• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.37-43
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• 2017

Ultrasonic transducers with high resolution and resonant frequency are required to detect small defects (less than hundreds of ${\mu}m$) by ultrasonic testing. The resonance frequency and resolution of an ultrasonic transducer are closely related to the thickness of piezo-electric materials, backing materials, and the electric impedance matching technique. Among these factors, electrical impedance matching plays an important role because it can reduce the loss and reflection of ultrasonic energy differences in electrical impedance between an ultrasonic transducer and an ultrasonic defects detecting system. An LC matching circuit is the most frequently used electric matching method. It is necessary for the electrical impedance of an ultrasonic transducer to correspond to approximately $50{\Omega}$ to compensate the difference in electrical impedance between both connections. In this study, a 15 MHz immersion ultrasonic transducer was fabricated and an LC electrical impedance circuit was applied to that for having broad-band frequency characteristic.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.286-294
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• 2001

In this study, 3-D underwater object recognition using the self-made 3-3 type composite ultrasonic transducer and modified SOFM(Self Organizing Feature Map) neural network are investigated. Properties of the self-made 3-3 type composite specimens are satisfied considerably with requirements as an underwater ultrasonic transducer's materials. 3-D underwater all object's recognition rates obtained from both the training data and testing data in different objects, such as a rectangular block, regular triangular block, square block and cylinderical block, were 100% and 94.0%, respectively. All object's recognition rates are obtained by utilizing the self-made 3-3 type composite transducer and SOFM neural network. From the object recognition rates, it could be seen that an ultrasonic transducer fabricated with the self-made 3-3 type composite resonator will be able to have application for the underwater object recognition.

• Herbal Formula Science
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• v.10 no.2
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• pp.143-158
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• 2002

The purpose of the present study is to determine the effect of Jakyakgamchotang on histamine or acetylcholine induced tracheal smooth muscle contraction in rats and guinea pigs. Guinea pig(500g, male) and Sprague Dawley rats(250g, male) were killed by $CO_2$ exposure and a segment (4-5mm) of the thoracic trachea from each rat and guinea pig was cut into equal segments and mounted 'in pairs' in a tissue bath. Contractile force was measured with force displacement transducers under 0.5g loading tension. The dose of histamine(His) which evoked 50% of maximal response($ED_{50}$) was obtained from cumulative dose response curves for histamine($10^{-7}{\sim}10^{-4}M$). Contractions evoked by His($ED_{50}$) were inhibited significantly by Jakyakgamchotang. In guinea pig tracheal smooth muscle, the mean percent inhibition of histamine induced contraction was 90.8% (p〈0.001) after $100{\mu}l/ml$ Jakyakgamchotang. In rat tracheal smooth muscle, the mean percent inhibition of acetylcholine induced contraction was 22.1% (p〈0.05) after $100{\mu}l/ml$ Jakyakgamchotang. Propranolol indomethacin and methylene blue($10^{-7}M$) slightly but significantly attenuated the inhibitory effects of Jakyakgamchotang. These results indicate that Jakyakgamchotang can relax histamine or acetylcholine induced contraction of guinea pig and rat tracheal smooth muscle.

• The Journal of the Acoustical Society of Korea
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• v.24 no.3
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• pp.127-132
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• 2005

Transducers for implantable hearing aids need to be small and to have good performance in frequency responses and vibration properties. From this viewpoint, we Proposed a multi-layer actuator with the piezoelectric single crystal, PMN-PT. for the implantable hearing aid. and verified its adequacy through finite element analyses and experiments. PMN-PT multi-layer actuator samples were fabricated by stacking fourteen layers of the PMN-PT crystal. Each layer were $0.2{\cal}mm$ thick and the actuator sample was $2.8{\cal}mm$ thick in total. We evaluated the performance of the PMN-PT actuator through impedance analyses and vibration displacement measurements, and compared the result with that of a PZT actuator. Results of all the process confirmed the feasibility of the PMN-PT actuator as a good transducer for an implantable hearing aid.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.265-271
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• 2007

