Unmanned underwater systems become increasingly important in the maritime and offshore, security and defence domain. TNO conducts research and experimentation on autonomous
underwater vehicles and underwater communication to advise government and industry on this topic and develop new concept solutions. An overview of the current development will be given
with focus on autonomous decision making for underwater application, cooperative autonomy and new application of underwater autonomous systems for maritime and offshore operations
Development of an FHMA-based Underwater Acoustic Communications System for Mu...Waqas Tariq
This paper describes the design of an underwater acoustic communications system for multiple underwater vehicles, based on frequency-hopping multiple-access (FHMA) and tamed spread-spectrum communications. The system makes used of the tamed spread-spectrum method, frequency hopping, 4FSK, and a rake receiver. In order to make the system more practical, the underwater channel and the effect of the number of users on the bit error ratio (BER) are also taken into account. Since the necessary proving experiments are not easily conducted in the ocean, a platform is developed that uses the sound card of a computer, combined with a sound box and microphone, to transduce energy for acoustic communications. Simulated and experimental results indicate that this system could provide reliable underwater communications between multiple underwater vehicles.
Design of an axial mode helical antenna with buffer layer for underwater app...IJECEIAES
Recently, there is an increasing demand for high-speed wireless communication network for short-range underwater communication. From previous research, most underwater antennas produced omnidirectional radiation pattern which has lower antenna gain. There are a few considerations that need to be taken if the antenna is designed to operate in water environment. This paper discusses the electromagnetic properties which affect the underwater antenna design. Physical properties such as electrical permittivity and conductivity of water contribute significant effect to the size of the antenna as it influences the behavior of electromagnetic signal that propagates in water. In this study, an axial mode helical antenna with waterproof container is presented which operates at 433 MHz. The axial mode helical antenna has circular polarization and is suitable to support wireless application which is surrounded by some obstruction. The proposed antenna produces a bidirectional radiation pattern by placing it into a waterproof casing. Good agreement between the simulation and measurement results validates the concept. However, a little discrepancy between the simulated and measured results may be attributed to the noise originated from the equipment and the environment.
Unmanned underwater systems become increasingly important in the maritime and offshore, security and defence domain. TNO conducts research and experimentation on autonomous
underwater vehicles and underwater communication to advise government and industry on this topic and develop new concept solutions. An overview of the current development will be given
with focus on autonomous decision making for underwater application, cooperative autonomy and new application of underwater autonomous systems for maritime and offshore operations
Development of an FHMA-based Underwater Acoustic Communications System for Mu...Waqas Tariq
This paper describes the design of an underwater acoustic communications system for multiple underwater vehicles, based on frequency-hopping multiple-access (FHMA) and tamed spread-spectrum communications. The system makes used of the tamed spread-spectrum method, frequency hopping, 4FSK, and a rake receiver. In order to make the system more practical, the underwater channel and the effect of the number of users on the bit error ratio (BER) are also taken into account. Since the necessary proving experiments are not easily conducted in the ocean, a platform is developed that uses the sound card of a computer, combined with a sound box and microphone, to transduce energy for acoustic communications. Simulated and experimental results indicate that this system could provide reliable underwater communications between multiple underwater vehicles.
Design of an axial mode helical antenna with buffer layer for underwater app...IJECEIAES
Recently, there is an increasing demand for high-speed wireless communication network for short-range underwater communication. From previous research, most underwater antennas produced omnidirectional radiation pattern which has lower antenna gain. There are a few considerations that need to be taken if the antenna is designed to operate in water environment. This paper discusses the electromagnetic properties which affect the underwater antenna design. Physical properties such as electrical permittivity and conductivity of water contribute significant effect to the size of the antenna as it influences the behavior of electromagnetic signal that propagates in water. In this study, an axial mode helical antenna with waterproof container is presented which operates at 433 MHz. The axial mode helical antenna has circular polarization and is suitable to support wireless application which is surrounded by some obstruction. The proposed antenna produces a bidirectional radiation pattern by placing it into a waterproof casing. Good agreement between the simulation and measurement results validates the concept. However, a little discrepancy between the simulated and measured results may be attributed to the noise originated from the equipment and the environment.
Seawater salinity modelling based on electromagnetic wave characterizationIJECEIAES
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.
Design of Underwater wireless optical/acoustic link for reduction of back-sca...theijes
Underwater communication plays a significant role in the study of climate change through ocean monitoring and associated sensor networks. It is severely limited when compared to free space communication because water is essentially opaque to electromagnetic radiation except in the visible band. Even in the visible band, light penetrates only a few hundred meters in the clearest waters and much less in turbid waters due to the presence of suspended sediment or high concentrations of marine life. Consequently, acoustic techniques are been used for underwater communication systems which is relatively mature and robust. Acoustic systems are capable of long range communication. But traditional underwater acoustic communications cannot provide high enough data rates to enable monitoring technology. Optical wireless communications, centred around blue-green wavelengths, are being used as an alternative. Here a hybrid design is being introduced using an optical/acoustic link to reduce back scattering of transmitted light.
An implementation of_partial_transmit_seWaleed Raza
In this article we research about underwater
acoustics transceivers. As Underwater acoustic transceivers
consume more power than Radio frequency transceivers.
The techniques which are being utilized in radio frequency
cannot be implemented directly in underwater acoustic
system it needs to be re investigated to design new methods.
To achieve reliable acoustic data transmission new
techniques should be achieved or the traditional
Orthogonal frequency divisional multiplexing techniques
should be revised. The power consumption also relies upon
underwater acoustic signal propagation and transmission
distances. Several underwater acoustic applications require
long-term monitoring of the sea. For the battery powered
modems, it becomes very serious problem. By designing an
Energy efficient OFDM Communication system we can
solve this problem. We study about peak to average power
ratio in an Orthogonal frequency divisional multiplexing
system by reducing the major draw-back of OFDM system.
