Jae Wan Kwon was an inquisitive kid, the kind some parents dread.
When he was an 11- or 12-year-old boy in South Korea, Kwon took apart his father’s watch. It was just too tempting to see what was inside. “I didn’t know how to close it. My dad was really upset about it,” Kwon, 40, recalls. “But he finally gave it to me to play with.” Maybe his father knew he had an inveterate tinkerer and future inventor on his hands.
Kwon, now an assistant professor of electrical and computer engineering at the University of Missouri, never lost his childhood curiosity. He no longer builds model airplanes and cars or dismantles radios and home appliances. Now he develops innovative miniaturized devices, and along the way has solved problems that have vexed engineers for decades.
Kwon heads MU’s Micro-nano Devices and Systems, or MIDAS, Laboratory, where the modern-day equivalents of watchmakers are looking for ways to shrink technological wonders to ever smaller proportions, down even to the molecular—or nano—scale.
He has recently, for example, developed a tiny nuclear battery that increases both the energy efficiency and lifetime of current nuclear models.
The nuclear battery is a surprisingly old technology that scientists are giving a second look as they search for new ways to power today’s electronics. They can be made to be far more reliable and longer-lasting than even the most advanced chemically based batteries. Someday they may power up critical circuitry in military planes and missiles, or could be used to run implantable medical devices that would last a lifetime.
Kwon also has developed a new biological sensor, one no larger than the period at the end of this sentence, that could make it possible to almost instantly diagnose a multitude of medical conditions—from infections to cancers—in a doctor’s office. Faster tests will mean starting treatment sooner and relieving the anxiety of long waits for lab results.
Kwon’s work has been recognized with a National Science Foundation CAREER award and awards from the Institute of Electrical and Electronics Engineers for two of his research papers. “I always liked to make something that was unique and interesting,” Kwon said. “And if I see something new to me I still want to see how it works—at least in principle.”
Scientists have been working on nuclear-powered batteries since the eve of World War I, when the English physicist Henry Moseley used a silvered glass globe that collected charged particles emitted by a radium source positioned inside.
Interest in nuclear batteries picked up in the 1950s and 1960s when atomic age scientists saw their potential for powering spacecraft and medical devices. The earliest pacemakers were powered by nuclear batteries that used the radioactive element promethium.
Modern nuclear batteries use semiconductors to snatch energy from the electrons released as radioactive isotopes decay. The process is analogous to how solar cells use semiconductors to convert light energy to electricity.
The isotopes used in batteries produce beta rays, much safer than more-deeply penetrating gamma rays. From the kind of radiation they employ the batteries get their name, betavoltaics.
Nuclear batteries have distinct advantages. They’re energy-dense, meaning a small amount of material packs a lot of energy. And their power source can last a long time—from several months to centuries of continuous use, depending on which radioactive isotope is used.
But the batteries also have flaws. They’re generally inefficient and produce low levels of current. And practically speaking, their life spans have been limited to about five years. That’s because the radiation that powers the batteries also slowly destroys the semiconductor, causing the batteries to self-destruct. Thus did cheaper, long-lasting lithium-ion batteries eventually displace nuclear batteries in the marketplace.
But as scientists have run up against the limitations of chemically based batteries, interest has turned again to betavoltaics. The Ithaca, New York-based company, Widetronix Inc., along with Lockheed Martin, are developing nuclear batteries to power remote warning sensors for military bases and the computer chips that are embedded in military electronics to prevent tampering. Nuclear batteries will be able to withstand the severe vibrations, temperature extremes and humidity that cause conventional batteries to fail.
In the past, betavoltaics generally were designed with the radioactive isotopes facing the semiconductor; only about half the radiation ever got converted to electricity. Kwon found an ingenious way to solve this problem. He mixed the powdered isotopes, in this case radioactive sulfur, with the selenium-based semiconductor material and melted them together. This way, radiation from all directions strikes the semiconductor.
The radioactive sulfur has a half-life of 87 days, which means it can produce a significant amount of power for at least three months. Other isotopes can last much longer. Tritium has a half-life of about 12 years; nickel 63’s half-life is a century.
Kwon’s first penny-size battery pumped out 17 nanowatts of power. His second version produced 76 nanowatts. Now, it shows much higher power, though still hardly enough power to run a power drill or even an iPod.
Still, the new battery is much more powerful than the previous best nuclear batteries. And Kwon says the future generation of his battery will be much more powerful.
Kwon says he also has solved the problem of radiation harming the battery’s semiconductor. In his battery, the semiconductor material stays in a liquid state, heated by the isotope’s radiation. As a liquid, the semiconductor has no fixed crystalline structure to damage.
Kwon says he can’t build a nuclear battery powerful enough to run a cell phone. Not yet. “It’s probably possible, but we have a long way to go,” he says.
There are logistical, as well as technological hurdles to overcome. Reactors are needed to create the isotopes, which are very expensive. Active and aggressive nuclear research activities might help bring the cost down. Kwon has been working with J. David Robertson, research director of the MU Research Reactor, to make the isotopes for his research.
Nuclear batteries are also expensive, so for now they will probably be limited to military and medical applications, Kwon says. But that will change.
