Benton H. Calhoun Continues to Pioneer Design and Commercialization of Ultra Low-power Circuits for the Internet of Things

Ten years ago, Benton H. Calhoun, professor of electrical and computer engineering at the University of Virginia, published a proof-of-concept for the first fully integrated self-powering wearable sensor chip. Calhoun’s success created a buzz among those developing hardware for the burgeoning “internet of things.”

Calhoun debuted the sensor node in 2012 in collaboration with Brian Otis, then associate professor of electrical engineering at the University of Washington. Their wearable bioelectric monitor runs exclusively on energy harvested from body heat, consuming only 19 microwatts to keep itself running while taking an electrocardiogram (EKG) and sending the results over the radio.

That same year, Calhoun joined the National Science Foundation’s Nanosystems Engineering Research Center for Advanced Self-powered Systems of Integrated Sensors in Technologies, commonly known as ASSIST. Calhoun serves as technical thrust leader for the low-power systems-on-chip research and UVA’s campus director.

In recognition of Calhoun’s original and fundamental contributions in integrated circuit design, the Institute of Electrical and Electronics Engineers elected Calhoun as a Fellow in December 2020.

Calhoun joined the faculty of the Charles L. Brown Department of Electrical and Computer Engineering in UVA’s School of Engineering in 2006. His choice brought him full circle to his alma mater; he had graduated just six years earlier, earning a B.S. in electrical engineering with a concentration in computer science. Two of his own students will graduate from UVA Engineering this May. Cumulatively, Calhoun has helped 22 Ph.D students graduate from UVA.

“Professor Calhoun teaches in deliberately unconventional ways—through lessons in personal development,” Nikolaos Sidiropoulos, Louis T. Rader Professor of electrical and computer engineering and department chair, said. “Ben leads a large and extremely successful group that has made our department a world-class hub in ultra-low-power IoT circuits. His relentless drive and enthusiasm are contagious!"

Calhoun pursued his research ambitions at the Massachusetts Institute of Technology, where he earned his M.S. and Ph.D. degrees in electrical engineering. Recalling his dissertation research with advisor Anantha Chandrakasan, now Dean of Engineering at MIT, “the idea for a batteryless sensor node did not spring fully formed,” Calhoun said. “As I worked on more and more pieces that were really low power in the wireless sensing space, I thought about where they are most useful. I became convinced that those chips made most sense if they ran on harvested energy.”

Calhoun’s graduate school research, especially his successful demonstration of sub-threshold static random access memory, launched a rich sub-field and resulted in the invention of numerous new bitcell topologies and low-power memory design incorporated in today’s academic and commercial chips.

“Ben’s academic excellence, collaborative approach, and fundamental contributions in the area of ultra-low-power systems have led to him emerging as a leading researcher and scholar in this area,” Chandrakasan said. “He has successfully transitioned and implemented innovative ideas and concepts from the lab and is continuously making an impact on self-powered IoT devices. Ben likewise impacts the next generation of students in IC design as an amazing mentor – he empowers and encourages his students throughout every step of their academic and research journeys.”

Calhoun realized that getting rid of batteries would not only be good for the environment, it would enable the chips to be deployed in larger numbers, transforming applications including personal health, green buildings, and industrial operations and maintenance. Calhoun was eager to participate and help lead the next computing revolution, a huge-scale internet of things with trillions of devices made possible only with batteryless sensors.

“We could empower people by providing access to new kinds of data, higher volumes of data, and entirely new data streams,” Calhoun said. “The value of any innovation comes from what you do with it and actually put into practice.”

Pursuing his passion for people and the planet, and encouraged by unsolicited offers of funding to develop and commercialize his self-powered sensor, Calhoun co-founded Everactive, Inc. in 2012, initially named PsiKick, Inc., with David Wentzloff, University of Michigan professor of electrical engineering and computer science, and Brendan Richardson, a venture capital specialist and faculty member of the UVA McIntire School of Commerce.

Everactive is a deep technology company headquartered in Santa Clara, California, with offices in Charlottesville, Virginia, and Ann Arbor, Michigan, that offers a suite of industrial sensing products to generate data intelligence.

At the time, many industry experts and analysts were predicting up to 1 trillion internet of things devices deployed by 2020. The founders recognized that this could not be achieved with battery-operated devices, simply because of the sheer number of battery replacements that would be required.

