• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.550-556
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• 2009

In an application of a time reversal(TR) focusing of array transducer on a defect inside the test material, we employ a new time delay focusing technique based the TR process. In order to realize this idea, a multi-channel ultrasonic system is constructed capable of applying necessary time delays to each channel. The TR-based focusing procedure first measures the backscattered signals after firing one of the array elements. A phase slope method is then used to determine the time-of-flights of the backscattered signals received by all elements of the array. These time delays are used to adjust the time of excitation of the elements for transmission focusing on the defect. In addition to the TR focusing, the classical phased array focusing is also considered for comparison. Experimental results show that the TR-based time delay focusing produces much stronger backscattered signals than the phased array focusing, demonstrating the enhanced capability of the TR focusing.

• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.803-810
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• 2007

Although synthetic aperture focusing techniques can improve the spatial resolution of ultrasound imaging, they have not been employed in a commercial product because they require a real-time N-channel beamformer with a tremendously increased hardware complexity for simultaneous beamforming along M multiple lines. In this paper, a hardware-efficient beamformer architecture for synthetic aperture focusing is presented. In contrast to the straightforward design using NM delay calculators, the proposed method utilizes only M delay calculators by sharing the same values among the focusing delays which should be calculated at the same time between the N channels for all imaging points along the M scan lines. In general, synthetic aperture beamforming requires M 2-port memories. In the proposed beamformer, the input data for each channel is first upsampled with a 4-fold interpolator and each polyphase component of the interpolator output is stored into a 2-port memory separately, requiring 4M 2-port memories for each channel. By properly limiting the area formed with the synthetic aperture focusing, the input memory buffer can be implemented with only 4 2-port memories and one short multi-port memory.

• IEIE Transactions on Smart Processing and Computing
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• v.1 no.3
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• pp.133-142
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• 2012

This paper presents a salient region detection algorithm for auto-focusing based on the characteristics of a human's visual attention. To describe the saliency at the local, regional, and global levels, this paper proposes a set of novel features including multi-scale local contrast, variance, center-surround entropy, and closeness to the center. Those features are then prioritized to produce a saliency map. The major advantage of the proposed approach is twofold; i) robustness to changes in focus and ii) low computational complexity. The experimental results showed that the proposed method outperforms the existing low-level feature-based methods in the sense of both robustness and accuracy for auto-focusing.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.6
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• pp.635-641
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• 2011

In ultrasonic testing of dissimilar metal welds, application of phased array technique in terms of incident beam focusing is not easy because of complicated material structures formed during the multi-pass welding process. Time reversal(TR) techniques can overcome some limitations of phased array since they are self-focusing that does not depend on the geometrical and physical properties of testing components. In this paper, we test the possibility of TR focusing on a defect within anisotropic, heterogeneous austenitic welds. A commercial simulation software is employed for TR focusing and imaging of a side-drilled hole. The performance of time reversed adaptive focal law is compared with those of calculated focal laws for both anisotropic and isotropic welds.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.324-329
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• 2022

This paper proposes a shift-register-based multichannel ultrasonic focusing delay control method using a complex programmable logic device (CPLD) for a high resolution of ultrasonic focusing system. The proposed method can achieve the ultrasonic focusing through the delay control of driving signals of each ultrasonic transducer of an ultrasonic array. The delay of the driving signals of all ultrasonic channels can be controlled by setting the shift register in the CPLD. The experiment verified that the frequency of the clock used for the delay control increased, the error of the focusing point decreased, and the diameter of the focusing point decreased as the length of the shift register in the proposed method. The proposed method used only one CPLD for ultrasonic focusing and did not require to use complex hardware circuits. Therefore, the resources required for the design of an ultrasonic focusing system could be reduced. The proposed method can be applied to the fields of human computer interaction (HCI), virtual reality (VR) and augmented reality (AR).

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.64-70
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• 1999

A new multi-beam optical system is presented on the grounds of tri-positioning systems in this paper. The system has been developed to improve the data transfer rate for the optical disk system. The actuating system is composed of a tracking and focusing actuating system basically and a newly developed beam rotating actuator. The beam rotating actuator is employed in a multi-beam optical system to trace more than one track simultaneously. The multi-beam optics is established through the optical simulation and several experimental trials. The differential phase tracking method is used in the tracking error signal detection based on the only one beam spot. We also analyze the characteristics of multi-beam optical system. The experimental result shows that the multi-beam positioning system has performance adequate to the multi-beam optical disk system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.2 s.245
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• pp.128-134
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• 2006

Topology optimization is an effective scheme to obtain the initial design concept: however, it is hard to apply in case of non-linear or multi-objective problems. In this study, a modified topology optimization method is proposed to generate a structure of a swing arm type actuator satisfying maximum compliance as well. as maximum stiffness using the multi-objective optimization. approach. The multi-objective function is defined to maximize the compliance in the direction of focusing of the actuator and the second eigen-frequency of the structure. The design of experiments are performed and the response surface functions are formulated to construct the multi-objective function. The weighting factors between conflicting functions are determined by the back-error propagation neural network and the solution of multi-objective function is acquired using the genetic algorithm.

• Journal of radiological science and technology
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• v.5 no.1
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• pp.63-70
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• 1982

In order to estimate characteristics and functions of multi hole focusing type collimator, the authors measured the sensitivity and resolution varing with the distance between the face of collimator and source by experimental study. The results obtained with this study are as follows. 1. In comparison with focal distance obtained fram sensitivity measurement of various multi hole focusing type collimator, collimator A, C, E was 10 cm and collimator B, D was 12 cm in focal distance. 2. In regard of resolution of collimators having 10 cm focal distance, collimator A showed the finest resolutions than any other collimator(C, E). 3. By comparison regarding sensitivity by focal dist ante, the shorter the distance than a give focal distance of collimator, the worse the sensitivity of collimator. 4. With regard to resolution by focal distance, the shorter the distance than a given focal distance of collimator, the worse the resolution of collimator.

• The Journal of Korea Robotics Society
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• v.6 no.2
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• pp.118-129
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• 2011

In this paper, we suggest a new camera capturing and synthesizing algorithm with the multi-captured left and right images for the better comfortable feeling of 3D depth and also propose 3D image capturing hardware system based on the this new algorithm. We also suggest the simple control algorithm for the calibration of camera capture system with zooming function based on a performance index measure which is used as feedback information for the stabilization of focusing control problem. We also comment on the theoretical mapping theory concerning projection under the assumption that human is sitting 50cm in front of and watching the 3D LCD screen for the captured image based on the modeling of pinhole Camera. We choose 9 segmentations and propose the method to find optimal alignment and focusing based on the measure of alignment and sharpness and propose the synthesizing fusion with the optimized 9 segmentation images for the best 3D depth feeling.

• Journal of Ocean Engineering and Technology
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• v.17 no.6
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• pp.1-6
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• 2003

Wave energy dissipation and energy transfer between wave components, during the directional wave breakings, are investigated. Directional incipient and plunging breakers were generated by focusing the multi-frequency and multi-directional wave components at a designed location, based on a constant wave amplitude and a constant wave steepness frequency spectrum. The time series of surface wave elevation was measured at 9 different locations around the wave focusing point, using a wave gauge array. In order to examine the variation of the directional spreading function, the horizontal velocity of fluid motion was also measured. By comparing energy spectrums, before and after the breaking, the characteristics of energy dissipation and energy transfer, caused by wave breaking, are investigated. Their dependencies on directionality, as well as frequency, are analyzed. The breakings significantly dissipate wave energy, through energy transfer, in the upper region of the peak-frequency band, while enhancing wave energy in the low-frequency band.