Category Archives: electronics

How memristors retain information without a power source? A mystery solved

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A September 10, 2024 news item on ScienceDaily provides a technical explanation of how memristors, without a power source, can retain information,

Phase separation, when molecules part like oil and water, works alongside oxygen diffusion to help memristors — electrical components that store information using electrical resistance — retain information even after the power is shut off, according to a University of Michigan led study recently published in Matter.

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A September 11, 2024 University of Michigan press release (also on EurekAltert but published September 10, 2024), which originated the news item, delves further into the research,

Up to this point, explanations have not fully grasped how memristors retain information without a power source, known as nonvolatile memory, because models and experiments do not match up.

“While experiments have shown devices can retain information for over 10 years, the models used in the community show that information can only be retained for a few hours,” said Jingxian Li, U-M doctoral graduate of materials science and engineering and first author of the study.

To better understand the underlying phenomenon driving nonvolatile memristor memory, the researchers focused on a device known as resistive random access memory or RRAM, an alternative to the volatile RAM used in classical computing, and are particularly promising for energy-efficient artificial intelligence applications. 

The specific RRAM studied, a filament-type valence change memory (VCM), sandwiches an insulating tantalum oxide layer between two platinum electrodes. When a certain voltage is applied to the platinum electrodes, a conductive filament forms a tantalum ion bridge passing through the insulator to the electrodes, which allows electricity to flow, putting the cell in a low resistance state representing a “1” in binary code. If a different voltage is applied, the filament is dissolved as returning oxygen atoms react with the tantalum ions, “rusting” the conductive bridge and returning to a high resistance state, representing a binary code of “0”. 

It was once thought that RRAM retains information over time because oxygen is too slow to diffuse back. However, a series of experiments revealed that previous models have neglected the role of phase separation. 

“In these devices, oxygen ions prefer to be away from the filament and will never diffuse back, even after an indefinite period of time. This process is analogous to how a mixture of water and oil will not mix, no matter how much time we wait, because they have lower energy in a de-mixed state,” said Yiyang Li, U-M assistant professor of materials science and engineering and senior author of the study.

To test retention time, the researchers sped up experiments by increasing the temperature. One hour at 250°C is equivalent to about 100 years at 85°C—the typical temperature of a computer chip.

Using the extremely high-resolution imaging of atomic force microscopy, the researchers imaged filaments, which measure only about five nanometers or 20 atoms wide, forming within the one micron wide RRAM device.  

“We were surprised that we could find the filament in the device. It’s like finding a needle in a haystack,” Li said. 

The research team found that different sized filaments yielded different retention behavior. Filaments smaller than about 5 nanometers dissolved over time, whereas filaments larger than 5 nanometers strengthened over time. The size-based difference cannot be explained by diffusion alone.

Together, experimental results and models incorporating thermodynamic principles showed the formation and stability of conductive filaments depend on phase separation. 

The research team leveraged phase separation to extend memory retention from one day to well over 10 years in a rad-hard memory chip—a memory device built to withstand radiation exposure for use in space exploration. 

Other applications include in-memory computing for more energy efficient AI applications or memory devices for electronic skin—a stretchable electronic interface designed to mimic the sensory capabilities of human skin. Also known as e-skin, this material could be used to provide sensory feedback to prosthetic limbs, create new wearable fitness trackers or help robots develop tactile sensing for delicate tasks.

“We hope that our findings can inspire new ways to use phase separation to create information storage devices,” Li said.

Researchers at Ford Research, Dearborn; Oak Ridge National Laboratory; University at Albany; NY CREATES; Sandia National Laboratories; and Arizona State University, Tempe contributed to this study.

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

Thermodynamic origin of nonvolatility in resistive memory by Jingxian Li, Anirudh Appachar, Sabrina L. Peczonczyk, Elisa T. Harrison, Anton V. Ievlev, Ryan Hood, Dongjae Shin, Sangmin Yoo, Brianna Roest, Kai Sun, Karsten Beckmann, Olya Popova, Tony Chiang, William S. Wahby, Robin B. Jacobs-Godrim, Matthew J. Marinella, Petro Maksymovych, John T. Heron, Nathaniel Cady, Wei D. Lu, Suhas Kumar, A. Alec Talin, Wenhao Sun, Yiyang Li. Matter DOI: https://doi.org/10.1016/j.matt.2024.07.018 Published online: August 26, 2024

This paper is behind a paywall.

Fungus-controlled robots

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Where robots are concerned, mushrooms and other fungi aren’t usually considered as part of the equipment but one would be wrong according to a September 4, 2024 news item on ScienceDaily,

Building a robot takes time, technical skill, the right materials — and sometimes, a little fungus.

In creating a pair of new robots, Cornell University researchers cultivated an unlikely component, one found on the forest floor: fungal mycelia.

By harnessing mycelia’s innate electrical signals, the researchers discovered a new way of controlling “biohybrid” robots that can potentially react to their environment better than their purely synthetic counterparts.

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An August 28, 2024 Cornell University news release (also on EurekAlert but published August 29, 2024) by David Nutt, which originated the news item, describes this (I’m tempted to call it, revolutionary) new technique, Note: Links have been removed.

“This paper is the first of many that will use the fungal kingdom to provide environmental sensing and command signals to robots to improve their levels of autonomy,” Shepherd [Rob Shepherd, professor of mechanical and aerospace engineering at Cornell University] said. “By growing mycelium into the electronics of a robot, we were able to allow the biohybrid machine to sense and respond to the environment. In this case we used light as the input, but in the future it will be chemical. The potential for future robots could be to sense soil chemistry in row crops and decide when to add more fertilizer, for example, perhaps mitigating downstream effects of agriculture like harmful algal blooms.”

In designing the robots of tomorrow, engineers have taken many of their cues from the animal kingdom, with machines that mimic the way living creatures move, sense their environment and even regulate their internal temperature through perspiration. Some robots have incorporated living material, such as cells from muscle tissue, but those complex biological systems are difficult to keep healthy and functional. It’s not always easy, after all, to keep a robot alive.

