Short Dipole Research Articles

Modeling and Simulation of Electric and Magnetic Fields of a Short Dipole Antenna at Low Frequencies in the Far Field

Modeling and Simulation of Electric and Magnetic Fields of a Short Dipole Antenna at Low Frequencies in the Far Field

Electron density measurement of an ionospheric-like plasma using an impedance probe.

In this work, an impedance probe was designed to measure ionospheric low-density plasma. The probe is made of short cylindrical dipoles with an antenna 20cm in length and 0.25cm in diameter, which can operate in the frequency range of 0-100 MHz. Combined with a vector network analyzer, the performance of the probe was tested in laboratory-created ionospheric-like plasma, and the results were compared with those of the Langmuir probe measurements. The densities measured by the two methods show a consistent trend, and the impedance probe data show much smaller uncertainties, which suggests that the impedance probe can achieve high-precision measurements. Furthermore, by fitting the antenna phase data, the electron-neutral collision frequency can also be obtained. Therefore, the impedance probe provides a feasible method for exploring low-density partially ionized plasma and can be expanded to actual ionospheric exploration in the future.

Proposal for the generation of an ion vortex beam and study of its electromagnetic fields

We propose a scheme for the generation of an ion vortex beam and we study the properties of its electromagnetic field on a plane transverse to its propagation direction. The ion vortex is created by the diffraction of an ionic beam by a light mask with a spiral-like transverse intensity pattern. The diffraction is a result of a short time optical dipole interaction between the light mask and the ion which results to a phase imprint on the ionic wave function. It is shown that as the order of the vortex states that are generated by the various diffraction gets higher the electromagnetic field components have reduced magnitudes. The properties of these fields are studied against the various parameters of the problem.

Investigation of the OAM EM wave tissue irradiation at millimeter-wave frequencies

Recently, there has been an increase of interest in the use of electromagnetic (EM) waves with helical wavefronts, known as the orbital angular momentum (OAM) waves. Applications in the field of biomedicine have been foreseen, such as medical imaging and diagnosis, deep-tissue imaging, biosensing, and communication with medical implants. Other possible applications include various localized tissue treatments or tissue ablation. The available references mainly study the interaction of OAM light with biological structures, offering some insights into the biophotonics effects, but without the investigation of how to plan tissue exposures or how to estimate the EM field parameters in a particular case of application. We use the previously developed short dipole modeling of OAM EM fields to study the above problems by altering the OAM beam parameters and the distance from the target tissue. The results could guide the design of components and devices based on OAM EM waves.

Feasibility study of permanent magnet dipoles for SILA facility

The 40 cell lattice of the new Russian synchrotron radiation facility SILA is envisaged to employ permanent magnet (PM) dipoles as bend magnets. Numerical study of the basic concept for short PM dipoles is described. Iterative 3D simulations with a detailed model were used to assess anticipated field distribution and magnetic forces. A scope of critical aspects was investigated to move up to the engineering design including candidate materials, geometry, thermal stability, magnetic interaction, and field tuning. Aggregated results made it possible to optimize the initial concept and get guidance to practical implementation.

Cost-Efficient High-Resolution Linear Absorption Spectra through Extrapolating the Dipole Moment from Real-Time Time-Dependent Electronic-Structure Theory.

We present a novel function fitting method for approximating the propagation of the time-dependent electric dipole moment from real-time electronic structure calculations. Real-time calculations of the electronic absorption spectrum require discrete Fourier transforms of the electric dipole moment. The spectral resolution is determined by the total propagation time, i.e., the trajectory length of the dipole moment, causing a high computational cost. Our developed method uses function fitting on shorter trajectories of the dipole moment, achieving arbitrary spectral resolution through extrapolation. Numerical testing shows that the fitting method can reproduce high-resolution spectra by using short dipole trajectories. The method converges with as little as 100 a.u. dipole trajectories for some systems, though the difficulty converging increases with the spectral density. We also introduce an error estimate of the fit, reliably assessing its convergence and hence the quality of the approximated spectrum.

Aroyl-S,N-Ketene Acetals: Luminous Renaissance of a Class of Heterocyclic Compounds.