The PAPR reduction utilized in this paper is Partial
Transmit Sequences for underwater acoustic OFDM
communication system which has lesser complexity. The
results have provided better performance in underwater
acoustic OFDM communication system.
While wireless communication technology today has become part of our daily life, the
idea of wireless undersea communications may still seem far-fetched. However, research has
been active for over a decade on designing the methods for wireless information transmission
underwater. Human knowledge and understanding of the world’s oceans, which constitute
the major part of our planet, rests on our ability to collect information from remote undersea
locations.
The major discoveries of the past decades, such as the remains of Titanic, or the hydrothermal
vents at bottom of deep ocean, were made using cabled submersibles. Although such
systems remain indispensable if high-speed communication link is to exists between the
remote end and the surface, it is natural to wonder what one could accomplish without the
burden (and cost) of heavy cables.
Hence the motivation, and interest in wireless underwater communications. Together with
sensor technology and vehicular technology, wireless communications will enable new
applications ranging from environmental monitoring to gathering of oceanographic data,
marine archaeology, and search and rescue missions.
Measuring the underwater received power behavior for 433 mhz radio frequency ...journalBEEI
Underwater wireless sensor network (UWSN) important to enhance the widely use of the application of the Internet of things (IoT) for underwater. Uses of the acoustics base of wave propagations are the best ways to establish the UWSN. But the unpracticality of the hardware due to the size and cost has limited the application of UWSN. Radio frequency (RF) wave propagation is the best way to overcome this situation. Low frequency of the RF wave is proven feasible and suitable for underwater communication. 433 MHz RF were chosen to measuring the underwater received power behavior between the transmitter node and receiver node based on different distance and depth. HC12 transceiver module was used as a transmitter and spectrum analyzer with the telescopic antenna was used as a receiver. The received power give a good reading when the transmitter note was at 0.5-meter depth with a maximum operating range within 12 meters from the receiver.
Microstrip Antenna for ISM Band (2.4GHz) Applications-A reviewIJERA Editor
The past decade has seen a rapid development of wireless communication systems. This continuous trend is bringing about a wave of new wireless devices placing several demands on the antenna such as size miniaturization, power consumption, simplicity, compatibility with printed-circuit technology, low profile, light weight, lower return loss and good radiation properties. This paper provides a comprehensive review of the research work done in the recent past by various authors on the design and optimization of the planar microstrip antenna operating in ISM band. An exhaustive list of reference has been provided.
In this i tried to explain about under water communication.
Introduction of underwater communication.
Problem due to Multipath Propagation
Techniques used for underwater communication
1. Single Carrier Systems
2. MCM Techniques
3. Space-Time Modulation Techniques
Applications
Limitations
Conclusion
Inverted Diamond-shaped Notched Substrate and Patch for High-frequency Interf...IJECEIAES
Notches loaded on a patch antenna can affect significantly on the antenna impedance matching. Therefore, notching technique is an efficient way to reduce the electromagnetic interference with unwanted bands. In this paper, a novel inverted diamond - shaped closed-end slot on a substrate and vertexfed printed hexagonal patch ultra - wideband antenna is proposed for highfrequency band rejection. This antenna is fed using coplanar waveguide, and it is optimised by veering several patch parameters which further improved the inter bandwidth at both the lower and upper bands. However, the centrenotched band is shifted from 6GHz to 7.5GHz by cutting the inverted diamond shape in a special process. The developed ultra-wideband antenna is verified by comparing the simulation results with the measurement results. The measured results with a fractional bandwidth of 133% have a good agreement with the simulation results 146%. Moreover, the measured radiation showed omnidirectional patterns.
This work presents a rectangular of microstrip ultra wideband patch antenna for worldwide interoperability for microwave access (Wi-Max) and wireless local area network (WLAN) with a dual band-notched feature. The planned an antenna consists the rectangular of patch antenna with the largely deficient of ground structure. Through inserting slots in the radiating patch, dual notch characteristics may be produced. The suggested antenna is 20×30×1.6 mm3 in volume. The first notch, made by slots operating at the first notch, produced by slots running at 3.5 GHz, for Wi-Max (from 3.3-3.7 GHz), while of a second, created by slots operating at 5.5 GHz, for WLAN (from 5.1-5.8 GHz). An antenna covers the whole ultra-wideband frequency range (3.1-10.6 GHz). Computer simulation technology (CST) 2021 simulation software used for simulate proposed of antenna. A simulated antenna’s emission pattern is almost omnidirectional, and the recommended antenna’s gain is approximately constant over the ultra-wideband (UWB) spectrum, excluding notch areas.
This lesson describes the concept of VPN and introduces some VPN terminology.
Importance
This lesson is the foundation lesson for the MPLS VPN Curriculum.
Objectives
Upon completion of this lesson, the learner will be able to perform the following
tasks:
■ Describe the concept of VPN
■ Explain VPN terminology as defined by MPLS VPN architecture
This lesson describes the concept of VPN and introduces some VPN terminology.
Importance
This lesson is the foundation lesson for the MPLS VPN Curriculum.
Objectives
Upon completion of this lesson, the learner will be able to perform the following
tasks:
■ Describe the concept of VPN
■ Explain VPN terminology as defined by MPLS VPN architecture
This lesson describes the concept of VPN and introduces some VPN terminology.
Importance
This lesson is the foundation lesson for the MPLS VPN Curriculum.
Objectives
Upon completion of this lesson, the learner will be able to perform the following
tasks:
■ Describe the concept of VPN
■ Explain VPN terminology as defined by MPLS VPN architecture
This lesson describes the concept of VPN and introduces some VPN terminology.
Importance
This lesson is the foundation lesson for the MPLS VPN Curriculum.
Objectives
Upon completion of this lesson, the learner will be able to perform the following
tasks:
■ Describe the concept of VPN
■ Explain VPN terminology as defined by MPLS VPN architecture
This lesson describes the concept of VPN and introduces some VPN terminology.
