Bongyoung Ahn

Fabrication and comparison of PMN-PT single crystal, PZT and PZT-based 1-3 composite ultrasonic transducers for NDE applications.

This paper describes fabrication and comparison of PMN-PT single crystal, PZT, and PZT-based 1-3 composite ultrasonic transducers for NDE applications. As a front matching layer between test material (Austenite stainless steel, SUS316) and piezoelectric materials, alumina ceramics was selected. The appropriate acoustic impedance of the backing materials for each transducer was determined based on the results of KLM model simulation. Prototype ultrasonic transducers with the center frequencies of approximately 2.25 and 5MHz for contact measurement were fabricated and compared to each other. The PMN-PT single crystal ultrasonic transducer shows considerably improved performance in sensitivity over the PZT and PZT-based 1-3 composite ultrasonic transducers.

Elastic constants determination of thin cold-rolled stainless steels by dynamic elastic modulus measurements

Temperature dependence of elastic constants of thin cold-rolled stainless steel has been measured by using the acoustic resonance method. Identification of the vibration mode has been examined numerically and experimentally. The elastic constants at room temperature have also been measured by the pulse echo method. In addition, the texture effect on the elastic constants has been analysed by assuming the specimen has orthorhombic structure.

Effect of microstructure of low carbon steels on ultrasonic attenuation

The ultrasonic attenuation in low carbon steel with 0.04 wt% C to 0.80 wt% C was measured over a frequency range of 5 to 15 MHz, and the effects of the carbon content and normalizing temperature were analyzed. In pure iron, the attenuation is determined from the average grain size, which increases as the normalizing temperature increases; there is a noticeable effect caused by a few large grains. In the case of the hypoeutectoid steels, the proeutectoid ferrite grain, the size of which depends on prior austenite grain size, acts as the main scatterer. The prior austenite grain size increases as the carbon content decreases and the normalizing temperature increases. The colony is responsible for scattering in the eutectoid steel; scattering by pearlite is greater than that by ferrite.

Characterization of delamination in titanium nitride coating on steel using acoustic microscopy

Wear resistance of Titanium Nitride (TiN) coating on steel is partly influenced by delamination located beneath the surface. Acoustic microscopy is particularly suited to analyze the subsurface defects. To examine the delamination defects introduced by sliding contacts in TiN coating on steel the Lamb wave velocities have been measured by V(z) curves and compared with the theoretically calculated velocities from dispersion curves.

Construction of Static 3D Ultrasonography Image by Radiation Beam Tracking Method from 1D Array Probe

Abstract This paper describes the construction of a static 3D ultrasonography image by tracking the radiation beam position during the handy operation of a 1D array probe to enable point-of-care use. The theoretical model of the transformation from the translational and rotational information of the sensor mounted on the probe to the reference Cartesian coordinate system was given. The signal amplification and serial communication interface module was made using a commercially available sensor. A test phantom was also made using silicone putty in a donut shape. During the movement of the hand-held probe, B-mode movie and sensor signals were recorded. B-mode images were periodically selected from the movie, and the gray levels of the pixels for each image were converted to the gray levels of 3D voxels. 3D and 2D images of arbitrary cross-section of the B-mode type were also constructed from the voxel data, and agreed well with the shape of the test phantom. Keywords: Ultrasound, 3D Image, Position Angle Sensor, Beam Tracking Method[Received: January 9, 2015, Revised: February 3, 2015, Accepted: February 3, 2015] *한국표준과학연구원 의료융합측정표준센터, **과학기술연합대학원대학교 의학물리학과, ***㈜메타바이오메드 HCP사업부, ✝Corresponding Author: Center for Medical Metrology, Korea Research Institute of Standards and Science, Daejeon 305-340, Korea (E-mail: il.doh@kriss.re.kr)

Finite Element Analysis of a Particle Manipulation System Using Ultrasonic Standing Wave

