Electronics

Subterms

    More stories

    • 88 Shares179 Views

      in Energy

      Propelling atomically layered magnets toward green computers

      by

      Globally, computation is booming at an unprecedented rate, fueled by the boons of artificial intelligence. With this, the staggering energy demand of the world’s computing infrastructure has become a major concern, and the development of computing devices that are far more energy-efficient is a leading challenge for the scientific community. 

      Use of magnetic materials to build computing devices like memories and processors has emerged as a promising avenue for creating “beyond-CMOS” computers, which would use far less energy compared to traditional computers. Magnetization switching in magnets can be used in computation the same way that a transistor switches from open or closed to represent the 0s and 1s of binary code. 

      While much of the research along this direction has focused on using bulk magnetic materials, a new class of magnetic materials — called two-dimensional van der Waals magnets — provides superior properties that can improve the scalability and energy efficiency of magnetic devices to make them commercially viable. 

      Although the benefits of shifting to 2D magnetic materials are evident, their practical induction into computers has been hindered by some fundamental challenges. Until recently, 2D magnetic materials could operate only at very low temperatures, much like superconductors. So bringing their operating temperatures above room temperature has remained a primary goal. Additionally, for use in computers, it is important that they can be controlled electrically, without the need for magnetic fields. Bridging this fundamental gap, where 2D magnetic materials can be electrically switched above room temperature without any magnetic fields, could potentially catapult the translation of 2D magnets into the next generation of “green” computers.

      A team of MIT researchers has now achieved this critical milestone by designing a “van der Waals atomically layered heterostructure” device where a 2D van der Waals magnet, iron gallium telluride, is interfaced with another 2D material, tungsten ditelluride. In an open-access paper published March 15 in Science Advances, the team shows that the magnet can be toggled between the 0 and 1 states simply by applying pulses of electrical current across their two-layer device. 

      Play video

      The Future of Spintronics: Manipulating Spins in Atomic Layers without External Magnetic FieldsVideo: Deblina Sarkar

      “Our device enables robust magnetization switching without the need for an external magnetic field, opening up unprecedented opportunities for ultra-low power and environmentally sustainable computing technology for big data and AI,” says lead author Deblina Sarkar, the AT&T Career Development Assistant Professor at the MIT Media Lab and Center for Neurobiological Engineering, and head of the Nano-Cybernetic Biotrek research group. “Moreover, the atomically layered structure of our device provides unique capabilities including improved interface and possibilities of gate voltage tunability, as well as flexible and transparent spintronic technologies.”

      Sarkar is joined on the paper by first author Shivam Kajale, a graduate student in Sarkar’s research group at the Media Lab; Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Nguyen Tuan Hung, an MIT visiting scholar in NSE and an assistant professor at Tohoku University in Japan; and Mingda Li, associate professor of NSE.

      Breaking the mirror symmetries 

      When electric current flows through heavy metals like platinum or tantalum, the electrons get segregated in the materials based on their spin component, a phenomenon called the spin Hall effect, says Kajale. The way this segregation happens depends on the material, and particularly its symmetries.

      “The conversion of electric current to spin currents in heavy metals lies at the heart of controlling magnets electrically,” Kajale notes. “The microscopic structure of conventionally used materials, like platinum, have a kind of mirror symmetry, which restricts the spin currents only to in-plane spin polarization.”

      Kajale explains that two mirror symmetries must be broken to produce an “out-of-plane” spin component that can be transferred to a magnetic layer to induce field-free switching. “Electrical current can ‘break’ the mirror symmetry along one plane in platinum, but its crystal structure prevents the mirror symmetry from being broken in a second plane.”

      In their earlier experiments, the researchers used a small magnetic field to break the second mirror plane. To get rid of the need for a magnetic nudge, Kajale and Sarkar and colleagues looked instead for a material with a structure that could break the second mirror plane without outside help. This led them to another 2D material, tungsten ditelluride. The tungsten ditelluride that the researchers used has an orthorhombic crystal structure. The material itself has one broken mirror plane. Thus, by applying current along its low-symmetry axis (parallel to the broken mirror plane), the resulting spin current has an out-of-plane spin component that can directly induce switching in the ultra-thin magnet interfaced with the tungsten ditelluride. 

      “Because it’s also a 2D van der Waals material, it can also ensure that when we stack the two materials together, we get pristine interfaces and a good flow of electron spins between the materials,” says Kajale. 

      Becoming more energy-efficient 

      Computer memory and processors built from magnetic materials use less energy than traditional silicon-based devices. And the van der Waals magnets can offer higher energy efficiency and better scalability compared to bulk magnetic material, the researchers note. 

      The electrical current density used for switching the magnet translates to how much energy is dissipated during switching. A lower density means a much more energy-efficient material. “The new design has one of the lowest current densities in van der Waals magnetic materials,” Kajale says. “This new design has an order of magnitude lower in terms of the switching current required in bulk materials. This translates to something like two orders of magnitude improvement in energy efficiency.”

      The research team is now looking at similar low-symmetry van der Waals materials to see if they can reduce current density even further. They are also hoping to collaborate with other researchers to find ways to manufacture the 2D magnetic switch devices at commercial scale. 

      This work was carried out, in part, using the facilities at MIT.nano. It was funded by the Media Lab, the U.S. National Science Foundation, and the U.S. Department of Energy. More

    • 125 Shares169 Views

      in Energy

      New MIT.nano equipment to accelerate innovation in “tough tech” sectors

      by

      A new set of advanced nanofabrication equipment will make MIT.nano one of the world’s most advanced research facilities in microelectronics and related technologies, unlocking new opportunities for experimentation and widening the path for promising inventions to become impactful new products.

