Dipole Length Research Articles

The Effect of Turbulence on Dynamic Radar Cross Section of Chaff Clouds

Objective: This research reports the effect of turbulence on the dynamic Radar Cross Section (RCS) of chaff cloud. In the era of modern warfare technologies, most efficacious electronic countermeasure employed by the armed forces of various major powers is the Chaff. Chaff is based on the expulsion of numerous electrical dipoles of different length to cover the broad spectrum of radar frequency. This mechanism helps in deceiving the enemy missile by producing the required RCS. RCS of chaff cloud is a dynamic entity and rely on several aerodynamic factors. Methodology: Effects of turbulence on dynamic RCS are studied using Ansys Fluent for aerodynamic blooming simulation and Ansys HFSS for simulation of RCS of the bloomed chaff cloud. Findings: The subject of the paper corresponds to the significant effect of turbulence on the expeditious blooming of chaff cloud. The RCS of turbulent flow was higher by 1.5dBsm to 2.5dBsm for 50msec. The turbulence effect has reduced the blooming time of chaff filaments in the range of 25msec - 50msec. Novelty: Turbulence plays important role in faster blooming of chaff cloud and achieving minimum threshold RCS required for deception of RF seeker missiles. Keywords: Chaff; RCS; Turbulence; Modelling and Simulation

Cavity-excited Huygens’ metasurface for wavefront manipulation

In this paper, cavity-excited Huygens’ metasurface is proposed for high-efficiency wavefront manipulation. By adjusting the length of electric dipole and magnetic dipole , the proposed Huygens’ metasurface meta unit can provide nearly 360° phase coverage with sufficiently high transmission efficiency. Based on the analysis of the resonance mode of the cavity, the Huygens’ metasurface has successfully performed its function by adopting integrated feeding method. According to the generalized Snell’s law, metasurfaces with different phase gradients are designed. Combined with the cavity structure, one-dimensional Huygens’ metasurfaces excited by cavity is realized, which can directionally emit the electromagnetic waves from the cavity. Both the simulation and experimental results show that the proposed cavity excited metasurfaces can effectively manipulate the direction of the emitted beam. Such a kind of cavity-excited metasurface can flexibly control the emission angle of the electromagnetic wave, reduce the energy loss and improve the efficiency of the electromagnetic wave. These designs have the advantages of compact, light and easy integration.

Surface Waves Analysis of Efficient Underwater Radio-Based Wireless Link

The domain of underwater wireless communication (UWC) link is gaining much attention due to an increase in various underwater activities such as offshore hydrocarbon exploration, underwater unmanned vehicles (UUV), and military practices. Increased bandwidth and a reliable data link are mainly required for such activities. Both requirements of the domain are heavily affected by the highly conductive property of the seawater. This paper demonstrates the performance evaluation of radiofrequency-UWC, focusing on surface wave analysis, to propose a reliable solution for offshore activities. A constructive interference scheme can be useful due to the sharp difference in the properties of the two mediums (air and seawater). To that end, an experimental setup is created, and a corresponding finite element method (FEM) based simulation of the radio-based wireless link is run. This is because it has higher bandwidth and speed than acoustic and optical approaches. A conduction current mechanism transmits and receives data in a synthetic water tank containing a prepared conductive media (saltwater). The study of changing depths of transmitter-receiver nodes in saltwater shows that surface waves cause significant noise reception in shallow water (less than dipole length, below water level). During a series of experiments in the tank, the lowest bit error rate (BER) is observed only when the node’s submerged height was greater than dipole length. As a result, it is meant to provide a genuine data channel model. The discovery and analysis will aid in the development of a dependable underwater data link, with applications including short-range diver-to-diver communication, and UUV capability.

Design Optimization of Wearable Multiband Antenna Using Evolutionary Algorithm Tuned with Dipole Benchmark Problem

In this paper we present the optimal design of wearable four band antenna that is suitable to work in the fifth-generation wireless systems as well as in cellular systems and in unlicensed bands. The design of the antenna relies on a careful study of optimization algorithms that are suitable for antenna design. We have proposed a benchmark problem to compare different optimization algorithms. It is the space of voltage standing wave ratio and the gain of dipole antenna that was identified for wide range of dipole length and radius. Using this pre-calculated data, we have tuned the parameters of optimization routine for optimal performance with our benchmark. After this, we optimized the geometry of four-band wearable antenna. In the optimization process, we used finite-difference time-domain method together with simplified model of human body. The antenna design was assessed with a fabricated prototype.