ABSTRACT Micro particles in fluid can be manipulated by using ultrasonic standing wave since the ultrasound makes particles move by means of its acoustic radiation force. This work concerns the micro particle manipulation system using ultrasonic standing wave which consists of a microchannel, a reflector, and an ultrasonic transduer. In the present system, the effects of the structural elements should be carefully considered to comprehend the system and find the optimal operational condition. In this investigation, finite element analysis was employed to analyze the system. Some interesting characteristics on the reflector thickness, the channel width, and the operational frequency were observed. Several experimental results were compared with the analytic results. Consequently, this work solidifies the importance of those system parameters and reveals the possibility of various applications of the particle manipulation using ultrasonic standing wave. * 1. 서 론 최근 산업계 및 다양한 학문 분야에서 미세입자(micro particle)의 응용이 활발해지면서 미세입자제어(micro particle manipulation)에 대한 관심과 중요성이 제고되고 있다

Measurement of the depth of narrow slotted sections in eddy current reference standards

The dimensions of the slots in eddy current (EC) reference standards are too narrow to be measured by general depth measurement methods such as the optical (laser) or stylus methods. However, measurement of the dimensions of the machined slots is a prerequisite to using the blocks as references. The present paper suggests a measurement method for the slotted section using an ultrasonic test. The width and depth of the slots measured in our study are roughly 0.1?mm and 0.5?mm, respectively. The time of flight (TOF) of the ultrasonic wave was measured precisely. The ultrasonic velocity in the material of the EC reference standard was calculated with the measured values of the TOF and its thickness. Reflected waves from the tip of the slot and the bottom surface of the EC standard were successfully classified. Using this method we have successfully determined the depth of the slotted section.

Evaluation on Material Properties of 3Cr-lMo-0.25V Steel by Electromagnetic Methods

It is advantageous to use NDE methods to assess the mechanical properties of materials since the conventional method is time-consuming and sometimes requires cutting of sample from the component. The NDE parameters such as ultrasonic velocity and attenuation, electric resistivity, and magnetic coercive force and remanance have been utilized to evaluate changes of material properties due to heat treatment condition. It has been found that changes of materials properties under quenched and tempered/PWHT treatments could not be detected using EMAT and Electrical resistivity methods. However, victors hardness and magnetic hysteresis loop decreased with heat treatment procedures. These results were obtained using 3Cr-lMo-0.25V steel. The magnetic parameters were found to be most sensitive to changes of material properties.

Evaluation of 1Cr-1Mo-0.25V Steel Degradation Using Magnetic Barkhausen Noise

It is inevitable to evaluate the life of turbine rotor because the operating periods of power plants need to be extended. For the test, seven kinds of specimens with different degradation levels were prepared by the isothermal heat treatment at . Magnetic methods utilizing Barkhausen noise coercive force() were applied to detect the degradation caused by thermal aging. Magnetic property of material is related with domain dynamics and that is affected by the microstructure of material. Therefore is very sensitive to the microstructure change of the material. With the increase of degradation, was decreased and this phenomenon is considered due to precipitations and grain size. The result was compared with Vickers hardness() and coercive force() to detect the relative variation, and was related with and YS to estimate the change of the mechanical properties with the degradation.

Realization of an ultrathin acoustic lens for subwavelength focusing in the megasonic range.

In this study, we report the first experimental realization of an ultrathin (0.14λ, λ = 1.482 mm means wavelength at 1 MHz in the water medium) subwavelength focusing acoustic lens that can surpass the Rayleigh diffraction limit (0.61λ/NA, NA means numerical aperture). It is termed a Super-Oscillatory Acoustic Lens (SOAL), and it operates in the megasonic range. The SOAL represents an interesting feature allowing the achievement of subwavelength focusing without the need to operate in close proximity to the object to be imaged. The optimal layout of the SOAL is obtained by utilizing a systematic design approach, referred to here as topology optimization. To this end, the optimization formulation is newly defined. The optimized SOAL is fabricated using a photo-etching process and its subwavelength focusing performance is verified experimentally via an acoustic intensity measurement system. From these measurements, we found that the proposed optimized SOAL can achieve superior focusing features with a Full Width at Half Maximum (FWHM) of ~0.40λ/NA ≃ 0.84 mm (for our SOAL, NA = 0.707) with the transmission efficiency of 26.5%.