• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.15-24
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• 1996

In this study, as a part of the basic study for the application of optical fiber sensors to smart composite structures, the integrity of optical fiber sensors embedded within the composite structures was examined and then the laser signal transmitted through optical fiber sensors during the deformation of host structures was investigated. Firstly, it was found that bending test could be substituted for tensile test by comparing cumulative failure distribution based on weakest link theory and introducing the correction factor. Weibull parameters were obtained through the experiments and the correction factor was found to be applied to cumulative failure distribution derived from bending test. The integrity of embedded optical fiber sensors due to the thermal effect was evaluated by the comparison of the mean tensile strengths of cured and uncured optical fibers. Secondly, relationships between stress-strain curve obtained in tensile test of composite laminate and the intensity of laser signal transmitted through embedded optical fibers were examined and the possibility of the effective damage detection using optical fiber sensors was studied.

• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.35-42
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• 1996

In this paper, a development of model based battery SOC indicator is described. The proposed method is independent upon initial SOC, is reliable on the sudden change of load, and could estimate the available driving distance. The mathematical model of battery which has relation of the current, voltage and SOC estimates the SOC by least square estimation to minimize the error between measured voltage and estimated voltage. For experiment, the charging and discharging system using computer was designed to acquire the current and voltage data for model. The feasibility in electric vehicle was confirmed by variable load testing using the developed SOC indicator by stand-alone type microcontroller.

• Journal of Sensor Science and Technology
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• v.25 no.1
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• pp.20-26
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• 2016

The bioelectrical impedance (BI) for the young and the elderly was measured using bioelectrical impedance spectroscopy (BIS). First, while applying a current of $600{\mu}A$ to the foot and hand, BI was measured at 50 frequencies ranging from 5 to 1000 kHz. The BI for young subjects was considerably lower than that for old subjects since young subjects have more lean mass (hydration). The prediction marker was 0.74 for young subjects and 0.78 for old subjects. Second, a Cole-Cole diagram was obtained for young subjects and old subjects, indicating the different characteristic frequencies. At 50 kHz, the average phase angle was $7.8^{\circ}$ for young subjects whereas that was $6.1^{\circ}$ for old subjects. Third, BIVA was analyzed for young subjects and old subjects. The vector length was 210.89 [${\Omega}/m$] for young subjects and 326.12 [${\Omega}/m$] for old subjects. At 50 kHz, the resistance (R/H) and the reactance ($X_C/H$) divided by height were 208.94 [${\Omega}/m$] and 28.68 [${\Omega}/m$] for young subject, and 324.33 [${\Omega}/m$] and 34.09 [${\Omega}/m$] for old subjects.

• Journal of Sensor Science and Technology
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• v.25 no.1
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• pp.1-7
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• 2016

Bioelectrical impedance (BI) at popliteal regions was measured using a bioelectrical impedance measurement system (BIMS), which employs the multi-frequency and the two-electrode method. Experiments were performed as follows. First, a constant AC current of $800{\mu}A$ was applied to the popliteal regions (left and right) and the BI was measured at eight different frequencies from 10 to 500 kHz. When the applied frequency greater than 50 kHz was applied to human's popliteal regions, the BI was decreased significantly. Logarithmic plot of impedance vs. frequency indicated two different mechanisms in the impedance phenomena before and after 50 kHz. Second, the relationship between resistance and reactance was obtained with respect to the applied frequency using BI (resistance and reactance) acquired from the popliteal regions. The phase angle (PA) was found to be strongly dependent on frequency. At 50 kHz, the PA at the right popliteal region was $7.8^{\circ}$ slightly larger than $7.6^{\circ}$ at the left popliteal region. Third, BI values of extracellular fluid (ECF) and intracellular fluid (ICF) were calculated using BIMS. At 10 kHz, the BI values of ECF at the left and right popliteal regions were $1664.14{\Omega}$ and $1614.08{\Omega}$, respectively. The BI values of ECF and ICF decreased sharply in the frequency range of 10 to 50 kHz, and gradually decreased up to 500 kHz. Logarithmic plot of BI vs. frequency shows that the BI of ICF decreased noticeably at high frequency above 300 kHz because of a large decrease in the capacitance of the cell membrane.

• Journal of Sensor Science and Technology
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• v.25 no.1
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• pp.46-50
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• 2016

During KSTAR plasma experiments, torsional $Alfv\acute{e}n$ waves in the frequency of few GHz or below were detected. To understand this plasma waves during the crash of MHD instabilities, an RF spectrometer has been developed for detection of the radiated RF signals in the KSTAR Tokamak. It has the capability of broadband RF spectral measurement (50 ~ 400 MHz). To detect the broadband RF signals which are radiated from the KSTAR systems, a broadband antenna is the key feature of the RF spectrometer. In this paper, a broadband bowtie antenna for detection of $Alfv\acute{e}n$-waves in the KSTAR Tokamak is presented. Planar-type bowtie antenna is designed and fabricated on an FR4 substrate with thickness of 1.6 mm. The antenna consists of bowtie shaped balanced radiators and broadband planar balun. The antenna is designed to have an input impedance of 50 Ohm, and a taper-shaped balun is adopted for field and impedance matching between 50 Ohm transmission line to 110 Ohm feeding network of balanced radiators. The implemented antenna provides around -3 to 3 dBi of gain for the whole frequency band. The VSWR of the bowtie antenna is less than 12:1 over the frequency bandwidth of 50 to 2000 MHz.

