No abstract

No abstract

This paper aims to systematically investigate the effect of gas bubbles formation on the performance of a horizontal photoelectrode exposed to normally incident light during photoelectrochemical water splitting. The presence...

International audienceThis study aims to quantify systematically the effect of non-absorbing cap-shaped droplets condensed on the backside of transparent windows on their directional-hemispherical transmittance and reflectance. Condensed water droplets have been blamed to reduce light transfer through windows in greenhouses, solar desalination plants, and photobioreactors. Here, the directional-hemispherical transmittance was predicted by Monte Carlo ray-tracing method. For the first time, both monodisperse and polydisperse droplets were considered, with contact angle between 0 and 180°, arranged either in an ordered hexagonal pattern or randomly distributed on the window backside with projected surface area coverage between 0 and 90%. The directional-hemispherical transmittance was found to be independent of the size and spatial distributions of the droplets. Instead, it depended on (i) the incident angle, (ii) the optical properties of the window and droplets, and on (iii) the droplet contact angle and (iv) projected surface area coverage. In fact, the directional-hemispherical transmittance decreased with increasing incident angle. Four optical regimes were identified in the normal-hemispherical transmittance. It was nearly constant for droplet contact angles either smaller than the critical angle θ cr (predicted by Snell's law) for total internal reflection at the droplet/air interface or larger than 180°-θ cr. However, between these critical contact angles, the normal-hemispherical transmittance decreased rapidly to reach a minimum at 90° and increased rapidly with increasing contact angles up to 180°-θ cr. This was attributed to total internal reflection at the droplet/air interface which led to increasing reflectance. In addition, the normal -hemispherical transmittance increased slightly with increasing projected surface area coverage for contact angle was smaller than θ cr. However, it decreased monotonously with increasing droplet projected surface area coverage for contact angle larger than θ cr. These results can be used to select the material or surface coating with advantageous surface properties for applications when dropwise condensation may otherwise have a negative effect on light transmittance

In this Letter, we propose a symmetric metasurface composed of single-sized amorphous-silicon (a-Si) cuboids tetramer clusters that support two resonances with opposite symmetry, i.e., in-plane magnetic dipole (MD) resonance and in-plane toroidal dipole (TD) resonance governed by symmetry-protected bound states in the continuum (SP-BIC) in the near-infrared region. Since the cuboids tetramer of the metasurface retains C 4 v symmetry and mirror symmetry, both resonances are polarization independent. Multipolar decomposition of scattering power and electromagnetic distribution are performed to clarify the physical mechanism of dual quasi-BIC resonances. The effects of geometric parameters on both high-quality (Q) resonances are also studied. Additionally, the sensing performance of the designed metasurface is evaluated. The effects of the material’s loss on both resonances are also studied. Our work provides a new route to designing dual mode polarization- independent resonators without multi-sized complex structures that may facilitate designing high-performance sensing applications.

We propose a mechanism of active near-field heat transfer modulation relying on externally tunable metamaterials. A large modulation effect is observed and can be explained by the coupling of surface modes, which is dramatically varied in the presence of controllable magnetoelectric coupling in metamaterials. We finally discuss how a practical picosecond-scale thermal modulator can be made. This modulator allows manipulating nanoscale heat flux in an ultrafast and noncontact (by optical means) manner.Radiative heat transfer between surfaces in close proximity has attracted much attention since it has been predicted that the heat flux can break the Planck's blackbody radiation law. 1 This effect, due to the tunneling of evanescent waves, is pronounced only in the near-field, i.e., at separation of surfaces smaller than the characteristic thermal wavelength. Particularly, enhancement that is several orders of magnitude over blackbody limit occurs if the heat transfer involves thermally excited surface modes, 2-5 such as surface plasmon and phonon polaritons.Considerable theoretical effort has been devoted to understand the detailed mechanism of near-field heat transfer in a number of geometries 6-12 and materials. [13][14][15][16][17][18][19] Near-field thermal effect has been verified in recent experiments, 20-23 and holds promise for applications such as imaging, 24,25 energy conversion, 26-28 and noncontact localized heating. 29 Despite these progress, relatively little attention has been focused on how to actively control this transfer. This has deep implications for applications in photonic thermal circuits and thermal management in nanoelectronics. Since near-field heat flux is intimately related to optical properties of materials, one possibility is to modulate heat flow by using materials whose properties can be tuned by external stimulus. To this end, several schemes have been put forward by employing phase-change materials, 30-32 graphene, 33,34 anisotropic structures, 35 as well as temperature dependent materials. 36,37 However, limited by properties of the applied materials, existing schemes involve only tuning the dielectric response. The potential to control heat flux with tunable magnetic and magnetoelectric coupling response has not been explored yet. In this paper, we present an alternative scheme for controlling near-field heat flux. It shows that, by using the size and sign of magnetoelectric coupling in metamaterials as controllable parameters,

No abstract

No abstract