A robotic skin and wearable device so thin you don’t even notice it

Cunjiang Yu, Bill D. Cook Associate Professor of Mechanical Engineering at UH, led a project to develop a multifunctional, ultra-thin wearable human-machine interface.

Device Also Can Serve as Robotic Skin, Relaying Information Back to the User

Wearable human-machine interfaces – devices that can collect and store important health information about the wearer, among other uses – have benefited from advances in electronics, materials and mechanical designs. But current models still can be bulky and uncomfortable, and they can’t always handle multiple functions at one time.

Researchers reported Friday, Aug. 2, the discovery of a multifunctional ultra-thin wearable electronic device that is imperceptible to the wearer.

The device allows the wearer to move naturally and is less noticeable than wearing a Band-Aid, said Cunjiang Yu, Bill D. Cook Associate Professor of Mechanical Engineering at the University of Houston and lead author for the paper, published as the cover story in Science Advances.

“Everything is very thin, just a few microns thick,” said Yu, who also is a principal investigator at the Texas Center for Superconductivity at UH. “You will not be able to feel it.”

It has the potential to work as a prosthetic skin for a robotic hand or other robotic devices, with a robust human-machine interface that allows it to automatically collect information and relay it back to the wearer.

That has applications for health care – “What if when you shook hands with a robotic hand, it was able to instantly deduce physical condition?” Yu asked – as well as for situations such as chemical spills, which are risky for humans but require human decision-making based on physical inspection.

While current devices are gaining in popularity, the researchers said they can be bulky to wear, offer slow response times and suffer a drop in performance over time. More flexible versions are unable to provide multiple functions at once – sensing, switching, stimulation and data storage, for example – and are generally expensive and complicated to manufacture.

The device described in the paper, a metal oxide semiconductor on a polymer base, offers manufacturing advantages and can be processed at temperatures lower than 300 C.

“We report an ultrathin, mechanically imperceptible, and stretchable (human-machine interface) HMI device, which is worn on human skin to capture multiple physical data and also on a robot to offer intelligent feedback, forming a closed-loop HMI,” the researchers wrote. “The multifunctional soft stretchy HMI device is based on a one-step formed, sol-gel-on-polymer-processed indium zinc oxide semiconductor nanomembrane electronics.”

Learn more: A Wearable Device So Thin and Soft You Won’t Even Notice It

 

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A new thermoelectric material works efficiently at room temperature at much lower cost

Texas Center for Superconductivity at UH Director Zhifeng Ren, right, and post-doctoral researcher Jun Mao say a new thermoelectric cooling material is inexpensive to produce and works efficiently at room temperature.

Has your steering wheel been too hot to touch this summer? A new thermoelectric material reported in the journal Science could offer relief.

The widespread adoption of thermoelectric devices that can directly convert electricity into thermal energy for cooling and heating has been hindered, in part, by the lack of materials that are both inexpensive and highly efficient at room temperature.

Now researchers from the University of Houston and the Massachusetts Institute of Technology have reported the discovery of a new material that works efficiently at room temperature while requiring almost no costly tellurium, a major component of the current state-of-the-art material.

The work, described in a paper published online by Science Thursday, July 18, has potential applications for keeping electronic devices, vehicles and other components from overheating, said Zhifeng Ren, corresponding author on the work and director of the Texas Center for Superconductivity at UH, where he is also M.D. Anderson Professor of Physics.

“We have produced a new material, which is inexpensive but still performs almost as well as the traditional, more expensive material,” Ren said. The researchers say future work could close the slight performance gap between their new material and the traditional material, a bismuth-tellurium based alloy.

Thermoelectric materials work by exploiting the flow of heat current from a warmer area to a cooler area, and thermoelectric cooling modules operate according to the Peltier effect, which describes the transfer of heat between two electrical junctions.

Thermoelectric materials can also be used to turn waste heat – from power plants, automobile tailpipes and other sources – into electricity, and a number of new materials have been reported for that application, which requires materials to perform at far higher temperatures.

Thermoelectric cooling modules have posed a great challenge because they have to work at cooler temperatures, where the thermoelectric figure-of-merit, or ZT, is low because it is dependent on temperature. The figure-of-merit is a metric used to determine how efficiently a thermoelectric material works.

Despite the challenge, thermoelectric cooling modules also, at least for now, offer more commercial potential, in part because they can operate for a long lifespan at cooler temperatures; thermoelectric power generation is complicated by issues related to the high temperatures at which it operates, including oxidation and thermal instability.

