The Sum of the Parts Is Greater Than the Whole

Among the various systems in modern drones ripe for innovation, energy storage stands out as arguably the most critical component in need of an upgrade. After all, without power the vehicle is incapable of flight, and nothing else really matters at that point. And due to the relative inefficiency of the spinning rotors that drones most commonly rely on for flight, that point comes much too quickly. As such, novel solutions are needed to address this problem. Without innovation in this area, the potential applications of drones will continue to be limited to those that only require short flights.

With no radically different battery technologies seemingly on the horizon, researchers have turned to lightweight microdrones in an effort to keep aerial vehicles in the sky longer. Microdrones commonly use more efficient methods of flight, like flapping wings inspired by nature. To make this possible on ultra-tiny vehicles, piezoelectric microactuators are typically utilized. But there is a catch — these actuators require tens to hundreds of volts for operation, which is far more than a typical rechargeable battery can supply.

Of course the voltage can be stepped up with inductors or capacitors, but this adds weight and bulk that a little microdrone simply cannot bear. As a result, these drones still can rarely operate for more than a few minutes at a time, despite their more efficient mode of operation. This extra weight may no longer be necessary in the future, however, thanks to the work of a team led by researchers at the University of California San Diego. They have developed a new type of power delivery system that can supply much higher voltages than traditional batteries without any bulky hardware.

A smarter way to power microdrones

The research team has developed an innovative circuit configuration that utilizes miniaturized solid-state batteries. These batteries, known for their high energy density, can be sliced into multiple smaller units without reducing the energy density of each unit. By incorporating what the researchers call a "flying battery" design, the system can dynamically switch how the individual battery units are connected, adapting in real-time to the energy needs of the drone.

For instance, when the microdrone requires high voltage to power its piezoelectric actuators, the system connects the batteries in series, stacking their voltages to meet demand. When less power is needed, the batteries switch to a parallel arrangement to maximize energy storage efficiency. This process occurs within milliseconds, eliminating the need for large passive components that would otherwise add excess weight.

It keeps going and going

Another major advantage of this system is its ability to recover and recycle energy. The piezoelectric microactuator itself can function like a capacitor, storing and then releasing energy efficiently. When the actuator discharges, instead of wasting that energy, the system channels it back into the solid-state batteries through an adiabatic recharging process — similar to regenerative braking in electric vehicles.

Using 18 battery units from a commercial solid-state battery design, the researchers were able to generate up to 56.1 volts while maintaining continuous operation for over 50 hours. The entire system weighed just 1.8 grams. After incorporating even smaller, custom-designed solid-state batteries into the system, the total weight was reduced to a very impressive 14 milligrams.

With the team continuing to refine their design, the potential for microdrones to play a larger role in fields like disaster response, environmental monitoring, and search-and-rescue missions is growing. Instead of being limited by short flight times, these tiny yet powerful robots could soon operate for extended periods, significantly expanding their usefulness in real-world applications.