@article{sargolzaeiaval_ramesh_ozturk_2022, title={A comprehensive analytical model for thermoelectric body heat harvesting incorporating the impact of human metabolism and physical activity}, volume={324}, ISSN={["1872-9118"]}, DOI={10.1016/j.apenergy.2022.119738}, abstractNote={Wearable electronic devices, which can provide hassle-free, long-term, continuous monitoring for different health parameters are of interest for a variety of applications including managing chronic diseases and post-operative patient care. Thermoelectric generators (TEGs) that rely on the Seebeck effect provide a promising path to self-powered wearable electronics via harvesting body heat. The net harvested energy depends on several factors including metabolic heat, core body temperature, and skin resistance, which are regulated by the human thermoregulatory system. These factors are influenced by age, sex, height and body mass index (BMI) and they can cause appreciable differences in the amount of harvested energy. In this paper, we present a comprehensive model, which combines an analytical TEG model with established biological models for the human body to accurately predict the performance of a wearable TEG. The model calculates variations in metabolic rate and core body temperature during physical activity, which are then used to calculate the skin resistance and the skin temperature following an iterative procedure. These parameters are then used to determine the temperature differential across the TEG and the resulting output power delivered to an external load. Experimental validation of the model was achieved using a wrist worn flexible TEG during different physical activities, which were carefully designed to separate the impact of convection from the human thermoregulatory response. It was determined that increase in metabolism from normal walking could lead to a 20% increase in the TEG output voltage. The model was used to predict the impact of age and sex on TEG output power. The results indicate that age can have a significant impact on TEG performance. It is shown that the power generated by adults over the age of 65 can be 30%–35% less than the power generated by younger adults under the age of 30. This reduction in power was attributed to an increase in skin resistance, which was found to be 13% for females and 25% for males. The skin resistance of females was also found to be higher, which correlated well with their higher average fat content. The overall impact of sex was found to be smaller than age, females generating 5%–10% less power than males. The model takes into account all pertinent TEG parameters including properties of the semiconductor materials, physical dimensions of the semiconductor legs, fill factor and electrical and thermal parasitic resistances. Using these input parameters, and modeling of the human body as a heat source, the model can help optimize TEG module design for a specific wearable application.}, journal={APPLIED ENERGY}, author={Sargolzaeiaval, Yasaman and Ramesh, Viswanath Padmanabhan and Ozturk, Mehmet C.}, year={2022}, month={Oct} }
 @article{neumann_kara_sargolzaeiaval_im_ma_yang_ozturk_dickey_2021, title={Aerosol Spray Deposition of Liquid Metal and Elastomer Coatings for Rapid Processing of Stretchable Electronics}, volume={12}, ISSN={["2072-666X"]}, url={https://doi.org/10.3390/mi12020146}, DOI={10.3390/mi12020146}, abstractNote={We report a spray deposition technique for patterning liquid metal alloys to form stretchable conductors, which can then be encapsulated in silicone elastomers via the same spraying procedure. While spraying has been used previously to deposit many materials, including liquid metals, this work focuses on quantifying the spraying process and combining it with silicones. Spraying generates liquid metal microparticles (~5 μm diameter) that pass through openings in a stencil to produce traces with high resolution (~300 µm resolution using stencils from a craft cutter) on a substrate. The spraying produces sufficient kinetic energy (~14 m/s) to distort the particles on impact, which allows them to merge together. This merging process depends on both particle size and velocity. Particles of similar size do not merge when cast as a film. Likewise, smaller particles (<1 µm) moving at the same speed do not rupture on impact either, though calculations suggest that such particles could rupture at higher velocities. The liquid metal features can be encased by spraying uncured silicone elastomer from a volatile solvent to form a conformal coating that does not disrupt the liquid metal features during spraying. Alternating layers of liquid metal and elastomer may be patterned sequentially to build multilayer devices, such as soft and stretchable sensors.