Search Results (53)

Electric dipole antennas can be designed in a variety of geometries and applied across a wide range of configurations. Appropriately designed dipole antennas can provide deep tissue penetration and low radiofrequency (RF) power deposition in magnetic resonance imaging (MRI), making them attractive for applications requiring safe and effective RF transmission in deep regions. On clinical 3 T MRI systems, however, conventional dipoles are too large in size for practical imaging of the head. Inspired by telecommunications designs, the present work adapts meandered dipoles (where the conductor is folded to shorten the antenna) with the resonance frequency controlled through trace geometry. Additionally, multi-channel configurations are considered to improve RF power transmission. A straight dipole was progressively transformed into meandered geometries and characterized using benchtop measurements and electromagnetic simulations. Analyses evaluated frequency response, near-field behavior, power-flow directionality, and distributions of local tissue heating and transmitted RF magnetic field in multi-channel arrays. A four-channel parallel-transmit (pTx) prototype was also used to show the feasibility of dipole-based head imaging at 3 T. The present work demonstrates a practical implementation of compact, low-heating dipole arrays for head MRI, with potential for extension to ultra-high-field or multinuclear imaging. Full article

Reconfigurable photonic metasurfaces enable tunable thermal-emission engineering in the long-wave infrared (LWIR), particularly within the 8–13 μm atmospheric window. This work includes the investigation on a concentric-ring VO₂/SiO₂/Au metasurface for LWIR spectral-emissivity modulation. Full-wave simulations showed that, in the metallic phase (σ = 2 × 10⁵ S/m where σ is conductivity), the structure exhibited an absorption over 90% across the 9.3–15 μm sub-band, with two near-unity resonances near 10.2 and 13.3 μm. Control structures, gap-dependent spectra, E-field maps, and current-density Cartesian multipole decomposition supported a hybridized-ring mechanism in which both dominant resonances were predominantly electric-dipole-like ring branches whose spectral positions and field localizations were modified by inter-ring coupling. Across the conductivity sweep, the normal-incidence band-averaged 8–13 μm emissivity changed from 0.0184 to 0.8844, corresponding to a switching ratio of 48.06. The four-fold symmetry of unit cell also yielded polarization-insensitive and angularly robust LWIR absorption, while the simplified endpoint thermal-balance estimate indicated a metallic-state net cooling power of 49.3 W m⁻² at T = T_amb = 300 K, where T_amb was the ambient temperature, and an estimated equilibrium temperature drop of 4.4 K below the ambient for the metallic-state endpoint, whereas the insulating-state one suppressed this response. These results identify concentric VO₂ ring metasurfaces as promising candidates for switchable LWIR thermal-emission control. Full article

Radio frequency identification (RFID) technology has been widely adopted in a variety of practical applications. Usually, the size of a passive tag antenna largely determines the read performance of tag. However, excessively large tag antennas can hinder their practical application and a tag that is too small has poor performance. In this paper, a compact, flexible and corrosion-resistant folding dipole tag antenna is proposed, which has a geometrical dimension of 24 mm × 13 mm (0.074${\mathsf{\lambda }}_0\times 0.040{\mathsf{\lambda }}_0$). It is designed on only one surface of a flexible polyethylene terephthalate (PET) substrate, which can be folded. The paper proposes a single-sided laser-patterned GAF/PET flexible RFID tag that is mechanically folded to form a backside dipole arm without vias, targeting compact and corrosion-resistant UHF RFID operation. Changing the size of the folding arm can effectively adjust the resonant frequency and impedance of the tag antenna. A stepped radiation arm is used to extend the current path and lower the resonance frequency. The capacitance and inductance effects introduced by loading a T match for reducing the resonant frequency of the tag to the useful UHF RFID band. Finally, it can achieve a power transfer coefficient of 99.9% and exhibit high impedance matching between the tag antenna and the chip. The proposed tag antenna uses graphene-assembled film (GAF) as its conductor material. Thanks to the physicochemical properties of GAF, the proposed tag antenna maintains stable radiation performance even after prolonged exposure to acidic (5 wt%), alkaline (5 wt%), and salt (5 wt%) corrosion, as well as more than 1000 mechanical bending cycles. When the EIRP of the reader is 2.2 W, the maximum read range of the tag in the 800–1000 MHz is 1.38 m. Full article

