A battery-free sensor for underwater exploration

A battery-free sensor for underwater exploration

Trending Technologies   September 16, 2019

The submerged system uses the vibration of “piezoelectric” materials to generate power and send and receive data.

To investigate the vastly unexplored oceans covering most of our planet, researchers aim to build a submerged network of interconnected sensors that send data to the surface — an underwater “internet of things.” But how to supply constant power to scores of sensors designed to stay for long durations in the ocean’s deep?

MIT researchers have an answer: a battery-free underwater communication system that uses near-zero power to transmit sensor data. The system could be used to monitor sea temperatures to study climate change and track marine life over long periods — and even sample waters on distant planets. They are presenting the system at the SIGCOMM conference this week, in a paper that has won the conference’s “best paper” award.

The system makes use of two key phenomena. One, called the “piezoelectric effect,” occurs when vibrations in certain materials generate an electrical charge. The other is “backscatter,” a communication technique commonly used for RFID tags, that transmits data by reflecting modulated wireless signals off a tag and back to a reader.

In the researchers’ system, a transmitter sends acoustic waves through water toward a piezoelectric sensor that has stored data. When the wave hits the sensor, the material vibrates and stores the resulting electrical charge. Then the sensor uses the stored energy to reflect a wave back to a receiver — or it doesn’t reflect one at all. Alternating between reflection in that way corresponds to the bits in the transmitted data: For a reflected wave, the receiver decodes a 1; for no reflected wave, the receiver decodes a 0.

“Once you have a way to transmit 1s and 0s, you can send any information,” says co-author Fadel Adib, an assistant professor in the MIT Media Lab and the Department of Electrical Engineering and Computer Science and founding director of the Signal Kinetics Research Group. “Basically, we can communicate with underwater sensors based solely on the incoming sound signals whose energy we are harvesting.”

The researchers demonstrated their Piezo-Acoustic Backscatter System in an MIT pool, using it to collect water temperature and pressure measurements. The system was able to transmit 3 kilobits per second of accurate data from two sensors simultaneously at a distance of 10 meters between sensor and receiver.

Applications go beyond our own planet. The system, Adib says, could be used to collect data in the recently discovered subsurface ocean on Saturn’s largest moon, Titan. In June, NASA announced the Dragonfly mission to send a rover in 2026 to explore the moon, sampling water reservoirs and other sites.

“How can you put a sensor under the water on Titan that lasts for long periods of time in a place that’s difficult to get energy?” says Adib, who co-wrote the paper with Media Lab researcher JunSu Jang. “Sensors that communicate without a battery open up possibilities for sensing in extreme environments.”

Preventing deformation

Inspiration for the system hit while Adib was watching “Blue Planet,” a nature documentary series exploring various aspects of sea life. Oceans cover about 72 per cent of Earth’s surface. “It occurred to me how little we know of the ocean and how marine animals evolve and procreate,” he says. Internet-of-things (IoT) devices could aid that research, “but underwater you can’t use Wi-Fi or Bluetooth signals … and you don’t want to put batteries all over the ocean, because that raises issues with pollution.”

That led Adib to piezoelectric materials, which have been around and used in microphones and other devices for about 150 years. They produce a small voltage in response to vibrations. But that effect is also reversible: Applying voltage causes the material to deform. If placed underwater, that effect produces a pressure wave that travels through the water. They’re often used to detect sunken vessels, fish, and other underwater objects.

“That reversibility is what allows us to develop a very powerful underwater backscatter communication technology,” Adib says.

Communicating relies on preventing the piezoelectric resonator from naturally deforming in response to strain. At the heart of the system is a submerged node, a circuit board that houses a piezoelectric resonator, an energy-harvesting unit, and a microcontroller. Any type of sensor can be integrated into the node by programming the microcontroller. An acoustic projector (transmitter) and underwater listening device, called a hydrophone (receiver), are placed some distance away.

Say the sensor wants to send a 0 bit. When the transmitter sends its acoustic wave at the node, the piezoelectric resonator absorbs the wave and naturally deforms, and the energy harvester stores a little charge from the resulting vibrations. The receiver then sees no reflected signal and decodes a 0.

However, when the sensor wants to send a 1 bit, the nature changes. When the transmitter sends a wave, the microcontroller uses the stored charge to send a little voltage to the piezoelectric resonator. That voltage reorients the material’s structure in a way that stops it from deforming, and instead reflects the wave. Sensing a reflected wave, the receiver decodes a 1.

Long-term deep-sea sensing

The transmitter and receiver must have power but can be planted on ships or buoys, where batteries are easier to replace, or connected to outlets on land. One transmitter and one receiver can gather information from many sensors covering one area or many areas.

“When you’re tracking a marine animal, for instance, you want to track it over a long-range and want to keep the sensor on them for a long period of time. You don’t want to worry about the battery running out,” Adib says. “Or, if you want to track temperature gradients in the ocean, you can get information from sensors covering a number of different places.”