      The equipment, provided by Applied Materials, will significantly expand MIT.nano’s nanofabrication capabilities, making them compatible with wafers — thin, round slices of semiconductor material — up to 200 millimeters, or 8 inches, in diameter, a size widely used in industry. The new tools will allow researchers to prototype a vast array of new microelectronic devices using state-of-the-art materials and fabrication processes. At the same time, the 200-millimeter compatibility will support close collaboration with industry and enable innovations to be rapidly adopted by companies and mass produced.

      MIT.nano’s leaders say the equipment, which will also be available to scientists outside of MIT, will dramatically enhance their facility’s capabilities, allowing experts in the region to more efficiently explore new approaches in “tough tech” sectors, including advanced electronics, next-generation batteries, renewable energies, optical computing, biological sensing, and a host of other areas — many likely yet to be imagined.

      “The toolsets will provide an accelerative boost to our ability to launch new technologies that can then be given to the world at scale,” says MIT.nano Director Vladimir Bulović, who is also the Fariborz Maseeh Professor of Emerging Technology. “MIT.nano is committed to its expansive mission — to build a better world. We provide toolsets and capabilities that, in the hands of brilliant researchers, can effectively move the world forward.”

      The announcement comes as part of an agreement between MIT and Applied Materials, Inc. that, together with a grant to MIT from the Northeast Microelectronics Coalition (NEMC) Hub, commits more than $40 million of estimated private and public investment to add advanced nano-fabrication equipment and capabilities at MIT.nano.

      “We don’t believe there is another space in the United States that will offer the same kind of versatility, capability, and accessibility, with 8-inch toolsets integrated right next to more fundamental toolsets for research discoveries,” Bulović says. “It will create a seamless path to accelerate the pace of innovation.”

      Pushing the boundaries of innovation

      Applied Materials is the world’s largest supplier of equipment for manufacturing semiconductors, displays, and other advanced electronics. The company will provide at MIT.nano several state-of-the-art process tools capable of supporting 150- and 200-millimeter wafers and will enhance and upgrade an existing tool owned by MIT. In addition to assisting MIT.nano in the day-to-day operation and maintenance of the equipment, Applied Materials engineers will develop new process capabilities to benefit researchers and students from MIT and beyond.

      “This investment will significantly accelerate the pace of innovation and discovery in microelectronics and microsystems,” says Tomás Palacios, director of MIT’s Microsystems Technology Laboratories and the Clarence J. Lebel Professor in Electrical Engineering. “It’s wonderful news for our community, wonderful news for the state, and, in my view, a tremendous step forward toward implementing the national vision for the future of innovation in microelectronics.”

      Nanoscale research at universities is traditionally conducted on machines that are less compatible with industry, which makes academic innovations more difficult to turn into impactful, mass-produced products. Jorg Scholvin, associate director for MIT.nano’s shared fabrication facility, says the new machines, when combined with MIT.nano’s existing equipment, represent a step-change improvement in that area: Researchers will be able to take an industry-standard wafer and build their technology on top of it to prove to companies it works on existing devices, or to co-fabricate new ideas in close collaboration with industry partners.

      “In the journey from an idea to a fully working device, the ability to begin on a small scale, figure out what you want to do, rapidly debug your designs, and then scale it up to an industry-scale wafer is critical,” Scholvin says. “It means a student can test out their idea on wafer-scale quickly and directly incorporate insights into their project so that their processes are scalable. Providing such proof-of-principle early on will accelerate the idea out of the academic environment, potentially reducing years of added effort. Other tools at MIT.nano can supplement work on the 200-millimeter wafer scale, but the higher throughput and higher precision of the Applied equipment will provide researchers with repeatability and accuracy that is unprecedented for academic research environments. Essentially what you have is a sharper, faster, more precise tool to do your work.”

      Scholvin predicts the equipment will lead to exponential growth in research opportunities.

      “I think a key benefit of these tools is they allow us to push the boundary of research in a variety of different ways that we can predict today,” Scholvin says. “But then there are also unpredictable benefits, which are hiding in the shadows waiting to be discovered by the creativity of the researchers at MIT. With each new application, more ideas and paths usually come to mind — so that over time, more and more opportunities are discovered.”

      Because the equipment is available for use by people outside of the MIT community, including regional researchers, industry partners, nonprofit organizations, and local startups, they will also enable new collaborations.

      “The tools themselves will be an incredible meeting place — a place that can, I think, transpose the best of our ideas in a much more effective way than before,” Bulović says. “I’m extremely excited about that.”

      Palacios notes that while microelectronics is best known for work making transistors smaller to fit on microprocessors, it’s a vast field that enables virtually all the technology around us, from wireless communications and high-speed internet to energy management, personalized health care, and more.

      He says he’s personally excited to use the new machines to do research around power electronics and semiconductors, including exploring promising new materials like gallium nitride, which could dramatically improve the efficiency of electronic devices.

      Fulfilling a mission

      MIT.nano’s leaders say a key driver of commercialization will be startups, both from MIT and beyond.

      “This is not only going to help the MIT research community innovate faster, it’s also going to enable a new wave of entrepreneurship,” Palacios says. “We’re reducing the barriers for students, faculty, and other entrepreneurs to be able to take innovation and get it to market. That fits nicely with MIT’s mission of making the world a better place through technology. I cannot wait to see the amazing new inventions that our colleagues and students will come out with.”

      Bulović says the announcement aligns with the mission laid out by MIT’s leaders at MIT.nano’s inception.

      “We have the space in MIT.nano to accommodate these tools, we have the capabilities inside MIT.nano to manage their operation, and as a shared and open facility, we have methodologies by which we can welcome anyone from the region to use the tools,” Bulović says. “That is the vision MIT laid out as we were designing MIT.nano, and this announcement helps to fulfill that vision.” More

    • 138 Shares109 Views

      in Security

      Engineers develop a vibrating, ingestible capsule that might help treat obesity

      by

      When you eat a large meal, your stomach sends signals to your brain that create a feeling of fullness, which helps you realize it’s time to stop eating. A stomach full of liquid can also send these messages, which is why dieters are often advised to drink a glass of water before eating.

