• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.219-219
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• 2008

Energy harvesting from the environment has been of great interest as a standalone power source of wireless sensor nodes for ubiquitous sensor networks (USN). There are several power generating methods such as thermal gradients, solar cell, energy produced by human action, mechanical vibration energy, and so on. Most of all, mechanical vibration is easily accessible and has no limitation of weather and environment of outdoor or indoor. In particular, the piezoelectric energy harvesting from ambient vibration sources has attracted attention because it has a relative high power density comparing with other energy scavenging methods. Through recent advances in low power consumption RF transmitters and sensors, it is possible to adopt a micro-power energy harvesting system realized by MEMS technology for the system-on-chip. However, the MEMS energy harvesting system hassome drawbacks such as a high natural frequency over 300 Hz and a small power generation due to a small dimension. To overcome these limitations, we devised a novel power generator with a spiral spring structure. In this case, the energy harvester has a lower natural frequency under 200 Hz than a normal cantilever structure. Moreover, it has higher an energy conversion efficient because shear mode ($d_{15}$) is much larger than 33 mode ($d_{33}$) and the energy conversion efficiency is proportional to the piezoelectric constant (d). We expect the spiral type MEMS power generator would be a good candidate as a standalone power generator for USN.

• Journal of Sensor Science and Technology
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• v.9 no.1
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• pp.83-89
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• 2000

BST thin films were deposited on the ITO coated glass for using TFELD insulating layer by rf magnetron sputtering method. $O_2/(Ar+O_2)$ mixing ratio was 10%, substrate temperature was changed from R.T. to $500^{\circ}C$, and working pressure was changed from 5 mTorr to 30 mTorr. BST thin films deposited with various conditions were investigated electrical, optical, structural properties, and stoichiometry. The result of investigation was achieved good fabrication condition that substrate temperature of $400^{\circ}C$, and working pressure of 30 mTorr. Relative dielectric constant of 254 at 1 kHz, leakage current density was below $3.3{\times}10^{-7\;}A/cm^2$ at 5\;MV/cm applied electric field, and transmittance was over 82% at visible range.

• Journal of Korea Spatial Information System Society
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• v.10 no.1
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• pp.51-63
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• 2008

Previous studies for routing In USN (Ubiquitous Sensor Networks) appear to be unreliable due to the dependence on non-spatial data and the lack of map overlay analysis. Multiple spatial parameters and radio propagation modeling techniques were integrated to derive RSSI (Received Signal Strength Indicator) value between route nodes and produce a highly reliable path map. It was possible to identify area-wide patterns of USN route subject to many different Influences (e.g. the specific effects of radio blocking factors such as the visible area, road area, cell duplicated area, and building density), which cannot be acquired by traditional non-spatial modeling. The quantitative evidence concerning the USN route for individual cell as well as entire study area would be utilized as major tools to visualize paths in real-time and to select alternative path when failure or audition of route node occurs.

• Proceedings of the KIEE Conference
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• 2001.07e
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• pp.35-39
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• 2001

The purpose of this paper is improvement the piezoelectric of Polyvinylidene fluoride(PVDF) organic thin films is fabricated by vapor deposition method. The piezoelectric of PVDF organic thin films attributed to dipole orientation in crystalline region. Also, the piezoelectric characteristic reduced that dipole moments orientation in crystalline region interfered with impurity carriers. Therefore, PVDF organic thin films fabricated with high substrate temperature condition for crystallinity improvement. The crystallinity of PVDF organic thin films fabricated by this condition increase from 47 to 67.8%. The ion density of PVDF organic thin films fabricated by substrate temperature variation from $30^{\circ}C$ to $105^{\circ}C$ decreased from $1.62{\times}10^{16}cm^3$ to $6.75{\times}10^{11}cm^3$ when temperature and frequency were $100^{\circ}C$, 10Hz, respectively. The $d_{33}$ and piezo-voltage coefficient of PVDF organic thin films increased from 20pPC/N to 33pC/N and $162.9{\times}10^{-3}V{\cdot}m/N$ to $283.2{\times}10^{-3}V{\cdot}m/N$, respectively. For the sake of the applications of piezoelectric sensor, we analyzed the output voltage characteristic as a function of the distance between an oscillator of 28kHz and PVDF organic thin film transducer. From this, we found that the output voltage is inversely proportional to the distance. At this time, the period was about $35.798{\mu}s$ and equal the oscillator frequency.

• Journal of the Korean Magnetics Society
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• v.8 no.2
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• pp.86-92
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• 1998

Homegeneous feedstock is necessary to make plastic magents with uniform magnetic properties, therefore the optrimized mixing route and the homogeneity evaluation method are demanded. In this paper, method of homogeneity evaluation and effect of homogeneity on the magnetic prperites were investigated using Sr-ferrite /EVA plastic magnets. The feedstocks with different homogeneity were prepared using batch mixer and single screw extruder. The homogeneities of feedstocks were tested by torgue sensor, capilary rheometer, and measurement of magnetic properties. Mixing torque measurement using torque sensor was an effective method to determine the critical powder loading, but it was nor suitable to suitable to determine the feedstock mixing quality. Particle alignment measurement of a plastic magent was very accurate to evaluate the homogeneity, but expensive equipments were required to make and measure the samples. Pressure measurement using capillary rheometer was a very effective and easy method with high accuracy. Homogeneous feedstock increased the particle alignment of plastic magnet. Remanet flux density and maximum energy product increased linearly and quadratically with increasing particle alignment, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.7-7
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• 2010