Another interesting application is monitoring brine pools, large areas of brine that sit in pools in ocean basins, and are difficult to monitor long-term. They exist, for instance, on the Antarctic Shelf, where salt settles during the formation of sea ice and could aid in studying melting ice and marine life interaction with the pools. “We could sense what’s happening down there, without needing to keep hauling sensors up when their batteries die,” Adib says.

Polly Huang, a professor of electrical engineering at Taiwan National University, praised the work for its technical novelty and potential impact on environmental science. “This is a cool idea,” Huang says. “It's not news one uses piezoelectric crystals to harvest energy … [but is the] first time to see it being used as a radio at the same time [which] is unheard of to the sensor network/system research community. Also interesting and unique is the hardware design and fabrication. The circuit and the design of the encapsulation are both sound and interesting.”

While noting that the system still needs more experimentation, especially in seawater, Huang adds that “this might be the ultimate solution for researchers in marine biography, oceanography, or even meteorology — those in need of long-term, low-human-effort underwater sensing.”

Next, the researchers aim to demonstrate that the system can work at farther distances and communicate with more sensors simultaneously. They’re also hoping to test if the system can transmit sound and low-resolution images.

The work is sponsored, in part, by the U.S Office of Naval Research.

New 3-D chip combines computing and data storage.

New 3-D chip combines computing and data storage.

Trending Technologies   December 11, 2018

As embedded intelligence is finding its way into ever more areas of our lives, fields ranging from autonomous driving to personalized medicine are generating huge amounts of data. But just as the flood of data is reaching massive proportions, the ability of computer chips to process it into useful information is stalling.

Now, researchers at Stanford University and MIT have built a new chip to overcome this hurdle. The results are published today in the journal Nature, by lead author Max Shulaker, an assistant professor of electrical engineering and computer science at MIT. Shulaker began the work as a PhD student alongside H.-S. Philip Wong and his advisor Subhasish Mitra, professors of electrical engineering and computer science at Stanford. The team also included professors Roger Howe and Krishna Saraswat, also from Stanford.

Computers today comprise different chips cobbled together. There is a chip for computing and a separate chip for data storage, and the connections between the two are limited. As applications analyze increasingly massive volumes of data, the limited rate at which data can be moved between different chips is creating a critical communication “bottleneck.” And with limited real estate on the chip, there is not enough room to place them side-by-side, even as they have been miniaturized (a phenomenon known as Moore’s Law).

To make matters worse, the underlying devices, transistors made from silicon, are no longer improving at the historic rate that they have for decades.

The new prototype chip is a radical change from today’s chips. It uses multiple nanotechnologies, together with a new computer architecture, to reverse both of these trends.

Instead of relying on silicon-based devices, the chip uses carbon nanotubes, which are sheets of 2-D graphene formed into nanocylinders, and resistive random-access memory (RRAM) cells, a type of nonvolatile memory that operates by changing the resistance of a solid dielectric material. The researchers integrated over 1 million RRAM cells and 2 million carbon nanotube field-effect transistors, making the most complex nanoelectronic system ever made with emerging nanotechnologies.

The RRAM and carbon nanotubes are built vertically over one another, making a new, dense 3-D computer architecture with interleaving layers of logic and memory. By inserting ultradense wires between these layers, this 3-D architecture promises to address the communication bottleneck.

However, such an architecture is not possible with existing silicon-based technology, according to the paper’s lead author, Max Shulaker, who is a core member of MIT’s Microsystems Technology Laboratories. “Circuits today are 2-D, since building conventional silicon transistors involves extremely high temperatures of over 1,000 degrees Celsius,” says Shulaker. “If you then build a second layer of silicon circuits on top, that high temperature will damage the bottom layer of circuits.”

The key in this work is that carbon nanotube circuits and RRAM memory can be fabricated at much lower temperatures, below 200 C. “This means they can be built up in layers without harming the circuits beneath,” Shulaker says.

This provides several simultaneous benefits for future computing systems. “The devices are better: Logic made from carbon nanotubes can be an order of magnitude more energy-efficient compared to today’s logic made from silicon, and similarly, RRAM can be denser, faster, and more energy-efficient compared to DRAM,” Wong says, referring to a conventional memory known as dynamic random-access memory.

“In addition to improved devices, 3-D integration can address another key consideration in systems: the interconnects within and between chips,” Saraswat adds.

“The new 3-D computer architecture provides dense and fine-grained integration of computing and data storage, drastically overcoming the bottleneck from moving data between chips,” Mitra says. “As a result, the chip is able to store massive amounts of data and perform on-chip processing to transform a data deluge into useful information.”

