GT/ Battery tech breakthrough paves way for mass adoption of affordable electric car
Energy & green technology biweekly vol.35, 11th October — 25th October
TL;DR
- A breakthrough in electric vehicle battery design has enabled a 10-minute charge time for a typical EV battery. This is a record-breaking combination of a shorter charge time and more energy acquired for longer travel range.
- Scientists have developed a low-cost device that can harness energy from wind as gentle as a light breeze and store it as electricity.
- Engineers have achieved a power conversion efficiency of 23.50% in a perovskite-silicon tandem solar cell built with a special textured anti-reflective coating (ARC) polymeric film.
- Discarded electronic devices, such as cell phones, are a fast-growing source of waste. One way to mitigate the problem could be to use components that are made with renewable resources and that are easy to dispose of responsibly. Now, researchers have created a prototype circuit board that is made of a sheet paper with fully integrated electrical components, and that can be burned or left to degrade.
- Researchers have taken a key step toward greatly expanding the range of plastics that can be recycled.
- A new study suggests that while mechanical devices do remove plastics and other items of litter from marinas and harbors, the quantities of litter removed can be comparatively low and they can also trap marine organisms.
- Researchers have devised a method to determine the impact of climate change on the supply and variability of local renewable energy. An increase in unusual weather patterns related to climate change means the demand for power and the availability of solar, hydro and wind energy can all become more variable.
- In order to produce green hydrogen, water can be split up via electrocatalysis, powered by renewable sources such as sun or wind. A review article shows how modern X-ray sources such as BESSY II can advance the development of suitable electrocatalysts. In particular, X-ray absorption spectroscopy can be used to determine the active states of catalytically active materials for the oxygen evolution reaction. This is an important contribution to developing efficient catalysts from inexpensive and widely available elements.
- Researchers built a battery-free, wireless underwater camera, powered by sound waves, that can take high-quality, color images, even in dark environments. It transmits image data through the open water to a receiver that reconstructs the color image.
- A new nanophotonic material has broken records for high-temperature stability, potentially ushering in more efficient electricity production and opening a variety of new possibilities in the control and conversion of thermal radiation.
- And more!
Green Technology Market
Green technology is an applicable combination of advanced tools and solutions to conserve natural resources and environment, minimize or mitigate negative impacts from human activities on the environment, and ensure sustainability development. Green technology is also referred to as clean technology or environmental technology which includes technologies, such as IoT, AI, analytics, blockchain, digital twin, security, and cloud, which collect, integrate, and analyze data from various real-time data sources, such as sensors, cameras, and Global Positioning System (GPS).
Green technology, also known as sustainable technology, protects the environment by using various forms of sustainable energy. Some of the best examples of green technologies include solar panels, LED lighting, wind energy, electric vehicles, vertical farming, and composting.
The global Green Technology and Sustainability market size to grow from USD 11.2 billion in 2020 to USD 36.6 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 26.6% during the forecast period. The growing consumer and industrial interest for the use of clean energy resources to conserve environment and increasing use of Radio Frequency Identification sensors across industries are driving the adoption of green technology and sustainability solutions and services in the market.
The blockchain segment is estimated to grow at the highest CAGR: Energy-intensive cryptocurrency mining has caused a spike in carbon emission, and hence blockchain is capable of driving innovation in the field of green technology.
Latest Research
Fast charging of energy-dense lithium-ion batteries
by Chao-Yang Wang, Teng Liu, Xiao-Guang Yang, Shanhai Ge, Nathaniel V. Stanley, Eric S. Rountree, Yongjun Leng, Brian D. McCarthy in Nature
A breakthrough in electric vehicle battery design has enabled a 10-minute charge time for a typical EV battery. The record-breaking combination of a shorter charge time and more energy acquired for longer travel range was announced.
“The need for smaller, faster-charging batteries is greater than ever,” said Chao-Yang Wang, the William E. Diefenderfer Professor of Mechanical Engineering at Penn State and lead author on the study. “There are simply not enough batteries and critical raw materials, especially those produced domestically, to meet anticipated demand.”
In August, California’s Air Resources Board passed an extensive plan to restrict and ultimately ban the sale of gasoline-powered cars within the state. By 2035, the largest auto market in the United States will effectively retire the internal combustion engine.
