Antenna Response Research Articles

Generation and tuning of notched bands in wideband THz antennas using graphene/metal strips

Abstract A technique is implemented for obtaining tunable band notch/filtering features in terahertz (THz) monopole wideband antennas. A parasitic metal strip is engraved in the antenna radiator, which creates the band notch characteristics in the wideband response. The tunability of the created notched band can be obtained by engraving a non-resonant U-shaped graphene strip in the radiator. The change in the material properties of the graphene strip alters the nature of field confinement in the antenna structure, enabling tunability in the filtering frequency band. Moreover, multiple notch bands can be obtained by carefully selecting the material of the parasitic element U-shaped graphene strip. Thus, the antenna response can be configured for dual- and triple- band filtering operation by varying the materials used for the strips to obtain band notch operation and a U-shaped graphene sheet.

Reconfigurable super‐low‐frequency magnetoelectric antenna for underwater frequency‐hopping communication

AbstractBased on the mechanical regulation mechanism, a super‐low‐frequency (SLF) reconfigurable magnetoelectric (ME) antenna is proposed for underwater frequency‐hopping communication. By constructing the mechanical model of the ME antenna loaded with an adjustable spring, the antenna's working frequency is predicted to be tuned in an extensive dynamic range from 148 to 331 Hz by changing the states of a loaded spring. The experiment is implemented in the frequency‐response test platform and the practical communication system using the minimum shift keying modulation. The former experiment well validates the tunable frequency response of the reconfigurable ME antenna, while the latter successfully achieves the information transmission at different working frequencies. The proposed SLF reconfigurable ME antenna serves as a potential candidate for under‐water frequency‐hopping communication.

Machine Learning-Aided Dual-Function Microfluidic SIW Sensor Antenna for Frost and Wildfire Detection Applications

In this paper, which represents a fundamental step in ongoing research, a new smart low-energy dual-function half-mode substrate integrated waveguide cavity-interdigital capacitor (HMSIWC-DIC) antenna-based sensor is developed and investigated for remote frost and wildfire detection applications at 5.7 GHz. The proposed methodology exploits the HMSIW antenna-based sensor, a microfluidic channel (microliter water channel (50 μL)), interdigital capacitor technologies, and the resonance frequency parameters combined with machine learning algorithms. This allows for superior interaction between the water channel and the TE101 mode, resulting in high sensitivity (∆f/∆ε = 5.5 MHz/ε (F/m) and ∆f/∆°C = 1.83 MHz/°C) within the sensing range. Additionally, it exhibits high decision-making ability and immunity to interference, demonstrating a best-in-class sensory response to weather temperature across two ranges: positive (≥0 °C, including frost and wildfire) and negative (<0 °C, including ice accumulation). To address the challenges posed by the non-linear, unpredictable behavior of resonance frequency results, even when dealing with weak sensor antenna responses, an innovative sensory intelligent system was proposed. This system utilizes resonance frequency results as features to classify and predict weather temperature ranges into three environmental states: Early Frost, Normal, and Early Wildfire, achieving an accuracy of 96.4%. Several machine learning techniques are employed, including artificial neural networks (ANNs), random forests (RF), decision trees (DT), support vector machines (SVMs), and Gaussian processes (GPs). This sensor serves as an ideal solution for energy management through its utilization in RF-based weather temperature sensing applications. It boasts stable performance, minimal energy consumption, and real-time sensitivity, eliminating the necessity for manual data recording.

Antenna optimization using machine learning with reduced-dimensionality surrogates