Mycelia are the underground vegetative part of mushrooms, and they have a number of advantages. They can grow in harsh conditions. They also have the ability to sense chemical and biological signals and respond to multiple inputs.

“If you think about a synthetic system – let’s say, any passive sensor – we just use it for one purpose. But living systems respond to touch, they respond to light, they respond to heat, they respond to even some unknowns, like signals,” Mishra [Anand Mishra, a research associate in the Organic Robotics Lab at Cornell University] said. “That’s why we think, OK, if you wanted to build future robots, how can they work in an unexpected environment? We can leverage these living systems, and any unknown input comes in, the robot will respond to that.”

However, finding a way to integrate mushrooms and robots requires more than just tech savvy and a green thumb.

“You have to have a background in mechanical engineering, electronics, some mycology, some neurobiology, some kind of signal processing,” Mishra said. “All these fields come together to build this kind of system.”

Mishra collaborated with a range of interdisciplinary researchers. He consulted with Bruce Johnson, senior research associate in neurobiology and behavior, and learned how to record the electrical signals that are carried in the neuron-like ionic channels in the mycelia membrane. Kathie Hodge, associate professor of plant pathology and plant-microbe biology in the School of Integrative Plant Science in the College of Agriculture and Life Sciences, taught Mishra how to grow clean mycelia cultures, because contamination turns out to be quite a challenge when you are sticking electrodes in fungus.

The system Mishra developed consists of an electrical interface that blocks out vibration and electromagnetic interference and accurately records and processes the mycelia’s electrophysiological activity in real time, and a controller inspired by central pattern generators – a kind of neural circuit. Essentially, the system reads the raw electrical signal, processes it and identifies the mycelia’s rhythmic spikes, then converts that information into a digital control signal, which is sent to the robot’s actuators.

Two biohybrid robots were built: a soft robot shaped like a spider and a wheeled bot.

The robots completed three experiments. In the first, the robots walked and rolled, respectively, as a response to the natural continuous spikes in the mycelia’s signal. Then the researchers stimulated the robots with ultraviolet light, which caused them to change their gaits, demonstrating mycelia’s ability to react to their environment. In the third scenario, the researchers were able to override the mycelia’s native signal entirely.

The implications go far beyond the fields of robotics and fungi.

“This kind of project is not just about controlling a robot,” Mishra said. “It is also about creating a true connection with the living system. Because once you hear the signal, you also understand what’s going on. Maybe that signal is coming from some kind of stresses. So you’re seeing the physical response, because those signals we can’t visualize, but the robot is making a visualization.”

Co-authors include Johnson, Hodge, Jaeseok Kim with the University of Florence, Italy, and undergraduate research assistant Hannah Baghdadi.

The research was supported by the National Science Foundation (NSF) CROPPS Science and Technology Center; the U.S. Department of Agriculture’s National Institute of Food and Agriculture; and the NSF Signal in Soil program.

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

Sensorimotor control of robots mediated by electrophysiological measurements of fungal mycelia by Anand Kumar Mishra, Jaeseok Kim, Hannah Baghdadi, Bruce R. Johnson, Kathie T. Hodge, and Robert F. Shepherd. Science Robotics 28 Aug 2024 Vol 9, Issue 93 DOI: 10.1126/scirobotics.adk8019

This paper is behind a paywall.

Early morning run could power your electrical wearables

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I don’t think this is going to be happening tomorrow but here’s a relatively recent news item on ScienceDaily from August 22, 2024 about bioenergy harvesting and wearable technology,

Your early morning run could soon help harvest enough electricity to power your wearable devices, thanks to new nanotechnology developed at the University of Surrey [UK].

Surrey’s Advanced Technology Institute (ATI) has developed highly energy-efficient, flexible nanogenerators, which demonstrate a 140-fold increase in power density when compared to conventional nanogenerators. ATI researchers believe that this development could pave the way for nano-devices that are as efficient as today’s solar cells.

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An August 21, 2024 University of Surrey press release (also on EurekAlert but published August 22, 2024), which originated the news item, provides more information about the research,

Surrey’s devices can convert small amounts of everyday mechanical energy, like motion, into a significantly higher amount of electrical power, similar to how an amplifier boosts sound in an electronic system. For instance, if a traditional nanogenerator produces 10 milliwatts of power, this new technology could increase that output to over 1,000 milliwatts, making it suitable for energy harvesting in various everyday applications. 

ATI’s nanogenerator works like a relay team – instead of one electrode (the runner) passing energy (charge) by itself. Each runner collects a baton (charge), adds more and then passes all batons to the next runner, boosting the overall energy that is collected in a process called the charge regeneration effect. 

Lead author of the study from the University of Surrey, Md Delowar Hussain, said: 

“The dream of nanogenerators is to capture and use energy from everyday movements, like your morning run, mechanical vibrations, ocean waves or opening a door. The key innovation with our nanogenerator is that we’ve fine-tuned the technology with 34 tiny energy collectors using a laser technique that can be scaled up for manufacture to increase energy efficiency further. 

“What’s really exciting is that our little device with high energy harvesting density could one day rival the power of solar panels and could be used to run anything from self-powered sensors to smart home systems that run without ever needing a battery change.” 

The device is a triboelectric nanogenerator (TENG) – a device that can capture and turn the energy from simple, everyday movements into electricity. They work by using materials that become electrically charged when they come into contact and then separate – similar to when you rub a balloon on your hair, and it sticks due to static electricity.  

Dr Bhaskar Dudem, co-author of the study from the University of Surrey, said:  

“We are soon going to launch a company focused on self-powered, non-invasive healthcare sensors using triboelectric technology. Innovations like these will enable us to drive new spin-out activities in sustainable health tech, improve sensitivity, and emphasize industrial scalability.” 

