System Bits: Aug. 20

Blockchain integrated into energy systems
Researchers at Canada’s University of Waterloo integrated blockchain technology into energy systems, a development that may expand charging infrastructure for electric vehicles.

In a study that outlines the new blockchain-oriented charging system, the researchers found that there is a lack of trust among charging service providers, property owners, and owners of EVs.

With an open blockchain platform, all parties will have access to the data and can see if it has been tampered with. Using a blockchain-oriented charging system will, therefore, allow EV owners to see if they are being overcharged while property owners will know if they are being underpaid.

“Energy services are increasingly being provided by entities that do not have well-established trust relationships with their customers and partners,” said Christian Gorenflo, a PhD candidate in Waterloo’s David R. Cheriton School of Computer Science. “In this context, blockchains are a promising approach for replacing a central trusted party, for example, making it possible to implement direct peer-to-peer energy trading.”

In undertaking the study, Gorenflo, his supervisor, professor Srinivasan Keshav of the Cheriton School of Computer Science, and Lukasz Golab, professor of management science, collaborated with an EV-charging service provider. The provider works with property owners to install EV supply equipment that is used by EV owners for a fee. The revenue stream from these charging stations is then shared between the charging service provider and each property owner. The EV supply equipment is operated by the charging service provider, so the property owners must trust the provider to compensate them fairly for the electricity used.

From the case study, the researchers were able to identify three steps necessary for the incorporation of blockchain technology into an energy system. The first is to identify the involved parties and their trust relations. If the level of trust in a relation is insufficient to achieve the application’s goal or if it restricts an action necessary to reach that goal, this should be recorded as a trust issue.

Secondly, design a minimal blockchain system, including smart contracts, that resolves the trust issues identified in the first step. If parts of a legacy system need to be replaced, the new system should closely mimic existing interfaces so that dependencies can continue to work with minimal modifications.

Finally, with the trust-mitigating blockchain in place, the rest of the system can be migrated iteratively over time. This allows the business model to eventually grow from a legacy/blockchain hybrid into a truly decentralized solution.

“Mitigating trust issues in EV charging could result in people who have charging stations and even those who just have an outdoor outlet being much more willing to team up with an EV charging service provider resulting in much better coverage of charging stations,” said Gorenflo.

“In the end, we could even have a system where there is machine-to-machine communication rather than people-to-machine. If an autonomous vehicle needs power, it could detect that and drive to the nearest charging station and communicate on a platform with that charging station for the power.”

The study, “Mitigating Trust Issues in Electric Vehicle Charging using a Blockchain,” authored by Waterloo’s Faculty of Mathematics researchers Gorenflo, Keshav, and Golab from the Faculty of Engineering was published recently in the Proceedings of the Tenth ACM International Conference on Future Energy Systems.

Topological superconductor may advance quantum logic circuits
National Institute of Standards and Technology scientists employed uranium ditelluride, a superconducting compound material, as a topological insulator to produce quantum bits, or qubits.

Newly discovered properties in the compound uranium ditelluride, or UTe2, show that it could prove highly resistant to one of the nemeses of quantum computer development — the difficulty with making such a computer’s memory storage switches, called qubits, function long enough to finish a computation before losing the delicate physical relationship that allows them to operate as a group. This relationship, called quantum coherence, is hard to maintain because of disturbances from the surrounding world.

The compound’s unusual and strong resistance to magnetic fields makes it a rare bird among superconducting materials, which offer distinct advantages for qubit design, chiefly their resistance to the errors that can easily creep into quantum computation. UTe2’s exceptional behaviors could make it attractive to the nascent quantum computer industry, according to the research team’s Nick Butch.

“This is potentially the silicon of the quantum information age,” said Butch, a physicist at the NIST Center for Neutron Research. “You could use uranium ditelluride to build the qubits of an efficient quantum computer.”

Research results from the team, which also includes scientists from the University of Maryland and Ames Laboratory, appear in the journal Science. Their paper details UTe2’s uncommon properties, which are interesting from the perspectives of both technological application and fundamental science.

One of these is the unusual way the electrons that conduct electricity through UTe2 partner up. In copper wire or some other ordinary conductor, electrons travel as individual particles, but in all SCs they form what are called Cooper pairs. The electromagnetic interactions that cause these pairings are responsible for the material’s superconductivity. The explanation for this kind of superconductivity is named BCS theory after the three scientists who uncovered the pairings (and shared the Nobel Prize for doing so).

What’s specifically important to this Cooper pairing is a property that all electrons have. Known as quantum “spin,” it makes electrons behave as if they each have a little bar magnet running through them. In most SCs, the paired electrons have their quantum spins oriented in a single way — one electron’s points upward, while its partner points down. This opposed pairing is called a spin singlet.

A small number of known superconductors, though, are nonconformists, and UTe2 looks to be among them. Their Cooper pairs can have their spins oriented in one of three combinations, making them spin triplets. These combinations allow for the Cooper-pair spins to be oriented in parallel rather than in opposition. Most spin-triplet SCs are predicted to be “topological” SCs as well, with a highly useful property in which the superconductivity would occur on the surface of the material and would remain superconducting even in the face of external disturbances.