Origin invariant full optical rotation tensor in the length dipole gauge without London atomic orbitals.

We present an origin-invariant approach to compute the full optical rotation tensor (Buckingham/Dunn tensor) in the length dipole gauge without recourse to London atomic orbitals, called LG(OI). The LG(OI) approach is simpler and less computationally demanding than the more common length gauge (LG)-London and modified velocity gauge (MVG) approaches, and it can be used with any approximate wave function or density functional method. We report an implementation at the coupled cluster with single and double excitations level (CCSD), for which we present the first simulations of the origin-invariant Buckingham/Dunn tensor in the LG. We compare LG(OI) and MVG results on a series of 22 organic molecules, showing good linear correlation between the approaches, although for small tensor elements, they provide values of opposite sign. We also attempt to decouple the effects of electron correlation and basis set incompleteness on the choice of gauge for specific rotation calculations on simple test systems. The simulations show a smooth convergence of the LG(OI) and MVG results with the basis set size toward the complete basis set limit. However, these preliminary results indicate that CCSD may not be close to a complete description of the electron correlation effects on this property even for small molecules and that basis set incompleteness may be a less important cause of discrepancy between choices of gauge than electron correlation incompleteness.

Impacts of solvent electric dipole and ion valency on energy storage in ultrananoporous supercapacitor: An ising model study

A four-state BEG model is constructed to investigate effects of electric dipole of solvent molecule and ion valency on differential capacitance Cd and energy storage Eof the supercapacitor based on electrical double layer inside an ultranano-cylindrical pore about the size of the ions and solvent. In the model, existence of voids is permitted, solvent molecule is modelled as neutral hard sphere with an electrical dipole moment and ions are described by the primitive model; all electrostatic interactions between cation, anion, and polarized charges on the solvent molecule are limited to the nearest neighbor interactions. The present investigation is limited to weak solvent-solvent electrostatic interaction in comparison to that of the solvent-ion and ion-ion. New effects are found and summarized as follows. (i) There appears a zero Cd and zero E platform around the zero surface potential, which widens with the increase of the solvent transfer energy w0 and moves to positive surface potential side with replacement of the monovalent cation by bivalent cation. (ii) The saturated surface potential |Usat|, beyond which Cd reduces to zero and E reaches its saturation value Esat, is positively correlated with the w0 value. The correlation strength reduces with the counter-ion valence. (iii) For appropriate positive w0 value, both |Usat| and Esat always increase with the solvent polarized charge valence b and dipole length l whether the electrolyte type is +1: 1 or +2: 1; whereas for negative w0 value, the value and l value effects are very small and graphically unobservable. (iv) Presence of bivalent counter-ions causes an increase of the Cd peak strength and Esat value, whereas the presence of bivalent co-ion almost does not bring graphically observed effect. (v) Within the ranges of the b and l values considered, the energy storage is raised by increasing the solvent electrical dipole moment (whether by increasing b valueb or l value) without paying for the cost of high surface potential applied.

Pattern-Reconfigurable Yagi–Uda Antenna Based on Liquid Metal

A pattern-reconfigurable Yagi–Uda antenna based on liquid metal is presented. The antenna consists of a balun-fed active dipole and a pair of stretchable passive parasitic dipoles, which are implemented by eutectic gallium-indium (EGaIn) alloy embedded in microfluidic channels. The parasitic dipoles are driven at each end by two low-cost, three-dimensional printed media rods. Afterward, spinning the rods at different angles leads to varying degrees of stretching upon the stretchable dipoles. Note the length of passive parasitic dipoles is a vital factor for antenna radiation reconfiguration. The antenna exhibits bidirectional radiation if the parasitic dipoles are equal in length. Otherwise, directional radiation toward the shorter parasitic dipole direction can be obtained. Based on the above-mentioned working principle, a pattern-reconfigurable antenna working in wireless local area network (WLAN) band is fabricated and measured. Apart from the reconfigurable capability, the proposed antenna keeps operating in the WLAN band of 2.4–2.48 GHz during the whole shape deformation.

Numerical Investigation of Dielectric Relaxation in Interacting Systems

Three dimensional dielectric systems are simulated to obtain the relaxational polarization responses. The dielectric system consists of randomly distributed permanent dipoles that fluctuate due to thermal activation in double well potentials between two plane-parallel electrodes. The barrier height between the wells is assumed to be proportional to the dipole length. The electrodes' effect is considered with the method of images. The relaxational phenomena of two dielectric systems, one with fixed and the other with distributed dipole lengths having single and distributed relaxation times, respectively, are calculated with a Monte-Carlo simulation method. The local field at every dipole and consequently the transition probabilities are computed to determine the transient polarization response iteratively. Both dielectric systems are simulated over a wide range of temperatures for interacting and non-interacting cases. The mean relaxation times exhibit a Vogel-Fulcher law for interacting systems and an Arrhenius law for non-interacting systems.