In modern times, antenna design has become more demanding than ever. The escalating requirements for performance and functionality drive the development of intricately structured antennas, where parameters must be meticulously adjusted to achieve peak performance. Often, global adjustments to geometry are necessary for optimal results. However, direct manipulation of antenna responses evaluated with full-wave electromagnetic (EM) simulation models using conventional nature-inspired methods entails significant computational costs. Alternatively, surrogate-based techniques show promise but are impeded by dimensionality-related challenges and nonlinearity of antenna outputs. This study introduces an innovative technique for swiftly optimizing antennas. It leverages a machine learning framework with an infill criterion employing predicted enhancement of the merit function, utilizing a particle swarm optimizer as the primary search engine, and employs kriging for constructing the underlying surrogate model. The surrogate model operates within a reduced-dimensionality domain, guided by directions corresponding to maximum antenna response variability identified through fast global sensitivity analysis, tailored explicitly for domain determination. Operating within this reduced domain enables building dependable metamodels at a significantly lower computational cost. To address accuracy loss resulting from dimensionality reduction, the global optimization phase is supplemented by local sensitivity-based parameter adjustment. Extensive comparative experiments involving various planar antennas demonstrate the competitive operation of the presented technique over machine learning algorithms operating in full-dimensionality space and direct EM-driven bio-inspired optimization techniques.

Study on the Conductivity Effect on the Characteristics of a Wideband Printed Dipole Antenna Implemented with Silver Nanoparticle Ink

This study examined a flexible composite wideband dipole antenna implemented with conductive silver nanoparticle ink having different conductivities. Two identical split ring resonators (SRRs) were designed to encompass each arm of a dipole element, and each dipole arm and its coupled SRR were printed on the top and bottom sides of a dielectric substrate. The overall dimensions of the compact antenna were 10 mm × 74.8 mm × 0.254 mm (0.053λo × 0.399λo × 0.0014λo at 1.6 GHz). The characteristics of the antenna with different conductivities were numerically investigated and experimentally confirmed. Our investigation aimed to ascertain the proposed antenna's response to different conductivity values and to determine the range of conductivity values that generates major changes in the antenna's performance characteristics in terms of impedance bandwidth, gain, and radiation efficiency. At conductivity values less than approximately 6.0 × 104 S/m, the number of generated resonances changed from three to two, and the antenna experienced a nearly 3-dB gain reduction when the conductivity approached 5.8 × 104 S/m.

Spectral redundancy for calibrating interferometers and suppressing the foreground wedge in 21 cm cosmology

ABSTRACT Observations of 21 cm line from neutral hydrogen promise to be an exciting new probe of astrophysics and cosmology during the Cosmic Dawn and through the Epoch of Reionization (EoR) to when dark energy accelerates the expansion of our Universe. At each of these epochs, separating bright foregrounds from the cosmological signal is a primary challenge that requires exquisite calibration. In this paper, we present a new calibration method called nucal that extends redundant-baseline calibration, allowing spectral variation in antenna responses to be solved for by using correlations between visibilities measuring the same angular Fourier modes at different frequencies. By modelling the chromaticity of the beam-weighted sky with a tunable set of discrete prolate spheroidal sequences, we develop a calibration loop that optimizes for spectrally smooth calibrated visibilities. Crucially, this technique does not require explicit models of the sky or the primary beam. With simulations that incorporate realistic source and beam chromaticity, we show that this method solves for unsmooth bandpass features, exposes narrow-band interference systematics, and suppresses smooth-spectrum foregrounds below the level of 21 cm reionization models, even within much of the so-called wedge region where current foreground mitigation techniques struggle. We show that this foreground subtraction can be performed with minimal cosmological signal loss for certain well-sampled angular Fourier modes, making spectral-redundant calibration a promising technique for current and next-generation 21 cm intensity mapping experiments.

Meander-Lined Implantable Antenna Design at 2.45 GHz Using Transmission Line Model

Scientists mostly follow a trial-and-error approach using simulators for designing implantable antennas which may increase time complexity and memory usage. In this article, the Transmission Line Model (TLM) is utilized to design a miniaturized meander-line implantable antenna at 2.45 GHz for reducing time and memory requirements. The meander-line antenna is first decomposed into different segments – x-directed, y-directed, and bends. Each segment is considered a transmission line and each line is replaced by its equivalent lumped LC network. The lumped parameters are calculated using the dimensions of the segment and guided wavelength inside the body. Here, a three-layered body model is represented by a T-type resistor, inductor and capacitor (RLC) network. The antenna within the human body is then simulated using Finite Element Method (FEM)-based CST Microwave Studio software. FEM technique is taking 4.94-MB memory space and 13-minutes time to analyze this implanted system whereas TLM is analyzing the same system by considering 726-KB memory within 52 s. TLM is predicting implanted antenna performance considering ∼0.8% error concerning simulated response. The designed antenna is fabricated and measured within a homogeneous body phantom and minced pork to verify the simulated response. The effect of chamfering of the corners of the meander-line antenna is also analyzed here. From this study, it is observed that TLM can predict implantable antenna response efficiently with low memory and less time requirement with respect to FEM which is helpful for antenna engineers. Analysis of implantable antenna with low memory and time requirements using TLM is a novel approach to this work.

