Printing flexible electronics on almost anything using a new heat-free technique

Martin Thuo and his research group have developed heat-free technology that can print conductive, metallic lines and traces on just about anything, including a rose petal. Photo courtesy of Martin Thuo.

Martin Thuo of Iowa State University and the Ames Laboratory clicked through the photo gallery for one of his research projects.

How about this one? There was a rose with metal traces printed on a delicate petal.

Or this? A curled sheet of paper with a flexible, programmable LED display.

Maybe this? A gelatin cylinder with metal traces printed across the top.

All those photos showed the latest application of undercooled metal technology developed by Thuo and his research group. The technology features liquid metal (in this case Field’s metal, an alloy of bismuth, indium and tin) trapped below its melting point in polished, oxide shells, creating particles about 10 millionths of a meter across.

When the shells are broken – with mechanical pressure or chemical dissolving – the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials, everything from a concrete wall to a leaf.

That could have all kinds of applications, including sensors to measure the structural integrity of a building or the growth of crops. The technology was also tested in paper-based remote controls that read changes in electrical currents when the paper is curved. Engineers also tested the technology by making electrical contacts for solar cells and by screen printing conductive lines on gelatin, a model for soft biological tissues, including the brain.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” Thuo and a team of researchers wrote in a paper describing the technology recently published online by the journal Advanced Functional Materials.

Thuo – an assistant professor of materials science and engineering at Iowa State, an associate of the U.S. Department of Energy’s Ames Laboratory and a co-founder of the Ames startup SAFI-Tech Inc. that’s commercializing the liquid-metal particles – is the lead author. Co-authors are Andrew Martin, a former undergraduate in Thuo’s lab and now an Iowa State doctoral student in materials science and engineering; Boyce Chang, a postdoctoral fellow at the University of California, Berkeley, who earned his doctoral degree at Iowa State; Zachariah Martin, Dipak Paramanik and Ian Tevis, of SAFI-Tech; Christophe Frankiewicz, a co-founder of Sep-All in Ames and a former Iowa State postdoctoral research associate; and Souvik Kundu, an Iowa State graduate student in electrical and computer engineering.

The project was supported by university startup funds to establish Thuo’s research lab at Iowa State, Thuo’s Black & Veatch faculty fellowship and a National Science Foundation Small Business Innovation Research grant.

Thuo said he launched the project three years ago as a teaching exercise.

“I started this with undergraduate students,” he said. “I thought it would be fun to get students to make something like this. It’s a really beneficial teaching tool because you don’t need to solve 2 million equations to do sophisticated science.”

And once students learned to use a few metal-processing tools, they started solving some of the technical challenges of flexible, metal electronics.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

And so the researchers have learned how to effectively bond metal traces to everything from water-repelling rose petals to watery gelatin. Based on what they now know, Thuo said it would be easy for them to print metallic traces on ice cubes or biological tissue.

All the experiments “highlight the versatility of this approach,” the researchers wrote in their paper, “allowing a multitude of conductive products to be fabricated without damaging the base material.”

Learn more: Self-sterilizing polymer proves effective against drug-resistant pathogens

 

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Enabling ultrafast quantum computing

Jigang Wang and his collaborators have demonstrated light-induced acceleration of supercurrents, which could enable practical applications of quantum mechanics such as computing, sensing and communicating. Larger image. Image courtesy of Jigang Wang.

Jigang Wang patiently explained his latest discovery in quantum control that could lead to superfast computing based on quantum mechanics. He mentioned light-induced superconductivity without energy gap. He brought up forbidden supercurrent quantum beats. And he mentioned terahertz-speed symmetry breaking.

Then he backed up and clarified all that. After all, the quantum world of matter and energy at terahertz and nanometer scales – trillions of cycles per second and billionths of meters – is still a mystery to most of us.

“I like to study quantum control of superconductivity exceeding the gigahertz, or billions of cycles per second, bottleneck in current state-of-the-art quantum computation applications,” said Wang, a professor of physics and astronomy at Iowa State University whose research has been supported by the Army Research Office. “We’re using terahertz light as a control knob to accelerate supercurrents.”

Superconductivity is the movement of electricity through certain materials without resistance. It typically occurs at very, very cold temperatures. Think -400 Fahrenheit for “high-temperature” superconductors.

Terahertz light is light at very, very high frequencies. Think trillions of cycles per second. It’s essentially extremely strong and powerful microwave bursts firing at very short time frames.

