• Journal of the Korean Geotechnical Society
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• v.31 no.8
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• pp.17-28
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• 2015

The purpose of this study is to measure the volumetric water content of unsaturated soils during drying and wetting process by using volumetric pressure plate extractor (VPPE) incorporated with time domain reflectometry (TDR). The VPPE consists of a pressure cell, a pressure regulator, a burette system and a TDR probe. Two samples with different initial void ratios were prepared in the pressure cell, and the air pressure at the range of 0.1 kPa - 50 kPa was applied to adjust the matric suction by the pressure regulator. The burette system was used to measure the volumetric water content change of the sample according to the matric suction. In addition, the TDR probe, installed in the cell, was used to evaluate the dielectric constant from the reflected signal of the electromagnetic wave at the probe. The volumetric water content of specimen was estimated by the empirical equation between the volumetric water content and dielectric constant, which was calibrated with the Jumunjin sand. The test results show that the volumetric water content calculated by TDR probe is strongly correlated to the measured value by burette system. The hysteresis occurs during drying and wetting process. Furthermore, the degree of hysteresis reduces in the repeated process. This study suggests that TDR may be effectively used to evaluate the water content soil for the determination of water characteristic curve of unsaturated soils.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.85-91
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• 2024

To realize stable use of ground treated with cementitious materials, the curing process must be evaluated. In this study, a time domain reflectometry (TDR) measurement system was employed to evaluate the curing process of cementitious grout based on the electromagnetic property. A coated probe was manufactured to prevent electrical connection between the electrodes by the electrically conductive cementitious grout, and a calibration process was performed to estimate the actual relative permittivity using the coated probe. To assess the curing process of cementitious grout using the TDR measurement system, cementitious grout with added retarder was prepared with a water-to-cement ratio of 45%. A preliminary measurement was conducted immediately after pouring the cementitious grout into the mold to test the applicability of the coated probe, and TDR signals and relative permittivity were measured at 3~288 hours of curing time. The experimental results demonstrate that the relative permittivity of the cementitious grout immediately after pouring was greater than 100, decreased rapidly over time, and converged to approximately 13.8 at 144 hours, which is considered the fully cured time. This findings of this study demonstrate that the TDR measurement system with a coated probe is applicable to electrically conductive materials. In addition, the TDR measurement system can be used effectively to monitor the curing process of cementitious grout based on electromagnetic properties.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.2
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• pp.214-217
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• 2013

In this paper, a waveguide-type resonator with a slot is proposed to measure permittivity of thin film from resonant frequency shifting by an attached MUT(Material Under Test). The MUT on the slot shifts resonant frequency by perturbation of electromagnetic field. Amount of shifting resonance frequency is dependent on the permittivity of MUT, and that relation is obtained from numerical simulation. The measured relative permittivity of a thin film with thickness of $65{\mu}m$ is 3.3492 with standard error of ${\pm}0.0605$ in the frequency range of 2 GHz to 3 GHz. Also the proposed method is compared with other measuring methods such as dielectric resonator and waveguide probe systems.

• International Journal of Control, Automation, and Systems
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• v.6 no.5
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• pp.767-775
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• 2008

Methods used for exploring marine resources and spaces include positioning a probe under water and then recalling it after a specified time. Hydro-acoustic Releasers are commonly used for positioning and retrieving of such exploration equipment. The most important factor in this kind of system is the reliability for recalling the instruments. The frequently used ultrasonic signal detection method can detect ultrasonic signals using a fixed comparator, but because of increased rates of errors due to outside interferences, information is repetitively acquired. This study presents an effective ultrasonic signal detection algorithm using the characteristics of a resonance and adaptive comparator Combined with the FSK+ASK modulator. As a result, approximately 8.8% of ultrasonic wave communication errors caused by background noise and transmission losses were reduced for effectively detecting ultrasonic waves. Furthermore, the resonance circuit's quality factor was enhanced (Q = 120 to 160). As such, the bias voltage of the transistor (Vb= 3.3 to 6.8V) was increased thereby enhancing the frequency's selectivity.