      MIT engineers have now come up with a new way to take advantage of that phenomenon, using an ingestible capsule that vibrates within the stomach. These vibrations activate the same stretch receptors that sense when the stomach is distended, creating an illusory sense of fullness.

      In animals who were given this pill 20 minutes before eating, the researchers found that this treatment not only stimulated the release of hormones that signal satiety, but also reduced the animals’ food intake by about 40 percent. Scientists have much more to learn about the mechanisms that influence human body weight, but if further research suggests this technology could be safely used in humans, such a pill might offer a minimally invasive way to treat obesity, the researchers say.

      “For somebody who wants to lose weight or control their appetite, it could be taken before each meal,” says Shriya Srinivasan PhD ’20, a former MIT graduate student and postdoc who is now an assistant professor of bioengineering at Harvard University. “This could be really interesting in that it would provide an option that could minimize the side effects that we see with the other pharmacological treatments out there.”

      Srinivasan is the lead author of the new study, which appears today in Science Advances. Giovanni Traverso, an associate professor of mechanical engineering at MIT and a gastroenterologist at Brigham and Women’s Hospital, is the senior author of the paper.

      A sense of fullness

      When the stomach becomes distended, specialized cells called mechanoreceptors sense that stretching and send signals to the brain via the vagus nerve. As a result, the brain stimulates production of insulin, as well as hormones such as C-peptide, Pyy, and GLP-1. All of these hormones work together to help people digest their food, feel full, and stop eating. At the same time, levels of ghrelin, a hunger-promoting hormone, go down.

      While a graduate student at MIT, Srinivasan became interested in the idea of controlling this process by artificially stretching the mechanoreceptors that line the stomach, through vibration. Previous research had shown that vibration applied to a muscle can induce a sense that the muscle has stretched farther than it actually has.

      “I wondered if we could activate stretch receptors in the stomach by vibrating them and having them perceive that the entire stomach has been expanded, to create an illusory sense of distension that could modulate hormones and eating patterns,” Srinivasan says.

      As a postdoc in MIT’s Koch Institute for Integrative Cancer Research, Srinivasan worked closely with Traverso’s lab, which has developed many novel approaches to oral delivery of drugs and electronic devices. For this study, Srinivasan, Traverso, and a team of researchers designed a capsule about the size of a multivitamin, that includes a vibrating element. When the pill, which is powered by a small silver oxide battery, reaches the stomach, acidic gastric fluids dissolve a gelatinous membrane that covers the capsule, completing the electronic circuit that activates the vibrating motor.

      In a study in animals, the researchers showed that once the pill begins vibrating, it activates mechanoreceptors, which send signals to the brain through stimulation of the vagus nerve. The researchers tracked hormone levels during the periods when the device was vibrating and found that they mirrored the hormone release patterns seen following a meal, even when the animals had fasted.

      The researchers then tested the effects of this stimulation on the animals’ appetite. They found that when the pill was activated for about 20 minutes, before the animals were offered food, they consumed 40 percent less, on average, than they did when the pill was not activated. The animals also gained weight more slowly during periods when they were treated with the vibrating pill.

      “The behavioral change is profound, and that’s using the endogenous system rather than any exogenous therapeutic. We have the potential to overcome some of the challenges and costs associated with delivery of biologic drugs by modulating the enteric nervous system,” Traverso says.

      The current version of the pill is designed to vibrate for about 30 minutes after arriving in the stomach, but the researchers plan to explore the possibility of adapting it to remain in the stomach for longer periods of time, where it could be turned on and off wirelessly as needed. In the animal studies, the pills passed through the digestive tract within four or five days.

      The study also found that the animals did not show any signs of obstruction, perforation, or other negative impacts while the pill was in their digestive tract.

      An alternative approach

      This type of pill could offer an alternative to the current approaches to treating obesity, the researchers say. Nonmedical interventions such as diet exercise don’t always work, and many of the existing medical interventions are fairly invasive. These include gastric bypass surgery, as well as gastric balloons, which are no longer used widely in the United States due to safety concerns.

      Drugs such as GLP-1 agonists can also aid weight loss, but most of them have to be injected, and they are unaffordable for many people. According to Srinivasan, the MIT capsules could be manufactured at a cost that would make them available to people who don’t have access to more expensive treatment options.

      “For a lot of populations, some of the more effective therapies for obesity are very costly. At scale, our device could be manufactured at a pretty cost-effective price point,” she says. “I’d love to see how this would transform care and therapy for people in global health settings who may not have access to some of the more sophisticated or expensive options that are available today.”

      The researchers now plan to explore ways to scale up the manufacturing of the capsules, which could enable clinical trials in humans. Such studies would be important to learn more about the devices’ safety, as well as determine the best time to swallow the capsule before to a meal and how often it would need to be administered.

      Other authors of the paper include Amro Alshareef, Alexandria Hwang, Ceara Byrne, Johannes Kuosmann, Keiko Ishida, Joshua Jenkins, Sabrina Liu, Wiam Abdalla Mohammed Madani, Alison Hayward, and Niora Fabian.

      The research was funded by the National Institutes of Health, Novo Nordisk, the Department of Mechanical Engineering at MIT, a Schmidt Science Fellowship, and the National Science Foundation. More

    • 75 Shares149 Views

      in Environment

      Devices offers long-distance, low-power underwater communication

      by

      MIT researchers have demonstrated the first system for ultra-low-power underwater networking and communication, which can transmit signals across kilometer-scale distances.

      This technique, which the researchers began developing several years ago, uses about one-millionth the power that existing underwater communication methods use. By expanding their battery-free system’s communication range, the researchers have made the technology more feasible for applications such as aquaculture, coastal hurricane prediction, and climate change modeling.

