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.

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.

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

scholarly journals A Multi-Mode Broadband Vibration Energy Harvester Composed of Symmetrically Distributed U-Shaped Cantilever Beams

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 203
Author(s):  
Xiaohua Huang ◽  
Cheng Zhang ◽  
Keren Dai
Keyword(s):  
Energy Harvester ◽  
Low Frequency ◽  
Experimental Results ◽  
Vibration Energy ◽  
Cantilever Beams ◽  
Resonant Frequencies ◽  
Promising Alternative ◽  
Piezoelectric Energy ◽  
Straight Beam ◽  
Resonance Frequencies

Using the piezoelectric effect to harvest energy from surrounding vibrations is a promising alternative solution for powering small electronic devices such as wireless sensors and portable devices. A conventional piezoelectric energy harvester (PEH) can only efficiently collect energy within a small range around the resonance frequency. To realize broadband vibration energy harvesting, the idea of multiple-degrees-of-freedom (DOF) PEH to realize multiple resonant frequencies within a certain range has been recently proposed and some preliminary research has validated its feasibility. Therefore, this paper proposed a multi-DOF wideband PEH based on the frequency interval shortening mechanism to realize five resonance frequencies close enough to each other. The PEH consists of five tip masses, two U-shaped cantilever beams and a straight beam, and tuning of the resonance frequencies is realized by specific parameter design. The electrical characteristics of the PEH are analyzed by simulation and experiment, validating that the PEH can effectively expand the operating bandwidth and collect vibration energy in the low frequency. Experimental results show that the PEH has five low-frequency resonant frequencies, which are 13, 15, 18, 21 and 24 Hz; under the action of 0.5 g acceleration, the maximum output power is 52.2, 49.4, 61.3, 39.2 and 32.1 μW, respectively. In view of the difference between the simulation and the experimental results, this paper conducted an error analysis and revealed that the material parameters and parasitic capacitance are important factors that affect the simulation results. Based on the analysis, the simulation is improved for better agreement with experiments.

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
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