}, number={2}, journal={MICROMACHINES}, publisher={MDPI AG}, author={Neumann, Taylor V. and Kara, Berra and Sargolzaeiaval, Yasaman and Im, Sooik and Ma, Jinwoo and Yang, Jiayi and Ozturk, Mehmet C. and Dickey, Michael D.}, year={2021}, month={Feb} }
 @misc{vallem_sargolzaeiaval_ozturk_lai_dickey_2021, title={Energy Harvesting and Storage with Soft and Stretchable Materials}, volume={33}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202004832}, DOI={10.1002/adma.202004832}, abstractNote={Abstract}, number={19}, journal={ADVANCED MATERIALS}, author={Vallem, Veenasri and Sargolzaeiaval, Yasaman and Ozturk, Mehmet and Lai, Ying-Chih and Dickey, Michael D.}, year={2021}, month={May} }
 @article{padmanabhan ramesh_sargolzaeiaval_neumann_misra_vashaee_dickey_ozturk_2021, title={Flexible thermoelectric generator with liquid metal interconnects and low thermal conductivity silicone filler}, volume={5}, ISSN={["2397-4621"]}, DOI={10.1038/s41528-021-00101-3}, abstractNote={Abstract}, number={1}, journal={NPJ FLEXIBLE ELECTRONICS}, author={Padmanabhan Ramesh, Viswanath and Sargolzaeiaval, Yasaman and Neumann, Taylor and Misra, Veena and Vashaee, Daryoosh and Dickey, Michael D. and Ozturk, Mehmet C.}, year={2021}, month={Mar} }
 @article{sargolzaeiaval_ramesh_neumann_misra_vashaee_dickey_ozturk_2020, title={Flexible thermoelectric generators for body heat harvesting - Enhanced device performance using high thermal conductivity elastomer encapsulation on liquid metal interconnects}, volume={262}, ISSN={["1872-9118"]}, DOI={10.1016/j.apenergy.2019.114370}, abstractNote={This paper reports flexible thermoelectric generators (TEGs) employing eutectic gallium indium (EGaIn) liquid metal interconnects encased in a novel, high thermal conductivity (HTC) elastomer. These TEGs are part of a broader effort to harvest thermal energy from the body and convert it into electrical energy to power wearable electronics. The flexible TEGs reported in this paper employ the same thermoelectric legs' used in rigid TEGs, thus eliminating the need to develop new materials specifically for flexible TEGs that often sacrifice the so-called figure of merit' for flexibility. Flexible TEGs reported here embed rigid thermoelectric legs' in soft and flexible packaging, using stretchable EGaIn interconnects. The use of liquid metal interconnects provides ultimate stretchability and low electrical resistance between the thermoelectric legs. The liquid metal lines are encased in a new stretchable silicone elastomer doped with both graphene nano-platelets and EGaIn to increase its thermal conductivity. This high thermal conductivity elastomer not only reduces the parasitic thermal resistance of the encapsulation layer but it also serves as a heat spreader, leading to 1.7X improvement in the output power density of TEGs compared to devices fabricated with a conventional elastomer. The device performance is further improved by a thin Cu layer acting as a heat spreader providing an additional 1.3X enhancement in the output power at 1.2 m/s air velocity (typical walking speed). Worn on the wrist, our best devices achieve power levels in excess of 30 μW/cm2 at an air velocity of 1.2 m/s outperforming previously reported flexible TEGs.}, journal={APPLIED ENERGY}, author={Sargolzaeiaval, Yasaman and Ramesh, Viswanath Padmanabhan and Neumann, Taylor V and Misra, Veena and Vashaee, Daryoosh and Dickey, Michael D. and Ozturk, Mehmet C.}, year={2020}, month={Mar} }