If new car sales are going to shift to battery-powered electric vehicles (EVs), Wang explained, they’ll need to overcome two major drawbacks: they are too slow to recharge and too large to be efficient and affordable. Instead of taking a few minutes at the gas pump, depending on the battery, some EVs can take all day to recharge.
“Our fast-charging technology works for most energy-dense batteries and will open a new possibility to downsize electric vehicle batteries from 150 to 50 kWh without causing drivers to feel range anxiety,” said Wang, whose lab partnered with State College-based startup EC Power to develop the technology. “The smaller, faster-charging batteries will dramatically cut down battery cost and usage of critical raw materials such as cobalt, graphite and lithium, enabling mass adoption of affordable electric cars.”
The technology relies on internal thermal modulation, an active method of temperature control to demand the best performance possible from the battery, Wang explained. Batteries operate most efficiently when they are hot, but not too hot. Keeping batteries consistently at just the right temperature has been major challenge for battery engineers. Historically, they have relied on external, bulky heating and cooling systems to regulate battery temperature, which respond slowly and waste a lot of energy, Wang said.
Wang and his team decided to instead regulate the temperature from inside the battery. The researchers developed a new battery structure that adds an ultrathin nickel foil as the fourth component besides anode, electrolyte and cathode. Acting as a stimulus, the nickel foil self-regulates the battery’s temperature and reactivity which allows for 10-minute fast charging on just about any EV battery, Wang explained.
“True fast-charging batteries would have immediate impact,” the researchers write. “Since there are not enough raw minerals for every internal combustion engine car to be replaced by a 150 kWh-equipped EV, fast charging is imperative for EVs to go mainstream.”
A cantilever-type vibro-impact triboelectric energy harvester for wind energy harvesting
by Chaoyang Zhao, Guobiao Hu, Yaowen Yang in Mechanical Systems and Signal Processing
Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a low-cost device that can harness energy from wind as gentle as a light breeze and store it as electricity.
When exposed to winds with a velocity as low as two metres per second (m/s), the device can produce a voltage of three volts and generate electricity power of up to 290 microwatts, which is sufficient to power a commercial sensor device and for it to also send the data to a mobile phone or a computer. The light and durable device, called a wind harvester, also diverts any electricity that is not in use to a battery, where it can be stored to power devices in the absence of wind.
The scientists say their invention has the potential to replace batteries in powering light emitting diode (LED) lights and structural health monitoring sensors. Those are used on urban structures, such as bridges and skyscrapers, to monitor their structural health, alerting engineers to issues such as instabilities or physical damage. Measuring only 15 centimetres by 20 centimetres, the device can easily be mounted on the sides of buildings, and would be ideal for urban environments, such as Singaporean suburbs, where average wind speeds are less than 2.5 m/s, outside of thunderstorms.
Professor Yang Yaowen, a structural engineer from NTU’s School of Civil and Environmental Engineering (CEE), who led the project, said: “As a renewable and clean energy source, wind power generation has attracted extensive research attention. Our research aims to tackle the lack of a small-scale energy harvester for more targeted functions, such as to power smaller sensors and electronic devices. The device we developed also serves as a potential alternative to smaller lithium-ion batteries, as our wind harvester is self-sufficient and would only require occasional maintenance, and does not use heavy metals, which if not disposed of properly, could cause environmental problems.”
The innovation has received interest from the industry. The NTU research team is also working towards commercialising their invention. The study, which presents an innovation that could help cut down on electronic waste and find alternative sources for energy, reflects NTU’s commitment to mitigate our impact on the environment, which is one of four humanity’s grand challenges that the University seeks to address through its NTU 2025 strategic plan.
The device was developed to harness efficient wind energy at low cost and with low wear and tear. Its body is made of fibre epoxy, a highly durable polymer, with the main attachment that interacts with the wind and is made of inexpensive materials, such as copper, aluminium foil, and polytetrafluoroethylene, a durable polymer that is also known as Teflon.
Due to the dynamic design of its structure, when the harvester is exposed to wind flow, it begins to vibrate, causing its plate to approach to and depart from the stopper. This causes charges to be formed on the film, and an electrical current is formed as they flow from the aluminium foil to the copper film.
