One-step solution-coating method to advance perovskite solar cell manufacturing and commercialization

Peer-Reviewed Publication

CITY UNIVERSITY OF HONG KONG

 

IMAGE: PEROVSKITE SOLAR CELLS FABRICATED BY THE ONE-STEP SOLUTION SPIN-COATING METHOD. view more 

CREDIT: DR ZHU ZONGLONG’S RESEARCH GROUP / CITY UNIVERSITY OF HONG KONG

Perovskite solar cells (PSCs) are considered a promising candidate for next-generation photovoltaic technology with high efficiency and low production cost, potentially revolutionizing the renewable energy industry. However, the existing layer-by-layer manufacturing process presents challenges that have hindered the commercialisation of this technology. Recently, researchers from City University of Hong Kong (CityU) and the National Renewable Energy Laboratory (NREL) in the US jointly developed an innovative one-step solution-coating approach that simplifies the manufacturing process and lowers the commercialisation barriers for PSCs.

“Reducing the number of device-processing steps without sacrificing device efficiency will help reduce the process complexity and manufacturing cost, which will enhance the manufacturability of PSCs,” explained Dr Zhu Zonglong, a co-leader of the research and an assistant professor in the Department of Chemistry at CityU. 

“We addressed the manufacturing issue with a novel approach to co-process the hole-selective contact and perovskite layer in a single step, resulting in state-of-the-art efficiency of 24.5% and exceptional stability for inverted perovskite solar cells. This helps bring the commercialisation of the technology one step closer,” he said. 

Typically, PSCs are fabricated using a layer-by-layer process, which involves sequentially depositing different layers of the solar cell on top of each other. While this approach has been successful in producing high-performance perovskite solar cells, it causes issues that may hinder their commercialisation, such as increased fabrication cost, unsatisfactory uniformity and reproducibility. 

To improve the manufacturability of PSCs, Dr Zhu collaborated with Dr Joseph M. Luther, from NREL, to jointly invent a new approach for fabricating efficient inverted perovskite solar cells in which the hole-selective contact and perovskite light absorber can spontaneously form in a single solution-coating procedure.

They found that if specific phosphonic or carboxylic acids are added to perovskite precursor solutions, the solution will self-assemble on the indium tin oxide substrate during perovskite film processing. They form a robust self-assembled monolayer as an excellent hole-selective contact while the perovskite crystallizes. This single solution-coating procedure not only solves wettability issues, but also simplifies device fabrication by creating both the hole-selective contact and the perovskite light absorber simultaneously, instead of the traditional layer-by-layer process. 

The newly created PSC device has a power conversion efficiency of 24.5% and can retain more than 90% of its initial efficiency even after 1,200 hours of operating at the maximum power point under continuous illumination. Its efficiency is comparable to that of similar PSCs in the market.

The collaborative team also showed that the new approach is compatible with various self-assembled monolayer molecular systems, perovskite compositions, solvents and scalable processing methods, such as spin-coating and blade-coating techniques. And the PSC fabricated with the new approach have comparable performance with those produced from other methods. 

“By introducing this innovative approach, we hope to contribute to the perovskite research community by proposing a more straightforward method for manufacturing high-performance perovskite solar cells and potentially accelerating the process of bring them to market,” said Dr Zhu.

The research team plans to further explore the relationship between self-assembled monolayer molecule structures and perovskite precursors to identify an optimal group of self-assembled monolayer molecules for this technique, thereby enhancing the overall performance of the PSCs.

The findings were published in the scientific journal Nature Energy under the title "Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells".

Dr Zhu and Dr Luther are the corresponding authors of the research. The co-first authors are Dr Zheng Xiaopeng and Dr Chen Min from NREL, Mr Li Zhen from CityU, and Dr Zhang Yi from the Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. The research work conducted at CityU was supported by the Innovation and Technology Fund and the Green Tech Fund in Hong Kong.

https://www.cityu.edu.hk/research/stories/2023/04/20/one-step-solution-coating-method-advance-perovskite-solar-cell-manufacturing-and-commercialisation

Large-area perovskite films (5 x 5 cm) fabricated by the one-step solution blade-coating method.