Fast EM-driven nature-inspired optimization of antenna input characteristics using response features and variable-resolution simulation models

Utilization of optimization technique is a must in the design of contemporary antenna systems. Often, global search methods are necessary, which are associated with high computational costs when conducted at the level of full-wave electromagnetic (EM) models. In this study, we introduce an innovative method for globally optimizing reflection responses of multi-band antennas. Our approach uses surrogates constructed based on response features, smoothing the objective function landscape processed by the algorithm. We begin with initial parameter space screening and surrogate model construction using coarse-discretization EM analysis. Subsequently, the surrogate evolves iteratively into a co-kriging model, refining itself using accumulated high-fidelity EM simulation results, with the infill criterion focusing on minimizing the predicted objective function. Employing a particle swarm optimizer (PSO) as the underlying search routine, extensive verification case studies showcase the efficiency and superiority of our procedure over benchmarks. The average optimization cost translates to just around ninety high-fidelity EM antenna analyses, showcasing excellent solution repeatability. Leveraging variable-resolution simulations achieves up to a seventy percent speedup compared to the single-fidelity algorithm.

Split ring resonator geometry inspired crossed flower shaped fractal antenna for satellite and 5G communication applications

This work suggests a fractal antenna in the shape of a crossed flower with a split ring resonator geometry. This suggested antenna serves the Sub-6 GHz 5G and satellite repeater applications for wireless devices operating in the frequency range of 4.01–4.82 and 7.6–7.94 GHz, respectively. The suggested antenna's performance parameters have been empirically confirmed by creating a printed prototype. The antenna geometry is based on a lower-cost FR4 substrate and consists of a mix of crossed floral square-shaped split-ring resonators organized in a Minkowski fractal configuration. A thorough examination of both manufactured and simulated antennas is conducted to demonstrate the uniqueness and edge over traditional dual-band antennas. The suggested fractal antenna's overall physical dimensions measure 0.90λ x 0.96λ at a lower resonant frequency. The response of the unit cell antenna is recorded when Split Ring Resonators are grouped in a fractal antenna with a flower shape. The measured findings verify that the proposed and constructed antenna has an electrical impedance bandwidth of −10 dB at lower frequency band (18.80 %, 4.01–4.82 GHz) and upper frequency band (4.41 %, 7.6–7.94 GHz) of −10 dB. The simulated and fabricated prototypes exhibit good agreement with respect to the stable gain and radiation patterns. Because of its consistent radiation efficiency in the realized resonating bands, the suggested prototype is a strong contender for 5G Sub-6 GHz and X band satellite applications.

Flexible and Wearable Antenna Design for Bluetooth and Wi-Fi Application

The emergence of wearable technology has revolutionized the way we interact with electronic devices, integrating them into our daily routines. From fitness trackers, smart watches to augmented reality glasses and medical monitoring devices, wearable have become increasingly prevalent. Among the most commonly employed wireless technologies within wearables are Bluetooth and Wi-Fi. The design of efficient and reliable antennas for Bluetooth and Wi-Fi applications in wearable is of paramount importance to ensure optimal performance and user satisfaction. In this paper presented a flexible and wearable antenna design for Bluetooth and Wi-Fi application utilizing the Rogers RT5880 flexible substrate, characterized by a dielectric constant of 2.2 and a thickness of 20mil. The study delves into various analyses of the antenna, including its performance concerning on-body and off-body communication, along with an exploration of the antenna's response to different bending effects. Moreover, the research investigates how the antenna interacts with a human tissue model, providing insights into its behavior and performance in diverse usage scenarios.

