Nanotechnology Now – Press Release: CityU award invention: Ultra-thin photonic materials gently cool wearable electronics
Home > Press > CityU award-winning invention: Ultra-thin, soft photonic materials cool wearable electronics
| The “ultrathin, soft, radiative-cooling interface” layer improves heat dissipation of electronic devices such as skin. Hong Kong City University CREDITS |
Abstract:
Wearable electronic skin-like devices overheat increase the risk of sunburn and result in reduced performance. A team of researchers led by City University of Hong Kong (CityU) invented a “soft, ultrathin, radiation-cooled interface” based on photonic materials that greatly improves heat dissipation in devices, with a temperature drop of over 56°C, offering an alternative to better thermal management. effective in high-end wearable electronics.
CityU award-winning invention: Ultra-thin, soft photonic materials cool wearable electronics
Hong Kong, China | Posted on June 30, 2023
“Skin-like electronics is an emerging development in wearables,” said Dr Yu Xinge, Associate Professor in the Department of Biomedical Engineering (BME) at CityU, who co-led the research. “Effective heat dissipation is essential for maintaining good sensing stability and user experience. Our ultrathin, soft, radiative cooling interface, made of specially designed photonic materials, provides a revolutionary solution to enable convenient long-term healthcare monitoring, as well as virtual and augmented reality (VR/AR) applications.”
In electronic devices, heat can be generated from both internal electronic components, when an electric current passes through a conductor, a process known as Joule heating, and external sources, such as sunlight and hot air. To cool the device, both radiant (i.e. thermal radiation – emitting heat energy from the surface of the device) and non-radiative (i.e. convection and conduction – heat loss to the still air layer around the device and through direct contact with cold objects) heat transfer processes can play a role .
However, current technology mostly relies on non-radiative means to dissipate accumulated Joule heat. In addition, the materials are usually bulky and stiff and offer limited portability, hindering the flexibility of wireless wearables.
To overcome this shortcoming, the research team developed multifunctional composite polymer coatings with radiative and non-radiative cooling capacities without the use of electricity and with advances in wearability and flexibility.
The cooling interfacial layer consists of hollow silicon dioxide (SiO2) microspheres, to enhance infrared radiation, and titanium dioxide (TiO2) nanoparticles and fluorescent pigments, to enhance solar reflection. It is less than one millimeter thick, light in weight (about 1.27g/cm2), and has strong mechanical flexibility.
When heat is generated in electronic devices, it flows into the cooling interface layer and dissipates to the surrounding environment through thermal radiation and air convection. The open space above the interface layer provides a cooler heat sink and additional thermal exchange channels. The interface also exhibits excellent anti-ambient-interference capabilities due to its lower thermal conductivity, making it less susceptible to environmental heat sources which will affect the cooling effect and performance of the device.
To check its cooling capacity, the cooler interface layer is suitably coated onto a metal resistance wire – a typical component that causes temperature rises in electronics. With a layer thickness of 75 μm, the wire temperature drops from 140.5°C to 101.3°C, compared to an uncoated wire at an input current of 0.5 A, and drops to 84.2°C with a thickness of 600 μm, achieving a reduction temperatures over 56°C.
“It is necessary to keep the temperature of the device below 44°C to avoid sunburn,” said Dr Yu. “Our cooling interface can cool resistance cables from 64.1°C to 42.1°C with a coating up to 150 µm thick.”
With its efficient passive radiation cooling capacity and advanced nonradiative thermal design, the performance of several skin electronic devices developed by the team is significantly improved, including the efficiency of wireless power transfer to light emitting diodes (LEDs) and the signal stability of skin-wireless sensor interfaces under environmental barriers (e.g. sunlight, hot wind and water).
“The intrinsically flexible nature of the cooling interface enables electronic devices to experience stable cooling even under extreme deformations, such as bending, twisting, folding and flexing many times,” said Dr Lei Dangyuan, Associate Professor in the Department of Materials Science and Engineering (MSE). ) at CityU, another co-lead research.
For example, a wireless stretchable based epidermal lighting system integrated with a cooling interface exhibits higher illumination intensity and maintains stable performance even after stretching from 5% to 50% 1,000 times.
The team applied for a US patent for the invention. They won the Gold Medal, one of 36 awards won by the CityU team, the highest number of awards among local institutions at the 48th Geneva International Invention Exhibition, with their project named “Cooling Technology for Epidermal Electronics”.
Next, the research team will focus on practical applications of cooling interfaces for advanced thermal management of wearable electronics in healthcare monitoring, wireless communications, and VR/AR fields.
These findings were published in the scientific journal Science Advances under the title “Ultrathin, soft, radiative cooling interfaces for advanced thermal management in skin electronics”.
The first co-authors are Dr Li Jiyu, postdoc at BME, and Mr Fu Yang, a PhD student in MSE at CityU. The corresponding authors are Dr Yu and Dr Lei.
This research was supported by CityU, the Hong Kong Center for Cerebro-cardiovascular Health Engineering (COCHE) at InnoHK, and the Research Grants Council of Hong Kong.
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