Half-wave Dipole Research Articles

Stochastic Analysis of Epithelial/Absorbed Power Density in Multilayered Planar Skin Model With Uncertain Tissue Electric Properties

AbstractStochastic analysis of the absorbed power density (APD) on skin surface exposed to radiation of halfwave dipole at 10, 30 and 90 GHz and for different antenna‐body distances is presented. Skin tissue is modeled as a half‐space consisting of one layer (skin) or three layers (skin, fat and muscle) whose permittivities and conductivities are uncertain. Deterministic part is based on numerical solution of Pocklington equation via Galerkin Bubnov Indirect Boundary Element method (GB‐IBEM) and numerical integration of the corresponding field integrals. Uncertainty from tissue electric parameters is propagated to APD via non‐intrusive Stochastic Collocation method (SCM) in order to compute stochastic moments of APD. For 1‐layered model APD stochastic moments are computed with 3 deterministic simulations. On the other hand APD mean and variance for 3 layered model are successfully computed with 13 deterministic simulations while skewness and kurtosis require 85 deterministic simulations. The ratio of APD standard deviation and mean decreases with frequency thus indicating that the uncertainty in the tissue electric properties has smaller effect on APD uncertainty at higher frequencies. Finally, sensitivity analysis carried out for both 1‐layered and 3‐layered models indicates the same conclusions. At 10 GHz skin permittivity and conductivity are the two most important parameters. However, as frequency increases the impact of skin conductivity prevails. This indicates that in frequency range 10–90 GHz the APD uncertainty quantification and sensitivity analysis can be carried out by using only 2‐dimensional stochastic model.

Textronic Capacitive Sensor with an RFID Interface.

This article presents an innovative combination of textile electrical circuits with advanced capabilities of electronic RFID sensors, indicating the revolutionary nature of the development of textronics, which is used in various areas of life, from fashion to medicine. A review of the literature relating to the construction of textronic RFID identifiers and capacitive textronic sensors is performed. Various approaches to measuring capacity using RFID tags are discussed. This article focuses on presenting the concept of a capacitive sensor with an RFID interface, consisting of a microelectronic part and a textile part. The textile part is based on the WL4007 material, where antennas and capacitive sensors are embroidered using SPARKFUN DEV 11791 conductive thread. The antenna is a half-wave dipole designed to operate at a frequency of 860 MHZ. The microelectronic part is sewn to the textile part and consists of a microcontroller, an RFID-integrated circuit and a coupling loop, placed on the PCB. The embroidered antenna is coupled with a loop on the microelectronic module. This article focuses on presenting various designs of textronic electrodes, enabling various types of measurements. Article presents capacitance measurements of individual sensor electrodes, made using a measuring bridge and a built RFID tag. The sensors' capacity measurement results are shown.

Theoretical researches of the chiral metamaterial screen characteristics in the cellular radio

Metamaterial structures are currently being used to reduce the mutual influence of antennas and antenna arrays of different frequency ranges. In this work, the authors carried out studies of metamaterial screen designed for a resonant frequency of 900 MHz. The purpose of this work was the synthesis and theoretical studies of the characteristics of a screen made of chiral metamaterial in the cellular radio range. The results of studies were obtained to determine the natural resonant frequency of metamaterial screen when it is excited by a plane wave and a half-wave dipole. Frequency dependences of the isolation between two dipoles in the presence of metamaterial screen and without it were also obtained. It is shown that a metamaterial screen at the established resonant frequency provides an isolation of 25 dB. The screen synthesized and studied in this work can be used to reduce the influence of cellular radio antennas on other antennas present on a complex telecommunications objects.

Development and Field Testing of a Wireless Data Relay System for Amphibious Drones

Amphibious (air and water) drones, capable of both aerial and aquatic operations, have the potential to provide valuable drone applications in aquatic environments. However, the limited range of wireless data transmission caused by the low antenna height on water and reflection from the water surface (e.g., 45 m for vertical half-wave dipole antennas with the XBee S2CTM, estimated using the two-ray ground reflection model) persists as a formidable challenge for amphibious systems. To overcome this difficulty, we developed a wireless data relay system for amphibious drones using the mesh-type networking functions of the XBeeTM. We then conducted field tests of the developed system in a large marsh pond to provide experimental evidence of the efficiency of the multiple-drone network in amphibious settings. In these tests, hovering relaying over water was attempted for extension and bypassing obstacles using the XBee S2CTM (6.3 mW, 2.4 GHz). During testing, the hovering drone (<10 m height from the drone controller) successfully relayed water quality data from the transmitter to the receiver located approximately 757 m away, but shoreline vegetation decreased the reachable distance. A bypassing relay test for vegetation indicated the need to confirm a connected path formed by pair(s) of mutually observable drones.

