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Showing papers by "Daryoosh Vashaee published in 2016"


Journal ArticleDOI
TL;DR: In this paper, the authors present a computationally efficient, quasi-three-dimensional TEG model and use this model to explore the design criteria for current state-of-the-art rigid TEG modules as well as prospective flexible modules for body wearable applications.
Abstract: Body wearable sensors and electronics for health and environment monitoring are becoming increasingly popular as their functionality increases. Thermoelectric generators (TEGs) are of interest to make these wearables self-powered by making them rely entirely on the heat harvested from the human body. The challenge with using thermoelectrics on the human body is the large thermal resistances experienced at the skin/TEG and TEG/ambient interfaces. These parasitics can be potentially so large that they can dominate the device performance. Therefore, it is critical to have accurate models to predict the device performance considering material properties, module design and parasitics. In this paper, we present a computationally efficient, quasi three-dimensional TEG model and use this model to explore the design criteria for current state-of-the-art rigid TEG modules as well as prospective flexible modules for body wearable applications. We show the impact of the properties of the thermoelectric material, module design and dimensions, heat spreaders, filler material, heat sink and skin contact resistance on device performance. We also identify the significance of material thermal conductivity over the Seebeck coefficient and electrical resistivity in improving the output power for wearable applications. For flexible TEGs, we identify the thermal conductivity of the filler material as one of the critical parameters that need to be taken into consideration for optimal performance. Finally, the model was used to design a custom TEG with improved material properties and device design. The measurements indicate a nearly 3× improvement in power output over a commercial TEG with similar area as successfully predicted by the calculations.

286 citations


Journal ArticleDOI
TL;DR: In this paper, an optimum TEG design was developed and experiments were conducted both on a temperature controlled hot plate and on different body locations including the wrist, upper arm, and chest.

251 citations


Journal ArticleDOI
TL;DR: It is concluded that, although all of these composites possess in-vitro biocompatibility, adding hydroxyapatite and magnetite to the chitosan matrix can noticeably enhance the mechanical properties of the pure chitOSan.

68 citations


Journal ArticleDOI
TL;DR: Particular emphasis is given to the concepts based on metal-semiconductor superlattices, graded materials, non-equilibrium thermoelectric devices, Thomson coolers, and photon assisted Peltier coolers as promising methods for efficient solid-state cooling.
Abstract: The recent developments in nanoscale solid-state cooling are reviewed. This includes both theoretical and experimental studies of different physical concepts, as well as nanostructured material design and device configurations. We primarily focus on thermoelectric, thermionic and thermo-magnetic coolers. Particular emphasis is given to the concepts based on metal-semiconductor superlattices, graded materials, non-equilibrium thermoelectric devices, Thomson coolers, and photon assisted Peltier coolers as promising methods for efficient solid-state cooling. Thermomagnetic effects such as magneto-Peltier and Nernst-Ettingshausen cooling are briefly described and recent advances and future trends in these areas are reviewed. The ongoing progress in solid-state cooling concepts such as spin-calorimetrics, electrocalorics, non-equilibrium/nonlinear Peltier devices, superconducting junctions and two-dimensional materials are also elucidated and practical achievements are reviewed. We explain the thermoreflectance thermal imaging microscopy and the transient Harman method as two unique techniques developed for characterization of thermoelectric microrefrigerators. The future prospects for solid-state cooling are briefly summarized.

67 citations


Journal ArticleDOI
TL;DR: It is shown that a degenerate multivalley bandst structure cannot be a general design rule for ZT enhancement and a detailed transport study is required to engineer the optimum bandstructure.
Abstract: The theory of valleytronics as a material design tool for engineering both thermal and electrical transport properties is presented. It is shown that the interplay among the valleytronics parameters such as the degeneracy of the band, intervalley transitions, effective mass, scattering exponent, and the Fermi energy may deteriorate or ameliorate any or all of the main thermoelectric properties. A flowchart classifying the different paths through which the valleytronics can influence the thermoelectric figure-of-merit ZT is derived and discussed in detail. To exemplify the application of the flowchart, valleytronics in four different semiconductors, Mg2Si, Si0.8Ge0.2, AlxGa1−xAs and clathrate Si46-VIII were studied, which showed different trends. Therefore, a degenerate multivalley bandstructure, which is typically anticipated for a good thermoelectric material, cannot be a general design rule for ZT enhancement and a detailed transport study is required to engineer the optimum bandstructure.

