Imagine your wearable power device being powered by body heat rather than having to be taken off and plugged into a charger.
Researchers at North Carolina State University have developed a new “thermoelectric harvester” technology that will help power flexible wearable devices through capture of body heat. And they are seeking a patent on the technology.
“We wanted to design a flexible thermoelectric harvester that does not compromise on the material quality of rigid devices yet provides similar or better efficiency,” says Mehmet Ozturk, a professor of electrical and computer engineering at NC State and corresponding author of a paper describing the work. “Using rigid devices is not the best option when you consider a number of different factors.”
The researchers believe their proof-of-concept study has resulted in the design of a flexible thermoelectric energy harvester that could rival the effectiveness of existing power wearable electronic devices while using body heat as the source of energy.
The project includes use of liquid metal.
“We use a liquid metal of gallium and indium – a common, non-toxic alloy called EGaIn – to connect the thermoelectric ‘legs,’” Ozturk said. “The electric resistance of these connections is very low, which is critical since the generated power is inversely proportional to the resistance: Low resistance means more power.
“Using liquid metal also adds a self-healing function: If a connection is broken, the liquid metal will reconnect to make the device work efficiently again. Rigid devices are not able to heal themselves,” Ozturk added.
Liquid metal in the flexible thermoelectric device allows for self-healing. Rigid devices do not have the ability to heal themselves, Ozturk noted.
“Wearable devices used to monitor a variety of health and environmental measures are becoming increasingly popular. The performance and efficiency of flexible devices, however, pale in comparison to rigid devices, which have been superior in their ability to convert body heat into usable energy,” reports Mick Kulikowski for NCSU’s news service.
Ozturk worked with Michael Dickey and Daryoosh Vashaee on the project.
Results of their project were published in Applied Energy.
An abstract of the paper follows.
“Flexible thermoelectric generator using bulk legs and liquid metal interconnects for wearable electronics”
Authors: Francisco Suarez, Dishit P. Parekh, Collin Ladd, Daryoosh Vashaee, Michael D. Dickey, Mehmet C. Ozturk, North Carolina State University
Published: June 14, 2017, online in Applied Energy
Abstract: Interest in wearable electronics for continuous, long-term health and performance monitoring is rapidly increasing. The reduction in power levels consumed by sensors and electronic circuits accompanied by the advances in energy harvesting methods allows for the realization of self-powered monitoring systems that do not have to rely on batteries. For wearable electronics, thermoelectric generators (TEGs) offer the unique ability to continuously convert body heat into usable energy. For body harvesting, it is preferable to have TEGs that are thin, soft and flexible. Unfortunately, the performances of flexible modules reported to date have been far behind those of their rigid counterparts. This is largely due to lower efficiencies of the thermoelectric materials, electrical or thermal parasitic losses and limitations on leg dimensions posed by the synthesis techniques. In this work, we present an entirely new approach and explore the possibility of using standard bulk legs in a flexible package. Bulk thermoelectric legs cut from solid ingots are far superior to thermoelectric materials synthesized using other techniques. A key enabler of the proposed technology is the use of EGaIn liquid metal interconnects, which not only provide extremely low interconnect resistance but also stretchability with self-healing, both of which are essential for flexible TE modules. The results suggest that this novel approach can finally produce flexible TEGs that have the potential to challenge the rigid TEGs and provide a pathway for the realization of self-powered wearable electronics.