan­ical prop­er­ties of the mate­rial. That con­trol is crit­ical if you’re crafting devices with com­plex archi­tec­tures, such as cus­tomized minia­ture bio­med­ical devices. Within a single patient-specific device, the cor­ners, the curves, and the holes must all be rein­forced by ceramic fibers arranged in just the right con­fig­u­ra­tion to make the device durable.

This is the strategy taken by many nat­ural com­pos­ites from bones to trees. Fibers of cal­cium phos­phate, the min­eral com­po­nent of bone, are nat­u­rally ori­ented precisely around the holes for blood ves­sels to ensure the bone’s strength and sta­bility to enable, say, your femur to with­stand a daily jog.

Aligning fibers with magnets

The 3D magnetic-printer setup. A digital light processor (DLP) photo-polymerizes resin with UV while a magnetic field is simultaneously applied via electromagnetic solenoids. (credit: Joshua J. Martin et al./Nature Communications)

Erb ini­tially described the role of magnets in the composite-making process in a 2012 paper in the journal Sci­ence. First the researchers “mag­ne­tize” the ceramic fibers by dusting them very lightly with iron oxide, which has been FDA-approved for drug-delivery appli­ca­tions.

They then apply ultra-low mag­netic fields to indi­vidual sec­tions of the com­posite material — the ceramic fibers immersed in liquid plastic — to align the fibers according to the exacting spec­i­fi­ca­tions dic­tated by the product they are printing.

In a video accom­pa­nying the Sci­ence article, you can see the fibers spring to atten­tion when the mag­netic field is turned on. “Mag­netic fields are very easy to apply,” says Erb. “They’re safe, and they pen­e­trate not only our bodies but many other materials.”

Finally, in a process called “stere­olith­o­g­raphy,” they build the product, layer by layer, using a computer-controlled laser beam that hardens the plastic. Each six-by-six inch layer takes a minute to complete.

Using mag­nets, the new printing method aligns each minus­cule fiber in the direc­tion that con­forms pre­cisely to the geom­etry of the item being printed.

“If you can print a catheter whose geom­etry is spe­cific to the indi­vidual patient, you can insert it up to a cer­tain crit­ical spot, you can avoid punc­turing veins, and you can expe­dite delivery of the contents.”

The engineers’ open-access paper on the new tech­nology appears in the Oct. 23 issue of Nature Com­mu­ni­ca­tions.

Custom-designing neonatal catheters

Erb has received a $225,000 Small Busi­ness Tech­nology Transfer grant from the National Institutes of Health to develop neonatal catheters with a local com­pany. “Another of our goals is to use cal­cium phos­phate fibers and bio­com­pat­ible plas­tics to design sur­gical implants.”

Neonatal preemie with catheters (credit: March of Dimes Foundation)

The new technology is especially valuable for prema­ture babies (“preemies”) in neonatal care units, some weighing just a bit over a pound, with plastic tubes snaking through their nose or mouth, or dis­ap­pearing into veins or other parts of the body. Those tubes, or “catheters,” are how the babies get the nec­es­sary oxygen, nutri­ents, fluid, and med­ica­tions to stay alive.

The problem is, today’s catheters only come in stan­dard sizes and shapes, which means they cannot accom­mo­date the needs of all pre­ma­ture babies. “With neonatal care, each baby is a dif­ferent size, each baby has a dif­ferent set of prob­lems,” says Erb.

Worldwide, “15 million babies are born too soon every year” and of those, “1 million children die each year due to complications of preterm birth,” according to a report by the World Health Organization. This data was cited in the “March of Dimes Premature Birth Report Card,” issued today (Nov. 5) by March of Dimes. “Babies who survive an early birth often face serious and lifelong health problems, including breathing problems, jaundice, vision loss, cerebral palsy, and intellectual delays,” the March of Dimes report noted.

The report provides rates and grades for major cities or counties in each U.S. state and Puerto Rico. It also provides preterm birth rates by race and ethnicity. The U.S. preterm birth rate ranks among the worst of high-resource countries, the March of Dimes says.

