Low profile cavity antenna with small pitch angle helix feed

A new low-profile variable pitch angle cylindrical helical antenna employing a copper strip as impedance transformer is proposed in this paper. Under the circumstance of a limited antenna height, the circular polarization performance of the antenna has been enhanced by changing the pitch angle and the input impedance matching has been improved by adjusting the copper strip match stub. The design method of the proposed antenna is given. The optimal antenna structure for INMARSAT application has been fabricated and measured. The measured results show that in the whole maritime satellite communication work band the VSWR is less than 1.2, its antenna gain is higher than 9 dBi, and the axial ratio is lower than 2.5 dB. The experimental results have a good agreement with the simulations. The proposed antenna is compact and easy tuning. It provides a promising antenna element for maritime satellite communication applications.

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Pattern generation and motion control of a vortex-like paramagnetic nanoparticle swarm

The International Journal of Robotics Research ◽

10.1177/0278364918784366 ◽

2018 ◽

Vol 37 (8) ◽

pp. 912-930 ◽

Cited By ~ 31

Author(s):

Jiangfan Yu ◽

Lidong Yang ◽

Li Zhang

Keyword(s):

Magnetic Field ◽

Targeted Delivery ◽

Pitch Angle ◽

Dynamic Equilibrium ◽

Equilibrium Structure ◽

Pattern Generation ◽

Analytical Models ◽

Generation Process ◽

Rotating Magnetic Fields ◽

Small Pitch

Controlling a swarm of microrobots with external fields is one of the major challenges for untethered microrobots. In this work, we present a new method to generate a vortex-like paramagnetic nanoparticle swarm (VPNS) from dispersed nanoparticles with a diameter of 500 nm, using rotating magnetic fields. The VPNS exhibits a dynamic-equilibrium structure, in which the nanoparticles perform synchronized motions. The mechanisms of the pattern-generation process are analyzed, simulated, and validated by experiments. By tuning the rotating frequency of the input magnetic field, the pattern of a VPNS changes accordingly. Analytical models for estimating the areal change of the pattern are proposed, and they have good agreement with the experimental data. Moreover, reversible merging and splitting of vortex-like swarms are demonstrated and investigated. Serving as a mobile robotic end-effector, a VPNS is capable of making locomotion by tuning the pitch angle of the actuating rotating field. With a small pitch angle, e.g. 2°, the whole swarm moves as an entity, and the shape of the pattern remains intact. In addition, the trapping forces of VPNSs are verified, showing the critical input parameters of the magnetic field that affect the morphology of the swarm. Finally, we demonstrate that VPNSs pass through curved and branched channels with high positioning precision, and the access rates for targeted delivery are over 90%, which are significantly higher than those in the cases of particle swarms moving with tumbling motions.

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Short helical antenna with extremely small pitch angle

Microwave and Optical Technology Letters ◽

10.1002/mop.22054 ◽

2006 ◽

Vol 49 (1) ◽

pp. 17-19

Author(s):

Ze-Hai Wu ◽

Edward K. N. Yung

Keyword(s):

Pitch Angle ◽

Helical Antenna ◽

Small Pitch

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Implications of unusual pitch-angle distributions observed by ISEE-1 and 2

Annales Geophysicae ◽

10.5194/angeo-24-3099-2006 ◽

2006 ◽

Vol 24 (11) ◽

pp. 3099-3113 ◽

Cited By ~ 2

Author(s):

C. A. Zuluaga ◽

E. S. Beiser ◽

J. Chen ◽

T. A. Fritz

Keyword(s):