Professor Ravi Silva, co-author of the study and Director of the Advanced Technology Institute at the University of Surrey, said: 

“With the ever-increasing technology around us, it is predicted that we will have over 50 billion Internet of Things (IoT) devices in the next few years that will need energy to be powered. Local green energy solutions are needed, and this could be a convenient wireless technology that harnesses energy from any mechanical movements to power small devices. It offers an opportunity for the scientific and engineering community to find innovative and sustainable solutions to global challenges.” 

“We are incredibly excited about the potential of these nanogenerators to transform how we think about energy. You could also imagine these devices being used in IoT-based self-powered smart systems like autonomous wireless operations, security monitoring, and smart home systems, or even for supporting dementia patients, an area in which the University of Surrey has great expertise.” 

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

Exploring charge regeneration effect in interdigitated array electrodes-based TENGs for a more than 100-fold enhanced power density by Md Delowar Hussain, Bhaskar Dudem, Dimitar I. Kutsarov, S. Ravi P. Silva. Nano Energy Volume 130, November 2024, 110112 DOI: https://doi.org/10.1016/j.nanoen.2024.110112 Available online 13 August 2024, Version of Record 21 August 2024

This paper is open access under a Creative Commons license.

Multifunctional smart windows that lower indoor temperatures without consuming power and can generate electricity from raindrops

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Caption: Figure 1: The main functions of the multifunctional smart windows for implementing Plus Energy (transparent radiative cooling, power generation, and fog and frost removal technology). Credit: © Seoul National University College of Engineering

I’m always a sucker for a ‘smart window’ story and this one from Korea with its reference to harvesting energy from raindrops seems particularly intriguing. From an August 13, 2024 Seoul National University (SNU) press release, also on EurekAlert but published August 22, 2024,

■ Research Necessity

o Recently, with the significant increase in cooling demand due to global warming, a vast amount of energy is being consumed for heat management inside buildings. Existing windows, which have a high solar absorption rate and low reflectance, lead to considerable energy loss. Therefore, energy-saving windows are emerging as a practical solution to global challenges such as responding to climate change and ensuring energy sustainability. These windows not only provide optimal thermal comfort to occupants but also contribute to economic development by reducing dependence on conventional cooling systems.

o For windows to effectively save energy in buildings, it is necessary to adopt energy-efficient cooling technology (Zero Energy) and further ensure energy harvesting methods (Plus Energy) that guarantee sustainable power supply. Additionally, windows must maintain high transparency, which is their fundamental function, even on cold or foggy days.

■ Research Achievements / Expected Effects

o The multifunctional smart windows developed in this research demonstrate their effectiveness as next-generation energy-saving devices by implementing three main functions.

o First, they provide radiative cooling that lowers indoor temperature on sunny days without energy input. Second, they generate electricity using raindrops on rainy days. Third, they implement a transparent heater function to quickly remove frost from the windows on cold days.

■ Research Details 

□ Research Content Overview

o The research team led by Professor Seung Hwan Ko from the Department of Mechanical Engineering at Seoul National University has developed “multifunctional smart window technology” that lowers indoor temperatures without electricity consumption and generates power using the frictional electricity from raindrops. This research is significant in that it pioneers new possibilities for Plus Energy technology, surpassing Zero Energy to contribute to improving energy self-sufficiency in response to global warming.

□ Background

o Recently, implementing Plus Energy Buildings (PEBs) that surpass Zero Energy has become a key task for achieving energy self-sufficiency in buildings. Next-generation PEBs are buildings that go beyond minimizing energy loads and can autonomously produce energy. Buildings inherently consume a massive amount of energy for heat management, and with the rise in cooling demand due to global warming, energy usage has surged dramatically. Furthermore, existing windows with high solar absorption and low reflectivity result in substantial energy losses during cooling. Therefore, to realize economically efficient next-generation Plus Energy Buildings, it is necessary to develop multifunctional smart windows equipped with transparent cooling technology (Zero Energy-based) and further energy-harvesting technology (Plus Energy-based) that ensures sustainable power supply.
o To address these issues, researchers worldwide are focusing on the development of smart windows that maximize energy savings. Smart windows are often thought to adjust internal temperatures by changing color to control sunlight. However, this method has limitations since the windows become opaque during the cooling process, thus failing to maintain high transparency, which is the window’s primary function.

□ Key Research Methods

o The research team is actively working on developing new technologies that improve energy efficiency while preserving the transparency of windows. As part of this effort, Professor Ko’s research team developed a Zero Energy-based “transparent radiative cooling technology” that maintains transparency while enabling cooling without using electricity. Additionally, they developed energy-harvesting technology that produces electricity through the friction generated when raindrops contact the window surface, introducing a Plus Energy-based smart window technology that surpasses Zero Energy. The team also developed a transparent heater technology that quickly clears frost from windows on cold or foggy days, thereby implementing three functions—radiative cooling, power generation, and frost removal—simultaneously in a single device for the first time in the world.
o The research team achieved these three functionalities in a single device by fabricating windows with a layered structure of silver and ITO (Indium Tin Oxide), materials with excellent electrical conductivity and unique optical properties. First, the “transparent radiative cooling technology” minimizes the absorption of sunlight entering indoors while emitting radiant heat outdoors to lower the temperature. Unlike conventional air conditioning systems that use refrigerants, this radiative cooling technology offers cooling performance without consuming electrical energy. The research team focused on allowing only the visible light spectrum from sunlight to pass through the window while selectively reflecting near-infrared sunlight to lower indoor temperatures and maximize cooling. Second, the “frictional electricity-based power generation technology” generates electricity when raindrops contact the window surface on rainy days. For this purpose, an electrode material covering the window surface is necessary, and thanks to the excellent electrical conductivity of the layered silver and ITO structure, the smart window can generate electricity through frictional electricity. Lastly, through “Joule heating,” the transparent electrodes also serve as a heater that quickly removes frost or ice from the window, ensuring clear visibility on cold days. The multifunctional smart windows developed by the research team can provide transparent radiative cooling on sunny days, generate power on rainy days, and remove frost or ice on cold days.