• Journal of Sensor Science and Technology
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• v.20 no.2
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• pp.124-130
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• 2011

In this study, in order to evaluate the yield of bubble by ultrasonic cavitation in HIFU sonication, the bubble image analysis was performed. The changing phenomenon of cavitation effect according to the sonication condition was discussed by analyzing the bubble image. Especially the appearance of bubble cloud, the size of micro-bubble, and the yield of bubble were considered. The 500 KHz and 1.1 MHz concave type ultrasonic transducers were used for HIFU sonication. Computer controlled digital camera was used to obtain the bubble image, and the binary image processing(binarization coefficient : 0.15) was performed to analyze them. In results of 500 KHz and 1.1 MHz transducer, the area of bubble cloud was increased in proportion to the rise in sonication intensity($R^2$ : 0.7031 and 0.811). The mean size of single microbubble was measured as 98.18 um in 500 KHz sonication, and 63.38 um in 1.1 MHz sonication. In addition, the amount of produced bubble was increased in proportion to sonication intensity. Through the result of this study and further study for variable image processing method, the quantitative evaluation of ultrasonic cavitation effects in HIFU operation could be possible with the linearity associated with the sonication conditions.

• Journal of Sensor Science and Technology
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• v.19 no.4
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• pp.291-296
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• 2010

Recently, recycling method of waste wafer has been an area of solar cell to cut costs. Micro_blasting is one of the promising candidates for recycling of waste wafer due to their extremely simple and cost-effective process. In this paper, we attempt to explore the effect of micro_blasting and DRE(damage removal etching) process for solar cell. The optimal process conditions of micro_blasting are as follows: $10{\mu}m$ sized $Al_2O_3$ powder, jetting pressure of 400 kPa, and scan_speed of 30 cm/s. And the particles formed on micro_blasted wafer were removed by DRE precess which was performed by using HNA(HF/$HNO_3$/$CH_3COOH$) and TMAH(tetramethyl ammonium hydroxide). Structural analysis was done using a-step and the XRD patterns.

• Journal of Sensor Science and Technology
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• v.19 no.6
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• pp.449-455
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• 2010

Implantable middle ear hearing devices(IMEHDs) have being actively studied to overcome the problems of conventional hearing aids. Vibration transducer, an output devices of IMEHDs, is attached on the ossicular chain and transmits mechanical vibration to cochlea. This approach allows us to hear more clear sound because mechanical vibration is effective to transfer high frequency acoustics, but occurs some problems such as fatigue accumulation to ossicular chian and reduction of vibration displacement caused by mass loading effect. Recently, many studies for the round window stimulation are announced, because it does not cause such problems. It have been studied by older transducers designed for attaching on ossicular chain. In this paper, we proposed a new electromagnetic transducer which consists of two magnets, three coils and a vibration membrane. The magnet assembly, magnet coupled in opposite direction, were placed in the center of three coils, and the optimum length of each coil generating maximum vibrational force was calculated by finite element analysis(FEA). The transducer was implemented as the calculated length of each coil, and measured vibration displacement. From the results, it is verified the vibration displacement can be improved by optimizing the length of coils.

• Journal of Sensor Science and Technology
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• v.17 no.6
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• pp.437-446
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• 2008

Single crystalline ${ZnIn_2}{Se_4}$ layers were grown on thoroughly etched semi-insulating GaAs (100) substrate at $400^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating ${ZnIn_2}{Se_4}$ source at $630^{\circ}C$. The crystalline structure of the single crystalline thick films was investigated by the photoluminescence (PL) and Double crystalline X-ray rocking curve (DCRC). The carrier density and mobility of ${ZnIn_2}{Se_4}$ single crystalline thick films measured from Hall effect by van der Pauw method are $9.41{\times}10^{16}cm^{-3}$ and $292cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ${ZnIn_2}{Se_4}$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)$=1.8622 eV-$(5.23{\times}10^{-4}eV/K)T^2$/(T+775.5 K). After the as-grown ${ZnIn_2}{Se_4}$ single crystalline thick films was annealed in Zn-, Se-, and In-atmospheres, the origin of point defects of ${ZnIn_2}{Se_4}$ single crystalline thick films has been investigated by the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_{Se}$, $Zn_{int}$, and $Se_{int}$ obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Se-atmosphere converted ${ZnIn_2}{Se_4}$ single crystalline thick films to an optical p-type. Also, we confirmed that In in ${ZnIn_2}{Se_4}$/GaAs did not form the native defects because In in ${ZnIn_2}{Se_4}$ single crystalline thick films existed in the form of stable bonds.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.333-337
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• 2013

This study proposes a simply fabricated micro stator for higher output power than previously reported micro stators. The stator has been fabricated by inserting enamel coil in silicon mold formed by micro etching process. The most merits of the proposed micro stator are the simple fabrication process and high output power. Previously reported micro stators have high resistance because the micro coil is fabricated by relatively thin-film-based deposition process such as sputtering and electroplating. In addition, the previously reported micro coil has many electrical contact points for forming the coil structure. These characteristics of the micro stator can lead to low performance in output power. However, the proposed micro stator adopts commercially available enamel coil without any contact point. Therefore, the enamel coil of the proposed micro stator has low junction resistance due to the good electrical quality compared with the deposited or electroplated metal coil. Power generation tests were performed and the fabricated stator can produce 5.4 mW in 4000 RPM, $1{\Omega}$ and 0.3 mm gap. The proposed micro stator can produce larger output power than the previously reported stator spite of low RPM and the larger gap between the permanent magnet and the stator.