Importance
This lesson is the foundation lesson for the MPLS VPN Curriculum.
Objectives
Upon completion of this lesson, the learner will be able to perform the following
tasks:
■ Describe the concept of VPN
■ Explain VPN terminology as defined by MPLS VPN architecture
Trong quá trình phát triển của con người, những cuộc các mạng về công nghệ đóng một vai trò rất quan trọng, chúng làm thay đổi từng ngày từng giờ cuộc sống của con người, theo hướng hiện đại hơn. Đi đôi với quá trình phát triển của con người, những thay đổi do chính tác động của con người trong tự nhiên, trong môi trường sống cũng đang diễn ra, tác động trở lại chúng ta, như ô nhiễm môi trường, khí hậu thay đổi, v.v... Dân số càng tăng, nhu cầu cũng tăng theo, các dịch vụ, các tiện ích từ đó cũng được hình thành và phát triển theo. Đặc biệt là áp dụng các công nghệ của các ngành điện tử, công nghệ thông tin và viễn thông vào trong thực tiễn cuộc sống con người. Công nghệ cảm biến không dây được tích hợp từ các kỹ thuật điện tử, tin học và viễn thông tiên tiến vào trong mục đích nghiên cứu, giải trí, sản xuất, kinh doanh, v.v..., phạm vi này ngày càng được mở rộng, để tạo ra các ứng dụng đáp ứng cho các nhu cầu trên các lĩnh vực khác nhau. Hiện nay, công nghệ cảm biến không dây chưa được áp dụng một các rộng rãi ở nước ta, do những điều kiện về kỹ thuật, kinh tế, nhu cầu sử dụng. Song nó vẫn hứa hẹn là một đích đến tiêu biểu cho các nhà nghiên cứu, cho những mục đích phát triển đầy tiềm năng. Để áp dụng công nghệ này vào
thực tế trong tương lai, đã có không ít các nhà khoa học đã tập trung nghiên cứu, nắm bắt những thay đổi trong công nghệ này.
Experimental Evaluation of Distortion in Amplitude Modulation Techniques for ...Huynh MVT
Experimental Evaluation of Distortion in Amplitude Modulation Techniques for Parametric Loudspeakers
A PC (Intel Xeon with 16Gb of RAM, Intel Corporation, Santa Clara, California, USA)
Audio Measurements in the Presence of a High-Level Ultrasonic Carrier
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
1. Journal of
Marine Science
and Engineering
Article
Development of Broadband Underwater Radio
Communication for Application in Unmanned
Underwater Vehicles
Igor Smolyaninov 1,* , Quirino Balzano 2 and Dendy Young 1
1 Saltenna LLC, 1751 Pinnacle Drive, Suite 600, McLean, VA 22102-4903, USA; dendy.young@saltenna.com
2 Electrical and Computer Engineering Department, University of Maryland, College Park, MD 20742, USA;
qbalzano@umd.edu
* Correspondence: smoly@umd.edu
Received: 31 March 2020; Accepted: 18 May 2020; Published: 23 May 2020
Abstract: This paper presents several novel designs of small form factor underwater radio antennas
operating in the 2 MHz, 50 MHz and 2.4 GHz bands. These antennas efficiently excite surface
electromagnetic waves (SEW) which propagate along the surface of seawater. The antenna operation
is made possible due to implementation of an impedance matching enclosure, which is filled with
de-ionized water. Enhanced coupling to surface electromagnetic waves is enabled by the enhancement
of the electromagnetic field at the antenna apex. These features allow us to make antenna dimensions
considerably smaller compared to typical free space designs. They also considerably improve coupling
of electromagnetic energy to the surrounding seawater. Since SEW propagation length is considerably
larger than the skin depth in seawater, this technique is useful for underwater broadband wireless
communication. We conclude that the developed broadband underwater radio communication
technique will be useful in networking of unmanned underwater vehicles.
Keywords: unmanned underwater vehicle; broadband radio communication; surface electromagnetic
wave
1. Introduction
Wide band communication remains the limiting bottleneck for command and control of unmanned
underwater vehicles (UUV). Acoustic communication is bandwidth limited due to slow propagation
speeds and is susceptible to high error rates due to multi-path effects. Conventional radio frequency
(RF) signals may be used for wide bandwidth communications. However, they are severely limited in
communication range due to rapid attenuation in seawater. Directional optical links are capable of
providing bandwidth over 200 Mbps in seawater but, until now, have not been successfully integrated
into operational UUVs due to the need for sophisticated pointing, acquisition and tracking. Moreover,
water turbidity strongly affects performance of the optical links. As a result, the use of optical wireless
communication for reliable UUV-to-UUV links remains highly challenging. Thus, underwater wide
bandwidth wireless communication remains a critical technology gap that needs to be filled.
Very recently we have reported a novel design of a SEW RF antenna, which operates in the
2.4 GHz band and which efficient launches surface electromagnetic waves along an interface between
a conductor and a dielectric [1]. The antenna operation is based on the strong field enhancement at the
antenna tip, which results in efficient excitation of surface electromagnetic waves propagating along
nearby conductive surfaces. It was demonstrated that this antenna may be used to send broadband
radio communication signals through such conductive enclosures as commercial Faraday cages. It was
also hypothesized that a similar design could be used for broadband underwater communication.
Indeed, a successful adaptation of the surface wave antenna design was reported in [2] which operates
J. Mar. Sci. Eng. 2020, 8, 370; doi:10.3390/jmse8050370 www.mdpi.com/journal/jmse
2. J. Mar. Sci. Eng. 2020, 8, 370 2 of 10
in the 50 MHz band and is able for launch SEWs along the seawater surface. In addition to the
enhancement of electromagnetic field near the antenna apex, the antenna design implements an
impedance matching enclosure which uses de-ionized water [3]. This enclosure enables reduction
of the antenna dimensions. It also improves coupling of electromagnetic energy to the surrounding
seawater. Since the propagation length of SEW considerably exceeds the skin depth of radio waves
at the same frequency, the surface wave technique may be used for underwater broadband wireless
communication over long distances.
