Project description:Shared-aperture technology for multifunctional planar systems, performing several simultaneous tasks, was first introduced in the field of radar antennas. In photonics, effective control of the electromagnetic response can be achieved by a geometric-phase mechanism implemented within a metasurface, enabling spin-controlled phase modulation. The synthesis of the shared-aperture and geometric-phase concepts facilitates the generation of multifunctional metasurfaces. Here shared-aperture geometric-phase metasurfaces were realized via the interleaving of sparse antenna sub-arrays, forming Si-based devices consisting of multiplexed geometric-phase profiles. We study the performance limitations of interleaved nanoantenna arrays by means of a Wigner phase-space distribution to establish the ultimate information capacity of a metasurface-based photonic system. Within these limitations, we present multifunctional spin-dependent dielectric metasurfaces, and demonstrate multiple-beam technology for optical rotation sensing. We also demonstrate the possibility of achieving complete real-time control and measurement of the fundamental, intrinsic properties of light, including frequency, polarization and orbital angular momentum.
Project description:In this study, a hybrid energy harvesting system based on a conventional solar cell combined with 3D-printed metasurface units is studied. Millimeter-scale metasurface units were fabricated via the stereolithography technique, and then they were covered with conductive silver paint, in order to achieve high electric conductivity. The performance of single, as well as two-unit metasurface harvesters, was thoroughly investigated. It was found that both of them produced voltage, which peaks at their resonance frequency, demonstrating efficient energy harvesting behavior in the microwave regime. Then, the metasurface units were connected with a commercially available photovoltaic panel and the performance of the hybrid system was examined under different environmental conditions, modifying the light intensity (i.e., light, dark and shadow). It was shown that the proposed hybrid harvesting system produces a sizable voltage output, which persists, even in the case when one of the components does not contribute. Furthermore, the performance of the hybrid harvester is found to be adequate enough, although optimization of the harvesting circuit is required in order to achieve high efficiency levels. All in all, the presented experimental evidence clearly indicates the realization of a rather promising hybrid energy harvesting system, exploiting two distinct ambient energy sources, namely light and microwaves.
Project description:We have investigated the spatiotemporal chaotic dynamics of unjamming and jamming of particles in a model experiment - a rotating drum partially filled with bidisperse disks to create avalanches. The magnitudes of the first Lyapunov vector δu(t) and velocity v(t) of particles are directly measured for the first time to yield insights into their spatial correlation Cδu,v, which is on statistical average slightly larger near the unjamming than the value near the jamming transition. These results are consistent with the recent work of Banigan et al (Nature Phys. 2013), and it is for the first time to validate their theoretical models in a real scenario. v(t) shows rich dynamics: it grows exponentially for unstable particles and keeps increasing despite stochastic interactions; after the maximum, it decays with large fluctuations. Hence the spatiotemporal chaotic dynamics of avalanche particles are entangled, causing temporal correlations of macroscopic quantities of the system. We propose a simple model for these observations.
Project description:Polarimetry plays an indispensable role in modern optics. Nevertheless, the current strategies generally suffer from bulky system volume or spatial multiplexing scheme, resulting in limited performances when dealing with inhomogeneous polarizations. Here, we propose a non-interleaved, interferometric method to analyze the polarizations based on a tri-channel chiral metasurface. A deep convolutional neural network is also incorporated to enable fast, robust and accurate polarimetry. Spatially uniform and nonuniform polarizations are both measured through the metasurface experimentally. Distinction between two semblable glasses is also demonstrated. Our strategy features the merits of compactness and high spatial resolution, and would inspire more intriguing design for detecting and sensing.
Project description:Facilitated by ultrafast dynamic modulations, spatiotemporal metasurfaces have been identified as a pivotal platform for manipulating electromagnetic waves and creating exotic physical phenomena, such as dispersion cancellation, Lorentz reciprocity breakage, and Doppler illusions. Motivated by emerging information-oriented technologies, we hereby probe the information transition mechanisms induced by spatiotemporal variations and present a general model to characterize the information processing capabilities of the spatiotemporal metasurface. Group theory and abstract number theory are adopted through this investigation, by which the group extension and independent controls of multiple harmonics are proposed and demonstrated as two major tools for information transitions from the spatiotemporal domain to the spectra-wavevector domain. By incorporating Shannon's entropy theory into the proposed model, we further discover the corresponding information transition efficiencies and the upper bound of the channel capacity of the spatiotemporal metasurface. The results of harmonic information transitions show great potential in achieving high-capacity versatile information processing systems with spatiotemporal metasurfaces.