In laboratory tests, the NTU-developed harvester could power 40 LEDs consistently at a wind speed of 4 m/s. It could also trigger a sensor device, and power it sufficiently to send the room temperature information to a mobile phone wirelessly. This demonstrated that the harvester could not only generate electricity to consistently power a device, but that it could store excess charge that was sufficient to keep the device powered for an extended period in the absence of wind.
Prof Yang added: “Wind energy is a source of renewable energy. It does not contaminate, it is inexhaustible and reduces the use of fossil fuels, which are the origin of greenhouse gasses that cause global warming. Our invention has been shown to effectively harness this sustainable source of energy to charge batteries and light LEDs, demonstrating its potential as an energy generator to power the next generation of electronics, which are smaller in size and require less power.”
The NTU team will be conducting further research to further improve the energy storage functions of their device, as well as experiment with different materials to improve its output power. The research team is also in the process of filing for a patent with NTUitive, NTU’s innovation and enterprise company.
What X‐Ray Absorption Spectroscopy Can Tell Us About the Active State of Earth‐Abundant Electrocatalysts for the Oxygen Evolution Reaction
by Marcel Risch, Dulce M. Morales, Javier Villalobos, Denis Antipin in Angewandte Chemie
Green hydrogen is an energy carrier with a future. It is obtained by electrolytically splitting water with energy from wind or sun and stores this energy in chemical form. To make the splitting of water molecules easier (and to reduce the energy input), the electrodes are coated with catalytically active materials. Dr. Marcel Risch and his Young Investigator Group Oxygen Evolution Mechanism Engineering are investigating oxygen evolution in the electrocatalysis of water. This is because oxygen evolution in particular must run more efficiently for economical hydrogen production.
In order to produce green hydrogen, water can be split up via electrocatalysis, powered by renewable sources such as sun or wind. A review article shows how modern X-ray sources such as BESSY II can advance the development of suitable electrocatalysts. In particular, X-ray absorption spectroscopy can be used to determine the active states of catalytically active materials for the oxygen evolution reaction. This is an important contribution to developing efficient catalysts from inexpensive and widely available elements.
An exciting class of materials for electrocatalysts are manganese oxides, which occur in many different structural variants. “A decisive criterion for suitability as an electrocatalyst is the oxidation number of the material and how it changes in the course of the reaction,” explains Risch. In the case of manganese oxides, there is also a great diversity in possible oxidation states. X-ray absorption spectroscopy (XAS) provides information about the oxidation states: X-ray quanta with suitable energy excite electrons on the innermost shells, which absorb these quanta. Depending on the oxidation number, this absorption can be observed at different excitation energies. Risch’s team has constructed an electrolysis cell that enables XAS measurements during electrolysis.
“With X-ray absorption spectroscopy, we can not only determine the oxidation numbers, but also observe corrosion processes or phase changes in the material,” says Risch. Combined with electrochemical measurements, the measurement data thus provide a much better understanding of the material during electrocatalysis. However, the required high intensity of the X-rays is only available at modern synchrotron light sources. In Berlin, HZB operates BESSY II for this purpose. There are about 50 such light sources for research worldwide.
Risch still sees great potential for the application of X-ray absorption spectroscopy, especially with regard to the time scales of observation. This is because typical measurement times are a few minutes per measurement. Electrocatalytic reactions, however, take place on shorter time scales. “If we could watch electrocatalysis as it happens, we could better understand important details,” says Risch. With this knowledge, cheap and environmentally friendly catalysts could be developed more quickly. On the other hand, many “ageing” processes take place within weeks or months. “We could, for example, examine the same sample again and again at regular intervals to understand these processes,” Risch advises. This would also make it possible to develop electrocatalysts with long term stability.
Improving Light Absorption in a Perovskite/Si Tandem Solar Cell via Light Scattering and UV‐Down Shifting by a Mixture of SiO 2 Nanoparticles and Phosphors
by Seongha Lee, Chan Ul Kim, Sumin Bae, Yulin Liu, Young Im Noh, Ziyu Zhou, Paul W Leu, Kyoung Jin Choi, Jung‐Kun Lee in Advanced Functional Materials
A research team, affiliated with UNIST has succeeded in achieving a power conversion efficiency (PEC) of 23.50% in a perovskite-silicon tandem solar cell built with a special textured anti-reflective coating (ARC) polymeric film. According to the research team, the PCE of the device with the ARC film was sustained for 120 hours, maintaining 91% of its initial value.