Charged Particle ◽

High Latitude ◽

Pitch Angle ◽

Angular Resolution ◽

Radial Distance ◽

Local Magnetic Field ◽

Particle Source ◽

Small Pitch ◽

Short Period ◽

Geosynchronous Satellites

Abstract. Unusual energetic particle pitch angle distributions (PADs) were observed by the ISEE-1 and 2 satellites at 3 h MLT and a radial distance of about 10–15 RE during the time period of 07:00-14:00 UT on 3 March 1979. The ISEE-1 satellite obtained complete 3-D distributions of energetic proton and electron fluxes as a function of energy, while ISEE-2 was configured to provide higher time resolution but less angular resolution than ISEE-1. The ISEE-1 observed a butterfly PAD (a minimum in the 90° PA particle flux) for a period of about 2 h (10:00–12:00 UT) for the electrons, and 3 h (09:00–12:00 UT) for the protons over an energy range of 22.5–189 keV (E1–E4) for the electrons and 24–142 keV (P1–P4) for the protons. The small pitch angle (15°, 30°) charged particles (electrons and protons) are seen to behave collectively in all four energy ranges. The relative differences in electron fluxes between 15° PA and 90° PA are more significant for higher energy channels during the butterfly PAD period. Three different types of electron PADs (butterfly, isotropic, and peaked-at-90°) were observed at the same location and time as a function of energy for a short period of time before 10:00 UT. Electron butterfly distributions were also observed by the ISEE-2 for about 1.5 h over 28–62 keV (E2–E4), although less well resolved than ISEE-1. Unlike the ISEE-1, no butterfly distributions were resolved in the ISEE-2 proton PADs due to less angular resolution. The measured drift effects by ISEE-1 suggest that the detected protons were much closer to the particle source than the electrons along their trajectories, and thus ruled out a nightside source within 18:00 MLT to 03:00 MLT. Compared to 07:30 UT, the charged particle fluxes measured by ISEE-1 were enhanced by up to three orders of magnitude during the period 08:30–12:00 UT. From 09:10:00 UT to 11:50 UT, the geomagnetic conditions were quiet (AE<100 nT), the LANL geosynchronous satellites observed no substorms, and the local magnetic field measured by ISEE-1 was almost constant, while the small PA charged particle (both electron and proton) fluxes measured by ISEE-1 increased gradually, which implies a particle source other than the substorm source. Based on detailed particle trajectory tracings in a realistic geomagnetic field model, the 50–200 keV protons with small PA at 10:00 UT ISEE-1 location on 3 March 1979 were passing through the northern high-altitude and high-latitude morningside region where the cusp should be located under a dawnward IMF component condition, while those protons with large PA may connect to the high-latitude morningside magnetopause. It is possible that the cusp source is responsible for the all particles observed during the event.

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Parametric study of flapwise and edgewise vibration of horizontal axis wind turbine blades

Advances in Mechanical Engineering ◽

10.1177/16878140211050801 ◽

2021 ◽

Vol 13 (9) ◽

pp. 168781402110508

Author(s):

Hamza Diken ◽

Saeed Asiri

Keyword(s):

Wind Turbine ◽

Natural Frequency ◽

Pitch Angle ◽

Natural Frequencies ◽

Slenderness Ratio ◽

Ritz Method ◽

Lagrange Function ◽

Horizontal Axis ◽

Horizontal Axis Wind Turbine ◽

Small Pitch

In this paper, flapwise and edgewise vibrations of a horizontal axis wind turbine (HAWT) blade are studied. Rayleigh-Ritz method is used in which; orthogonal mode functions of the Euler-Bernoulli beam having fixed-free boundary are introduced into the Lagrange function and then the dynamic equations are derived. Effect of gravity, pitch angle, centrifugal stiffening, and rotary inertia are considered. Nondimensional equations are obtained by defining nondimensional parameters like; natural frequency, blade rotation, slenderness ratio, and simple pendulum frequency. The stiffness term of the natural frequency has two speed dependent elements and it is shown that, for small pitch angles, flapwise natural frequencies of the blade are increased by the increasing blade speed while the edgewise natural frequencies of the blade are decreased with the increasing blade speed. Pitch angle values ranging from 0° to 15° has negligible effect on the nondimensional natural frequencies of the blade up to the nondimensional blade speed of 4. Since the natural frequencies are the function of the blade speed, rotor critical speeds should be calculated with Campbell diagrams. Vibrational response of the blade tip to the gravity is dominant and much greater than that of the wind speed in the edgewise and flapwise vibration.

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Eight new astrometry results of 6.7 GHz CH3OH and 22 GHz H2O masers in the Perseus arm

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010110 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 168-171 ◽

Cited By ~ 1

Author(s):

Nobuyuki Sakai ◽

Keyword(s):

Pitch Angle ◽

Three Dimensional ◽

Weighted Mean ◽

Large Sample ◽

Small Pitch ◽

Trigonometric Parallaxes ◽

Perseus Arm ◽

Spiral Arm ◽

Interior Side

AbstractWe report astrometric results for seven 6.7 GHz CH3OH and one 22 GHz H2O masers in the Perseus arm with VLBA and VERA observations. Among the eight sources, we succeeded in obtaining trigonometric parallaxes for all sources, except G098.03+1.44 at 6.7 GHz band. By combining our results with previous astrometry results (Choi et al. 2014), we determined an arm width of 0.41 kpc and a pitch angle of 8.2 ± 2.5 deg for the Perseus arm. By using a large sample of the Perseus arm (26 sources), we examined the three-dimensional, non-circular motions (defined as U, V and W) of sources in the Perseus arm as a function of the distance (D) perpendicular to the arm. Interestingly, we found a weighted mean of <U > = 12.7 ± 1.2 km s−1 for 14 sources with D < 0 kpc (i.e. sources on the interior side of the arm) and <U > = −0.3 ± 1.5 km s−1 for 12 sources with D > 0 kpc (i.e. sources exterior to the arm). These findings might be the first observational indication of the ”damping phase of a spiral arm” suggested by the non-steady spiral arm model of Baba et al. (2013). The small pitch angle of the Perseus arm (< 10 deg) also supports the damping phase, based on ”pitch angle vs. arm amplitude” relation shown in Grøsbol et al. (2004).