Narrowband to Narrowband Frequency Tunable Slotted Dipole Antenna

In this paper, the slotted dipole antenna structure is proposed to have four narrowband frequencies with ability to be reconfigured. Narrowband reconfiguration can be achieved by controlling the length of slotted dipole by using switches. The narrowband frequency is to be at 1.8 GHz (GSM), 2.4 GHz (WLAN), 2.6 GHz (4G), and 3.5 GHz (5G) respectively. The longest dipole length produced 1.8 GHz, the second-longest dipole length produced 2.4 GHz, the third-longest dipole length produced 2.6 GHz, while the smallest dipole length produced 3.5 GHz. To maintain the stability of the RF current in the system, sixteen capacitors were used. As well eight inductors were used to isolate the RF current and power supply. The PIN diode was used as a switch to allow the induced current to stop and pass into the slot which means that it can be used to select the desired frequency. Depending on switching configuration, the operating frequency is tuned. Good matching is achieved for all configurations. The simulated result of gain for the four operating is higher than 2 dB while the omnidirectional radiation pattern has been obtained thus makes the proposed antenna suitable for wireless application.

Universal relations for dipolar quantum gases

We establish that two-dimensional dipolar quantum gases admit a universal description, i.e., their thermodynamic properties are independent of details of the interaction at short distances. The only relevant parameters are the dipole length as well as the scattering length of the combined short-range plus dipolar interaction potential. We derive adiabatic relations that link the change in the thermodynamic potentials with respect to the scattering length and the dipole length to a generalized Tan contact parameter and a new dipolar contact, which involves an integral of a short-distance regularized pair distribution function. These two quantities determine the scale anomaly in the difference between pressure and energy density and also the internal energy in the presence of a harmonic confinement. For a weak transverse confinement, configurations with attractive interactions appear, which lead to a density-wave instability beyond a critical strength of the dipolar interaction. We show that this instability essentially coincides with the onset of a roton minimum in the excitation spectrum and may be understood in terms of a quantum analog of the Hansen-Verlet criterion for freezing of a classical fluid.

Анализ условий существования стабильных микротрещин в упругом поле напряжений от ротационно-сдвигового мезодефекта

During plastic flow, simultaneously with the formation of junction disclinations, which are linear mesodefects, planar shear mesodefects appear at the grain boundaries and facets of the boundaries, the stress fields from which can significantly affect the orientation and characteristics of a microcrack formed at the junction. The configurational force method is used to analyze the conditions for the existence of stable cracks in the elastic field of a combined mesodefect, which is a superposition of a wedge disclinations dipole and a planar mesodefect. In the configuration space of the parameters of the system under consideration (the strength of the disclinations dipole and the planar mesodefect, the length of the mesodefect, and the angle that specifies the orientation of the crack), the ranges of parameter values are determined at which such cracks can appear. The dependences of the critical strength of the disclination dipole and the length of the nuclear crack arising in the vicinity of the negative disclination of the dipole on the length of the mesodefect are calculated for different values of the strength of the planar mesodefect. It was assumed that the opening of the crack occurs in the direction coinciding with the orientation at which the length of the nuclear crack at fixed values of the strength of the disclinations dipole, the strength of the planar mesodefect and the length of the mesodefect is minimal, and, therefore, the energy for its creation is minimal. It is generally concluded that shear-type mesodefects can significantly facilitate the initiation of microcracks in the vicinity of junction disclinations. In the range of parameter values that allow the existence of stable cracks, the length of the nuclear crack decreases with increasing strength of the planar mesodefect. It is shown that the critical length of the crack is tenths of the length of the disclination dipole.

Optimization of Coating Thickness of Conducting Material on Base Fiber to make it as a Radar Reflector

Chaff is one of the most extensively used passive electronic countermeasure to disrupt radar tracking and are designed to cover wide frequency range from 2-18 GHz. There are various factors to improve backscattered RCS of the chaff cloud at higher frequencies. In this paper, the effect of coating thickness of conducting material of electrically conducting fibre (which is used as chaff) on its backscattered RCS has been studied. The relationship between fiber coating thickness of conducting material and its backscattered RCS were obtained by performing simulations in Ansys HFSS with dipole length of 50mm and 15mm and later validating the same with the measured results. It is observed that with an increase in coating thickness of conducting material of the fibre there is increase in its backscattered RCS. When coating thickness of conducting metal becomes greater than the skin depth of the conducting metal, the increase in observed RCS with increase in coating thickness is marginal. Thus, further increase in coating thickness greater than the skin depth of the conducting metal will not improve the backscattered RCS of the fiber significantly but it will add weight penalty for the fiber.