Ultra-conformal epidermal antenna for multifunctional motion artifact-free sensing and point-of-care monitoring

Accurate acquisition of physiological and physical information from human tissue is essential for health monitoring, disease prevention and treatment. The existing antennas with traditional rigid or flexible substrates are susceptible to motion artifacts in wearable applications due to the miniaturization limitation and lack of proper adhesion and conformal interfaces with the skin. Recent advances in wearable radio frequency (RF) bioelectronics directly drawn on the skin are a promising solution for future skin-interfaced devices. Herein, we present a first-of-its kind epidermal antenna architecture with skin as the antenna substrate, which is ultra-low profile, ultra-conformal, ultra-compact, and simple fabrication without specialized equipment. The radiation unit and ground of antenna are drawn directly on the skin with the strong adhesion and ultra conformality. Therefore, this RF device is highly adaptable to motion. As a proof-of- feasibility, epidermal antenna can be freely drawn on demand at different locations on the skin for the development of temperature sensor, skin hydration sensor, strain sensor, glucose sensor and other devices. An epidermal antenna-based temperature sensor can offer accurate and real-time monitoring of human body temperature changes in the ultra-wideband (UWB) range. The results during the monitoring of hydration level with and without stretching show that the epidermal antenna drawn on the skin is motion artifact-free. We also designed an epidermal antenna array employing a horseshoe-shaped configuration for the precise identification of various gestures. In addition, the non-invasive blood glucose level (BGL) monitoring results during the in-vivo experiments report high correlation between the epidermal antenna responses and BGLs, without any time hysteresis. After the prediction of BGL by BP network, all the predicted BGL values are fallen 100% into the clinically acceptable zones. Together, these results show that epidermal antenna offers a promising new approach for biosensing platform.

On Accelerated Metaheuristic-Based Electromagnetic-Driven Design Optimization of Antenna Structures Using Response Features

Development of present-day antenna systems is an intricate and multi-step process requiring, among others, meticulous tuning of designable (mainly geometry) parameters. Concerning the latter, the most reliable approach is rigorous numerical optimization, which tends to be resource-intensive in terms of computing due to involving full-wave electromagnetic (EM) simulations. The cost-related issues are particularly pronounced whenever global optimization is necessary, typically carried out using nature-inspired algorithms. Although capable of escaping from local optima, population-based algorithms exhibit poor computational efficiency, to the extent of being hardly feasible when directly handling EM simulation models. A popular mitigation approach involves surrogate modeling techniques, facilitating the search process by replacing costly EM analyses with a fast metamodel. Yet, surrogate-assisted procedures feature complex implementations, and their range of applicability is limited in terms of design space dimensionality that can be efficiently handled. Rendering reliable surrogates is additionally encumbered by highly nonlinear antenna characteristics. This paper investigates potential benefits of employing problem-relevant knowledge in the form of response features into nature-inspired antenna optimization. As demonstrated in the recent literature, re-formulating the design task with the use of appropriately selected characteristic locations of the antenna responses permits flattening the functional landscape of the objective function, leading to faster convergence of optimization procedures. Here, we apply this concept to nature-inspired global optimization of multi-band antenna structures, and demonstrate its relevance, both in terms of accelerating the search process but also improving its reliability. The advantages of feature-based nature-inspired optimization are corroborated through comprehensive (based on three antenna structures) comparisons with a population-based search involving conventional (e.g., minimax) design problem formulation.