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Compact variable extragalactic objects and small-pitch-angle synchrotron theory

The Astrophysical Journal ◽

10.1086/156982 ◽

1979 ◽

Vol 229 ◽

pp. 503 ◽

Cited By ~ 1

Author(s):

W. J. Cocke ◽

M. S. Giampapa ◽

A. G. Pacholczyk

Keyword(s):

Pitch Angle ◽

Small Pitch

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Diffusion of Cosmic Rays in MHD Turbulence with Magnetic Mirrors

The Astrophysical Journal ◽

10.3847/1538-4357/ac2de9 ◽

2021 ◽

Vol 923 (1) ◽

pp. 53

Author(s):

Alex Lazarian ◽

Siyao Xu

Keyword(s):

Cosmic Rays ◽

Diffusion Coefficients ◽

Pitch Angle ◽

Mirror Reflection ◽

Mhd Turbulence ◽

Magnetic Mirrors ◽

Parallel Diffusion ◽

Angle Scattering ◽

Small Pitch ◽

New Type

Abstract As the fundamental physical process with many astrophysical implications, the diffusion of cosmic rays (CRs) is determined by their interaction with magnetohydrodynamic (MHD) turbulence. We consider the magnetic mirroring effect arising from MHD turbulence on the diffusion of CRs. Due to the intrinsic superdiffusion of turbulent magnetic fields, CRs with large pitch angles that undergo mirror reflection, i.e., bouncing CRs, are not trapped between magnetic mirrors, but move diffusively along the turbulent magnetic field, leading to a new type of parallel diffusion, i.e., mirror diffusion. This mirror diffusion is in general slower than the diffusion of nonbouncing CRs with small pitch angles that undergo gyroresonant scattering. The critical pitch angle at the balance between magnetic mirroring and pitch-angle scattering is important for determining the diffusion coefficients of both bouncing and nonbouncing CRs and their scalings with the CR energy. We find nonuniversal energy scalings of diffusion coefficients, depending on the properties of MHD turbulence.

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Radiation Resistance of a Helical Antenna in a Compressible Electron Plasma

Australian Journal of Physics ◽

10.1071/ph780071 ◽

1978 ◽

Vol 31 (1) ◽

pp. 71

Author(s):

KR Soni

Keyword(s):

Radiation Resistance ◽

Pitch Angle ◽

Electron Plasma ◽

Travelling Wave ◽

Helical Antenna ◽

Radiation Fields ◽

Integral Number ◽

Circular Arcs ◽

Small Pitch ◽

Special Cases

Earlier work on the radiation fields of a travelling-wave helical antenna in a compressible electron plasma has been extended to evolve expressions for the electromagnetic mode component R. and the electroacoustic or plasma mode component Rp of its radiation resistance. These expressions, - which are general in nature but involve complicated integrals, cover the special cases of multiturn loops, circular arcs and linear antennas. Analytical expressions for R. are then derived for the particular example of a helical antenna of small pitch angle with a fractional or integral number of turns. It is found that R. increases with pitch angle for some values of plasma frequency.

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A Computational Study on the Aeroacoustics of a Multi-Rotor Unmanned Aerial System

Applied Sciences ◽

10.3390/app11209732 ◽

2021 ◽

Vol 11 (20) ◽

pp. 9732

Author(s):

Morteza Heydari ◽

Hamid Sadat ◽

Rajneesh Singh

Keyword(s):

Pitch Angle ◽

Sound Pressure ◽

Computational Study ◽

Unmanned Aerial System ◽

Vehicle Speed ◽

Circular Array ◽

Noise Sources ◽

Local Flow ◽

Small Pitch ◽

Sst Turbulence Model

The noise generated by a quadrotor biplane unmanned aerial system (UAS) is studied computationally for various conditions in terms of the UAS pitch angle, propellers rotating velocity (RPM), and the UAS speed to understand the physics involved in its aeroacoustics and structure-borne noise. The k-ω SST turbulence model and Ffowcs Williams-Hawkings equations are used to solve the flow and acoustics fields, respectively. The sound pressure level is measured using a circular array of microphones positioned around the UAS, as well as at specific locations on its structure. The local flow is studied to detect the noise sources and evaluate the pressure fluctuation on the UAS surface. This study found that the UAS noise increases with pitch angle and the propellers’ rotating velocity, but it shows an irregular trend with the vehicle speed. The major source of the UAS noise is from its propellers and their interactions with each other at small pitch angle. The propeller and CRC-3 structure interaction contributes to the noise at large pitch angle. The results also showed that the propellers and structure of the UAS impose unsteadiness on each other through a two-way mechanism, resulting in structure-born noises which depend on the propeller RPM, velocity and pitch angle.

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