RESEARCH

Materials Discovery

Wearable Electronics

Renewable Energies

1. Materials Discovery

The interaction of electromagnetic field (such as microwave) radiation with materials is categorized into thermal and non-thermal effects. The thermal effect contains characteristics of dielectric heating, such as overheating, hot spots, and selective heating. The non-thermal effect is more profound and includes different material responses such as electromagnetic field-induced alloy decomposition, de-crystallization, enhanced solid-state reactions, and defect generation. These phenomena are thermodynamically non-equilibrium and have not completely known yet.

Microwave radiation enables creating bulk amorphous and amorphous-crystalline materials in a convenient way where the interaction of a high frequency high electric field with the material results in its rapid decrystallization. This method can develop high performance bulk materials as well as thin films. Also, microwave radiation can decompose continuous solid-solution materials into their constituent phases e a process that is thermodynamically unfavorable at equilibrium.

References:

1. A. Nozariasbmarz, M. Hosseini, and D. Vashaee, Interfacial Ponderomotive Force in Solids Leads to Field Induced Dissolution of Materials and Formation of Non-equilibrium Nanocomposites, Acta Materialia, 179, 85-92 (2019).

2. A. Nozariasbmarz, K. Dsouza, D. Vashaee, Field Induced Decrystallization of Silicon: Evidence of a Microwave Non-Thermal Effect, Applied Physics Letters, 112, 093103 (2018).

3. D. Vashaee, A. Nozariasbmarz, L. Tayebi, Jerzy S. Krasinski, Microwave processing of thermoelectric materials and use of glass inclusions for improving the mechanical and thermoelectric properties, US Patent, Publication No. WO2017095972 A1, Application No. PCT/US2016/064292, June 2017.

4. A. Nozariasbmarz, J. H. Dycus, M. J. Cabral, C. M. Flack, J. S. Krasinski, J. M. LeBeau, D. Vashaee, Efficient Self-Powered Wearable Electronic Systems Enabled by Microwave Processed Thermoelectric Materials, Applied Energy, 283, 116211 (2021).

5. A. Nozariasbmarz, D. Vashaee, Effect of Microwave Processing and Glass Inclusions on Thermoelectric Properties of P-Type Bismuth Antimony Telluride Alloys for Wearable Applications, Energies, 13, 4524 (2020).

2. Wearable Electronics

I) Power Generation: Global demand for battery-free metrics and health monitoring devices has urged leading research agencies and their subordinate centers to set human energy harvesting and self-powered wearable technologies as one of their primary research objectives.

Body heat harvesting systems based on thermoelectric generators (TEGs) can play a significant role in wearable electronics intended for continuous, long-term health monitoring. However, to date, the harvested power density from the body using TEGs is limited to a few micro-watts per square centimeter, which is not sufficient to turn on many wearables.

The thermoelectric materials research has been mainly focused on enhancing the single parameter zT, which is insufficient to meet the requirements for wearable applications. To develop TEGs that work effectively in wearable devices, one has to consider the material, device, and system requirements concurrently. Due to the lack of an efficient heatsink and the skin thermal resistance, a key challenge to achieving this goal is to design systems that maximize the temperature differential across the TEG while not compromising the body comfort. This requires favoring approaches that deliver the largest possible device thermal resistance relative to the external parasitic resistances. Therefore, materials with low thermal conductivity are critically important to maximize the temperature gradient. Also, to achieve a high boost converter efficiency, wearable TEGs need to have the highest possible output voltage, which calls for a high Seebeck coefficient. At the device level, dimensions of the legs (length versus the base area) and fill factor are both critical parameters to ensure that the parasitic thermal resistances are again negligible compared to the resistance of the module itself. In this study, the concurrent impact of material and device parameters on the efficiency of wearable TEGs is considered.

References:

II) Cooling: Thermoelectric coolers are attracting significant attention for replacing age-old cooling and refrigeration devices. Localized cooling by wearable thermoelectric coolers will decrease the usage of traditional systems, thereby reducing global warming and providing savings on energy costs. Since human skin as well as ambient air is a poor conductor of heat, wearable thermoelectric coolers operate under huge thermally resistive environment. The external thermal resistances greatly influence thermoelectric material behavior, device design, and device performance, which presents a fundamental challenge in achieving high efficiency for on-body applications.

References:

3. Renewable Energies

I) Thermoelectric Generators (TEGs): Waste heat recovery promises a low-cost and sustainable power source for a wide range of applications by converting rejected heat into electricity. TEGs enable direct energy conversion from heat to electricity. Being solid-state energy conversion technique, it has advantages of reliability, simplicity, light-weight, compactness, and environmental friendliness. To make TE technology feasible, it requires significant improvement in conversion efficiency which is jointly determined by the Carnot efficiency and the dimensionless figure of merit, zT.

In TEGs, my research on materials applicable from near room temperature to 1000 degrees Celsius such as Bi2Te3 alloys, GeTe, Half-Heusler, and SiGe alloys. Utilizing the recent advancements in nanotechnology and advanced manufacturing, we fabricate high performance thermoelectric materials and devices which show record high power density and efficiency. Having state-of-the-art materials fabrication and characterization facility together with device fabrication and testing capability available in one laboratory provides a unique research experience and opportunity to conduct the research efficiently developing new materials and power generation devices.

Also, TEGs are desirable for low-grade waste heat recovery application. We demonstrated converting the waste heat from hot water pipe into electricity.

References:

II) Thermal Management: Future advancements in three-dimensional (3D) electronics require robust thermal management methodology. Thermoelectric coolers (TECs) are reliable and solid-state heat pumping devices with high cooling capacity that can meet the requirements of emerging 3D microelectronic devices.

References:

A. Nozariasbmarz, R. A. Kishore, W. Li, Y. Zhang, L. Zheng, M. Sanghadasa, B. Poudel, and Shashank Priya, Thermoelectric Coolers for High-power-density 3D Electronics Heat Management, Applied Physics Letters, 120, 164101 (2022).

III) Thermomagnetic Generators: Thermomagnetic materials provide a fundamentally diﬀerent approach for harnessing low-grade thermal energy and converting it into mechanical or electrical energy using the thermomagnetic eﬀect. The concept of a thermomagnetic generator was first proposed in the late 19th century but this promising technology was not implemented due to lack of a suitable ferromagnetic material. Gadolinium (Gd) having a low Curie temperature of 22 ⁰C, has been proposed as a suitable thermomagnetic material for a thermomagnetic generator. The ferromagnetic to paramagnetic transition normally occurs in a narrow temperature range; therefore, in comparison with conventional ferromagnetic materials, Gd is expected to exhibit a higher Carnot efficiency for the same value of temperature gradient.

References:

R. A. Kishore, B. Davis, J. Greathouse, A. Hannon, D. Kennedy, A. Millar, D. Mittel, A. Nozariasbmarz, M. G. Kang, H.B. Kang, M. Sanghadasa and S. Priya, Energy Scavenging from Ultra-low Temperature Gradients, Energy & Environmental Science, 12(3), 1008-1018 (2019).