This paper presents a non-imaging landmine detection system that integrates a highly sensitive multiple-input multiple-output (MIMO) microwave sensor with a machine learning (ML) classifier for automated classification. The proposed sensor consists of two circular patch elements fed with two ports designed in a unique configuration, comprising a dual loop with a cross dipole, for enhancing sensitivity to changes in the environmental electrical properties (dielectric constant and electrical conductivity) induced by buried metallic objects. It operates in dual bands of 1.58 GHz and 1.75 GHz, within the operating frequency range of 1.3 to 2 GHz. The system’s performance was assessed using full-wave simulations and experimental measurements, involving a sand-filled foam container with a metal surrogate landmine placed at different depths. The sensor’s performance was evaluated by monitoring changes in the magnitude and phase of the reflection coefficient ($S_{11}$) and the transmission coefficient ($S_{21}$). The acquired scattering parameters data were processed using a Support Vector Machine (SVM) algorithm for automated classification. Results demonstrate the sensor’s high capability in detecting metallic targets at various depths and standoff distances. Compared to conventional imaging technologies, this system offers significant advantages in cost, simplicity, and ease of data processing. The SVM models trained on measurement data with proper feature selection showed a high level of agreement with their counterparts trained on simulation data. Stratified k-fold cross-validation was used to improve the reliability of accuracy metrics, with results showing 85% or higher mean accuracy in all classification scenarios. Full article

Continuous introduction of advanced optimization algorithms promotes the development of electromagnetic (EM) technology in radar and communication systems. Wideband antenna design within a given space and wideband array pattern synthesis, especially in the scenario of strong mutual coupling, are two typical challenging electromagnetic problems. In this paper, a nature-inspired algorithm, i.e., the water cycle algorithm (WCA), is introduced to resolve the above two EM problems. Two typical wideband antennas, i.e., the dual-band E-shaped microstrip antenna and the typical magnetoelectric (ME) dipole antenna, are designed on the basis of the established WCA-based antenna design scheme. Compared with the well-known algorithms that have been introduced in antenna design, including the differential evolution (DE) algorithm and the gray wolf optimizer (GWO), better results can be achieved with WCA. In the sequel, a WCA-based low peak sidelobe level (PSLL) pattern synthesis is implemented based on a uniformly spaced 27-element folded fractal ME dipole array antenna with mutual coupling as high as −10 dB, the results of which further validate the superiority of WCA in array pattern synthesis and demonstrate the value of this application innovation. Full article

Realizing high-quality-factor (high-Q) plasmonic resonances in the visible regime is critical for enhancing light-matter interactions and advancing biochemical sensing. However, traditional localized surface plasmon resonances (LSPRs) typically suffer from broad spectral linewidths due to severe radiative damping. In this work, we propose a simple two-dimensional symmetric gold nanohole-array metasurface that supports a symmetry-protected bound state in the continuum (SP-BIC) at normal incidence. By introducing extrinsic symmetry breaking via oblique incidence, this non-radiative dark state is successfully transformed into an observable high-Q quasi-BIC Fano resonance. Cartesian multipole decomposition reveals that this sharp mode ($\lambda \approx 688$ nm) is predominantly driven by a tightly confined Magnetic Dipole (MD) excitation, which drastically suppresses radiative leakage compared to the highly damped Electric Dipole (ED)-dominated LSPR. Consequently, the quasi-BIC mode exhibits an ultra-narrow spectral linewidth ($\mathrm{FWHM}\approx 17.4$ nm). While its bulk sensitivity ($236.9$ nm/RIU) is slightly lower than that of the LSPR mode, the exceptionally sharp resonance yields a remarkably low Limit of Detection (LOD) of $7.35\times {10}^{-3}$ RIU, achieving a nearly five-fold improvement over the traditional LSPR. Furthermore, the quasi-BIC mode maintains an outstanding Figure of Merit (FOM up to ∼19.7 ${\mathrm{RIU}}^{-1}$) across the entire sensing range. By eliminating the need for complex asymmetric nanofabrication, this robust angle-tuned design strategy provides a highly promising platform for the development of high-resolution, low-cost optical biosensors. Full article

