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An ambient-curable hybrid resin (ACHR) terminated with trimethoxysilane functional groups, synthesized through a simple ring-opening reaction between 3-glycidyloxypropyltrimethoxysilane (KH560) and 4,4′-methylenebis (cyclohexylamine) (PACM), was applied to the surface of a transparent organic polymer to produce a robust, flexible, and transparent protective hybrid film, moisture cured at room temperature. The structure, morphology, and optical, mechanical, and thermal properties of the obtained hybrid film were evaluated. The hybrid film allowed the transmittance of more than 87% of visible light (at 600 nm), maintaining almost the same high transparency as bare PET film. The unique flexible segments and rigid segments in the inorganic–organic hybrid structure of the film realized superior resistance to bending and scratching. The hybrid film-coated PET demonstrated excellent flexibility, with an extremely low bending radius, illustrated by wrapping around a 1-mm mandrel bar without cracking. In addition, the hybrid film exhibited superior pencil hardness (of 2H) and excellent wear durability, i.e., no scratching after being subjected to 200 abrasion cycles using #0000 steel wool under a 19.6 kPa load. The robust, flexible, and transparent protective film developed here, and its simple and efficient preparation method, should have extensive application prospects.

Exploring flexible dielectrics with high dielectric constant and low loss is pertinent for many applications in electronic devices. In the present work, a non-ferroelectric polymer, polyvinyl alcohol (PVA), was used to fabricate homogeneous dielectric composite films with a relatively high dielectric constant and a low dielectric loss by using 2D nano sheets (Ti3C2Tx MXene) as the filler. To limit dielectric loss, SiO2 was coated onto the surface of MXene to provide interfacial barrier effect and suppress dielectric loss. MXene@SiO2/PVA composite films showed lower dielectric losses at low frequencies (from 20 Hz to ~ 10 kHz) compared with MXene/PVA composite films. MXene@SiO2/PVA composite films with 2.5 wt% MXene loading and 5 wt% (with respect to MXene content) SiO2 coating had a dielectric constant of 27.2 (a 292.5% rise compared to neat PVA film) and a dielectric loss of only 0.057 (a 259.6% reduction compared to MXene/PVA composite film) at 100 Hz and room temperature (RT). In addition, this SiO2-coated composite film had stable dielectric properties (dielectric constant and loss change from 27.2 to 29.3 and 0.057 to 0.104, respectively) in the temperature range of RT to 60 °C. This work provides a promising way to fabricate PVA-based dielectric composites with excellent dielectric properties for practical applications in electronics.

CaCu3Ti4O12 (CCTO) ceramics with desirable dielectric properties were prepared by a green gelcasting forming method combined with pressureless sintering. A non-toxic natural macromolecule, glutinous rice flour (GRF) was used as the gelling agent for the gelcasting process. The significant parameter, namely, the dosage of gelling agent was carefully studied so as to optimize the gelcasting process. The results showed that the dosage of GRF had evident effect on both gelcasting process and the final dielectric properties of CCTO ceramics. CCTO ceramics from the green body solidified with 3.5 wt% GRF showed relatively optimal dielectric properties, namely a dielectric constant up to 1.60 × 104 and a loss of only 0.063 (at 1 kHz test frequency). CCTO ceramics fabricated by this green gelcasting method have superior dielectric properties compared with that of the ceramics obtained by the dry pressing method.

This paper presents an ultra-wideband Phased Array Feed (PAF) based on novel flat bend crossed dipole fed by 50Ohm coaxial line. The PAF is dual-polarized and made from all-metal to minimize Ohmic losses and simplify cryogenic integration. It is optimized for 1-2 GHz band and can be good PAF candidate for the Five hundred meter Aperture Spherical Telescope (FAST) and Qi Tai Telescope (QTT) as well as other radio telescopes.

In this paper, a novel approach of surface damage localization for the Five hundred meters Aperture Spherical radio Telescope (FAST) based on the focal-field distribution (FFD) is proposed. Firstly, according to the structure of the FAST, we model the FAST with surface damage caused by down-tied cables fatigue fractures. Then the FFD with different damage locations obtained by simulation are collected to form a full FFD feature database. Finally, the received signals of the FAST array feeds with surface damage is matched with the database to obtain the damage location. Simulation results show that the matching algorithm can effectively estimate the damage location.