In this article, we report further development of this concept. We will describe several designs
of portable underwater radio antennas operating in the 2 MHz, 50 MHz and 2.4 GHz bands, which
can be used for efficient launching of SEWs along the seawater surface. In all cases, the developed
surface wave underwater antennas are capable of broadband underwater wireless communication
over distances which are much larger than the skin depth in seawater. We infer that the developed
broadband underwater radio communication technique will be useful in communication among
unmanned underwater vehicles.
2. Methods
Typically, it is impossible to establish RF communication through conductive media and enclosures,
such as communication through seawater, metallic chambers, etc. Performance of conventional radio
communication schemes in these geometries is limited by the very small skin depth δ of a conductive
medium, which may be calculated as:
δ =
s
1
πµ0σν
(1)
where ν is the communication frequency and σ is the medium conductivity [4]. In the case of seawater
(3.5% salinity, 5 S/m conductivity), the frequency dependent RF skin depth may be estimated by
δ ≈
270m
√
ν
(2)
This effect severely limits the ability to use radio communication in seawater. For example, the
skin depth of seawater at 50 MHz equals approximately 3.8 cm, so it is impractical to use conventional
radio communication over useful distances. In addition, conventional RF signals cannot penetrate
through small defects and openings in conductive barriers. For example, transmission of a conventional
transverse electromagnetic wave through a subwavelength aperture was found by Bethe [5] to be
equal to
T ∝
a
λ
4
, (3)
where λ is the free space wavelength and a is the aperture size. It produces negligible transmission if
a λ. Therefore, conventional radio communication techniques are also impractical in situations
where an enclosure is surrounded by conductive walls.
On the other hand, it is well established that efficient coupling to surface electromagnetic modes
which exist at conductor/dielectric interfaces [6] enables efficient signal transmission through continuous
conductive barriers (including even metal layers) and through deeply subwavelength apertures in
such barriers [7,8]. Following this approach, we have designed a 2.45-GHz SEW antenna [1], which can
transmit video signals from inside a −90 dB isolation Faraday cage. We believe that this novel ability
may be utilized for remote examination of metal enclosures, as well as improving Wi-Fi connectivity in
underground tunnels and buildings. Moreover, a similar surface electromagnetic wave-based approach
3. J. Mar. Sci. Eng. 2020, 8, 370 3 of 10
may be used to implement broadband radio communication in seawater over long distances, which
considerably exceed the skin depth of radio waves in seawater [2].
The operating principle of the SEW antenna is illustrated in Figure 1a. The electric field of the
SEW has a nonzero component in the longitudinal direction, which means that a good SEW antenna
needs to be located near of a conductive surface, and it needs to produce a strong field enhancement
at its tip, which will push charges along the conductive surface. When such an antenna is adapted
for surface wave-based underwater communication, it is encapsulated in an impedance matching
enclosure, which is filled with de-ionized water, as illustrated in Figure 1b. This enclosure enables
reduction of the antenna dimensions by approximately factor of 9 compared to the dimensions of
similar antenna in free space. The enclosure also improves coupling of electromagnetic energy to the
surrounding seawater, since compared to the air/seawater interface, an interface between de-ionized
water and seawater is much better impedance-matched. In addition, it also reduces the ohmic losses
which would arise due to the immersion of the antenna in seawater. Examples of such antenna designs
optimized for operation in the 50 MHz and 2 MHz bands are presented in Figure 2.
A tuning procedure of the surface wave antenna is illustrated in Figure 3. It illustrates measurements
of S11 of the 2.45 GHz helical SEW antennas as a function of distance to a large planar conductive
surface. As illustrated in Figure 3b, depending on the location of the tapping point, the radiative
behavior of the antenna may be optimized for either surface wave radiation or radiation into free
space. The antenna tuning was also checked by maximizing the received video signal outside a closed
Faraday cage, as described in detail in [1]. A comprehensive description of antenna geometry shown
in Figure 1a and its fabrication, tuning and testing may be found in [1,2].
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 3 of 11
in seawater over long distances, which considerably exceed the skin depth of radio waves in seawater
[2].
The operating principle of the SEW antenna is illustrated in Figure 1a. The electric field of the
SEW has a nonzero component in the longitudinal direction, which means that a good SEW antenna
needs to be located near of a conductive surface, and it needs to produce a strong field enhancement
at its tip, which will push charges along the conductive surface. When such an antenna is adapted for
surface wave-based underwater communication, it is encapsulated in an impedance matching
enclosure, which is filled with de-ionized water, as illustrated in Figure 1b. This enclosure enables
reduction of the antenna dimensions by approximately factor of 9 compared to the dimensions of
similar antenna in free space. The enclosure also improves coupling of electromagnetic energy to the
surrounding seawater, since compared to the air/seawater interface, an interface between de-ionized
water and seawater is much better impedance-matched. In addition, it also reduces the ohmic losses
which would arise due to the immersion of the antenna in seawater. Examples of such antenna
designs optimized for operation in the 50 MHz and 2 MHz bands are presented in Figure 2.
(a) (b)
Figure 1. Operation of the SEW antenna near a conductor/dielectric interface where the antenna is
placed either on the dielectric (air) side of the interface, or on the conductor (seawater) side near the
interface: (a) Schematic geometry of a 2.4 GHz surface wave antenna design based on helical
monopole shorted to its feed line outer conductor. The tip of the antenna is shown near a flat
conductive surface where it excites an omnidirectional surface electromagnetic wave. The
electromagnetic field of the surface electromagnetic wave is partially longitudinal, which means that
an efficient surface wave antenna needs a strong field enhancement at its apex, which “pushes”
charges along the metal surface; (b) Principle of operation of a similar underwater surface
electromagnetic wave RF transmitter.