“For the past several years that I’ve worked on micro devices for space exploration, I’ve understood that the nuclear battery may be the best, if not the only, solution for outer-space missions, especially for deep-space missions, which will be far from the sun,” Yu says.
“Although the miniaturization of space mission vehicles has been much improved, there’s been no significant upgrading of batteries for decades. Dr. Kwon’s research on nuclear batteries is unique. It has provided huge potential for the future of outer planetary missions. It is truly a breakthrough.”
Kwon foresees the batteries one day powering tiny, implantable sensors that monitor vital signs. Nuclear batteries might also be able to replace power sources in common household products that drain dozens of batteries over the course of their functional lives. Smoke detectors, for example, Kwon says.
While Kwon’s batteries are small, his other invention is incredibly tiny. It, too, solves a problem that has bedeviled scientists: how to directly and quickly measure the mass of something at the molecular level in a liquid environment.
Laboratories have microbalances that are good at measuring such substances in an air environment. But biology is a wet world. Things such as pathogens and cancer antigens exist in liquids. And measuring them in their natural environments has been a problem for current technology.
Consider how microbalances work: A field is applied to a tiny crystal to make it resonate at a certain frequency. Something that’s on the scale will generate a measurable change in that frequency. This works fine in the open air, but a liquid environment muffles the vibrating crystal, making the scale less sensitive.
Other approaches with optical sensors, such as fluorescent tags and scanning devices, have been developed. But they’re not convenient ways to measure things in liquid, Kwon says. So scientists have tried to find a way to make microscales that work in liquid. “There was a lot of scientific activity,” Kwon says. “For decades, people could not solve this problem.”
Then Kwon came up with a way. He covered the crystal with a layer of metal and created a vacuum between them so that the crystal’s vibrations would not dissipate in water. Tiny metal posts transmit changes in mass from the metal layer to the crystal. Even more remarkable: The sensor is smaller than a pen point, and Kwon is working on making it smaller yet.
“We’ll be reducing the size to nano scale and increasing the sensitivity higher and higher,” he says. That will shrink the sensor down to microbe size. Kwon is working with MU biochemistry professor Thomas Quinn to use the sensor to create a non-invasive test for breast cancer. The sensor would use a tiny amount of nipple-aspirate fluid from a woman to see if it contains a specific protein associated with cancer.
“This device can respond almost instantaneously,” Kwon said. The target protein in the small volume can be detected in 10 minutes; current methods may require a larger amount and a longer time.
Ultimately, as the sensors become smaller, Kwon foresees putting more than 100 on a one-square-centimeter chip to test for a whole host of conditions. Doctors would place a few drops of blood on a chip and plug it into a small computer unit that would read the results and display them on a screen.
“This will revolutionize many methods of testing things on a small scale,” Kwon predicts. His dream is to make the sensors cheap and simple enough to be sold as home kits, the way pregnancy tests and blood pressure monitoring systems are today.
Kwon has filed a U.S. patent application, and a couple of companies have shown an interest in it. “Here at the University we proved the concept. As for the rest, it’s a manufacturing concern, but it’s not a problem at all,” Kwon says.
Kwon said he’ll leave development of his inventions to entrepreneurs. He’ll stay in the lab. “I’m just a scientist,” he says. At heart, Kwon remains a tinkerer. When he came to MU in 2005 from the University of Southern California, the fields of micro and nano-electro-mechanical systems, which go by the acronyms MEMS and NEMS, were still new to the University.
He built his two-story MIDAS laboratory in the century-old Lafferre Hall from scratch, designing his own clean room, collecting surplus parts from companies and assembling them himself, even claiming an old lab furnace and other equipment that he discovered stored away on campus, collecting dust.
“Dr. Kwon’s research on nuclear batteries is unique. It has provided huge potential for the future of outer planetary missions.”
Kwon also built the M/NEMS academic program, teaching both theory and laboratory courses. About 15 students take the laboratory course each semester, and there’s usually a waiting list. The course covers the newest technologies, the kind that microchip companies like Intel Corp. want new hires to know. Students design, build and test their own devices. Recently, they created tiny tools for mixing microfluids. “This is cutting-edge technology. I wanted to provide a lab environment to students so they could have hands-on experience,” Kwon said.
After studying electrical engineering as an undergraduate in South Korea, Kwon went to USC for graduate school. Kwon started out studying integrated circuit design and MEMS for master’s and doctoral degrees. “I didn’t know much about MEMS. When I started studying it, it was really exciting for me,” he says.
Kwon says he feels right at home in Columbia. His youth in South Korea straddled city and country life. While his family lived in the city, Kwon’s family had a farm on the outskirts of town that they worked on weekends.
“I like the country life,” he says. “It’s like my home country here. And weather-wise, it’s the same.” His wife, a city girl from Seoul, took some time acclimating. “She’s totally fine now,” he says. The couple has two children, an eight-year-old son and a five-year-old daughter.
Perhaps not surprisingly, even when Kwon is away from the lab he’s still tinkering. But not with electronic gadgets, miniature or otherwise. He builds furniture and tends a vegetable garden.