This breakthrough has been led by Professor Kyoung Jin Choi and his research team in the Department of Materials Science and Engineering at UNIST, in collaboration with Professor Jung-Kun Lee and his research team from the University of Pittsburgh in the United States.
In the work, the research team systematically demonstrated that a combination of silicon dioxide (SiO2) nanoparticles and large phosphor particles can convert ultraviolet (UV) to visible light and increase total transmittance of ARC film. Their experimental and computational results also show that SiO2 nanoparticles in the ARC film decrease the reflectance by increasing the diffuse transmittance.
Moreover, the PCE of the device with the ARC film was sustained for 120 hours, maintaining 91% of its initial value, while the PCE of existing devices dropped to 90% of its initial efficiency after 5 hours, and then decreased to 50% after 20 hours. In addition, the initial efficiency of the solar cell has also increased by nearly 4.5% compared to the previous one.
“This optically engineered ARC film successfully promotes the light absorption of the perovskite/silicon tandem solar cell, leading to the improvement of power conversion efficiency of the tandem cell from 22.48% to 23.50%,” noted the research team.
Integrated Papertronic Techniques: Highly Customizable Resistor, Supercapacitor, and Transistor Circuitry on a Single Sheet of Paper
by Mya Landers, Anwar Elhadad, Maryam Rezaie, Seokheun Choi in ACS Applied Materials & Interfaces
Discarded electronic devices, such as cell phones, are a fast-growing source of waste. One way to mitigate the problem could be to use components that are made with renewable resources and that are easy to dispose of responsibly. Now, researchers have created a prototype circuit board that is made of a sheet paper with fully integrated electrical components, and that can be burned or left to degrade.
Most small electronic devices contain circuit boards that are made from glass fibers, resins and metal wiring. These boards are not easy to recycle and are relatively bulky, making them undesirable for use in point-of-care medical devices, environmental monitors or personal wearable devices. One alternative is to use paper-based circuit boards, which should be easier to dispose of, less expensive and more flexible. However, current options require specialized paper, or they simply have traditional metal circuitry components mounted onto a sheet of paper. Instead, Choi and colleagues wanted to develop circuitry that would be simple to manufacture and that had all the electronic components fully integrated into the sheet.
The team designed a paper-based amplifier-type circuit that incorporated resistors, capacitors and a transistor. They first used wax to print channels onto a sheet of paper in a simple pattern. After melting the wax so that it soaked into the paper, the team printed semi-conductive and conductive inks, which soaked into the areas not blocked by wax. Then, the researchers screen-printed additional conductive metal components and casted a gel-based electrolyte onto the sheet.
Tests confirmed that the resistor, capacitor and transistor designs performed properly. The final circuit was very flexible and thin, just like paper, even after adding the components. To demonstrate the degradability of the circuit, the team showed that the entire unit quickly burned to ash after being lit on fire. The researchers say this represents a step toward producing completely disposable electronic devices.
Evaluating the performance of the ‘Seabin’ — A fixed point mechanical litter removal device for sheltered waters
by Florence N.F. Parker-Jurd, Natalie S. Smith, Liam Gibson, Sohvi Nuojua, Richard C. Thompson in Marine Pollution Bulletin
Mechanical devices are increasingly being considered as a potential way to help address plastic pollution found globally in marine environments.
However, a new study suggests that while they do remove plastics and other items of marine litter, the quantities of litter removed can be comparatively low and they can also trap marine organisms. The study was led by researchers from the International Marine Litter Research Unit at the University of Plymouth, who have been studying the issue of marine microplastics for more than two decades. Their research was conducted in Plymouth (UK), and provides the first formal independent evaluation of the performance of a Seabin device.
The devices are designed to continuously suck water inwards using a submersible pump which is then filtered, and the cleaned water is returned to the surrounding area leaving the litter in the catch bag. Hundreds have been installed globally and are reported to have captured over 2.5million kg of litter from calm sheltered environments such as marinas, ports, and yacht clubs.