Aroyl-S,N-ketene acetals represent a peculiar class of heterocyclic merocyanines, compounds bearing pronounced and rather short dipoles with great push-pull characteristics that define their rich properties. They are accessible via a wide array of synthetic concepts and procedures, ranging from addition-elimination and condensation procedures up to rearrangement and metal-mediated reactions. With our work from 2020, aroyl-S,N-ketene acetals have been identified as powerful and promising dyes with pronounced and vastly tunable solid-state emission and aggregation-induced emission properties. One characteristic trademark of this class of dye molecules is the level of control that could be exerted and which was thoroughly explored. Based on these results, the field was opened to extend the system to bi- and multichromophoric systems by the full toolkit of synthetic organic chemistry thus giving access to even more exciting properties and manifolded substance libraries capitalizing on the AIE properties. This review aims at outlining the reaction-based principles that allow for a swift and facile access to aroyl-S,N-ketene acetals, their methodological and structural evolution and the plethora of fluorescence and aggregation properties.

Quench Protection of Nb3Sn High Field Magnets Using Heaters, a Strategy Applied to the Graded Racetrack Dipole R2D2

The quench protection for the Future Circular Collider (FCC) 16 T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipoles was based either on the CLIQ (Coupling Loss Induced Quench) system, or on resistive quench protection heaters. Several heater designs were sketched during the iterative magnet design processes. This led to identifying some rules about an effective heater design in the full-scale 14-m-long magnets. Following the FCC study, short dipole magnet models are being built to test the novel features that were envisioned for the FCC magnets. In this work, we review the principles of effective heater design, and then apply this methodology to the graded block dipole short model R2D2, which is being designed at CEA Saclay. This magnet has high current density in copper after quench, which makes the protection challenging and requires pushing the heater technology to its limits.

Zero Thickness Surface Susceptibilities and Extended GSTCs—Part I: Spatially Dispersive Metasurfaces

A simple method to describe spatially dispersive metasurfaces is proposed where the angle-dependent surface susceptibilities are explicitly used to formulate the zero thickness sheet model of practical metasurface structures. It is shown that if the surface susceptibilities of a given metasurface are expressed as a ratio of two polynomials of tangential spatial frequencies, k|| with complex coefficients, they can be conveniently expressed as spatial derivatives of the difference and average fields around the metasurface in the space domain, leading to extended forms of the standard generalized sheet transition conditions (GSTCs) accounting for the spatial dispersion. Using two simple examples of a short electric dipole and an all-dielectric cylindrical puck unit cells, which exhibit purely tangential surface susceptibilities and reciprocal/symmetric transmission and reflection characteristics, the proposed concept is numerically confirmed in 2D. A Lorentzian representation with angle-dependent parameters is further proposed and found to accurately model the complex temporal-spatial frequency response via their electric and magnetic susceptibilities of two unit cell examples - a metallic dipole and a dielectric puck resonator. For both cases, the appropriate spatial boundary conditions are derived.

Benchmarking Computational Electromagnetics With the Large Resonant Circular Array of Electrically Short and Thick Dipoles

The phenomenon of resonances in large circular arrays of electrically short and thick dipoles was studied intensively in the nineties by Harvard’s Antenna Group, led by R. W. P. King and T. T. Wu. Here, we propose these arrays as a benchmark for modern 3-D computational electromagnetics (CEM) solvers. Our proposed benchmark is challenging because it exhibits resonances which, for judicious choices of the parameters, can be extremely narrow. We present exploratory simulations of our proposed benchmark using COMSOL multiphysics and ANSYS HFSS and give detailed comparisons with previously published results.

Broadband Magnetoelectric Dipole Filtering Antenna for 5G Application

A magnetoelectric (ME) dipole filtering antenna with high out-of-band suppression level and high selectivity is proposed in this letter. The intrinsic radiation null of the traditional ME dipole antenna is used, which produces a good filtering response at the edge of the lower passsband. A pair of vertical parasitic metal planes are introduced between the shorted walls and fed through slot coupling, which can be equivalent to an additional magnetic dipole. The radiated electric field of the magnetic dipole is opposite to that of the original antenna at higher frequency, forming a wide stopband radiation null, which greatly improves the high-frequency stopband suppression level of the antenna. Furthermore, a pair of T-shaped coupling stubs are inserted between the shorted wall and electric dipole, producing another radiation null with high roll-off rate at higher frequency. The measurement results show that the −10 dB impedance bandwidth of the proposed antenna is 49.4% (3.2–5.3 GHz). Its low-frequency stopband suppression level is greater than 16.6 dB and high-frequency stopband suppression level is greater than 26.0 dB. Moreover, the antenna radiation pattern is stable and symmetrical in the whole operating passband, and the filtering response is desirable.