“These parallel spin pairs could help the computer remain functional,” Butch said. “It can’t spontaneously crash because of quantum fluctuations.”

All quantum computers up until this point have needed a way to correct the errors that creep in from their surroundings. SCs have long been understood to have general advantages as the basis for quantum computer components, and several recent commercial advances in quantum computer development have involved circuits made from superconductors. A topological SC’s properties — which a quantum computer might employ — would have the added advantage of not needing quantum error correction.

“We want a topological SC because it would give you error-free qubits. They could have very long lifetimes,” Butch said. “Topological SCs are an alternate route to quantum computing because they would protect the qubit from the environment.”

The team stumbled upon UTe2 while exploring uranium-based magnets, whose electronic properties can be tuned as desired by changing their chemistry, pressure or magnetic field — a useful feature to have when you want customizable materials. (None of these parameters are based on radioactivity. The material contains “depleted uranium,” which is only slightly radioactive. Qubits made from UTe2 would be tiny, and they could easily be shielded from their environment by the rest of the computer.)

The team did not expect the compound to possess the properties they discovered.

“UTe2 had first been created back in the 1970s, and even fairly recent research articles described it as unremarkable,” Butch said. “We happened to make some UTe2 while we were synthesizing related materials, so we tested it at lower temperatures to see if perhaps some phenomenon might have been overlooked. We quickly realized that we had something very special on our hands.”

The NIST team started exploring UTe2 with specialized tools at both the NCNR and the University of Maryland. They saw that it became superconducting at low temperatures (below -271.5 degrees Celsius, or 1.6 kelvin). Its superconducting properties resembled those of rare superconductors that are also simultaneously ferromagnetic – acting like low-temperature permanent magnets. Yet, curiously, UTe2 is itself not ferromagnetic.

“That makes UTe2 fundamentally new for that reason alone,” Butch said.

It is also highly resistant to magnetic fields. Typically, a field will destroy superconductivity, but depending on the direction in which the field is applied, UTe2 can withstand fields as high as 35 teslas. This is 3,500 times as strong as a typical refrigerator magnet, and many times more than most low-temperature topological SCs can endure.

While the team has not yet proved conclusively that UTe2 is a topological SC, Butch says this unusual resistance to strong magnetic fields means that it must be a spin-triplet SC, and therefore it is likely a topological SC as well. This resistance also might help scientists understand the nature of UTe2 and perhaps superconductivity itself.

“Exploring it further might give us insight into what stabilizes these parallel-spin SCs,” he said. “A major goal of SC research is to be able to understand superconductivity well enough that we know where to look for undiscovered SC materials. Right now, we can’t do that. What about them is essential? We are hoping this material will tell us more.”

Wearable sensor R&D at two universities
Researchers at Stanford University and the University of California, Berkeley, separately came up with wireless wearable sensors to provide data useful in personal health care.

Stanford engineers developed a way to detect physiological signals emanating from the skin with sensors that stick like Band-Aids and beam wireless readings to a receiver clipped onto clothing.

To demonstrate this wearable technology, the researchers stuck sensors to the wrist and abdomen of one test subject to monitor the person’s pulse and respiration by detecting how their skin stretched and contracted with each heartbeat or breath. Likewise, stickers on the person’s elbows and knees tracked arm and leg motions by gauging the minute tightening or relaxation of the skin each time the corresponding muscle flexed.

Zhenan Bao, the chemical engineering professor whose lab described the system in an article in Nature Electronics, thinks this wearable technology, which they call BodyNet, will first be used in medical settings such as monitoring patients with sleep disorders or heart conditions. Her lab is already trying to develop new stickers to sense sweat and other secretions to track variables such as body temperature and stress. Her goal is to create an array of wireless sensors that stick to the skin and work in conjunction with smart clothing to more accurately track a wider variety of health indicators than the smart phones or watches consumers use today.

“We think one day it will be possible to create a full-body skin-sensor array to collect physiological data without interfering with a person’s normal behavior,” said Bao, who is also the K.K. Lee Professor in the School of Engineering.

Postdoctoral scholars Simiao Niu and Naoji Matsuhisa led the 14-person team that spent three years designing the sensors. Their goal was to develop a technology that would be comfortable to wear and have no batteries or rigid circuits to prevent the stickers from stretching and contracting with the skin.

Their eventual design met these parameters with a variation of radio-frequency identification (RFID) technology used to control keyless entry to locked rooms. When a person holds an ID card up to an RFID receiver, an antenna in the ID card harvests a tiny bit of RFID energy from the receiver and uses this to generate a code that it then beams back to the receiver.

The BodyNet sticker is like the ID card: It has an antenna that harvests a bit of the incoming RFID energy from a receiver on the clothing to power its sensors. It then takes readings from the skin and beams them back to the nearby receiver.