Abstract of Designing bioinspired composite reinforcement architectures via 3D magnetic printing

Discontinuous fibre composites represent a class of materials that are strong, lightweight and have remarkable fracture toughness. These advantages partially explain the abundance and variety of discontinuous fibre composites that have evolved in the natural world. Many natural structures out-perform the conventional synthetic counterparts due, in part, to the more elaborate reinforcement architectures that occur in natural composites. Here we present an additive manufacturing approach that combines real-time colloidal assembly with existing additive manufacturing technologies to create highly programmable discontinuous fibre composites. This technology, termed as ‘3D magnetic printing’, has enabled us to recreate complex bioinspired reinforcement architectures that deliver enhanced material performance compared with monolithic structures. Further, we demonstrate that we can now design and evolve elaborate reinforcement architectures that are not found in nature, demonstrating a high level of possible customization in discontinuous fibre composites with arbitrary geometries.

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Chemical storage advance may enable more cost-effective concentrated solar-power storage

An advance in the storage of concentrated solar thermal energy may reduce reduce its cost and make it more practical to supply 24-hour on-demand electrical power (credit: Kelvin Randhir, courtesy of the University of Florida)

Oregon State University (OSU) engineers have developed an innovation in chemical storage of concentrated solar thermal energy that may reduce its cost and make it more practical for wider use.

The new system uses thermochemical storage, in which chemical transformation is used in repeated cycles to hold heat, use it to drive turbines to create electricity, and then be re-heated to continue the cycle. Most commonly, this might be done over a 24-hour period, with variable levels of solar-powered electricity available at any time of day, as dictated by demand.

Unlike conventional solar photovoltaic cells, concentrated solar thermal (a.k.a. concentrated solar power, or CSP) uses huge arrays of mirrors to focus light, typically onto a tower, for temporarily storing the energy, which is more cost-effective than batteries. (See Australian researchers set new world record in solar-energy efficiency.)

The PS10 Solar Power Plant in Spain concentrates sunlight from a field of  624 heliostats (movable mirrors) onto a central solar power tower, generating 11 megawatts (credit: Abengoa Solar, S.A.)

Storage of this type helps eliminate one of the key factors limiting the wider use of solar energy: The need to deliver the electricity immediately.

A ten-fold increase in energy density and twice as efficient

The OSU development overcomes a limitation in thermochemical energy storage. “In these types of systems, energy efficiency is closely related to use of the highest temperatures possible,” said Nick AuYeung, an assistant professor of chemical engineering in the OSU College of Engineering and corresponding author of a paper in ChemSusChem, a professional journal covering sustainable chemistry.

Thermochemical storage functions like a battery, in which chemical bonds are used to store and release heat (not electrical) energy.  However, the molten salts now being used to store solar thermal energy can only work at about 600 degrees centigrade, and also require large containers and corrosive materials, he explained. “The compound we’re studying can be used at up to 1,200 degrees, and might be twice as efficient as existing systems. There’s a significant potential to lower costs and increase efficiency.”

AuYeung said the new OSU system is based on the reversible decomposition of strontium carbonate into strontium oxide and carbon dioxide, which consumes thermal energy. During discharge, the recombination of strontium oxide and carbon dioxide releases the stored heat. These materials are nonflammable, readily available, and environmentally safe.

In comparison to existing thermochemical approaches, the new system could also allow a ten-fold increase in energy density (energy storage per unit volume), and it’s physically much smaller and would be cheaper to build. The proposed system could first be used to directly heat air, which would drive a turbine to produce electricity, and then residual heat could be used to make steam to drive yet another turbine.

However, in laboratory tests, the current energy storage capacity of the process declined after 45 heating and cooling cycles, due to some changes in the underlying materials. Further research will be needed to identify ways to reprocess the materials or significantly extend the number of cycles that could be performed before any reprocessing was needed, AuYeung said.