High quality factor (Q factor) resonant metasurfaces enable efficient mid-infrared (MIR) upconversion, yet their narrow operating bandwidths severely limit practical broadband detection and imaging applications. Although high Q magnetic toroidal dipole (MTD) modes exhibit outstanding momentum space ($k$-space) stability in linear optics, their application in nonlinear processes has primarily been confined to degenerate second-harmonic generation (SHG), leaving complex non-degenerate processes such as sum-frequency generation (SFG) largely unexplored. Here, we propose a tunable MIR upconversion platform based on an all-dielectric gallium phosphide (GaP) dimer metasurface. Breaking the in-plane symmetry to trigger Brillouin zone folding excites robust MTD quasi-guided modes (MTD-QGM), tightly confining the locally enhanced optical fields within the highly nonlinear GaP nanostructure. Synchronizing this high Q resonance with a spatially overlapping pump mode yields an exceptional SFG conversion efficiency of $7.9\times {10}^{-4}$, successfully translating a 3101.8 nm MIR signal to the 903 nm near-infrared band. Crucially, the intrinsic $k$-space stability of the MTD-QGM enables continuous, broadband upconversion through simple angle tuning. This mechanism effectively overcomes the narrow-band limitations characteristic of typical symmetry-protected resonators, establishing a robust paradigm for room-temperature MIR detection. Full article

The development of sustainable and environmentally benign N-methylation methodologies is essential for enhancing sustainable synthetic practice in pharmaceutical manufacturing. In this study, we demonstrate that microwave heating (MWH) markedly enhanced the efficiency of cobalt-catalyzed N-methylation using methanol or methanol-d₄ as green C1 sources. Compared with conventional heating (CH), MWH enabled highly efficient syntheses of key pharmaceutical intermediates—including 6-dimethylamino-1-hexanol, imipramine hydrochloride, and butenafine hydrochloride—under milder conditions and shorter reaction times and without generating hazardous halogen-containing waste. UV–vis spectroscopic analysis revealed that MWH accelerated the transformation of Co(acac)₂ into catalytically active Co species by approximately four-fold, providing a mechanistic basis for the enhanced reactivity. We hypothesized that this effect was caused by the selective microwave heating of the catalyst, which in turn promoted the rapid generation of catalytically active species. Notably, MWH also significantly improved the N-trideuteromethylation of amines using methanol-d₄, achieving a 95% yield for imipramine-d₃ hydrochloride versus 32% under CH. Molecular dynamics simulations indicated that methanol-d₄ exhibited slower dipole relaxation and enhanced cluster fragmentation under microwave fields, improving catalyst–substrate contact, while kinetic isotope effects stabilized reactive intermediates. These synergistic effects account for the pronounced microwave promotion observed in deuterated systems. Overall, the combination of MWH and cobalt catalysis offers an energy-efficient, waste-minimizing, and environmentally benign strategy for the scalable synthesis of both methylated and deuterated amines. Full article

Addressing the pressing need to extend the communication range of RF RFID tag antennas, this paper introduces a novel UHF RFID tag antenna technology based on resonant superstrate regulation using a Split-Ring Resonator (SRR). First, a finite element model of the UHF RFID folded dipole antenna was constructed based on the tag chip’s port impedance. Subsequently, a Two-element SRR resonant superstrate was employed to enhance the dipole antenna’s gain through “resonance and near-field coupling” technology. A folded dipole antenna gain-enhancing SRR resonant superstrate unit was designed, and a multi-parameter joint optimization method was adopted to obtain the optimal SRR resonant superstrate configuration for regulating the dipole antenna. Near-field coupling technology was used to design SRR resonant superstrate elements that enhance the folded dipole antenna’s gain. A multi-parameter joint optimization method was employed to obtain the optimal structural parameter set for the SRR resonant superstrate-controlled dipole antenna. Finally, simulations and experimental measurements of the RFID antenna performance revealed that: within the 920–925 MHz band, the maximum measured forward reading distance enhancement reached 62.1%. The research findings significantly enhance the practical performance of UHF RFID tags in complex environments, enabling more stable and efficient long-range identification in applications such as logistics tracking, asset management, and smart warehousing. Full article