CREDIT

Dr Zhu Zonglong’s research group / City University of Hong Kong

JOURNAL

Nature Energy

DOI

10.1038/s41560-023-01227-6 

METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells

Body extension by using two mobile manipulators

Peer-Reviewed Publication

BEIJING INSTITUTE OF TECHNOLOGY PRESS CO., LTD

 

IMAGE: ROBOTICISTS FROM OSAKA UNIVERSITY DEVELOPED A REMOTELY OPERATED ROBOTIC SYSTEM FOR OPERATING TASKS ON DANGEROUS OR HUMAN UNFRIENDLY ENVIRONMENTS view more 

CREDIT: CYBORG AND BIONIC SYSTEMS

Imagine lying on a bed, you just have to move your fingers to guide a mobile robot to bring you a cup of water, open the door to fetch some deliveries, or even do some laundry. If you are interested, you may want to learn more about a new remotely operated robotic system based on two mobile manipulators. This system was developed by roboticists from Osaka University. They published a research paper describing this robotic system on Feb. 10 in the journal Cyborg and Bionic Systems.

 

Back in the year of 2013, Fukushima nuclear power plant witnessed a catastrophic radioactive leakage and contamination, which makes the surrounding area extremely dangerous for humans to stay and perform emergency tasks. Under this circumstance, many robots were deployed and controlled remotely, which greatly reduced the risks and harm to rescuers. Since then, remotely operated robotic systems have been a hot research topic.

 

“More than being used in radiation-exposed areas, there were also many field robots developed for collecting data at distant damaged sites caused by earthquakes or other man-made and natural disasters, medical sites without expert doctors, and outer space, etc.” said the study authors.

 

“The research interest in remote control has been further signified in the past 2 years as the coronavirus disease 2019 (COVID-19) pandemic restricted people’s movement. A series of robots were developed and remotely deployed at the Wuhan hospitals to assist doctors and patients” said Weiwei Wan, the corresponding author of this study, from the Graduate School of Engineering, Osaka University.

 

Compared with former research, which tends to contain one mobile base and one or two robotic arms mounted on this base, this study features two separate mobile bases. Each base is mounted with a manipulator. Each manipulator-mounted base is controlled by one hand. In particular, the human teleoperator’s poses of each hand were recorded by a motion capture system to control the poses of the respective robotic arm. In addition, the operator can move the two mobile bases using two joysticks. Therefore, these two mobile manipulators can work in a cooperative manner, like how we use our hands.

 

“The proposed idea of incorporating two independently movable manipulators for motion-tracking-based teleoperation is intriguing. However, there are some inherent issues to be addressed.” Said Wan, “First of all, how to map the postures of the human teleoperator’s two arms to the corresponding manipulator’s poses. In addition, how to avoid it when under some circumstances, the manipulator may collide with itself. Moreover, how to remotely monitor the two manipulators with the large operating range.” They believe they have addressed these issues by applying special routines and hand-mounted cameras.

 

They demonstrate this robotic system by picking up a coffee mug and handing over it using only one mobile manipulator. More importantly, the two mobile manipulators can work in a cooperative manner to pick up and place long sticks. “Since there are two mobile manipulators, the presented system could keep the advantages of having two arms while extending the human body functions.” said Wan, “The results demonstrated the effectiveness of the proposed system, resulting in extending the human body to a large space while keeping the benefits of having two limbs.”

 

In the future, they will focus on addressing several remaining problems including a) developing an automatic calibration method to match the direction of the human teleoperator’s arms and the manipulators; b) using a joystick with built-in IMU sensor to allow the teleoperator more flexibly control the joystick; c) minimizing the coordination errors between two manipulators; d) providing a feedback interface for teleoperation in a distant and unseen workspace.

 

The authors of the paper include Yusuke Hirao, Weiwei Wan, Dimitrios Kanoulas, and Kensuke Harada.

 

The research is funded by the UKRI Future Leaders Fellowship (RoboHike) and the UCL-Osaka University Strategic Partner Fund 2021. 

 

The paper, “Body Extension by Using Two Mobile Manipulators,” was published in the journal Cyborg and Bionic Systems on Feburary 10, 2023, at DOI: https://doi.org/10.34133/cbsystems.0014

 

 

Reference

Authors: Yusuke Hirao1, Weiwei Wan1, Dimitrios Kanoulas2, and Kensuke Harada1

Title of original paper: Body Extension by Using Two Mobile Manipulators

Journal: Cyborg and Bionic Systems

DOI: 10.34133/cbsystems.0014

 

Affiliations:

1Graduate School of Engineering Science, Osaka University, Osaka, Japan.