The market for thermoelectric cooling is growing. “The global thermoelectric module market was worth ~0.6 billion US dollars in 2018 and it is anticipated to reach ~1.7 billion US dollars by 2027,” the researchers wrote.

Bismuth-tellurium alloys have been considered the best-performing material for thermal cooling for decades, but the researchers said the high cost of tellurium has limited widespread use. Jun Mao, a post-doctoral researcher at UH and first author on the paper, said the cost has recently dropped but remains about $50/kilogram. That compares to about $6/kilogram for magnesium, a primary component of the new material.

In addition to Ren and Mao, additional authors on the paper include Hangtian Zhu, Zihang Liu and Geethal Amila Gamage, all of the UH Department of Physics and TcSUH, and Zhiwei Ding and Gang Chen of the Department of Mechanical Engineering at the Massachusetts Institute of Technology.

They reported that the new material, comprised of magnesium and bismuth and created in a form carrying a negative charge, known as n-type, was almost as efficient as the traditional bismuth-tellurium material. That, combined with the lower cost, should expand the use of thermoelectric modules for cooling, they said.

To produce a thermoelectric module using the new material, researchers combined it with a positive-charge carrying, or p-type, version of the traditional bismuth-tellurium alloy. Mao said that allowed them to use just half as much tellurium as most current modules.

Because the cost of materials accounts for about one-third of the cost of the device, that savings adds up, he said.

The new material also more successfully maintains electrical contact than most nanostructured materials, the researchers reported.

Learn more: New Low-Cost Thermoelectric Material Works at Room Temperature

 

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AI brain-computer interface improves on its own and learns about its subject without having to be programed

Professor of biomedical engineering Joe Francis is reporting work that represents a significant step forward for prosthetics that perform more naturally.

Findings Could Help Seamlessly Integrate Prosthetics

A University of Houston engineer is reporting in eNeuro that a brain-computer interface, a form of artificial intelligence, can sense when its user is expecting a reward by examining the interactions between single-neuron activities and the information flowing to these neurons, called the local field potential.

Professor of biomedical engineering Joe Francis reports his team’s findings allow for the development of an autonomously updating brain-computer interface (BCI) that improves on its own, learning about its subject without having to be programed.

The findings potentially have applications for robotic prosthetics, which would sense what a user wants to do (pick up a glass, for example) and do it. The work represents a significant step forward for prosthetics that perform more naturally.

“This will help prosthetics work the way the user wants them to,” said Francis. “The BCI quickly interprets what you’re going to do and what you expect as far as whether the outcome will be good or bad.” Francis said that information drives scientists’ abilities to predict reward outcome to 97%, up from the mid-70s.

To understand the effects of reward on the brain’s primary motor cortex activity, Francis used implanted electrodes to investigate brainwaves and spikes in brain activity while tasks were performed to see how interactions are modulated by conditioned reward expectations.

“We assume intention is in there, and we decode that information by an algorithm and have it control either a computer cursor, for example, or a robotic arm,” said Francis. Interestingly even when the task called for no movement, just passively observing an activity, the BCI was able to determine intention because the pattern of neural activity resembled that during movement.

“This is important because we are going to have to extract this information and brain activity out of people who cannot actually move, so this is our way of showing we can still get the information even if there is no movement,” said Francis. This process utilizes mirror neurons, which fire when action is taken and action is observed.

“This examination of reward motivation in the primary motor cortex could be useful in developing an autonomously updating brain machine interface,” said Francis.

Learn more: Research Moves Closer to Brain-Machine Interface Autonomy

 

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A solid-state sodium-ion battery arrives

via EurekAlert!

Solid-state sodium-ion batteries are far safer than conventional lithium-ion batteries, which pose a risk of fire and explosions, but their performance has been too weak to offset the safety advantages. Researchers Friday reported developing an organic cathode that dramatically improves both stability and energy density.

The improved performance, reported in the journal Joule, is related to two key findings:

  • The resistive interface between the electrolyte and cathode that commonly forms during cycling can be reversed, extending cycle life, and
  • The flexibility of the organic cathode allowed it to maintain intimate contact at the interface with the solid electrolyte, even as the cathode expanded and contracted during cycling.

Yan Yao, associate professor of electrical and computer engineering at the University of Houston and corresponding author of the paper, said the organic cathode – known as PTO, for pyrene-4,5,9,10-tetraone – offers unique advantages over previous inorganic cathodes. But he said the underlying principles are equally significant.