Double-band circular polarization conversion based on novel e -shape resonators is proposed and studied both numerically and experimentally. Both the simulated results and experimental results are in good agreement. At two resonant frequencies, i.e., 11.65 GHz and 13.02 GHz, the incident y-direction linearly polarized wave can be transformed into right- and left-handed circularly polarized waves, respectively. The proposed structure can transmit a nearly pure circularly polarized wave, with a polarization extinction ratio of greater than 30 dB. Moreover, the metasurface is compact with simple geometry, which is not only extremely thin in the propagating direction but also very small in the transverse direction. The retrieval results reveal that the effective refractive index of the e -shape structure is nearly negative in the vicinity of resonant frequencies. The surface current distributions are investigated to illustrate the polarization transformation mechanism. We also analyze the influence of several main geometric parameters for regulating the polarization properties. The proposed e -shape structure is promising for use in the design of polarization control devices.

In this paper, we report a novel tri-layer structure consisting of diamond-shaped metallic strips sandwiched between two sub-wavelength gratings arrays and printed on two dielectric substrates with a broadband asymmetric transmission phenomenon. Due to the Fabry-Perot-like effect, the cross-polarization conversion can reach a maximum of 0.94 and exceed 0.7 from 10 GHz to 30 GHz exhibiting a broadband characteristic in microwave spectra. Moreover, our structure is compactness both in the propagating direction and in the transverse directions. It is hoped that the proposed simple, easily fabricated metasurface can be used in further polarization conversion devices and nonreciprocal EM devices.

The current ceramic/618 epoxy resin piezoelectric composite material is easily deformed due to temperature, which affects the performance of the transducer to send and receive signals. Therefore, finding piezoelectric composite materials with higher temperature stability has become an urgent task. In this paper, the temperature stability of two piezoelectric composite materials of ceramic/ 618 epoxy resin and ceramic/9110 W silicone resin in the range of 25 °C ~ 120 °C was investigated via the fiber Bragg grating method. The results show that, during 25 °C to 120 °C, the ceramic/9110 W silicone resin piezoelectric composite has obvious less deformation and more stable electromechanical properties than the ceramic/ 618 epoxy resin piezoelectric composite; its increase rate of deformation in three directions of length, width and thickness are 8.269 × 10−5 mm/°C, 6.728 × 10−6 mm/°C, and 8.476 × 10−6 mm/°C respectively; its resonant frequency, relative rate of change of frequency constant, quasi-static capacitance, relative dielectric constant and conductance increase with increasing temperature, and the maximum values are 289 kHz, 0.1529%, 1.67 nF, 1083.225 and 11.300 ms, respectively; its electromechanical coupling coefficient changes little with increasing temperature, the maximum and minimum values are 0.63 and 0.60, respectively. The ceramic/9110 W silicone resin piezoelectric composite can better ensure the stability of the transducer performance.

In this paper, we theoretically and experimentally report an achiral dual-band metasurface with linear birefringence. The unit cell of the achiral metasurface consists of non-twisted Q-shape metallic ring resonators with a stub breaking the rotational symmetry. Moreover, due to the presence of the stub, we find the proposed metasurface emits dual-band circularly polarized wave with low transmission loss and high polarization extinction for a normal incident y-direction linearly polarized wave. We also systematically investigate the dependence of the electromagnetic response of the proposed structure on the geometric parameters. It is hoped that the proposed simple, easily fabricated model of achiral metasurface can be used in further polarization control applications

The geopolymer containing the special porous structure unit sod (t-toc) cage, which can be made from fly ash, is a possible economic solution to reduce toxicity of hazardous heavy metals by its excellent immobilization potential. Herein, the zeolite sodalite which is composed of sod (t-toc) cage was selected to model the geopolymer to uncover the immobilization mechanisms for the hazardous heavy metal ions Cr3+, Pb2+, Zn2+, Cu2+, Hg+, Cd2+ and Ni2+ in this work. Based on experimental crystalline structures, exchange energy was introduced for the first time to quantitatively evaluate the immobilization long-term stability theoretically. The immobilization of hazardous heavy metal ions were discovered to be determined by the solvation from the crystalline H2O and bonding from the sod (t-toc) cage. Based on the analysis of exchange energies, it was found that the immobilization for these heavy metals was correlated with the solvation radius: the larger the solvation radius was, the more favorable the immobilization was. Further detailed solvation effect analysis indicates that the immobilization of heavy metal ions is very sensitive to solvation effect based on the crystalline H2O molecules. Due to the synergistic effect between the solvation effect and the adsorption of the sod (t-toc) cage, the immobilization of Zn2+ is always favorable inside sodalite whereas Cr3+, Cd2+, Cu2+, Ni2+ and Pb2+ could be unfavorable in the case of insufficient solvation. This study provides a fast, convenient and objective way to evaluate the immobilization of heavy metals.