Height Measurement for Meter Wave Polarimetric MIMO Radar with Electrically Long Dipole under Complex Terrain

Height measurement of meter wave radar is a difficult and important problem. This paper studies the height measurement of meter wave polarimetric (MWP)-MIMO array radar under complex terrain. The traditional electrically short dipole has low radiation efficiency, and the collocated dipole vector antenna has strong mutual coupling. This paper proposes to use electrically long dipoles and separated vector antennae to solve the problems of low radiation efficiency and strong mutual coupling. In addition, different from the traditional flat terrain, the research of this paper is based on the conditions of complex undulating terrain. First, the height measurement signal model of the MWP-MIMO radar with separated electrically long dipole under the complex terrain is derived. Then, a preprocessing method of block orthogonal matching pursuit is proposed to obtain the coarse estimation of the target’s elevation. Then, under the guidance of the coarse estimation, the generalized MUSIC algorithm is used to obtain the high-precision elevation estimation of the target, and then the height measurement of the target is obtained according to the geometric relationship. Finally, the effectiveness of the proposed algorithm is proved by computer simulations.

Time-Switching Symmetric Transmitter Array to Increase Sweet Region for Far-Field Wireless Power Transmission Under Receiver Rotation and Location Variation

For wireless power transfer using linear-polarized transmitter (TX) and receiver antennas, the rotation and movement of receiving antenna cause received power variation. The received power pattern is proposed to describe the received power variation from a specific TX antenna under receiver rotation. By placing the peak of the received power pattern of additional TX antennas in null directions of the previous TX antenna, received power variation due to rotation can be compensated. With symmetrically placed TX antennas, the power variation due to location variation can be compensated. This article proposes a time-switching symmetric transmitting array combining both techniques to increase the sweet region for far-field wireless power transfer under rotation and location variation. A sweet region is an area in the 2-D case or volume in the 3-D case, which is defined as an area or a volume inside the TX array that can get guaranteed minimum received power under rotation. The received power calculation using the Friis equation with short dipole antenna pattern shows that a symmetric TX array can achieve a larger sweet region than an asymmetric TX array under the same total transmitted power. The efficiency for the receiver at the origin is 1/2 at the 2-D case and 1/3 at the 3-D case. In the experiment, a linear-polarized TX array at 915 MHz with monopole receiver antenna and power detector is used as the receiver to measure received power under rotation and location variation. Measurement results at 2-D and 3-D cases confirm the received power level predicted by calculation using the Friis equation. The power budget calculation for wirelessly powering a sensor module attached on a bee inside a beehive using the proposed 3-D TX array shows that it is feasible to deliver sufficient power to the sensor module regardless of the orientation and location of the bee inside the beehive.

Parameters of a Short Dipole Antenna Placed Over a Two-Layer Lunar Soil

In this paper, the performance characteristics of a horizontal symmetrical dipole antenna, located in the immediate vicinity of the Moon’s surface, are numerically analyzed. The lunar soil is assumed as a flat-layered medium composed of two lossy dielectrics, the upper layer with a thickness of 5–10[Formula: see text]m, filled with regolith, and solid bedrock in the form of granite or basalt. Calculations were performed in the frequency range of 1–100[Formula: see text]MHz, which is interesting for low-frequency (LF) and very low-frequency (VLF) radio astronomy. The frequency dependences of the impedance, the radiation efficiency, and the effective area of a thin wire dipole with a short length are investigated. All calculations were carried out by simulation of the dipole using the well-known Altair Feko software. As a result of the calculations, it was found that the frequency characteristics of the dipole parameters above the two-layer medium have characteristic differences from the same for the dipole above a homogeneous medium, namely, they have oscillating components, the period and magnitude of which depend on the parameters of these media and the thickness of the upper layer. The presence of this oscillating component is largely manifested in the dipole efficiency and effective area but to a lesser in its impedance. The dependence of the dipole radiation pattern (RP) on the frequency also is analyzed in detail, making it possible to detect the quasi-periodic changes in its shape, which are clearly synchronized with the oscillating component of the dipole radiation efficiency.

