• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.1
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• pp.85-95
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• 1998

The broadband ultrasonic transducers have been designed to use in obtaining the broadband echo signals from fish schools in relation to the identification of fish species. The broadening of bandwidth was achieved by attaching double acoustic matching layers on the front face of a Tonpilz transducer consisted of an aluminum head, a piezoelectric ring, a brass tail and to evaluate the performance characteristics, such as the transmitting voltage response(TVR) of transducers. The constructed transducers were tested experimentally and numerically by changing the parameters such as impedances and thicknesses of the head, tail and matching layers, in the water tank. Also, the developed transducer was excited by a chirp signal and the received chirp waveforms were analyzed. According to the measured TVR results, the available 3 dB bandwidth of the transducer with double matching layers of an $Al_O_3/epoxy$ composite of 7 mm thick and a polyurethane window of 18 mm thick was 7.3 kHz with a center frequency of 38.8 kHz, and the maximum and the minimum values of the TVR in this frequency region were 135.7 dB and 132.7 dB re $1\;{\mu}Pa/V$ at 1 m, respectively. Also, the available 3 dB bandwidth of the transducer with double matching layers of an $Al_O_3/epoxy$ composite of 11 mm thick and a polyurethane window of 15 mm thick was 6.2 kHz with a center frequency of 38.6 kHz, and the maximum TVR value in the frequency region was 136.3 dB re $1\;{\mu}Pa/V$ at 1 m. Reasonable agreement between the experimental results and the numerical results for the TVR of the developed transducers was achieved. The frequency dependant characteristics of experimentally observed chirp signals closely matched to the measured TVR results. These results suggest that there is potential for increasing the bandwidth by varying other parameters in the transducer design and the material of the acoustic matching layers.

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.79-86
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• 2012

Cemented soils have been used for subbase or base materials of roads, backfill materials of retaining walls and cofferdam. Such cemented soils can be degraded due to repeated wetting and drying or various weathering actions. Unlike rocks, a standard method was not defined for evaluating the durability of cemented soils. In this study, a slaking durability test and an ultrasound cleaner were used for developing a new durability test method for cemented soils. For durability tests, cemented sands with different cement ratios (4, 6, 8, and 12%) with cylindrical specimens were prepared and then air cured or under-water cured for three days. Three-day-cured specimens were dried for one day and then submerged for one day before testing. The weight loss after the slake durability test or ultrasonic cleaner operation for 10 or 20 min was measured and used for assessing durability. When a cement ratio was 4%, the weight loss from ultrasonic cleaner test was 7-25% but that from slake durability test was as much as 30-60%. For specimens with cement ratio of more than 8%, the weight loss was less than 10% from both tests. A durability index increased with increasing a cement ratio. The durability index of under-water cured specimen was higher than that of air cured specimen. The ultrasonic cleaner test was found to be an effective tool for durability assessment of cemented sands rather than the slake durability test.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.2
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• pp.182-189
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• 2014

This paper proposed a framework of recognition and tracking for underwater objects using sonar images as an alternative of underwater optical camera which has the limitation of usage due to turbidity. In Part 1, a design and recognition method for 2D artificial landmark was proposed considering the practical performance of current imaging sonars. In particular, its materials are selected in order to maximize detectability based on characteristics of imaging sonar and ultrasonic waves. It has a simple and omni-directional shape which allows an easy modeling of object, and it includes region based features as identifications. Also, we proposed a real-time recognition algorithm including edge detector, Hough circle transforms, and shape matrix based recognition algorithm. The proposed methods are verified by basin tests using DIDSON.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.78-85
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• 2005

Initial alignment and localization are important topics in inertial navigation systems, since misalignment and initial position error wholly propagate into the navigation systems and deteriorate the performance of the systems. This paper presents the error convergence characteristics of the hybrid navigation system for underwater vehicles initial position, which is based on an inertial measurement unit (IMU) accompanying a range sensor. This paper demonstrates the improvement on the navigational performance oj the hybrid system with the range information, especially focused on the convergence of the estimation of underwater vehicles initial position error. Simulations are performed with experimental data obtained from a rotating ann test with a fish model. The convergence speed and condition of the initial error removal for random initial position errors are examined with Monte Carlo simulation. In addition, numerical simulation is conducted with an AUV model in lawn-mowing survey mode to illustrate the error convergence of the hybrid navigation System for initial position error.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.385-391
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• 2001