2Department of Computer Science, University College London, London, UK.

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DOI

10.34133/cbsystems.0014 

New USC Schaeffer Center white paper finds Medicare coverage for weight loss therapies could generate significant cost-offsets

USC Schaeffer white paper finds that increasing access to obesity treatments would help save lives and reduce healthcare costs.

Reports and Proceedings

UNIVERSITY OF SOUTHERN CALIFORNIA

A new USC Schaeffer Center white paper finds the value to society of Medicare coverage for new classes of weight loss drugs would equal nearly $1 trillion over ten years.

Obesity is one of the United States’ most urgent health issues—and also one of the most treatable. Yet because Medicare and most private insurers do not cover weight-loss medications and many devices, just 1% of eligible patients receive treatments.  

“Obesity is a leading risk factor for mortality in the U.S.,” says Darius Lakdawalla, director of research at the USC Schaeffer Center for Health Policy & Economics and co-author of the study. “Our modeling shows that new treatments generate substantial benefits to Medicare and its beneficiaries. Developing strategies for unlocking that value should be a priority for policymakers.”

Leveraging the Schaeffer Center’s Future Adult Model, an economic-demographic microsimulation model, the researchers estimated the benefits of treating Americans suffering from obesity and the cost-offsets that Medicare and society could accrue if laws were changed to allow Medicare to cover anti-obesity medications. 

Coverage for new obesity treatments could generate approximately $175 billion in cost offsets to Medicare in the first 10 years alone. By 30 years, cost offsets to Medicare would increase to $700 billion.

The positive impacts extend beyond Medicare: society could reap as much as $100 billion per year (or $1 trillion over 10 years) of social benefit in the form of reduced healthcare spending and improvements in quality of life from reduced disability and pain if all eligible Americans were treated.

 

Models Show the Ripple Effects of Obesity on the Healthcare System

Despite safe and effective treatments, federal law currently prohibits Medicare from paying for most forms of obesity procedures and medications. Legislation has been introduced, including the bipartisan Treat and Reduce Obesity Act, that would expand Medicare Part D’s prescription benefits to include FDA-approved drugs for chronic weight management.

Researchers discovered that most of the cost savings to Medicare—more than 60%—would flow to Medicare Part A, which covers hospital, hospice, nursing facility and home care.  This could significantly help Medicare, which risks becoming insolvent by 2028.

“Because obesity is associated with many chronic conditions that significantly impact patients’ lives—and Medicare’s costs—reducing obesity rates has a ripple effect in the prevalence of other conditions,” says Alison Sexton Ward, one of the co-authors of the paper and research scientist at the USC Schaeffer Center.

The researchers find that if all Americans eligible for obesity treatments gained access, the prevalence of obesity in the Medicare population would fall by 53% after the first decade.  In addition, the researchers show that treating obesity will reduce the incidence of many related diseases, including diabetes (a 5.5% reduction in prevalence after 10 years), hypertension (1.2%) and heart disease (1.7%).

 

 

Covering Obesity Treatments Reduces Health Disparities

Improving access to obesity medications could also enhance health equity, since obesity disproportionately affects Black, Hispanic and lower-income communities. More than half of the Black Medicare population has obesity and two-thirds have hypertension.

“Black and other historically marginalized communities have been disproportionately burdened by obesity,” says one of the paper’s co-authors, Bryan Tysinger, director of health policy simulation at the USC Schaeffer Center.

Medical breakthroughs that simplify healthcare and reduce patient effort can reduce disparities, but only if access is prioritized.

Outcomes-Based Pricing Models Would Ensure Access

New obesity treatments promise substantial benefits to patients if policymakers can solve the problem of how to pay for them.  The researchers point to outcomes-based valuation models, including a novel pricing approach that allows for real-world evaluation of the treatments while also encouraging broad coverage.  

“About half the decline in U.S. deaths from coronary heart disease over the past 50 years can be attributed to new drugs to lower cholesterol and blood pressure,” says one of the paper’s co-authors, Dana Goldman, co-director of the USC Schaeffer Center and dean of the USC Price School. “Now imagine if Congress had prohibited coverage for these lifesaving drugs.  Novel pricing solutions can ensure access for all patients who would benefit from these important new anti-obesity treatments.”  

PhuongGiang Nguyen also contributed to the paper. Funding for the paper was provided by the Schaeffer Center, which receives funding from foundations, government agencies, individuals, and corporations— including Eli Lilly & Company and other companies that may have interests in obesity treatments. The Future Adult Model was developed with support from the National Institute on Aging (P30AG024968).          