 @misc{nozariasbmarz_collins_dsouza_polash_hosseini_hyland_liu_malhotra_ortiz_mohaddes_et al._2020, title={Review of wearable thermoelectric energy harvesting: From body temperature to electronic systems}, volume={258}, ISSN={["1872-9118"]}, url={https://publons.com/publon/30967440/}, DOI={10.1016/j.apenergy.2019.114069}, abstractNote={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. After an overview of wearables market trends, different active and passive methods of body energy harvesting for powering low-consumption electronic devices are introduced, and challenges of device fabrication are discussed. The discussion continues with the primary emphasis on thermoelectric generators for body heat harvesting. The physiological aspects of the human body involved in heat generation are elaborated. System requirements and the influence of different parameters on the performance of thermoelectric generators are studied at the material, device, and system levels. Finally, the advancements in the development of rigid and flexible thermoelectric generators for wearable and textile integration are presented.}, journal={APPLIED ENERGY}, author={Nozariasbmarz, Amin and Collins, Henry and Dsouza, Kelvin and Polash, Mobarak Hossain and Hosseini, Mahshid and Hyland, Melissa and Liu, Jie and Malhotra, Abhishek and Ortiz, Francisco Matos and Mohaddes, Farzad and et al.}, year={2020}, month={Jan} }
 @article{sargolzaeiaval_ramesh_neumann_miles_dickey_ozturk_2019, title={High Thermal Conductivity Silicone Elastomer Doped with Graphene Nanoplatelets and Eutectic GaIn Liquid Metal Alloy}, volume={8}, ISSN={["2162-8769"]}, DOI={10.1149/2.0271906jss}, abstractNote={This paper reports the thermal conductivity and mechanical properties of Sylgard 184 polydimethylsiloxane (PDMS) elastomer loaded with graphene nano-platelets (GnPs) and eutectic Ga-In (EGaIn) liquid metal droplets. We fabricated samples with different GnP and EGaIn concentrations and measured their thermal conductivity using the steady-state absolute technique. The results show that the thermal conductivity of the elastomer can be enhanced up to 5.6X when both GNP and EGaIn are included in the elastomer. Without EGaIn, the enhancement is limited to 4.4X. The results suggest that EGaIn inclusion did not change the viscosity of the uncured material significantly at any GnP loading level. We also observed that addition of just EGaIn to PDMS did not have a significant impact on the material's stiffness while lowering its ultimate tensile strength by a factor of 2X and the maximum elongation at the break point by a factor of 1.6X. On the other hand, it was demonstrated that GnP addition to pure PDMS or EGaIn doped PDMS made the elastomer stiffer and less tear resistant with lower elongation at the break point.}, number={6}, journal={ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY}, author={Sargolzaeiaval, Yasaman and Ramesh, Viswanath Padmanabhan and Neumann, Taylor V. and Miles, Rebecca and Dickey, Michael D. and Ozturk, Mehmet C.}, year={2019}, month={Jun}, pages={P357–P362} }
 @misc{nozariasbmarz_agarwal_coutant_hall_liu_liu_malhotra_norouzzadeh_oeztuerk_ramesh_et al._2017, title={Thermoelectric silicides: A review}, volume={56}, ISSN={["1347-4065"]}, url={http://dx.doi.org/10.7567/jjap.56.05da04}, DOI={10.7567/jjap.56.05da04}, abstractNote={Traditional research on thermoelectric materials focused on improving the figure-of-merit zT to enhance the energy conversion efficiency. With further growth and commercialization of thermoelectric technology beyond niche applications, other factors such as materials availability, toxicity, cost, recyclability, thermal stability, chemical and mechanical properties, and ease of fabrication become important for making viable technologies. Several silicide alloys were identified that have the potential to fulfill these requirements. These materials are of interest due to their abundancy in earth’s crust (e.g., silicon), non-toxicity, and good physical and chemical properties. In this paper, an overview of the silicide thermoelectrics from traditional alloys to advanced material structures is presented. In addition, some of the most effective approaches as well as fundamental physical concepts for designing and developing efficient thermoelectric materials are presented and future perspectives are discussed.}, number={5}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS}, author={Nozariasbmarz, Amin and Agarwal, Aditi and Coutant, Zachary A. and Hall, Michael J. and Liu, Jie and Liu, Runze and Malhotra, Abhishek and Norouzzadeh, Payam and Oeztuerk, Mehmet C. and Ramesh, Viswanath P. and et al.}, year={2017}, month={May} }