“The next generation of computers will be self-powered systems, which will drive the semiconductor industry’s volume for decades to come,” Wentzloff said. “Everactive is ushering in the self-powered computing revolution.”

Everactive’s first product, a full-stack remote monitoring system for industrial internet of things applications for industrial motors and steam traps, is composed of self-powered wireless sensors that stream data to the cloud for failure detection, analysis and decision-making. Released in December 2018, Everactive’s platforms reach thousands of batteryless nodes deployed across multiple Fortune 100 customers.

“We have been able to take some really profound technical innovations, deep down in the technical weeds of circuits and systems, and put them into practice in a useful way. We offer a full solution that provides value to our customers,” Calhoun said.

Calhoun said his entrepreneurial experience is “like being in the cockpit of a rocket ship trying to reach escape velocity. Each funding round is an opportunity to hit the thrusters. But if the fundraising round is incomplete, if you hit even the slightest bit of turbulence, you would pitch downward and crash in short order.”

The moonshot aptly captures Calhoun’s research and teaching philosophy.

“I encourage my students and my partners to push themselves toward an ambitious goal, a moonshot vision. My own moonshot is to enable self-powered sensing that empowers people with information and insight,” Calhoun said.

Calhoun credits his many talented students as fellow innovators in self-powered wireless sensors and sub-threshold circuits, which use CMOS transistors with a supply voltage lower than their threshold voltage.

In this state, the transistor is “off,” but continues to enable digital operation using leakage current, which Calhoun describes as analogous to doing useful work with drips of water from a leaking faucet. The design reduces energy consumption by over ten times and allows memory and digital circuits to overcome variations in process parameters, voltage, and temperature to ensure reliable operation.

“Ben encourages us to set our sights high and try to produce the best results in the field,” Daniel S. Truesdell, a 2021 Ph.D. graduate of electrical engineering, said. “It can feel discouraging to hit obstacles along the way, but Ben’s enthusiasm and positivity are constantly lifting us up and re-energizing us to go tackle our toughest problems. The potential for my work to produce moonshot results makes me feel like my time and effort are going toward something truly important.”

As an early career faculty member, Calhoun established and ran his Robust Low Power VLSI Group like a start-up, although he didn’t realize it at the time.

“Everybody wins with this structure. Students learn how to lead groups on research projects, and I can grow a much larger team trained to lead multiple research projects,” Calhoun said. In contrast to the customary one-on-one professor-mentor relationship, Calhoun set out to build his group more like a team-driven organization.

“Our various technical backgrounds enable us to do more complex research and solve problems with greater agility. The large group enables agile problem-solving and flexibility to meet tight deadlines. If I encounter some trouble when I am designing a chip or if I am running behind schedule, I can rely on my peers to jump in and help me out,” Truesdell said.

Truesdell describes Calhoun as intentional about educating his students on leadership and management skills. “We focus on tangible concepts that add immediate leadership value, such as taking intellectual ownership of your whole project to ensure that collaborations run smoothly. We also focus on improving our ability for self-reflection and self-improvement, which will produce growing returns over time,” Truesdell said.

“Ben is patient and always very empathetic, which I believe helps diffuse many of the issues that could potentially derail our research progress. For my future career, I will remember how valuable these traits were at fostering a happy and productive work environment and try to lead in a similar way.

“The diversity in our group has also exposed me to other cultures and helped me learn about the different approaches to research and careers that exist around the world. Gaining this more holistic view of my field has helped me produce more impactful research and inspired my long-term career goals,” Truesdell said.

Truesdell plans to continue his high-impact work at Everactive in Charlottesville, following the path of Calhoun’s research group alumni Chris Lukas and Farah Yahya, both 2017 Ph.D. graduates in electrical engineering.

“Ben has always been invested in mentoring his students. He would run a weekly meeting that we used to develop soft skills that helped us become more well-rounded researchers,” Lukas said. These meetings were designed to give students deliberative practice with activities such as writing persuasive papers, tailoring resumes for a job and giving presentations.

“These sessions allowed me to gain a breadth of skills in addition to the classic depth that you get in a graduate degree. Ben has supported my personal professional growth by helping me to be a better leader and a better collaborator with those in related fields,” Lukas said.

“Ben also emphasized teamwork and collaboration,” Yahya said. “He encourages his students to teach and learn from each other, work effectively in a team, contribute to bigger projects with other schools, and always seek excellence through rigorous, honest thinking. These skills empower us to excel in industry and academic jobs.”