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DOI

10.25549/4rf9-kh77 

METHOD OF RESEARCH

Data/statistical analysis

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Benefits of Medicare Coverage for Weight Loss Drugs

ARTICLE PUBLICATION DATE

18-Apr-2023

COI STATEMENT

The Schaeffer Center White Paper Series is published by the Leonard D. Schaeffer Center for Health Policy & Economics at the University of Southern California. Papers published in this series undergo a rigorous peer review process, led by the Director of Quality Assurance at the USC Schaeffer Center. This process includes external review by at least two scholars not affiliated with the Center. This white paper was supported by the Schaeffer Center, which receives funding from foundations, government agencies, individuals, and corporations — including Eli Lilly & Company and other companies that may have interests in obesity treatments. The Future Adult Model was developed with support from the National Institute on Aging (P30AG024968). A complete list of sponsors can be found in our annual report (available here). At all times, the independence and integrity of the research is paramount and the Center retains the right to publish all findings from its research activities. The views expressed herein are those of the authors and do not necessarily represent the views of the Schaeffer Center or its sponsors. Disclosures reported by authors are available here.

Towards more efficient and eco-friendly thermoelectric oxides with hydrogen substitution

Peer-Reviewed Publication

TOKYO INSTITUTE OF TECHNOLOGY

 

IMAGE: - view more 

CREDIT: TOKYO TECH

Today, over half of the total energy produced from fossil fuels is discarded as waste heat, which accelerates global warming. If we could convert the waste heat into a more useful form of energy like electricity, we could minimize fuel consumption and reduce our carbon footprint. In this regard, thermoelectric energy conversion has gained momentum as a technology for generating electricity from waste heat.

For efficient conversion, a thermoelectric material must have a high conversion efficiency (ZT). So far, realizing a high ZT has been possible only with the use of heavy elements like lead, bismuth, and tellurium. However, the use of rare, expensive, and environmentally toxic elements such as these has limited the large-scale application of thermoelectric energy conversion.

To tackle these issues, transition metal oxides based on platforms such as SrTiO3 have emerged as a more inexpensive and benign alternative. However, their ZT is typically limited by a high thermal conductivity (κ), since for a high κ, the temperature across the material becomes uniform more quickly, and the lowered temperature difference – the driving force behind the thermoelectric conversion – causes electric power generation to decrease as well.

Against this backdrop, a research team including Associate Professor Takayoshi Katase from Tokyo Institute of Technology (Tokyo Tech), Japan recently discovered a new approach to reducing κ and boosting the performance of SrTiO3 by hydrogen substitution.

Conventionally, the use of light elements is expected to increase the κ originating from lattice vibration (κlat), leading to the adoption of heavy elements to reduce the κlat. In contrast, in their study published in Advanced Functional Materials, the team discovered that the κlat of SrTiO3 could be reduced to less than half its original value by substituting a light element, namely hydrogen.

They clarified the mechanism underlying their observation using first-principles calculations, which showed that substituting a portion of the oxygen anions (O−) with hydrogen anions (H−), yielding compounds of the form SrTiO3−xHx, results in a mixture comprising a strong Ti-O bond and a weak Ti-H bond. These randomly distributed Ti-(O,H) bonds, in turn, largely decrease κlat.

The team also found that SrTiO3−xHx polycrystals exhibit high electron mobility comparable to that of single-crystal materials without any deterioration in electron conduction across grain boundaries. Based on these two effects, a low thermal conductivity along with a high electrical output power are realized at the same time, resulting in an improved thermoelectric conversion efficiency in the SrTiO3−xHx polycrystal.

Overall, these findings can open doors to innovative strategies for developing next-generation thermoelectric materials. “In future, the hydrogen substitution approach would realize excellent environmentally benign thermoelectric materials that do not require the use of heavy elements,” concludes Dr. Katase.

Let us hope further studies in this field will lead to a widespread adoption of thermoelectric conversion technology so that even waste heat will not go to waste!