This study found that a total of 1,828 items, 0.18kg of litter, was retained by the Plymouth device during 750 hours of operation between April and June 2021. This was equivalent to 58 items a day, and was mainly comprised of plastic pellets, polystyrene balls and plastic fragments. However, the Seabin also captured one marine organism for every 3.6 items of litter, around 13 organisms a day including species such as sandeels, brown shrimp and crabs. Around 60% of those organisms were found to be dead upon retrieval, and the study indicates some organisms died after entering the device.
During the deployment, five manual trawls were conducted at the same marina using nets from pontoons or vessels. Manual cleaning collected an average of 19.3g of litter during cleans of up to five minutes. By comparison, the Seabin only captured the equivalent of 0.0059g in a similar timeframe.
Writing in the study, the researchers say that — based on their findings — the device was of minimal benefit in terms of marine litter removal in this particular location. They also warn that the presence of such devices could also precipitate techno-optimism, a reliance on technological innovations, rather than systemic changes in our production, use, and disposal of plastics.
Florence Parker-Jurd, Research Assistant at the University of Plymouth and the study’s lead author, said: “At its current state of development, this study suggests that manual cleaning of ports, harbours and marinas, is more efficient and cost-effective. Notably manual cleans are selective, and this could lessen any potential risk to marine life. Given the increasing reliance on technological innovations, formal evaluations are necessary to their efficiency as similar may apply to other types of device.”
Professor Richard Thompson OBE, Head of the International Marine Litter Research Unit, added: “The UN Treaty to end plastic pollution presents an amazing opportunity to start to use plastics more responsibly, halting their accumulation in the environment. Ultimately, the best way to achieve that is by preventing the issue at its source rather than clean-up. However, The Treaty sets an urgent ambitious timeline and this could lead to increased investment in clean up as opposed to longer term systemic change. This study and others from my team highlight the critical importance of evidence to inform decisions about which type of intervention to invest in as we move to tackle this global environmental challenge.”
Mixed plastics waste valorization through tandem chemical oxidation and biological funneling
by Kevin P. Sullivan, Allison Z. Werner, Kelsey J. Ramirez, et al in Science
Researchers including an Oregon State University College of Engineering faculty member have taken a key step toward greatly expanding the range of plastics that can be recycled.
The findings are important because plastic waste is a massive problem both globally and in the United States, where only about 5% of used plastic is recycled, according to the U.S. Department of Energy’s National Renewable Energy Laboratory, which led the study.
Packaging materials, containers and other discarded items are filling up landfills and littering the environment at a pace so rapid that scientists estimate by 2050 the ocean will have more plastic by weight than fish, according to NREL.
A collaboration led by NREL’s Gregg Beckham and including Lucas Ellis, an OSU researcher who was an NREL postdoctoral fellow during the project, combined chemical and biological processes in a proof of concept to “valorize” mixed plastic waste. Valorize means to enhance the value of something.
The research builds on the use of chemical oxidation to break down a variety of plastic types, a method pioneered a decade ago by chemical industry giant DuPont.
“We developed a technology that used oxygen and catalysts to break down plastics into smaller, biologically friendly chemical building blocks,” said Ellis, an assistant professor of chemical engineering. “From there we used a biologically engineered soil microbe capable of consuming and ‘funneling’ those building blocks into either a biopolymer or a component for advanced nylon production.”
Beckham, a senior research fellow at NREL and the head of the Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment Consortium — known as BOTTLE — said the work provides a “potential entry point into processing plastics that cannot be recycled at all today.”
Current recycling technologies can only operate effectively if the plastic inputs are clean and separated by type, Beckham explains. Plastics can be made from different polymers, each with its own unique chemical building blocks. When polymer chemistries are mixed in a collection bin, or formulated together in certain products like multilayer packaging, recycling becomes expensive and nearly impossible because the polymers often have to be separated before they can be recycled.
“Our work has resulted in a process that can convert mixed plastics to a single chemical product,” Ellis said. “In other words, it is a technology that recyclers could use without the task of sorting plastics by type.”
Researchers applied the process to a mix of three common plastics: polystyrene, used in disposable coffee cups; polyethylene terephthalate, the basis for carpets, polyester clothing and single-use beverage bottles; and high-density polyethylene, used in milk jugs and many other consumer plastics. The oxidation process broke down the plastics into a mixture of compounds including benzoic acid, terephthalic acid and dicarboxylic acids that, in the absence of the engineered soil microbe, would require advanced and costly separations to yield pure products.