Project description:The intersection of nanotechnology and interfacial science has opened up new avenues for understanding complex phenomena occurring at liquid interfaces. The assembly of nanoparticles at liquid/liquid interfaces provides valuable insights into their interactions with fluid interfaces, essential for various applications, including drug delivery. In this study, we focus on the shape and concentration effects of nanoscale particles on interfacial affinity. Using pendant drop tensiometry, we monitor the real-time interfacial tension between an oil droplet and an aqueous solution containing nanoparticles. We measure two different types of nanoparticles: spherical gold nanoparticles (AuNPs) and anisotropic gold nanorods (AuNRs), each functionalized with surfactants to facilitate interaction at the interface. We observe that the interface equilibrium behaviour is mediated by kinetic processes, namely, diffusion, adsorption and rearrangement of particles. For anisotropic AuNRs, we observe shape-induced jamming of particles at the interface, as evidenced by their slower diffusivity and invariant rearrangement rate. In contrast, the adsorption of spherical AuNPs is dynamic and requires more time to reach equilibrium, indicating weaker interface affinity. By detailed analysis of the interfacial tension data and interaction energy calculations, we show that the anisotropic particle shape achieves stable equilibrium inter-particle separation compared to the isotropic particles. Our findings demonstrate that anisotropic particles are a better design choice for drug delivery applications as they provide better affinity for fluid interface attachment, a crucial requirement for efficient drug transport across cell membranes. Additionally, anisotropic shapes can stabilize interfaces at low particle concentrations compared to isotropic particles, thus minimizing side effects associated with biocompatibility and toxicity.
Project description:Representing tangential motion between objects and the skin using tactile displays enables humans to manipulate virtual objects and recognize their surface properties. To design effective tactile stimuli that accurately represent motion, it is important to understand how humans perceive tactile motion based on spatiotemporal features, an area that remains relatively unexplored. This study elucidates the spatiotemporal features that influence the perceived speed of tactile motion represented by a tactile display with discrete stimulation points. The findings show that the average spatial spacing between stimulation points affects the perceived speed, even though the average spatial spacing does not vary with the speed itself, but rather varies with the stimulation point layout of the tactile display. No significant effects from other features were observed on the perceived speed. The results suggest that perceived speed can be controlled by considering the average spatial spacing during tactile stimulus design.
Project description:This study proposes a novel skinny button with multimodal audio and haptic feedback to enhance the touch user interface of electronic devices. The active material in the film-type actuator is relaxor ferroelectric polymer (RFP) poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] blended with poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], which produces mechanical vibrations via the fretting vibration phenomenon. Normal pressure applied by a human fingertip on the film-type skinny button mechanically activates the locally concentrated electric field under the contact area, thereby producing a large electrostrictive strain in the blended RFP film. Multimodal audio and haptic feedback is obtained by simultaneously applying various electric signals to the pairs of ribbon-shaped top and bottom electrodes. The fretting vibration provides tactile feedback at frequencies of 50-300 Hz and audible sounds at higher frequencies of 500 Hz to 1 kHz through a simple on-off mechanism. The advantage of the proposed audio-tactile skinny button is that it restores the "click" sensation to the popular virtual touch buttons employed in contemporary electronic devices.
Project description:Control of light absorption and transmission by metal-insulator-metal (MIM) metasurfaces are promising for applications in optical windows. This study shows the realization of photo-thermal energy conversion for radiative cooling by MIM metasurfaces with thin metal substrate and Indium-Tin-Oxide (ITO). High transparency of ITO at visible wavelengths and high absorption at mid-infrared wavelengths were realized for future applications of efficient cooling or heating applicable for living and working spaces. The MIM (ITO/CaF2/ITO) metasurface was patterned with low-resolution photo-lithography as a demonstration of further simplification and possible scalability of the patterning for practical window applications.