Figure 1. Operation of the SEW antenna near a conductor/dielectric interface where the antenna is
placed either on the dielectric (air) side of the interface, or on the conductor (seawater) side near the
interface: (a) Schematic geometry of a 2.4 GHz surface wave antenna design based on helical monopole
shorted to its feed line outer conductor. The tip of the antenna is shown near a flat conductive surface
where it excites an omnidirectional surface electromagnetic wave. The electromagnetic field of the
surface electromagnetic wave is partially longitudinal, which means that an efficient surface wave
antenna needs a strong field enhancement at its apex, which “pushes” charges along the metal surface;
(b) Principle of operation of a similar underwater surface electromagnetic wave RF transmitter.
4. J. Mar. Sci. Eng. 2020, 8, 370 4 of 10
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 4 of 11
(a) (b)
Figure 2. (a) SEW underwater antennas attached to Yaesu VX-8 radios operated at 50 MHz. The
impedance-matching enclosures are filled with de-ionized water; (b) Assembled surface wave
underwater antenna operating in the 2 MHz band attached to a Yaesu FT-857 radio operated at 5 W
output power. The impedance-matching enclosure (seen in the bottom section of the assembly) is
filled with de-ionized water.
A tuning procedure of the surface wave antenna is illustrated in Figure 3. It illustrates
measurements of S11 of the 2.45 GHz helical SEW antennas as a function of distance to a large planar
conductive surface. As illustrated in Figure 3b, depending on the location of the tapping point, the
radiative behavior of the antenna may be optimized for either surface wave radiation or radiation
into free space. The antenna tuning was also checked by maximizing the received video signal outside
a closed Faraday cage, as described in detail in [1]. A comprehensive description of antenna geometry
shown in Figure 1a and its fabrication, tuning and testing may be found in [1,2].
(a) (b)
Figure 2. (a) SEW underwater antennas attached to Yaesu VX-8 radios operated at 50 MHz.
The impedance-matching enclosures are filled with de-ionized water; (b) Assembled surface wave
underwater antenna operating in the 2 MHz band attached to a Yaesu FT-857 radio operated at 5 W
output power. The impedance-matching enclosure (seen in the bottom section of the assembly) is filled
with de-ionized water.
(a) (b)
Figure 2. (a) SEW underwater antennas attached to Yaesu VX-8 radios operated at 50 MHz. The
impedance-matching enclosures are filled with de-ionized water; (b) Assembled surface wave
underwater antenna operating in the 2 MHz band attached to a Yaesu FT-857 radio operated at 5 W
output power. The impedance-matching enclosure (seen in the bottom section of the assembly) is
filled with de-ionized water.
A tuning procedure of the surface wave antenna is illustrated in Figure 3. It illustrates
measurements of S11 of the 2.45 GHz helical SEW antennas as a function of distance to a large planar
conductive surface. As illustrated in Figure 3b, depending on the location of the tapping point, the
radiative behavior of the antenna may be optimized for either surface wave radiation or radiation
into free space. The antenna tuning was also checked by maximizing the received video signal outside
a closed Faraday cage, as described in detail in [1]. A comprehensive description of antenna geometry
shown in Figure 1a and its fabrication, tuning and testing may be found in [1,2].
(a) (b)
Figure 3. (a) Measurements of S11 of the fabricated helical antenna resonant at 2.45 GHz near a large
copper plane. The micro-positioning stage is located below the copper plane. The inset shows a photo
of the antenna; (b) Tuning of the fabricated helical antennas resonant at 2.45 GHz via measurements of
S11 as a function of distance from the large copper plane. The tuning parameter is the tapping point of
a feeding coaxial line. The red, green and blue curves correspond to different positions of the tapping
point on the same antenna. Behavior of a conventional dipole antenna is presented for a comparison.
5. J. Mar. Sci. Eng. 2020, 8, 370 5 of 10
3. Results
3.1. Broadband Transmission through Faraday Cage
The performance of the designed SEW antenna in the 2.4 GHz band has been tested by verifying
Wi-Fi video signal transmission through a −90 dB isolation Faraday cage, as illustrated in Figure 4.
The video signal was generated inside a locked Faraday cage and transmitted through free space live.
There was no cabling or connecting ground between the transmitter and receiver. The video signal
received outside the enclosure by a similar antenna at a distance on the order of 10 to 100 cm was
displayed on a live TV monitor.
Figure 3. (a) Measurements of S11 of the fabricated helical antenna resonant at 2.45 GHz near a large
copper plane. The micro-positioning stage is located below the copper plane. The inset shows a photo
of the antenna; (b) Tuning of the fabricated helical antennas resonant at 2.45 GHz via measurements
of S11 as a function of distance from the large copper plane. The tuning parameter is the tapping point
of a feeding coaxial line. The red, green and blue curves correspond to different positions of the
tapping point on the same antenna. Behavior of a conventional dipole antenna is presented for a
comparison.
3. Results
3.1. Broadband Transmission through Faraday Cage
The performance of the designed SEW antenna in the 2.4 GHz band has been tested by verifying
Wi-Fi video signal transmission through a −90 dB isolation Faraday cage, as illustrated in Figure 4.
The video signal was generated inside a locked Faraday cage and transmitted through free space live.
There was no cabling or connecting ground between the transmitter and receiver. The video signal
received outside the enclosure by a similar antenna at a distance on the order of 10 to 100 cm was
displayed on a live TV monitor.
(a) (b)
Figure 4. (a) SEW antenna maintains transmission of video signal from a locked −90 dB Faraday cage
(JRE Test, model 0709). (b) Conventional dipole antenna cannot transmit the video signal when used
in the same experimental configuration.
