Tag Archives: bendable electronics

‘Green’, flexible electronics with nanocellulose materials

Bendable or flexible electronics based on nanocellulose paper present a ‘green’ alternative to other solutions according to a May 20, 2015 American Chemical Society (ACS) news release (also on EurekAlert),

Technology experts have long predicted the coming age of flexible electronics, and researchers have been working on multiple fronts to reach that goal. But many of the advances rely on petroleum-based plastics and toxic materials. Yu-Zhong Wang, Fei Song and colleagues wanted to seek a “greener” way forward.

The researchers developed a thin, clear nanocellulose paper made out of wood flour and infused it with biocompatible quantum dots — tiny, semiconducting crystals — made out of zinc and selenium. The paper glowed at room temperature and could be rolled and unrolled without cracking.

(h’t Nanotechnology Now, May 20, 2015)

There’s no mention in the news release or abstract as to what material (wood, carrot, banana, etc.) was used to derive the nanocellulose. Regardless, here’s a link to and a citation for the paper,

Let It Shine: A Transparent and Photoluminescent Foldable Nanocellulose/Quantum Dot Paper by Juan Xue, Fei Song, Xue-wu Yin, Xiu-li Wang, and Yu-zhong Wang. ACS Appl. Mater. Interfaces, 2015, 7 (19), pp 10076–10079 DOI: 10.1021/acsami.5b02011 Publication Date (Web): May 4, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Fully textile-embedded transparent and flexible technology?

There are a lot of research teams jockeying for position in the transparent, flexible electrodes stakes (for anyone unfamiliar with the slang, I’m comparing the competition between various research teams to a horse race). A May 11, 2015 news item on Nanowerk describes work from an international collaboration at the University of Exeter (UK), Note: A link has been removed,

An international team of scientists, including Professor Monica Craciun from the University of Exeter, have pioneered a new technique to embed transparent, flexible graphene electrodes into fibres commonly associated with the textile industry.

The discovery could revolutionise the creation of wearable electronic devices, such as clothing containing computers, phones and MP3 players, which are lightweight, durable and easily transportable.

The international collaborative research, which includes experts from the Centre for Graphene Science at the University of Exeter, the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel), is published in the leading scientific journal Scientific Reports (“Transparent conductive graphene textile fibers”).

A May 11, 2015 University of Exeter press release (also on EurekAlert*), which originated the news item,  describes the current situation regarding transparent and flexible electrodes in textiles and how the research at Exeter improves the situation,

Professor Craciun, co-author of the research said: “This is a pivotal point in the future of wearable electronic devices. The potential has been there for a number of years, and transparent and flexible electrodes are already widely used in plastics and glass, for example. But this is the first example of a textile electrode being truly embedded in a yarn. The possibilities for its use are endless, including textile GPS systems, to biomedical monitoring, personal security or even communication tools for those who are sensory impaired.  The only limits are really within our own imagination.”

At just one atom thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for the use in wearable electronic devices in recent years.

This new research has identified that ‘monolayer graphene’, which has exceptional electrical, mechanical and optical properties, make it a highly attractive proposition as a transparent electrode for applications in wearable electronics. In this work graphene was created by a growth method called chemical vapour deposition (CVD) onto copper foil, using a state-of-the-art nanoCVD system recently developed by Moorfield.

The collaborative team established a technique to transfer graphene from the copper foils to a polypropylene fibre already commonly used in the textile industry.

Dr Helena Alves who led the research team from INESC-MN and the University of Aveiro said: “The concept of wearable technology is emerging, but so far having fully textile-embedded transparent and flexible technology is currently non-existing. Therefore, the development of processes and engineering for the integration of graphene in textiles would give rise to a new universe of commercial applications. “

Dr Ana Neves, Associate Research Fellow in Prof Craciun’s team from Exeter’s Engineering Department and former postdoctoral researcher at INESC added: “We are surrounded by fabrics, the carpet floors in our homes or offices, the seats in our cars, and obviously all our garments and clothing accessories. The incorporation of electronic devices on fabrics would certainly be a game-changer in modern technology.

