Dopamine (DA) is a critical neurotransmitter whose abnormal levels are associated with neurological disorders, including Parkinson's disease, Alzheimer's disease, and schizophrenia. The development of sensitive and reliable detection methods is therefore essential for diagnosis and treatment monitoring. Here we report a phase-interrogated surface plasmon resonance (SPR) biosensor based on a graphene oxide (GO)-functionalized glass/Ti/Ag/Al2O3/ZnSe multilayer platform. The high refractive index (RI) ZnSe layer confined the evanescent field through a waveguide-coupled mode, which produced a sharp resonance with a measured FWHM of 0.077 degrees, a Q-factor of 799, and a figure of merit (FOM) of 1527 RIU-1. The slight broadening relative to the simulated FWHM of 0.034 degrees is consistent with practical fabrication imperfections and beam angular divergence, though sensor performance was not meaningfully affected. The bulk RI calibration with glucose solutions confirmed a phase sensitivity of 4.53 & times; 104 deg RIU-1 and an angular sensitivity of 120.1 degrees/RIU. For DA detection, the ZnSe surface was functionalized with (3-aminopropyl)triethoxysilane (APTES) and GO and then exposed to different DA concentrations from 1 pM to 10 nM. A semi-log linear fit over the range of 1 pM to 1 nM showed a sensitivity of 1.15 degrees/decade (R2 = 0.9547), and a Langmuir isotherm yielded a maximum phase shift of 3.74 degrees, a dissociation constant of 10 pM with R2 of 0.9987. The limit of detection was 10 pM, and the signal-to-noise ratios (SNRs) ranged from 1.12 at 1 pM to 11.52 at 1 nM. The intra-chip coefficients of variation remained between 0.70% and 2.47%. Beyond clinical diagnostics, this platform holds promise for pharmaceutical applications, including drug development, pharmacokinetic/pharmacodynamic profiling, and therapeutic drug monitoring, where reliable small-molecule detection is increasingly required. This work, therefore, offers a straightforward, label-free route to picomolar DA detection with a clear path toward real-sample validation and selectivity assessment.
As the need for rapid data transmission and dependable wireless networks grows, so does the need for advanced antenna technology. This has become a major focus of modern communication technologies. This paper describes the design of a 4-port multiple-input multiple-output (MIMO) microstrip patch working at 28 GHz in the Ka-band. This antenna is fabricated on a substrate measuring 21 & times; 21 & times; 3.97 mm3, composed of FR4, foam, and RT/Duroid 5880. It uses a microstrip feed. Performance enhancements are achieved by positioning the feeds orthogonally, incorporating a U-shaped slot into the MIMO antennas, and implementing a metamaterial (MTM) superstrate. Additionally, a single-layer MTM superstrate with rectangular slots is created to improve gain while keeping good impedance matching. The design process systematically improves gain and mutual coupling while keeping the overall size compact. The specific challenge addressed by the design is to improve peak gain and radiation efficiency by employing MTM elements operating at 28 GHz. The 4-port MIMO antenna achieves an impedance bandwidth (IB) of 27.11-29.21 GHz, with a peak gain of 14.5 dB, respectively. This antenna is used in next-generation communication systems, vehicular networks, and 5G systems.
This research proposes a microwave sensor based on a dual-split-ring-resonator (DSRR) structure designed for the detection of the permittivity of solid samples and defective materials. The DSRR structure was chosen because it has a high-quality factor Q, is highly sensitive to changes in permittivity, and is easy to integrate into a planar substrate. The designed sensor is fabricated using a Rogers RO5880 substrate having a dielectric constant epsilon r of 2.2, tan delta of 0.0009, and a substrate thickness h of 1.58; the sensor operates in the frequency range of 1 GHz-2 GHz and adopts a dual-port configuration by observing changes in the transmission parameter S21. The measurements used the perturbation theory method, where the resonance frequency shift occurs when a material is inserted into the sensor area. This sensor area is defined as the location of maximum electric-field concentration within the resonator. Polynomial equations are derived for measurements on dielectric materials with known permittivity values ranging from 1 to 9.8. The proposed sensor demonstrates high performance, with a measured accuracy of 99.6%, a normalized sensitivity of 2.6%, and a frequency detection resolution (FDR) of 0.026 GHz. These results indicate that the sensor using the DSRR method with hole integration offers reliable and precise permittivity detection, particularly for detecting defects in materials.