The surface wave mediated mechanism of 2.4 GHz video signal transmission has been verified
by measurements of the transmitted signal near the Faraday cage as a function of distance from the
outside wall of the cage [1]. The surface wave character of the transmitted signal was confirmed by
an exponential decay of the transmitted signal outside of the cage. However, the signal received
farther away from the cage was a conventional TEM signal, which originated due to the transmitted
SEW field reaching the cage corners and scattering into the conventional TEM fields.
3.2. Broadband Underwater RF Communication Experiments in Laboratory Settings
It is obvious that the experiments with a Faraday cage depicted in Figure 4 above are
topologically equivalent to the experiments with the same 2.4 GHz SEW antennas performed in a
seawater aquarium, which are depicted in Figure 5. In these experiments, the seawater surrounding
the Wi-Fi video transmitter (which is enclosed in a watertight plastic case) plays the role of a Faraday
cage.
Figure 4. (a) SEW antenna maintains transmission of video signal from a locked −90 dB Faraday cage
(JRE Test, model 0709). (b) Conventional dipole antenna cannot transmit the video signal when used in
the same experimental configuration.
The surface wave mediated mechanism of 2.4 GHz video signal transmission has been verified
by measurements of the transmitted signal near the Faraday cage as a function of distance from the
outside wall of the cage [1]. The surface wave character of the transmitted signal was confirmed by an
exponential decay of the transmitted signal outside of the cage. However, the signal received farther
away from the cage was a conventional TEM signal, which originated due to the transmitted SEW field
reaching the cage corners and scattering into the conventional TEM fields.
3.2. Broadband Underwater RF Communication Experiments in Laboratory Settings
It is obvious that the experiments with a Faraday cage depicted in Figure 4 above are topologically
equivalent to the experiments with the same 2.4 GHz SEW antennas performed in a seawater aquarium,
which are depicted in Figure 5. In these experiments, the seawater surrounding the Wi-Fi video
transmitter (which is enclosed in a watertight plastic case) plays the role of a Faraday cage.
Note that the skin depth of seawater at 2.4 GHz is 3 mm, while the thickness of seawater layer
around the watertight plastic case was at least 15 cm on each side. Note also that water turbidity did
not affect video signal transmission, as illustrated in Figure 5b. Thus, similar to transmission through
a Faraday cage, the SEW antenna clearly demonstrates increased capacity for Wi-Fi transmission
through seawater. This increased capacity may be understood based on the theoretical values for
SEW propagation length Lr along the seawater-air interface, and the penetration depth Lz of SEW field
into the seawater [2]. Based on the detailed theoretical consideration in [6,9], they are given by the
following expressions:
Lz ≈
λ0
4π
√
ε00
, (4)
6. J. Mar. Sci. Eng. 2020, 8, 370 6 of 10
and
Lr ≈
λ0ε00
π
, (5)
respectively [4], where λ0 is the free space wavelength, and ε” is the imaginary part of the dielectric
constant of saltwater. For example, at 50 MHz the theoretical SEW propagation distance is quite large
(Lr = 60 m), while the communication depth Lz may reach several meters assuming Tx operation down
to −90 dB relative signal level. These distances appear to be much larger than the 3.8 cm skin depth of
seawater at 50 MHz. These observations are illustrated in Figure 6, which demonstrates the radio field
distribution near the seawater surface, which is produced by a point source of radio waves located
near the air/seawater interface (these simulations were performed using the RF module of COMSOL
Multiphysics). At some distance from a source (which is much longer than the bulk skin depth of
seawater) the RF field is dominated by the SEW contribution, which enables radio communication
from point A to point B. This communication would be impossible in the absence of the surface wave.
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 6 of 11
(a) (b)
Figure 5. (a) Similar to experiments depicted in Figure 4, a 2.4 GHz surface wave antenna transmits
video signal from inside an aquarium filled with seawater; (b) The video transmission is not affected
by water turbidity.
Note that the skin depth of seawater at 2.4 GHz is 3 mm, while the thickness of seawater layer
around the watertight plastic case was at least 15 cm on each side. Note also that water turbidity did
not affect video signal transmission, as illustrated in Figure 5b. Thus, similar to transmission through
a Faraday cage, the SEW antenna clearly demonstrates increased capacity for Wi-Fi transmission
through seawater. This increased capacity may be understood based on the theoretical values for
SEW propagation length Lr along the seawater-air interface, and the penetration depth Lz of SEW field
into the seawater [2]. Based on the detailed theoretical consideration in [6,9], they are given by the
following expressions:
4
0
ε
π
λ
≈
z
L
,
(4)
and
π
ε
λ
0
≈
r
L
,
(5)
respectively [4], where λ0 is the free space wavelength, and ε” is the imaginary part of the dielectric
constant of saltwater. For example, at 50 MHz the theoretical SEW propagation distance is quite large
(Lr = 60 m), while the communication depth Lz may reach several meters assuming Tx operation down
to −90 dB relative signal level. These distances appear to be much larger than the 3.8 cm skin depth
of seawater at 50 MHz. These observations are illustrated in Figure 6, which demonstrates the radio
field distribution near the seawater surface, which is produced by a point source of radio waves
located near the air/seawater interface (these simulations were performed using the RF module of
COMSOL Multiphysics). At some distance from a source (which is much longer than the bulk skin
depth of seawater) the RF field is dominated by the SEW contribution, which enables radio
communication from point A to point B. This communication would be impossible in the absence of
the surface wave.
Figure 5. (a) Similar to experiments depicted in Figure 4, a 2.4 GHz surface wave antenna transmits
video signal from inside an aquarium filled with seawater; (b) The video transmission is not affected by
water turbidity.
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 7 of 11
Figure 6. Numerical simulations of radio field distribution near the air/seawater interface, which is
produced by a point source located near the sea surface. At large distances from a SEW antenna, the
field is dominated by the SEW contribution. These simulations were performed using COMSOL
Multiphysics solver.
