Acoustic radiation efficiency of trucated conical shells

Acoustic radiation efficiency and structural vibration characteristics of truncated conical shell

Composite antenna feed system operates from VHF to X-band

System has high radiation efficiency and minimal interaction between elements when inserted between a multimode, multifrequency transponder and a parabolic reflector in an airborne communications system

Where have all the black holes gone?

We have calculated stationary models for accretion disks around super-massive black holes in galactic nuclei. Our models show that below a critical mass flow rate of ~3 10**-3 M_Edd advection will dominate the energy budget while above that rate all the viscously liberated energy is radiated. The radiation efficiency declines steeply below that critical rate. This leads to a clear dichotomy between AGN and normal galaxies which is not so much given by differences in the mass flow rate but by the radiation efficiency. At very low mass accretion rates below 5 10**-5 M_Edd synchrotron emission and Bremsstrahlung dominate the SED, while above 2 10**-4 M Edd the inverse Compton radiation from synchrotron seed photons produce flat to inverted SEDs from the radio to X-rays. Finally we discuss the implications of these findings for AGN duty cycles and the long-term AGN evolution.Comment: 7 pages, 5 figures, accepted for publication in A&

Acoustical analysis of gear housing vibration

The modal and acoustical analysis of the NASA gear-noise rig is described. Experimental modal analysis techniques were used to determine the modes of vibration of the transmission housing. The resulting modal data were then used in a boundary element method (BEM) analysis to calculate the sound pressure and sound intensity on the surface of the housing as well as the radiation efficiency of each mode. The radiation efficiencies of the transmission housing modes are compared with theoretical results for finite, baffled plates. A method that uses the measured mode shapes and the BEM to predict the effect of simple structural changes on the sound radiation efficiency of the modes of vibration is also described

Antenna With Tapered Array

An antenna with improved radiation efficiency is provided. The antenna includes an antenna array proximately coupled to a feed line. The antenna array includes a plurality of resonating lines. Each resonating line includes a plurality of axially aligned resonators. The resonators have a resonating surface. The resonating surfaces of the resonators at the ends of the resonating lines are larger than resonating surfaces of the resonators in the middle of the resonating lines. Power is supplied to each resonating ling through a feed line. Electrical field is uniformly distributed along the antenna array so as to improve the radiation efficiency of the antenna.Toyota Motor Engineering & Manufacturing North America, Inc.Georgia Tech Research Corporatio

Radiation efficiency optimization of electrically small antennas: Application to 3D folded dipole

International audienceThis paper deals with the radiation efficiency optimization of Electrically Small Antennas (ESAs). Based on the well-known tradeoff between antenna maximum dimensions, Q-factor and radiation efficiency, several authors focused on minimizing the Q-factor for a given antenna size in order to increase its bandwidth. For some applications (Wireless Sensor Network), only a narrow bandwidth is needed and the radiation efficiency is a crucial parameter to shrink the required power. Thus, this paper presents the radiation efficiency optimization of 3D folded dipole antennas for a given size. First, we compare different folding topologies and then we study the effect of the wire diameter and the material on the ESAs performances