This study presents a broadband, switchable, and bifunctional terahertz device based on the phase transition of vanadium dioxide (VO2). When VO2 is in the metallic state, the device operates as a linear polarization converter (LPC). When VO2 transitions to the insulating state, the device functions as a broadband linear-to-circular polarization converter (LTC-PC). Numerical simulations are conducted to verify the device performance. To further optimize metamaterial performance and accelerate the design process, a deep learning framework that integrates convolutional neural networks (CNNs) and the Transformer architecture via an adaptive mechanism is proposed. Numerical simulations indicate that this LPC achieves a polarization conversion ratio (PCR) exceeding 90% across the 1.92-2.93 THz band and maintains angular stability for incidence angles up to 50 degrees. The LTC-PC operates effectively within the 2.40-4.33 THz range. Featuring broadband operation and bi-functional capabilities, the converter holds significant potential for applications in terahertz imaging, sensing, solar energy harvesting, and communications.
This work presents deep neural networks for the inverse design of an ITO-film angular-selective metasurface absorber. A tandem deep neural network (T-DNN) framework is developed for the inverse design of electromagnetic metasurfaces. A forward network is first trained independently to learn the complex physical mapping between metasurface structures and their electromagnetic responses. An inverse network is then trained in tandem with the pre-trained forward network, eliminating conventional parameter-by-parameter tuning and establishing a performance-driven pipeline that directly maps target electromagnetic responses to structural parameters. Using the trained network, several metasurface absorbers with distinct angular sensitivities are rapidly designed, and their angle-dependent applications are preliminarily investigated. Results show that deep learning enables the fast design of metasurface absorbers customized to realistic incident angle distributions, yielding efficient omnidirectional radar cross-section (RCS) reduction at sensitive angles. This work offers a new strategy for the fast design of omnidirectional scattering suppression.
This paper presents a wideband four-port microstrip antenna operating from 2.75 GHz to 6.75 GHz with frequency reconfigurability and controllable notch characteristics. The antenna employs an asymmetric radiating structure to realize circular polarization around 5.5 GHz, while multilayer graphene (MLG) pads are introduced to enable bias-controlled frequency tuning and adjustable band rejection. The four-port configuration, implemented on an RT/Duroid 5880 substrate (epsilon r = 2.2, thickness = 1.6 mm), achieves inter-element isolation better than 20 dB without additional decoupling structures. The proposed design also exhibits strong diversity performance with an envelope correlation coefficient below 0.02 and diversity gain above 9.97 dB. The results demonstrate that the proposed antenna provides a compact and low-complexity solution for wideband and reconfigurable sub-6 GHz wireless communication applications.
An improved S-parameter extraction method, based on the forward and backward propagating waves under oblique incidence on metamaterials (MMs), is proposed to accurately extract electromagnetic parameters for asymmetric uniaxial MMs in a broad frequency range. The proposed approach equivalently models asymmetric MMs as two isotropic media (distinct from the 3 & times; 3 matrix-form anisotropic medium). To validate the effectiveness of the proposed method, a low-thickness asymmetric absorptive frequency-selective surface (AFSS) and a high-thickness 7-layer absorber are designed, simulated, and analyzed.
To meet the stringent space constraints and diverse connectivity requirements of modern intelligent connected vehicles, a compact MIMO antenna system designed for microwave and millimeter-wave (mm-wave) vehicle-to-everything (V2X) communications is presented. The proposed antenna features a compact footprint adaptable for integration into space-limited automotive modules, such as shark fin antenna housings. By employing a structure reuse technique, the system integrates a four-element microwave MIMO array and two orthogonal mm-wave phased arrays within a size of 30 mm & times; 30 mm & times; 2 mm. In the microwave band, a parasitic patch is introduced to achieve dual-mode resonance, ensuring a wide bandwidth for reliable control signaling. Two orthogonal rows of metallized cavities serve a dual purpose: acting as decoupling structures for the microwave MIMO system and functioning as mm-wave arrays to enable two-dimensional beam scanning. This capability is crucial for overcoming blockage effects in dynamic vehicular environments. Experimental results demonstrate that the proposed antenna achieves wide coverage in the microwave band (4.62-5.11 GHz) and high-gain beam scanning (+/- 40 degrees) in the mm-wave band (25.8-30.4 GHz). The measured isolation exceeds 17 dB with an envelope correlation coefficient below 0.11, validating its suitability for next-generation vehicle terminals.