We should also note that waviness of the seawater–air interface may further promote coupling
of the electromagnetic energy into the SEW modes. Such an increased coupling is well established in
the closely related field of plasmonics [6], and it was observed in our model experiments performed
in a seawater aquarium at 2.4 GHz (see Figure 7). These simple experiments indicate that an agitated
sea state may not necessarily present a problem for SEW-based broadband underwater RF
Figure 6. Numerical simulations of radio field distribution near the air/seawater interface, which is
produced by a point source located near the sea surface. At large distances from a SEW antenna,
the field is dominated by the SEW contribution. These simulations were performed using COMSOL
Multiphysics solver.
7. J. Mar. Sci. Eng. 2020, 8, 370 7 of 10
We should also note that waviness of the seawater–air interface may further promote coupling of
the electromagnetic energy into the SEW modes. Such an increased coupling is well established in the
closely related field of plasmonics [6], and it was observed in our model experiments performed in a
seawater aquarium at 2.4 GHz (see Figure 7). These simple experiments indicate that an agitated sea
state may not necessarily present a problem for SEW-based broadband underwater RF communication.
Figure 6. Numerical simulations of radio field distribution near the air/seawater interface, which is
produced by a point source located near the sea surface. At large distances from a SEW antenna, the
field is dominated by the SEW contribution. These simulations were performed using COMSOL
Multiphysics solver.
We should also note that waviness of the seawater–air interface may further promote coupling
of the electromagnetic energy into the SEW modes. Such an increased coupling is well established in
the closely related field of plasmonics [6], and it was observed in our model experiments performed
in a seawater aquarium at 2.4 GHz (see Figure 7). These simple experiments indicate that an agitated
sea state may not necessarily present a problem for SEW-based broadband underwater RF
communication.
(a) (b)
Figure 7. (a) The Wi-Fi underwater video transmitter is moved beyond the free space communication
range in a seawater aquarium with still water surface; (b) The video link is re-established when the
seawater surface is agitated.
Directionality of SEW beams, which is also well known in plasmonics [6,10] may further
improve performance of underwater RF communication links, since it may to some extent alleviate
deterioration of link performance due to high propagation losses in seawater. We were able to
demonstrate directional excitation and propagation of SEW waves in model experiments performed
in a freshwater aquarium in laboratory settings, as illustrated in Figure 8.
Figure 7. (a) The Wi-Fi underwater video transmitter is moved beyond the free space communication
range in a seawater aquarium with still water surface; (b) The video link is re-established when the
seawater surface is agitated.
Directionality of SEW beams, which is also well known in plasmonics [6,10] may further improve
performance of underwater RF communication links, since it may to some extent alleviate deterioration
of link performance due to high propagation losses in seawater. We were able to demonstrate directional
excitation and propagation of SEW waves in model experiments performed in a freshwater aquarium
in laboratory settings, as illustrated in Figure 8.
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 8 of 11
(a) (b)
Figure 8. (a) 400 MHz SEW field of an antenna array submerged into a fresh-water aquarium is probed
by a distant dipole receiver; (b) Antenna array field measured in the transverse direction at 12 and 24
cm from the array. The inset shows numerical modeling of SEW directional beaming from the antenna
array.
In these experiments, we have used an array of four dipole antennas spaced at 5 cm distances,
which resonate at 2.4 GHz in air. After the array was submerged into a freshwater aquarium, its
resonant frequency shifted to 400 MHz. The antenna array field was probed by a distant dipole
receiver identical to individual antennas in the array, as illustrated in Figure 8a. It was verified that
there was no relevant coupling between the feed lines above water. The antenna array field measured
in the transverse direction at two distances from the array is plotted in Figure 8b, which also shows
our numerical modeling of SEW beaming.
3.3. Field Testing of Broadband Underwater RF Communication
The field performance of the developed SEW antennas has been tested at an underwater testing
facility near Panama City, Florida (average water salinity 3.0%) [2]. The SEW antennas were tested in
Figure 8. (a) 400 MHz SEW field of an antenna array submerged into a fresh-water aquarium is probed
by a distant dipole receiver; (b) Antenna array field measured in the transverse direction at 12 and
24 cm from the array. The inset shows numerical modeling of SEW directional beaming from the
antenna array.
In these experiments, we have used an array of four dipole antennas spaced at 5 cm distances,
which resonate at 2.4 GHz in air. After the array was submerged into a freshwater aquarium, its
resonant frequency shifted to 400 MHz. The antenna array field was probed by a distant dipole receiver
identical to individual antennas in the array, as illustrated in Figure 8a. It was verified that there was
no relevant coupling between the feed lines above water. The antenna array field measured in the
transverse direction at two distances from the array is plotted in Figure 8b, which also shows our
numerical modeling of SEW beaming.
8. J. Mar. Sci. Eng. 2020, 8, 370 8 of 10
3.3. Field Testing of Broadband Underwater RF Communication
The field performance of the developed SEW antennas has been tested at an underwater testing
facility near Panama City, Florida (average water salinity 3.0%) [2]. The SEW antennas were tested in the
50 MHz band. The seawater testing environment was sufficiently large, so that no significant boundary
effects were present. These tests were conducted using separate battery-operated transmitting (TX)
and receiving (RX) antenna and radio systems, which were enclosed in watertight containers shown in
Figure 2a. The underwater radio systems were operated by divers as illustrated in Figure 9a. The divers
verified their respective depth and distance from each other using fixed markers made of buoys and
ropes. The signal propagation data were read by the divers from the LED indicator and the S-meter
of the Yaesu radios. These data were reported by the divers to the test personnel, which was located
on a nearby vessel. The measured averaged measured link probability data are plotted in Figure 9b.
