• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.20-25
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• 2005

The thickness, loading, and broadband noise generated from the trailing edge of the UH-1H main rotor are numerically compared each other. The Kocureck and Tangler's prescribed wake model is adopted to represent the wake geometry during the hovering motion. Three tip Mach numbers of $M_{T}$ = 0.2, 0.4, and 0.8, are selected to analyze the effects of different tip Mach numbers. At $M_{T}$ = 0.8, in considering the A-weighting and audible frequency band, the random noise is smaller than the tonal noises such as the thickness and the loading noise which have the low frequency characteristics. Especially most of the random noise frequency spread on the ultrasound region. On the other hand, below $M_{T}$ = 0.4, the band of random noise moves to the audible frequency region, and the random noise becomes larger than the tonal noise. It turns out that the random noise analysis of the rotor should be necessary at low speed operating condition.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.295-298
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• 2018

The proposed paper proposes an algorithm that automatically extracts the region of interest using image processing techniques for medical images. In general, the robust boundary segmentation technique provides robust and accurate segmentation results in object boundaries with various noise and direction generated during image acquisition through optimal segmentation of the edges considering noise characteristics and directionality in noise images. In this paper, it is possible to apply adaptive filter type and size to the structural information of the image object and apply it to the boundary division of various object objects. In addition, it is possible to divide the boundary between various noise images such as an ultrasound image and an optical image.

• Journal of the Korean Society of Radiology
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• v.17 no.1
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• pp.157-165
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• 2023

Ultrasound imaging uses sound waves of frequencies to cause physical actions such as reflection, absorption, refraction, and transmission at the edge between different tissues. Improvement is needed because there is a lot of noise due to the characteristics of the data generated from the ultrasound equipment, and it is difficult to grasp the shape of the tissue to be actually observed because the edge is vague. The edge enhancement method is used as a method to solve the case where the edge surface looks clumped due to a decrease in image quality. In this paper, as a method to strengthen the interface, the quality improvement was confirmed by strengthening the interface, which is the high-frequency part, in each image using an unsharpening mask and high boost. The mask filtering used for each image was evaluated by measuring PSNR and SNR. Abdominal, head, heart, liver, kidney, breast, and fetal images were obtained from Philips epiq5g and affiniti70g and Alpinion E-cube 15 ultrasound equipment. The program used to implement the algorithm was implemented with MATLAB R2022a of MathWorks. The unsharpening and high-boost mask array size was set to 3*3, and the laplacian filter, a spatial filter used to create outline-enhanced images, was applied equally to both masks. ImageJ program was used for quantitative evaluation of image quality. As a result of applying the mask filter to various ultrasound images, the subjective image quality showed that the overall contour lines of the image were clearly visible when unsharpening and high-boost mask were applied to the original image. When comparing the quantitative image quality, the image quality of the image to which the unsharpening mask and the high boost mask were applied was evaluated higher than that of the original image. In the portal vein, head, gallbladder, and kidney images, the SNR, PSNR, RMSE and MAE of the image to which the high-boost mask was applied were measured to be high. Conversely, for images of the heart, breast, and fetus, SNR, PSNR, RMSE and MAE values were measured as images with the unsharpening mask applied. It is thought that using the optimal mask according to the image will help to improve the image quality, and the contour information was provided to improve the image quality.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.350-355
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• 2001

In order to verify the performance of acoustic-based communication systems, a reliable check-up method is needed, which simulates similar oceanic conditions in low cost. One of the possible candidates would be the performance test in an underwater anechoic basin producing no reflecting waves. For this purpose KRISO (Korea Research Institute of Ships and Ocean Engineering) have constructed an underwater semi-anechoic basin from 1999 to 2001. This paper describes its design procedure, especially, how the material and size of the absorbing walls were chosen. Experiments were also performed to check its anechoic quality, Comparing the results with simple analytical results we concluded that the anechoic basin is working well for some selected frequency ranges.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.559-562
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• 1997

In this paper, we propose the method that reduce the grating lobe in the ultrasound synthetic focusing images. synthetic focusing images have more larger and closer grating lobe than conventional phased array images and more lower signal to noise ratio. so, we represent the method that reduce the grating lobe by using multi element receive focusing. experimental results are showed that the proposed multi element receiving method reduce the grating lobe and increase the signal to noise ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.7
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• pp.455-461
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• 2015

The paper deals with the accuracy comparison between two kinds of ultrasonic paths for flow rate measurement. In the Z-path, two transducers are installed on the opposite sides of each other on a pipe, and the ultrasonic waves generated at one transducer propagate to arrive at the other one only by refraction. In the V-path, two transducers are installed on one side of a pipe, and the ultrasonic waves reflected at the inner wall of the pipe are received. Transit times were confirmed to identify the propagation paths by comparing the theoretically calculated results and measured ones. The flow rate measurements with two kinds of ultrasonic paths appeared very similar. It would be possible to select either of the paths by considering the advantages and disadvantages.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.736-738
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• 2014

The paper deals with the accuracy comparison between two kinds of ultrasonic paths for flow rate measurement. In the Z-path, two transducers are installed on the opposite side of each other on a pipe, and the ultrasonic waves generated of one transducer propagate and arrive at the other one only through refraction. In the V-path, two transducers are installed on one side of a pipe, and the ultrasonic waves reflected at the inner wall of the pipe are received. The backgrounds were established to select one path to fit the usage by considering the advantages and disadvantages.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.2
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• pp.124-132
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• 2015

The paper deals with the energy transmission of the elastic waves obliquely transmitting and refracting through a plate and a pipe. By calculating the transmitting ratio depending on the incidence angle, the angle corresponding to the maximum transmission was determined theoretically and considered in the design of ultrasonic transducers for flow velocimetry. Experiments were carried out by using prototypes of the transducers. Experimentally-obtained transmission ratios were compared with and confirmed the theoretically-calculated results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.8
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• pp.559-567
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• 2015

The paper deals with an ultrasonic transducer invented for measuring both flow velocity and pipe thickness. The structure of the transducer is based on the conventional transducers for measuring flow velocity by obliquely transmitting ultrasonic waves to the flow direction. The transducer additionally generates ultrasonic waves transmitting vertically to a pipe for measuring pipe thickness. By measuring flow velocity with the invented transducer and a conventional oblique-incidence transducer and comparing their results, the accuracy of the flow velocity measurement of the invented one was evaluated. By measuring specimen thickness with the invented transducer and a conventional normal-incidence transducer and comparing their results, the accuracy of the thickness measurement of the invented one was evaluated.

• Proceedings of the KOSOMBE Conference
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• v.1993 no.05
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• pp.81-85
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• 1993

Despite the simplicity of processing, conventional autocorrelation function (ACF) method for the precise determination of fetal heart rate (FHR) has many problems. In the case of weak or noise corrupted Doppler ultrasound singnals, the ACF method is very sensitive to the threshold level and data window length. It is real troublesome to extract FHR when there is a data loss. To overcome these problems, the high resolution pitch detection algorithm is adapted to estimate the FHR. The FHR is determined from the correlation of two interconnected segments by its maximum correlation value. FHR is compensated with a constant correlation threshold in a greatly smeared noise signal. This method yields more accurate, robust and reliable than the ACF method.