• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.04a
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• pp.176-194
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• 1991

A study on the Manufactiring of High-Precision Linear Scale by the Use of He-Ne Laser Interference Of late, along with the advancement of procision machining technology, the reauirement of super-precision measurement increases as time goes on, and the precision and accuracy of standard scale which is a basis of procision measurement has been cognized as a oriterion of industrial development in a nation. Up to now, mechanical and chemical methods have been widely employed to carve scale lines on linear scale, and it is impossible for the linear scale manufactured by means of those methods to guarantee the measurement with sub-micron level owing to errors attended with various problems. And the measuring length also bears errors subjected to the influence of surroundings condition, and shows inefficient circumstances in measurement on the ground of the complexity of measuring procedure as well as massive measuring apparatus. Hence in this paper, we described on technology by which we can carve scale lines thru optical method under the condition of laboratory by using rhcoherence of He-Ne two-mode stabilized laser and in turn, put it to practical use as linear scale for the measurment of lengrh. In this researchin the case of setting scale interval to 20 .mu. m, we employed super-precision scale-carving device associated by Ar larser and acoustic optical modulator in lieu of flsahing lamp scale-carving device, and we consequently obtained superior linear scales carved with precision and accuracy of .+-. 0.3 .mu. m.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.4
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• pp.534-540
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• 1990

In this paper the characteristics of submicron gate GaAs MESFET's have been studied using a particle model which takes into account the hot-electron transport phenomena, i.e., the velocity overshoot. \ulcornervalley(<000> direction), L valley (<111>direction), X valley (<100>direction) as the GaAs conduction energy band and optical phonon, acoustic phonon, equivalent intervalley, nonequivalent intervalley scattering as the scattering models, have been considered in this simulation. And the GaAs material and the device simulation have been done by determination of the free flight time, scattering mechanism and scattering angle according to Monte-Carlo algorithm which makes use of a particle model. As a result of the particle simulation, firstly the electron distribution, the potential energy distribution and the situation of electron displacement in 0.6 \ulcorner gate length device have been obtained. Secondly, the cutoff frequency, obtained by this method, is k47GHz which is in good agreement with the calculated result of theory. And the current-voltage characteristics curve which takes account of the buffer layer effect has been obtained. Lastly it has been verified that parasitic current at the buffer layer can be analyzed using channel depth modulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.4
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• pp.336-339
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• 2004

In this paper the two-dimensional scattering rates were calculated in pseudomorphic Al/sub x//Ga/sub 1-x//As/Ga/sub y/In/sub l -y//As/GaAs heterostructure systems. The electronic states of the square quantum well were determined by the numerical self-consistent solution of Poisson's and Schrodinger's equations. The numerically obtained wave functions and energy levels were used to obtain the major two-dimensional scattering rates in this structure. Polar optical- and acoustic-phonon scattering, piezoelectric, ionized impurity and alloy scattering were considered for the first two sub-bands. The results were compared to the three-dimensional scattering rates also calculated in the same region.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.9
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• pp.417-422
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• 2002

ZnO thin films were deposited on various substrates, such as Si-(111), SiO$_2$(5000 $\AA$ by thermal CVD)/Si-(100), and SiO$_2$(2000 $\AA$ by RF sputtering)/Si-(100). The (002)-orientation, surface morphology and roughness, and electrical resistivity of deposited films were measured and compared in terms of substrate. Surface acoustic wave(SAW) filters with a multilayered configuration of IDT/ZnO/SiO$_2$/Si were also fabricated and the IDT was obtained using a lift-off method. From the frequency-response characteristics of fabricated devices, the insertion loss and side-lobe rejection were estimated. The experimental results showed that the (002)-oriented growth nature of ZnO films, which played a crucial role of determining the characteristic of SAW device, was strong1y dependent upon the SiO$_2$buffer.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.5
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• pp.90-96
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• 2008

This paper presents an algorithm of a single chip acoustic speech enhancement for telematics device. The algorithm consists of two stages, i.e. noise reduction and echo cancellation. An adaptive filter based on cross spectral estimation is used to cancel echo. The external background noise is eliminated and the clear speech is estimated by using MMSE log-spectral magnitude estimation. To be suitable for use in consumer electronics, we also design a low cost, high speed and flexible hardware architecture. The performance of the proposed speech enhancement algorithms were measured both by the signal-to-noise ratio(SNR) and recognition accuracy of an automatic speech recognition(ASR) and yields better results compared with the conventional methods.