The skin depth at 50 MHz in seawater (3.8 cm) is shown near the bottom left corner of the plot for
comparison. These results clearly demonstrate that the novel underwater SEW antennas described
above enable radio communication over range/depth combinations which go far beyond the known
skin depth of seawater. Note that the relatively large variations of the link probability observed in
our experiments may be explained by the variations in seawater salinity during the experiments and
changes in the sea state (the seawater ripples), bubbles and biological objects, which scatter the surface
electromagnetic waves.
J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 9 of 11
0 1 2 3 4 5
2.5
2.0
1.5
1.0
0.5
0.0
Distance (m)
Depth
(m)
0
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.000
link probability
sea floor
sea surface
skin depth at 50 MHz is 3.8 cm
(shown to the scale)
(a) (b)
Figure 9. (a) Photo of the underwater test range used in our experiments. The inset shows
experimental configuration; (b) Contour plot of the link probability measured in seawater as a
function of diver depth and distance between the divers. The sea floor was located at 9 m depth. The
skin depth at 50 MHz in seawater is shown to the scale.
The underwater experiments depicted in Figure 9 were conducted without any external cables,
in order to exclude any possibility of a spurious crosstalk. All the transmitter and receiver radios and
antennas were placed underwater as shown in the inset in Figure 9a. In the absence of a network
analyzer underwater, the values of S11 and S22 were not measured during the experiments depicted in
Figure 9. However, these values were measured in the lab in a seawater tank, as depicted in Figure
10.
Figure 9. (a) Photo of the underwater test range used in our experiments. The inset shows experimental
configuration; (b) Contour plot of the link probability measured in seawater as a function of diver
depth and distance between the divers. The sea floor was located at 9 m depth. The skin depth at
50 MHz in seawater is shown to the scale.
The underwater experiments depicted in Figure 9 were conducted without any external cables,
in order to exclude any possibility of a spurious crosstalk. All the transmitter and receiver radios and
antennas were placed underwater as shown in the inset in Figure 9a. In the absence of a network
analyzer underwater, the values of S11 and S22 were not measured during the experiments depicted in
Figure 9. However, these values were measured in the lab in a seawater tank, as depicted in Figure 10.
While the observed SEW signal propagation at 50 MHz was considerably below the theoretically
projected Lr = 60 m, we anticipate that further optimization of the SEW antenna will result in reaching the
theoretical depth and distance limits, which are described by Equations (4) and (5). These performance
limits are summarized in Table 1 for the set of RF bands explored in this paper. Note that predictions
given by Equation (5) may not be reliable at smaller frequencies due to the fact that it was derived for a
planar conductor-dielectric interface.
9. J. Mar. Sci. Eng. 2020, 8, 370 9 of 10
The underwater experiments depicted in Figure 9 were conducted without any external cables,
in order to exclude any possibility of a spurious crosstalk. All the transmitter and receiver radios and
antennas were placed underwater as shown in the inset in Figure 9a. In the absence of a network
analyzer underwater, the values of S11 and S22 were not measured during the experiments depicted in
Figure 9. However, these values were measured in the lab in a seawater tank, as depicted in Figure
10.
Figure 10. S11 and S22 of the antennas used in the experiments depicted in Figure 9. These parameters
were measured in the lab in a seawater tank. A de-ionized water antenna enclosure was implemented
during these measurements.
While the observed SEW signal propagation at 50 MHz was considerably below the theoretically
projected Lr = 60 m, we anticipate that further optimization of the SEW antenna will result in reaching
the theoretical depth and distance limits, which are described by Equations (4) and (5). These
performance limits are summarized in Table 1 for the set of RF bands explored in this paper. Note
that predictions given by Equation (5) may not be reliable at smaller frequencies due to the fact that
it was derived for a planar conductor-dielectric interface.
Figure 10. S11 and S22 of the antennas used in the experiments depicted in Figure 9. These parameters
were measured in the lab in a seawater tank. A de-ionized water antenna enclosure was implemented
during these measurements.
Table 1. Summary of the theoretically predicted propagation range Lr and communication depth Lz
(@ 5W transmit power) at the RF bands explored in this paper.
2.4 GHz Band 50 MHz Band 2 MHz Band
Lz 0.054 m 0.7 m 3.5 m
Lr 3.8 m 60 m 900 km 1
1 Theoretical numbers given by Equation (5) may not be reliable in this band due to Earth curvature.
4. Discussion and Conclusions
The communication distance/depth combinations summarized in Table 1 provide quite an
optimistic outlook for potential applications of SEW antennas in underwater communication between
divers and UUVs, since even larger communication depth may be achieved at lower frequencies.
For example, it appears that Lz~15 m is achievable in the 0.1 MHz band at quite modest 5 W transmit
power. Our experimental and theoretical results appear to be novel and important since, until very
recently, the general belief was that broadband RF communication through seawater is impossible
over any practical distance. We anticipate that further development of SEW antennas and further
optimization of the antenna parameters will result in reaching the theoretical limits on underwater
depth and communication distance, which are described by Equations (4) and (5). These developments
will enable novel technology for wide bandwidth radio signal communication through seawater. We
should also note that our SEW-based RF communication scheme should be able to breach the seawater
barrier for UAV to UUV communication, since the surface wave EM field is present both above and
below the seawater surface. This would enable, for example, a drone skimming the surface of the water
to pick up signal transmitted from a UUV. The described antennas may also be made multi-spectral so
that the communication bandwidth at a given distance/depth combination may be optimized under
software control, shifting to larger bandwidths over shorter distances. Our communication scheme
may also find applications in frogman to frogman communication, underwater object detection, UUV
swarming and mesh networked UUVs, offshore oil platforms, etc. We also expect that our technology
will enable considerable improvements in Wi-Fi connectivity in buildings and underground tunnels.
Remote examination of metal and partially metal enclosures, such as shipping containers and metallic
test chambers, should also become possible in the near future.