Projeto de Up-Down Converter e Antena para Comunicações Wi-Fi Sub-Aquáticas

As ondas de rádio são altamente atenuadas em ambientes sub-aquáticos. Contudo, como essa atenuação aumenta com o aumento da frequência, o uso de baixas frequências permite obter maior distancias de comunicação. A possibilidade de usar cartas Wi-Fi comerciais é extremamente atractiva devido ao seu baixo custo e à sua grande compatibilidade com o protocolo IP, permitindo o uso de Internet em ambientes aquáticos. Há vários cenários de aplicação, entre os quais destaca-se a monitorização ambiental, vigilância marinha, uso em portos marinhos e ainda na industria petrolífera, gas e matéria-prima. Este trabalho prende-se com o desenvolvimento de um sistema de conversão de frequências e de uma antena que permitirá o uso de cartas comerciais Wi-Fi para estabelecer uma comunicação sub-aquática a distâncias maiores. O sistema desenvolvido irá converter o sinal RF da carta Wi-Fi centrado nos canais de 2.4 GHz) para uma frequência IF centrada em 100MHz. Este sinal é o que se propaga pelo ambiente aquático. No lado do receptor o sinal será convertido de volta para a banda Wi-Fi e a comunicação é estabelecida desta forma. O circuito desenvolvido usa um oscilador/PLL, um misturador de frequências, e uma cadeia de amplificação tanto na transmissão tanto na transmissão como na recepção como comutação automática. O projecto inclui a especificação e o desenho da PCB e da antena bem como os resultados obtidos em testes feitos em ambientes reais.Radio-waves are strongly attenuated in an underwater environment. However, as the attenuation increases with frequency, the use of lower frequencies may allow to obtain higher range communications. The possibility to use commercial Wi-Fi cards is extremely attractive due to the low cost and due to its large compatibility with IP protocol, allowing the use of Internet in underwater environment. There are several scenarios of application, among which stand out the environmental monitoring and aquaculture surveillance, sea ports as well as the oil, gas and raw materials industry. The work proposal concerns the development of an up-down converter system and an antenna that will allow the use of commercial Wi-Fi cards to establish an underwater communication with higher ranges. The developed system will downconvert the RF signal from the Wi-Fi card ($\sim$ 2.4GHz) to an IF frequency of around 100MHz. This signal will be the one that propagates through the underwater medium. On the receiver side, this signal will be upconverted to the Wi-Fi band again and the communication is established in this way. The circuit design uses an oscillator/PLL, a mixer, and it has amplification chain in the transmission and reception with automatic switching. The project includes the specification and design of the PCB and the antenna as well as the obtained results in measurements performed in a real field

Exploiting W. Ellison model for seawater communication at gigahertz frequencies based on world ocean atlas data

Electromagnetic (EM) waves used to send signals under seawater are normally restricted to low frequencies (f) because of sudden exponential increases of attenuation (α) at higher f. The mathematics of EM wave propagation in seawater demonstrate dependence on relative permeability (μr), relative permittivity (εr), conductivity (σ), and f of transmission. Estimation of εr and σ based on the W. Ellison interpolation model was performed for averaged real‐time data of temperature (T) and salinity (S) from 1955 to 2012 for all oceans with 41088 latitude/longitude points and 101 depth points up to 5500 m. Estimation of parameters such as real and imaginary parts of εr, εr′, εr″, σ, loss tangent (tan δ), propagation velocity (Vp), phase constant (β), and α contributes to absorption loss (La) for seawater channels carried out by using normal distribution fit in the 3 GHz–40 GHz f range. We also estimated total path loss (LPL) in seawater for given transmission power Pt and antenna (dipole) gain. MATLAB is the simulation tool used for analysis

Performance of electromagnetic communication in underwater wireless sensor networks

