• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.05a
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• pp.351-358
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• 1998

This paper deals with the underwater image transmission system which includes in AUV(Autonomous Underwater Vehicle) Project(that is VORAM(Vehicle for Ocean Research And Monitoring)), developed by KIMM for survey and investigation of a sea-bed through transmitting the underwater image to the mother ship. The system presented in this paper consists of a transducer which has a 136KHz center frequency and it's 10KHz bandwidth, pre-amplifier, $\pi$/4 QPSK(Quadreature Phase Shift Keying) modulation/demodulation method, image compressing method using JPEG technique and modified Stop & protocol. The experimental results of the system is verified to a high performance with 9600 bps for transmitting the underwater image through the basin test. The results of test are also verified which allows to desirable transmission performance compared with the existing developed system and the possibility to put the practical use of survey and investigation. And, the viterbi coding and adaptive equalizer for cancelling the multipath effect are developing for more effective image transmission system. Also, these technique will very effectively adapt to realtime image transmission system.

• The Journal of the Acoustical Society of Korea
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• v.35 no.5
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• pp.349-357
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• 2016

In this work, we proposed various structural methods to reduce the crosstalk between elements in a planar array of underwater acoustic transducers and investigated the efficacy of each method through finite element analysis. It is shown that the effects of crosstalk reduction increase as the depth of the kerf among elements and the width of the kerf increase, and the elastic stiffness of the kerf filler decreases. Results of this study are expected to be useful in designing the structure of underwater acoustic planar array transducers to maximize their performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.179-189
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• 2000

Recently, due to the increasing interests in deep sea development, all possible efforts to the development of underwater unmanned working vehicles such as AUV(Autonomous Underwater Vehicle) or underwater robot are exerted. This paper proposes a new efficient acoustic-based underwater image data communication system, which ensures a certain level of maximum throughput regardless of the propagation delay of ultrasonic and allowsfast data transmission through the multiple ultrasonic communication channel. Proposed system consists of an acoustic transducer which operates at 136kHz center frequency and it's 10kHz bandwidth, pre-amplifier, $\pi/4 QPSK$(Quadrature Phase Shift Keying) modulation/demodu-lation method, image compressing method using JPEG technique and modified Stop & Wait protocol. The experimental result of the system make it possible to transfer the underwater image as a high throughput at the basin test. The results of test are also verified which allows to desirable transmission performance compared with the existing developed system and the possibility to put the practical use of survey and investigation in the water.

• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.94-101
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• 2014

In this work, we present an underwater acoustic transducer with a cavity-type head mass to achieve a wide frequency bandwidth. We analyzed the effects of design variables on the transducer characteristics, and optimized the structure of the Tonpilz transducer based on the analysis results. Further, validity of the design was verified by manufacturing a prototype of the transducer and measuring its properties. The designed transducer had a far wider -6 dB fractional bandwidth which is 131 % than that of a single mode transducer, and the measured results were confirmed to be in good agreement with the analysis results.

• The Journal of the Acoustical Society of Korea
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• v.11 no.3
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• pp.67-73
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• 1992

An electromagnetic induction transducer which radiates an implusive ultrasonic wave, could be useful for high power sound source in underwater acoustical survey. The aim of this study is to investigate the waveforms and the spectral characteristics of the waves produced by the transducer which was on the basis of the design criteria proposed by Eisenmenger. It was found that the sound pressure levels of the impulsive ultrasonic waves were directly proportional to the capacitance of the energy stored in the capacitor and inversely proportional to the thickness of the vibrating copper foil, while the center frequencies and the fractional bandwidths were vice versa.

• Journal of Sensor Science and Technology
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• v.9 no.4
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• pp.307-315
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• 2000

To set up the arrays system of FBG(Fiber Bragg Grating) Hydrophone sensor and realize the multi-point signal detection for the wide scope underwater, using WDM(Wavelength Division Multiplexing) method and Passive band-pass filter system, underwater acoustic signal detection of the newly designed two FBG Transducers is successfully experimented. As a result of the experiment, it was possible each signal with different frequent signals is detected for the multi-point up to 1.3KHz in underwater. We can, therefore, prove the possibility on the system design of Hydrophone sensor arrays, using the newly made FBG Transducers.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4
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• pp.77-82
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• 1996

In this paper an identification method is presented to obtain the equivalent electric model of a sandwitch type piezoelectric transducer. Unknown parameters related to the equivalent circuit are identified by solving a nonlinear optimization problem which can minimize an error between the experimental and analytical admittances in air. The proposed method is applied to an example transducer. The validity of equivalent circuit model is demonstrated by the comparison between the experimental measurements and analytical calculations of transmitting voltage response(TVR) and receiving voltage response(RVS).

• Journal of Ocean Engineering and Technology
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• v.13 no.3B
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• pp.73-82
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• 1999

In this research, an experimental study is presented to check the possibilities of offshore structures monitoring using AE techniques. The underwater transducer and preamplifier are fabricated. And, it is proved that this unit can be used for the detection of AE in offshore structures. Wave propagation studies have shown that supplementary attenuations due to seawater are significantly reducing the detection range of the sensors. It excludes the possibility of offshore structures monitoring with a small number of sensors. We conclude that AE waves would be correctly detected for a path of about 3m. Tubular joints have been tested in air and underwater using simulated elastic wave. Ability of AE techniques to detect and locate cracks early in their evolution has been demonstrated. Several parameters of AE generation have been set in evidence. It has also been shown that crack development goes with an increase of AE parameter. Conclusively, it is shown that AE techniques can provide practical alternatives to present methods being used for inspection of deep-water offshore structures undergoing structural degradation due to fatigue crack growth.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.312-322
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• 1999

A ultrasonic transduce with a single acoustic matching layer has been designed as an attempt to increase the bandwidth of underwater transducer. The wideband resonance condition was accomplished by attaching a single matching layer on the front face of a ceramic resonator composed of a piezoelectric bar, a taper part and a head part. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedance and thickness of the matching layer in the water tank.The obtained results are summarized as follows:1. Measured resonant and antiresonant frequencies of the piezoelectric transducer with no matching layer in air were 24.7 kHz and 25.6 kHz, respectively. 2. Two resonant frequencies of the piezoelectric transducer with a single matching layer were 21.7 kHx and 26.9 kHz, respectively, in air and 21.4 kHz and 22.7 kHz, respectively, with a water load.3. Two distinct resonance peaks in the transmitting voltage response(TVR) of the developed transducer were observed at 22.0 kHz and 25.8 kHz, respectively, with center frequency of 24.0 kHz. The values of TVR at these frequencies were 130.1 dB re $1 \muPa$/V at 22.0 kHz and 128.5 dB re $1 \muPa$/V at 25.8 kHz, respectively.Reasonable agreement between the experimental results and the numerical values was achieved.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.559-567
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• 1999

A piezoelectric flextentional sonar transducer has been simulated using a coupled FE-BEM. The dynamics of the sonar transducer is modelled in three dimensions and is analyzed with external electrical excitation conditions. Different results are available such as steady-state displacement modes, underwater directivity patterns, resonant frequencies, bandwidths, quality factors, output acoustic powers and transmitting voltage responses. It is shown that the present barrel-stave sonar transducer of the piezoelectric material produces flextentional displacements which could be related with higher output power, lower quality factor and more omnidirectional beam pattern than other types of sonar transducers. The results of the present sonar transducer modelling are also compared with those of a commercial package such as ATILA.