Magnetic anapole states associated with the destructive interference between magnetic dipole and magnetic toroidal moments result in suppressed scattering accompanied by strongly enhanced near fields. Here, we demonstrate the existence of such modes in the gap of a gold oblate nano-ellipsoid on gold mirror (ONEOM) structures and observe a pronounced Purcell factor enhancement for magnetic dipole radiation upon introducing magnetic dipoles into the gap. We systematically investigate the dependence of the magnetic radiation Purcell factor on gap size and structural parameters. Notably, a 230-fold Purcell factor enhancement is achieved for the ONEOM configuration. This result highlights the potential of ONEOM structures in applications requiring efficient magnetic dipole emission, including nonlinear frequency conversion, plasmonic sensing, and single-photon sources. Full article

Against the backdrop of global energy transition and strict environmental regulations, supercritical carbon dioxide (scCO₂) fracturing and oil displacement technologies have emerged as pivotal green approaches in shale gas exploitation, offering the dual advantages of zero water consumption and carbon sequestration. However, the inherent low viscosity of scCO₂ severely restricts its sand-carrying capacity, fracture propagation efficiency, and oil recovery rate, necessitating the urgent development of high-performance thickeners. The current research on scCO₂ thickeners faces a critical trade-off: traditional fluorinated polymers exhibit excellent philicity CO₂, but suffer from high costs and environmental hazards, while non-fluorinated systems often struggle to balance solubility and thickening performance. The development of new thickeners primarily involves two directions. On one hand, efforts focus on modifying non-fluorinated polymers, driven by environmental protection needs—traditional fluorinated thickeners may cause environmental pollution, and improving non-fluorinated polymers can maintain good thickening performance while reducing environmental impacts. On the other hand, there is a commitment to developing non-noble metal-catalyzed siloxane modification and synthesis processes, aiming to enhance the technical and economic feasibility of scCO₂ thickeners. Compared with noble metal catalysts like platinum, non-noble metal catalysts can reduce production costs, making the synthesis process more economically viable for large-scale industrial applications. These studies are crucial for promoting the practical application of scCO₂ technology in unconventional oil and gas development, including improving fracturing efficiency and oil displacement efficiency, and providing new technical support for the sustainable development of the energy industry. This study innovatively designed an amphiphilic modified amino silicone oil polymer (MA-co-MPEGA-AS) by combining maleic anhydride (MA), methoxy polyethylene glycol acrylate (MPEGA), and amino silicone oil (AS) through a molecular bridge strategy. The synthesis process involved three key steps: radical polymerization of MA and MPEGA, amidation with AS, and in situ network formation. Fourier transform infrared spectroscopy (FT-IR) confirmed the successful introduction of ether-based CO₂-philic groups. Rheological tests conducted under scCO₂ conditions demonstrated a 114-fold increase in viscosity for MA-co-MPEGA-AS. Mechanistic studies revealed that the ether oxygen atoms (Lewis base) in MPEGA formed dipole–quadrupole interactions with CO₂ (Lewis acid), enhancing solubility by 47%. Simultaneously, the self-assembly of siloxane chains into a three-dimensional network suppressed interlayer sliding in scCO₂ and maintained over 90% viscosity retention at 80 °C. This fluorine-free design eliminates the need for platinum-based catalysts and reduces production costs compared to fluorinated polymers. The hierarchical interactions (coordination bonds and hydrogen bonds) within the system provide a novel synthetic paradigm for scCO₂ thickeners. This research lays the foundation for green CO₂-based energy extraction technologies. Full article