• ETRI Journal
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• v.37 no.1
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• pp.26-31
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• 2015

Axial-ratio (AR) bandwidth enhancement is achieved for a circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) using a wideband hybrid coupler (WHC) combined with dual probe feed. The presented WHC, comprised of a Wilkinson power divider and a wideband $90^{\circ}$ shifter, delivers good characteristics in terms of 3 dB power splitting and consistent $90^{\circ}$ (${\pm}5^{\circ}$) phase shifting over a wide bandwidth. In turn, the proposed CP DRA, for the employment of the WHC, in place of conventional designs, provides a significant enhancement on AR bandwidth and impedance matching. The antenna prototype with the WHC exhibits a 3 dB AR bandwidth of 48.66%, an impedance bandwidth of 52.5% for voltage standing wave ratio (VSWR) ${\leq}2$, and a bandwidth of 44.66% for a gain of no less than 3 dBi. Experiments demonstrate that the proposed WHC is suitable for broadband CP DRA design.

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1075-1080
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• 2003

We have investigated femtosecond coherent vibrational motions of Zn(II)-5,15-diphenylporphyrin in toluene using chirp-controlled ultrashort pulses. The oscillatory features superimposed on the temporal profiles of the pump-probe transient absorption signal are affected by the chirping and energy of excitation pulses. Using chirp- and excitation energy-controlled femtosecond pulses, we are able to obtain information on the structural changes between the electronic ground and excited states based on a comparative analysis of the Fouriertransformed frequency-domain spectra retrieved from the oscillatory components with the ground state resonance Raman spectra and normal mode calculations.

• Journal of the Korean Applied Science and Technology
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• v.34 no.3
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• pp.595-601
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• 2017

In vivo assay of glucose detection was described using a skin tattoo film electrode (STF), and the probe was made from carbon nano tube paste modification film paper. Here in the square-wave stripping anodic working range obtained of $20-100mgL^{-1}$ within an accumulation time of 0 seconds only in sea water electrolyte solutions of pH 7.0. The relative standard deviations of 50 mg glucose that were observed of 0.14 % (n=12), respectively, using optimum stripping accumulation of 30 sec, the low detection limit (S/N) was pegged at 15.8 mg/L. The developed results can be applied to the detect of in vivo skin sensing in real time. Which confirms the results are usable for in vitro or vivo diagnostic clinical analysis.

• Tribology and Lubricants
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• v.26 no.6
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• pp.341-345
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• 2010

The NAUT(Non contact Air coupled Ultrasonic Testing) is one of the ultrasonic wave inspection methods. It compensates High power ultrasound Pulser Receiver, pre-amp, air probe of high sensitivity in air to generate loss energy by NAUT methods. Generally, in case of ultrasound inspection, it applies contact methods by using couplant. However it can inspect of UT without couplant by this NAUT. The ultrasound transmission reception is composed in stable condition in NAUT. It can inspect high low material or the specimen of rough part, the narrow spot, too. The spot welding is applying the inosculation of automobile component, car body, all boards. The CFRP is necessity of NDE because of the solidity changes material according to lamella tearing. Therefore it checked on realization whether and commercialization in the spot welding and CFRP inspection that the NAUT would be applied them.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.10-10
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• 1998

천음속 익형에서 발생하는 응축충격파와 경계층의 간섭을 피동제어 하여 항력감소에 대한 연구를 2.5$\times$7$\textrm{cm}^2$ 천음속 풍동에서 수행하였다. 익형표면에 설치한 정압공으로 정압을, 익형후방에 설치한 8개의 Pitot probe로 전압을 동시에 측정하여 충격파를 통한 에너지의 손실과 항력의 변화를 계산하였고, 또한 유동장과 충격파의 형상을 가시화하기 위해 슈리렌 가시화 시스템을 사용하였다. 실험은 NACA 0012 익형에서 기공률 변화에 따른 피동제어의 항력감소 초과를 조사한 다음 NACA 64-018 익형에서는 기공률과 공동의 크기의 변화가 미치는 효과를 연구하였다. 피동제어의 개념은 충격파가 발생하는 하부벽을 다공벽으로 만들고 그 아래를 공동으로 만들면 충격파 후방의 상대적으로 높은 압력이 기류의 일부를 공동으로 자연스럽게 유입시키고 다시 공동에서 낮은 압력의 충격파 상류로 유출시키는 것이다.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.264-267
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• 1993

A high plasma density of $10^{12}cm^{-3}$ can be produced at the pressure of few mTorr with R. F input power of 300-400W. A radially uniform plasma to a radius of 7cm at the substrate was produced at the pressure of 1 mTorr. The electron density and temperature were confirmed with double Langmuir probe, $\mu$-wave interferometer. It has bee found that the dispersion relation N/B=constant not be applied at the low R.F input power(<600W) but can be applied at high R.F input power(>600W).