• Journal of Biomedical Engineering Research
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• v.23 no.6
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• pp.419-430
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• 2002

In this paper. we propose an efficient method for implementing hi-directional pixel-based focusing(BiPBF) based on a sparse array imaging technique. The proposed method can improve spatial resolution and frame rate of ultrasound imaging with reduced hardware complexity by synthesizing transmit apertures with a small number of sparsely distributed subapertures. As the distance between adjacent subapertures increases, however. the image resolution tends to decrease due to the elevation of grating lobes. Such grating lobes can be eliminated in conventional synthetic aperture imaging techniques. On the contrary, grating lobes arisen from employing sparse synthetic transmit apertures can not be eliminated, which has been shown analytically in this paper. We also propose the condition and method for suppressing the grating lobes below -40dB, which is generally required in practical imaging. by placing the transmit focal depth at a near depth and properly selecting the subaperture distance in Proportion to receive aperture size. The results of both the Phantom and in vivo experiments show that the proposed method implements two-wav dynamic focusing using a smaller number of subapertures, resulting in reduced system complexity and increased frame rate.

• The Journal of the Acoustical Society of Korea
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• v.25 no.4
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• pp.164-171
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• 2006

If the velocities of longitudinal, transverse and leaky surface acoustic waves in an isotropic material are given, the elastic constants and density of the material can be deduced analytically. Those velocities have been measured using three ultrasonic transducers with different vibrational modes so far. In this paper a line-focusing PVDF transducer with divided electrodes was newly proposed and designed for measuring approximate velocities of the three waves. The measurement method established in this study for each waves using the transducer was applied to several isotropic materials including fused quartz. The elastic stiffness constants and densities of the materials were calculated using the measured velocities, and the accuracies were discussed. It was shown that the obtained results are in good accord with the reference values.

• Journal of Biomedical Engineering Research
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• v.20 no.4
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• pp.503-513
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• 1999

A general expression for the beam patterns of various synthetic aperture(SA) techniques was derived based on a unified SA model. This model was used to analyze and compare the performance of existing SA methods. Based on the theoretical studies, we propose a new synthetic aperture technique that is best suitable for the linear-scan imaging. The proposed method enables dynamic tow-way focusing in real imaging so that the B-mode image resolution can be greatly improved. Compared to the conventional focusing technique, the focused beam pattern by the proposed shows the mainlobe width reduced by half and comparable sidelobe levels. Computer simulation results demonstrated the validity of the theoretical analysis and the proposed SA method.

• The Journal of the Acoustical Society of Korea
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• v.14 no.5
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• pp.36-43
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• 1995

This paper presents the lousing characteristics and the time. response of ultrasonic focusing transducer which is a coupled system with an electromechanical and an acoustical component. The Finite Element Method and the Hybrid Type Infinite Element Method are applied for the analysis. The position of the focal points and the resolutions is obtained from the loosing characteristics and the time response. It is found that the transducer with the damper, which stabilizes the displacement of the radiation surface, gives a better resolution. In conclusion, the results could be applied to the design and the performance analysis of the ultrasonic focusing transducer.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.62-67
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• 2001

Velocities of leaky surface acoustic waves (LSAW/sub s/) were measured by using a line-focus polyvinylidene fluoride (PVDF) transducer and compared with theoretically calculated ones. Isotropic materials of Cu, Al, fused quartz, and anisotropic one of Z-cut α-quartz crystal were used as specimens. The velocities were obtained by the separation time between wave components reflected directly from the surface of specimen and LSAW components according to the defocusing distance. The measured velocities well agree with the theoretical results within 1％ error, and it was shown that the leaky pseudo-surface acoustic wave (LPSAW) as well as the LSAW propagates with the typical 6-fold anisotropy on the (0,0,1) surface of α-quartz.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.357-358
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• 2004

생체 피부하 약 5mm이내 영역에 대한 고분해능의 B-모드 영상을 얻는 데 사용할 수 있는 축 방향 분해능 $30{\mu}m$ 이하인 VHF 대역 초음파 트랜스듀서로서 용융석영을 음향버퍼의 하여 그 양단에 송신용 2-2 composite와 수신용 P(VDF-TrFE)를 설치한 송수신 분리형의 집속 트랜스듀서의 구조를 새로이 제안하고, 그 전기적 음향적 특성을 시뮬레이션 하였다. 그 결과, 2-2 composite 투께 $18{\mu}m$와 P(VDF-TrFE) 두께 $12{\mu}m$의 트랜스듀서는 중심주파수 43.0MHz, 비대역 $74\%$이며, 삽입손실이 25dB인 비교적 우수한 트랜스듀서가 될 수 있음을 알았다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.1
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• pp.1-7
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• 1974

This paper discribes the reflector type ultrasonic concentrator which makes hghintencity of ultrasonic field. This was made by rotating parabolic surface which only using total reflection aria, that makes boundary by the critical angle of reflection of sound. I made two binds of concentrator acording to the type of ultrasonic transduser: one is internal surface reflector type concentrator, which is available for disc type transducer, and the other is external surface reflector type concentrator which is available cylinderical transduser. In the mony aspects the reflector tripe concentrator is supel'ier to the reflection type concentrator as plastics lens; It is more durable in high temperature and high intencity ultrasonicfield then refrector type concentrator because of it is made by glass or metal, and it has higher. efficiency because of it wasts made by only total reflection aria that is without absoption lose. I think this is useful ultrasonic concentrator in mony industrial field, in which high intencitr of ultrasonic energy was used.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.885-886
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• 2012

• Journal of Biomedical Engineering Research
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• v.21 no.4
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• pp.419-431
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• 2000

In this paper, a new beamforming technique is proposed, which can completely eliminate all the artifacts caused by digital scan converter. In the proposed method, named display-pixel-based focusing(DPBF) by the authors, ultrasound waves are focused directly at the display pixels instead of sampling points on the polar coordinate. Consequently. the DPBF system does not require the digital scan converter. To verify the proposed method, we modified a commercial scanner and performed experiments with a 3.5 MHz convex array and a 7.5 MHz linear array. We also defined and measured ICRA/B(Image Coarseness Ratio) to compare the image quality quantitatively. The experimental results with in vivo and in vitro data show that the proposed method improves the ICRA/B considerably, resulting in much smoother and finer images.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.441-451
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• 2023

Ultrasound transducers are an essential component of combined photoacoustic and ultrasound imaging systems and play an important role in image evaluation. However, ultrasound transducers are opaque; therefore, light must bypass the ultrasound transducer to reach the target point to produce a photoacoustic image. Providing different paths for the optical and acoustic signals results in a complicated system design, increasing the system volume. To overcome these problems, an optically Transparent Ultrasound Transducer (TUT) was developed. Unlike conventional opaque ultrasound transducers, optically TUT can be fabricated by a variety of manufacturing methods and they are suitable for use with specific piezoelectric elements and serve various purposes. In this study, a comparative analysis of the results of using Lithium Niobate (LNO), Lead Magnesium Niobate-Lead Titanate (PMN-PT), and Polyvinylidene Difluoride (PVDF), which are materials used in piezoelectric element-based TUT. LNO is a piezoelectric element widely used in TUT, and PMN-PT has been actively studied recently with a higher transmission and reception rate than LNO. Existing TUT have lower ultrasound resolution than photoacoustic resolution, but they have recently been manufacturing focused TUT with high ultrasound resolution using PVDF. A comparative analysis of the production results of these TUT was performed.