The researchers engineered the microbe, Pseudomonas putida, to biologically funnel the mixture into one of two products — polyhydroxyalkanoates, an emerging form of biodegradable bioplastics, and beta-ketoadipate, which can be used in the manufacture of performance-advantaged nylon. Trying the process with other types of plastics including polypropylene and polyvinyl chloride will be the focus of upcoming work, the researchers said.
“The chemical catalysis process we have used is just a way of accelerating a process that occurs naturally, so instead of degrading over several hundred years, you can break down these plastics in hours or minutes,” said co-author Kevin Sullivan, a postdoctoral researcher at NREL.
The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources
by Uma S. Bhatt, Benjamin A. Carreras, José Miguel Reynolds Barredo, David E. Newman, Pere Collet, Damiá Gomila in Land.
Researchers have devised a method to determine the impact of climate change on the supply and variability of local renewable energy.
An increase in unusual weather patterns related to climate change means the demand for power and the availability of solar, hydro and wind energy can all become more variable. The method by researchers at the University of Alaska Fairbanks Geophysical Institute and in Spain will help local energy planners determine the optimal mix of renewable energy sources and energy storage needs. Geophysical Institute atmospheric sciences professor Uma Bhatt is the lead author.
“It is important for society to understand the impact of climate change and variability on renewable energy resources in order to design a resilient power system and prepare for the future,” Bhatt said.
The researchers studied intermittency, power production and energy storage in the context of historical climate data at two locations: the Alaska city of Cordova in Prince William Sound, which has a subpolar oceanic climate, and Palma de Mallorca, a city on a subtropical Spanish island. The researchers obtained 60 years of climate data for each location.
Wind, solar and hydropower are all susceptible to a climate that is becoming less predictable and producing more extreme weather events. Increased cloud cover could decrease the availability of solar power. Decreased precipitation could reduce the availability of hydropower. Increased winds could increase the availability of wind power.
Without proper planning, power grids risk becoming less reliable as renewables make up an increasingly larger portion of the supply.
“If you have too high a percentage of high-variability renewable power without appropriate backup power in your system, it actually degrades the system’s reliability a lot,” said David Newman, a study co-author and physics professor at the UAF Geophysical Institute.
Further complicating the situation, the demand for power changes in unpredictable ways as the weather becomes increasingly variable. Even when demand is normal, a sudden drop in the availability of a renewable source — wind ceasing to turn the turbines, for example — can cause blackouts if a backup source is not in place for immediate use.
“How do you fix it? You have to find a way to remove the variability or to have a way to quickly compensate for it,” Newman said.
The easiest and most obvious way is to have fossil fuel-based generators on standby. Of those, generators powered by natural gas can be started fairly quickly when needed. But it’s still a fossil fuel product, though cleaner than other fossil-fuel sources. Another, cleaner method is to store excess energy produced by renewable sources during times of normal demand. Advances in technology have improved grid-scale batteries, which can store excess power that can be distributed for short-term use during a widespread blackout. Other storage methods include pumped storage hydropower, gravity energy storage, flywheel energy storage and compressed air energy storage. All are fundamentally simple methods and explained by the National Renewable Energy Laboratory.
“This is one of the really exciting areas [of study] right now,’ Newman said.
Pumped storage hydropower accounts for 95% of all utility-scale energy storage capacity in the United States. Water is pumped from one hydropower reservoir to another at a higher elevation during times of excess power, raising the level of the higher reservoir. That water is released to the generators of the lower reservoir when needed.
Gravity energy storage involves using excess energy to raise massive weights consisting of sand, gravel or rock and leaving the weights suspended. When power is needed, the weights are allowed to fall, with their attached cables turning a generator.
Flywheel energy storage is typically used in small applications and for much shorter energy needs than other storage methods. A motor powersturns a flywheel, a heavy wheel that spins freely when the motor loses power. The freely spinning wheel turns a generator, which produces electricity for several minutes.
Compressed air energy storage can provide power on a grid-scale for several days. Electricity is used to compress and store air underground, often in salt caverns. When needed, the air is released and heated to expansion to power a generator.
“Both climate and energy are interconnected complex systems, and it is important that we educate the next generation to think across disciplines so they are prepared to address the complex problems that are looming,” Bhatt said.