To demonstrate the potential of the technology, the researchers took advantage of the ability of carbon nanotubes to also act as sensors. On the top layer of the chip they placed over 1 million carbon nanotube-based sensors, which they used to detect and classify ambient gases.

Due to the layering of sensing, data storage, and computing, the chip was able to measure each of the sensors in parallel, and then write directly into its memory, generating huge bandwidth, Shulaker says.

Three-dimensional integration is the most promising approach to continue the technology scaling path set forth by Moore’s laws, allowing an increasing number of devices to be integrated per unit volume, according to Jan Rabaey, a professor of electrical engineering and computer science at the University of California at Berkeley, who was not involved in the research.

“It leads to a fundamentally different perspective on computing architectures, enabling an intimate interweaving of memory and logic,” Rabaey says. “These structures may be particularly suited for alternative learning-based computational paradigms such as brain-inspired systems and deep neural nets, and the approach presented by the authors is definitely a great first step in that direction.”

“One big advantage of our demonstration is that it is compatible with today’s silicon infrastructure, both in terms of fabrication and design,” says Howe.

“The fact that this strategy is both CMOS [complementary metal-oxide-semiconductor] compatible and viable for a variety of applications suggests that it is a significant step in the continued advancement of Moore’s Law,” says Ken Hansen, president and CEO of the Semiconductor Research Corporation, which supported the research. “To sustain the promise of Moore’s Law economics, innovative heterogeneous approaches are required as dimensional scaling is no longer sufficient. This pioneering work embodies that philosophy.”

The team is working to improve the underlying nanotechnologies, while exploring the new 3-D computer architecture. For Shulaker, the next step is working with Massachusetts-based semiconductor company Analog Devices to develop new versions of the system that take advantage of its ability to carry out sensing and data processing on the same chip.

So, for example, the devices could be used to detect signs of disease by sensing particular compounds in a patient’s breath, says Shulaker.

“The technology could not only improve traditional computing, but it also opens up a whole new range of applications that we can target,” he says. “My students are now investigating how we can produce chips that do more than just computing.”

“This demonstration of the 3-D integration of sensors, memory, and logic is an exceptionally innovative development that leverages current CMOS technology with the new capabilities of carbon nanotube field–effect transistors,” says Sam Fuller, CTO emeritus of Analog Devices, who was not involved in the research. “This has the potential to be the platform for many revolutionary applications in the future.” 

This work was funded by the Defense Advanced Research Projects Agency, the National Science Foundation, Semiconductor Research Corporation, STARnet SONIC, and member companies of the Stanford SystemX Alliance.

A novel way to advance a better battery design

A novel way to advance a better battery design

Trending Technologies   November 14, 2018

Led by “Queen of Batteries” Christina Lampe-Onnerud, Cadenza Innovation is licensing its lithium-ion battery cell architecture to manufacturers around the world. Cadenza Innovation Founder and CEO Christina Lampe-Onnerud at the World Economic Forum’s Annual Meeting of the New Champions.

Cadenza Innovation has developed a new design that improves the performance, cost, and safety of large lithium-ion batteries. Now, with an unusual strategy for disseminating that technology, the company is poised to have an impact in industries including energy grid storage, industrial machines, and electric vehicles.

Rather than produce the batteries itself, Cadenza licenses its technology to manufacturers producing batteries for diverse applications. The company also works with licensees to both optimize their manufacturing processes and sell the new batteries to end users. The strategy ensures that the four-year-old company’s technology is deployed more quickly and widely than would otherwise be possible.

For Cadenza founder Christina Lampe-Onnerud, a former MIT postdoc and a battery industry veteran of more than 20 years, the goal is to help advance the industry just as the global demand for batteries reaches an inflection point.

“The crazy idea at the time [of the company’s founding] was to see if there was a different way to engage with the industry and help it accept a new technology in existing applications like cars or computers,” Lampe-Onnerud says. “Our thought was, if we really want to have an impact, we could inspire the industry to use existing capital deployed to get a better technology into the market globally and be a positive part of the climate change arena.”

With that lofty goal in mind, the Connecticut-based company has secured partnerships with organizations at every level of the battery supply chain, including suppliers of industrial minerals, original equipment manufacturers, and end users. Cadenza has demonstrated its proprietary “supercell” battery architecture in Fiat’s 500e car model and is in the process of completing a demonstration energy storage system to be used by the New York Power Authority, the largest state public utility company in the U.S., when energy demand is at its peak.

The company’s most significant partnership to date, however, was announced in September with Shenzen BAK Battery Company, one of the world’s largest lithium-ion battery manufacturers. The companies announced BAK would begin mass producing batteries based on Cadenza’s supercell architecture in the first half of 2019.

The supercell architecture

Lampe-Onnerud’s extensive contacts in the lithium-ion battery space and a world-renown technical team have quickened the pace of Cadenza’s rise, but the underlying driver of the company’s success is simple economics: Its technology has been shown to offer manufacturers increased energy density in battery cells while reducing production costs.