      “What started as a very exciting intellectual idea a few years ago — underwater communication with a million times lower power — is now practical and realistic. There are still a few interesting technical challenges to address, but there is a clear path from where we are now to deployment,” 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.

      Underwater backscatter enables low-power communication by encoding data in sound waves that it reflects, or scatters, back toward a receiver. These innovations enable reflected signals to be more precisely directed at their source.

      Due to this “retrodirectivity,” less signal scatters in the wrong directions, allowing for more efficient and longer-range communication.

      When tested in a river and an ocean, the retrodirective device exhibited a communication range that was more than 15 times farther than previous devices. However, the experiments were limited by the length of the docks available to the researchers.

      To better understand the limits of underwater backscatter, the team also developed an analytical model to predict the technology’s maximum range. The model, which they validated using experimental data, showed that their retrodirective system could communicate across kilometer-scale distances.

      The researchers shared these findings in two papers which will be presented at this year’s ACM SIGCOMM and MobiCom conferences. Adib, senior author on both papers, is joined on the SIGCOMM paper by co-lead authors Aline Eid, a former postdoc who is now an assistant professor at the University of Michigan, and Jack Rademacher, a research assistant; as well as research assistants Waleed Akbar and Purui Wang, and postdoc Ahmed Allam. The MobiCom paper is also written by co-lead authors Akbar and Allam.

      Communicating with sound waves

      Underwater backscatter communication devices utilize an array of nodes made from “piezoelectric” materials to receive and reflect sound waves. These materials produce an electric signal when mechanical force is applied to them.

      When sound waves strike the nodes, they vibrate and convert the mechanical energy to an electric charge. The nodes use that charge to scatter some of the acoustic energy back to the source, transmitting data that a receiver decodes based on the sequence of reflections.

      But because the backscattered signal travels in all directions, only a small fraction reaches the source, reducing the signal strength and limiting the communication range.

      To overcome this challenge, the researchers leveraged a 70-year-old radio device called a Van Atta array, in which symmetric pairs of antennas are connected in such a way that the array reflects energy back in the direction it came from.

      But connecting piezoelectric nodes to make a Van Atta array reduces their efficiency. The researchers avoided this problem by placing a transformer between pairs of connected nodes. The transformer, which transfers electric energy from one circuit to another, allows the nodes to reflect the maximum amount of energy back to the source.

      “Both nodes are receiving and both nodes are reflecting, so it is a very interesting system. As you increase the number of elements in that system, you build an array that allows you to achieve much longer communication ranges,” Eid explains.

      In addition, they used a technique called cross-polarity switching to encode binary data in the reflected signal. Each node has a positive and a negative terminal (like a car battery), so when the positive terminals of two nodes are connected and the negative terminals of two nodes are connected, that reflected signal is a “bit one.”

      But if the researchers switch the polarity, and the negative and positive terminals are connected to each other instead, then the reflection is a “bit zero.”

      “Just connecting the piezoelectric nodes together is not enough. By alternating the polarities between the two nodes, we are able to transmit data back to the remote receiver,” Rademacher explains.

      When building the Van Atta array, the researchers found that if the connected nodes were too close, they would block each other’s signals. They devised a new design with staggered nodes that enables signals to reach the array from any direction. With this scalable design, the more nodes an array has, the greater its communication range.

      They tested the array in more than 1,500 experimental trials in the Charles River in Cambridge, Massachusetts, and in the Atlantic Ocean, off the coast of Falmouth, Massachusetts, in collaboration with the Woods Hole Oceanographic Institution. The device achieved communication ranges of 300 meters, more than 15 times longer than they previously demonstrated.

      However, they had to cut the experiments short because they ran out of space on the dock.

      Modeling the maximum

      That inspired the researchers to build an analytical model to determine the theoretical and practical communication limits of this new underwater backscatter technology.

      Building off their group’s work on RFIDs, the team carefully crafted a model that captured the impact of system parameters, like the size of the piezoelectric nodes and the input power of the signal, on the underwater operation range of the device.

      “It is not a traditional communication technology, so you need to understand how you can quantify the reflection. What are the roles of the different components in that process?” Akbar says.

      For instance, the researchers needed to derive a function that captures the amount of signal reflected out of an underwater piezoelectric node with a specific size, which was among the biggest challenges of developing the model, he adds.

      They used these insights to create a plug-and-play model into a which a user could enter information like input power and piezoelectric node dimensions and receive an output that shows the expected range of the system.

      They evaluated the model on data from their experimental trials and found that it could accurately predict the range of retrodirected acoustic signals with an average error of less than one decibel.

      Using this model, they showed that an underwater backscatter array can potentially achieve kilometer-long communication ranges.

      “We are creating a new ocean technology and propelling it into the realm of the things we have been doing for 6G cellular networks. For us, it is very rewarding because we are starting to see this now very close to reality,” Adib says.

      The researchers plan to continue studying underwater backscatter Van Atta arrays, perhaps using boats so they could evaluate longer communication ranges. Along the way, they intend to release tools and datasets so other researchers can build on their work. At the same time, they are beginning to move toward commercialization of this technology.

      “Limited range has been an open problem in underwater backscatter networks, preventing them from being used in real-world applications. This paper takes a significant step forward in the future of underwater communication, by enabling them to operate on minimum energy while achieving long range,” says Omid Abari, assistant professor of computer science at the University of California at Los Angeles, who was not involved with this work. “The paper is the first to bring Van Atta Reflector array technique into underwater backscatter settings and demonstrate its benefits in improving the communication range by orders of magnitude. This can take battery-free underwater communication one step closer to reality, enabling applications such as underwater climate change monitoring and coastal monitoring.”

