• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.95-103
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• 2013

An underwater acoustic (UWA) communication in shallow water is strongly affected by the water surface and the seabed acoustical properties. Every reflected signal to receiver experiences a time-variant scattering in sea surface roughness and a grazing-angle-dependent reflection loss in bottom. Consequently, the performance of UWA communication systems is degraded, and high-speed digital communication is disrupted. If there is a dominant signal path such as a direct path, the received signal is modeled statistically as Rice fading but if not, it is modeled as Rayleigh fading. However, it has been known to be very difficult to reproduce the statistical estimation by real experimental evaluation in the sea. To give an insight for this scattering and grazing-angle-dependent bottom reflection loss effect in UWA communication, authors conduct experiments to quantify these effects. The image is transmitted using binary frequency shift keying (BFSK) modulation. The quality of the received image is shown to be affected by water surface scattering and grazing-angle-dependent bottom reflection loss. The analysis is based on the transmitter to receiver range and the receiver depth dependent image quality and bit error rate (BER). The results show that the received image quality is highly dependent on the transmitter-receiver range and receiver depth which characterizes the channel coherence bandwidth.

• The Journal of the Acoustical Society of Korea
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• v.25 no.1
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• pp.1-6
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• 2006

The Possibility of using acoustic impedance as an input Parameter for computation of underwater acoustic field in shallow waters was investigated. Analysis of the acoustic reflection from the ocean bottom with shear wave effect showed that acoustic impedances below the critical grazing angle have nearly angle-independent property and could be approximated with a single value of near-grazing impedance $Z_0$. Computations of the Propagation loss based on the concept of 'effective depth' indicate that near-grazing bottom acoustic impedances could be used as an input parameter for simulation of the acoustic fields in shallow waters.

• Journal of Software Assessment and Valuation
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• v.15 no.1
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• pp.109-114
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• 2019

In this paper, simulations of S-parameter and characteristic impedance for the probe pin are performed and its high-frequency performance is analyzed. The probe pins are arranged with one signal pin in the center and four ground pins on the top, bottom, left and right sides. The insertion loss and return loss of the probe pin are calculated while increasing the separation between the probe pins to 0.35 mm, 0.40 mm, and 0.50 mm, respectively. It is confirmed that the probe pin has different features of the insertion loss due to its periodic resonance phenomenon. Effect of the characteristic impedance on pitch and assignment of the probe pin is also analyzed. It is verified that there are a number of ground pins whose characteristic impedance is close to 50 Ω.

• Journal of the Institute of Convergence Signal Processing
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• v.20 no.4
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• pp.186-192
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• 2019

In general, many marine organisms are attached to the bottom of a ship in operation or a ship in construction. Due to this phenomenon, the roughness of the ship surface increases, resulting in loss of ship speed, resulting in economic losses and environmental pollution. This study acquires / utilizes camera images attached to ship's bottom and underwater drones to check the condition of bottom. The acquired image will determine the roughness according to marine life by the administrator's visual confirmation. Therefore, by applying a filter algorithm to correct the image to the original image can help in the correct determination of whether or not attached to marine life. Various correction filters are required for the underwater image correction algorithm, and the lighting suitable for the dark underwater environment has a great influence on the judgment. The results of the research test according to the calibration algorithm and the roughness of each algorithm are considered to be applicable to many fields.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.419-426
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• 2016

Measurements of bottom loss as a function of grazing angle (in range of $9{\sim}14^{\circ}$) at a frequency range of 4 ~ 8 kHz were conducted on an experimental site off Geoje island in October 2015. Geoacoustic inversion of the surficial sediment thickness is performed using the arrival time difference between the surficial layer and the sub-bottom layer reflected signal. To invert the thickness of surficial sediment, we used the grain size of $8{\sim}10{\phi}$ obtained by KIGAM (Korea Institute of Geoscience and Mineral Resources). The thickness of the surficial sediment was estimated to be 4 ~ 7 m. Finally, this inversion result was compared with the geoacoustic observation conducted by the KIOST (Korea Institute of Ocean Science & Technology) using sub-bottom profiler.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.573-579
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• 2011

Highly textured Ag, Al and Al:Si back reflectors for flexible n-i-p silicon thin-film solar cells were prepared on 100-${\mu}m$-thick stainless steel substrates by DC magnetron sputtering and the influence of their surface textures on the light-scattering properties were investigated. The surface texture of the metal back reflectors was influenced by the increased grain size and by the bimodal distribution that arose due to the abnormal grain growth at elevated deposition temperatures. This can be explained by the structure zone model (SZM). With an increase in the deposition temperatures from room temperature to $500^{\circ}C$, the surface roughness of the Al:Si films increased from 11 nm to 95 nm, whereas that of the pure Ag films increased from 6 nm to 47 nm at the same deposition temperature. Although Al:Si back reflectors with larger surface feature dimensions than pure Ag can be fabricated at lower deposition temperatures due to the lower melting point and the Si impurity drag effect, they show poor total and diffuse reflectance, resulting from the low reflectivity and reflection loss on the textured surface. For a further improvement of the light-trapping efficiency in solar cells, a new type of back reflector consisting of Ag/Al:Si bilayer is suggested. The surface morphology and reflectance of this reflector are closely dependent on the Al:Si bottom layer and the Ag top layer. The relationship between the surface topography and the light-scattering properties of the bilayer back reflectors is also reported in this paper.