New microactuator driving system could give microdrones a jump-start

An innovative circuit design could enable miniature devices, such as microdrones and other microrobotics, to be powered for longer periods of time while staying lightweight and compact. Researchers from the University of California San Diego and CEA-Leti developed a novel self-sustaining circuit configuration—featuring miniaturized solid-state batteries—that combines high energy density with an ultra lightweight design. 

The results will be presented at the 2025 IEEE International Solid-State Circuits Conference (ISSCC), which will take place from Feb. 16 to 20 in San Francisco. 

One important application envisioned for microdrones is how they could assist first responders in disaster cases. When a building collapses, for example, current robots might be too large to maneuver in the resulting confined areas. Yet, a swarm of tiny wing-flapping drones—so tiny that one can rest on a fingernail—could enter the tight spaces to inspect the building for chemical hazards or even to search for trapped people.   

The design dilemma, however, is that these devices need lasting power to fly around long enough. But because they are so small (tens of grams or ideally less), carrying a large battery is impractical. As a result, current microdrones can only fly for a few minutes. 

“In order to maximize the flight time, you need to minimize the weight of all the components of the system, and that includes the battery and all electronics needed to process power,” said Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering and co-senior author of the paper. “It’s a very difficult and delicate trade-off.”

Slice and dice

To move around, most microrobots use piezoelectric microactuators, which translate an electrical signal to a precisely controlled physical movement. However, these microactuators need high voltages to work—as much as tens to hundreds of volts—while today’s lithium-ion batteries supply only 4 volts. Boosting the voltage typically requires bulky inductors or capacitors, which add significant weight and volume, making them suboptimal for such small devices.

Consequently, Mercier and his team, including the study’s co-first author Zixiao Lin, an electrical and computer engineering Ph.D. student at UC San Diego, turned away from conventional small batteries to something more compact and lightweight. “The breakthrough in our approach comes from utilizing emerging solid-state batteries, which possess the unique capability to scale down without sacrificing energy density,” said Gaël Pillonnet, scientific director of CEA-Leti’s Silicon Component Division and co-senior author of the paper.

“Instead of having one larger battery, we could take that exact same battery and slice and dice it up into 10 or 20 or more individual batteries,” said Mercier. And each of those individual batteries will have the same energy density as the larger parent battery.

Then, with those sliced-up batteries, the team built a driving circuit with a so-called flying battery configuration. Unlike conventional battery setups, which are typically fixed in one arrangement, the flying battery offers versatility. It allows the system to dynamically switch how individual battery units are connected, adapting in real time to the system's shifting energy needs.

Here, the batteries can either be connected in series (where the voltages of individual batteries add up) or in parallel (where the total energy capacity increases but the voltage stays the same). For example, when the drone needs higher voltage to operate its microactuator, the system dynamically connects individual batteries in series, stacking them step by step, until the required voltage is reached. And when less power is needed, the batteries can be rearranged in parallel to maximize energy storage efficiency.

This switching between series and parallel configurations happens in tens of milliseconds, all without the weight of additional passive components.

Charge and recharge

The system takes efficiency a step further by incorporating energy recovery. This is made possible in part due to the rechargeable nature of the solid-state batteries and the ability of the microactuator to function as a capacitor. The microactuator gets charged up to a high voltage to actuate, then discharges that energy back into the batteries recharging them via a step-by-step destacking process. As in the charging stage, it recharges adiabatically—that is, without the transfer of heat—in the most efficient way possible.

Mercier likens it to how regenerative braking works in a hybrid or electric vehicle. “We can drive the microactuator extremely efficiently and recover some of the energy that we deliver to it, such that the battery continues to last even longer,” he said.

Using 18 battery units of an early commercially available solid-state battery, the system generated up to 56.1 volts while operating continuously for 50+ hours. The entire system weighed just 1.8 grams.

The team achieved even better results with tinier solid-state batteries that were custom developed at CEA-Leti to have higher energy density. Using these batteries, the system’s weight dropped to a mere 14 milligrams. “Our results demonstrate that the concept is scalable to different target frequencies or voltages beyond the initial proof of concept,” said Pillonnet.

The next step will be to test the drive system in an actual microrobot. Beyond that, the team will continue to optimize the solid-state batteries and push for even higher voltage outputs.

Paper: “An Autonomous and Lightweight Microactuator Driving System Using Flying Solid-State Batteries.” Co-authors include Zixiao Lin* and Patrick Mercier, UC San Diego; and Jim Wouda*, Sami Oukassi, and Gaël Pillonnet, CEA-Leti, France.

*These authors contributed equally

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