“All electronic devices need wiring, so the first issue to be address in this strategy is the development of conducting textile fibres while keeping the same aspect, comfort and lightness. The methodology that we have developed to prepare transparent and conductive textile fibres by coating them with graphene will now open way to the integration of electronic devices on these textile fibres.”

Dr Isabel De Schrijver,an expert of smart textiles from CenTexBel said: “Successful manufacturing of wearable electronics has the potential for a disruptive technology with a wide array of potential new applications. We are very excited about the potential of this breakthrough and look forward to seeing where it can take the electronics industry in the future.”

Professor Saverio Russo, co-author and also from the University of Exeter, added: “This breakthrough will also nurture the birth of novel and transformative research directions benefitting a wide range of sectors ranging from defence to health care. “

In 2012 Professor Craciun and Professor Russo, from the University of Exeter’s Centre for Graphene Science, discovered GraphExeter – sandwiched molecules of ferric chloride between two graphene layers which makes a whole new system that is the best known transparent material able to conduct electricity.  The same team recently discovered that GraphExeter is also more stable than many transparent conductors commonly used by, for example, the display industry.

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

Electron transport of WS2 transistors in a hexagonal boron nitride dielectric environment by Freddie Withers, Thomas Hardisty Bointon, David Christopher Hudson, Monica Felicia Craciun, & Saverio Russo. Scientific Reports 4, Article number: 4967 doi:10.1038/srep04967 Published 15 May 2014

Did they wait a year to announce the research or is this a second-go-round? In any event, it is an open access paper.

* Added EurekAlert link 1120 hours PDT on May 12, 2015.

Just how bendy are the new organic semiconductors?

In all the excitement about flexible electronics, an interesting question about performance, which seems to have been overlooked until now (how bendy are they?), is being answered by scientists, according to a May 5, 2015 University of Massachusetts at Amherst news release (also on EurekAlert),

A revolution is coming in flexible electronic technologies as cheaper, more flexible, organic transistors come on the scene to replace expensive, rigid, silicone-based semiconductors, but not enough is known about how bending in these new thin-film electronic devices will affect their performance, say materials scientists at the University of Massachusetts Amherst.

They are the first to apply inhomogeneous deformations, that is strain, to the conducting channel of an organic transistor and to understand the observed effects, says Reyes-Martinez [Marcos Reyes-Martinez], who conducted the series of experiments as part of his doctoral work.

As he explains, “This is relevant to today’s tech industry because transistors drive the logic of all the consumer electronics we use. In the screen on your smart phone, for example, every little pixel that makes up the image is turned on and off by hundreds of thousands or even millions of miniaturized transistors.”

“Traditionally, the transistors are rigid, made of an inorganic material such as silicon,” he adds. “We’re working with a crystalline semiconductorcalled rubrene, which is an organic, carbon-based material that has performance factors, such as charge-carrier mobility, surpassing those measured in amorphous silicon. Organic semiconductors are an interesting alternative to silicon because their properties can be tuned to make them easily processed, allowing them to coat a variety of surfaces, including soft substrates at relatively low temperatures. As a result, devices based on organic semiconductors are projected to be cheaper since they do not require high temperatures, clean rooms and expensive processing steps like silicon does.”

Until now, Reyes-Martinez notes, most researchers have focused on controlling the detrimental effects of mechanical deformation to atransistor’s electrical properties. But in their series of systematic experiments, the UMass Amherst team discovered that mechanical deformations only decrease performance under certain conditions, and actually can enhance or have no effect in other instances.

“Our goal was not only to show these effects, but to explain and understand them. What we’ve done istake advantage of the ordered structure of ultra-thin organic single crystals of rubrene to fabricate high-perfomance, thin-film transistors,” he says. “This is the first time that anyone has carried out detailed fundamental work at these length scales with a single crystal.”