      This research was funded, in part, by the Office of Naval Research, the Sloan Research Fellowship, the National Science Foundation, the MIT Media Lab, and the Doherty Chair in Ocean Utilization. More

    • 150 Shares189 Views

      in Energy

      Simple superconducting device could dramatically cut energy use in computing, other applications

      by

      MIT scientists and their colleagues have created a simple superconducting device that could transfer current through electronic devices much more efficiently than is possible today. As a result, the new diode, a kind of switch, could dramatically cut the amount of energy used in high-power computing systems, a major problem that is estimated to become much worse. Even though it is in the early stages of development, the diode is more than twice as efficient as similar ones reported by others. It could even be integral to emerging quantum computing technologies.

      The work, which is reported in the July 13 online issue of Physical Review Letters, is also the subject of a news story in Physics Magazine.

      “This paper showcases that the superconducting diode is an entirely solved problem from an engineering perspective,” says Philip Moll, director of the Max Planck Institute for the Structure and Dynamics of Matter in Germany. Moll was not involved in the work. “The beauty of [this] work is that [Moodera and colleagues] obtained record efficiencies without even trying [and] their structures are far from optimized yet.”

      “Our engineering of a superconducting diode effect that is robust and can operate over a wide temperature range in simple systems can potentially open the door for novel technologies,” says Jagadeesh Moodera, leader of the current work and a senior research scientist in MIT’s Department of Physics. Moodera is also affiliated with the Materials Research Laboratory, the Francis Bitter Magnet Laboratory, and the Plasma Science and Fusion Center (PSFC).

      The nanoscopic rectangular diode — about 1,000 times thinner than the diameter of a human hair — is easily scalable. Millions could be produced on a single silicon wafer.

      Toward a superconducting switch

      Diodes, devices that allow current to travel easily in one direction but not in the reverse, are ubiquitous in computing systems. Modern semiconductor computer chips contain billions of diode-like devices known as transistors. However, these devices can get very hot due to electrical resistance, requiring vast amounts of energy to cool the high-power systems in the data centers behind myriad modern technologies, including cloud computing. According to a 2018 news feature in Nature, these systems could use nearly 20 percent of the world’s power in 10 years.

      As a result, work toward creating diodes made of superconductors has been a hot topic in condensed matter physics. That’s because superconductors transmit current with no resistance at all below a certain low temperature (the critical temperature), and are therefore much more efficient than their semiconducting cousins, which have noticeable energy loss in the form of heat.

      Until now, however, other approaches to the problem have involved much more complicated physics. “The effect we found is due [in part] to a ubiquitous property of superconductors that can be realized in a very simple, straightforward manner. It just stares you in the face,” says Moodera.

      Says Moll of the Max Planck Institute, “The work is an important counterpoint to the current fashion to associate superconducting diodes [with] exotic physics, such as finite-momentum pairing states. While in reality, a superconducting diode is a common and widespread phenomenon present in classical materials, as a result of certain broken symmetries.”

      A somewhat serendipitous discovery

      In 2020 Moodera and colleagues observed evidence of an exotic particle pair known as Majorana fermions. These particle pairs could lead to a new family of topological qubits, the building blocks of quantum computers. While pondering approaches to creating superconducting diodes, the team realized that the material platform they developed for the Majorana work might also be applied to the diode problem.

      They were right. Using that general platform, they developed different iterations of superconducting diodes, each more efficient than the last. The first, for example, consisted of a nanoscopically thin layer of vanadium, a superconductor, which was patterned into a structure common to electronics (the Hall bar). When they applied a tiny magnetic field comparable to the Earth’s magnetic field, they saw the diode effect — a giant polarity dependence for current flow.

      They then created another diode, this time layering a superconductor with a ferromagnet (a ferromagnetic insulator in their case), a material that produces its own tiny magnetic field. After applying a tiny magnetic field to magnetize the ferromagnet so that it produces its own field, they found an even bigger diode effect that was stable even after the original magnetic field was turned off.

      Ubiquitous properties

      The team went on to figure out what was happening.

      In addition to transmitting current with no resistance, superconductors also have other, less well-known but just as ubiquitous properties. For example, they don’t like magnetic fields getting inside. When exposed to a tiny magnetic field, superconductors produce an internal supercurrent that induces its own magnetic flux that cancels the external field, thereby maintaining their superconducting state. This phenomenon, known as the Meissner screening effect, can be thought of as akin to our bodies’ immune system releasing antibodies to fight the infection of bacteria and other pathogens. This works, however, only up to some limit. Similarly, superconductors cannot entirely keep out large magnetic fields.

      The diodes the team created make use of this universal Meissner screening effect. The tiny magnetic field they applied — either directly, or through the adjacent ferromagnetic layer — activates the material’s screening current mechanism for expelling the external magnetic field and maintaining superconductivity.

      The team also found that another key factor in optimizing these superconductor diodes is tiny differences between the two sides, or edges, of the diode devices. These differences “create some sort of asymmetry in the way the magnetic field enters the superconductor,” Moodera says.

      By engineering their own form of edges on diodes to optimize these differences — for example, one edge with sawtooth features, while the other edge not intentionally altered — the team found that they could increase the efficiency from 20 percent to more than 50 percent. This discovery opens the door for devices whose edges could be “tuned” for even higher efficiencies, Moodera says.

      In sum, the team discovered that the edge asymmetries within superconducting diodes, the ubiquitous Meissner screening effect found in all superconductors, and a third property of superconductors known as vortex pinning all came together to produce the diode effect.

      “It is fascinating to see how inconspicuous yet ubiquitous factors can create a significant effect in observing the diode effect,” says Yasen Hou, first author of the paper and a postdoc at the Francis Bitter Magnet Laboratory and the PSFC. “What’s more exciting is that [this work] provides a straightforward approach with huge potential to further improve the efficiency.”