Surface Wave Propagation on Carbon Nanotube Bundle and Characteristics by High Attenuation

We have studied the surface wave propagation on carbon nanotube bundle and its characteristics by high attenuation. The slow wave propagation along conducting carbon nanotubes and the high conductivity compared with metallic conductors like copper made these structures for high frequency applications. The property reduced the size of antenna and passive circuits. It was found that the complex surface wave propagation has a significant attenuation coefficient at lower frequency band. This attenuation coefficient induces highly damping effect which reduces the active part of the dipole length. Thus, dipole lie always below resonance and input impedance be always capacitive. The conductivity and electromagnetic wave interaction of the conducting carbon nanotubes have also important features in comparison with traditional conductors like copper wires of the same size. The quantum capacitances of the order of the electrostatic capacitance of the transmission line. This property has two main effects on electromagnetic wave propagation along the carbon nanotube transmission line, slow wave propagation and high characteristic impedance. The wave propagation on the arms of the dipole is highly attenuated such that the active part of the dipole is such smaller than the physical length of the dipole itself. Thus, the dipole always be a short dipole and could not be resonant in any case. The result shows that the advantage of size reduction combined with surface wave propagation is used only in high frequency bands above 100 GHz. The attenuation coefficient has a moderate effect in the frequency band from 10 to 100 GHz. The resonance mechanism occurred when the incident wave at the feeding point adds constructively with reflected wave from dipole ends. The obtained results were found in good agreement with previously obtained results.

Permittivity order modulation by intrinsic dielectric coupling

The room-temperature permittivity is reduced by one order of magnitude in a wide frequency range during each step, when the stoichiometric proportion of Cu in CaCu3Ti4O12 is decreased from 3 to 2 and then to 1. The frequency-independent reduction can be applied down to 140 K. Such an almost frequency- and temperature-independent decrease in the permittivity magnitude order suggests the existence of intrinsic dielectric coupling between binary dielectric polarization species, by which the less polaron-like 3d electrons from B-site copper ions more strongly depress the permittivity contribution from one-dimensional, anti-parallel, mutually independent, and finite length dipole chains of thermally activated off-center displacements of A-site titanium ions.

How Varying the Dipole Lengths of a Uniform Linear Array Affects the Performance of an ESPRIT based Direction Finding Algorithm

Popularly used to collect data for the direction-of-arrival estimation of an incident source. Since the dipole elements of the uniform linear array are electromagnetically and mutually coupled, the presence of mutual coupling may degrade the performance of any direction finding algorithms. In order to mitigate mutual coupling, several references introduced modifications of the well-known ESPRIT algorithm. These modifications involve discarding the data collected by linear array at the two ends. However, the assumption of several literature that the mutual coupling matrix to be both Toeplitz and banded are invalid. This is pointed out by the “method of moments” based computer simulation tool used in this paper. The Toeplitz-and-banded coupling-matrix assumption leads to the mutual coupling being mis-modeled. Furthermore, previous studies failed to consider how varying the dipoles’ electrical length affect the performance of the direction-of-arrival estimation under mutual coupling.

Origin invariant optical rotation in the length dipole gauge without London atomic orbitals.

We present an approach to perform origin invariant optical rotation calculations in the length dipole gauge without recourse to London atomic orbitals, called origin invariant length gauge [LG(OI)]. The LG(OI) approach works with any approximate wave function or density functional method, but here we focus on the implementation with the coupled cluster (CC) with single and double excitations method because of the lack of production-level alternatives. Preliminary numerical tests show the efficacy of the LG(OI) procedure and indicate that putting the origin in the center of mass of a molecule may not be an optimal choice for conventional CC-LG calculations.