A compact, double split-ring H-shaped resonator-based polarization-independent dual-band metamaterial microwave absorber (MMA) with an outstanding absorption efficiency was designed and analyzed for satellite communication applications. The H-shaped resonator-based unit cell was printed on an FR4 material using copper as the conducting material. Copper material was chosen for the radiating patch and the ground plane. A detailed parametric analysis was performed by tuning the geometrical parameters of the H-shaped MMA to achieve dual absorption bands with broad bandwidth and high absorptivity. The recommended H-shaped absorber exhibits dual absorption bandwidths of 710 MHz and 1630 MHz with FBWs of 22.95% and 19.35%. Furthermore, it maintains an absorptivity of greater than 90% across the entire spectrum of dual operating bands with almost perfect absorption of 99.99% at the resonant frequencies (3.17 GHz, 7.78 GHz) of each band. The MMA maintains an area of 0.09 lambda & times; 0.09 lambda. A simulated absorber model was fabricated, and the results have been tested using an Anritsu Combinational Analyzer (MS2037C) for experimental validation. The simulated and tested outcomes of the developed prototype are in strong alignment, rendering the absorber suitable for S-band and LEO and geostationary satellite uplinks/downlinks, with specific bands often at 7.145-7.235 GHz (uplink) and 8.4-8.5 GHz (downlink).
Long-range wireless power transfer (WPT) is difficult with unguided radio waves or magnetic coupling. In this work, a plasma-assisted quasi-parallel planar waveguiding medium is proposed for overcoming the transmission range issues. Method: A dielectric layer sitting on a conductive object or grid was used as a medium for WPT. At the transmitting end, a plasma ball shielded with a spark-gap activated hemispheric metal cap was used to ionize the air in the space, thereby forming the top cladding layer of the quasi parallel-plate waveguide. At the receiving end, the transmitted power was coupled out of the waveguide over the entire ultrasonic spectrum using Avramenko diode configurations. A Kretschmann-like configuration was used at both ends for conversion between a plasmonic current and the surface waves. Results: In the proposed experimental setups, the transmitted power was successfully harvested over a frequency range from near DC to 230 MHz, with the ratio of the received power to the transmitted power significantly surpassing the value predicted by the Friis' two-ray ground reflection model. Conclusion: WPT based on surface waves is technically feasible with the help of Kretschmann-like configurations.
This study presents a method which improves the accuracy of Preisach model that is able to reproduce the magnetic response of ferromagnetic material to change of magnetic fields, especially at higher frequency. The approach consists in extending an existing model and uses mathematical tools like combining a closed-form Everett function for hysteresis modeling with the Monte Carlo integration method to approximate the Preisach function, making calculations faster and more reliable. To find the best settings for the model, two optimization techniques are used: genetic algorithms (GA) and artificial bee colony (ABC). The model is tested by comparing its predictions to real-world experimental data, and it shows excellent accuracy and efficiency. Between the two techniques, GA performs better in terms of precision and reliability, making it a good choice for solving complex problems in modeling magnetic behavior.
A circularly polarized (CP) millimeter-wave phased array antenna (PAA) is proposed for wide-angle scanning applications. The antenna is composed of radiating patches, coupling patches, and a ground plane. A single element consists of a centrally fed microstrip CP antenna with double arc-shaped slots, with a parasitic patch loaded on its top. A sequentially fed 2 & times; 2 subarray is constructed by arranging single elements in a specific orientation, and the central disc-ring structure is combined with a square ring patch structure based on the beam complementarity principle to broaden the beamwidth. Both simulations and measurements are performed on a 4 & times; 4 prototype array. The proposed antenna operates over a frequency band of 27.6-30.4 GHz, and 3 dB AR bandwidth covers working bandwidth. When the beam scans to +/- 60 degrees, the gain degradation relative to the boresight direction is only 1.1 dB, with the AR at the beam pointing angle maintained <= 3.5 dB. The proposed antenna boasts a compact size, facile fabrication process, and excellent wideangle scanning capability, and it provides a novel design paradigm and a practical solution for CP millimeter-wave wide-angle scanning PAA systems.