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JOURNAL

Advanced Functional Materials

DOI

10.1002/adfm.202213144 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Hydride anion substitution boosts thermoelectric performance of polycrystalline SrTiO3 via simultaneous realization of reduced thermal conductivity and high electronic conductivity

For people with epilepsy, neighborhood may be tied to memory, mental health

Peer-Reviewed Publication

AMERICAN ACADEMY OF NEUROLOGY

MINNEAPOLIS – People with epilepsy living in disadvantaged neighborhoods—areas with higher poverty levels and fewer educational and employment opportunities— may be more likely to have memory, thinking, and mental health problems compared to people with epilepsy living in neighborhoods with fewer disadvantages, according to new research published in the April 19, 2023, online issue of Neurology®, the medical journal of the American Academy of Neurology. The study does not prove that living in disadvantaged neighborhoods causes memory and mental health problems. It only shows an association.

“Epilepsy research has arguably ignored the potential impact of the social determinants of health in neighborhoods on cognition—factors that have been hiding in plain sight for many years,” said study author Robyn Busch, PhD, of Cleveland Clinic in Ohio. “Our study shows that these neighborhood social factors are linked to epilepsy outcomes.” 

For the study, researchers reviewed a registry of people with temporal lobe epilepsy, the most common adult form of epilepsy, which is associated with high risk for thinking problems and depressed mood. Researchers identified 800 people with an average age of 38 whose epilepsy was resistant to treatment and who were evaluated for potential epilepsy surgery.

Researchers compared the participants’ scores on measures of intelligence, attention, memory and other thinking skills, depression and anxiety.

Researchers used the home address of each participant and a measure called the Area Deprivation Index to determine if each participant lived in an advantaged or disadvantaged neighborhood. The index incorporates information on the socioeconomic conditions of each neighborhood and its residents, ranking neighborhoods based on 17 indicators including income, employment, education and housing quality. Neighborhoods in the index are determined by census areas of about 1,500 residents.

Researchers divided participants into five groups based on neighborhood advantage.

In a composite score of all attention tests, with scores ranging from 60 to 135, people in neighborhoods with the most disadvantage had an average score of 85 compared to those in neighborhoods with the least disadvantage who had an average score of 95. Higher scores indicate better attention. Similar results were seen on measures of intelligence, processing speed, language, visuospatial skills, and memory, with people in the most disadvantaged neighborhoods showing lower test scores than those in less disadvantaged neighborhoods.

When compared to people in neighborhoods with the least disadvantage, people in neighborhoods with the most disadvantage were more likely to have worse cognitive outcomes across tests of different thinking skills. People who self-identified as Black, Hispanic or from other non-white groups were overrepresented in the most disadvantaged neighborhood group and were nearly three times more likely to have reduced scores on multiple cognitive tests than non-Hispanic white people.

Based on their self-reported symptoms, people in neighborhoods with the most disadvantage reported mild symptoms of depression and anxiety compared to those in neighborhoods with the least disadvantage who reported minimal symptoms of depression and anxiety.

“These study findings elevate the need to consider the role of social and neighborhood issues in assessing the outcomes for people with epilepsy,” said editorial author Lidia M. V. R. Moura, MD, MPH, PhD of Massachusetts General Hospital in Boston and Fellow of the American Academy of Neurology. “More research is needed to identify these social factors that may be modifiable that can help improve cognition and prevent further worsening. More community-based partnerships and the usage of screening and mapping tools may help reduce these disparities among people with epilepsy.”

A limitation of the study was that Area Deprivation Index scores were measured at only one point in adulthood. This does not include neighborhood information during critical periods of early development or changes throughout life.

The study was supported by the Cleveland Clinic Epilepsy Center.

Learn more about epilepsy at BrainandLife.org, home of the American Academy of Neurology’s free patient and caregiver magazine focused on the intersection of neurologic disease and brain health. Follow Brain & Life® on Facebook, Twitter and Instagram.

Simple test may predict cognitive impairment long before symptoms appear

Peer-Reviewed Publication

AMERICAN ACADEMY OF NEUROLOGY

MINNEAPOLIS – In people with no thinking and memory problems, a simple test may predict the risk of developing cognitive impairment years later, according to a study published in the April 19, 2023, online issue of Neurology®, the medical journal of the American Academy of Neurology.

“There is increasing evidence that some people with no thinking and memory problems may actually have very subtle signs of early cognitive impairment,” said study author Ellen Grober, PhD, of Albert Einstein College of Medicine in the Bronx, New York. “In our study, a sensitive and simple memory test predicted the risk of developing cognitive impairment in people who were otherwise considered to have normal cognition.”