Wang and a team of researchers demonstrated such light can be used to control some of the essential quantum properties of superconducting states, including macroscopic supercurrent flowing, broken symmetry and accessing certain very high frequency quantum oscillations thought to be forbidden by symmetry.

It all sounds esoteric and strange. But it could have very practical applications.

“Light-induced supercurrents chart a path forward for electromagnetic design of emergent materials properties and collective coherent oscillations for quantum engineering applications,” Wang and several co-authors wrote in a research paper just published online by the journal Nature Photonics.

In other words, the discovery could help physicists “create crazy-fast quantum computers by nudging supercurrents,” Wang wrote in a summary of the research team’s findings.

Finding ways to control, access and manipulate the special characteristics of the quantum world and connect them to real-world problems is a major scientific push these days. The National Science Foundation has included the “Quantum Leap” in its “10 big ideas” for future research and development.

“By exploiting interactions of these quantum systems, next-generation technologies for sensing, computing, modeling and communicating will be more accurate and efficient,” says a summary of the science foundation’s support of quantum studies. “To reach these capabilities, researchers need understanding of quantum mechanics to observe, manipulate and control the behavior of particles and energy at dimensions at least a million times smaller than the width of a human hair.”

Wang and his collaborators – Xu Yang, Chirag Vaswani and Liang Luo from Iowa State, responsible for terahertz instrumentation and experiments; Chris Sundahl, Jong-Hoon Kang and Chang-Beom Eom from the University of Wisconsin-Madison, responsible for high-quality superconducting materials and their characterizations; Martin Mootz and Ilias E. Perakis from the University of Alabama at Birmingham, responsible for model building and theoretical simulations – are advancing the quantum frontier by finding new macroscopic supercurrent flowing states and developing quantum controls for switching and modulating them.

A summary of the research team’s study says experimental data obtained from a terahertz spectroscopy instrument indicates terahertz light-wave tuning of supercurrents is a universal tool “and is key for pushing quantum functionalities to reach their ultimate limits in many cross-cutting disciplines” such as those mentioned by the science foundation.

And so, the researchers wrote, “We believe that it is fair to say that the present study opens a new arena of light-wave superconducting electronics via terahertz quantum control for many years to come.”

Learn more: Physicists use light waves to accelerate supercurrents, enable ultrafast quantum computing

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Fleets of drones can become real – just a few obstacles to overcome

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Search and rescue crews are already using drones to locate missing hikers. Farmers are flying them over fields to survey crops. And delivery companies will soon use drones to drop packages at your doorstep.

With so many applications for the technology, an Iowa State University researcher says the next step is to expand capacity by deploying fleets of drones. But making that happen is not as simple as launching multiple aircraft at once. Borzoo Bonakdarpour, an assistant professor of computer science, says unlike piloting a single drone by remote control, operating a fleet requires an automated system to coordinate the task, but allows drones to independently respond to weather, a crash or unexpected events.

“The operating system must be reliable and secure. The drones need to talk to one another without a central command telling each unit where to go and what to do when conditions change,” Bonakdarpour said. “We also want to optimize the time and energy to complete the task, because drone batteries only last around 15 or 20 minutes.”

To tackle this problem, Bonakdarpour and his colleagues developed a mathematical model to calculate the cost – time and energy – to complete a task based on the number of drones and recharging stations available. The model considers the energy required for each drone to complete its portion of the task and fly to a charging station as needed.

On paper the solution is relatively simple for a team of computer scientists, but Bonakdarpour says moving from theory to implementation is not as easy. “As we work on one problem, we actually find new problems we must solve. It’s challenging, but that’s also what makes it exciting,” he said.

For example, if a battery lasts 15 minutes in the lab, it may drop to 10 minutes on a hot or cold day outside. Locating charging stations is another issue. The optimal placement may be in the middle of a lake and inaccessible in reality.

Managing tradeoff between energy and security

Based on their model, Bonakdarpour, Anh-Duy Vu with McMaster University, Canada; and Ramy Medhat with Google in Waterloo, Canada, developed four operating methods – three offline optimization techniques and one online algorithm. While an offline technique is limited because the preprogrammed flight paths do not allow drones to respond to unexpected events or changing conditions, Bonakdarpour says it provides the foundation for the online algorithm to operate.

The researchers conducted a series of simulations (see sidebar for video) using four drones to test for efficiency and security. They found the online algorithm successfully managed the security-energy tradeoff within the energy limits of the drones. The fleet completed all assigned tasks and more than half of the authentication checks. The researchers recently presented the findings at the International Conference on Cyber-Physical Systems in Canada.