Though single crystals were once thought to be too fragile for flexible applications, the UMass Amherst team found that crystals ranging in thickness from about 150 nanometers to 1 micrometer were thin enough to be wrinkled and applied to any elastomer substrate. Reyes-Martinez also notes, “Our experiments are especially important because they help scientists working on flexible electronic devices to determine performance limitations of new materials under extreme mechanical deformations, such as when electronic devices conform to skin.”

They developed an analytical model based on plate bending theoryto quantifythe different local strains imposed on the transistor structure by the wrinkle deformations. Using their model they are able to predict how different deformations modulate charge mobility, which no one had quantified before, Reyes-Martinez notes.

These contributions “represent a significant step forward in structure-function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices,” the authors point out.

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

Rubrene crystal field-effect mobility modulation via conducting channel wrinkling by Marcos A. Reyes-Martinez, Alfred J. Crosby,  & Alejandro L. Briseno. Nature Communications 6, Article number: 6948 doi:10.1038/ncomms7948 Published 05 May 2015

This is an open access paper.

Hyper stretchable nanogenerator

There’s a lot of talk about flexibility, stretchability and bendability in electronics and the latest is coming from Korea. An April 13, 2015 Korea Advanced Institute for Science and Technology (KAIST) news release on EurekAlert describes the situation and the Korean scientists’ most recent research into stretchable electronics,

A research team led by Professor Keon Jae Lee of the Department of Materials Science and Engineering at the Korea Advanced Institute of Science and Technology (KAIST) has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator.

Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly.

Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy.

Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.”

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

A Hyper-Stretchable Elastic-Composite Energy Harvester by Chang Kyu Jeong, Jinhwan Lee, Seungyong Han, Jungho Ryu, Geon-Tae Hwang, Dae Yong Park, Jung Hwan Park, Seung Seob Lee, Mynghwan Byun, Seung Hwan Ko, and Keon Jae Lee. Advanced Materials DOI: 10.1002/adma.201500367 30 March 2015Full

This paper is behind a paywall.

The researchers have prepared a short video (22 secs. and silent),

3D printing soft robots and flexible electronics with metal alloys

This research comes from Purdue University (Indiana, US) which seems to be on a publishing binge these days. From an April 7, 2015 news item on Nanowerk,

New research shows how inkjet-printing technology can be used to mass-produce electronic circuits made of liquid-metal alloys for “soft robots” and flexible electronics.

Elastic technologies could make possible a new class of pliable robots and stretchable garments that people might wear to interact with computers or for therapeutic purposes. However, new manufacturing techniques must be developed before soft machines become commercially feasible, said Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University.

“We want to create stretchable electronics that might be compatible with soft machines, such as robots that need to squeeze through small spaces, or wearable technologies that aren’t restrictive of motion,” she said. “Conductors made from liquid metal can stretch and deform without breaking.”

A new potential manufacturing approach focuses on harnessing inkjet printing to create devices made of liquid alloys.

“This process now allows us to print flexible and stretchable conductors onto anything, including elastic materials and fabrics,” Kramer said.

An April 7, 2015 Purdue University news release (also on EurekAlert) by Emil Venere, which originated the news item, expands on the theme,

A research paper about the method will appear on April 18 [2015] in the journal Advanced Materials. The paper generally introduces the method, called mechanically sintered gallium-indium nanoparticles, and describes research leading up to the project. It was authored by postdoctoral researcher John William Boley, graduate student Edward L. White and Kramer.

A printable ink is made by dispersing the liquid metal in a non-metallic solvent using ultrasound, which breaks up the bulk liquid metal into nanoparticles. This nanoparticle-filled ink is compatible with inkjet printing.

“Liquid metal in its native form is not inkjet-able,” Kramer said. “So what we do is create liquid metal nanoparticles that are small enough to pass through an inkjet nozzle. Sonicating liquid metal in a carrier solvent, such as ethanol, both creates the nanoparticles and disperses them in the solvent. Then we can print the ink onto any substrate. The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface.”