      Christoph Strunk is a professor at the University of Regensburg in Germany. Says Strunk, who was not involved in the research, “the present work demonstrates that the supercurrent in simple superconducting strips can become nonreciprocal. Moreover, when combined with a ferromagnetic insulator, the diode effect can even be maintained in the absence of an external magnetic field. The rectification direction can be programmed by the remnant magnetization of the magnetic layer, which may have high potential for future applications. The work is important and appealing both from the basic research and from the applications point of view.”

      Teenage contributors

      Moodera noted that the two researchers who created the engineered edges did so while still in high school during a summer at Moodera’s lab. They are Ourania Glezakou-Elbert of Richland, Washington, who will be going to Princeton University this fall, and Amith Varambally of Vestavia Hills, Alabama, who will be entering Caltech.

      Says Varambally, “I didn’t know what to expect when I set foot in Boston last summer, and certainly never expected to [be] a coauthor in a Physical Review Letters paper.

      “Every day was exciting, whether I was reading dozens of papers to better understand the diode phenomena, or operating machinery to fabricate new diodes for study, or engaging in conversations with Ourania, Dr. Hou, and Dr. Moodera about our research.

      “I am profoundly grateful to Dr. Moodera and Dr. Hou for providing me with the opportunity to work on such a fascinating project, and to Ourania for being a great research partner and friend.”

      In addition to Moodera and Hou, corresponding authors of the paper are professors Patrick A. Lee of the MIT Department of Physics and Akashdeep Kamra of Autonomous University of Madrid. Other authors from MIT are Liang Fu and Margarita Davydova of the Department of Physics, and Hang Chi, Alessandro Lodesani, and Yingying Wu, all of the Francis Bitter Magnet Laboratory and the Plasma Science and Fusion Center. Chi is also affiliated with the U.S. Army CCDC Research Laboratory.

      Authors also include Fabrizio Nichele, Markus F. Ritter, and Daniel Z. Haxwell of IBM Research Europe; Stefan Ilićof Materials Physics Center (CFM-MPC); and F. Sebastian Bergeret of CFM-MPC and Donostia International Physics Center.

      This work was supported by the Air Force Office of Sponsored Research, the Office of Naval Research, the National Science Foundation, and the Army Research Office. Additional funders are the European Research Council, the European Union’s Horizon 2020 Research and Innovation Framework Programme, the Spanish Ministry of Science and Innovation, the A. v. Humboldt Foundation, and the Department of Energy’s Office of Basic Sciences. More

    • 138 Shares129 Views

      in Energy

      3 Questions: What’s it like winning the MIT $100K Entrepreneurship Competition?

      by

      Solar power plays a major role in nearly every roadmap for global decarbonization. But solar panels are large, heavy, and expensive, which limits their deployment. But what if solar panels looked more like a yoga mat?

      Such a technology could be transported in a roll, carried to the top of a building, and rolled out across the roof in a matter of minutes, slashing installation costs and dramatically expanding the places where rooftop solar makes sense.

      That was the vision laid out by the MIT spinout Active Surfaces as part of the winning pitch at this year’s MIT $100K Entrepreneurship Competition, which took place May 15. The company is leveraging materials science and manufacturing innovations from labs across MIT to make ultra-thin, lightweight, and durable solar a reality.

      The $100K is one of MIT’s most visible entrepreneurship competitions, and past winners say the prize money is only part of the benefit that winning brings to a burgeoning new company. MIT News sat down with Active Surface founders Shiv Bhakta, a graduate student in MIT’s Leaders for Global Operations dual-degree program within the MIT Sloan School of Management and Department of Civil and Environmental Engineering, and Richard Swartwout SM ’18 PhD ’21, an electrical engineering and computer science graduate and former Research Laboratory of Electronics postdoc and MIT.nano innovation fellow, to learn what the last couple of months have been like since they won.

      Q: What is Active Surfaces’ solution, and what is its potential?

      Bhakta: We’re commercializing an ultrathin film, flexible solar technology. Solar is one of the most broadly distributed resources in the world, but access is limited today. It’s heavy — it weighs 50 to 60 pounds a panel — it requires large teams to move around, and the form factor can only be deployed in specific environments.

      Our approach is to develop a solar technology for the built environment. In a nutshell, we can create flexible solar panels that are as thin as paper, just as efficient as traditional panels, and at unprecedented cost floors, all while being applied to any surface. Same area, same power. That’s our motto.

      When I came to MIT, my north star was to dive deeper in my climate journey and help make the world a better, greener place. Now, as we build Active Surfaces, I’m excited to see that dream taking shape. The prospect of transforming any surface into an energy source, thereby expanding solar accessibility globally, holds the promise of significantly reducing CO2 emissions at a gigaton scale. That’s what gets me out of bed in the morning.

      Swartwout: Solar and a lot of other renewables tend to be pretty land-inefficient. Solar 1.0 is using low hanging fruit: cheap land next to easy interconnects and new buildings designed to handle the weight of current panels. But as we ramp up solar, those things will run out. We need to utilize spaces and assets better. That’s what I think solar 2.0 will be: urban PV deployments, solar that’s closer to demand, and integrated into the built environment. These next-generation use cases aren’t just a racking system in the middle of nowhere.

      We’re going after commercial roofs, which would cover most [building] energy demand. Something like 80-90 percent of building electricity demands in the space can be met by rooftop solar.

      The goal is to do the manufacturing in-house. We use roll-to-roll manufacturing, so we can buy tons of equipment off the shelf, but most roll-to-roll manufacturing is made for things like labeling and tape, and not a semiconductor, so our plan is to be the core of semiconductor roll-to-roll manufacturing. There’s never been roll-to-roll semiconductor manufacturing before.

      Q: What have the last few months been like since you won the $100K competition?

