Surface Waves Analysis of Efficient Underwater Radio-Based Wireless Link

The domain of underwater wireless communication (UWC) link is gaining much attention due to an increase in various underwater activities such as offshore hydrocarbon exploration, underwater unmanned vehicles (UUV), and military practices. Increased bandwidth and a reliable data link are mainly required for such activities. Both requirements of the domain are heavily affected by the highly conductive property of the seawater. This paper demonstrates the performance evaluation of radiofrequency-UWC, focusing on surface wave analysis, to propose a reliable solution for offshore activities. A constructive interference scheme can be useful due to the sharp difference in the properties of the two mediums (air and seawater). To that end, an experimental setup is created, and a corresponding finite element method (FEM) based simulation of the radio-based wireless link is run. This is because it has higher bandwidth and speed than acoustic and optical approaches. A conduction current mechanism transmits and receives data in a synthetic water tank containing a prepared conductive media (saltwater). The study of changing depths of transmitter-receiver nodes in saltwater shows that surface waves cause significant noise reception in shallow water (less than dipole length, below water level). During a series of experiments in the tank, the lowest bit error rate (BER) is observed only when the node’s submerged height was greater than dipole length. As a result, it is meant to provide a genuine data channel model. The discovery and analysis will aid in the development of a dependable underwater data link, with applications including short-range diver-to-diver communication, and UUV capability.

Interpretasi Bawah Permukaan Gunung Merapi dengan Metode Magnetotellurik

ABSTRAKSurvei magnetotellurik (MT) telah dilakukan di Gunung Merapi dengan menggunakan alat Phoenix Geophysics MTU5 pada Oktober 2016 dan Mei 2017. Pengukuran dilakukan dengan jarak tiap titik sekitar 1 km, durasi pengukuran untuk satu titik ±12 jam, dan lebar dipole 50 s/d 80 meter utara-selatan dan timur barat. Sebanyak 8 titik sounding digunakan untuk menyusun profil resistivitas 2-D di lereng utara dan selatan. Hasil menunjukkan bahwa resistivitas bawah permukaan Merapi terdiri dari 2 (dua) karakteristik nilai resistivitas yaitu zona resistivitas tinggi dengan nilai 183-50.000 ohm.m dan zona resistivitas rendah dengan nilai 20-175 ohm.m. Zona resistivitas tinggi dapat diinterpretasikan sebagai zona produk erupsi sebelumnya yaitu aliran lava dan material piroklastik lainnya. Sedangkan zona resistivitas rendah diinterpretasikan sebagai kantong magma terbagi menjadi dua bagian, bagian atas berada pada kedalaman 0 s/d 2.000 meter dengan diameter mencapai 1.000 meter yang mengindikasikan sebuah kantong magma dangkal, sedangkan bagian bawah terlihat menerus dari kedalaman 3.000 s/d 11.000 meter sebagai kenampakan dapur magma yang cukup besar dengan diameter rata-rata sekitar 2.000 meter yang diindikasikan sebagai kantong magma dalam. Hasil zonasi ini senada dengan posisi hiposenter dari kejadian gempa vulkanik periode tahun 2010. Selain itu, terlihat adanya struktur yang diindikasikan sebagai sesar yang memotong lintasan di sekitar puncak.Kata kunci: Gunung Merapi, kantong magma, magnetotellurik, resistivitasABSTRACTMagnetotelluric (MT) survey has been carried out on Phoenix Geophysics MTU-5 in October 2016 and May 2017. The measurement has been done with the distance between them approximately 1 km, its duration of each sounding was 12 hours, and dipole length varied from 50-80 meters on North-South and East-West direction. Here we use the result from 8 MT sounding to construct a 2-D electrical resistivity image of the northern and southern flank of Merapi. The results show that the subsurface resistivity in Merapi consists of two types of resistivity features, i.e. the high resistivity zone which having resistivity value 183-50.000 ohm.m and the low one which varied from 20-175 ohm.m. The high resistivity zone are the lava flow and another pyroclastic material, while the low resistivity zone interpreted as magma chamber divided into two parts: upper part, at a depth of 0-2,000 meters with 1,000 meters diameter which is indicated as a shallow magma chamber, lower part, continuously from the depth of 3,000-11,000 meters as the large magma chamber with an average diameter of about 2,000 meters. The zone can be correlated to the hypocenter position taken from the volcanic earthquake event of 2010 period. In addition, there is a structure which indicated as a fault that cuts the trajectory around the summit. Keywords: Merapi Volcano, magma chamber, magnetotelluric, resistivity

Сингулярное интегральное уравнение для плотности тока на поверхности полоскового вибратора, расположенного в свободном пространстве

The problem of current density distribution over the surface of a strip dipole antenna occurring in the free space is reduced to a singular integral equation with the Cauchy singularity. Patterns of current distribution on the antenna surface for various values of the dipole length are presented.

2D Geoelectric Imaging of the Uneme-Nekhua Fracture Zone

We have employed 2D geoelectric imaging to reveal the geometry and nature of a fracture zone in Uneme-Nekhua, southwestern Nigeria. The fracture zone is discernable from an outcropping rock scarp and appears to define the course of a seasonal stream. Data were acquired using the dipole-dipole survey array configuration with electrode separation of 6 m and a maximum dipole length of 60 m. Three traverses with lengths varying between 72 m and 120 m were laid orthogonal to the course of the seasonal stream. 2D geoelectric images of the subsurface along the profiles imaged a north-south trending fracture zone. This fracture zone appears to consist of two vertical fractures with more intense definition downstream. The eastern fracture is buried by recent sediment, while the western fracture appears to have experienced more recent tectonic activity as it appears to penetrate through the near surface. Perhaps at some point, deformation ceased on the eastern fracture and further strain was transferred to the western fracture. The fracture zone generally defines the course of the north-south seasonal stream with the exception of the downstream end where the fracture appears to have died out entirely. Two associated basement trenches lying parallel to and east of the fracture zone are also imaged.