A High-Gain and Wideband Series-Fed Angled Printed Dipole Array Antenna

In this communication, we have proposed a nonuniform series-fed angled dipole array antenna with a high gain, a wide bandwidth, a good sidelobe level (SLL), and a high front-to-back ratio characteristics. The proposed array antenna structure consisted of eight dipole elements, and each dipole was connected to a parallel stripline printed on the front and back sides of the substrate. From the first dipole element near the ground plane to the eighth dipole element at the end of the parallel stripline, the length of each dipole was reduced by ΔL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> . As with dipole length, the spacing between the dipole elements decreased by ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> from each previous dipole spacing. Compared to uniform array antennas, the impedance and gain bandwidths were greatly increased, and the SLL and front-to-back (F/B) ratio characteristics were improved. The proposed array antenna had an |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB, an impedance bandwidth of 23.3-51.0 GHz, and a 3 dB gain bandwidth of 22.0-44.0 GHz. At 28 GHz, the E- and H-plane SLLs of the proposed array antenna were -24.1 and -18.8 dB, respectively. The F/B ratio of the proposed antenna was less than -30 dB.

A parametric analysis of oilfield design factors affecting the detectability and characterization of electrically conductive hydrofracks

Electrical responses in the vicinity of energized steel-cased well sources offer significant potential for monitoring induced fractures. However, the high complexity of well-fracture-host models spanning multiple length scales compels analysts to simplify their numerical models due to enormous computational costs. This consequently limits our understanding regarding monitoring capabilities and the limitations of electrical measurements on realistic hydraulically fracturing systems. Here, we use the hierarchical finite element approach to construct geoelectric models in which geometrically complex fractures and steel-cased wells are discretely represented in 3D conducting media without sacrificing the model realism and computation efficiency. We have discovered systematic numerical analyses of the electrical responses to evaluate the influences of borehole material conductivity and the source type as well as the effects of well geometry, conductivity contrast, source location, fracture growth, and fracture propagation. The numerical results indicate that the borehole material property has a strong control on the electrical potentials along the production and monitoring wells. The monopole source located at a steel-cased well results in a current density distribution that decays away from the source location throughout the well length, whereas the dipole source produces a current density that dominates mainly along the dipole length. Moreover, the conductivity contrast between the fractures and host does not change the overall pattern of the electrical potentials but varies its amplitude. The fracture models near different well systems indicate that the well geometry controls the entire distribution of potentials, whereas the characteristics of the voltage difference profiles along the wells before and after fracturing are insensitive to the well geometry and the well in which the source is located. Further, the hydraulic-fracturing models indicate that the voltage differences along the production well before and after fracturing have strong sensitivity to fracture growth and fracture set propagation.

Spectral shift in high-order harmonic generation from periodic potentials

We theoretically investigate the high-order harmonic generation (HHG) of the solid by solving the one-dimensional time-dependent Schrödinger equation in the dipole approximation and length gauge. The spectral shift of the HHG with the solid can be observed. It is illustrated that the contribution to the HHG from the rising and falling parts of the laser pulse is asymmetric, which results in the occurrence of spectral shift. We have also investigated the HHG in laser field with the increase of the laser peak strength; the result shows that the intensity of the harmonic is not continuous, which is illustrated by the electron population.

Computational Analysis of a Dual Loop Dipole Antenna and Its Interleaving Array for Improving Transceiver ∣B1∣-field for MRI

This article intends to present the electromagnetic (EM) insight of the operation of a double loop shaped dual loop dipole (DLD) antenna as a single-channel transceiver coil and in an array configuration of multi-channel transceiver coil, designed to provide high signal-to-noise ratio (SNR) by using numerical simulations for 300 MHz magnetic resonance imaging (MRI). Thus, this section includes the comparison of DLD antenna and commonly used loop coils through EM simulations. The use of a DLD antenna is proposed to address the length issue that traditional straight dipole have by making a spiral type in a loop style, while having the same effective physical length of the straight dipole. The magnetic flux density (∣B1∣)-fields of the DLD antenna and the traditional loop coil are compared by field maps acquired by EM simulations. In addition, the DLD antenna has been extended to a 7-channels array, for which the magnetic field coupling between each coil is analyzed and presented through the noise correlation matrix. The use of the DLD antenna exhibits higher ∣B1∣-field intensity while keeping the similar uniformity than a surface loop coil. We use the DLD antenna 7-channel array to observe its utility as multi-channel with short distance overlap between elements; each element is approximately 37 mm away from neighboring element. Transceiver array arrangements also show improved coil performance, especially the interleaving configuration with loop coil indicates lowered mutual inductance coupling at calculated noise correlation matrix. The proposed DLD antenna is expected to induce rapid imaging and high ∣B1∣-field, when expanded to multi-channel planar or volume configuration since it can maximize the number of configuring coil elements within limited imaging area leading effective parallel imaging and deeper penetration depth due to the traveling wave.