Other refinements may also be necessary to test the system at larger scales and resolve issues such as thermal shocks, he said, before a prototype could be ready for testing at a national laboratory.

The work was supported by the SunShot Initiative of the U.S. Department of Energy, and done in collaboration with researchers at the University of Florida.

Abstract of Solar Thermochemical Energy Storage Through Carbonation Cycles of SrCO3/SrO Supported on SrZrO3

Solar thermochemical energy storage has enormous potential for enabling cost-effective concentrated solar power (CSP). A thermochemical storage system based on a SrO/SrCO3 carbonation cycle offers the ability to store and release high temperature (≈1200 °C) heat. The energy density of SrCO3/SrO systems supported by zirconia-based sintering inhibitors was investigated for 15 cycles of exothermic carbonation at 1150 °C followed by decomposition at 1235 °C. A sample with 40 wt % of SrO supported by yttria-stabilized zirconia (YSZ) shows good energy storage stability at 1450 MJ m−3 over fifteen cycles at the same cycling temperatures. After further testing over 45 cycles, a decrease in energy storage capacity to 1260 MJ m−3 is observed during the final cycle. The decrease is due to slowing carbonation kinetics, and the original value of energy density may be obtained by lengthening the carbonation steps.

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Is this the ‘ultimate’ battery?

False-color microscopic view of a reduced graphene oxide electrode (black), which hosts the large (about 20 micrometers) lithium hydroxide particles (pink) that form when a lithium-oxygen battery discharges (credit: T. Liu et al./Science)

University of Cambridge scientists have developed a working laboratory demonstrator of a lithium-oxygen battery that has very high energy density (storage capacity per unit volume), is more than 90% efficient, and can be recharged more than 2000 times (so far), showing how several of the problems holding back the development of more powerful batteries could be solved.

Lithium-oxygen (lithium-air) batteries have been touted as the “ultimate” battery due to their theoretical energy density, which is ten times higher than a lithium-ion battery. Such a high energy density would be comparable to that of gasoline — allowing for an electric car with a battery that is a fifth the cost and a fifth the weight of those currently on the market and that could drive about 666 km (414 miles) on a single charge. (This compares to 500 kilometers (311 miles) with the new University of Waterloo design, using a silicon anode — see “Longer-lasting, lighter lithium-ion batteries from silicon anodes.”)

The challenges associated with making a better battery are holding back the widespread adoption of two major clean technologies: electric cars and grid-scale storage for solar power.

A lab demonstrator based on graphene

The researchers have now demonstrated how some of the obstacles to the ultimate battery could be overcome in a lab-based demonstrator of a lithium-oxygen battery with higher capacity, increased energy efficiency, and improved stability over previous attempts.

SEM images of pristine, fully discharged, and charged reduced graphene oxide electrodes in lab demonstrator. Scale bars: 20 micrometers. (credit: Tao Liu et al./Science)

Their demonstrator relies on a highly porous, “fluffy” carbon electrode made from reduced graphene oxide (comprising one-atom-thick sheets of carbon atoms), and additives that alter the chemical reactions at work in the battery, making it more stable and more efficient. While the results, reported in the journal Science, are promising, the researchers caution that a practical lithium-air battery still remains at least a decade away.

“What we’ve achieved is a significant advance for this technology and suggests whole new areas for research — we haven’t solved all the problems inherent to this chemistry, but our results do show routes forward towards a practical device,” said Professor Clare Grey of Cambridge’s Department of Chemistry, the paper’s senior author.

Batteries are made of three components: a positive electrode, a negative electrode and an electrolyte. In the lithium-ion (Li-ion) batteries currently used in laptops and smartphones, the negative electrode is made of graphite (a form of carbon), the positive electrode is made of a metal oxide, such as lithium cobalt oxide, and the electrolyte is a lithium salt dissolved in an organic solvent. The action of the battery depends on the movement of lithium ions between the electrodes. Li-ion batteries are light, but their capacity deteriorates with age, and their relatively low energy densities mean that they need to be recharged frequently.

