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Dr. Mehmet Cevdet Ozturk

North Carolina State University, USA


Talk Title
Flexible Thermoelectric Generators using Bulk BiTe Legs and Stretchable Liquid Metal Interconnects for Harvesting Heat From the Human Body

Talk Abstract

Thermoelectric generators (TEGs) that can convert waste heat into electricity are of great interest for a variety of applications ranging from self-powered wearables to industrial applications with continuous sensing needs. For many of these applications, flexible TEGs that conform to the shape of the heat source are highly desirable. For wearables, a flexible TEG would provide a better contact to the skin and reduce the thermal contact resistance between the body and the device. Furthermore, without a flexible TEG, one would have to connect many rigid TEGs on a flexible band, an approach that would result in an aesthetically inferior wearable, which would also suffer from a high parasitic interconnect resistance. A variety of approaches have been previously proposed for manufacturing flexible TEGs. Unfortunately, none of these approaches were able to produce flexible TEGs that were able to rival the performance of their rigid counterparts for reasons that include poor quality of new flexible materials, limitations on leg dimensions imposed by fabrication techniques and parasitic resistances. With their maximum power levels limited to a few microwatts (or nanowatts in many of the cases), these modules were short of meeting the power needs of most applications including wearables. In this talk, we will review a novel approach to manufacturing flexible thermoelectric generators that can rival the performance of their rigid counterparts. The new technology was developed at NC State University with the objective to power wearables that relied entirely on body heat. The work was funded by the Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST), an NSF sponsored Engineering Research Center, whose mission is to develop self-powered wearables with multi-modal, long-term sensing and wireless communication capabilities. The new technology employs bulk thermoelectric materials similar to those presently used in rigid TEGs eliminating the need to develop entirely new, flexible materials. Additionally, the new technology is compatible with pick-and-place manufacturing widely used in manufacturing of rigid modules providing the existing manufacturers an easy, low-cost entry to the flexible TE market. In these modules, the thermoelectric legs are embedded in a stretchable elastomer and they are connected to each other by highly stretchable, self-healing liquid metal interconnects. The interconnects are made of EGaIn, a eutectic alloy of gallium (Ga) and indium (In). EGaIn provides excellent electrical conductivity, it is inexpensive, non-toxic and commercially available. The technology has the potential to enable a revolution in flexible thermoelectric module manufacturing and self-powered devices. The proof-of-concept devices produced in our laboratory yield performance figures better than any previously published flexible TEG to date. Furthermore, our predictive modeling shows that with improvements in materials and device design, our flexible TEGs have the potential to outperform rigid TEGs in wearable applications. 
The technical talk will provide the details of the manufacturing process and summarize our current efforts on system optimization through modeling and development of new materials with high or low thermal conductivities as needed in different parts of the modules. The talk will also provide on-body measurements of the electrical power generated under different ambient conditions.

Short Biography
Talk Keywords
Thermoelectric Module,Thermoelectric Energy Generator,Thermoelectric Energy Harvester,Thermoelectric Heat Harvester, Flexible Thermoelectrics, Stretchable Interconnects, Wearable Electronics, Self-Powered Wearables.
Target Audience
Researchers, Government policy makers, Industrail leaders, Students, General publics
Speaker-intro video

The International Conference on Innovative Applied Energy (IAPE’18)