Underwater wireless sensor networks (WSNs) composed of a number of sensor nodes that are deployed to conduct a collaborative monitoring task. Wireless signals are used for communication between the sensor nodes. Acoustic signals are the dominant signals used as a wireless communication medium in underwater WSNs due to the relatively low absorption in the underwater environments. Acoustic signals face a lot of challenges such as ambient noise, manmade noise, limited bandwidth, multipath and low propagation speed. Some of these challenges become more severe in shallow water environment where a high level of ambient and mankind noise, turbidity and multipath propagation are available. Therefore, electromagnetic signals can be applied as an alternative communication signal for underwater WSNs in the shallow water. In this project, the performance of EM communication in underwater WSNs is investigated for the shallow water environment. Theoretical calculations and practical experiments are conducted in fresh and seawater. It is shown that signals propagate for longer ranges in freshwater comparing to seawater. Theoretical results show that attenuation of electromagnetic communication in seawater is much higher than in fresh water. The attenuation is increasing with the increasing of frequency. In addition, velocity of the signal is increasing as the frequency is increasing while loss tangent is decreasing as the frequency increasing. Based on practical experiments, freshwater medium permits short ranges EM communication that does not exceed 25.1 cm for 2.4 GHz frequency. On the other hand, communication in seawater is very difficult to achieve for the same high frequency. Path loss exponent was estimated for freshwater environment based on logdistance path loss model. The estimation was achieved through a comparison between theoretical calculations and practical measurements. The path loss exponent for EM communication in fresh water was estimated to be in the range of 2.3 to 2.4

Underwater Optical Wireless Communication Systems: A Concise Review

Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated point‐to‐point links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly test‐bed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the “hidden” abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC

Seawater salinity modelling based on electromagnetic wave characterization

Wireless communications have experienced tremendous growth, and improving their performance based on specific parameters requires an accurate model. Salt seawater, being an abundant resource, could play a crucial role in various applications such as enhancing electrical conductivity, monitoring security, improving battery power efficiency, and creating liquid antennas. Salinity is an essential factor to consider when developing these applications. This paper focused on investigating the electromagnetic properties of seawater salinity in the context of marine wireless communications. The results of the study showed that salinity has a significant impact on the Fresnel reflection coefficient in terms of magnitude, phase shift, and polarization, and can either constructively or destructively affect it. The new model paved the way for the development of an integrated salt seawater model that addressed the complex salinity issues involved in these applications

Advanced monitoring systems for biological applications in marine environments

The increasing need to manage complex environmental problems demands a new approach and new technologies to provide the information required at a spatial and temporal resolution appropriate to the scales at which the biological processes occur. In particular sensor networks, now quite popular on land, still poses many difficult problems in underwater environments. In this context, it is necessary to develop an autonomous monitoring system that can be remotely interrogated and directed to address unforeseen or expected changes in such environmental conditions. This system, at the highest level, aims to provide a framework for combining observations from a wide range of different in-situ sensors and remote sensing instruments, with a long-term plan for how the network of sensing modalities will continue to evolve in terms of sensing modality, geographic location, and spatial and temporal density. The advances in sensor technology and digital electronics have made it possible to produce large amount of small tag-like sensors which integrate sensing, processing, and communication capabilities together and form an autonomous entity. To successfully use this kind of systems in under water environments2 , it becomes necessary to optimize the network lifetime and face the relative hindrances that such a field imposes, especially in terms of underwater information exchange

Physics of Absorption and Generation of Electromagnetic Radiation

The chapter is divided into two parts. In the first part, the chapter discusses the theory of propagation of electromagnetic waves in different media with the help of Maxwell’s equations of electromagnetic fields. The electromagnetic waves with low frequency are suitable for the communication in sea water and are illustrated with numerical examples. The underwater communication have been used for the oil (gas) field monitoring, underwater vehicles, coastline protection, oceanographic data collection, etc. The mathematical expression of penetration depth of electromagnetic waves is derived. The significance of penetration depth (skin depth) and loss angle are clarified with numerical examples. The interaction of electromagnetic waves with human tissue is also discussed. When an electric field is applied to a dielectric, the material takes a finite amount of time to polarize. The imaginary part of the permittivity is corresponds to the absorption length of radiation inside biological tissue. In the second part of the chapter, it has been shown that a high frequency wave can be generated through plasma under the presence of electron beam. The electron beam affects the oscillations of plasma and triggers the instability called as electron beam instability. In this section, we use magnetohydrodynamics theory to obtain the modified dispersion relation under the presence of electron beam with the help of the Poisson’s equation. The high frequency instability in plasma grow with the magnetic field, wave length, collision frequency and the beam density. The growth rate linearly increases with collision frequency of electrons but it is decreases with the drift velocity of electrons. The real frequency of the instability increases with magnetic field, azimuthal wave number and beam density. The real frequency is almost independent with the collision frequency of the electrons