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Dielectric chiral metasurface is a new type of planar and efficient chiral optical device that shows strong circular dichroism or optical activity, which has important application potential in optical sensing and display. However, the two types of chiral optical responses in conventional chiral metasurfaces are often interdependent, as their modulation of the amplitudes and phases of orthogonal circularly polarized components is correlated, which limits the further progress of chiral meta-devices. Here we propose a new scheme for independently designing the circular dichroism and optical activity of chiral metasurfaces to further control the polarization and wavefront of transmitted waves. Inspired by mixtures of chiral molecular isomers, we use the dielectric isomer resonators to form “super-units” instead of single meta-atoms for chiral responses in terahertz band, which is called racemic metasurface. By introducing two levels of Pancharatnam-Berry phases between meta-atoms and “super-units”, the polarization rotation angle and wavefront of the beam can be designed without the far-field circular dichroism. We demonstrate the strong control ability on terahertz waves of this scheme through simulation and experiments. In addition, this new type of device with near-field chirality but no far-field circular dichroism may also have important value in optical sensing and other technologies.

Abstract Large-scale stretchable strain sensor arrays capable of mapping two-dimensional strain distributions have gained interest for applications as wearable devices and relating to the Internet of Things. However, existing strain sensor arrays are usually unable to achieve accurate directional recognition and experience a trade-off between high sensing resolution and large area detection. Here, based on classical Mie resonance, we report a flexible meta-sensor array that can detect the in-plane direction and magnitude of preloaded strains by referencing a dynamically transmitted terahertz (THz) signal. By building a one-to-one correspondence between the intrinsic electrical/magnetic dipole resonance frequency and the horizontal/perpendicular tension level, arbitrary strain information across the meta-sensor array is accurately detected and quantified using a THz scanning setup. Particularly, with a simple preparation process of micro template-assisted assembly, this meta-sensor array offers ultrahigh sensor density (~11.1 cm−2) and has been seamlessly extended to a record-breaking size (110 × 130 mm2), demonstrating its promise in real-life applications.

Vehicle object detection using UAV images is a crucial undertaking in urban traffic management and the advancement of autonomous driving technologies. Conventional networks fail to achieve accuary in detecting vehicle objects from a drone’s perspective due to the significant variations in the size of the target items, unequal distribution of their positions in the image, and image degradation induced by the drone’s movement.In order to surmount this challenge, this research suggests an enhanced TOOD object detection model named Drone-TOOD. The first proposal is to create a lightweight network skeleton called CSPRegNet by merging CSPblock with Regblock. Secondly, we incorporate Regblock into CSPPAFPN to enhance CSPRegPAFPN and incorporate EVCblock at the upsampling location of deep features to capture corner area details and minimize the degradation of feature information. In addition, a efficient task decomposition attention module is also proposed to enhance the interaction ability of positioning and classification tasks. This task decomposition module can highlight the characteristics of a specific task while retaining the characteristics of another task, thereby improving detection capabilities. Experiments conducted on the Drone Vision Challenge Benchmark (VisDrone) demonstrate that the enhanced model can obtain superior performance compared to TOOD. The average precision (mAP) achieved by our approach is 64%, surpassing TOOD by 7.9%. The frames per second (FPS) stayed constant at 27.2. Drone-TOOD demonstrates superior performance compared to other lightweight models on the VisDrone-2021 dataset. In order to demonstrate the robustness of our approach, we additionally performed ablation experiments and conducted tests on the UAV Detection and Tracking Dataset (UAVDT), resulting in an achieved mean average precision (mAP) of 64.6%. Furthermore, Drone-TOOD possesses a total of parameter approximately 21.7 M.

Dielectric nanostructures exhibit intriguing optical properties and outstanding advantages in designing optical nanoantennas and metasurfaces compared to plasmonic nanostructures. This study employs classical electrodynamic methods to comprehensively explore the scattering characteristics of silicon triangular nanoprisms in monomer and oligomer forms. For monomeric nanoprisms, the scattering spectra reveal two distinct and prominent resonance peaks attributed to magnetic dipole (MD) and electric dipole (ED) modes. Reducing interparticle gaps within dimeric structures leads to noticeable blueshifts in MD resonance peaks with stable intensities, in contrast to the nearly constant position and significantly reduced intensities of the ED resonance peaks. A pronounced Fano-like resonance was observed upon transitioning to tetrameric and hexameric configurations, resulting from the coupling between MD and ED modes. A broad resonance peak also emerges in the long-wavelength region due to MD-to-MD coupling. The simulations conducted herein hold significant theoretical implications, advancing our comprehension of the scattering properties of dielectric nanoparticles and contributing valuable insights into fundamental nanophotonics.

