scholarly journals The influence of electromagnetic singularities on an active dipole antenna within a cavity

2003 ◽  
Vol 1 ◽  
pp. 57-61 ◽  
Author(s):  
F. Gronwald
Keyword(s):  
Quality Factor ◽  
Method Of Moments ◽  
Current Distribution ◽  
Dipole Antenna ◽  
Rectangular Cavity ◽  
Cavity Resonance ◽  
Cavity Resonances ◽  
Small Antenna ◽  
Active Dipole ◽  
Electromagnetic Source

Abstract. We study the influence of both the electromagnetic source singularity and electromagnetic cavity resonances on the current distribution of a dipole antenna within a rectangular cavity. These two types of electromagnetic singularities are triggered by the radius of the dipole antenna and the quality factor of the enclosing cavity, respectively. The key element of our investigation is a novel representation of the electromagnetic Green’s function for a lossy rectangular cavity. It allows to directly obtain the current distribution on the antenna by means of the method of moments. As a result it is recognized that a dominating source singularity, i.e., a small antenna radius, can inhibit resonating effects, even if a cavity resonance is excited and the quality factor of the cavity is high.

scholarly journals Source modification for efficiency enhancement of marine controlled-source electromagnetic method

2021 ◽  
Vol 18 (2) ◽  
Author(s):  
Amir Rostami ◽  
Noorhana Yahaya ◽  
Hassan Soleimani ◽  
Muhammad Rauf ◽  
Tadiwa E Nyamasvisva ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
Shallow Water ◽  
Method Of Moments ◽  
Experimental Setup ◽  
Efficiency Enhancement ◽  
Shooting Methods ◽  
Detection Capability ◽  
Controlled Source ◽  
Element Simulation ◽  
Electromagnetic Source

Abstract Controlled-source electromagnetics is a strongly efficient technique to explore deep-water marine hydrocarbon reservoirs. However, the shallow-water unsolved limitations of electromagnetic shooting methods still exist. In this regard, this work aims to alter the existing conventional electromagnetic source such that it can converge the down-going electromagnetic wave while simultaneously dispersing the up-going electromagnetic energy to minimise the airwave in shallow water. This work presents computed electric current distribution inside a modified transmitter, using a method of moments. Simulation and an experiment-based methodology are applied to this work. Finite element simulation of the response of the modified transmitter displayed the capability of the new transmitter in dispersing the airwave, by 15%. The experimental setup confirmed a better performance of the new transmitter, showing hydrocarbon delineation of up to 48%, compared to the existing conventional transmitter, with 25% oil delineation at the same depths in the same environment. Modification of the electromagnetic source to unbalance the up-down signals may have the potential to enhance the delineation magnitude of the target signal and, as a result, significantly improve oil detection capability.

Numerical simulation of aeroacoustic noise from landing gear and rectangular cavity

2020 ◽  
Vol 234 (7) ◽  
pp. 1259-1271
Author(s):  
Zhifei Guo ◽  
Peiqing Liu ◽  
Jin Zhang ◽  
Hao Guo
Keyword(s):  
Numerical Simulation ◽  
Low Frequency ◽  
Landing Gear ◽  
Rectangular Cavity ◽  
Cavity Resonance ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Radiation Mechanism ◽  
Ansys Fluent ◽  
Aeroacoustic Noise

This paper is aimed at researching the interaction between aeroacoustic noise radiated from a rectangular cavity (gear bay) and from landing gear. It is a complicated flow-induced noise problem, involving the nonlinear, unsteady evolution of the turbulent structure inside the airflow bypassing the landing gear and the cavity. The generation and radiation mechanism of aeroacoustic noise are also concerned. In fact, it is a problem about the nonlinear interaction between the vortices shedding from the boundary layer of bluff bodies and the cavity-limited shear layer. To simplify this issue, a two-wheel landing gear named LAGOON is chosen as the landing gear model. The unsteady flow field and aerodynamic noise from it is simulated by applying the commercial software ANSYS Fluent. Good agreement is achieved between the numerical simulation and wind tunnel measurements in terms of the aerodynamic and aeroacoustic results. According to the size of LAGOON, a simple rectangular cavity is designed as the landing gear bay. Both the cavity combined with LAGOON and the cavity alone are simulated and compared. The results show that under the blocking effect of a strut, most small pieces of vortices at the trailing edge of the cavity bottom would dissipate rather than move forward along with the backflow, leading to the correlation of cavity resonance being more contrasting and increasing its amplitude. The blockage effect induced by rear wall could also enhance the turbulence kinetic energy at the wake of the strut, thus increasing the low-frequency noise radiated from the strut and cavity.

Synthetic Jet Actuator Cavity Acoustics: Helmholtz Versus Quarter-Wave Resonance

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Tyler Van Buren ◽  
Edward Whalen ◽  
Michael Amitay
Keyword(s):  
Acoustic Resonance ◽  
Synthetic Jet ◽  
Cavity Resonance ◽  
Synthetic Jet Actuator ◽  
Acoustic Cavity ◽  
Wave Resonance ◽  
Cavity Resonances ◽  
Quarter Wave ◽  
Cavity Acoustics ◽  
The Impact

The impact of cavity geometry on the source of acoustic resonance (Helmholtz or quarter-wave) for synthetic jet type cavities is presented. The cavity resonance was measured through externally excited microphone measurements. It was found that, for pancake-shaped cavities, the Helmholtz resonance equation was inadequate (off by more than 130%) at predicting the acoustic cavity resonances associated with synthetic jet actuation, whereas a two-dimensional quarter-wave resonance was accurate to 15%. The changes in the geometry (cavity diameter, cavity height, and orifice length) could alter the cavity resonance by up to 50%, and a finite element solver was accurate at predicting this resonance in all cases. With better knowledge of the phenomena governing the acoustic resonance, prediction of the cavity resonance can become more accurate and improvements to current prediction tools can be made.

Method of Moment Determination of Current Distribution on Elements of Yagi-Uda Array

2017 ◽  
Vol 2 (9) ◽  
pp. 23-29
Author(s):  
Raji A. Abimbola
Keyword(s):  
Integral Equation ◽  
Method Of Moments ◽  
Current Distribution ◽  
Tangential Component ◽  
The Other ◽  
Induced Current ◽  
Method Of Moment ◽  
Current Distributions ◽  
Complex Coefficients

Presented in this paper is the numerical solution to the current distributions on two forms of Yagi-Uda antenna designs. One form consists of twelve elements while the other consists of fourteen elements. Employing method of moments technique in which the unknown current is expanded in terms of known expansion function and complex coefficients which are to be determined. It is demonstrated that, when the integral equation that expresses tangential component of an impressed field in terms of induced current on the elements of Yagi-Uda array is reduced into matrix form, the current distribution of interest becomes known. The profiles for the current distributions on elements of those arrays represented in graphical forms reveal that, the currents are symmetrical about the length of the element in each case. It is found that the highest magnitude of the current exists on the driven element. Furthermore, the characteristic profiles of the currents on elements of those arrays exhibit sinusoidal type of waveform and are largely similar when the frequencies of operation are 200MHz and 665MHz, respectively.

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