The study involved 969 people with an average age of 69 with no thinking or memory problems at the start of the study. They were given a simple memory test and were followed for up to 10 years.

The test includes two phases. For the study phase, people are shown four cards, each with drawings of four items. They are asked to identify the item belonging to a particular category. For example, participants would name the item “grapes” after being asked to identify a “fruit.” For the test phase, participants are first asked to recall the items. This measures their ability to retrieve information. Then, for items they did not remember, they are given category cues. This phase measures memory storage.

The participants were divided into five groups, or stages zero through four, based on their test scores, as part of the Stages of Objective Memory Impairment (SOMI) system. Stage zero represents no memory problems. Stages one and two reflect increasing difficulty with retrieving memories which can precede dementia by five to eight years. These participants continue to be able to remember items when given cues. In the third and fourth stages, people cannot remember all the items even after they are given cues. These stages precede dementia by one to three years.

A total of 47% of the participants were in stage zero, 35% in stage one, 13% in stage two and 5% in stages three and four combined.

Of the participants, 234 people developed cognitive impairment.

After adjusting for age, sex, education and a gene that affects a person’s risk of Alzheimer’s disease, APOE4, researchers found when compared to people who were at SOMI stage zero, people at stages one and two were twice as likely to develop cognitive impairment. People who were at stages three and four were three times as likely to develop cognitive impairment.

After adjusting for biomarkers of Alzheimer’s disease including brain amyloid plaques and tau tangles, the SOMI system continued to predict an increased risk of cognitive impairment.

Researchers estimated that after 10 years about 72% of those in the third and fourth stages would have developed cognitive impairment, compared to about 57% of those in the second stage, 35% in the first stage and 21% of those in stage zero.

“Our results support the use of the SOMI system to identify people most likely to develop cognitive impairment,” said Grober. “Detecting cognitive impairment at its earliest stages is beneficial to researchers investigating treatments. It also could benefit those people who are found to be at increased risk by consulting with their physician and implementing interventions to promote healthy brain aging.”

A limitation of the study was that most participants were white and well educated. Grober said more research is needed in larger and more diverse populations.

The study was funded by the National Institutes of Health, Alzheimer’s Association, Cure Alzheimer Fund and the Leonard and Sylvia Marx Foundation.

Learn more about brain health at BrainandLife.org, home of the American Academy of Neurology’s free patient and caregiver magazine focused on the intersection of neurologic disease and brain health. Follow Brain & Life® on Facebook, Twitter and Instagram.  

When posting to social media channels about this research, we encourage you to use the hashtags #Neurology and #AANscience. 

The American Academy of Neurology is the world’s largest association of neurologists and neuroscience professionals, with over 40,000 members. The AAN is dedicated to promoting the highest quality patient-centered neurologic care. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as Alzheimer’s disease, stroke, migraine, multiple sclerosis, concussion, Parkinson’s disease and epilepsy. 

For more information about the American Academy of Neurology, visit AAN.com or find us on Facebook, Twitter, Instagram, LinkedIn and YouTube.  

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JOURNAL

Neurology

Surface steers signals for next-gen networks

Reports and Proceedings

PRINCETON UNIVERSITY, ENGINEERING SCHOOL

 

IMAGE: COMPUTER SCIENCE PH.D. STUDENT KUN WOO CHO IS THE LEAD AUTHOR OF A STUDY ON MMWALL, A NEW DEVICE THAT STEERS HIGHER-FREQUENCY 5G SIGNALS, OR MMWAVE SIGNALS, TO GET AROUND OBSTACLES AND IMPROVE CONNECTIVITY. view more 

CREDIT: TORI REPP/FOTOBUDDY

5G communications’ superfast download speeds rely on the high frequencies that drive the transmissions. But the highest frequencies come with a tradeoff.

Frequencies at the upper end of the 5G spectrum hold the greatest amount of data and could be critical to high-resolution augmented and virtual reality, video streaming, video conferencing, and services in crowded urban areas. But those high-end frequencies are easily blocked by walls, furniture and even people. This has been a hurdle to achieving the technology’s full potential.

Now, a team led by Princeton researchers has developed a new device to help higher-frequency 5G signals, known as millimeter-wave or mmWave, overcome this obstacle. The device, called mmWall, is about the size of a small tablet. It can steer mmWave signals to reach all corners of a large room, and, when installed in a window, can bring signals from an outdoor transmitter indoors. The researchers presented their work on mmWall at the USENIX Symposium on Networked Systems Design and Implementation in Boston on April 19.

