In a groundbreaking development, researchers from the City University of Hong Kong (CityU) have pioneered a novel cooling technology that could revolutionize the wearable electronics industry.
The team has created a ‘soft, ultrathin, radiative-cooling interface’ using photonic materials, which dramatically enhances heat dissipation in devices, reducing temperatures by over 56°C. This innovative solution offers a promising avenue for effective thermal management in cutting-edge wearable electronics.
Dr Yu Xinge, an associate professor in the Department of Biomedical Engineering at CityU and co-leader of the research, explains that “skin-like electronics are an emerging trend in wearable devices.”
However, effective thermal dissipation is paramount for maintaining a stable sensory experience and ensuring user comfort. The newly developed cooling interface, made from specially designed photonic materials, offers a revolutionary solution for long-term healthcare monitoring and virtual and augmented reality (VR/AR) applications.
Electronic devices generate heat both internally, from electronic components via a process known as Joule heating (also known as resistive heating), and externally from sources such as sunlight and hot air. Cooling these devices involves radiative (emitting heat energy from the device surface) and non-radiative (losing heat through convection and conduction) heat-transfer processes. However, current technologies mainly rely on non-radiative methods to dissipate accumulated heat. This approach often involves bulky and rigid materials that limit the portability and flexibility of wireless wearable devices.
To address these challenges, the research team developed a multifunctional composite polymer coating with both radiative and non-radiative cooling capabilities. This advanced coating does not require electricity and offers improved wearability and stretchability. Composed of hollow silicon dioxide microspheres, titanium dioxide nanoparticles, and fluorescent pigments, this lightweight and flexible coating enhances infrared radiation and solar reflection.
The cooling interface layer acts as a heat sink when heat is generated in an electronic device, dissipating it to the surrounding environment through both thermal radiation and air convection. The layer’s low thermal conductivity also provides excellent resistance to ambient interference, making it less vulnerable to environmental heat sources that could impact the cooling effect and device performance.
The team tested the cooling capacity of the interface layer by coating it onto a metallic resistance wire, a common component in electronics. With a coating thickness of 75 μm, the temperature of the wire dropped from 140.5°C to 101.3°C. With a 600 μm thickness, the temperature dropped to 84.2°C, achieving a temperature drop of over 56°C.
Dr Yu states that it is crucial to keep device temperatures below 44°C to prevent skin burns. He notes that their cooling interface can reduce the temperature of the resistance wire from 64.1°C to 42.1°C with a 150 μm-thick coating.
The cooling interface’s flexible nature allows electronic devices to maintain stable cooling even under extreme deformation like bending, twisting, folding, and stretching. As a result, the team significantly improved the performance of several skin electronic devices they developed.
For instance, their cooling-interface-integrated stretchable wireless-based epidermal lighting system exhibited higher illumination intensity and maintained stable performance even when stretched from 5% to 50% 1,000 times.
The researchers have filed a US patent application for this invention and won a Gold Medal at the 48th International Exhibition of Inventions Geneva under the project name ‘Cooling Technology for Epidermal Electronics’.
Looking ahead, the research team plans to explore practical applications of these cooling interfaces for advanced thermal management in wearable electronics across healthcare monitoring, wireless communications, and VR/AR fields. This development represents a significant milestone in bringing high-tech wearable devices one large step closer to being market-ready.