This research article presents a low-profile ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with enhanced isolation and wideband performance, employing polyimide as the substrate. The suggested configuration consists of two symmetric radiating elements incorporating rectangular and circular slots within a compact footprint of 36 & times; 21.1 & times; 0.1 mm3. To effectively suppress mutual coupling, a slot-based metamaterial-inspired defected ground structure (DGS) with a meandered profile is introduced between the antenna elements. In addition, inverted U-shaped stubs and optimally placed slots are integrated to form a stub-loaded decoupling network, further improving inter-element isolation across the UWB spectrum. The antenna exhibits resonant modes at 4.16 GHz (WLAN), 5.49 GHz (IoT and smart home applications), 7.54 GHz (satellite and point-to-point communications), and 11.61 GHz (high-resolution imaging and sensing), covering the 4-12 GHz frequency range. Predicted and tested outcomes present good agreement, with key MIMO performance parameters achieving Channel Capacity Loss (CCL) below 0.4 bits/s/Hz, diversity gain (DG) above 9.9 dB, Envelope Correlation Coefficient (ECC) below 0.005, and Total Active Reflection Coefficient (TARC) less than -10 dB. Owing to its compact size, wideband operation, and high isolation characteristics, the suggested antenna is a strong candidate for wireless area networks and emerging IoT-based sensing applications.
This study proposes a broadband, wide-angle metasurface for bistatic radar cross-section (RCS) reduction by integrating a low-profile bent-line unit design with an Adaptive Binary Particle Swarm Optimization algorithm enhanced by Array Pattern Synthesis (ABPSO-APS). The optimized metasurface achieves over 10 dB of bistatic RCS reduction across 8.4-21 GHz (86.7% fractional bandwidth), with a peak reduction of 22 dB, outperforming conventional checkerboard, genetic algorithm, and particle swarm optimization layouts by 22.82%, 15.27%, and 7.91%, respectively. The design also exhibits angular stability up to 30 degrees and polarization insensitivity under both TE and TM incidences, while maintaining an ultrathin profile of only 0.1 lambda (where lambda is the wavelength at the center frequency). These results demonstrate its strong potential as a compact and efficient solution for advanced electromagnetic stealth and radar signature control applications.
This study explores the anisotropic electromagnetic properties of carbon nanotube (CNT)/polylactic acid (PLA) nanocomposites, fabricated in-house and shaped using traditional compression molding and advanced 3D printing techniques. By examining the effects of CNT content (ranging over 1-4 wt.% (weight percent)) and 3D printing path orientation, this research investigates how these factors influence shielding effectiveness (SE) and the corresponding nanocomposite complex dielectric permittivity tensor. Notably, a significant variation in SE was observed between the different printing path orientations, with a difference of over 20 dB at 4 wt.% CNT. Experimental measurements were used to develop an anisotropic model for the complex dielectric permittivity, with the permittivity components for samples at 4 wt.% CNT extracted to be 36.5-j44.5 along the printing direction (epsilon parallel to) and 8.3-j3.1 in the perpendicular direction (epsilon perpendicular to) over the X-band frequency range (8.2-12.4 GHz). These findings demonstrate that CNT alignment during 3D printing induces highly directional electromagnetic properties. Furthermore, we demonstrate that anisotropic simulation models provide a more accurate prediction of the electromagnetic response of 3D-printed nanocomposite structures than isotropic models. In brief, this study emphasizes the necessity of considering anisotropic properties in the design and simulation of 3D-printed nanocomposites for electromagnetic shielding and other applications.
We present the design, fabrication, and experimental characterization of two 150 mm Luneburg lenses for X-band (10 GHz), produced by FFF (Fused Filament Fabrication) using standard PLA. The printed PLA permittivity was measured with a 7 mm coaxial cell and EpsiMu, yielding epsilon r,PLA approximate to 2.5 at 100% infill; a volume-weighted mixing model with perimeter correction was used to set discrete radial infill fractions. Two infill patterns (grid and gyroid) were tested, and waveguide mounts were integrated for reproducible alignment. Insertion-loss tests give 1.5 dB (grid) and 1.1 dB (gyroid) at 10 GHz. Far-field measurements (R = 1.5 m) and Friis-based estimates yield peak gains of 20.5 dBi (grid) and 19.4 dBi (gyroid) (simulation: 20.8 dBi); the waveguide reference gain is 4.9 dBi. Near-field tests at R = 0.15 m show an on-axis S21 improvement of +2.33 dB, which corresponds to a low apparent near-field aperture efficiency (1.8-2.3%) while far-field efficiencies inferred from the measured gains are substantially higher (35-45%). These results confirm that discrete infill grading in low-cost FFF-printed PLA can realize effective Luneburg lenses at X-band, with quantifiable trade-offs among insertion loss, infill geometry, and realized aperture efficiency.