The highly sensitive and versatile technique of plasmonic sensing has been widely employed in detecting and analyzing chemical or biological substances. This work employs classical electrodynamics methods to investigate the sensing performance of nanoprisms systematically. By varying heights, base edge lengths, and rounding radii of base corners of triangular nanoprism, we explore their influence on sensitivity and the figure of merit (FOM) in both transverse and longitudinal polarization cases. Our findings indicate that enlarged triangular prisms exhibit enhanced sensitivity, but a decrease in FOM counterbalances this improvement. Conversely, reducing the rounding radius of the base corners of the triangular prism leads to simultaneous improvements in sensitivity and FOM. We suggest prioritizing triangular or tetrahedral prisms in fabricating nanosensors for higher FOM or sensitivity, respectively. These insights provide valuable directions for designing and optimizing plasmonic sensors in practical usage.

X-ray tomography has been widely used in various research fields thanks to its capability of observing 3D structures with high resolution non-destructively. However, due to the nonlinearity and inconsistency of detector pixels, ring artifacts usually appear in tomographic reconstruction, which may compromise image quality and cause nonuniform bias. This study proposes a new ring artifact correction method based on the residual neural network (ResNet) for X-ray tomography. The artifact correction network uses complementary information of each wavelet coefficient and a residual mechanism of the residual block to obtain high-precision artifacts through low operation costs. In addition, a regularization term is used to accurately extract stripe artifacts in sinograms, so that the network can better preserve image details while accurately separating artifacts. When applied to simulation and experimental data, the proposed method shows a good suppression of ring artifacts. To solve the problem of insufficient training data, ResNet is trained through the transfer learning strategy, which brings advantages of robustness, versatility and low computing cost.

Abstract Rational design of porous conductive hosts with high electrical conductivity, large surface area, and adequate interior space is desirable to suppressing dendritic lithium growth and accommodating large volume change of lithium metal anode during the Li plating/stripping process. However, due to the conductive nature of the conductive hosts, Li is easily deposited directly on the top of the hosts, which hinders it from fully functioning. To circumvent the issue, in this study, we designed a novel porous carbon host with a gradient‐pore‐size structure based on one‐dimensional (1D) carbon with different diameters. With this kind of host, stable cycling with high and stable Coulombic efficiency of ~98% is achieved at 0.5 mA cm−2 with an areal capacity of 1 mAh cm−2 over 320 cycles. In contrast, the normal three‐dimensional (3D) carbon nanotube host presents a moss‐like Li morphology with wildly fluctuating Coulombic efficiency after 100 cycles. The results reveal that the unique gradient‐pore‐size structure of the 3D conductive host greatly improves the performance of lithium metal batteries.

The electromagnetic multipole method has been extensively adopted for a better understanding of the physical mechanism of localized surface plasmon. In this work, we quantitatively decomposed the total extinction spectra of typical silver nanoparticles into multipole components, which are shown to be quite different from qualitative assignment of resonance peaks reported previously. Taking the quasi-normal mode method as reference standard, we examined the scope of application of the electromagnetic multipole method in assigning plasmonic resonance peaks, and pointed out the necessity of employing eigenmode-based approaches when interpreting plasmonic spectra, which can hopefully lead to more physical insights into the underlying mechanisms of plasmonics phenomena.