      Bhakta: After winning the $100K, we’ve gotten a lot of inbound contact from MIT alumni. I think that’s my favorite part about the MIT community — people stay connected. They’ve been congratulating us, asking to chat, looking to partner, deploy, and invest.

      We’ve also gotten contacted by previous $100K competition winners and other startups that have spun out of MIT that are a year or two or three ahead of us in terms of development. There are a lot of startup scaling challenges that other startup founders are best equipped to answer, and it’s been huge to get guidance from them.

      We’ve also gotten into top accelerators like Cleantech Open, Venture For Climatetech, and ACCEL at Greentown Labs. We also onboarded two rockstar MIT Sloan interns for the summer. Now we’re getting to the product-development phase, building relationships with potential pilot partners, and scaling up the area of our technology.      

      Swartwout: Winning the $100K competition was a great point of validation for the company, because the judges themselves are well known in the venture capital community as well as people who have been in the startup ecosystem for a long time, so that has really propelled us forward. Ideally, we’ll be getting more MIT alumni to join us to fulfill this mission.

      Q: What are your plans for the next year or so?

      Swartwout: We’re planning on leveraging open-access facilities like those at MIT.nano and the University of Massachusetts Amherst. We’re pretty focused now on scaling size. Out of the lab, [the technology] is a 4-inch by 4-inch solar module, and the goal is to get up to something that’s relevant for the industry to offset electricity for building owners and generate electricity for the grid at a reasonable cost.

      Bhakta: In the next year, through those open-access facilities, the goal is to go from 100-millimeter width to 300-millimeter width and a very long length using a roll-to-roll manufacturing process. That means getting through the engineering challenges of scaling technology and fine tuning the performance.

      When we’re ready to deliver a pilotable product, it’s my job to have customers lined up ready to demonstrate this works on their buildings, sign longer term contracts to get early revenue, and have the support we need to demonstrate this at scale. That’s the goal. More

    • 75 Shares169 Views

      in Security

      Ingestible “electroceutical” capsule stimulates hunger-regulating hormone

      by

      Hormones released by the stomach, such as ghrelin, play a key role in stimulating appetite. These hormones are produced by endocrine cells that are part of the enteric nervous system, which controls hunger, nausea, and feelings of fullness.

      MIT engineers have now shown that they can stimulate these endocrine cells to produce ghrelin, using an ingestible capsule that delivers an electrical current to the cells. This approach could prove useful for treating diseases that involve nausea or loss of appetite, such as cachexia (loss of body mass that can occur in patients with cancer or other chronic diseases).

      In tests in animals, the researchers showed that this “electroceutical” capsule could significantly boost ghrelin production in the stomach. They believe this approach could also be adapted to deliver electrical stimulation to other parts of the GI tract.

      “This study helps establish electrical stimulation by ingestible electroceuticals as a mode of triggering hormone release via the GI tract,” says Giovanni Traverso, an associate professor of mechanical engineering at MIT, a gastroenterologist at Brigham and Women’s Hospital, and the senior author of the study. “We show one example of how we’re able to engage with the stomach mucosa and release hormones, and we anticipate that this could be used in other sites in the GI tract that we haven’t explored here.”

      Khalil Ramadi SM ’16, PhD ’19, a graduate of the Department of Mechanical Engineering and the Harvard-MIT Program in Health Sciences and Technology who is now an assistant professor of bioengineering at the New York University (NYU) Tandon School of Engineering and the director of the Laboratory for Advanced Neuroengineering and Translational Medicine at NYU Abu Dhabi, and James McRae, an MIT graduate student, are the lead authors of the paper, which appears today in Science Robotics.

      Electrical stimulation

      The enteric nervous system controls all aspects of digestion, including the movement of food through the GI tract. Some patients with gastroparesis, a disorder of the stomach nerves that leads to very slow movement of food, have shown symptomatic improvement after electrical stimulation generated by a pacemaker-like device that can be surgically implanted in the stomach.

      Doctors had theorized that the electrical stimulation would provoke the stomach into contracting, which would help push food along. However, it was later found that while the treatment does help patients feel better, it affected motility to a lesser degree. The MIT team hypothesized that the electrical stimulation of the stomach might be leading to the release of ghrelin, which is known to promote hunger and reduce feelings of nausea.

      To test that hypothesis, the researchers used an electrical probe to deliver electrical stimulation in the stomachs of animals. They found that after 20 minutes of stimulation, ghrelin levels in the bloodstream were considerably elevated. They also found that electrical stimulation did not lead to any significant inflammation or other adverse effects.

      Once they established that electrical stimulation was provoking ghrelin release, the researchers set out to see if they could achieve the same thing using a device that could be swallowed and temporarily reside in the stomach. One of the main challenges in designing such a device is ensuring that the electrodes on the capsule can contact the stomach tissue, which are coated with fluid. 

      Play video

      To create a drier surface that electrodes can interact with, the researchers gave their capsule a grooved surface that wicks fluid away from the electrodes. The surface they designed is inspired by the skin of the Australian thorny devil lizard, which uses ridged scales to collect water. When the lizard touches water with any part of its skin, water is transported by capillary action along the channels to the lizard’s mouth.

      “We were inspired by that to incorporate surface textures and patterns onto the outside of this capsule,” McRae says. “That surface can manage the fluid that could potentially prevent the electrodes from touching the tissue in the stomach, so it can reliably deliver electrical stimulation.”

      The capsule surface consists of grooves with a hydrophilic coating. These grooves function as channels that draw fluid away from the stomach tissue. Inside the device are battery-powered electronics that produce an electric current that flows across electrodes on the surface of the capsule. In the prototype used in this study, the current runs constantly, but future versions could be designed so that the current can be wirelessly turned on and off, according to the researchers.

      Hormone boost

      The researchers tested their capsule by administering it into the stomachs of large animals, and they found that the capsule produced a substantial spike in ghrelin levels in the bloodstream.