Energy harvesting from the environment has been of great interest as a standalone power source of wireless sensor nodes for Ubiquitous Sensor Networks(USN). In particular, the piezoelectric energy harvesting from ambient vibration sources has intensively researched because it has a relatively high power density comparing with other energy scavenging methods. Through recent advances in low power consumption RF transmitters and sensors, it is possible to adopt a micro-power energy harvesting system realized by MEMS technology for the system-on-chip. However, the MEMS energy harvesting system has some drawbacks such as a high natural frequency over 300 Hz and a small power generation due to a small dimension. To overcome these limitations, we devised a novel power generator with a spiral spring structure as shown in the figure. The natural frequency of a cantilever could be decreased to the usable frequency region (under 300 Hz) because the natural frequency depends on the length of a cantilever. In this study, the natural frequency of the energy harvester was a lower than a normal cantilever structure and sufficiently controllable in 50 - 200 Hz frequency region as adjusting weight of a proof mass. Moreover, the MEMS energy harvester had a high energy conversion efficiency using a shear mode ($d_{15}$) is much larger than a 33 mode ($d_{33}$) and the energy conversion efficiency is proportional to the piezoelectric constant (d). We expect the spiral type MEMS power generator would be a good candidate for a standalone power generator for USN.

• Korean Journal of Crystallography
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• v.9 no.1
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• pp.30-38
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• 1998

A new frequency weighing sensor was applied to grow Bi12GeO20 crystals in the auto-di-ameter control system of Czochralski method. The rotation rate was varied in the range of 23 to 21 rpm to preserve flat interface in a given heat configuration. To prevent the constitutional super-cooling from the evaporation loss, 105% stoichiometric amount of Bi2O3 was employed, equivalent to 6.18 molar ratio of Bi2O3 to GeO2. Transparent and light brown Bi12GeO20 single crystal in uniform diameter was grown. The dislocation density was determined to be 103/cm2 corresponding to the optical quality in commercial applications. The grown crystal measured diameter 25 mm and length 70 mm and the preferred growth direction was confirmed to be <110>.

• Journal of Sensor Science and Technology
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• v.15 no.4
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• pp.237-244
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• 2006

Atomic force microscope (AFM) has become a common tool for the structural and physical studies of biological macromolecules, mainly because it provides the ability to perform experiments with samples in a buffer solution. In this study, structure of proteins and nucleic acids has been studied in their physiological environment that allows native intermolecular complexes to be formed. Cr and Au were deposited on p-Si (100) substrate by thermal evaporation method in sequence with the thickness of $200{\AA}$ and $500{\AA}$, respectively, since Au is adequate for immobilizing biomolecules by forming a self-assembled monolayer (SAM) with semiconductor-based biosensors. The SAM, streptavidin and biotin interacted each other with their specific binding energy and their adsorption was analyzed using the Bio-AFM both in a solution and under air environment. A silicon nitride tip was used as a contact tip of Bio-AFM measurement in a solution and an antimony doped silicon tip as a tapping tip under air environment. Actual morphology could also be obtained by 3-dimensional AFM images. The length and agglomerate size of biomolecules was measured in stages. Furthermore, $R_{a}$ (average of surface roughness) and $R_{ms}$ (mean square of surface roughness) and surface density for the adsorbed surface were also calculated from the AFM image.

• Journal of Sensor Science and Technology
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• v.5 no.3
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• pp.87-92
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• 1996

The PLT thin films on (100) cleaved MgO single crystal substrate have been fabricated by rf magnetron sputtering using a PbO-rich target. The dependence of physical and electrical properties on the degree of c-axis orientation has been studied. The degree of c-axis orientation of PLT thin films depends on fabrication conditions. Fabrication conditions of the PLT thin films were such that substrate temperature, working pressure, gas ratio of $Ar/O_{2}$, and rf power density were $640^{\circ}C$, 10 mTorr, 10 seem, and $1.7\;W/cm^{2}$, respectively. In these conditions, the PLT thin film showed the Pb/Ti ratio of 1/2 at the surface, the resistivity of $8{\times}10^{11}{\Omega}{\cdot}cm$, and dielectric constant of 110. The pyroelectric infrared sensors with these PLT thin films showed the peak to peak voltage of 450 m V and signal to noise ratio of 7.2.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.1
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• pp.61-73
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• 2002

This paper addresses the conceptual design results of the HAUSAT-1 (Hankuk Aviation University SATellite-1), developed by Space System Research Lab. of Hankuk Aviation Univ., which is a new generation picosatellite. This project has been funded by Korean Government for the purpose of developing the space core technology. This is the first attempt at the level of university in Korea to develop the satellite weighing less than 1kg and accelerates opportunities with low construction, low launch cost space experiment platforms. The purpose of the HAUSAT-1 project is to offer graduate and undergraduate students great opportunities to be able to understand the design process of satellite development as a team member. Its mission objectives are to track its position by the GPS receiver system, to deploy the thin film solar cell panel to generate extra power, and to measure plasma density and temperature with the plasma sensor. The HAUSAT-1 will orbit at the altitude of 650 km with 65 degree inclination angle with 12 months of design mission life. It is planned to be launched on November 2003 by Russian launch vehicle "Dnepr".