The enhancement of organic light-emitting diode (OLED) device performance has been a key area of research in organic optoelectronic devices. Optimizing carrier mobility within OLED devices is a crucial strategy. In this study, the hole transport layer was optimized using a self-assembled monolayer (SAM) subjected to different annealing temperatures. Through submitting the SAM to an annealing temperature of 100 °C, a maximum luminous intensity of 32,290 cd/m² and a maximum EQE of 1.77 were achieved, the latter being more than two-fold higher than that without the SAM. As the SAM annealing temperature increased from 80 °C to 120 °C, both the vertical orientation of molecules in the hole transport layer and the hole mobility in hole-only devices (HODs) improved. This vertical orientation is beneficial to enhancing hole mobility. Electrochemical impedance spectroscopy and surface morphology analysis revealed that the introduction of a SAM leads to the formation of interface resistance. The synergy effect between the variation in the molecular transition dipole moment and the interface morphology of the hole transport layer optimizes the hole mobility of HODs and leads to the enhancement of OLED performance. Full article

The substituent effect has a significant influence on the optical properties of spectral shape, width, and wavelength, and the intensities of the maximum peaks of emission (EMI) and circularly polarized luminescence (CPL). In this work, we conducted a systematic theoretical study to investigate how substituents alter the optical response in the EMI and CPL spectra of three [7]helicene derivatives at the vibronic level. To incorporate the vibronic effect, a state-of-the-art time-dependent (TD) method was used to achieve the fully converged spectra. In the meantime, a time-independent (TI) approach also provided a way to show the progression of the spectra, serving as a complementary strategy and creating reliable documentation for the experiment. The experimental spectra of EMI and CPL are nicely reproduced, which validates the reliability of the Adiabatic Hessian (AH) model in simulating experimental data. This allowed us to analyze in detail the effect of substituents, particularly on the optical responses. The introduction of cyano and methoxy groups is highlighted, as they altered the transition dipole moments and led to a 1000-fold increase in the intensity of EMI and CPL. Moreover, substituents can also rationally alter the spectral shape of EMI and CPL by affecting the responsible normal modes. The unique CN stretching and the MeO rotation in the substituted [7]helicene are highlighted as key factors contributing to the different behaviors of EMI and CPL. This sheds light on the design and synthesis of helicenes that can serve as ideal full-color EMI and CPL emitters. Full article

Photoreduction of CO₂ into the chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Nevertheless, undesirable charge separation and migration, as well as rapid reverse charge recombination results in the unsatisfactory photocatalytic activity of most conjugated microporous polymers (CMPs). Herein, a pair of donor–acceptor (D-A) CMPs for CO₂ photoconversion was developed through position isomerism by altering linkage sites. The results show that Py-D₂₇F with 2,7-site linkage exhibits a completely conjugated structure and a large molecular dipole moment, thus significantly accelerating charge separation and transfer. As a result, Py-D₂₇F achieves a higher yield of 320.9 μmol g⁻¹ h⁻¹ for CO₂-to-CO photoreduction (without the addition of any photosensitizers and precious metals), which is about three-fold greater than that of Py-D₃₆F (3,6-site linkage). This study provides a valuable idea for exploring outstanding CMP photocatalysts for the efficient processing of photocatalysis. Full article

A design framework for developing full-textile reconfigurable dipole antennas is proposed for wearable applications. To this end, a precise embroidery process using conductive threads is applied to properly manage the antenna structure. Further, mechanical reconfiguration to enhance antenna operation by using solely clothing components is outlined. As a proof-of-concept, we present a full-textile embroidered dipole antenna with mechanical frequency reconfiguration. Specifically, reconfiguration is achieved by folding the dipole arms through a triangular formation. Conductive Velcro strips are employed to guide the necessary dipole arrangement. As shown, the proposed design methodology enables frequency tunability that ranges from 780 to 1330 MHz for UHF and L bands, with satisfactory radiation performance. The measured and simulated results are in good agreement, in terms of achieving similar frequency reconfiguration concept, as predicted by the electromagnetic simulation models. Full article