□ Results

o The research team led by Professor Seung Hwan Ko confirmed that the smart windows they developed maintained a temperature approximately 7 degrees lower than regular windows in hot environments under direct sunlight. In an experiment simulating rainy conditions, the smart windows generated 8.3 W m-2 of power with just a single raindrop, while also clearing frost from the window twice as fast as regular windows through Joule heating, demonstrating both high performance and multifunctionality.

□ Expected Effects

o Professor Seung Hwan Ko stated, “This achievement of presenting next-generation smart window technology optimized for responding to the depletion of fossil fuels and global warming offers valuable insights into the technological advancements for Plus Energy buildings and the eco-friendly electric vehicle industry. Smart windows are expected to be applied across various industries because they address environmental pollution, reduce cooling energy, and overcome the limitations of conventional battery technologies through self-power generation.”

□ Achievements

o This research was supported by the Basic Science Research Program through the National Research Foundation of Korea, and it has gained global attention, being published in the October 2024 issue of the prestigious journal Nano Energy (Impact factor: 16.8, Top 5.3%) under the title: “Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities.”

o Meanwhile, Dr. Yeongju Jung, the lead author of this study, is currently conducting follow-up research at Professor Ko’s laboratory in the Department of Mechanical Engineering at Seoul National University and is preparing for a postdoctoral research fellowship abroad.

□ Introduction to the SNU College of Engineering

Seoul National University (SNU) founded in 1946 is the first national university in South Korea. The College of Engineering at SNU has worked tirelessly to achieve its goal of ‘fostering leaders for global industry and society.’ In 12 departments, 323 internationally recognized full-time professors lead the development of cutting-edge technology in South Korea and serving as a driving force for international development.

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

Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities by Yeongju Jung, Ji-Seok Kim, Junhyuk Bang, Seok Hwan Choi, Kangkyu Kwon, Min Jae Lee, Il-Kwon Oh, Jaeman Song, Jinwoo Lee, Seung Hwan Ko. Nano Energy DVolume 129, Part A, October 2024, 110004 DOI: https://doi.org/10.1016/j.nanoen.2024.110004 Available online 25 July 2024, Version of Record 25 July 2024

This paper is behind a paywall.

Converting body heat into electricity with smart fabric

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This bioenergy harvesting story is from the University of Waterloo (Ontario, Canada), where its researchers were part of an international collaboration. From an August 14, 2023 news item on ScienceDaily,

Imagine a coat that captures solar energy to keep you cozy on a chilly winter walk, or a shirt that can monitor your heart rate and temperature.Picture clothing athletes can wear to track their performance without the need for bulky battery packs.

University of Waterloo researchers have developed a smart fabric with these remarkable capabilities.

The fabric has the potential for energy harvesting, health monitoring, and movement tracking applications.

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An August 14, 2024 University of Waterloo news release (also on EurekAlert), which originated the news item, provides more information about the new fabric and the research team, Note: A link has been removed,

The new fabric developed by a Waterloo research team can convert body heat and solar energy into electricity, potentially enabling continuous operation with no need for an external power source. Different sensors monitoring temperature, stress, and more can be integrated into the material.

It can detect temperature changes and a range of other sensors to monitor pressure, chemical composition, and more. One promising application is smart face masks that can track breath temperature and rate and detect chemicals in breath to help identify viruses, lung cancer, and other conditions.

“We have developed a fabric material with multifunctional sensing capabilities and self-powering potential,” said Yuning Li, a professor in the Department of Chemical Engineering. “This innovation brings us closer to practical applications for smart fabrics.”

Unlike current wearable devices that often depend on external power sources or frequent recharging, this breakthrough research has created a novel fabric which is more stable, durable, and cost-effective than other fabrics on the market. 

This research, conducted in collaboration with Professor Chaoxia Wang and PhD student Jun Peng from the College of Textile Science and Engineering at Jiangnan University, showcases the potential of integrating advanced materials such as MXene and conductive polymers with cutting-edge textile technologies to advance smart fabrics for wearable technology.

Li, director of Waterloo’s Printable Electronic Materials Lab, highlighted the significance of this advancement, which is the latest in the university’s suite of technologies disrupting health boundaries.

“AI technology is evolving rapidly, offering sophisticated signal analysis for health monitoring, food and pharmaceutical storage, environmental monitoring, and more. However, this progress relies on extensive data collection, which conventional sensors, often bulky, heavy, and costly, cannot meet,” Li said. “Printed sensors, including those embedded in smart fabrics, are ideal for continuous data collection and monitoring. This new smart fabric is a step forward in making these applications practical.”

The next phase of research will focus on further enhancing the fabric’s performance and integrating it with electronic components in collaboration with electrical and computer engineers. Future developments may include a smartphone app to track and transmit data from the fabric to healthcare professionals, enabling real-time, non-invasive health monitoring and everyday use.

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

MXene-based thermoelectric fabric integrated with temperature and strain sensing for health monitoring by Jun Peng, Fangqing Ge, Weiyi Han, Tao Wu, Jinglei Tang, Yuning Li, Chaoxia Wang. Journal of Materials Science & Technology Volume 212, 20 March 2025, Pages 272-280

This paper is behind a paywall but you will be able to read snippets in a preview.

Connecting nerves to electronics with soft gold

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Gold nanowires that are tissue-like? That’s how this nanogold composite is described in a research paper from researchers at Linköping University (Sweden). Before getting to a link and citation for the paper, here’s an announcement about the work in an August 6, 2024 news item on ScienceDaily,

Gold does not readily lend itself to being turned into long, thin threads. But researchers at Linköping University in Sweden have now managed to create gold nanowires and develop soft electrodes that can be connected to the nervous system. The electrodes are soft as nerves, stretchable and electrically conductive, and are projected to last for a long time in the body.