The majority of rechargeable lithium ion batteries are powered by cylindrical sheets of metal known as “jelly rolls.” For use in big batteries, jelly rolls can be made either large, to limit the total cost of the battery assembly, or small, to leverage a more efficient cell design that brings higher energy density. Many electric vehicle (EV) companies use large jelly rolls to avoid the durability and safety concerns that come with tightly packing small jelly rolls into a battery, which can lead to the failure of the entire battery if one jelly roll overheats.

Tesla famously achieves longer vehicle ranges by using small jelly rolls in its batteries, addressing safety issues with cooling tubes, intricate circuitry, and by spacing out each roll. But Cadenza has patented a simpler battery system it calls the “supercell,” that allows small jelly rolls to be tightly packed together into one module.

The key to the supercell is a noncombustible ceramic fiber material that each jelly roll sits in like an egg in a carton. The material helps to control temperature throughout the cell and isolate damage caused by an overheated jelly roll. A metal shunt wrapped around each jelly roll and a flame retardant layer of the supercell wall that relieves pressure in the case of a thermal event add to its safety advantages.

The enhanced safety allows Cadenza to package the jelly rolls tightly for greater energy density, and the supercell’s straightforward design, which leverages many parts that are currently manufactured at low costs and high volumes, keeps production costs down. Finally, each supercell module is designed to click together like LEGO blocks, making it possible for manufacturers to easily scale their battery sizes to fit customer needs.

Cadenza’s safety, cost, and performance features were validated during a grant program with the Advanced Research Projects Agency-Energy (ARPA-E), which gave the company nearly $4 million to test the architecture beginning in 2013.

When the supercell architecture was publicly unveiled in 2016, Lampe-Onnerud made headlines by saying it could be used to boost the range of Tesla’s cars by 70 per cent. Now the goal is to get manufacturers to adopt the architecture.

“There will be many winners using this technology,” Lampe-Onnerud says. “We know we can deliver on the [safety, performance, and cost] claims. It’s going to be up to the licensee to decide how they leverage these advantages.”

At MIT, where “data gets to speak”

Lampe-Onnerud and her husband, Per Onnerud, who serves as Cadenza’s chief technology officer, held postdoctoral appointments at MIT after earning their PhDs at Uppsala University in their home country of Sweden. Lampe-Onnerud did lab work in inorganic chemistry in close collaboration with MIT materials science and mathematics professors, while Onnerud did research in the Department of Materials Science and Engineering. The experience left a strong impression on Lampe-Onnerud.

“MIT was a very formative experience,” she says. “You learn how to argue a point so that the data gets to speak. You just enable the data; there’s no spin. MIT has a special place in my heart.”

Lampe-Onnerud has maintained a strong connection with the Institute ever since, participating in alumni groups, giving guest lectures on campus, and serving as a member of the MIT Corporation visiting committee for the chemistry department — all while finding remarkable success in her career.

Lampe-Onnerud founded Boston-Power in 2004, which she grew into an internationally recognized manufacturer of batteries for consumer electronics, vehicles, and industrial applications while serving as the CEO until the company moved operations to China in 2012. In the early stages of the company, more than seven years after Lampe-Onnerud had finished her postdoc work, she discovered the enduring nature of support from the MIT community.

“We started looking for some angel investors, and one of the first groups that responded were the angels affiliated with MIT,” Lampe-Onnerud says. “We support each other because we tend to be attracted to intractable problems. It’s very much in the MIT spirit: We know, if we’re trying to solve big problems, it’s going to be difficult. So we like to collaborate.”

The high-profile experience at Boston Power earned her distinctions including the Technology Pioneer Award from the World Economic Forum, and Swedish Woman of the Year from the Swedish Women’s Educational Association. It also led some to deem her the “Queen of Batteries.”

Immediately after leaving Boston-Power, Lampe-Onnerud and her husband went to work on what would be Cadenza’s supercell architecture in their garage. They wanted to create a solution that would help lower the world’s carbon footprint, but they estimated that, at most, they’d be able to build one gigafactory every 18 months if they were to manufacture the batteries themselves. So they decided to license the technology instead.

The strategy has tradeoffs from a business perspective: Cadenza has needed to raise much less capital than Boston-Power but will allow licensees to generate top line and bottom-line growth while it receives a percentage of sales. Lampe-Onnerud is clearly happy to leverage her global network and share the upside to maximize Cadenza’s impact.

“My hope is that we are able to bring people together around this technology to do things that are really important, like taking down our carbon footprint, eliminating NOx [nitrogen oxide] emissions, or improving grid efficiency,” Lampe-Onnerud says. “It’s a different way to work together, so when an element of this ecosystem wins, we all win. It has been an inspiring process.”

Content Credits:  Massachusetts Institute of Technology