      “As far as we know, this is the first example of using electrical stimuli through an ingestible device to increase endogenous levels of hormones in the body, like ghrelin. And so, it has this effect of utilizing the body’s own systems rather than introducing external agents,” Ramadi says.

      The researchers found that in order for this stimulation to work, the vagus nerve, which controls digestion, must be intact. They theorize that the electrical pulses transmit to the brain via the vagus nerve, which then stimulates endocrine cells in the stomach to produce ghrelin.

      Traverso’s lab now plans to explore using this approach in other parts of the GI tract, and the researchers hope to test the device in human patients within the next three years. If developed for use in human patients, this type of treatment could potentially replace or complement some of the existing drugs used to prevent nausea and stimulate appetite in people with cachexia or anorexia, the researchers say.

      “It’s a relatively simple device, so we believe it’s something that we can get into humans on a relatively quick time scale,” Traverso says.

      The research was funded by the Koch Institute Support (core) Grant from the National Cancer Institute, the National Institute for Diabetes and Digestive and Kidney Diseases, the Division of Engineering at New York University Abu Dhabi, a National Science Foundation graduate research fellowship, Novo Nordisk, and the Department of Mechanical Engineering at MIT. More

    • 50 Shares149 Views

      in Energy

      Strengthening electron-triggered light emission

      by

      The way electrons interact with photons of light is a key part of many modern technologies, from lasers to solar panels to LEDs. But the interaction is inherently a weak one because of a major mismatch in scale: A wavelength of visible light is about 1,000 times larger than an electron, so the way the two things affect each other is limited by that disparity.

      Now, researchers at MIT and elsewhere have come up with an innovative way to make much stronger interactions between photons and electrons possible, in the process producing a hundredfold increase in the emission of light from a phenomenon called Smith-Purcell radiation. The finding has potential implications for both commercial applications and fundamental scientific research, although it will require more years of research to make it practical.

      The findings are reported today in the journal Nature, in a paper by MIT postdocs Yi Yang (now an assistant professor at the University of Hong Kong) and Charles Roques-Carmes, MIT professors Marin Soljačić and John Joannopoulos, and five others at MIT, Harvard University, and Technion-Israel Institute of Technology.

      In a combination of computer simulations and laboratory experiments, the team found that using a beam of electrons in combination with a specially designed photonic crystal — a slab of silicon on an insulator, etched with an array of nanometer-scale holes — they could theoretically predict stronger emission by many orders of magnitude than would ordinarily be possible in conventional Smith-Purcell radiation. They also experimentally recorded a one hundredfold increase in radiation in their proof-of-concept measurements.

      Unlike other approaches to producing sources of light or other electromagnetic radiation, the free-electron-based method is fully tunable — it can produce emissions of any desired wavelength, simply by adjusting the size of the photonic structure and the speed of the electrons. This may make it especially valuable for making sources of emission at wavelengths that are difficult to produce efficiently, including terahertz waves, ultraviolet light, and X-rays.

      The team has so far demonstrated the hundredfold enhancement in emission using a repurposed electron microscope to function as an electron beam source. But they say that the basic principle involved could potentially enable far greater enhancements using devices specifically adapted for this function.

      The approach is based on a concept called flatbands, which have been widely explored in recent years for condensed matter physics and photonics but have never been applied to affecting the basic interaction of photons and free electrons. The underlying principle involves the transfer of momentum from the electron to a group of photons, or vice versa. Whereas conventional light-electron interactions rely on producing light at a single angle, the photonic crystal is tuned in such a way that it enables the production of a whole range of angles.

      The same process could also be used in the opposite direction, using resonant light waves to propel electrons, increasing their velocity in a way that could potentially be harnessed to build miniaturized particle accelerators on a chip. These might ultimately be able to perform some functions that currently require giant underground tunnels, such as the 30-kilometer-wide Large Hadron Collider in Switzerland.

      “If you could actually build electron accelerators on a chip,” Soljačić says, “you could make much more compact accelerators for some of the applications of interest, which would still produce very energetic electrons. That obviously would be huge. For many applications, you wouldn’t have to build these huge facilities.”

      The new system could also potentially provide a highly controllable X-ray beam for radiotherapy purposes, Roques-Carmes says.

      And the system could be used to generate multiple entangled photons, a quantum effect that could be useful in the creation of quantum-based computational and communications systems, the researchers say. “You can use electrons to couple many photons together, which is a considerably hard problem if using a purely optical approach,” says Yang. “That is one of the most exciting future directions of our work.”

      Much work remains to translate these new findings into practical devices, Soljačić cautions. It may take some years to develop the necessary interfaces between the optical and electronic components and how to connect them on a single chip, and to develop the necessary on-chip electron source producing a continuous wavefront, among other challenges.

      “The reason this is exciting,” Roques-Carmes adds, “is because this is quite a different type of source.” While most technologies for generating light are restricted to very specific ranges of color or wavelength, and “it’s usually difficult to move that emission frequency. Here it’s completely tunable. Simply by changing the velocity of the electrons, you can change the emission frequency. … That excites us about the potential of these sources. Because they’re different, they offer new types of opportunities.”

      But, Soljačić concludes, “in order for them to become truly competitive with other types of sources, I think it will require some more years of research. I would say that with some serious effort, in two to five years they might start competing in at least some areas of radiation.”

      The research team also included Steven Kooi at MIT’s Institute for Soldier Nanotechnologies, Haoning Tang and Eric Mazur at Harvard University, Justin Beroz at MIT, and Ido Kaminer at Technion-Israel Institute of Technology. The work was supported by the U.S. Army Research Office through the Institute for Soldier Nanotechnologies, the U.S. Air Force Office of Scientific Research, and the U.S. Office of Naval Research. More