Over the past decade, researchers have been developing various alternatives to Li-ion batteries, and lithium-air batteries are considered the ultimate in next-generation energy storage, because of their extremely high theoretical energy density. However, attempts at working demonstrators so far have had low efficiency, poor rate performance, and unwanted chemical reactions. Also, they can only be cycled in pure oxygen.

What Liu, Grey and their colleagues have developed uses a very different chemistry: lithium hydroxide (LiOH) instead of lithium peroxide (Li2O2). With the addition of water and the use of lithium iodide as a “mediator,” their battery showed far less of the chemical reactions which can cause cells to die, making it far more stable after multiple charge and discharge cycles.

By precisely engineering the structure of the electrode, changing it to a highly porous form of graphene, adding lithium iodide, and changing the chemical makeup of the electrolyte, the researchers were able to reduce the “voltage gap” between charge and discharge to 0.2 volts. A small voltage gap equals a more efficient battery. Previous versions of a lithium-air battery have only managed to get the gap down to 0.5 – 1.0 volts, whereas 0.2 volts is closer to that of a Li-ion battery, and equates to an energy efficiency of 93%.

Problems to be solved

The highly porous graphene electrode also greatly increases the capacity of the demonstrator, although only at certain rates of charge and discharge. Other issues that still have to be addressed include finding a way to protect the metal electrode so that it doesn’t form spindly lithium metal fibers known as dendrites, which can cause batteries to explode if they grow too much and short-circuit the battery.

Additionally, the demonstrator can only be cycled in pure oxygen, while the air around us also contains carbon dioxide, nitrogen and moisture, all of which are generally harmful to the metal electrode.

The authors acknowledge support from the U.S. Department of Energy, the Engineering and Physical Sciences Research Council (EPSRC), Johnson Matthey, the European Union via Marie Curie Actions, and the Graphene Flagship. The technology has been patented and is being commercialized through Cambridge Enterprise, the University’s commercialization arm.

Abstract of Cycling Li-O2 batteries via LiOH formation and decomposition

The rechargeable aprotic lithium-air (Li-O2) battery is a promising potential technology for next-generation energy storage, but its practical realization still faces many challenges. In contrast to the standard Li-O2 cells, which cycle via the formation of Li2O2, we used a reduced graphene oxide electrode, the additive LiI, and the solvent dimethoxyethane to reversibly form and remove crystalline LiOH with particle sizes larger than 15 micrometers during discharge and charge. This leads to high specific capacities, excellent energy efficiency (93.2%) with a voltage gap of only 0.2 volt, and impressive rechargeability. The cells tolerate high concentrations of water, water being the dominant proton source for the LiOH; together with LiI, it has a decisive impact on the chemical nature of the discharge product and on battery performance.

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Flexible phototransistor is world’s fastest, most sensitive

New phototransistor is flexible yet fastest and most responsive in the world, according to UW engineers (credit: Jung-Hun Seo)

University of Wisconsin-Madison (UW) electrical engineers have created the fastest, most responsive flexible silicon phototransistor ever made, inspired by mammals’ eyes.

Phototransistors (an advanced type of photodetector) convert light to electricity. They are widely used in products ranging from digital cameras, night-vision goggles, and smoke detectors to surveillance systems and satellites.

Developed by UW-Madison collaborators Zhenqiang “Jack” Ma, professor of electrical and computer engineering, and research scientist Jung-Hun Seo, the new phototransistor design uses thin-film single-crystalline silicon nanomembranes and has the highest-ever sensitivity and response time, the engineers say.

They suggest it could improve performance of products that rely on electronic light sensors. Integrated into a digital camera lens, for example, it could reduce bulkiness and boost the acquisition speed and quality of video or still photos.

