A technology has been developed that can be simply attached to the body to produce electricity from body heat and supply power directly through the module using a heat energy harvesting technology that utilizes a gasket with a meta structure, and it is expected to see increased use in future IoT development.

A research team led by Dr. Hye-Kyung Choi and Dr. Min-Joo Yoon from the Korea Electrotechnology Research Institute (KERI)’s Center for Electrical Conversion Materials has developed a technology that can increase the elasticity and efficiency of thermoelectric power generation devices to the world’s highest level by utilizing ‘metamaterials’ that do not exist in nature.

Normally, when a force is applied to a material to stretch it horizontally, it is normal for the vertical direction to shrink. It is like when you squeeze a rubber ball, it flattens out to the side, and when you pull a rubber band, it stretches out. The ratio of compression and expansion in the vertical direction when force is applied is called 'Poisson's ratio'. On the other hand, metamaterials are artificially designed materials that, unlike natural materials, stretch in the horizontal direction and also stretch in the vertical direction. Metamaterials have a negative Poisson's ratio.

KERI succeeded in increasing the elasticity of thermoelectric elements by up to 35% by utilizing a 'gasket' with this meta structure. Thermoelectric elements are based on the principle of converting the temperature difference between the two ends into electrical energy. They are called next-generation eco-friendly energy harvesting elements because they can utilize the heat wasted in daily life as electricity.

Most thermoelectric devices used rigid ceramic substrates, making them difficult to apply to curved surfaces such as skin or hot water pipes. To solve this problem, flexible materials such as silicon or polymers were used, but high conductivity was a problem. Thermoelectric devices are more efficient when the temperature difference between the boundaries of each material is large, but flexible materials conduct current too well, causing heat loss and making it difficult to expect a large temperature difference. In other words, it is important for thermoelectric devices to have both flexibility and elasticity and efficiency.

The gasket utilized by Dr. Choi Hye-kyung and Dr. Yoon Min-joo’s team has a meta-structure, which greatly increases the structural stability of the thermoelectric element. It can be transformed into various shapes, stretches well like human skin, and can be easily attached anywhere. In addition, the air inside the gasket has excellent insulation properties, preventing heat loss and increasing the temperature difference by up to 30% compared to existing flexible thermoelectric elements, thereby securing the efficiency of the thermoelectric element.

KERI's thermoelectric generator has a flexibility of up to 35% or more, while its power generation density is 20 times higher (0.1 μW/㎠ ⇒ 2~3 μW/㎠). This means that even if the thermoelectric generator module is greatly increased, there is almost no deterioration in electrical characteristics. This flexibility and efficiency are the world's best. The research team also secured durability that allows the device to withstand repeated bending over 10,000 times without any loss of performance.

KERI’s Dr. Hye-Kyung Choi said, “Our research center possesses not only the know-how to develop high-performance thermoelectric materials, but also modularization technology dedicated to energy harvesting and technology related to stable autonomous power sources.” She added, “Through this convergence research, we were able to create synergy effects and consider everything from the development of original technologies to verification and real-life applications.”

This achievement is expected to receive significant attention in the IoT and AI-based wearable device sector. Existing wearable devices had the disadvantage of requiring a separate power supply device such as a battery, but with KERI’s thermal energy harvesting technology, they can be simply attached to the body to generate electricity from body heat and even supply power directly through the module. It can also be applied to the next-generation medical field.

The results of the related research were recently published as a cover paper in 'Advanced Energy Materials', a renowned international academic journal in the energy field, in recognition of its excellence (Impact Factor 27.8 / JCR top 2.5%).

The research team aims to bring forward the era of next-generation eco-friendly energy harvesting through continuous research and development, including improvements in cooling technology and power management circuits that can enhance the performance of thermoelectric devices.

Meanwhile, KERI is a government-funded research institute under the National Research Council of Science and Technology of the Ministry of Science and ICT.