Non-drude-like behavior of the photoinduced dielectric permittivity of GaAs and Si in the gigahertz range frequencies

A non-drude-like behavior of the real part of the photoinduced permittivity ReåP of GaAs and Si samples in the gigahertz range was detected by direct resonator measurements under conditions of fiber-optic irradiation at a wavelength of ë = 0.97 microns with power changes P in the range of 0÷1 W. It is shown that, in accordance with the hypothesis of the exciton mechanism of the photoinduced microwave dielectric permittivity, ReåP increases with increasing P (approaching saturation above P = 200 mW) instead of decreasing within the framework of free charge carriers by Drude. The generality of the behavior of the real parts of the photoinduced permittivity observed in semiconductors of different types (straight-band GaAs and non-straight-band Si) in different electrodynamic systems (waveguides, resonators, metastructures) testifying to the universality of the exciton mechanism is demonstrated. Optically controlled metastructures in the GHz band containing resonant electrically conductive elements loaded with GaAs and Si samples are proposed for the first time: a metastructure based on linear dipoles and a half-wave electric dipole based on a multi-pass spiral. Gigahertz responses of metastructures and the transformation of responses associated with changes in the dielectric permittivity of Si and GaAs during photoexcitation were measured for the first time. Based on the hypothesis put forward about the effect of excitons on photoexcitation, the observed saturation effect of gigahertz photoinduced permittivity is discussed.

The Influence of PE Initial Field Construction Method on Radio Wave Propagation Loss and Tropospheric Duct Inversion

Parabolic equations (PE) are commonly employed for calculating the spatial propagation loss of wireless signals. The initial field is a crucial factor. To investigate the impact of construction accuracy on the calculation of radio wave propagation loss, we selected the half-wave dipole antenna and its Gaussian approximation to examine the influence of wide-angle PE modeling. We analyzed the disparities between the actual antenna pattern and the Gaussian beam approximation, as well as the discrepancies in the corresponding initial field and the calculation of radio wave propagation loss in PE modeling. The simulation results indicate that the error of the Gaussian approximation increases as the angle of departure from the antenna main beam increases, with a relative error of approximately 30% in the initial field. A comparison between the experimental test of the broadcast signal and the simulation calculation reveals that the model based on the actual antenna aligns more closely with the measured value on a flat underlying surface. However, in mountainous areas with significant fluctuations, the simulation results are consistent with each other and higher than the measured value. The inversion results obtained through the particle swarm optimization algorithm demonstrate that the model based on the actual antenna exhibits superior inversion accuracy for the tropospheric atmospheric duct structure.

The method of images on lossless dielectric ground planes

This article is dedicated to the study of the images method, using half-wave dipoles on the dielectric ground plane, which is different from the widely known images method, which uses antennas on a ground plane (PEC). A review of the propagation models commonly used have been discussed. This paper presents a study of the images method at an air- dielectric ground plane interface. The experimental verification has been carried out by measuring the electric field as a function of distance, using half-wave dipole antennas for a frequency of 2.6 GHz, on a ceramic ground plane, for horizontal and vertical polarization. Ceramic floor at frequencies of f = 2.6 GHz can be considered a lossless dielectric media due to its negligible losses. The results of the images method have been modeled and discussed with a current image that has amplitude and phase for the dielectric ground plane.

Designing Smart Antennas Using Machine Learning Algorithms

Smart antenna technologies improve spectral efficiency, security, energy efficiency, and overall service quality in cellular networks by utilizing signal processing algorithms that provide radiation beams to users while producing nulls for interferers. In this paper, the performance of such ML solutions as the support vector machine (SVM) algorithm, the artificial neural network (ANN), the ensemble algorithm (EA), and the decision tree (DT) algorithm used for forming the beam of smart antennas are compared. A smart antenna array made up of 10 half-wave dipoles is considered. The ANN method is better than the remaining approaches when it comes to achieving beam and null directions, whereas EA offers better performance in terms of reducing the side lobe level (SLL). The maximum SLL is achieved using EA for all the user directions. The performance of the ANN algorithm in terms of forming the beam of a smart antenna is also compared with that of the variable-step size adaptive algorithm.