Silicon nanomembrane phototransistor design. An anti-reflection coating (ARC) with a low refractive index increases light absorption by the silicon nanomembrane (Si NM) below, which is backed by transistor electrodes (source, gate, and drain), a reflective metal layer, and protective polyethylene terephthalate (PET). (credit: Jung-Hun Seo et al./Advanced Optical Materials)

While many phototransistors are fabricated on rigid surfaces, and therefore are flat, the new devices are flexible, meaning they more easily mimic the behavior of mammalian eyes. “We actually can make the curve any shape we like to fit the optical system,” Ma says. The new “flip-transfer” fabrication method deposits electrodes under the phototransistor’s ultrathin silicon nanomembrane layer and a reflective metal layer on the bottom. The metal layer and electrodes act as reflectors and improve light absorption sensitivity without the need for an external amplifier.

“Light absorption can be much more efficient because light is not blocked by any metal layers or other materials,” Ma says.

The researchers published details this week in the journal Advanced Optical Materials. The work was supported by the U.S. Air Force. The researchers are patenting the technology through the Wisconsin Alumni Research Foundation.

Abstract of Flexible Phototransistors Based on Single-Crystalline Silicon Nanomembranes

In this work, flexible phototransistors with a back gate configuration based on transferrable single-crystalline Si nanomembrane (Si NM) have been demonstrated. Having the Si NM as the top layer enables full exposure of the active region to an incident light and thus allows for effective light sensing. Flexible phototransistors are performed in two operation modes: 1) the high light detection mode that exhibits a photo-to-dark current ratio of 105 at voltage bias of VGS < 0.5 V, and VDS = 50 mV and 2) the high responsivity mode that shows a maximum responsivity of 52 A W−1 under blue illumination at voltage bias of VGS = 1 V, and VDS = 3 V. Due to the good mechanical flexibility of Si NMs with the assistance of a polymer layer to enhance light absorption, the device exhibits stable responsivity with less than 5% of variation under bending at small radii of curvatures (up to 15 mm). Overall, such flexible phototransistors with the capabilities of high sensitivity light detection and stable performance under the bending conditions offer great promises for high-performance flexible optical sensor applications, with easy integration for multifunctional applications.

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Longer-lasting, lighter lithium-ion batteries from silicon anodes

Schematic of electrode process design. (a) Components mixing under ultrasonic irradiation, (b) an optical image of the as-fabricated electrode made of silicon nanoparticles (SiNP), sulpher-doped graphene (SG), and polyacrylonitrile (PAN), (c) the electrode after sluggish heat treatment (SHT), (d) Schematic of the atomic-scale structure of the electrode. (credit: Fathy M. Hassan et al./Nature Communications)

Zhongwei Chen, a chemical engineering professor at the University of Waterloo, and a team of graduate students have created a new low-cost battery design using silicon instead of graphite, boosting the performance and life of lithium-ion batteries.

Waterloo’s silicon battery technology promises a 40 to 60 per cent increase in energy density (energy storage per unit volume), which is important for consumers with smartphones, smart homes, and smart wearables. It also means an electric car could be driven up to 500 kilometers (311 miles) between charges while reducing its overall weight.

The graphite bottleneck

The Waterloo engineers found that silicon anode materials are capable of producing batteries that store almost 10 times more energy than with graphite.

“As batteries improve, graphite is slowly becoming a performance bottleneck because of the limited amount of energy that it can store,” said Chen, the Canada Research Chair in Advanced Materials for Clean Energy and a member of the Waterloo Institute for Nanotechnology and the Waterloo Institute for Sustainable Energy.

The most critical challenge the Waterloo researchers faced in the new design was the loss of energy that occurs when silicon contracts and then expands by as much as 300 per cent with each charge cycle. The resulting increase and decrease in silicon volume forms cracks that reduce battery performance, create short circuits, and eventually cause the battery to stop operating.

To overcome this problem, Chen’s team along with the General Motors Global Research and Development Centre developed a flash heat treatment for fabricated silicon-based lithium-ion electrodes that minimizes volume expansion while boosting the performance and cycle capability of lithium-ion batteries.

“The economical flash heat treatment creates uniquely structured silicon anode materials that deliver extended cycle life to more than 2000 cycles with increased energy capacity of the battery,” said Chen.

