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Register a new userSpectral self-adaptive absorber/emitter for harvesting energy from the sun and outer space
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The sun (~6000 K) and outer space (~3 K) are the original heat source and sink for human beings on Earth. The energy applications of absorbing solar irradiation and harvesting the coldness of outer space for energy utilization have attracted considerable interest from researchers. However, combining these two functions in a static device for continuous energy harvesting is unachievable due to the intrinsic infrared spectral conflict. In this study, we developed spectral self-adaptive absorber/emitter (SSA/E) for daytime photothermal and nighttime radiative sky cooling modes depending on the phase transition of the vanadium dioxide coated layer. A 24-hour day-night test showed that the fabricated SSA/E has continuous energy harvesting ability and improved overall energy utilization performance, thus showing remarkable potential in future energy applications.
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While solar power systems have offered a wide variety of electricity generation approaches including photovoltaics, solar thermal power systems, and solar thermoelectric generators, the ability of generating electricity at both the daytime and nighttime with no necessity of energy storage still remains challenging. Here, we propose and verify a strategy of harvesting solar energy by solar heating during the daytime and harnessing the coldness of the outer space through radiative cooling to produce electricity at night using a commercial thermoelectric module. It enables electricity generation for 24 hours a day. We experimentally demonstrate a peak power density of 37 mW/m2 at night and a peak value of 723 mW/m2 during the daytime. A theoretical model that accurately predicts the performance of the device is developed and validated. The feature of 24-hour electricity generation shows great potential energy applications of off-grid and battery-free lighting and sensing.
Energy harvesting from sun and outer space using thermoradiative devices (TRD), despite being promising renewable energy sources, are limited only to daytime and nighttime period, respectively. A system with 24-hour continuous energy generation remains an open question thus far. Here, we propose a TRD-based power generator that harvests solar energy via concentrated solar irradiation during daytime and via thermal infrared emission towards the outer space at nighttime, thus achieving the much sought-after 24-hour electrical power generation. We develop a rigorous thermodynamical model to investigate the performance characteristics, parametric optimum design, and the role of various energy loss mechanisms. Our model predicts that the TRD-based system yields a peak efficiency of 12.6% at daytime and a maximum power density of 10.8 Wm$^{-2}$ at nighttime, thus significantly outperforming the state-of-art record-setting thermoelectric generator. These findings reveal the potential of TRD towards 24-hour electricity generation and future renewable energy technology.
Optical interference is used to enhance light-matter interaction and harvest broadband light in ultrathin semiconductor absorber films on specular back-reflectors. However, the high-temperature processing in oxygen atmosphere required for oxide absorbers often degrades metallic back-reflectors and their specular reflectance. In order to overcome this problem, we present a newly developed film flip and transfer process that allows for high-temperature processing without degradation of the metallic back-reflector and without the need of passivation interlayers. The film flip and transfer process improves the performance of photoanodes for photoelectrochemical water splitting comprising ultrathin (< 20 nm) hematite (Fe2O3) films on silver-gold alloy (90 at% Ag-10 at% Au) back-reflectors. We obtain specular back-reflectors with high reflectance below hematite films, which is necessary for maximizing the productive light absorption in the hematite film and minimizing non-productive absorption in the back-reflector. Furthermore, the film flip and transfer process opens up a new route to attach thin film stacks onto a wide range of substrates including flexible or temperature sensitive materials.
This paper analyzes the communication between two energy harvesting wireless sensor nodes. The nodes use automatic repeat request and forward error correction mechanism for the error control. The random nature of available energy and arrivals of harvested energy may induce interruption to the signal sampling and decoding operations. We propose a selective sampling scheme where the length of the transmitted packet to be sampled depends on the available energy at the receiver. The receiver performs the decoding when complete samples of the packet are available. The selective sampling information bits are piggybacked on the automatic repeat request messages for the transmitter use. This way, the receiver node manages more efficiently its energy use. Besides, we present the partially observable Markov decision process formulation, which minimizes the long-term average pairwise error probability and optimizes the transmit power. Optimal and suboptimal power assignment strategies are introduced for retransmissions, which are adapted to the selective sampling and channel state information. With finite battery size and fixed power assignment policy, an analytical expression for the average packet drop probability is derived. Numerical simulations show the performance gain of the proposed scheme with power assignment strategy over the conventional scheme.
To explore the capabilities of metallic spintronic thin-film stacks as a source of intense and broadband terahertz electromagnetic fields, we excite a W/CoFeB/Pt trilayer on a large-area glass substrate (diameter of 7.5 cm) by a femtosecond laser pulse (energy 5.5 mJ, duration 40 fs, wavelength 800 nm). After focusing, the emitted terahertz pulse is measured to have a duration of 230 fs, a peak field of 300 kV cm$^{-1}$ and an energy of 5 nJ. In particular, the waveform exhibits a gapless spectrum extending from 1 to 10 THz at 10% of amplitude maximum, thereby facilitating nonlinear control over matter in this difficult-to-reach frequency range and on the sub-picosecond time scale.
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