After printing, the nanoparticles must be rejoined by applying light pressure, which renders the material conductive. This step is necessary because the liquid-metal nanoparticles are initially coated with oxidized gallium, which acts as a skin that prevents electrical conductivity.

“But it’s a fragile skin, so when you apply pressure it breaks the skin and everything coalesces into one uniform film,” Kramer said. “We can do this either by stamping or by dragging something across the surface, such as the sharp edge of a silicon tip.”

The approach makes it possible to select which portions to activate depending on particular designs, suggesting that a blank film might be manufactured for a multitude of potential applications.

“We selectively activate what electronics we want to turn on by applying pressure to just those areas,” said Kramer, who this year was awarded an Early Career Development award from the National Science Foundation, which supports research to determine how to best develop the liquid-metal ink.

The process could make it possible to rapidly mass-produce large quantities of the film.

Future research will explore how the interaction between the ink and the surface being printed on might be conducive to the production of specific types of devices.

“For example, how do the nanoparticles orient themselves on hydrophobic versus hydrophilic surfaces? How can we formulate the ink and exploit its interaction with a surface to enable self-assembly of the particles?” she said.

The researchers also will study and model how individual particles rupture when pressure is applied, providing information that could allow the manufacture of ultrathin traces and new types of sensors.

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

Nanoparticles: Mechanically Sintered Gallium–Indium Nanoparticles by John William Boley, Edward L. White and Rebecca K. Kramer. Advanced Materials Volume 27, Issue 14, page 2270, April 8, 2015 DOI: 10.1002/adma.201570094 Article first published online: 7 APR 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Think of your skin as a smartphone

A March 5, 2015 news item on Azonano highlights work on flexible, transparent electronics designed to adhere to your skin,

Someone wearing a smartwatch can look at a calendar or receive e-mails without having to reach further than their wrist. However, the interaction area offered by the watch face is both fixed and small, making it difficult to actually hit individual buttons with adequate precision. A method currently being developed by a team of computer scientists from Saarbrücken in collaboration with researchers from Carnegie Mellon University in the USA may provide a solution to this problem. They have developed touch-sensitive stickers made from flexible silicone and electrically conducting sensors that can be worn on the skin.

Here’s what the sticker looks like,

Caption: The stickers are skin-friendly and are attached to the skin with a biocompatible, medical-grade adhesive. Credit: Oliver Dietze

Caption: The stickers are skin-friendly and are attached to the skin with a biocompatible, medical-grade adhesive. Credit: Oliver Dietze Courtesy: Saarland University

A March 4, 2015 University of Saarland press release on EurekAlert, which originated the news item, expands on the theme on connecting technology to the body,

… The stickers can act as an input space that receives and executes commands and thus controls mobile devices. Depending on the type of skin sticker used, applying pressure to the sticker could, for example, answer an incoming call or adjust the volume of a music player. ‘The stickers allow us to enlarge the input space accessible to the user as they can be attached practically anywhere on the body,’ explains Martin Weigel, a PhD student in the team led by Jürgen Steimle at the Cluster of Excellence at Saarland University. The ‘iSkin’ approach enables the human body to become more closely connected to technology. [emphasis mine]

Users can also design their iSkin patches on a computer beforehand to suit their individual tastes. ‘A simple graphics program is all you need,’ says Weigel. One sticker, for instance, is based on musical notation, another is circular in shape like an LP. The silicone used to fabricate the sensor patches makes them flexible and stretchable. ‘This makes them easier to use in an everyday environment. The music player can simply be rolled up and put in a pocket,’ explains Jürgen Steimle, who heads the ‘Embodied Interaction Group’ in which Weigel is doing his research. ‘They are also skin-friendly, as they are attached to the skin with a biocompatible, medical-grade adhesive. Users can therefore decide where they want to position the sensor patch and how long they want to wear it.’

In addition to controlling music or phone calls, the iSkin technology could be used for many other applications. For example, a keyboard sticker could be used to type and send messages. Currently the sensor stickers are connected via cable to a computer system. According to Steimle, in-built microchips may in future allow the skin-worn sensor patches to communicate wirelessly with other mobile devices.