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An August 6, 2024 Linköping University press release (also on EurekAlert), which originated the news item, provides context for the research,

Some people have a “heart of gold”, so why not “nerves of gold”? In the future, it may be possible to use this precious metal in soft interfaces to connect electronics to the nervous system for medical purposes. Such technology could be used to alleviate conditions such as epilepsy, Parkinson’s disease, paralysis or chronic pain. However, creating an interface where electronics can meet the brain or other parts of the nervous system poses special challenges.

“The classical conductors used in electronics are metals, which are very hard and rigid. The mechanical properties of the nervous system are more reminiscent of soft jelly. In order to get an accurate signal transmission, we need to get very close to the nerve fibres in question, but as the body is constantly in motion, achieving close contact between something that is hard and something that is soft and fragile becomes a problem”, says Klas Tybrandt, professor of materials science at the Laboratory of Organic Electronics at Linköping University, who led the research.

Researchers therefore want to create electrodes that have good conductivity as well as mechanical properties similar to the softness of the body. In recent years, several studies have shown that soft electrodes do not damage the tissue as much as hard electrodes may do. In the current study, published in the journal Small, a group of researchers at Linköping University have developed gold nanowires – a thousand times thinner than a hair – and embedded them in an elastic material to create soft microelectrodes.

“We’ve succeeded in making a new, better nanomaterial from gold nanowires in combination with a very soft silicone rubber. Getting these to work together has resulted in a conductor that has high electrical conductivity, is very soft and made of biocompatible materials that function with the body,” says Klas Tybrandt.

Silicone rubber is used in medical implants, such as breast implants. The soft electrodes also include gold and platinum, metals that are common in medical devices for clinical use. 
However, making long, narrow gold nanostructures is very difficult. This has so far been a major obstacle, but the researchers have now come up with a new way to manufacture gold nanowires. And they do it by using silver nanowires.

As silver has unique properties that make it a very good material to create the kind of nanowires that the researchers are after, it is used in some stretchable nanomaterials. The problem with silver is that it is chemically reactive. In the same way that silver cutlery will discolour over time when chemical reactions occur on the surface, silver in nanowires breaks down so that silver ions leak out. In a high enough concentration, silver ions can be toxic to us.

It was when Laura Seufert, a doctoral student in Klas Tybrandt’s research group, was working on finding a way to synthesize, or “grow”, gold nanowires that she came up with a new approach that opened up new possibilities. At first, it was difficult to control the shape of the nanowires. But then she discovered a way that resulted in very smooth wires. Instead of trying to grow gold nanowires from the beginning, she started with a thin nanowire made of pure silver.

“As it’s possible to make silver nanowires, we take advantage of this and use the silver nanowire as a kind of template on which we grow gold. The next step in the process is to remove the silver. Once that’s done, we have a material that has over 99 per cent gold in it. So it’s a bit of a trick to get around the problem of making long narrow gold nanostructures,” says Klas Tybrandt.

In collaboration with Professor Simon Farnebo at the Department of Biomedical and Clinical Sciences at Linköping University, the researchers behind the study have shown that the soft and elastic microelectrodes can stimulate a rat nerve as well capture signals from the nerve. 

In applications where the soft electronics are to be embedded in the body, the material must last for a long time, preferably for life. The researchers have tested the stability of the new material and concluded that it will last for at least three years, which is better than many of the nanomaterials developed so far.

The research team is now working on refining the material and creating different types of electrodes that are even smaller and can come into closer contact with nerve cells.

The research has been funded with support from, among others, the Swedish Foundation for Strategic Research, the Swedish Research Council, the Knut and Alice Wallenberg Foundation and through the Swedish Government’s strategic research area in advanced functional materials, AFM, at Linköping University.

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

Stretchable Tissue-Like Gold Nanowire Composites with Long-Term Stability for Neural Interfaces by Laura Seufert, Mohammed Elmahmoudy, Charlotte Theunis, Samuel Lienemann, Yuyang Li, Mohsen Mohammadi, Ulrika Boda, Alejandro Carnicer-Lombarte, Renee Kroon, Per O.Å. Persson, Aiman Rahmanudin, Mary J. Donahue, Simon Farnebo, Klas Tybrandt. Small DOI: https://doi.org/10.1002/smll.202402214 First published: 30 June 2024

This paper is open access.

Nanoscale device, which steers & shifts frequency of optical light, could point way to future wireless communication channels

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It seems like there’s never enough memory or enough speed where telecommunication is concerned. According to a July 24, 2023 news item on ScienceDaily announces a new way of transmitting large of amounts of data on earth and in outer space,

It is a scene many of us are familiar with: You’re working on your laptop at the local coffee shop with maybe a half dozen other laptop users — each of you is trying to load websites or stream high-definition videos, and all are craving more bandwidth. Now imagine that each of you had a dedicated wireless channel for communication that was hundreds of times faster than the Wi-Fi we use today, with hundreds of times more bandwidth. That dream may not be far off thanks to the development of metasurfaces — tiny engineered sheets that can reflect and otherwise direct light in desired ways.

In a paper published today [July 24, 2024] in the journal Nature Nanotechnology, a team of Caltech engineers reports building such a metasurface patterned with miniscule tunable antennas capable of reflecting an incoming beam of optical light to create many sidebands, or channels, of different optical frequencies.

“With these metasurfaces, we’ve been able to show that one beam of light comes in, and multiple beams of light go out, each with different optical frequencies and going in different directions,” says Harry Atwater, the Otis Booth Leadership Chair of the Division of Engineering and Applied Science, the Howard Hughes Professor of Applied Physics and Materials Science, and senior author on the new paper. “It’s acting like an entire array of communication channels. And we’ve found a way to do this for free-space signals rather than signals carried on an optical fiber.”

The work points to a promising route for the development of not only a new type of wireless communication channel but also potentially new range-finding technologies and even a novel way to relay larger amounts of data to and from space.

