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Projecte llegit

Títol: Wave propagation with submarines

Estudiants que han llegit aquest projecte:

Director/a: ÚBEDA FARRE, EDUARD

Departament: TSC

Títol: Wave propagation with submarines

Data inici oferta: 06-02-2020     Data finalització oferta: 06-10-2020


Estudis d'assignació del projecte:
    GR ENG SIS TELECOMUN
Tipus: Individual
 
Lloc de realització: EETAC
 
Paraules clau:
e-folding depth, loaded antennas, buoy antennas, mast antennas, radiation efficiency, lossy medium
 
Descripció del contingut i pla d'activitats:
Radio-frequency (RF) communication with underwater submarines has been traditionally challenging because of the difficult propagation of electromagnetic (EM) waves over seawater, which behaves as a medium with losses (conductor). This happens all over the radio-frequency spectrum but it becomes especially serious at frequency bands above the MF band, where RF waves cannot even penetrate the seawater. Interestingly, the e-folding depth at seawater grows at low or very low frequencies. This allows effective EM- communication over these frequencies provided that the submarine is close enough to the air-sea interface. In this work, a thorough study on the types of successful technologies used for EM-propagation over ELF, ULF and VLF bands will be carried out. An overview of the different technological strategies will be presented. The suitability of such technologies in minimizing some of the downsides of the EM communication will be discussed; namely, to name a few, the very low radiation efficiency (due to comparatively high ohmic losses), the low transmitted power over the air-seawater interface, the narrowband match of the antenna feeder, the electrically small dimensions of the radiating antennas and the poor signal-to-noise ratios. This will be associated with more general concepts such as the allowed bitrates for successful communication or the inherent restriction to unidirectional communications. Moreover, a global view will be also addressed to other schemes of communication with underwater submarines, in the optical regime or through acoustic propagation, for which the pros and cons will be evaluated. The study will be supported with numerical simulations by wire-based Mom codes, such as NEC, or through ray-propagation theory.
 
Overview (resum en anglès):
Radio frequency communication with submerged submarines has been a great challenge due to the difficulty of propagating electromagnetic waves under the sea surface, as this medium acts as a lossy conductor. This behavior occurs throughout the radio spectrum and is more pronounced as the frequency increases. Above the LF band, electromagnetic waves are attenuated so sharply that their penetration into the sea cannot be be considered. At very low frequencies, the depth of penetration into seawater increases considerably, allowing communications using electromagnetic waves provided that the reception of the signal is done close enough to the surface.
This project will carry out an exhaustive analysis of the aspects that condition radio frequency communications with a submerged submarine. The adoption of the VLF band as preferred for the establishment of these communications has been justified based on its better radiation efficiency, compared to lower frequency systems, and sufficient word rate per minute. By using the numerical analysis software 4NEC2, the fundamental transmission parameters of various monopole antennas in the VLF band have been obtained and their improvement has been quantified by updating different loading or counterpoise strategies. Also, a loaded monopole with counterpoise transmitter system has been designed, so that it has obtained at theoretical level radiation parameters analogous to real radiation systems, such as Cutler's Trideco antenna (in Maine), installed by the US Navy for radio communication with submarines in the Atlantic Ocean. In addition, it has been estimated the capacity of penetration of electromagnetic waves into the sea through the VOACAP software, and it has been reasoned how the most common morphologies of reception antennas transported by submarines allow capturing the tiny component of tangential electric field to the underwater surface that penetrates into the sea. Finally, other alternatives have been presented for communication with submerged submarines: (1) optical communication (in the blue-green band), too dependent on the propagation meteorological conditions, and (2) quantum communication, still in the experimental stage.

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