The publication about ‘iSkin’ won the ‘Best Paper Award’ at the SIGCHI conference, which ranks among the most important conferences within the research area of human computer interaction. The researchers will present their project at the SIGCHI conference in April [2015] in Seoul, Korea, and beforehand at the computer expo Cebit, which takes place from the 16th until the 20th of March [2015] in Hannover (hall 9, booth E13).

Hopefully, you’ll have a chance to catch researchers’ presentation at the SIGCHI or Cebit events.

That quote about enabling “the human body to become more closely connected to technology” reminds me of a tag (machine/flesh) I created to categorize research of this nature. I explained the idea being explored in a May 9, 2012 posting titled: Everything becomes part machine,

Machine/flesh. That’s what I’ve taken to calling this process of integrating machinery into our and, as I newly realized, other animals’ flesh.

I think my latest previous post on this topic was a Jan. 10, 2014 post titled: Chemistry of Cyborgs: review of the state of the art by German researchers.

Flexible electronics and Inorganic-based Laser Lift-off (ILLO) in Korea

Korean scientists are trying to make the process of creating flexible electronics easier according to a Nov. 25, 2014 news item on ScienceDaily,

Flexible electronics have been touted as the next generation in electronics in various areas, ranging from consumer electronics to bio-integrated medical devices. In spite of their merits, insufficient performance of organic materials arising from inherent material properties and processing limitations in scalability have posed big challenges to developing all-in-one flexible electronics systems in which display, processor, memory, and energy devices are integrated. The high temperature processes, essential for high performance electronic devices, have severely restricted the development of flexible electronics because of the fundamental thermal instabilities of polymer materials.

A research team headed by Professor Keon Jae Lee of the Department of Materials Science and Engineering at KAIST provides an easier methodology to realize high performance flexible electronics by using the Inorganic-based Laser Lift-off (ILLO).

The process is described in a Nov. 26, 2014 KAIST news release on ResearchSEA, which originated the news item (despite the confusion of the date, probably due to timezone differentials), provides more detail about the technique for ILLO,

The ILLO process involves depositing a laser-reactive exfoliation layer on rigid substrates, and then fabricating ultrathin inorganic electronic devices, e.g., high density crossbar memristive memory on top of the exfoliation layer. By laser irradiation through the back of the substrate, only the ultrathin inorganic device layers are exfoliated from the substrate as a result of the reaction between laser and exfoliation layer, and then subsequently transferred onto any kind of receiver substrate such as plastic, paper, and even fabric.

This ILLO process can enable not only nanoscale processes for high density flexible devices but also the high temperature process that was previously difficult to achieve on plastic substrates. The transferred device successfully demonstrates fully-functional random access memory operation on flexible substrates even under severe bending.

Professor Lee said, “By selecting an optimized set of inorganic exfoliation layer and substrate, a nanoscale process at a high temperature of over 1000 °C can be utilized for high performance flexible electronics. The ILLO process can be applied to diverse flexible electronics, such as driving circuits for displays and inorganic-based energy devices such as battery, solar cell, and self-powered devices that require high temperature processes.”

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

Flexible Crossbar-Structured Resistive Memory Arrays on Plastic Substrates via Inorganic-Based Laser Lift-Off by Seungjun Kim, Jung Hwan Son, Seung Hyun Lee, Byoung Kuk You, Kwi-Il Park, Hwan Keon Lee, Myunghwan Byun and Keon Jae Lee. Advanced Materials Volume 26, Issue 44, pages 7480–7487, November 26, 2014 Article first published online: 8 SEP 2014 DOI: 10.1002/adma.201402472

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Here’s an image the researchers have made available,

This photo shows the flexible RRAM device on a plastic substrate. Courtesy: KAIST

This photo shows the flexible RRAM device on a plastic substrate. Courtesy: KAIST

Finally, the research paper is behind a paywall.