Battery-free wireless imaging of underwater environments
by Sayed Saad Afzal, Waleed Akbar, Osvy Rodriguez, Mario Doumet, Unsoo Ha, Reza Ghaffarivardavagh, Fadel Adib in Nature Communications
Scientists estimate that more than 95 percent of Earth’s oceans have never been observed, which means we have seen less of our planet’s ocean than we have the far side of the moon or the surface of Mars.
The high cost of powering an underwater camera for a long time, by tethering it to a research vessel or sending a ship to recharge its batteries, is a steep challenge preventing widespread undersea exploration. MIT researchers have taken a major step to overcome this problem by developing a battery-free, wireless underwater camera that is about 100,000 times more energy-efficient than other undersea cameras. The device takes color photos, even in dark underwater environments, and transmits image data wirelessly through the water.
The autonomous camera is powered by sound. It converts mechanical energy from sound waves traveling through water into electrical energy that powers its imaging and communications equipment. After capturing and encoding image data, the camera also uses sound waves to transmit data to a receiver that reconstructs the image. Because it doesn’t need a power source, the camera could run for weeks on end before retrieval, enabling scientists to search remote parts of the ocean for new species. It could also be used to capture images of ocean pollution or monitor the health and growth of fish raised in aquaculture farms.
“One of the most exciting applications of this camera for me personally is in the context of climate monitoring. We are building climate models, but we are missing data from over 95 percent of the ocean. This technology could help us build more accurate climate models and better understand how climate change impacts the underwater world,” says Fadel Adib, associate professor in the Department of Electrical Engineering and Computer Science and director of the Signal Kinetics group in the MIT Media Lab, and senior author of the paper. Joining Adib on the paper are co-lead authors and Signal Kinetics group research assistants Sayed Saad Afzal, Waleed Akbar, and Osvy Rodriguez, as well as research scientist Unsoo Ha, and former group researchers Mario Doumet and Reza Ghaffarivardavagh.
To build a camera that could operate autonomously for long periods, the researchers needed a device that could harvest energy underwater on its own while consuming very little power. The camera acquires energy using transducers made from piezoelectric materials that are placed around its exterior. Piezoelectric materials produce an electric signal when a mechanical force is applied to them. When a sound wave traveling through the water hits the transducers, they vibrate and convert that mechanical energy into electrical energy. Those sound waves could come from any source, like a passing ship or marine life. The camera stores harvested energy until it has built up enough to power the electronics that take photos and communicate data.
To keep power consumption as a low as possible, the researchers used off-the-shelf, ultra-low-power imaging sensors. But these sensors only capture grayscale images. And since most underwater environments lack a light source, they needed to develop a low-power flash, too.
“We were trying to minimize the hardware as much as possible, and that creates new constraints on how to build the system, send information, and perform image reconstruction. It took a fair amount of creativity to figure out how to do this,” Adib says.
They solved both problems simultaneously using red, green, and blue LEDs. When the camera captures an image, it shines a red LED and then uses image sensors to take the photo. It repeats the same process with green and blue LEDs. Even though the image looks black and white, the red, green, and blue colored light is reflected in the white part of each photo, Akbar explains. When the image data are combined in post-processing, the color image can be reconstructed.
“When we were kids in art class, we were taught that we could make all colors using three basic colors. The same rules follow for color images we see on our computers. We just need red, green, and blue — these three channels — to construct color images,” he says.
Once image data are captured, they are encoded as bits (1s and 0s) and sent to a receiver one bit at a time using a process called underwater backscatter. The receiver transmits sound waves through the water to the camera, which acts as a mirror to reflect those waves. The camera either reflects a wave back to the receiver or changes its mirror to an absorber so that it does not reflect back.
A hydrophone next to the transmitter senses if a signal is reflected back from the camera. If it receives a signal, that is a bit-1, and if there is no signal, that is a bit-0. The system uses this binary information to reconstruct and post-process the image.
“This whole process, since it just requires a single switch to convert the device from a nonreflective state to a reflective state, consumes five orders of magnitude less power than typical underwater communications systems,” Afzal says.
The researchers tested the camera in several underwater environments. In one, they captured color images of plastic bottles floating in a New Hampshire pond. They were also able to take such high-quality photos of an African starfish that tiny tubercles along its arms were clearly visible. The device was also effective at repeatedly imaging the underwater plant Aponogeton ulvaceus in a dark environment over the course of a week to monitor its growth.