In this paper, a reconfigurable sensing platform based on an asymmetrical metal-insulator-metal stacked structure integrating an indium tin oxide (ITO) ultrathin film is proposed and investigated numerically. The epsilon-near-zero (ENZ) mode and antisymmetric mode can be resonantly excited, generating near-perfect absorption of over 99.7% at 1144 and 1404 nm, respectively. The absorptivity for the ENZ mode can be modulated from 90.2% to 98.0% by varying the ENZ wavelength of ITO by applying different voltages. To obtain a highly sensitive biosensor, we show that the proposed structure has a full-width at half-maximum (FWHM) of 8.65 nm and a figure-of-merit (FOM) of 24.7 with a sensitivity of 213.3 nm/RI (refractive index) for the glucose solution. Our proposed device has potential for developing tunable biosensors for real-time health monitoring.

Herein, we propose an approach for sensitivity improvement of dual-axis strain sensing using the property of a metasurface (MS) that the phase response shifts sharply with the MS deformation. A feasible approach for phase measurement is first demonstrated by calculating multi-polarized reception when the incident electromagnetic (EM) wave has anisotropic phase values. A flexible MS consisting of periodically arranged lantern-shaped elements is designed and fabricated for dual-axis strain sensing and evaluation based on the proposed method. The simulation and measurement results demonstrated a high sensitivity of the proposed MS for strain sensing in the microwave band. The method can be used potentially in both pressure and tensile sensing. Moreover, the operational frequency can be extended to the THz range and even to the optical band.

In this study, special redispersible silica nanoparticles (SNP) was synthesized by a facile one-step one-pot approach. The synthesized amorphous SNP had a spherical and uniform particle morphology with a diameter of 30 nm and exhibited high monodispersity. The characteristics of the particles were investigated by fourier transform infrared spectroscopy and thermogravimetric analysis. The results revealed that there were a large number of methyl groups grafted on the surface of the SNP, and the organic materials content in the as-synthesized SNP was approximately 10%. After a simple ultrasonic process, the SNP solid powder showed excellent stable and transparent redispersion in various organic solvents. In addition, the results revealed that the different polarities of the solvents had a significant effect on the visible light transparency of the SNP redispersion. SNP showed the best redispersion performance in N-methyl-pyrrolidone, exhibiting a transmittance of more than 80% at 600 nm at a high concentration of 25 wt%. The synthesis process developed in this study is simple, inexpensive, and can be used in the industrial application of SNP.

Environmental non-governmental organization (ENGO) plays an important role in promoting public participation in environmental governance. By semi-structural interviews and participant observations, this paper examines a local ENGO in China to explore how the organization can mobilize and organize the local public to participate in environmental governance. The research finds that mobilizing public participation in local environmental governance is a continuous process in which ENGO needs to continuously enable, empower and emotionally invest in the public. Through emotion construction and capacity building, environmental organizations have been empowering the public to participate and play a major role in local environmental governance. Mobilizing public participation in environmental governance can promote the improvement of local environmental problems, but mobilizing and organizing public participation requires sufficient political opportunity space, sufficient funds, and a culture of public participation.

With the development of micro-fabrication techniques, multi-functional sensor networks have been created with many micro-sensor nodes for various functions. An UAV wing is integrated with a stretchable sensor network including piezoelectric transducer, strain gauge and resistance temperature detector embedded near the wing surface and this novel design intends to equip the wing with the self-sensing capability similar to bird feathers. One of the main challenges of the state-of-the-art research is how to make the wing aware its flight states in real-time through large amount of sensing signals. Features are extracted and further selected for neural network modelling. Both classic neural network and deep belief network are proposed respectively to map the relationship from the sensing data to physical flight states and compare the identification accuracy with each other. The simulation results show a relatively high identification accuracy of the proposed methods, enabling new perspectives in developing intelligent self-awareness capabilities for next generation smart wings.

Full life-cycle and real-time structural health monitoring (SHM) rely on numerous, heterogeneous sets of data collected from sensors and extracting feathers that support the estimation of the health condition of a bridge. It is the principal challenges facing the SHM application on transmission and storing such huge amounts of data. Compressive sensing (CS) is a novel data acquisition method whereby the compression is done in a sensor simultaneously with the sampling. In this work, we established the possibility of compressed sensing to address this challenges on bridge SHM. Based on the sparsity of the deformation data of bridge, we proposed a random sampling scheme based on CS to minimize the number of field data. The CS recovery performance is mostly determined by the decomposition basis which is associated with the sparsity of the sampling signal. Different bases have been tested to recover the deformation data. Experimental results demonstrate the proposed method allows a reduction of the measurement data with an acceptable recovery accuracy. And reconstruction performance based on DWT to sparse transform is better than that based on DCT to sparse transform. When the compression ratio is above 0.6, the reconstruction error grows moderately; whereas the reconstruction error grows rapidly as the compression ratio is below 0.6. With the compression ratio decreased from 0.6 to 0.2, reconstruction error is reduced about 2.5 times by using DWT and reduced about 2 times by using DCT.