In this study, we will develop the sea surface interpretation system that can aware the target in the bottom of the sea. we will setup the database whose records would be the signal patterns of formation about mud, sand, rock and sea shell achieved by using supersonic. then we will convert analog signal received in fish detector to digital one using A/D converter So we can process and analyze this signal pattern then compare it to the one in our Database at the real time to identify the target in the bottom of the sea. After enough times of experiments from the background of the results that have been achieved from many studies(including a water tank experiment and a field investigation), we can aware the exact information of the sediment and the sand in the sea. By analyzing the first, second and third signal of the supersonic characters reflected from the body of a fish categorized by its family and from the body of shellfish, muddy sand, sand and rocks, We will develop the sea surface decipherment system which abstracts the first signal that shows the target in the bottom of the sea and makes the second and third signals filtering.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.509-517
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• 2012

In the present study, temperature and frequency dependences of ultrasonic properties such as attenuation coefficient and phase velocity was investigated for six kinds of commercial MC-Nylon polymer samples. The ultrasonic properties of the samples were measured by using a pulse transmission method in water over a broadband frequency range of 2 to 8 MHz. Water temperature was varied from 10 to $60^{\circ}C$ with the $10^{\circ}C$ interval. The attenuation coefficients of the samples increased with the frequency and the exponent n of frequency dependence ranged within 1.16 to 1.44, slightly deviating from the linear dependence (n=1). The phase velocities of the samples exhibited negative dispersion, i.e., decreasing velocity with increasing frequency, except for ivory sample at $60^{\circ}C$. The frequency-dependent phase velocities of the samples showed the decreasing tendency with increasing temperature.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.51-65
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• 2007

The purpose of this study is the development and application of a high resolution ultrasonic wave imaging system to detect discontinuity plane in lab-scale rock models. This technique is based on received time series which capture the multiple reflections at interface. This study includes the fundamental aspects of ultrasonic wave propagation in rock mass, the selection of the optimal ultrasonic wave transducer, data gathering, a signal processing, imaging methods, and experiments. Experiments are carried out by the horizontal movement and rotation devices. Experimental studies show the discontinuity is well detected by the horizontal movement and rotation devices under water. Furthermore, the discontinuity and the cavity on the plaster block are identified by the rotation device. This study suggests that the new method may be an economical and effective tool for the detection of the discontinuity on rock mass.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.3
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• pp.164-173
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• 2014

In underwater robotics, vision would be a key element for recognition in underwater environments. However, due to turbidity an underwater optical camera is rarely available. An underwater imaging sonar, as an alternative, delivers low quality sonar images which are not stable and accurate enough to find out natural objects by image processing. For this, artificial landmarks based on the characteristics of ultrasonic waves and their recognition method by a shape matrix transformation were proposed and were proven in Part 1. But, this is not working properly in undulating and dynamically noisy sea-bottom. To solve this, we propose a framework providing a selection phase of likelihood candidates, a selection phase for final candidates, recognition phase and tracking phase in sequence images, where a particle filter based selection mechanism to eliminate fake candidates and a mean shift based tracking algorithm are also proposed. All 4 steps are running in parallel and real-time processing. The proposed framework is flexible to add and to modify internal algorithms. A pool test and sea trial are carried out to prove the performance, and detail analysis of experimental results are done. Information is obtained from tracking phase such as relative distance, bearing will be expected to be used for control and navigation of underwater robots.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.283-286
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• 2003

In this paper, we represent an implementation of burst QPSK receiver for underwater acoustic communication. Transmitter sends 5,000 symbols at 25kHz frequency with 200 kHz D/A sampling rate. The received signal is sampled at 100 kHz. Implemented receiver acquires the frame synchronization, coarse symbol timing estimate, and coarse phase offset estimate using 32 symbol length preamble. The estimated phase offset is used to initiate of 2nd order PLL. The transmission experiment results show that PLL is a mandatory to compensate Doppler shift due to the variation of tidal current.

• The Journal of Korea Robotics Society
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• v.13 no.2
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• pp.79-85
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• 2018

This study focuses on autonomous exploration based on map expansion for an underwater robot equipped with acoustic sonars. Map expansion is applicable to large-area mapping, but it may affect localization accuracy. Thus, as the key contribution of this paper, we propose a method for underwater autonomous exploration wherein the robot determines the trade-off between map expansion ratio and position accuracy, selects which of the two has higher priority, and then moves to a mission step. An occupancy grid map is synthesized by utilizing the measurements of an acoustic range sonar that determines the probability of occupancy. This information is then used to determine a path to the frontier, which becomes the new search point. During area searching and map building, the robot revisits artificial landmarks to improve its position accuracy as based on imaging sonar-based recognition and EKF-SLAM if the position accuracy is above the predetermined threshold. Additionally, real-time experiments were conducted by using an underwater robot, yShark, to validate the proposed method, and the analysis of the results is discussed herein.