Stretchable carbon nanotubes as supercapacitors

This Nov. 25, 2013 news item on phys.org was a bit of a walk down memory lane for me,

A mobile telephone display for your jacket sleeve, ECG probes for your workout clothes—wearable electronics are in demand. In order for textiles with built-in electronics to function over longer periods of time, all of the components need to be flexible and stretchable. In the journal Angewandte Chemie, Chinese researchers have now introduced a new type of supercapacitor that fulfills this requirement. Its components are fiber-shaped and based on carbon nanotubes.

The reference to a mobile telephone display on a jacket sleeve brought back memories of Nokia’s proposed Morph device,, from my Aug. 3, 2011 posting,

For anyone who’s not familiar with the Morph, it’s an idea that Nokia and the University of Cambridge’s Nanoscience Centre have been working on for the last few years. Originally announced as a type of flexible phone that you could wrap around your wrist, the Morph is now called a concept.  …

At the time I was writing about exploring the use of graphene to enable the morph (flexible phone). This latest work from China is focused on carbon nanotubes,. The Angewandte Chemie Nov. 25, 2013 press release, which originated the news item on phys.org,  provides more details,

For electronic devices to be incorporated into textiles or plastic films, their components must be stretchable. This is true for LEDS, solar cells, transistors, circuits, and batteries—as well as for the supercapacitors often used for static random access memory (SRAM). SRAM is often used as a cache in processors or for local storage on chips, as well as in devices that must maintain their data over several years with no source of power.

Previous stretchable electronic components have generally been produced in a conventional planar format, which has been an obstacle to their further development for use in small, lightweight, wearable electronics. Initial attempts to produce supercapacitors in the form of wires or fibers produced flexible—but not stretchable—components. However, stretchability is a required feature for a number of applications. For example, electronic textiles would easily tear if they were not stretchable.

A team led by Huisheng Peng at Fudan University has now developed a new family of highly stretchable, fiber-shaped, high-performance supercapacitors. The devices are made by a winding process with an elastic fiber at the core. The fiber is coated with an electrolyte gel and a thin layer of carbon nanotubes is wound around it like a sheet of paper. This is followed by a second layer of electrolyte gel, another layer of carbon nanotube wrap, and a final layer of electrolyte gel.

The delicate “sheets” of carbon nanotubes are produced by chemical vapor deposition and a spinning process. In the sheets this method produces, the tiny tubes are aligned in parallel. These types of layers display a remarkable combination of properties: They are highly flexible, tear-resistant, conductive, and thermally and mechanically stable. In the wound fibers, the two layers of carbon nanotubes act as electrodes. The electrolyte gel separates the electrodes from each other while stabilizing the nanotubes during stretching so that their alignment is maintained. This results in supercapacitor fibers with a high capacity that is maintained after many stretching cycles.

For the curious, here’s a link to and a citation for the paper,

A Highly Stretchable, Fiber-Shaped Supercapacitor by Zhibin Yang, Jue Deng, Xuli Chen, Jing Ren, and Prof. Huisheng Peng. Angewandte Chemie International Edition
Early View (Online Version of Record published before inclusion in an issue)Article first published online: 8 NOV 2013 DOI: 10.1002/anie.201307619

Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Bend it, twist it, any way you want to—a foldable lithium-ion battery

Feb. 26, 2013 news item on ScienceDaily features an extraordinary lithium-ion battery,

Northwestern University’s Yonggang Huang and the University of Illinois’ John A. Rogers are the first to demonstrate a stretchable lithium-ion battery — a flexible device capable of powering their innovative stretchable electronics.

No longer needing to be connected by a cord to an electrical outlet, the stretchable electronic devices now could be used anywhere, including inside the human body. The implantable electronics could monitor anything from brain waves to heart activity, succeeding where flat, rigid batteries would fail.

Huang and Rogers have demonstrated a battery that continues to work — powering a commercial light-emitting diode (LED) — even when stretched, folded, twisted and mounted on a human elbow. The battery can work for eight to nine hours before it needs recharging, which can be done wirelessly.