Vanadate with layered structures and large open frameworks has been extensively explored as cathodes materials for aqueous Zn-ion batteries (ZIBs), and superior Zn-ion storage performance have been achieved. The biphasic vanadate materials are investigated to be conducive for further performance improvement. However, the lack of rapid and scalable synthesis strategies poses stiff challenges for the wider industrial economy of vanadate. Herein, the 3D biphasic NH4V3O8/Zn3(OH)2V2O7·2H2O (NVO/ZVO) were obtained via rapid microwave irradiation assisted chemical precipitation. The prepared electrode by NVO/ZVO with multiple nanoflower-structures presents a high specific capacity (332 mAh g−1 at 0.1 A g−1), together with exceedingly good energy density (281 Wh kg−1) and power density (94 W kg−1). Moreover, it can maintain a specific capacity of 92 % (132 mAh g−1) after 1000 cycles at a high current density of 10 A g−1. The high electrochemical performance of the cathode can be ascribed to the energy storage mechanism of dual-ion intercalation. This work provides key insights into the rapid synthesis of high-performance biphasic vanadate cathode materials for advanced ZIBs.

In order to improve the wear resistance of titanium alloy, a Ti5Si3/Ti3Al composite coating with improved wear resistance was successfully prepared by laser cladding TA2 titanium alloy using the double-layer presetting method of Ti-63 wt.% Al mixed powder layer/Si powder layer. The microstructure, phase composition and wear resistance of the coating were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and pin-disk friction and wear method. The results show that the coating is mainly composed of the Ti5Si3 primary phase and Ti5Si3/Ti3Al eutectic structure. The microhardness of the coating is higher than that of the matrix. The average microhardness of the coating is about 668 HV0.1, which is 3.34 times that of the matrix. The coating significantly improves the wear resistance of the TA2 matrix, and the mass wear rate is 1/5.79 of that of the TA2 matrix. The main wear mechanisms of the coating are abrasive wear, adhesive wear and oxidative wear, whereas the main wear mechanisms of the TA2 matrix are adhesive wear and oxidative wear.

The combination of VO2 and metasurfaces has opened an attractive route to dynamically control terahertz (THz) waves based on the giant conductivity change. However, the high-precision control of microfabrication and single performance of conductivity change limit the multifunctional application of VO2-based metasurfaces. Here, we proposed a VO2-metallic hybrid metasurface by in situ depositing high-quality VO2 thin films onto a metasurface composed of asymmetric Fano resonance units. It exhibits agile frequency and amplitude modulation for THz transmission across tuning the dielectric constant and conductivity of VO2. The metallic metasurface is designed as a matrix to achieve high transmission at 0.61 and 0.78 THz due to the split-ring resonance. During the thermally triggered phase transition of VO2, we found that the resonance frequency and amplitude can be tuned dominantly by the change of dielectric constant and conductivity, respectively. In particular, the increased dielectric constant enables red shift of the frequency by around 0.48 THz and the conductivity increases lead to a giant THz amplitude modulation of 88%. These results provide a route for developing VO2-based THz smart devices combined with functional metasurfaces and hold great promise for applications in THz sensor and modulation.

Summary: Dynamic tuning of terahertz (THz) wave is vital for the development of next generation THz devices. Utilization of solar energy for tuning THz waves is a promising, eco-friendly, and sustainable way to expand THz application scenarios. Ti2O3 with an ultranarrow bandgap of 0.1eV exhibits intriguing thermal-induced metal-insulator transition (MIT), and possesses excellent photothermal conversion efficiency. Herein, Ti2O3 film was fabricated by a two-step magnetron sputtering method, and exhibited an excellent photothermal conversion efficiency of 90.45% and demonstrated temperature-dependent THz transmission characteristics with a wideband at 0.1–1 THz. We supposed to combine photothermal conversion characteristics with temperature-dependent THz transmission properties of Ti2O3 film, which could introduce solar light as the energy source for tuning THz waves. Our work will provide new sight for investigating MIT characteristics of Ti2O3 at THz regime and exhibit huge potential in the application of tuning terahertz waves in outdoor scenarios in the future.

Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown favorable application prospects in memory-related devices once combined with metamaterials or metasurfaces. However, to date, VO2-based memory meta-devices are usually in a single-channel read/write mode, which limits their storage capacity and speed. In this paper, we propose a reconfigurable meta-memory based on VO2, which favors a two-channel read/write mode. Our design consists of a pair of large and small split-ring resonators, and the corresponding VO2 patterns are embedded in the gap locations. By controlling the external power supply, the two operation bands can be controlled independently to achieve at least four amplitude states, including “00”, “01”, “10”, and “11”, which results in a two-channel storage function. In addition, our research may provide prospective applications in fields such as THz switching, photon storage, and THz communication systems in the future.