• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.798-802
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• 2007

The synthetic focusing in the ultrasonic imaging systems has been formed in the way that one element transmits a circular wave and receives an echo signal. The amplitude of the signal transmitted from one element is too small to propagate a long distance so that the SNR(Signal to Noise Ratio) is very low in an image obtained by the synthetic focusing. To solve this problem, a defocusing method which uses several elements has been proposed. In this method, the SNR is improved due to using several elements to transmit the circular wave. But if the number of transmitting elements increases, the phase distortion is severe in the defocusing method. In this paper, we propose a new method that can generate a circular wave using a lot of elements without phase distortion. At first, we generate limited plane waves with different propagation angles and then superpose them to make a circular wave. We show that the circular wave can be used to improve SNR in the real-time 3D ultrasonic imaging as well as the synthetic focusing through computer simulation and experiments.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.271-274
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• 2000

In this paper, the distortion of an electrical pulse with rise/fall time resulting from dispersion and reflection as it propagates along a tapered microstrip line is investigated, and the delay time and distortion rate with respect to input and load impedances are analyzed on triangular and exponential tapered lines and analyzed the influence of the reflection and frequency dispersion on the distorted voltage wave in the tapered lines. The observed overshoot in front of the distorted wave is caused due to the frequency dispersion and the sustained tail of that comes from the reflection in the tapered line.

• ETRI Journal
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• v.39 no.4
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• pp.480-492
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• 2017

A holographic display based on a viewing window enables the converging of a reconstruction wave into a viewing window by means of an optical system. Accordingly, a user can observe a reconstructed hologram image, even with a small diffraction angle. It is very difficult to manufacture an optical system with no aberrations; thus, it is inevitable that a certain amount of wave aberrations will exist. A viewing-window-based holographic display, therefore, always includes distortions in an image reconstructed from a hologram pattern. Compensating the distortions of a reconstructed image is a very important technical issue because it can dramatically improve the performance when reconstructing a digital three-dimensional content image from a hologram pattern. We therefore propose a method for suppressing image distortion by measuring and compensating the wave aberration calculated from a Zernike polynomial, which can represent arbitrary wave aberrations. Through our experimental configuration using only numerical calculations, our proposed method decreased the reconstructed image distortion by more than 28%.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.455-461
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• 2009

In a scanning electron microscopy, image distortion is a critical issue and it is needed to be eliminated by some kinds of schemes. In this work, scanning frequency and scanning wave form are adjusted to have an improved image. The relationship between scan coil and its driver is investigated and appropriate frequency and wave form are suggested. It is proved that the selected frequency and wave form showed an enhanced image with less distortion, which were done by experiments. In addition, a noise elimination is addressed, providing improved image with a GROUND signal integration with the amplifier and the scan driver.

• Journal of ILASS-Korea
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• v.1 no.2
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• pp.57-65
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• 1996

Breakup models are evaluated using the experimental drop trajectory ill this study. The experimental conditions corespond to Weber # 56, 260, 463. Computations are carried out using a modified KIVA-II program with 2 different breakup submodel(TAB and Wave breakup model) and dynamic drag model which the drag coefficient changes dynamically with distortion parameter. Results show that computation with wave breakup model represents the experimental drop trajectory better than that with TAB submodel. And result with wave breakup model shows similar breakup pattern to experimental breakup process. It is thought that in wave breakup model the small drops are shed from the parent drop throughout parcel lifetime such thai this modelling represents the real breakup process well.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.10
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• pp.1132-1141
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• 2004

The waveforms of the leakage currents for the surface discharge according to the degree of salt contamination and the variation of environmental condition on the EPDM polymer insulators, were shown in this paper. The variation phenomena of fundamental wave, 3rd and 5th harmonic waveforms were also shown from the beginning of the applied voltage and to the flashover voltage. To develop the technique of percentage contamination degree of EPDM polymer insulator according to the variation of environmental condition, the distortion degree of 3rd and 5th harmonic wave to the fundamental wave was utilized through the spectrum analysis for the waveforms of leakage current in the simulation of salt and fog test. The fact that distortion degree % of 3rd and 5th harmonics for fundamental wave is a necessary indicator for the assessment of contamination degree for the polymer insulators, was known.

• Journal of Electrical Engineering and information Science
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• v.1 no.2
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• pp.52-57
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• 1996

Detection of arcing high impedance faults has been a perplexing in the power distribution protection. Transient analysis of distribution disturbances for fault discrimination from other normal events is important for a secure protection of the power system. A simple parameter of wave form distortion quantification is used to analyze the behaviors of arcing faults and normal distribution disturbances. Theoretical perspectives of the transients were studied and actual disturbances were examined. From this investigation, a discrimination guideline based on the revised crest factor is developed. The discrimination method has a high potential to enhance the reliability and security for the distribution system protection.

• The Journal of the Acoustical Society of Korea
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• v.8 no.5
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• pp.33-50
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• 1989

In this paper, musical tone, especially instrument tones are synthesized using nonlinear distortion technique. Nonlinear distortion is very simple but versatile method when you synthesize musical instrument tones. It basically consists of one sine oscillator and amplifier which makes distortion to Input wave. Output wave has many harmonics that can be controlled by varying shaping function, which is the transfer function of nonlinear amplifier. Shaping function Is obtained from the analyzed harmonic amplitude data. Given harmonics amplitudes, Chebyshev polynomial is used to produce the shaping function that exactly makes the given harmonics at steady state. We contructed non -real time nonlinear distortion synthesizer program running at IBM-PC. To quantify the satis faction of synthesised tones, listening test is carried out, and the result is presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2315-2325
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• 1996

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.4
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• pp.24-30
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• 1984

Group delay distortion (phase distortion) is a characteristic which is of no account from a standpoint of voice transmission. But this distortion becomes the major source of distortion in wave form transmission such as data, FAX and others over the public switching telephone network (voice band transmission) so that it must be drastically studied. This paper makes analysis of group deray distortion of the telephone network, describs experimental and measuring results and refers also to the improvement of distortion for the purpose of opening the public switching telephone network to data transmission.