The researchers at Northwestern have produced a video where they demonstrate the battery’s ‘stretchability’,

The Northwestern University Feb. 26, 2013 news release by Megan Fellman, which originated the news item, offers this detail,

“We start with a lot of battery components side by side in a very small space, and we connect them with tightly packed, long wavy lines,” said Huang, a corresponding author of the paper. “These wires provide the flexibility. When we stretch the battery, the wavy interconnecting lines unfurl, much like yarn unspooling. And we can stretch the device a great deal and still have a working battery.”

The power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size, but the flexible battery can stretch up to 300 percent of its original size and still function.

Huang and Rogers have been working together for the last six years on stretchable electronics, and designing a cordless power supply has been a major challenge. Now they have solved the problem with their clever “space filling technique,” which delivers a small, high-powered battery.

For their stretchable electronic circuits, the two developed “pop-up” technology that allows circuits to bend, stretch and twist. They created an array of tiny circuit elements connected by metal wire “pop-up bridges.” When the array is stretched, the wires — not the rigid circuits — pop up.

This approach works for circuits but not for a stretchable battery. A lot of space is needed in between components for the “pop-up” interconnect to work. Circuits can be spaced out enough in an array, but battery components must be packed tightly to produce a powerful but small battery. There is not enough space between battery components for the “pop-up” technology to work.

Huang’s design solution is to use metal wire interconnects that are long, wavy lines, filling the small space between battery components. (The power travels through the interconnects.)

The unique mechanism is a “spring within a spring”: The line connecting the components is a large “S” shape and within that “S” are many smaller “S’s.” When the battery is stretched, the large “S” first stretches out and disappears, leaving a line of small squiggles. The stretching continues, with the small squiggles disappearing as the interconnect between electrodes becomes taut.

“We call this ordered unraveling,” Huang said. “And this is how we can produce a battery that stretches up to 300 percent of its original size.”

The stretching process is reversible, and the battery can be recharged wirelessly. The battery’s design allows for the integration of stretchable, inductive coils to enable charging through an external source but without the need for a physical connection.

Huang, Rogers and their teams found the battery capable of 20 cycles of recharging with little loss in capacity. The system they report in the paper consists of a square array of 100 electrode disks, electrically connected in parallel.

I’d like to see this battery actually powering a device even though the stretching is quite alluring in its way. For those who are interested here’s a citation and a link to the research paper,

Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems by Sheng Xu, Yihui Zhang, Jiung Cho, Juhwan Lee, Xian Huang, Lin Jia, Jonathan A. Fan, Yewang Su, Jessica Su, Huigang Zhang, Huanyu Cheng, Bingwei Lu,           Cunjiang Yu, Chi Chuang, Tae-il Kim, Taeseup Song, Kazuyo Shigeta, Sen Kang, Canan Dagdeviren, Ivan Petrov  et al.   Nature Communications 4, Article number: 1543 doi: 10.1038/ncomms2553  Published 26 February 2013

The article is behind a paywall.

Transparent image sensor has no electronics or internal components

This shows the world's first flexible and completely transparent image sensor. The plastic film is coated with fluorescent particles. Credit: Optics Express.

This shows the world’s first flexible and completely transparent image sensor. The plastic film is coated with fluorescent particles. Credit: Optics Express.

Stunning isn’t it? The work is from researchers at the Johannes Kepler University Linz in Austria and is featured in an article being published in Optics Express. From the Feb. 20, 2013 news release about the Optics Express article on EurekAlert,

Digital cameras, medical scanners, and other imaging technologies have advanced considerably during the past decade. Continuing this pace of innovation, an Austrian research team has developed an entirely new way of capturing images based on a flat, flexible, transparent, and potentially disposable polymer sheet. The team describes their new device and its possible applications in a paper published today in the Optical Society’s (OSA) open-access journal Optics Express.