Homogeneous microwave near-field power focusing using a cylindrical antenna array

This paper presents an investigation of a microwave near-field power focusing (NFPF) analytical approach utilizing a cylindrical array of electric line sources along the z-axis, applicable to any arbitrary homogeneous linear medium. A novel parameter, termed the “focus ability” (FA), is introduced to quantitatively assess a method's capabilities in achieving power focusing. In the following, the phases and amplitudes of the excitation signals of the array elements are obtained with optimization to maximize FA over a certain studied area. Each stage of the theoretical analysis is supported through COMSOL full-wave simulations, ensuring the validity of the results. Theoretical results relevant to focused power are then compared to outcomes obtained from CST full-wave simulations with the same array configuration while employing half-wave dipole antenna elements with excitations obtained via optimization. These comparisons indicate that the excitation signals obtained by theoretical analysis can be used for power focusing when the array of half-wave dipole antenna sources is utilized. Furthermore, the proposed method leads to a significant reduction in the optimization time. Also, in the provided examples, the FA parameter and NFPF are investigated for the different conditions consisting of the type of the homogeneous medium and the number of antennas.

Design constrains in three configurations of UCAs for distortion free orbital angular momentum modes generation

In this article, three different configurations of the uniform circular array (UCA), i.e., unidirectional element array, radial array and tangential array of 4.5 GHz half-wave dipole antennas at different array radii and for the different number of elements are demonstrated. The minimum radius of UCA for three configurations is presented first time from the aspect of practical design and mutual coupling. An extensive analysis on the generation of different OAM modes using three configurations is presented. This results as major findings: first, generation of the higher order OAM modes (3,4,5…) with small radius of UCA is not possible even if the number of elements are higher (8,12…) and second, the generation of the lower order OAM modes (1,2) with large radius of UCA is not possible even the number of elements are lesser (3,4,6). Also, the minimum radius required and an optimal range of controlling factor (a/l) for the generation of distortion free OAM modes using three configurations of UCA is presented.

Monitoring of Surgically Treated Upper Arm Fracture by Implanted Antenna at 402 MHz

Remote patient monitoring aims to reduce non-essential visits to clinics and hospitals, monitor high-risk patients outside clinical settings, and optimize clinical staff utilization. This paper proposes a new monitoring application for surgically treated upper arm fractures. The humerus fracture should be healed within four to six weeks. Traditional monitoring is conducted through repeated X-ray images and visits to clinical laboratories or hospitals. Our goal is to avoid the expected drawbacks due to repeated exposure to X-rays, such as vomiting, bleeding, fainting, and sometimes the risk of cancer. Furthermore, this study aims to improve the patient’s quality of life during the treatment period by monitoring them at home. The technique depends on implanting a 116 mm length half-wave dipole antenna in the fractured arm and recording the reflection coefficient and the transmitted power at the far-field of it outside the body at 402 MHz. The fracture is represented by an extra layer added to the humerus, which increases the loss of electromagnetic field in the human tissue and then reduces the value of the transmitted power. The existence of fractures shows a change in the transmitted average power densities (APDs) in the range of 11.54% to 15.75%, based on the fracture types, and an increase in reflection coefficients in the range of −22.35 dB to −22.65 dB compared to the normal bone, which monitors the bone healing status. The standard limit of the specific absorption rate was taken into account to guarantee the safety of the human body. Different fracture types were considered and monitored, and CST Microwave Studio was used for simulation. The technique was verified experimentally by measurements carried out on a lifeless front leg animal model. The technique can also be used for the monitoring of ulna and tibia fractures.

Mutual impedance computation using spherical harmonics between two closely spaced antennas

Mutual coupling between two identical radiators is computed using vector spherical harmonics and reaction theorem for small element spacing cases. For closely spaced antennas, the minimum spheres that enclose the antennas overlap, and the vector spherical harmonic expansions do not converge on the surface that separates the two antennas. The proposed method mainly uses addition theorems to translate the vector spherical harmonic expansions to a different center. These operations on spherical waves enable to redefine the minimum spheres and convergence regions. The proposed method has been validated by analyzing the coupling between two half-wave dipoles in a side-by-side configuration. The results clearly show excellent agreement with that obtained from induced EMF method. The theory is also tested experimentally. A printed dipole antenna is designed, and its spherical harmonic coefficients are obtained by spherical near field measurement. Mutual impedance between two such dipoles is computed using the proposed method. The computed results for different element spacings in a side-by-side configuration are compared to those obtained from s-parameter measurements.