Defending against hackers, rogue drones

Operating an automated fleet of drones poses security risks that are less of a concern when piloting a single drone by remote control. Bonakdarpour says with automation drones need to receive GPS signal and position frequently. If the signal drops or the drones fly into an area that is GPS-denied, it can quickly become a problem.

“If you’re driving your car and lose GPS, your driving skills don’t depend on that signal. You may miss an exit, but loss of signal for a minute is usually not a big deal. However, with drones just a few seconds is not tolerable,” Bonakdarpour said.

Software bugs or errors may cause a drone to fly off course and not follow direction to complete the mission. Bonakdarpour says hackers can also send the wrong signal or operate a drone to impersonate the fleet. While finding solutions will take time, Bonakdarpour says the technology exists to make it happen. However, it will also take industry support to build infrastructure and charging stations as well as regulatory changes to allow for the operation of a fleet of drones.

Learn more: Obstacles to overcome before operating fleets of drones becomes reality

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A new class of mosquito repellents based on naturally occurring compounds that are effective in repelling mosquitoes

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Nearly 700 million people suffer from mosquito-borne diseases — such as malaria, West Nile, Zika and dengue fever — each year, resulting in more than 1 million deaths. Increasingly, many species of mosquitoes have become resistant to the popular pyrethroid-based insecticides. Today, researchers report a new class of mosquito repellents based on naturally occurring compounds that are effective in repelling mosquitoes with potentially fewer environmental side effects than existing repellents.

The scientists will present their research today at the 256th National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 10,000 presentations on a wide range of science topics.

“Our new repellents are based on how nature already works,” Joel R. Coats, Ph.D., says. “For example, citronella, a spatial repellent that comes from lemongrass, contains naturally occurring essential oils that have been used for centuries to repel mosquitoes. But citronella doesn’t last long and blows away easily. Our new, next-generation spatial repellents are variations of natural products that are longer-lasting and have greater repellency.”

Coats and graduate students James S. Klimavicz and Caleb L. Corona at Iowa State University in Ames have been synthesizing and testing hundreds of compounds against mosquitoes. They knew that sesquiterpenoids, which are found in many plants, are effective insect repellents, but these large molecules are difficult to isolate from plants and hard to make and purify in the laboratory.

Because of the challenges of synthesizing sesquiterpenoids, Coats’ team designed their repellents using smaller, less complex, easily obtainable molecules — monoterpenoids and phenylpropanoid alcohols with known, short-term repellent activities against insects. By modifying these compounds chemically, they produced new potential repellents with higher molecular weights, making them less volatile and longer-lasting. Klimavicz has synthesized more than 300 compounds, the most effective of which are ?-terpinyl isovalerate (a natural compound), citronellyl cyclobutanecarboxylate and citronellyl 3,3-difluorocyclobutanecarboxylate.

To determine the compounds’ effectiveness as repellents against mosquitoes, Corona tests them in a tubular chamber developed in the Coats laboratory. The chamber has filter papers at either end. One filter paper has nothing on it; the other has the synthesized repellent applied. Then mosquitoes — raised in the Iowa State University medical entomology lab — are introduced into the chamber. Corona uses time-lapse photography and in-person monitoring over 2.5 hours to document whether the mosquitoes migrate away from the candidate repellents. The researchers are currently exploring computer tracking of mosquitoes using video footage to gain a better understanding of mosquito repellency and behavior when exposed to these compounds.

With this method, the researchers tested the repellents with Culex pipiens, the northern house mosquito, which is most closely linked to West Nile transmission in the Midwestern U.S.; Aedes aegypti, the yellow fever mosquito which is also known to transmit the Zika and dengue viruses; and Anopheles gambiae, which transmits malaria.

“We think the mechanism of our terpene-based repellents, which try to mimic what nature does, is different from that of the pyrethroids,” which many mosquito species have become resistant to, Coats says. “We believe these ‘next-gen’ spatial repellents are new tools that could provide additional protection against mosquitoes in treated yards, parks, campgrounds, horse stables and livestock facilities. Our next step is to understand more precisely how the repellents biologically affect the mosquitoes.”

This research will be presented at a meeting of the American Chemical Society

Learn more: Next-gen insect repellents to combat mosquito-borne diseases

 

 

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Cheap sensors-on-tape can be attached to plants and provide new kinds of data to researchers and farmers

Iowa State University researchers have developed these “plant tattoo sensors” to take real-time, direct measurements of water use in crops.
Photo courtesy of Liang Dong.