While computers and smartphones often connect to Wi-Fi indoors to get the best data speeds, outdoor 5G base stations could someday replace Wi-Fi systems and provide high-speed connectivity both indoors and outdoors, preventing glitches when devices switch between networks, said Kun Woo Cho, a Ph.D. student in Princeton’s Department of Computer Science and the lead author of the research. Boosting 5G signals with technology like mmWall will be crucial to this broader adoption, she said.

The mmWall is an accordion-like array of 76 vertical panels that can both reflect and refract radio waves at frequencies above 24 gigahertz, the lower bound of mmWave signals. These frequencies can provide a bandwidth five to 10 times greater than the maximum capability of 4G networks. The device can steer beams around obstacles, as well as efficiently align the beams of transmitter and receiver to establish connections quickly and maintain them seamlessly.

“Wireless transmissions at these higher frequencies resemble beams of light more than a broadcast in all directions, and so get blocked easily by humans and other obstacles,” said senior study author Kyle Jamieson, a professor of computer science who leads the Princeton Advanced Wireless Systems Lab (PAWS).

The mmWall surface is the first to be able to reflect such transmissions in such a way that the angle of reflection does not equal the angle of incidence, sidestepping a classic law of physics. The device can also “refract transmissions that hit one side of the surface through at a different angle of departure, and is fully electronically reconfigurable within microseconds, allowing it to keep up with the ‘line rate’ of tomorrow’s ultra-fast networks,” said Jamieson.

Each panel of mmWall holds two meandering lines of thin copper wire, flanking a line of 28 broken circles made of thicker wire, which constitute meta-atoms — materials whose geometry is designed to achieve tunable electrical and magnetic properties. Applying controlled electrical current to these meta-atoms can change the behavior of the mmWave signals that interact with the mmWall surface — dynamically steering the signals around obstacles by shifting their paths by up to 135 degrees.

“Just by changing the voltage, we can tune the phase,” or the relationship between the incoming and outgoing radio waves, said Cho. “We can basically steer to any angle for transmission and reflection. State-of-the-art surfaces generally only work for reflection or only work for transmission, but with this we can do both at any arbitrary angle with high amplitude.”

The process is analogous to light waves slowing down when they pass through a glass of water, said Cho. The water changes the direction of the light waves and makes objects appear distorted when viewed through the water.

Cho mathematically analyzed different parameters of the meta-atoms’ geometry to arrive at the optimal size, shape and arrangement for the copper meta-atoms and the pathways between them, which were fabricated with standard printed circuit board technology and mounted on a 3D-printed frame. In designing mmWall, the team aimed to use the smallest possible meta-atoms (each has a diameter of less than a millimeter), in order to optimize their interaction with mmWaves, as well as to simplify the device’s fabrication and minimize the amount of copper. The mmWall also uses only microwatts of electricity, about 1,000 times less than Wi-Fi routers which use an average of about 6 watts.

Cho tested mmWall’s ability to transmit and steer mmWave signals in a 900-square-foot lab in Princeton’s Computer Science building. With a transmitter in the room, mmWall improved the signal-to-noise ratio at nearly all of the 23 spots tested around the room. And when the transmitter was placed outdoors, mmWall again boosted signals all around the room, including in roughly 40% of spots that had been completely blocked without the use of mmWall.

The article, “mmWall: A Steerable, Transflective Metamaterial Surface for NextG mmWave Networks,” was presented April 19 at the USENIX Symposium on Networked Systems Design and Implementation. In addition to Cho and Jamieson, authors include Mohammad Mazaheri and Omid Abari of the University of California-Los Angeles, and Jeremy Gummeson of the University of Massachusetts-Amherst. The work was supported by the U.S. National Science Foundation, the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the Ontario Research Fund.

The mmWall is an accordion-like array of 76 vertical panels that can both reflect and refract radio waves at frequencies above 24 gigahertz, the lower bound of mmWave signals.

Each panel of mmWall holds two meandering lines of thin copper wire, flanking a line of 28 broken circles made of thicker wire, which constitute meta-atoms — materials whose geometry is designed to achieve tunable electrical and magnetic properties.

CREDIT

Tori Repp/Fotobuddy

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METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

mmWall: A Steerable, Transflective Metamaterial Surface for NextG mmWave Networks

ARTICLE PUBLICATION DATE

19-Apr-2023