Chen expects to see new batteries based on the design on the market next year.

Their findings are published in an open-access paper in the latest issue of Nature Communications.

Abstract of Evidence of covalent synergy in silicon–sulfur–graphene yielding highly efficient and long-life lithium-ion batteries

Silicon has the potential to revolutionize the energy storage capacities of lithium-ion batteries to meet the ever increasing power demands of next generation technologies. To avoid the operational stability problems of silicon-based anodes, we propose synergistic physicochemical alteration of electrode structures during their design. This capitalizes on covalent interaction of Si nanoparticles with sulfur-doped graphene and with cyclized polyacrylonitrile to provide a robust nanoarchitecture. This hierarchical structure stabilized the solid electrolyte interphase leading to superior reversible capacity of over 1,000 mAh g−1 for 2,275 cycles at 2 A g−1. Furthermore, the nanoarchitectured design lowered the contact of the electrolyte to the electrode leading to not only high coulombic efficiency of 99.9% but also maintaining high stability even with high electrode loading associated with 3.4 mAh cm−2. The excellent performance combined with the simplistic, scalable and non-hazardous approach render the process as a very promising candidate for Li-ion battery technology.

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Holographic sonic tractor beam lifts and moves objects using soundwaves

Holograms (3-D light fields) can be projected from a 2-dimensional surface to control objects. (credit: Asier Marzo, Bruce Drinkwater and Sriram Subramanian)

British researchers have built a working Star-Trek-style “tractor beam” — a device that can attract or repel one object to another from a distance. It uses high-amplitude soundwaves to generate an acoustic hologram that can grasp and move small objects.

The technique, published in an open-access paper in Nature Communications October 27, has a wide range of potential applications, the researchers say. A sonic production line could transport delicate objects and assemble them, all without physical contact. Or a miniature version could grip and transport drug capsules or microsurgical instruments through living tissue.

The device was developed at the Universities of Sussex and Bristol in collaboration with Ultrahaptics.


University of Sussex | Levitation using sound waves

The researchers used an array of 64 miniature loudspeakers. The whole system consumes just 9 Watts of power, used to create high-pitched (40Khz), high-intensity sound waves to levitate a spherical bead 4mm in diameter made of expanded polystyrene.

The tractor beam works by surrounding the object with high-intensity sound to create a force field that keeps the objects in place. By carefully controlling the output of the loudspeakers, the object can be held in place, moved, or rotated.

Three different shapes of acoustic force fields work as tractor beams: an acoustic force field that resembles a pair of fingers or tweezers; an acoustic vortex, the objects becoming trapped at the core; and a high-intensity “cage” that surrounds the objects and holds them in place from all directions.

Previous attempts surrounded the object with loudspeakers, which limits the extent of movement and restricts many applications. Last year, the University of Dundee presented the concept of a tractor beam, but no objects were held in the ray.

The team is now designing different variations of this system. A bigger version aims at levitating a soccer ball from 10 meters away and a smaller version aims at manipulating particles inside the human body.


Asier Marzo, Matt Sutton, Bruce Drinkwater and Sriram Subramanian | Acoustic holograms are projected from a flat surface and contrary to traditional holograms, they exert considerable forces on the objects contained within. The acoustic holograms can be updated in real time to translate, rotate and combine levitated particles enabling unprecedented contactless manipulators such as tractor beams.

Abstract of Holographic acoustic elements for manipulation of levitated objects

Sound can levitate objects of different sizes and materials through air, water and tissue. This allows us to manipulate cells, liquids, compounds or living things without touching or contaminating them. However, acoustic levitation has required the targets to be enclosed with acoustic elements or had limited maneuverability. Here we optimize the phases used to drive an ultrasonic phased array and show that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter. Furthermore, we introduce the holographic acoustic elements framework that permits the rapid generation of traps and provides a bridge between optical and acoustical trapping. Acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation. Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically controlled micro-machines that do not interfere with magnetic resonance imaging.