Eight element dual-band MIMO array antenna for modern fifth generation mobile phones

In this paper, an eight-element multiple-input multiple-output (MIMO) antenna with dual-band response is designed for fifth-generation (5G) mobile devices. The proposed MIMO systems’ radiators are placed in the inner side frame of the mobile phone board, which has a size of 150 × 7 mm2, each spanning an area of 21.5 × 5.5 mm2. All eight antenna elements are symmetrical to each other and are fed with a 50Ω feeding line. The proposed MIMO antenna covers two distinct 5G frequency bands, i.e., 3.5 and 5.3 GHz, and offers −6 dB impedance bandwidth in a frequency range of 3.4–3.65 and 4.8–5.8 GHz. It is worth mentioning that an isolation of more than 18 dB is achieved over the bands of interest without the use of a decoupling network. Similarly, the proposed MIMO antenna achieved an efficiency of more than 60% across the bands, an envelope correlation coefficient (ECC) below 0.04, antenna gain better than 5 dBi, a mean effective gain (MEG) between any two radiating elements found to be better than 3 dB, and a channel capacity (CC) above 38.5 bps/Hz, which is three times better compared to a 2 × 2 MIMO antenna system. Upon fabrication and testing of the proposed antenna, it was noted that the measured results are in good agreement with the simulated data. Furthermore, the MIMO antenna response was simulated in the presence of a human user and shows how the user phantom affects the radiation characteristics of the MIMO antenna. These performance parameters showed promising results, making the proposed design a better option to be deployed in modern-day 5G communication application scenarios, specifically cell phones.

Impact dynamic response of large aperture space deployable antenna supporting structures based on a dual-scale model

This study investigates the joint damage patterns and changes in shape accuracy of large aperture space deployable antenna supporting structures subject to hypervelocity impacts from micro space debris. Based on the dual-scale method, a joint scale model is constructed for a hexagonal prismatic space deployable truss antenna supporting structure with an aperture of six meters and 37 modules. ANSYS/AUTODYN is used for the impact damage analysis, with an equivalent model of impact force integrating the structure's actual damage characteristics in the structure scale model. The dynamic response and deformation performance of the antenna supporting structure under impact velocities from 2.5 to 15.0 km/s, with spherical space debris of 2.5 mm and 5.0 mm diameters, impacting modular central points in both positive and negative directions, are analyzed. The results show that the primary damage to the joint scale model after impact includes cratering, perforation, punch failure, and joint failure. The debris diameter significantly influences joint damage and deformation of the bolt hole diameter. Additionally, the debris cloud post-impact significantly affects the vertical bar's inner wall, spalling the wall and reducing the rod's strength. As the impact point moves towards the structure's centroid, the antenna's overall response increases. With higher impact velocities, the antenna supporting structure's overall deformation first increases, then decreases. At an impact velocity of 12.5 km/s, the impact area of the structure gradually reduces post-impact. Our proposed joint damage forms and three-case damage classification (no effect, repairable, and joint failure) may serve as a valuable reference for designing structural protection and impact identification for space deployable antennas.

Equivalent Circuits of Dipole Antennas for Broadband Applications

In this paper distributed parameter equivalent circuits are developed for linear dipoles, dielectric coated dipoles and lumped loaded dipoles. Theoretical solutions for each distributed parameter and the reasonable non-uniform segmentation of antennas serve as the foundation for the derivation. The accomplished validations of the modeling procedures indicate that the given equivalent circuits are capable of correctly describing dipole antennas in frequency and time domains, with the advantages of wideband, frequency independence and unambiguous physical meaning. Relying on the presented equivalent circuits, broadband issues such as simulating input impedance, predicting equivalent lengths and computing transient responses of dipole antennas can be readily addressed. In addition, the circuit model provides helpful insights into the analysis and design for the loaded dipole antennas.

Incident angle dependent tunable multiband infrared absorption based sensor

The effect of electromagnetic (EM) resonance in the graphene resonator and multiple reflections taking place in the dielectric spacer can provide the multiband infrared absorption. The intensity of resonance spectrum occurring due to the formation of EM dipoles in resonator can be controlled by patterning it using desired perturbation. The absorber response can be set with the multiple narrow and broad absorption peaks together by modulating the electrical properties of graphene material. The proposed absorber provides the incident angle dependent behavior with linear variation in the resonant wavelengths by maintaining the high absorption. This can provide a new way of tuning the antenna response by angle of incidence. The implemented absorber can provide the triple narrow bands which can be utilized for performing the refractive index sensing. The proposed absorber provides a significant value of sensing performance parameters including sensitivity, full-width-half-maxima, and figure-of-merit with the high value of quality factor. Moreover, the proposed absorber offers the ability of generating an extra narrow absorption band in the case of presence of sensing analyte of specific thickness and refractive index range making it highly sensitive for the detection of specific surroundings including the bio-cells, chemicals and humidity in the air. The broadband characteristics of the proposer absorber can be utilized in implementing the infrared EM shields and thermal storage components.

