A single blast of sound solves foldable electronics' biggest heat problem

Every time a foldable phone snaps shut or a flexible medical sensor hugs the skin, tiny computer chips pump out intense heat that can easily scorch delicate circuits or burn human tissue. Keeping these bendable gadgets cool requires paper-thin thermal sheets packed with microscopic heat spreaders.

For decades, manufacturing these materials required baking polymers under immense pressure for hours or freeze-drying them for days. This prolonged thermal abuse regularly cooks the flexible plastics until they turn brittle and crack, while trapping millions of insulating air pockets that choke heat flow.

In International Journal of Extreme Manufacturing, Prof. Zhizhu He at China Agricultural University and his co-workers have sidestepped this trade-off by enlisting acoustic vibration to assemble cooling films in a single second. Their method, termed rolled sonication-enabled microstructure orientation (RSMO), pairs a rotating mechanical drum with a high-frequency acoustic horn to instantly compact and align heat-conducting particles without any external furnaces. Operating continuously like an automated assembly line, the process churns out roughly 36 m² of cooling film per hour, about one hundred times faster than standard industrial hot-pressing machines.

The machine acts like a high-speed sonic iron. When a fluffy and porous mesh of plastic fibers passes between the roller and a horn vibrating 15,000 times per second, the intense friction generates an instant burst of heat that softens the plastic just enough for it to flow like warm dough without burning.

At the exact same instant, the combined forces of downward rolling pressure and acoustic micro-swirls spin chaotic microscopic flakes of boron nitride ceramic, flipping them completely flat. By adding droplets of room-temperature liquid gallium metal to the mix, the molten metal spreads out like microscopic solder, bridging the gaps between the ceramic flakes to create uninterrupted highways for heat vibrations.

This one-second acoustic treatment turns a loose fibrous mesh into an ultra-dense and paper-thin sheet that conducts heat along its surface at 12.67 W·m⁻¹·K⁻¹ while staying remarkably pliable. Squeezed down to a thickness four times thinner than a human hair, the resulting film can be folded completely in half or bent over 5,000 times around the tip of a pencil without cracking or losing its cooling power.

When placed inside a high-power 24-watt LED light, the film pulled heat away so rapidly that operating temperatures dropped by over 84 K, keeping the chip from melting. Tacked onto a flexible thermoelectric generator worn on the body, it doubled the electrical power harvested from body heat by keeping the outside of the device comfortably cool.

By taking long bake times completely out of the equation, this green rolling process provides a direct path to roll-to-roll mass manufacturing for wearable health patches, electric car electronics, and flexible displays. Before the equipment lands in commercial factories, the researchers are focused on engineering sound-dampening enclosures to muffle factory noise, designing cooling systems to keep the heavy-duty ultrasonic horns from overheating, and building wider vibrating rollers that can sweep across meter-wide industrial production lines.

International Journal of Extreme Manufacturing (IJEM, IF: 25.1) is devoted to publishing articles of the highest quality and significance to pushing the limits of scales, precision, performance and environments in manufacturing.

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