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. Experiments were performed to find the flow characteristics of a supersonic turbine with the cascade positions and to find a factor of the expansion loss. The supersonic cascade with a 2-dimensional supersonic nozzle was tested with the cascade positions. The flow was visualized by a Z-type Schlieren system. The static pressures at the turbine cascade inlet and outlet were measured by pressure transducers and a pressure scanner. Also, The total pressures at the turbine cascade back flow were measured. Highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions of the supersonic turbine were observed. And the flow characteristics in the supersonic turbine with the cascade positions were observed.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.467-475
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• 2012

Static and dynamic train load tests were conducted to evaluate the train load transfer mechanism in the roadbed which was retained by two types (fully and partially) of segmental retaining walls reinforced by geogrid. The test roadbed was 2.6m high, 5m wide, and 6m long. A combination of earth pressure gages, displacement transducers, and strain gages were placed in specific locations to measure the responses. Test results showed that the wall displacement pattern as well as the earth pressure for the fully reinforced retaining wall was different from those for the partially reinforced retaining wall. In the dynamic train load test, the strain in the upper part of the wall tended to decrease, and both the residual deformation and the rate of the deformation were significantly lower than those in the current design standard.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.73-86
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• 1995

The transducer section of the forward-looking ultrasound imaging catheter (FLUIC) consists of a circular piezoelectric element as a vibrator and a conical acoustic mirror as a perfect reflector. A small diameter piezoelectric transducer element is mounted on the side of a catheter's rotating shaft. The unique design of FLUIC provides the capability to form a two-dimensional image of a cross-section of vessel in front of the catheter, which is lacking in the present generation of intravascular ultrasound (IVUS) transducers, as well as a conventional side view image. The mirror configuration for the transducer section of the FLUIC is designed using an approximated ray tracing techniques. The diffraction transfer function approach [1] developed for the field prediction from primary sources is generalized and extended to predict the secondary diffraction characterstics from an acoustic mirror. The extended model is verified by simulation and experiment through a simple plane reflector and employed to analyzed the field characteristics of a FLUIC.

• Journal of the Korean Magnetics Society
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• v.25 no.1
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• pp.22-26
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• 2015

In this paper, a magneto-inductive wave generated in a chain of LC resonators fabricated with Ni-Zn ferrite cores and chip capacitors is presented. RF signal propagates to neighbor resonator one by one as a consequence of the magnetical coupling between two resonators in the device. The magnetical coupling is due to the mutual inductances along the chain of resonators. So, the signal amplitude (${\approx}$ coupling intensity) is dependent of the mutual inductance which can be adjusted by applied magnetic field. In order to demonstrate the device, some experiments have been carried out systemically. The transmission characteristics of a magneto-inductive wave could be controlled by applied external magnetic field. The device composed of 5 resonators; the center frequencies were estimated to be 32 MHz and 38 MHz with the external magnetic flux density of 75 Oe and 222 Oe, respectively. We expect that the reported results could open a promising way to a high variety of applications in one- and two-dimensional functional devices, such as transducers, delay lines, power dividers and couplers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1400-1409
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• 2001

This paper describes a fiber optic sensor suitable for non-contact detection of ultrasonic waves. This sensor is based on a fiber optic Sagnac interferometer. Quadrature phase bias between two interfering laser beams in Sagnac loop is introduced by a polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output versus phase bias. This method eliminates a digital signal processing for detection of ultrasonic waves using Sagnac interferometer. Interference intensity is affected by the frequency of ultrasonic waves and the time delay of Sagnac loop. Collimator is attached to the end of the probing fiber to focus the light beam onto the specimen surface and to collect the reflected light back into the fiber probe. Ultrasonic waves produced by conventional ultrasonic transducers are detected. This fiber optic sensor based on Sagnac interferometer is very effective for detection of small displacement with high frequency such as ultrasonic waves used in conventional non-destructive testing.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.3
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• pp.171-179
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• 2016

In order to study correlation of the propeller cavitation performance between a full-scale ship and a model ship for the MR Tanker, the full-scale ship and the model tests were conducted. The full-scale ship test is composed of cavitation observation, pressure fluctuation and noise measurements, which are conducted using 2 observation windows and 8 pressure transducers installed inside the full-scale ship above the propeller. The model test in the Large Cavitation Tunnel(LCT) was conducted at the same conditions as that of the full-scale ship and its results are compared with those of the full-scale ship. Through the model-ship correlation analysis, it is considered that the experimental technique for the MR Tanker class ship was verified in LCT.