scholarly journals Antenna impedance in a plasma : problems relevant to radio astronomy measurements from space vehicles

1965 ◽  
Vol 23 ◽  
pp. 335-343 ◽  
Author(s):  
D. Walsh ◽  
F. T. Haddock
Keyword(s):  
Magnetic Field ◽  
Radio Astronomy ◽  
Critical Review ◽  
Cold Plasma ◽  
Experimental Results ◽  
Space Vehicles ◽  
Electrically Small Antennas ◽  
Small Antennas ◽  
Warm Plasma ◽  
Antenna Impedance

A critical review is given of the theory and experimental observations of antenna impedance behaviour in a plasma, as related to radio astronomy. The emphasis is on electrically small antennas. Three simplified cases of plasma are considered, namely, cold plasma without magnetic field, cold plasma with magnetic field and warm plasma without magnetic field. Newly reduced experimental results are reported for the case of cold plasma without magnetic field, showing detailed agreement with theory in the neighbourhood of a cutoff in the propagation of the extraordinary magnetoionic wave.

scholarly journals Magnetic Pendulum Arrays for Efficient ULF Transmission

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Srinivas Prasad M N ◽  
Rustu Umut Tok ◽  
Foad Fereidoony ◽  
Yuanxun Ethan Wang ◽  
Rui Zhu ◽  
...  
Keyword(s):  
Quality Factor ◽  
Free Space ◽  
Low Frequency ◽  
Transmission Efficiency ◽  
Experimental Results ◽  
Proof Of Concept ◽  
Electrically Small Antennas ◽  
Fundamental Limits ◽  
Small Antennas ◽  
Order Of Magnitude

Abstract The frequencies lying between 300 Hz to 3 kHz have been designated as Ultra Low Frequency (ULF) with corresponding wavelengths from 1000 Km to 100 Km. Although ULF has very low bandwidth it is very reliable, penetrating and difficult to jam which makes it a great choice for communication in underwater and underground environments. Small and portable ULF antennas within a diameter of 1 meter would operate under an electrical length on the order of 10−4 to 10−6 wavelengths in free space, making them very inefficient because of fundamental limits on radiation from electrically small antennas. To overcome this problem, Mechanical Antennas or ‘Mechtennas’ for Ultra Low Frequency Communications have been proposed recently. For efficient generation of ULF radiation, we propose a portable electromechanical system called a Magnetic Pendulum Array (MPA). A proof of concept demonstration of the system at 1.03 kHz is presented. The theory and experimental results demonstrate that such a system can achieve a significantly higher quality factor than conventional coils and thus order of magnitude higher transmission efficiency. The concept can be easily scaled to the ULF range of frequencies.

Electrically small antennas for space vehicles

2010 ◽  
Author(s):  
V. V. Ovsyanikov ◽  
S. I. Romanov ◽  
A. L. Ol'shevskiy ◽  
V. M. Popel' ◽  
Y. D. Romanenko
Keyword(s):  
Space Vehicles ◽  
Electrically Small Antennas ◽  
Small Antennas

Novel Electrically Small Antennas and Metamaterial High Impedance Surfaces

2005 ◽  
Author(s):  
Ahmad Hoorfar ◽  
John McVay ◽  
Jinhui Zhu ◽  
Hui Huang
Keyword(s):  
Electrically Small Antennas ◽  
Small Antennas ◽  
High Impedance

Parametric Enhancement of Radiation from Electrically Small Antennas

2021 ◽  
Vol 15 (5) ◽  
Author(s):  
Ahmed Mekawy ◽  
Huanan Li ◽  
Younes Radi ◽  
Andrea Alù
Keyword(s):  
Electrically Small Antennas ◽  
Small Antennas

scholarly journals Two typical collective behaviors of the heavy ions expanding in cold plasma with ambient magnetic field

2021 ◽  
Vol 33 (7) ◽  
pp. 076602
Author(s):  
Guo-Liang Peng ◽  
Jun-Jie Zhang ◽  
Jian-Nan Chen ◽  
Tai-Jiao Du ◽  
Hai-Yan Xie
Keyword(s):  
Magnetic Field ◽  
Heavy Ions ◽  
Cold Plasma ◽  
Collective Behaviors ◽  
Ambient Magnetic Field

On the existence of compressional MHD oscillations in an inhomogeneous magnetoplasma

1990 ◽  
Vol 44 (2) ◽  
pp. 361-375 ◽  
Author(s):  
Andrew N. Wright
Keyword(s):  
Magnetic Field ◽  
Wave Equation ◽  
Density Distribution ◽  
Cold Plasma ◽  
Wave Equations ◽  
Perturbation Field ◽  
Plasma Density Distribution ◽  
Background Magnetic Field ◽  
Transverse Fields ◽  
The Magnetic Field

In a cold plasma the wave equation for solely compressional magnetic field perturbations appears to decouple in any surface orthogonal to the background magnetic field. However, the compressional fields in any two of these surfaces are related to each other by the condition that the perturbation field b be divergence-free. Hence the wave equations in these surfaces are not truly decoupled from one another. If the two solutions happen to be ‘matched’ (i.e. V.b = 0) then the medium may execute a solely compressional oscillation. If the two solutions are unmatched then transverse fields must evolve. We consider two classes of compressional solutions and derive a set of criteria for when the medium will be able to support pure compressional field oscillations. These criteria relate to the geometry of the magnetic field and the plasma density distribution. We present the conditions in such a manner that it is easy to see if a given magnetoplasma is able to executive either of the compressional solutions we investigate.

Design and Fabrication of a Magnetocaloric Microcooler

2005 ◽  
Author(s):  
Sangchae Kim ◽  
Bharath Bethala ◽  
Simone Ghirlanda ◽  
Senthil N. Sambandam ◽  
Shekhar Bhansali
Keyword(s):  
Magnetic Field ◽  
Ambient Temperature ◽  
Temperature Change ◽  
Entropy Change ◽  
Temperature Sensors ◽  
Experimental Results ◽  
Maximum Temperature ◽  
Alternative Technology ◽  
Temperature Conditions ◽  
Si Wafer

Magnetocaloric refrigeration is increasingly being explored as an alternative technology for cooling. This paper presents the design and fabrication of a micromachined magnetocaloric cooler. The cooler consists of fluidic microchannels (in a Si wafer), diffused temperature sensors, and a Gd5(Si2Ge2) magnetocaloric refrigeration element. A magnetic field of 1.5 T is applied using an electromagnet to change the entropy of the magnetocaloric element for different ambient temperature conditions ranging from 258 K to 280 K, and the results are discussed. The tests show a maximum temperature change of 7 K on the magnetocaloric element at 258 K. The experimental results co-relate well with the entropy change of the material.

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