Identification and characterization of odorant receptors in Plutella xylostella antenna response to 2,3-dimethyl-6-(1-hydroxy)-pyrazine

Diamondback moth (Plutella xylostella), a worldwide migratory pest that is developing strong resistance to various chemical insecticides. It has been determined that four natural pyrazines isolated from Allium tuberosum showed significant repellent activity to P. xylostella, but the molecular target still unknown. In the present study, a novel synthetic route for 2,3-dimethyl-6-(1-hydroxy)-pyrazine which has the most significant repellent activity with a purity of 90.60% was established. Simultaneously, the bioassay result declared that the repellent grade was IV at a dosage of 0.01 mg which was the same as to the published data. Transcriptomics analysis detected 1643 upregulated and 3837 downregulated genes in P. xylostella antennae following this pyrazine exposure. Then, 2142 differentially expressed genes were annotated using Gene Ontology and 2757 genes were annotated by Kyoto Encyclopedia of Genes and Genomes. Moreover, this procedure identified 84 odour perception-related genes, 58 odorant receptor (OR) genes including 57 conventional ORs and the odorant receptor co-receptor (Orco, atypical odorant receptor) gene, and 26 odorant-binding protein (OBP) genes. Based on quantitative real time PCR (RT-qPCR) and differential expression results, 9 OR genes including the Orco were cloned and characterised. In summary, this study provides important basis for the utilization of pyrazines as the main active ingredients or lead compounds to developing new botanical pesticides, which will reduce application of chemical pesticides and postpone the development of resistance.

Probing the electromagnetic response of dielectric antennas by vortex electron beams

Probing the electromagnetic response of dielectric antennas by vortex electron beams

Graphene based two-port MIMO yagi-uda antenna for THz applications

- This paper explores the concept of multi-input-multi-output (MIMO) antenna at terahertz (THz) frequency ranges. The proposed structure of a graphene-based two-port MIMO Yagi-Uda antenna comprises of the four-sets of array elements fed in pairs with the respective ports kept on a semi-circular graphene ring. The driven elements are excited through the vias to the graphene ring. The antenna provides the resonant frequency at 6.505 THz with the gain 5.85 dB and directivity 9.42 dBi. The isolation within the ports is maintained below −15 dB in the operating passband. The proposed antenna operation validates the existence of the higher-order TE61 mode. Further, the MIMO execution parameters including mean effective gain (MEG), envelop correlation coefficient (ECC), Total active reflection coefficient (TARC), and diversity gain (DG) have been studied and a reasonable agreement with the results is obtained. Later, parametric analysis is done for analyzing the sensitivity of the compact dimensions and tuning of the antenna response.

Improving the isolation of a tunable terahertz multi-input-multi-output dielectric resonator antenna using graphene coating

A technique is developed for enhancing the isolation between the ports of a terahertz (THz) dielectric resonator (DR) antenna (DRA) with two ports and single radiator. A two-port DRA provides the isolation of 6.88 dB which is further enhanced to 16.78 dB by inserting a circular slot in the ground plane of this antenna structure. The sidewalls of the DR at opposite to the source ends are then coated with the graphene material which enhances the value of isolation between the ports up to 25.05 dB. The coating of top surface of DR with graphene material enhances the isolation up to 35.10 dB. Coating of graphene material at all the open surfaces of the DR can enhance the isolation up to 63.06 dB. The frequency response of antenna can be tuned by applying the electrostatic field on the graphene coating at top surface of the DR. Moreover, the multi-input-multi-output performance parameters like envelope correlation coefficient and diversity gain remains less than 0.06 and 9.8 in the passband. The orthogonal feed arrangement used in the antenna structure can provide the polarization diversity.