41 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the thermal properties of nanostructured FeSi2, Mg2Si, and SiGe and found that the addition of silicide nanoinclusions to SiGe alloy maintained or increased the power factor while further reducing the thermal conductivity.
Abstract: Thermoelectric properties of nanostructured FeSi2, Mg2Si, and SiGe are compared with their nanocomposites of SiGe–Mg2Si and SiGe–FeSi2. It was found that the addition of silicide nanoinclusions to SiGe alloy maintained or increased the power factor while further reduced the thermal conductivity compared to the nanostructured single-phase SiGe alloy. This resulted in ZT enhancement of Si0.88Ge0.12–FeSi2 by ∼30% over the broad temperature range of 500-950 °C compared to the conventional Si0.80Ge0.20 alloy. The Si0.88Ge0.12–Mg2Si nanocomposite showed constantly increasing ZT versus temperature up to 950 °C (highest measured temperature) reaching ZT ∼ 1.3. These results confirm the concept of silicide nanoparticle-in-SiGe-alloy proposed earlier by Mingo et al. [Nano Lett. 9, 711–715 (2009)].

34 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented the experimental realization of an n-type silicon germanium alloy with an embedded metallic α-phase iron silicide (FeSi2), and the dimensionless thermoelectric figure of merit (ZT) of the nanocomposite material was higher than the peak ZT of the conventional single phase Si0.80Ge0.20 over a broad temperature range (650-1000 °C).
Abstract: Hypothetical efficient thermoelectrics based on nanoparticles in alloys of silicide nanocomposites were predicted by Mingo et al. This investigation presents the experimental realization of an n-type silicon germanium alloy with an embedded metallic α-phase iron silicide (FeSi2). The dimensionless thermoelectric figure of merit (ZT) of the nanocomposite material was higher than the peak ZT of the conventional single phase Si0.80Ge0.20 over a broad temperature range (650–1000 °C) while consuming smaller amounts of germanium. The addition of 2.5% silver to the nanocomposite, which acted as a sintering aid, reduced the sintering temperature and resulted in smaller thermal conductivity. The optimum material composition of (Si0.88Ge0.12)0.925–(FeSi2)0.05–Ag0.025 was found after investigation of a large number of nanocomposite materials. The combination of X-ray diffraction, energy-dispersive X-ray spectroscopy, and transmission electron microscopy analysis confirmed a uniform distribution of α-FeSi2 nanoparticles in the microstructure.

29 citations


Journal ArticleDOI
TL;DR: In this paper, water-soluble CdS QDs are synthesized through growth in a polyvinyl alcohol matrix using a chemical precipitation method, and the prepared QDs were then characterized with X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) analyses.
Abstract: Aflatoxins form a class of potent carcinogens that contaminate a wide range of food products and can be fatal to humans and livestock. We have designed cysteamine-capped CdS quantum dots (QDs) to serve as aflatoxin photodetectors for use in agricultural industries. Water-soluble CdS QDs are synthesized through growth in a poly(vinyl alcohol) matrix using a chemical precipitation method. The prepared QDs are then characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) analyses. The obtained results revealed that these CdS QDs have a 1- to 2-nm crystalline size, hexagonal wurtzite structure, and spherical morphology with a diameter less than 10 nm. Photoluminescence spectroscopy (PL) is performed to study the CdS QDs interactions with a standard solution of aflatoxins (B1, B2, G1, and G2 in a ratio of 5:1:5:1) in order to determine their effectiveness as aflatoxin detectors. A green emission peak is observed at 508 nm, with an intensity enhancement positively correlated with total aflatoxin concentration. The lower limit of detection for total aflatoxin concentration is found to be 0.05 ppb, well below international contamination allowances for food products. PL variations with aflatoxin concentration are best described by a Langmuir-type equation in the concentration range of this study (2.4–48 ppb).

26 citations


Journal ArticleDOI
TL;DR: In this article, water-soluble thioglycolic acid-capped ZnS quantum dots were synthesized by chemical precipitation method using x-ray diffraction and transmission electron microscopy.
Abstract: In this research, water-soluble thioglycolic acid-capped ZnS quantum dots (QDs) are synthesized by the chemical precipitation method. The prepared QDs are characterized using x-ray diffraction and transmission electron microscopy. Results revealed that ZnS QDs have a 2.73 nm crystallite size, cubic zinc blende structure, and spherical morphology with a diameter less than 10 nm. Photoluminescence (PL) spectroscopy is performed to determine the presence of low concentrations of starch. Four emission peaks are observed at 348 nm, 387 nm, 422 nm, and 486 nm and their intensities are quenched by increasing concentration of starch. PL intensity variations in the studied concentrations range (0–100 ppm) are best described by a Michaelis–Menten model. The Michaelis constant (K m) for immobilized α-amylase in this system is about 101.07 ppm. This implies a great tendency for the enzyme to hydrolyze the starch as substrate. Finally, the limit of detection is found to be about 6.64 ppm.