Smart structures revolutionize the traditional manned systems and challenge the structural health monitoring (SHM) field from a completely new perspective. Advanced sensing technology enables highly intelligent systems by embedding sensor networks into composite materials for smart structures such as fly-by-feel flights and intelligent robots. In this paper, we present a highly stretchable network with multifunctional sensor nodes microfabricated on a flexible polymer substrate. For the first time, we are capable of integrating three types of sensors with their appropriate materials into one single network. 6 platinum resistance temperature detectors (RTDs), 27 constantan strain gauges (SGs) and 8 lead zirconate titanate piezoelectric transducers (PZTs) with their unique patterns are distributed over the entire network. Finite element modeling has been performed to analyze the stress distribution along the node-wire connections during the stretching process in order to minimize nodal rotations. By taking advantage of a serpentine wire design, the network can be expanded 700% in area while maintaining high yield and low variation. A series of sensor characterizations have been conducted to validate the functionality of RTDs, SGs and PZTs. It is worth mentioning that the sensitivity of the RTD is 0.1 V/°C and the minimum detectable strain of the SG is as low as 2.26 μe. The multifunctional sensor network will be embedded into a composite wing to provide real-time aeroelastic feedbacks in a wind tunnel

We propose a novel and simple method to achieve perfect light absorption over a broadband by coupling a gap plasmon mode to an epsilon-near-zero (ENZ) mode, which is a new path for tailoring light-matter interactions. Near-perfect light absorption (over 99%) in the wavelength range of 1400 nm–1655 nm can be achieved utilizing a gold-disk periodically patterned metal-dielectric-metal (MDM) device by integrating an ultrathin ITO (indium tin oxide) film. The ENZ mode can be excited effectively by coupling the gap plasmon resonance to conducting ITO (indium tin oxide) nanolayer (ENZ wavelength of the ITO nanofilm close to 1403 nm) under normal incidence. Compared with the device without ITO nanolayer, the device integrating ITO ultrathin film shows wideband perfect light absorption. Besides, the thickness of SiO2 spacer layer is critical for the coupling strength of metamaterial resonator and ENZ mode. To achieve broadband absorption, the coupling strength of the ENZ mode and gap plasmon mode should be between the strong coupling and weak coupling regimes. The method is also effective for the design of multiband optoelectronic devices with simple structure and low cost.

A tri-layered chiral metasurface is proposed and demonstrated to exhibit broadband asymmetric transmission of linearly polarized electromagnetic waves in two opposite directions. The full wave simulation shows that the proposed metasurface can rigorously satisfy the asymmetric transmission (AT) theorem and can achieve cross-polarization conversion with high efficiencies for linearly polarization waves. Moreover, an extra-noticeable advantage of the proposed structure is its broad operation bandwidth in microwave band.

In this paper, we propose a chiral metamaterial structure that enables a dual-band 90° polarization rotator effect. The bilayered chiral metamaterial is composed by twisted different size “V” antenna resonators in four-fold rotation symmetry. Analysis also shows that such asymmetric twist structure can contribute to the induced asymmetric transmission which support strong optical activity. By scaling down the metamaterial structure, the concept can also be utilized at other frequency bands, such as submillimeter or even terahertz band.

A double-band circular polarizer based on novel e-shape resonators is proposed and studied numerically. At two resonant frequencies, i.e., 11.65 GHz and 13.02 GHz, the incident linearly polarized wave can be transformed into left/right-handed circularly polarized waves, respectively. The proposed polarizer transmits a nearly pure circularly polarized wave, with the polarization extinction ratio more than 30 dB. Moreover, the surface current distributions are investigated to illustrate the polarization transformation mechanism. The proposed polarizer is compact with simple geometry, which is promising to be intergrated with electrical small antennas.