Conducting Polymer Switches Permit the Development of a Frequency-Reconfigurable Antenna

Conjugated polymers (CPs) undergo a wide range of reversible intrinsic property changes including electrical conductivity, electromagnetic absorption, volume, and charge mobility upon electrochemical oxidation/reduction, which has made them popular as ON/OFF organic-based switchable materials. Recent studies on the insulating-to-conductive transition within CPs have paved the way for a next generation of flexible switches that permit the creation of “dynamic” electric circuits. Here, we present an approach to a low-voltage, low-power electrochemically controllable, switchable, and printable CP-based conductive element that acts as a platform for the configuration of frequency-reconfigurable radiative antennas. We demonstrate that the DC conductivity of a soluble PEDOT derivative, PE2, film can be switched electrochemically by 4 orders of magnitude across large insulating gaps up to 15 mm within 20 s. Its integration in a DC switching element that is incorporated along the poles of a half-wave dipole antenna structure is able to generate an AC resonant frequency switch, and thus a radiation frequency shift, in the microwave (i.e., 1–2 GHz) range. This type of printable antenna fills an important need for the demand of bandwidth that is growing beyond the crowded frequency spectrum, by relying on the development of frequency-reconfigurable antenna systems capable of dynamically tuning their spectral properties when desired.

An effective beamformer for interference suppression without knowing the direction

<span>This paper proposes an effective beamformer for uniform linear arrays of half-wave dipole antennas based on binary bat algorithm (BBA) by controlling complex weights (both amplitudes and phases) excited at elements in an array. The proposed beamformer can impose adaptive nulls at interferences without knowing directions in the sidelobe region by minimizing the total output power of an array, whereas the main lobe and sidelobe levels are maintained. To demonstrate this capability, the proposal will be evaluated in several scenarios, compared to a beamformer based on binary particle swarm optimization (BPSO).</span>

Active manipulation of radiated fields by a magnetoplasmonic half-wave dipole nanoantenna.

We demonstrate a concept for the active manipulation of radiated fields by a magnetoplasmonic half-wave dipole nanoantenna. Our idea comprises a two arms nanoantenna, made of metallic ferromagnetic cobalt-silver alloy (Co6Ag94), inspired by the analogous radio frequency half-wave dipole antenna design. Numerical results, obtained under the magnetization saturation condition, indicate a tilting of the radiated beam depending on the magnitude and sense of the magnetization of the ferromagnetic material. Significantly, we obtained tilting angles as large as ±9.7∘ around the y axis for the magnetization placed along the x or z axes, respectively. Results in this work not only open up a new, to the best of our knowledge, way to dynamically manipulate the beam steering at the chip-scale, but also contribute to unveil novel magneto-optical effects at the nanoscale.

A new class of transformable kirigami metamaterials for reconfigurable electromagnetic systems

The rapid development of radio frequency (RF) components requires smart multifunctional materials that can adapt their physical shapes and properties according to the environment. While most current reconfigurable systems provide limited flexibility with high manufacturing cost, this research proposes to harness the transformable properties of kirigami-inspired multistable mechanical metasurfaces that can repeatedly deform and lock into different configurations to realize a novel class of low-cost reconfigurable electromagnetic structures with a broad design space. The metasurfaces are formed by designing kinematic-based unit cells with metallised coating that can provide adjustable resonant electromagnetic (EM) properties while rotating with respect to each other. Tailoring the cut length and geometry parameters of the patterns, we demonstrate programming of the topologies and shapes of different configurations. The influence of critical parameters on the structural multistability is illustrated by means of both a simplified energy model and finite element simulations. As examples of the reconfigurable electromagnetic devices that can be realized, we report the development of a tuneable half-wave dipole and two frequency selective surface (FSS) designs featuring isotropic and anisotropic responses. While the kirigami dipole can be tuned by mechanically stretching its arms, the FSSs exhibit distinct transmittance and reflectance spectra in each of the kirigami patterns stable states. The functionality of these kirigami devices is validated both by full-wave EM simulations and experiments. The proposed transformable structures can be mechanically actuated to tune the EM response in frequency or induce anisotropies for wave propagation.