Short Asymmetrical Inductive Dipole Antenna for Direct Matching to High-Q Chips

A planar antenna structure based on a folded asymmetrical dipole is presented, whose geometrical parameters are seen to independently determine either the real or the imaginary parts of the complex radiation impedance. This unique feature allows very efficient and wideband conjugate matching coupling to nonconventional RF sources of arbitrary internal impedance, i.e., small resistance with large and negative reactance. The antenna theoretical framework is developed and an optimized design to match a photodiode is manufactured and measured. The results show a fractional bandwidth of about 20% in the 28 GHz band.

The l = 2 spherical harmonic expansion coefficients of the sky brightness distribution between 0.5 and 7 MHz

Context. The opacity of the ionosphere prevents comprehensive Earth-based surveys of low frequency ν ≲ 10 MHz astrophysical radio emissions. The limited available data in this frequency regime show a downturn in the mean sky brightness at ν ≲ 3 MHz in a divergence from the synchrotron emission power-law that is observed at higher frequencies. The turning over of the spectrum coincides with a shift in the region of maximum brightness from the Galactic plane to the poles. This implicates free-free absorption by interstellar ionized gas, whose concentration in the plane causes radiation that propagates in this region to suffer stronger absorption than radiation from the poles. Aims. Using observations from Parker Solar Probe (PSP), we evaluate the l = 0 and l = 2 spherical harmonic expansion coefficients of the radio brightness distribution at 56 frequencies between 0.5 and 7 MHz. These data quantify free-free absorption’s global effects on the brightness distribution, which provides new constraints on the distribution of free electrons in the Galaxy. Methods. The auto and cross spectra of the voltages induced on crossed short dipole antennas by radiation from a nonpolarized extended brightness distribution are linear combinations of the distribution’s l = 0 and l = 2 expansion coefficients. We extracted the least squares solution to these coefficients from PSP’s measurements of the radio background. Also, we generated hypothetical low frequency brightness maps that incorporated free-free absorption and tested their compatibility with the data. The maps primarily depended on models of the Galactic emissivity and distribution of free electrons. A comparison of the maps’ expansion coefficients with the empirical coefficients provided an indication of these input models’ accuracies. Results. An average reduced x2 ≈ 1.04 of the spherical harmonic analysis between 0.5 and 7 MHz indicates that PSP’s antennas act approximately as ideal short dipoles in this frequency band. The best-fit expansion coefficients show that, with decreasing frequency, the mean sky brightness decreases at ν &lt; 3 MHz and the Galactic plane darkens relative to the poles. At ν &gt; 0.6 MHz, these observations can be reproduced in synthetic brightness maps in which the Galactic emissivity maintains a power-law form and free-free absorption is modeled using free electron distributions derived from pulsar measurements. At lower frequencies, the empirical mean brightness falls below the mean in this model, possibly signifying a cutoff in the synchrotron power-law.

A Low-Profile Dual-Band Directional Antenna for Unmanned Aerial Vehicle Applications