The new imager, which resembles a flexible plastic film, uses fluorescent particles to capture incoming light and channel a portion of it to an array of sensors framing the sheet. With no electronics or internal components, the imager’s elegant design makes it ideal for a new breed of imaging technologies, including user interface devices that can respond not to a touch, but merely to a simple gesture.

The news release goes on to describe the technology,

The sensor is based on a polymer film known as a luminescent concentrator (LC), which is suffused with tiny fluorescent particles that absorb a very specific wavelength (blue light for example) and then reemit it at a longer wavelength (green light for example). Some of the reemitted fluorescent light is scattered out of the imager, but a portion of it travels throughout the interior of the film to the outer edges, where arrays of optical sensors (similar to 1-D pinhole cameras) capture the light. A computer then combines the signals to create a gray-scale image. “With fluorescence, a portion of the light that is reemitted actually stays inside the film,” says Bimber. [Oliver Bimber of the Johannes Kepler University Linz in Austria, co-author of the Optics Express paper] “This is the basic principle of our sensor.”

For the luminescent concentrator to work as an imager, Bimber and his colleagues had to determine precisely where light was falling across the entire surface of the film. This was the major technical challenge because the polymer sheet cannot be divided into individual pixels like the CCD camera inside a smartphone. Instead, fluorescent light from all points across its surface travels to all the edge sensors. Calculating where each bit of light entered the imager would be like determining where along a subway line a passenger got on after the train reached its final destination and all the passengers exited at once.

The solution came from the phenomenon of light attenuation, or dimming, as it travels through the polymer. The longer it travels, the dimmer it becomes. So by measuring the relative brightness of light reaching the sensor array, it was possible to calculate where the light entered the film. This same principle has already been employed in an input device that tracks the location of a single laser point on a screen.

The researchers were able to scale up this basic principle by measuring how much light arrives from every direction at each position on the image sensor at the film’s edge. They could then reconstruct the image by using a technique similar to X-ray computed tomography, more commonly known as a CT scan.

“In CT technology, it’s impossible to reconstruct an image from a single measurement of X-ray attenuation along one scanning direction alone,” says Bimber. “With a multiple of these measurements taken at different positions and directions, however, this becomes possible. Our system works in the same way, but where CT uses X-rays, our technique uses visible light.”

Currently, the resolution from this image sensor is low (32×32 pixels with the first prototypes). The main reason for this is the limited signal-to-noise ratio of the low-cost photodiodes being used. The researchers are planning better prototypes that cool the photodiodes to achieve a higher signal-to-noise ratio.

By applying advanced sampling techniques, the researchers can already enhance the resolution by reconstructing multiple images at different positions on the film. These positions differ by less than a single pixel (as determined by the final image, not the polymer itself). By having multiple of these slightly different images reconstructed, it’s possible to create a higher resolution image. “This does not require better photodiodes,” notes Bimber, “and does not make the sensor significantly slower. The more images we combine, the higher the final resolution is, up to a certain limit.”

The researchers discuss applications,

The main application the researchers envision for this new technology is in touch-free, transparent user interfaces that could seamlessly overlay a television or other display technology. This would give computer operators or video-game players full gesture control without the need for cameras or other external motion-tracking devices. The polymer sheet could also be wrapped around objects to provide them with sensor capabilities. Since the material is transparent, it’s also possible to use multiple layers that each fluoresce at different wavelengths to capture color images.

The researchers also are considering attaching their new sensor in front of a regular, high-resolution CCD sensor. This would allow recording of two images at the same time at two different exposures. “Combining both would give us a high-resolution image with less overexposed or underexposed regions if scenes with a high dynamic range or contrast are captured,” Bimber speculates. He also notes that the polymer sheet portion of the device is relatively inexpensive and therefore disposable. “I think there are many applications for this sensor that we are not yet aware of,” he concludes.

Here’s a citation and a link,

“Towards a transparent, flexible, scalable and disposable image sensor using thin-film luminescent concentrators,” A. Koppelhuber and O. Bimber, Optics Express, Vol. 21, Issue 4, pp. 4796-4810 (2013) (link: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-4-4796).