KAIST Researchers Develop Wearable Harvester Using Hot Pressing And Tape Casting Process

KAIST Researchers Develop Wearable Harvester
Fabrication process, structures, and output signals of a fabric-based wearable energy harvester. (Image credit: KAIST)

A team of researchers at KAIST (Korea Advanced Institute of Science and Technology) have developed what a flexible but sturdy wearable piezoelectric harvester using a process of hot pressing and tape casting. This energy harvester, which has record high interfacial adhesion strength, will take us one step closer to being able to manufacture embedded wearable electronics.

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The team, led by Professor Seungbum Hong, said that the novelty of this result lies in its simplicity, applicability, durability, and its new characterization of wearable electronic devices.

Wearable devices are increasingly being used in a wide array of applications from small electronics to embedded devices such as sensors, actuators, displays, and energy harvesters.

Despite their many advantages, high costs and complex fabrication processes remained challenges for reaching commercialization. In addition, their durability was frequently questioned. To address these issues, Professor Hong’s team developed a new fabrication process and analysis technology for testing the mechanical properties of affordable wearable devices, reports KAIST.

For this process, the research team used a hot pressing and tape casting procedure to connect the fabric structures of polyester and a polymer film. Hot pressing has usually been used when making batteries and fuel cells due to its high adhesiveness. Above all, the process takes only two to three minutes.

The newly developed fabrication process will enable the direct application of a device into general garments using hot pressing just as graphic patches can be attached to garments using a heat press.

Diagram of a wearable
Measurement of an interfacial adhesion strength using SAICAS. (Image credit: KAIST)

In particular, when the polymer film is hot-pressed onto a fabric below its crystallization temperature, it transforms into an amorphous state. In this state, it compactly attaches to the concave surface of the fabric and infiltrates into the gaps between the transverse wefts and longitudinal warps. These features result in high interfacial adhesion strength. For this reason, hot pressing has the potential to reduce the cost of fabrication through the direct application of fabric-based wearable devices to common garments.

In addition to the conventional durability test of bending cycles, the newly introduced surface and interfacial cutting analysis system proved the high mechanical durability of the fabric-based wearable device by measuring the high interfacial adhesion strength between the fabric and the polymer film. Professor Hong said the study lays a new foundation for the manufacturing process and analysis of wearable devices using fabrics and polymers.

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He added that his team first used the surface and interfacial cutting analysis system (SAICAS) in the field of wearable electronics to test the mechanical properties of polymer-based wearable devices. Their surface and interfacial cutting analysis system is more precise than conventional methods (peel test, tape test, and microstretch test) because it qualitatively and quantitatively measures the adhesion strength.

The team’s findings have been published in Nano Energy.

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Cathy Russey () is Online Editor at WT | Wearable Technologies and specialized in writing about the latest medical wearables and enabling technologies on the market. Cathy can be contacted at info(at)wearable-technologies.com.