23 citations


Journal ArticleDOI
TL;DR: In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method and the characteristics of prepared quantum dots were determined using X-Ray Diffraction and Transmission Electron Microscopy.
Abstract: In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method. The characteristics of prepared quantum dots were determined using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The obtained results revealed that CdS QDs have 5.60 nm crystallite size, hexagonal wurtzite structure and spherical morphology with less than 10 nm diameter. The photoluminescence (PL) spectroscopy was performed in order to study the effect of the presence of starch solutions. Blue emission peaks were positioned at 488 nm and its intensity quenched by increasing the concentration of starch solutions. The result of PL quenches in range of studied concentrations (0-100 ppm) was best described by Michaelis-Menten model. The amount of Michaelis constant (Km) for immobilized α-amylase in this system was about 68.08 ppm which showed a great tendency of enzyme to hydrolyze the starch as substrate. Finally, the limit of detection (LOD) was found to be about 2.24 ppm.

21 citations


Journal ArticleDOI
TL;DR: Results show that the coated scaffold can keep its mechanical integrity three times longer than the uncoated one, and cell viability and growth are acceptable on the Mg scaffold/PCL–BaG/Gel– BaG.
Abstract: Magnesium (Mg), as a biodegradable metal, has recently been considered to be used in hard tissue engineering scaffold design. However, the fast release of hydrogen gas during exposure of Mg to corroding biofluids significantly limits the cytocompatibility of the scaffolds. To overcome this key drawback, in this study, the surfaces of Mg scaffolds are modified by polymer/hydrogel/ceramic layers consisting of polycaprolactone (PCL), gelatin (Gel) and bioactive glass (BaG). A detailed study has been performed on the in vitro mechanical properties of the Mg scaffold coated by PCL–BaG/Gel–BaG compared with the uncoated one. Our results show that the coated scaffold can keep its mechanical integrity three times longer than the uncoated one. To assess cytocompatibility, human osteoblast Saos-2 cells were cultured on the surface of the scaffolds. Cell attachment and growth were evaluated by scanning electron microscopy and cell viability assays, respectively. While no cell could attach on the uncoated scaffold, cell viability and growth are acceptable on the Mg scaffold/PCL–BaG/Gel–BaG.

Journal ArticleDOI
TL;DR: In this article, the sol-gel reaction of magnesium chloride and silicon tetrachloride, directed at the Mg2SiO4 stoichiometry, using dry ethanol and glacial acetic acid as the solvent and chelating agent, respectively, was investigated.

Book ChapterDOI
01 Jan 2016
TL;DR: This chapter reviews different nanobiomaterials employed in periodontal tissue engineering for the effective regeneration of lost tissues and discusses their benefits and drawbacks.
Abstract: Periodontitis is an inflammatory disease of the gums which spreads and affects the supporting tooth structures possibly leading to the loosening and loss of the tooth. Periodontal tissue engineering is considered a relatively new technique for the stimulation of the periodontal tissue formation using the basics of regenerative medicine. In this method, biodegradable porous scaffolds are employed as a temporary substitution of the injured or lost tissues to facilitate the regeneration process. Scaffolds are usually made of natural or synthetic polymers and ceramics doped with various nanobiomaterials for an intended functionalization. The addition of nanoparticles into the scaffold structure not only enhances the biomineralization potential of the composite scaffolds, but also improves their mechanical properties. Nanosized ceramic particles are of special importance as they mimic the mineral crystal structure of the natural tissues. They have been demonstrated to induce a considerable enhancement in the protein absorption and the cell adhesion compared to their micro-sized counterparts. This chapter reviews different nanobiomaterials employed in periodontal tissue engineering for the effective regeneration of lost tissues and discuss their benefits and drawbacks.

Journal ArticleDOI
TL;DR: The microstructure and in vitro corrosion behavior of a new class of medical-grade stainless steels were correlated with adult human mesenchymal stem cell viability and it was found that a better cell viability on the surface of the less corrosion-resistant sample was unexpectedly found.

Patent
30 Nov 2016
TL;DR: In this paper, the authors provided a method of creating amorphous materials using microwave energy in the form of standing waves, which can be used to construct high efficiency bulk thermoelectric structures as well as thin and thick.
Abstract: According to an embodiment, there is provided a method of creating amorphous and amorphous-crystalline materials using microwave energy in the form of standing waves. The relatively quick processing time of the method allows investigating and creating a large number of material structures with various dimensions. An embodiment utilizes a scalable technique to produce high efficiency bulk thermoelectric structures as well as thin and thick.