A low-profile dual-band directional antenna operating at both 2.4 and 5 GHz for wireless local area networks (WLANs) for unmanned aerial vehicles (UAVs) applications is proposed in the paper. Two pairs of dipole antenna arrays with different electrical lengths are utilized to achieve dual-band directional radiation performance, which is desirable for a remote-control unit of the UAVs. Note that the directional radiation characteristic is obtained according to the double-dipole antennas driven by antiphase signals (W8JK), provided the distances between different dipole antennas are properly optimized. Note that the distance between the two longer dipoles, as well as the two shorter dipoles, can be calculated by equations. For each pair of dipoles with equal electrical lengths, an antiphase along the two dipoles can be obtained, and directional radiation characteristics can be achieved in the dual band. Coplanar strips (CPS) are employed as feeding networks, which lie on the same substrate layer as the antenna arrays, resulting in a low profile of merely 0.762 mm. Also, the overall size of the antenna together with the feeding network is 58.42 × 32.58 × 0.762 mm3. To verify the performance of the proposed antenna, a prototype is fabricated and measured. The measured gain is 5.2 and 7.0 dBi, respectively, in the 2.4 and 5.8 GHz bands. The measured reflection coefficients as well as radiation patterns are consistent with those of the simulated results. The proposed antenna scheme can be a good candidate for UAV applications with the advantages of a lower profile, dual-band characteristics, directional radiation characteristics, and a simple assembly. Since the remote-control unit operates at 2.4 GHz and 5.8 GHz to control the UAV unit, the low-profile dual-band directional radiation antenna has extensive application prospects when integrated into the space-limited unit.

A Compact Ultrawideband Frequency Selective Rasorber With Hybrid 2-D and 3-D Structure

A compact ultra-wideband frequency selective rasorber (CUWFSR) with hybrid two-dimensional (2-D) and 3-D structure is proposed in this letter. The wide absorption band is obtained by the multiple resonances excited by two dipole resonators and the hybrid structure. By inserting split-ring resonator into the short dipole to bypassing the losses in the passband, an FSR with an internal transmission window and ultrawideband absorption performance is finally realized. The proposed rasorber shows a fractional bandwidth of 140.8% with a transparent window from 14.2–15.8 GHz. Then an improved design which involves two approaches of bypassing the losses of the lossy layer is also provided. Finally, an FSR with a middle passband at 15 GHz and a fractional bandwidth of 137.3% for the absorption rate better than 90% is achieved. The prototype of the improved CUWFSR is fabricated and measured for validation.

Principle and Unified Design of Circularly Polarized Quadruple Inverted-F Antenna With Miniaturized Size and Enhanced Front-to-Back Ratio

The fundamental working principle of front-to-back ratio (FTBR) enhancement of the quadruple inverted-F antenna (QIFA) is clearly revealed for the first time, and a unified design method is then proposed in this article. The characteristic mode analysis (CMA) demonstrates that the QIFA actually operates in two orthogonal modes, and analytical derivation validates that each mode acts as a pair of parallel magnetoelectric (ME) short dipoles for radiation. More specifically, the FTBR of the antenna is determined by the amplitude ratio and phase difference of the two pairs of equivalent ME dipoles. The equivalent model and analytical method can greatly facilitate the design. First, by leading or lagging phase of either characteristic mode through excitation, the beam direction can be flexibly prescribed as forward and backward. Second, the bending direction and bending degree of radiators, respectively, determine the phase and amplitude of its equivalent magnetic dipole, by which the FTBR can be improved. A practical design is carried out with the proposed method, and the antenna achieves an electrically small size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.068\lambda _{0} \times 0.068\lambda _{0} \times 0.052\lambda _{0}$ </tex-math></inline-formula> and an FTBR of 12.3 dB.

Orientation-Insensitive Chipless RFID Achieved in Multiple Rotational Degrees of Freedom

Frequency-coded chipless radio frequency identification (RFID) suffers from resonant frequency detuning caused by misaligned orientations. The literature has employed topological symmetry to prevent shape variations; however, this scheme is effective only for the orientation in roll and cannot address other rotational degrees of freedom, including pitch and yaw. This study takes the first step to cope with the orientation mismatch against arbitrary roll, pitch, and yaw angles. The proposed technique requires the design of tag and new reader architecture, eliminating complex signal processing. The tag comprises resonators with the pattern of a short dipole. Two reader antennas are placed orthogonally and fed with equal power, illuminating co-polarized electromagnetic waves toward the tag. Based on the Pythagorean trigonometric identity, the sum of the backscattering power is unvarying against the rotations in pitch or yaw. The proposed technique is experimentally validated using a 6.97 bit system. When orientation mismatch in yaw appears, the proposed scheme improves the read reliability from 54.3% to 93.5%. Moreover, when mismatch in both roll and yaw occurs, the reliability is improved from 43.8% to 91.8%. Practical aspects, including various detection zones and the loading effect, are also analyzed.