Resonant Link

The key to decarbonization is the electrification of everything, but electrification often comes with an unfortunate tangle: the charging cable. In fixed systems like heating and cooling, the need for continuous power is easily solved with a wire. But nearly every other application is constrained by the necessity of onboard energy storage—and the need to plug it in. Resonant Link, a startup with roots at Dartmouth College and Stanford University, has developed a transformational wireless charging platform, powerful enough to allow device manufacturers in medicine, mobility, and consumer electronics to discard existing limitations and invent new solutions.

Conventional wireless charging systems have relied on bundles of hair-thin copper wires. The thinner these wires, the better the performance. But thinness comes at a price: manufacturing costs increase exponentially as strand-size decreases. And thinness comes with limits: it is impractical to make wires thinner than 70 microns. Today’s wireless charging components, as a result, are slow, inefficient, and clunky. Their applications have been prosaic: a billion mobile phones can now be charged wirelessly, if only over a distance of millimeters.

Resonant Link’s technology achieves near-equivalent performance of wired charging by replacing these thin strands with thin foils—“like the kind you wrap your lunch in,” as company co-founder Professor Charlie Sullivan likes to say. Charlie first tackled the problem in 2012, when he was asked to build a wireless power system for heating up magnetic nanoparticles in the body as a cutting-edge cancer treatment. In his Dartmouth College lab, he invented the idea of alternating layers of thin film and non-conductive dielectric, like a coaster-sized lasagna of aluminum foil and plastic wrap. The foil could be cheaply and easily manufactured at single-digit micron thicknesses—an order of magnitude thinner than existing wireless charging components—bringing an immediate gain in performance. And the combination of an inductor and a capacitor created a resonator, the crucial function needed for wireless power transfer, in a smaller package.

Charlie called it a multilayer self-resonant structure (MSRS), and published and patented the invention in 2013. Working in Carlie’s lab, Aaron Stein (now Chief Technology Officer) and Phyo Aung Kyaw (now Chief Science Officer) iterated hundreds of different ways of stacking the thin foils, until they developed a working prototype that shattered existing wireless charging metrics. Their MSRS charging coils showed over 5x improvements in overall ”Q,” or quality factor (the standard measure of wireless power transfer). They offered 5x lower power losses, 5x faster charging speeds, 10x lower costs-per-watt, and 3x lower size and weight.

But what could be built around them? The Dartmouth group joined up with Grayson Zulauf, a Stanford doctoral student in electrical engineering who had worked in Professor Sullivan’s lab as an undergraduate, and founded Resonant Link in 2017. “Wireless charging had always been a convenience add-on,” says Grayson, now Resonant Link’s CEO. “But where would the technology matter? Where are the places that can really move the needle?” In Stanford’s Climate Ventures class, Grayson, Aaron, and Phyo made hundreds of calls to potential customers, seeking out applications in which Resonant Link’s wireless power technology could not merely replace existing components, but transform the products in which they were embedded.

Implanted medical devices were the most vital opportunity. Since the adoption of the earliest modern pacemakers in the 1960s, doctors dreamed of removing their need for battery replacements, or, for high-power implants like heart pumps, their “driveline”—the tube that passes through the skin, for power and control. Drivelines have broad negative impacts on a patient’s quality of life, and are a leading source of infection. But wireless or continuously powered devices have been elusive, in part because of FDA regulations limiting the amount of heat they can emit. Resonant Link’s MSRS components—which can charge at greater distances, with a smaller footprint, and greater thermal efficiency—unlock a new category of fully implanted devices. “Our mission is to eliminate drivelines and battery replacement surgeries forever,” says Grayson. “We can open up new treatment opportunities, and make them last an entire lifetime for patients.”

Electric mobility offers similarly transformative possibilities. Both on the road and in factories, today’s vehicles are functionally constrained by a fixed formula of battery size, material costs, range, and uptime. The increased charging speed, looser component alignments, and greater range of Resonant Link’s technology allow for practical “opportunity charging”—meaning vehicles are powered while they work, at scheduled stops or while loading or unloading. Eliminating uptime and downtime cycles allows vehicle batteries to become an order of magnitude smaller, while keeping these all-electric fleets of the future operating 24/7.

Resonant Link’s vision reaches far beyond phone chargers, to be an essential component of the electric future. “We can’t be merely rebuilding gas stations, repeating the same unhealthy mistakes with outdated medical technologies, or stuck in restrictive schedules of uptime and downtime,” says Grayson. “In so many realms, wireless charging offers a way to break free, enabling solutions that are more productive, cleaner, easier-to-use, and healthier for people and planet. We aim for these solutions to be no-brainers to adopt, and to adopt today.”