But to make the wireless sticker work, the researchers had to create an antenna that could stretch and bend like skin. They did this by screen-printing metallic ink on a rubber sticker. However, whenever the antenna bent or stretched, those movements made its signal too weak and unstable to be useful.

To get around this problem, the Stanford researchers developed a new type of RFID system that could beam strong and accurate signals to the receiver despite constant fluctuations. The battery-powered receiver then uses Bluetooth to periodically upload data from the stickers to a smartphone, computer or other permanent storage system.

The initial version of the stickers relied on tiny motion sensors to take respiration and pulse readings. The researchers are now studying how to integrate sweat, temperature and other sensors into their antenna systems.

To move their technology beyond clinical applications and into consumer-friendly devices, the researchers need to overcome another challenge – keeping the sensor and receiver close to each other. In their experiments, the researchers clipped a receiver on clothing just above each sensor. One-to-one pairings of sensors and receivers would be fine in medical monitoring, but to create a BodyNet that someone could wear while exercising, antennas would have to be woven into clothing to receive and transmit signals no matter where a person sticks a sensor.

A team of scientists at UC Berkeley is developing wearable skin sensors that can detect what’s in your sweat.

They hope that one day, monitoring perspiration could bypass the need for more invasive procedures like blood draws, and provide real-time updates on health problems such as dehydration or fatigue.

In a paper appearing in Science Advances, the team describes a new sensor design that can be rapidly manufactured using a “roll-to-roll” processing technique that essentially prints the sensors onto a sheet of plastic like words on a newspaper.

They used the sensors to monitor the sweat rate, and the electrolytes and metabolites in sweat, from volunteers who were exercising, and others who were experiencing chemically induced perspiration.

“The goal of the project is not just to make the sensors but start to do many subject studies and see what sweat tells us — I always say ‘decoding’ sweat composition,” said Ali Javey, a professor of electrical engineering and computer science at UC Berkeley and senior author on the paper.

“For that we need sensors that are reliable, reproducible, and that we can fabricate to scale so that we can put multiple sensors in different spots of the body and put them on many subjects,” said Javey, who also serves as a faculty scientist at Lawrence Berkeley National Laboratory.

The new sensors contain a spiraling microscopic tube, or microfluidic, that wicks sweat from the skin. By tracking how fast the sweat moves through the microfluidic, the sensors can report how much a person is sweating, or their sweat rate.

The microfluidics are also outfitted with chemical sensors that can detect concentrations of electrolytes like potassium and sodium, and metabolites like glucose.

Javey and his team worked with researchers at the VTT Technical Research Center of Finland to develop a way to quickly manufacture the sensor patches in a roll-to-roll processing technique like screen printing.

“Roll-to-roll processing enables high-volume production of disposable patches at low cost,” Jussi Hiltunen of VTT said. “Academic groups gain significant benefit from roll-to-roll technology when the number of test devices is not limiting the research. Additionally, up-scaled fabrication demonstrates the potential to apply the sweat-sensing concept in practical applications.”

To better understand what sweat can say about the real-time health of the human body, the researchers first placed the sweat sensors on different spots on volunteers’ bodies — including the forehead, forearm, underarm and upper back — and measured their sweat rates and the sodium and potassium levels in their sweat while they rode on an exercise bike.

They found that local sweat rate could indicate the body’s overall liquid loss during exercise, meaning that tracking sweat rate might be a way to give athletes a heads up when they may be pushing themselves too hard.

“Traditionally what people have done is they would collect sweat from the body for a certain amount of time and then analyze it,” said Hnin Yin Yin Nyein, a graduate student in materials science and engineering at UC Berkeley and one of the lead authors on the paper. “So, you couldn’t really see the dynamic changes very well with good resolution. Using these wearable devices, we can now continuously collect data from different parts of the body, for example to understand how the local sweat loss can estimate whole-body fluid loss.”

They also used the sensors to compare sweat glucose levels and blood glucose levels in healthy and diabetic patients, finding that a single sweat glucose measurement cannot necessarily indicate a person’s blood glucose level.

“There’s been a lot of hope that non-invasive sweat tests could replace blood-based measurements for diagnosing and monitoring diabetes, but we’ve shown that there isn’t a simple, universal correlation between sweat and blood glucose levels,” said Mallika Bariya, a graduate student in materials science and engineering at UC Berkeley and the other lead author on the paper. “This is important for the community to know, so that going forward we focus on investigating individualized or multi-parameter correlations.”

Co-authors on the paper include Liisa Kivimaki, Sanna Uusitalo, Elina Jansson, Tuomas Happonen, and Christina Liedert of the VTT Technical Research Center of Finland; and Tiffany Sun Liaw, Christine Heera Ahn, John A. Hangasky, Jianqi Zhao, Yuanjing Lin, Minghan Chao, Yingbo Zhao, and Li-Chia Tai of UC Berkeley.

This work was supported by the National Science Foundation’s Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT) program, the Berkeley Sensor and Actuator Center, and the Bakar fellowship.