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A July 24, 2024 California Institute of Technology (CalTech) news release (also on EurekAlert) by Kimm Fesenmaier, which originated the news item, delves further into the research,

Going beyond conventional optical elements

Co-lead author on the new paper Prachi Thureja, a graduate student in Atwater’s group, says to understand their work, first consider the word “metasurface.” The root, “meta,” comes from a Greek prefix meaning “beyond.” Metasurfaces are designed to go beyond what we can do with conventional bulky optical elements, such as camera or microscope lenses. The multilayer transistor-like devices are engineered with a carefully selected pattern of nanoscale antennas that can reflect, scatter, or otherwise control light. These flat devices can focus light, in the style of a lens, or reflect it, like a mirror, by strategically designing an array of nanoscale elements that modify the way that light responds.

Much previous work with metasurfaces has focused on creating passive devices that have a single light-directing functionality that is fixed in time. In contrast, Atwater’s group focuses on what are known as active metasurfaces. “Now we can apply an external stimulus, such as an array of different voltages, to these devices and tune between different passive functionalities,” says Jared Sisler, also a graduate student in Atwater’s lab and co-lead author on the paper.

In the latest work, the team describes what they call a space-time metasurface that can reflect light in specific directions and also at particular frequencies (a function of time, since frequency is defined as the number of waves that pass a point per second). This metasurface device, the core of which is just 120 microns wide and 120 microns long, operates in reflection mode at optical frequencies typically used for telecommunications, specifically at 1,530 nanometers. This is thousands of times higher than radio frequencies, which means there is much more available bandwidth.

At radio frequencies, electronics can easily steer a beam of light in different directions. This is routinely accomplished by the radar navigation devices used on airplanes. But there are currently no electronic devices that can do this at the much higher optical frequencies. Therefore, the researchers had to try something different, which was to change the properties of the antennas themselves.

Sisler and Thureja created their metasurface to consist of gold antennas, with an underlying electrically tunable semiconductor layer of indium tin oxide. By applying a known voltage profile across the device, they can locally modulate the density of electrons in the semiconductor layer below each antenna, changing its refractive index (the material’s light-bending ability). “By having the spatial configuration of different voltages across the device, we can then redirect the reflected light at specified angles in real time without the need to swap out any bulky components,” Thureja says.

“We have an incident laser hitting our metasurface at a certain frequency, and we modulate the antennas in time with a high-frequency voltage signal. This generates multiple new frequencies, or sidebands, that are carried by the incident laser light and can be used as high-data-rate channels for sending information. On top of this, we still have spatial control, meaning we can choose where each channel goes in space,” explains Sisler. “We are generating frequencies and steering them in space. That’s the space-time component of this metasurface.”

Looking toward the future

Beyond demonstrating that such a metasurface is capable of splitting and redirecting light at optical frequencies in free space (rather than in optical fibers), the team says the work points to several possible applications. These metasurfaces could be useful in LiDAR applications, the light equivalent of radar, where light is used to capture the depth information from a three-dimensional scene. The ultimate dream is to develop a “universal metasurface” that would create multiple optical channels, each carrying information in different directions in free space.

“If optical metasurfaces become a realizable technology that proliferates, a decade from now you’ll be able to sit in a Starbucks with a bunch of other people on their laptops and instead of each person getting a radio frequency Wi-Fi signal, they will get their own high-fidelity light beam signal,” says Atwater, who is also the director of the Liquid Sunlight Alliance at Caltech. “One metasurface will be able to beam a different frequency to each person.”

The group is collaborating with the Optical Communications Laboratory at JPL, which is working on using optical frequencies rather than radio frequency waves for communicating with space missions because this would enable the ability to send much more data at higher frequencies. “These devices would be perfect for what they’re doing,” says Sisler.

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

Electrically tunable space–time metasurfaces at optical frequencies by Jared Sisler, Prachi Thureja, Meir Y. Grajower, Ruzan Sokhoyan, Ivy Huang & Harry A. Atwater. Nature Nanotechnology (2024) DOI: https://doi.org/10.1038/s41565-024-01728-9 Published: 24 July 2024

This paper is behind a paywall.

Are electrochromic films like sunglasses for your windows?

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According to a May 29, 2024 news item on ScienceDaily, elctrochromic film is like having a pair of sunglasses for your windows,

Advances in electrochromic coatings may bring us closer to environmentally friendly ways to keep inside spaces cool. Like eyeglasses that darken to provide sun protection, the optical properties of these transparent films can be tuned with electricity to block out solar heat and light. Now, researchers in ACS Energy Letters report demonstrating a new electrochromic film design based on metal-organic frameworks (MOFs) that quickly and reliably switch from transparent to glare-diminishing green to thermal-insulating red.

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This seems to be a popular way to describe electrochomic film as the title for my February 1, 2010 posting suggests, “Window sunglasses; insect microids; open access to science research?; theatre and science.”

A May 29, 2024 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, offers more detail about how the electrochromic film works, Note: Links have been removed,

Hongbo Xu and colleagues used MOFs in their electrochromic film because of the crystalline substances’ abilities to form thin films with pore sizes that can be customized by changing the length of the organic ligand that binds to the metal ion. These features enable improved current flow, more precise control over colors and durability. In demonstrations, Xu’s MOF electrochromic film took 2 seconds to switch from colorless to green with an electric potential of 0.8 volts, and 2 seconds to switch to dark red with 1.6 V. The film maintained the green or red color for 40 hours when the potential dropped, unless a reverse voltage was applied to return the film to its transparent state. The film also performed reliably through 4,500 cycles of switching from colored to clear. With further optimization, the researchers say their tunable coatings could be used in smart windows that regulate indoor temperatures, as well as in smaller scale intelligent optical devices and sensors.

In addition to Xu’s MOF-based electrochromic film, several other research groups have reported electrochromic coating designs, including a UV-blocking but visually transparent radiative cooling film, a colorful plant-based film that gets cooler when exposed to sunlight, and a temperature-responsive film that turns darker in cold weather and lighter when it’s hot.

The authors acknowledge funding from the National Natural Science Foundation of China, Natural Science Foundation of Heilongjiang Province and the Scientific Research Startup Project of Quzhou University.