Iowa State University plant scientist Patrick Schnable quickly described how he measured the time it takes for two kinds of corn plants to move water from their roots, to their lower leaves and then to their upper leaves.

This was no technical, precise, poster talk. This was a researcher interested in working with new, low-cost, easily produced, graphene-based, sensors-on-tape that can be attached to plants and can provide new kinds of data to researchers and farmers.

“With a tool like this, we can begin to breed plants that are more efficient in using water,” he said. “That’s exciting. We couldn’t do this before. But, once we can measure something, we can begin to understand it.”

The tool making these water measurements possible is a tiny graphene sensor that can be taped to plants – researchers have dubbed it a “plant tattoo sensor.” Graphene is a wonder material. It’s a carbon honeycomb just an atom thick, it’s great at conducting electricity and heat, and it’s strong and stable. The graphene-on-tape technology in this study has also been used to produce wearable strain and pressure sensors, including sensors built into a “smart glove” that measures hand movements.

Researchers describe the various sensors and the “simple and versatile method for patterning and transferring graphene-based nanomaterials” to create the flexible sensors in a paper featured on the cover of the December 2017 issue of the journal Advanced Materials Technologies.

The research has been primarily supported by the Faculty Scholars Program of Iowa State’s Plant Sciences Institute.

Liang Dong, an Iowa State associate professor of electrical and computer engineering, is the lead author of the paper and developer of the technology. Seval Oren, a doctoral student in electrical and computer engineering, is a co-author who helped develop the sensor-fabrication technology. Co-authors who helped test applications of the sensors are Schnable, director of Iowa State’s Plant Sciences Institute, a Charles F. Curtiss Distinguished Professor in Agriculture and Life Sciences, the Iowa Corn Promotion Board Endowed Chair in Genetics and the Baker Scholar of Agricultural Entrepreneurship; and Halil Ceylan, a professor of civil, construction and environmental engineering.

“We’re trying to make sensors that are cheaper and still high performing,” Dong said.

To do that, the researchers have developed a process for fabricating intricate graphene patterns on tape. Dong said the first step is creating indented patterns on the surface of a polymer block, either with a molding process or with 3-D printing. Engineers apply a liquid graphene solution to the block, filling the indented patterns. They use tape to remove the excess graphene. Then they take another strip of tape to pull away the graphene patterns, creating a sensor on the tape.

The process can produce precise patterns as small as 5 millionths of a meter wide – just a twentieth of the diameter of the average human hair. Dong said making the patterns so small increases the sensitivity of the sensors.

(The process, for example, produced a detailed image of Iowa State’s Cyclone mascot that was less than 2 millimeters across. “I think this is probably the smallest Cyclone,” Dong said.)

“This fabrication process is very simple,” Dong said. “You just use tape to manufacture these sensors. The cost is just cents.”

In the case of plant studies, the sensors are made with graphene oxide, a material very sensitive to water vapor. The presence of water vapor changes the conductivity of the material, and that can be quantified to accurately measure transpiration (the release of water vapor) from a leaf.

The plant sensors have been successfully tested in lab and pilot field experiments, Dong said.

A new three-year, $472,363 grant from the U.S. Department of Agriculture’s Agriculture and Food Research Initiative will support more field testing of water transport in corn plants. Michael Castellano, an Iowa State associate professor of agronomy and William T. Frankenberger Professor in Soil Science, will lead the project. Co-investigators include Dong and Schnable.

The Iowa State University Research Foundation has applied for a patent on the sensor technology. The research foundation has also granted an option to commercialize the technology to EnGeniousAg – an Ames startup company co-founded by Dong, Schnable, Castellano and James Schnable, an assistant professor of agronomy and horticulture at the University of Nebraska-Lincoln, a collaborator on another Iowa State sensor project that sparked establishment of the company (and Patrick Schnable’s son).

“The most exciting application of the tape-based sensors we’ve tested so far is the plant sensor,” Dong said. “The concept of wearable electronic sensors for plants is brand new. And the plant sensors are so tiny they can detect transpiration from plants, but they won’t affect plant growth or crop production.”

But that’s not all the sensors can do. The technology could “open a new route” for a wide variety of applications, the authors wrote in their paper, including sensors for biomedical diagnostics, for checking the structural integrity of buildings, for monitoring the environment and, after appropriate modifications, for testing crops for diseases or pesticides.

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