• Journal of Soil and Groundwater Environment
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• v.25 no.4
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• pp.58-66
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• 2020

Since the typical horn-type ultrasonic equipment induces a reaction at the probe tip, the sonochemical reaction has a limitation that it occurs only in a specific area. As one of the ways to overcome this limitation, an ultrasonic device with multi-stepped horn equipped with several oscillators has been developed. The objective of this study was to investigate the sonochemical effects induced by acoustic cavitation system in 20 kHz multi-stepped ultrasonic horn using calorimetry, KI dosimetry and the luminol test. The sonochemical effects of multi-stepped ultrasonic horn were compared with that of the typical horn-type 20 kHz ultrasonic device. The effect of immersion depth and power on the sonochemical reaction was investigated in the ultrasonic system with multi-stepped ultrasonic horn. Higher calorimetric energy was obtained at higher immersion depth and power conditions. Sonochemical effects increased significantly when using the high immersion depth and input power. However, as the input power increased, the cavitation reaction zone concentrated around the ultrasonic horn. Additionally, the experiments to examine the effect of liquid temperature was conducted. The smaller sonochemical reaction was obtained for the higher liquid temperature. The effect on temperature seems to be closely related to liquid conditions such as viscosity and vapor pressure of water.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.1
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• pp.27-40
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• 2013

This study is about development of technology system for an advanced deep-sea unmanned underwater robot of S. Korea analysed by the application of scenario planning. It was developed a 6000m class next-generation deep-sea unmanned underwater vehicle(or robot, UUV) system, soonly ROV 'Hemire' and Depressor 'Henuvy' in 2006 at S. Korea and motion control, adaptive control algolithm, a work-space manipulator control algolithm, especially the underwater inertial-acoustic navigation system robust to initial errors and sensor failures. But there are remained matters on position tracking of the USBL, inertial-acoustic navigation system, attitude sensor, designed sonar sensors. So this study suggest the new idea for settle the matters and then this idea help the development of the underwater inertial-acoustic navigation system robust to initial errors and sensor failures, such as acoustic signal drop-out, by modifying the error covariance of the failed sonar signal when drop-out occurs. As a result, the future policy for deep-sea unmanned underwater robot of S. Korea is to further spur the development of new technology and more improvement of the technology level for deep-sea unmanned underwater robot system with indicator and imaginary wall as external device.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.1-10
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• 2008

A series of the studies on the applied physical properties of domestic species have been conducted last three years. Pinus koraiensis and Larix kaempferi were two of the three species examined for the first year. Because the same apparatus and experimental procedures were used for all species, their results can be easily comparable. The experiments for sorption property were conducted with 20- and 80-mesh wood powder and resulted in their EMCs and sorption isotherms at various RH conditions. The thermal conductivity and diffusivity, and electric resistance and volumetric electric resistivity were measured with a thermal-wire device and a high electric resistance meter. The differences in the thermal and electric properties between quarter- and flat-sawn specimens were observed, which were partially attributed to their anatomical differences. An acoustic measurement system was used to evaluate dynamic MOE and internal friction. This paper provides the useful fundamental data for designing a wood structure, correcting a portable resistance-type moisture meter, and acoustic properties of wood.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.473-479
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• 2016

We report a highly selective and sensitive 200 MHz Surface Acoustic Wave (SAW) sensor that can detect cyanide ion in aqueous solution using surface immobilized thioester molecules in combination with gold nanoparticles (AuNPs). To construct the sensor device, a monolayer of thioester compound was immobilized on the SAW sensor surface. At the sensor surface, hydrolysis of thioester group by nucleophilic addition of cyanide occurred and the resulting free thiol unit bound to AuNP to form thiol-AuNP conjugate. For the signal enhancement, gold staining signal amplification process was introduced subsequently with gold (III) chloride trihydrate and reducing agent, hydroxylamine hydrochloride. The SAW sensor showed a detection ability of $17.7{\mu}M$ for cyanide in aqueous solution and demonstrated a saturation behavior between the frequency shift and the concentration of cyanide ion. On the other hand, our SAW sensor had no activities for other anions such as fluoride ion, acetate ion and sulfate ion, moreover, no significant interference observed by other anions. Finally, all the experiments were carried out in-house developed sensor and fluidics modules to obtain highly reproducible results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.94-99
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• 2003

For the assessment of combustion stability of a liquid rocket engine, a device called "Pulse Gun" should be developed first, which can induce artificial perturbations that may lead to excitations of pressure oscillations in a combustion chamber. A model chamber has been used for identifying design parameters of a pulse gun that defines its characteristics. Dynamic pressure measurements showed that shock waves generated from pulse guns are axisymmetric around the axis of a pulse gun barrel. Pressure waves perturbed by a pulse gun induce resonant acoustic frequencies of a model chamber. This fact indicates that successful pressure field perturbations of the KSR-III combustion chamber can be performed by a newly developed pulse gun device. A maximum value of dynamic pressure peaks measured at the opposite point against a pulse gun outlet becomes stronger as charge mass of pulse gun powder increases.