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

Biphenyl Dicarboxylic-Based Ni-IRMOF-74 Film for Fast-Switching and High-Stability Electrochromism by Xueying Fan, Shen Wang, Mengyao Pan, Huan Pang, and Hongbo Xu. ACS Energy Lett. 2024, 9, 6, 2840–2847 DOI: https://doi.org/10.1021/acsenergylett.4c00492 Publication Date:May 29, 2024 Copyright © 2024 American Chemical Society

This paper is behind a paywall.

‘Jelly’ batteries

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Caption: Researchers have developed soft, stretchable ‘jelly batteries’ that could be used for wearable devices or soft robotics, or even implanted in the brain to deliver drugs or treat conditions such as epilepsy. Credit: University of Cambridge

A July 18, 2024 news item on Nanowerk announces bioinspried stretchy batteries from the University of Cambridge,

Researchers have developed soft, stretchable ‘jelly batteries’ that could be used for wearable devices or soft robotics, or even implanted in the brain to deliver drugs or treat conditions such as epilepsy.

The researchers, from the University of Cambridge, took their inspiration from electric eels, which stun their prey with modified muscle cells called electrocytes.

Like electrocytes, the jelly-like materials developed by the Cambridge researchers have a layered structure, like sticky Lego, that makes them capable of delivering an electric current.

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A July 17, 2024 University of Cambridge press release (also on EurekAlert), which originated the news item, offers more details,

The self-healing jelly batteries can stretch to over ten times their original length without affecting their conductivity – the first time that such stretchability and conductivity has been combined in a single material. The results are reported in the journal Science Advances.

The jelly batteries are made from hydrogels: 3D networks of polymers that contain over 60% water. The polymers are held together by reversible on/off interactions that control the jelly’s mechanical properties.

The ability to precisely control mechanical properties and mimic the characteristics of human tissue makes hydrogels ideal candidates for soft robotics and bioelectronics; however, they need to be both conductive and stretchy for such applications.

“It’s difficult to design a material that is both highly stretchable and highly conductive, since those two properties are normally at odds with one another,” said first author Stephen O’Neill, from Cambridge’s Yusuf Hamied Department of Chemistry. “Typically, conductivity decreases when a material is stretched.”

“Normally, hydrogels are made of polymers that have a neutral charge, but if we charge them, they can become conductive,” said co-author Dr Jade McCune, also from the Department of Chemistry. “And by changing the salt component of each gel, we can make them sticky and squish them together in multiple layers, so we can build up a larger energy potential.”

Conventional electronics use rigid metallic materials with electrons as charge carriers, while the jelly batteries use ions to carry charge, like electric eels.

The hydrogels stick strongly to each other because of reversible bonds that can form between the different layers, using barrel-shaped molecules called cucurbiturils that are like molecular handcuffs. The strong adhesion between layers provided by the molecular handcuffs allows for the jelly batteries to be stretched, without the layers coming apart and crucially, without any loss of conductivity.

The properties of the jelly batteries make them promising for future use in biomedical implants, since they are soft and mould to human tissue. “We can customise the mechanical properties of the hydrogels so they match human tissue,” said Professor Oren Scherman, Director of the Melville Laboratory for Polymer Synthesis, who led the research in collaboration with Professor George Malliaras from the Department of Engineering. “Since they contain no rigid components such as metal, a hydrogel implant would be much less likely to be rejected by the body or cause the build-up of scar tissue.”

In addition to their softness, the hydrogels are also surprisingly tough. They can withstand being squashed without permanently losing their original shape, and can self-heal when damaged.

The researchers are planning future experiments to test the hydrogels in living organisms to assess their suitability for a range of medical applications.

The research was funded by the European Research Council and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Oren Scherman is a Fellow of Jesus College, Cambridge.

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

Highly stretchable dynamic hydrogels for soft multilayer electronics by Stephen J. K. O’Neill, Zehuan Huang, Xiaoyi Chen, Renata L. Sala, Jade A. McCune, George G. Malliaras, and Oren A. Scherman. Science Advances 17 Jul 2024 Vol 10, Issue 29 DOI: 10.1126/sciadv.adn5142

This paper appears to be open access.

Light-based neural networks

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It’s unusual to see the same headline used to highlight research from two different teams released in such proximity, February 2024 and July 2024, respectively. Both of these are neuromorphic (brainlike) computing stories.

February 2024: Neural networks made of light

The first team’s work is announced in a February 21, 2024 Friedrich Schiller University press release, Note: A link has been removed,

Researchers from the Leibniz Institute of Photonic Technology (Leibniz IPHT) and the Friedrich Schiller University in Jena, along with an international team, have developed a new technology that could significantly reduce the high energy demands of future AI systems. This innovation utilizes light for neuronal computing, inspired by the neural networks of the human brain. It promises not only more efficient data processing but also speeds many times faster than current methods, all while consuming considerably less energy. Published in the prestigious journal „Advanced Science,“ their work introduces new avenues for environmentally friendly AI applications, as well as advancements in computerless diagnostics and intelligent microscopy.

Artificial intelligence (AI) is pivotal in advancing biotechnology and medical procedures, ranging from cancer diagnostics to the creation of new antibiotics. However, the ecological footprint of large-scale AI systems is substantial. For instance, training extensive language models like ChatGPT-3 requires several gigawatt-hours of energy—enough to power an average nuclear power plant at full capacity for several hours.

Prof. Mario Chemnitz, new Junior Professor of Intelligent Photonic SystemsExternal link at Friedrich Schiller University Jena, and Dr Bennet Fischer from Leibniz IPHT in Jena, in collaboration with their international team, have devised an innovative method to develop potentially energy-efficient computing systems that forego the need for extensive electronic infrastructure. They harness the unique interactions of light waves within optical fibers to forge an advanced artificial learning system.