Folded-Dipole Antenna Geometrical Analysis for THz Microbolometer

To improve the responsivity of terahertz (THz) antenna-coupled bolometer, heater (load) resistance has to be increased to suppress the thermal conduction and realize larger temperature rise of the thermistor. Proper design of antenna is therefore essential to assure the impedance matching between antenna and heater. From this viewpoint, a high-impedance folded-dipole antenna (FDA) has been studied numerically by the finite element simulation. The effect of FDA structural parameters such as number of arms, antenna width, and arm spacing are discussed with the lumped port and resistive heater coupled to the antenna gap for the cases of radiating and receiving modes, respectively. The product of resonant resistance and area efficiency is used to predict the improvement made by FDA as a figure of merit (FOM) correlated to the bolometer responsivity. This study revealed that the optimum FOM in FDA-coupled bolometer operating at 1 THz was obtained with three arms, 1-μm antenna width and 4-μm arm spacing. A comparison was made with the result from a half-wave dipole antenna and revealed that FDA could enhance the bolometer responsivity by a factor of 15. This research demonstrated the effectiveness of the FDA to improve the performance of THz antenna-coupled bolometer for applications such as imaging for non-destructive inspection.

Synthesis of Continuous Source Current for Gain Enhancement and Sidelobe Suppression of High-Order Mode Dipoles

A synthesis method of continuous source current on a high-order mode dipole is proposed to enhance gain and suppress sidelobe levels (SLLs) based on compression coefficients. First, a high-order mode dipole with the current distribution determined by designed compression coefficients is proposed to generate a typical continuous source. Then, a pattern synthesis method of continuous source current is presented to enhance gain with desired SLLs by calculating the compression coefficients. Finally, the fifth-order mode dipole is designed to verify the proposed synthesis method. Both measurement and theoretical prediction show the gain of 6.6 dBi and an SLL of −13.3 dB by the single dipole of the length of 1.5 wavelengths at 3.25 GHz. Compared with an array composed of three convention half-wave dipoles, the proposed fifth-order mode dipole of a similar length achieves a gain increase up to 1.13 dBi, or an effective length increases up to 30% while the SLL keeps unchanged.

Study of the Antenna System of the Marine Vessels Phase Radio Navigation System

Currently the antenna in the form of a half-wave dipole with a gain of about 2 dB is used in the ‘Krabik’ phase radio navigation system. To increase the range of the RNS of sea vessels, various options of more complex antenna systems are considered in the work, providing an increase in the gain compared to the existing antenna. It is shown that the most optimal solution is a collinear antenna with a gain of about 5 dB based on two wave vibrators.

Simulation of electric field response of horizontal circular electric half wave dipole antenna for seabed logging

Seabed logging (SBL) is a direct and remote application of controlled source electromagnetic (CSEM) method to detect hydrocarbon resources beneath the seafloor in offshore conditions. In this method, electromagnetic waves are used to detect the resistivity contrast between various sediment layers. The current source of electromagnetic waves is a horizontal electric dipole (HED) antenna. The antenna design represents a challenge in shallow waters (less than500 m seawater depth) due to the presence of airwaves that lead to a low signal-to-noise ratio, hence hindering the detection of a hydrocarbon reservoir. A horizontal circular electric half-wave dipole will be used in this work as the source of electromagnetic waves. The numerical solution for the electric field response will be developed based on solving the Maxwell equations in two modes: the poloidal and toroidal modes. Simulation results have shown that the new antenna is able to detect the presence of deep hydrocarbon reservoirs (up to 5000 m) in shallow-water environment. Comparison of the average percentage difference in delineation between the circular and the HED was carried out. The new antenna results in 61 % delineation compared to 15 % for the HED at 5000 m hydrocarbon depth and 200 m seawater depth, indicating the ability of the antenna to disperse the airwaves. The results also show that the airwaves are significantly reduced from nearly 15000 m (for the HED) to 10000 m offset for the proposed antenna, hence increasing the signal-to-noise ratio. These results seem to indicate the potential for the new antenna to be used as an EM source for SBL in shallow-water environment.