Shanhui Fan, Postdoctoral Faculty Sponsor
Radiative-cooling-based nighttime electricity generation with power density exceeding 100 mW/m2.
2022; 25 (8): 104858
The outer space (3 K) represents an important thermodynamic resource. It has been known for decades that at nighttime, a sky-facing thermal emitter radiating strongly within the atmospheric transparency window (8-13mum), can reach below the ambient temperature. In recent studies, thermoelectric generators were used to harness this temperature difference between the emitter and ambient to generate electricity. However, the demonstrated power density has been limited by parasitic thermal losses. Here we show that these parasitic losses can be reduced through thermal engineering. We present a simple model showing the optimum power density can be approached by controlling the relation between the emitter area and the thermal resistance of the thermoelectric generator. We show that the stacking of multiple thermoelectric generators is an effective way to approach this optimum. We experimentally demonstrate a generated electric power density >100 mW/m2, representing>2-fold improvement over the previous results for nighttime radiative cooling.
View details for DOI 10.1016/j.isci.2022.104858
View details for PubMedID 35996585
- Nighttime electric power generation at a density of 50 mW/m(2) via radiative cooling of a photovoltaic cell APPLIED PHYSICS LETTERS 2022; 120 (14)
High-performance photonic transformers for DC voltage conversion.
2021; 12 (1): 4684
Direct current (DC) converters play an essential role in electronic circuits. Conventional high-efficiency DC voltage converters, especially step-up type, rely on switching operation, where energy is periodically stored within and released from inductors and/or capacitors connected in a variety of circuit topologies. Since these energy storage components, especially inductors, are fundamentally difficult to scale down, miniaturization of switching converters proves challenging. Furthermore, the resulting switching currents produce significant electromagnetic noise. To overcome the limitations of switching converters, photonic transformers, where voltage conversion is achieved through light emission and detection processes, have been demonstrated. However, the demonstrated efficiency is significantly below that of the switching converter. Here we perform a detailed balance analysis and show that with a monolithically integrated design that enables efficient photon transport, the photonic transformer can operate with a near-unity conversion efficiency and high voltage conversion ratio. We validate the theory with a transformer constructed with off-the-shelf discrete components. Our experiment showcases near noiseless operation and a voltage conversion ratio that is significantly higher than obtained in previous photonic transformers. Our findings point to the possibility of a high-performance optical solution to miniaturizing DC power converters and improving the electromagnetic compatibility and quality of electrical power.
View details for DOI 10.1038/s41467-021-24955-3
View details for PubMedID 34344884
- Robust and efficient wireless power transfer using a switch-mode implementation of a nonlinear parity-time symmetric circuit NATURE ELECTRONICS 2020
Dynamics for encircling an exceptional point in a nonlinear non-Hermitian system
View details for Web of Science ID 000612090002171
- Efficient and Robust Wireless Power Transfer based on Parity-Time Symmetry AMER INST PHYSICS. 2020
Dynamics for encircling an exceptions point in a nonlinear non-Hermitian system
2019; 44 (3): 638–41
We study the dynamics near an exceptional point in a nonlinear non-Hermitian system consisting of a pair of resonators. One of the resonators has a linear loss, and the other resonator has a saturable gain. We show that the system dynamics exhibit chiral characteristics. And moreover, unique to the nonlinear system, such dynamics allow one to adiabatically switch between bistable states at the same system parameter. Such bistable switching is potentially interesting in optical memory based on coupled laser systems.
View details for DOI 10.1364/OL.44.000638
View details for Web of Science ID 000457292400044
View details for PubMedID 30702698
Robust wireless power transfer using a nonlinear parity-time-symmetric circuit
2017; 546 (7658): 387-+
Considerable progress in wireless power transfer has been made in the realm of non-radiative transfer, which employs magnetic-field coupling in the near field. A combination of circuit resonance and impedance transformation is often used to help to achieve efficient transfer of power over a predetermined distance of about the size of the resonators. The development of non-radiative wireless power transfer has paved the way towards real-world applications such as wireless powering of implantable medical devices and wireless charging of stationary electric vehicles. However, it remains a fundamental challenge to create a wireless power transfer system in which the transfer efficiency is robust against the variation of operating conditions. Here we propose theoretically and demonstrate experimentally that a parity-time-symmetric circuit incorporating a nonlinear gain saturation element provides robust wireless power transfer. Our results show that the transfer efficiency remains near unity over a distance variation of approximately one metre, without the need for any tuning. This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied. The use of a nonlinear parity-time-symmetric circuit should enable robust wireless power transfer to moving devices or vehicles.
View details for PubMedID 28617463