We propose an optical nanoantenna, which is an individual nanosphere consisting of two identical metal strips separated by a dielectric spacer (Ag–Ge–Ag) with a notch. Such design integrates the advantages of array dielectric antenna and plasmonic antenna such as high directivity, emission direction control, and highly localized field enhancement based on excitation of electric and magnetic multipoles of high-orders and localized surface plasmons in the symmetry breaking of this nanomatryoshka. Major properties of this nanoantenna have been revealed theoretically and numerically. We compare our hybrid nanoantenna with plasmonic and dielectric nanoantenna of similar geometry, and the proposed nanoantenna exhibits better directivity and efficiency. By suitably positioning the feed inside the notch, this compact nanoantenna can spectrally sort the electromagnetic emission, together with a high value in directivity up to 13.5. In addition, we have also revealed that displacement of the emitter along the y-axis leads to beam rotation. In contrast to other conventional nanoantenna in subwavelength, the proposed nanoantenna may exhibit higher directivity and Purcell factor due to effective excitation of electric and magnetic multipoles of high-orders inside the nanoparticle and localized surface plasmons in the outmost metal shell. The ultradirectional nanoantenna may shed light to the design of compact nanoantennas, which may find various applications in biosensing and quantum communications.

A high performance metamaterial device for electromagnetic energy harvesting is presented. The unit cell of the metamaterial device consists of four identical omega ring resonators arranged in rotational symmetry, and each omega ring is loaded with a 50 Ω resistor that mimics the input impedance of a rectifier circuit. A proof-of-concept prototype is designed for operation at the frequency of 5.8 GHz. Here, the efficient energy harvesting is validated by the energy dissipated in each resistor. Based on the full absorption concept, the metamaterial device achieves a harvesting efficiency up to 93.1% under normal incidence. In addition, the energy harvester shows polarization independent and wide-angle incident frequency responses with good harvesting characteristics over the entire operating range. The surface current distribution is analyzed to gain an insight into the energy harvesting mechanism. Moreover, the harvester prototype is manufactured and measured, and the simulated and measured results are in good agreement. Due to the enhanced electromagnetic energy harvesting efficiency, the proposed device is a good candidate for microwave power transmission.

In this paper, a metamaterial electromagnetic energy harvester constructed via the capacitive loading of metal circular split rings is presented. Each energy-harvesting cell is loaded with a resistance that imitates the input impedance of a rectifier circuit. Specifically, the metamaterial energy harvester has high selective harvesting for left- and right-handed circularly polarized waves. Here, the energy absorption is mostly induced by the resistive load; thus, effective energy harvesting can be achieved. Moreover, the proposed energy harvester exhibits a high-efficiency harvesting for right-handed circularly polarized waves over a wide range of incident angles. Further, a transmission line model is adopted to interpret the energy harvesting mechanism, which shows that a good impedance matching and low dielectric loss can further enhance the harvesting efficiency. To demonstrate the design, a 15 × 15 unit-cell prototype is fabricated and measured, and the measured results reasonably agree with the simulated ones.

In this study, the design, realization, and characterization of an ultrathin triple-band polarization-insensitive wide-angle metamaterial absorber are reported. The metamaterial absorber comprises a periodic array of modified six-fold symmetric snowflake-shaped resonators with strip spiral line load, which is printed on a dielectric substrate backed by a metal ground plane. It is shown that the absorber exhibits three distinct near-unity absorption peaks, which are distributed across C, X, Ku bands, respectively. Owing to the six-fold symmetry, the absorber is insensitive to the polarization of the incident radiation. In addition, the absorber shows excellent absorption performance over wide oblique incident angles for both transverse electric and transverse magnetic polarizations. Simulated surface current and field distributions at the three absorption peaks are demonstrated to understand the absorption mechanism. Particularly, the absorption modes come from the fundamental and high-order dipole resonances. Furthermore, the experimental verification of the designed absorber is conducted, and the measured results are in reasonable agreement with the simulated ones. The proposed ultrathin (∼0.018λ0, λ0 corresponding to the lowest peak absorption frequency) compact (0.168λ0×0.168λ0 corresponding to the area of a unit cell) absorber enables potential applications such as stealth technology, electromagnetic interference and spectrum identification.

In this paper, the problem of two-dimensional (2D) direction-of-arrival (DOA) estimation with parallel linear arrays is addressed. Two array manifold matching (AMM) approaches, in this work, are developed for the incoherent and coherent signals, respectively. The proposed AMM methods estimate the azimuth angle only with the assumption that the elevation angles are known or estimated. The proposed methods are time efficient since they do not require eigenvalue decomposition (EVD) or peak searching. In addition, the complexity analysis shows the proposed AMM approaches have lower computational complexity than many current state-of-the-art algorithms. The estimated azimuth angles produced by the AMM approaches are automatically paired with the elevation angles. More importantly, for estimating the azimuth angles of coherent signals, the aperture loss issue is avoided since a decorrelation procedure is not required for the proposed AMM method. Numerical studies demonstrate the effectiveness of the proposed approaches.