Now that they have demonstrated a working prototype, the researchers plan to enhance the device so it is practical for deployment in real-world settings. They want to increase the camera’s memory so it could capture photos in real-time, stream images, or even shoot underwater video. They also want to extend the camera’s range. They successfully transmitted data 40 meters from the receiver, but pushing that range wider would enable the camera to be used in more underwater settings.
Nanophotonic control of thermal emission under extreme temperatures in air
by Sean McSherry, Matthew Webb, Jonathan Kaufman, Zihao Deng, Ali Davoodabadi, Tao Ma, Emmanouil Kioupakis, Keivan Esfarjani, John T. Heron, Andrej Lenert in Nature Nanotechnology
A new nanophotonic material has broken records for high-temperature stability, potentially ushering in more efficient electricity production and opening a variety of new possibilities in the control and conversion of thermal radiation.
Developed by a University of Michigan-led team of chemical and materials science engineers, the material controls the flow of infrared radiation and is stable at temperatures of 2,000 degrees Fahrenheit in air, a nearly twofold improvement over existing approaches.
The material uses a phenomenon called destructive interference to reflect infrared energy while letting shorter wavelengths pass through. This could potentially reduce heat waste in thermophotovoltaic cells, which convert heat into electricity but can’t use infrared energy, by reflecting infrared waves back into the system. The material could also be useful in optical photovoltaics, thermal imaging, environmental barrier coatings, sensing, camouflage from infrared surveillance devices and other applications.
“It’s similar to the way butterfly wings use wave interference to get their color. Butterfly wings are made up of colorless materials, but those materials are structured and patterned in a way that absorbs some wavelengths of white light but reflects others, producing the appearance of color,” said Andrej Lenert, U-M assistant professor of chemical engineering and co-corresponding author of the study.
“This material does something similar with infrared energy. The challenging part has been preventing breakdown of that color-producing structure under high heat.”
The approach is a major departure from the current state of engineered thermal emitters, which typically use foams and ceramics to limit infrared emissions. These materials are stable at high temperature but offer very limited control over which wavelengths they let through. Nanophotonics could offer much more tunable control, but past efforts haven’t been stable at high temperatures, often melting or oxidizing (the process that forms rust on iron). In addition, many nanophotonic materials only maintain their stability in a vacuum.
The new material works toward solving that problem, besting the previous record for heat resistance among air-stable photonic crystals by more than 900 degrees Fahrenheit in open air. In addition, the material is tunable, enabling researchers to tweak it to modify energy for a wide variety of potential applications. The research team predicted that applying this material to existing TPVs will increase efficiency by 10% and believes that much greater efficiency gains will be possible with further optimization.
The team developed the solution by combining chemical engineering and materials science expertise. Lenert’s chemical engineering team began by looking for materials that wouldn’t mix even if they started to melt.
“The goal is to find materials that will maintain nice, crisp layers that reflect light in the way we want, even when things get very hot,” Lenert said. “So we looked for materials with very different crystal structures, because they tend not to want to mix.”
They hypothesized that a combination of rock salt and perovskite, a mineral made of calcium and titanium oxides, fit the bill. Collaborators at U-M and the University of Virginia ran supercomputer simulations to confirm that the combination was a good bet.
John Heron, co-corresponding author of the study and an assistant professor of materials science and engineering at U-M, and Matthew Webb, a doctoral student in materials science and engineering, then carefully deposited the material using pulsed laser deposition to achieve precise layers with smooth interfaces. To make the material even more durable, they used oxides rather than conventional photonic materials; the oxides can be layered more precisely and are less likely to degrade under high heat.
“In previous work, traditional materials oxidized under high heat, losing their orderly layered structure,” Heron said. “But when you start out with oxides, that degradation has essentially already taken place. That produces increased stability in the final layered structure.”
After testing confirmed that the material worked as designed, Sean McSherry, first author of the study and a doctoral student in materials science and engineering at U-M, used computer modeling to identify hundreds of other combinations of materials that are also likely to work. While commercial implementation of the material tested in the study is likely years away, the core discovery opens up a new line of research into a variety of other nanophotonic materials that could help future researchers develop a range of new materials for a variety of applications.
MISC
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