A single fiber instead of thousands of components

Unlike traditional systems that rely on computer chips containing thousands of electronic components, their system uses a single optical fiber. This fiber is capable of performing the tasks of various neural networks—at the speed of light. “We utilize a single optical fiber to mimic the computational power of numerous neural networks,“ Mario Chemnitz, who is also leader of the “Smart Photonics“ junior research group at Leibniz IPHT, explains. “By leveraging the unique physical properties of light, this system will enable the rapid and efficient processing of vast amounts of data in the future.“

Delving into the mechanics reveals how information transmission occurs through the mixing of light frequencies: Data—whether pixel values from images or frequency components of an audio track—are encoded onto the color channels of ultrashort light pulses. These pulses carry the information through the fiber, undergoing various combinations, amplifications, or attenuations. The emergence of new color combinations at the fiber’s output enables the prediction of data types or contexts. For example, specific color channels can indicate visible objects in images or signs of illness in a voice.

A prime example of machine learning is identifying different numbers from thousands of handwritten characters. Mario Chemnitz, Bennet Fischer, and their colleagues from the Institut National de la Recherche Scientifique (INRS) in Québec utilized their technique to encode images of handwritten digits onto light signals and classify them via the optical fiber. The alteration in color composition at the fiber’s end forms a unique color spectrum—a „fingerprint“ for each digit. Following training, the system can analyze and recognize new handwriting digits with significantly reduced energy consumption.

System recognizes COVID-19 from voice samples

“In simpler terms, pixel values are converted into varying intensities of primary colors—more red or less blue, for instance,“ Mario Chemnitz details. “Within the fiber, these primary colors blend to create the full spectrum of the rainbow. The shade of our mixed purple, for example, reveals much about the data processed by our system.“

The team has also successfully applied this method in a pilot study to diagnose COVID-19 infections using voice samples, achieving a detection rate that surpasses the best digital systems to date.

“We are the first to demonstrate that such a vibrant interplay of light waves in optical fibers can directly classify complex information without any additional intelligent software,“ Mario Chemnitz states.

Since December 2023, Mario Chemnitz has held the position of Junior Professor of Intelligent Photonic Systems at Friedrich Schiller University Jena. Following his return from INRS in Canada in 2022, where he served as a postdoc, Chemnitz has been leading an international team at Leibniz IPHT in Jena. With Nexus funding support from the Carl Zeiss Foundation, their research focuses on exploring the potentials of non-linear optics. Their goal is to develop computer-free intelligent sensor systems and microscopes, as well as techniques for green computing.

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

Neuromorphic Computing via Fission-based Broadband Frequency Generation by Bennet Fischer, Mario Chemnitz, Yi Zhu, Nicolas Perron, Piotr Roztocki, Benjamin MacLellan, Luigi Di Lauro, A. Aadhi, Cristina Rimoldi, Tiago H. Falk, Roberto Morandotti. Advanced Science Volume 10, Issue 35 December 15, 2023 2303835 DOI: https://doi.org/10.1002/advs.202303835. First published: 02 October 2023

This paper is open access.

July 2024: Neural networks made of light

A July 12, 2024 news item on ScienceDaily announces research from another German team,

Scientists propose a new way of implementing a neural network with an optical system which could make machine learning more sustainable in the future. The researchers at the Max Planck Institute for the Science of Light have published their new method in Nature Physics, demonstrating a method much simpler than previous approaches.

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A July 12, 2024 Max Planck Institute for the Science of Light press release (also on EurekAlert), which originated the news item, provides more detail about their approach to neuromorphic computiing,

Machine learning and artificial intelligence are becoming increasingly widespread with applications ranging from computer vision to text generation, as demonstrated by ChatGPT. However, these complex tasks require increasingly complex neural networks; some with many billion parameters. This rapid growth of neural network size has put the technologies on an unsustainable path due to their exponentially growing energy consumption and training times. For instance, it is estimated that training GPT-3 consumed more than 1,000 MWh of energy, which amounts to the daily electrical energy consumption of a small town. This trend has created a need for faster, more energy- and cost-efficient alternatives, sparking the rapidly developing field of neuromorphic computing. The aim of this field is to replace the neural networks on our digital computers with physical neural networks. These are engineered to perform the required mathematical operations physically in a potentially faster and more energy-efficient way.

Optics and photonics are particularly promising platforms for neuromorphic computing since energy consumption can be kept to a minimum. Computations can be performed in parallel at very high speeds only limited by the speed of light. However, so far, there have been two significant challenges: Firstly, realizing the necessary complex mathematical computations requires high laser powers. Secondly, the lack of an efficient general training method for such physical neural networks.

Both challenges can be overcome with the new method proposed by Clara Wanjura and Florian Marquardt from the Max Planck Institute for the Science of Light in their new article in Nature Physics. “Normally, the data input is imprinted on the light field. However, in our new methods we propose to imprint the input by changing the light transmission,” explains Florian Marquardt, Director at the Institute. In this way, the input signal can be processed in an arbitrary fashion. This is true even though the light field itself behaves in the simplest way possible in which waves interfere without otherwise influencing each other. Therefore, their approach allows one to avoid complicated physical interactions to realize the required mathematical functions which would otherwise require high-power light fields. Evaluating and training this physical neural network would then become very straightforward: “It would really be as simple as sending light through the system and observing the transmitted light. This lets us evaluate the output of the network. At the same time, this allows one to measure all relevant information for the training”, says Clara Wanjura, the first author of the study. The authors demonstrated in simulations that their approach can be used to perform image classification tasks with the same accuracy as digital neural networks.

In the future, the authors are planning to collaborate with experimental groups to explore the implementation of their method. Since their proposal significantly relaxes the experimental requirements, it can be applied to many physically very different systems. This opens up new possibilities for neuromorphic devices allowing physical training over a broad range of platforms.

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

Fully nonlinear neuromorphic computing with linear wave scattering by Clara C. Wanjura & Florian Marquardt. Nature Physics (2024) DOI: https://doi.org/10.1038/s41567-024-02534-9 Published: 09 July 2024

This paper is open access.