“We found for the first time that the resistive interface that forms between the cathode and the electrolyte can be reversed,” Yao said. “That can contribute to stability and longer cycle life.” Yao also is a principal investigator at the Texas Center for Superconductivity at UH. His research group focuses on green and sustainable organic materials for energy generation and storage.

Yanliang “Leonard” Liang, a research assistant professor in the UH Department of Electrical and Computer Engineering, said that reversibility of the interface is the key, allowing the solid-state battery to reach a higher energy density without sacrificing cycle life. Normally, a solid-state battery’s ability to store energy is halted when the resistive cathode-electrolyte interface forms; reversing that resistance allows energy density to remain high during cycling, he said.

Lithium-ion batteries with their liquid electrolytes are able to store relatively high amounts of energy and are commonly used to power the tools of modern life, from cell phones to hearing aids. But the risk of fire and explosion has heightened interest in other types of batteries, and a solid-state sodium-ion battery offers the promise of increased safety at a lower cost.

Xiaowei Chi, a post-doctoral researcher in Yao’s group, said a key challenge had been to find a solid electrolyte that is as conductive as the liquid electrolytes used in lithium-ion batteries. Now that sufficiently conductive solid electrolytes are available, a remaining challenge has been the solid interfaces.

One issue raised by a solid electrolyte: the electrolyte struggles to maintain intimate contact with a traditional rigid cathode as the latter expands and contracts during battery cycling. Fang Hao, a PhD student working in Yao’s group, said the organic cathode is more pliable and thus able to remain in contact with the interface, improving cycling life. The researchers said the contact remained steady through at least 200 cycles.

“If you have reliable contact between the electrode and electrolyte, you will have a great chance of creating a high-performance solid-state battery,” Hao said.

Learn more: Researchers Report High Performance Solid-State Sodium-Ion Battery

 

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A genuine breakthrough in ice-repelling material

Researchers led by Hadi Ghasemi, Bill D. Cook Assistant Professor of mechanical engineering at UH, have created a durable silicone polymer coating capable of repelling ice from any surface.

Work Has Implications for Aircraft, Power Transmission Lines and More

Icy weather is blamed for multibillion dollar losses every year in the United States, including delays and damage related to air travel, infrastructure and power generation and transmission facilities. Finding effective, durable and environmentally stable de-icing materials has been stymied by the stubborn tenacity with which ice adheres to the materials on which it forms.

Researchers from the University of Houston have reported a new theory in physics called stress localization, which they used to tune and predict the properties of new materials. Based on those predictions, the researchers reported in Materials Horizons that they have created a durable silicone polymer coating capable of repelling ice from any surface.

“We have developed a new physical concept and the corresponding icephobic material that shows extremely low ice adhesion while having long-term mechanical, chemical and environmental durability,” they wrote.

Hadi Ghasemi, Bill D. Cook Assistant Professor of mechanical engineering at UH and corresponding author for the work, said the findings suggest a way to take trial and error out of the search for new materials, in keeping with the movement of materials science toward a physics-driven approach.

“You put in the properties you want, and the principle will tell you what material you need to synthesize,” he said, noting that the concept can also be used to predict materials with superb antibacterial or other desirable properties.

His collaborators on the project include Payman Irajizad, Abdullah Al-Bayati, Bahareh Eslami, Taha Shafquat, Masoumeh Nazari, Parham Jafari, Varun Kashyap and Ali Masoudi, all with the UH Department of Mechanical Engineering, and Daniel Araya, a former UH faculty member who is now at the Johns Hopkins University Applied Physics Laboratory.

Ghasemi previously has reported developing several new icephobic materials, but he said those, like other existing materials, haven’t been able to completely overcome the problem of ice adhering to the surface, along with issues of mechanical and environmental durability. The new understanding of stress localization allows the new material to avoid that, he said.

The new material uses elastic energy localization where ice meets the material, triggering cracks at the interface that slough off the ice. Ghasemi said it requires minimal force to cause the cracks; the flow of air over the surface of an airplane acts as a trigger, for example.

The material, which is applied as a spray, can be used on any surface, and Ghasemi said testing showed it is not only mechanically durable and unaffected by ultraviolet rays – important for aircraft which face constant sun exposure – but also does not change the aircraft’s aerodynamic performance. Testing indicates it will last for more than 10 years, with no need to reapply, he said.

Learn more: Researchers Report Breakthrough in Ice-Repelling Materials

 

 

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