Flexible Thermoelectric Generator Based on Polycrystalline SiGe Thin Films

Flexible and reliable thermoelectric generators (TEGs) will be essential for future energy harvesting sensors. In this study, we synthesized p- and n-type SiGe layers on a high heat-resistant polyimide film using metal-induced layer exchange (LE) and demonstrated TEG operation. Despite the low process temperature (<500 °C), the polycrystalline SiGe layers showed high power factors of 560 µW m−1 K−2 for p-type Si0.4Ge0.6 and 390 µW m−1 K−2 for n-type Si0.85Ge0.15, owing to self-organized doping in LE. Furthermore, the power factors indicated stable behavior with changing measurement temperature, an advantage of SiGe as an inorganic material. An in-plane π-type TEG based on these SiGe layers showed an output power of 0.45 µW cm−2 at near room temperature for a 30 K temperature gradient. This achievement will enable the development of environmentally friendly and highly reliable flexible TEGs for operating micro-energy devices in the future Internet of Things.

Generalization of Kirchhoff’s Law: The inherent relations between quantum efficiency and emissivity

Planck’s law of thermal radiation depends on the temperature, \(T\), and the emissivity, \(\epsilon\), which is the coupling of heat to radiation depending on both phonon-electron nonradiative-interactions and electron-photon radiative-interactions. In contrast, absorptivity, \(\alpha\), only depends on the electron-photon radiative-interactions. At thermodynamic equilibrium, nonradiative-interactions are balanced, resulting in Kirchhoff’s law of thermal radiation, \(\epsilon =\alpha\). For non-equilibrium, Quantum efficiency (QE) describes the statistics of photon emission, which like emissivity depends on both radiative and nonradiative interactions. Past generalized Planck’s equation extends Kirchhoff’s law out of equilibrium by scaling the emissivity with the pump-dependent chemical-potential \(\mu\), obscuring the relations between the body properties. Here we theoretically and experimentally demonstrate a prime equation relating these properties in the form of \(\epsilon =\alpha \left(1-QE\right)\). At equilibrium, these relations are reduced to Kirchhoff’s law. Our work lays out the evolution of non-thermal emission with temperature, which is critical for the development of lighting and energy devices.

Trends on the Development of Hybrid Supercapacitor Electrodes from the Combination of Graphene and Polyaniline

The high demand for efficient energy devices leads to the rapid development of energy storage systems with excellent electrochemical properties, such as long life cycles, high cycling stability, and high power density. SC is postulated as a potential candidate to fulfill this demand. The combination of graphene and polyaniline can create SC electrodes with excellent electrical conductivity, high specific surface area, and high capacitance. The graphene/polyaniline hybrid electrodes represent an attractive means to overcome the major drawbacks of graphene or polyaniline non-hybrid (single) electrode materials. In this review article, the trend in the development of various graphene/polyaniline hybrid electrodes is summarized, which includes the zero-dimension graphene-quantum-dots/polyaniline hybrid, one-dimension graphene/polyaniline hybrid, two-dimension graphene/polyaniline hybrid, and three-dimension hydrogel-shaped graphene/polyaniline hybrid. Several strategies and approaches to enhance the capacitance value and cycling stability of graphene/polyaniline hybrid electrodes are discussed in this review article, such as the addition of transition metal oxides and metal-organic frameworks, and modification of graphene into functionalized-graphene. The performance of the electrodes prepared from the combination of graphene with other conducting polymers (i.e., polypyrrole, polythiophene, and polythiophene-derivatives) is also discussed.

A Review of SPH Techniques for Hydrodynamic Simulations of Ocean Energy Devices

This article is dedicated to providing a detailed review concerning the SPH-based hydrodynamic simulations for ocean energy devices (OEDs). Attention is particularly focused on three topics that are tightly related to the concerning field, covering (1) SPH-based numerical fluid tanks, (2) multi-physics SPH techniques towards simulating OEDs, and finally (3) computational efficiency and capacity. In addition, the striking challenges of the SPH method with respect to simulating OEDs are elaborated, and the future prospects of the SPH method for the concerning topics are also provided.

What’s in My Toolkit? A Review of Technologies for Assessing Changes in Habitats Caused by Marine Energy Development

Marine energy devices are installed in highly dynamic environments and have the potential to affect the benthic and pelagic habitats around them. Regulatory bodies often require baseline characterization and/or post-installation monitoring to determine whether changes in these habitats are being observed. However, a great diversity of technologies is available for surveying and sampling marine habitats, and selecting the most suitable instrument to identify and measure changes in habitats at marine energy sites can become a daunting task. We conducted a thorough review of journal articles, survey reports, and grey literature to extract information about the technologies used, the data collection and processing methods, and the performance and effectiveness of these instruments. We examined documents related to marine energy development, offshore wind farms, oil and gas offshore sites, and other marine industries around the world over the last 20 years. A total of 120 different technologies were identified across six main habitat categories: seafloor, sediment, infauna, epifauna, pelagic, and biofouling. The technologies were organized into 12 broad technology classes: acoustic, corer, dredge, grab, hook and line, net and trawl, plate, remote sensing, scrape samples, trap, visual, and others. Visual was the most common and the most diverse technology class, with applications across all six habitat categories. Technologies and sampling methods that are designed for working efficiently in energetic environments have greater success at marine energy sites. In addition, sampling designs and statistical analyses should be carefully thought through to identify differences in faunal assemblages and spatiotemporal changes in habitats.

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

Active surface morphing is a nonintrusive flow control technique that can delay separation in laminar and turbulent boundary layers. Most of the experimental studies of such control strategy have been carried out in wind tunnels at low Reynolds numbers with costly actuators. In contrast, the implementation of such a control strategy at low cost for an underwater environment remains vastly unexplored. This paper explores active surface morphing at low cost and at low Reynolds for underwater applications. We do this with a 3D printed foil submerged in a water tunnel. The suction surface of the foil is covered with a magnetoelastic membrane. The membrane is actuated via two electromagnets that are positioned inside of the foil. Three actuation frequencies (slow, intermediate, fast) are tested and the deformation of the membrane is measured with an optosensor. We show that lift increases by 1%, whilst drag decreases by 6% at a Strouhal number of 0.3, i.e., at the fast actuation case. We demonstrate that surface actuation is applicable to the marine environment through an off the shelf approach, and that this method is more economical than existing active surface morphing technologies. Since the actuation mechanism is not energy intensive, it is envisioned that it could be applied to marine energy devices, boat appendages, and autonomous underwater vehicles.

Overview on Oscillating Water Column Devices

Oscillating-water-column (OWC) converters, of fixed structure or floating, are an important class of wave energy devices. A large part of wave energy converter prototypes deployed so far into the sea are of OWC type. The paper presents a review of recent advances in OWC technology, including sea-tested prototypes and plants, new concepts, air turbines, model testing techniques and control.