• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.6
• /
• pp.789-795
• /
• 2003

It is studied that the measuring method of the spectral emissivity by using hemispherical mirror with an inclined observation hole. The in-service calibration method of mirror reflectivity is also dealed with. It is possible to apply this method on measuring emissivity of conductor or non-conductor.

• Journal of the Korean Institute of Navigation
• /
• v.18 no.2
• /
• pp.151-158
• /
• 1994

A wide band design method of an electromagnetic wave absorber using exponentially tapered ferrite, which has very wide band frequency characteristics, is proposed and discussed. The wide band electroma-gnetic wave absorber can be designed by the proposed equivalent material constants method for the re-gions varying spatially in the shape of ferrite. Futhermore, the wide band ferrite electromagnetic wave absorber with taper, which have not only exce-llent reflectivity frequency characteristics but also the band width of 30MHz to 2150 or 2450MHz under the tolerance limits of -20dB reflectivity, were designed.

• Journal of the Korean institute of surface engineering
• /
• v.8 no.3
• /
• pp.1-4
• /
• 1975

To study optical properties of Ag-Au alloys as the simplest homogeneous diordered alloys, the dependence of the reflectivity of Ag-Au alloys on their composition has been measured with the wave lengths ranging from 700m${\mu}$ to 900m${\mu}$. Measurements were made on mechanically polished bulk samples and the experimental results are discussed in terms of the Drude-Zender theory. The distributions on the reflectivity of various wavelengths are also discussed.

• Journal of the Korean Vacuum Society
• /
• v.16 no.3
• /
• pp.221-226
• /
• 2007

DBR (distributed Bragg reflectors) PSi (porous silicon) composite films displaying dual optical properties, both optical reflectivity and photoluminescence had been developed. DBR PSi samples were prepared by electrochemical etch of heavily doped $p^{++}-type$ silicon wafers (boron doped, polished on the <100> face, resistivity of $0.8-1.2m{\Omega}-cm$, Siltronix, Inc.). Free-standing DBR PSi films were treated with PMMA (polymethyl methacrylate) to produce flexible, stable composite materials in which the PSi matrix is covered with PMMA containing photoluminescent polysiloles. Optical characteristics of DBR PSi/polysilole-impregnated PMMA composite materials exhibit both their photonic reflectivity at 565 nm and photoluminescence at 510 nm, simultaneously. A possible application of this materials will be discussed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.9 no.1
• /
• pp.29-34
• /
• 2008

We fabricated the 4 channel wave function generator with variable frequency, pulse width, amplitude and rising/falling slope to develop driving method of charged particle type display. The selective sell driving is ascertained by fabricated panel with black and yellow particles. To measure CIE point, reflectivity, contrast ratio and viewing angle, experimental apparatus is integrated with optical circular$(1^{\circ})$ moving emitting/receiving part and spectrometer connected to emitting part. The yellow particles in glass have reflectivity of $35{\sim}40%$ and wavelength of 571.2nm and black one has reflectivity of $15{\sim}20%$ in case of only 1 layer of particle, and the case of 3 layer the optical property is promoted.

• Composites Research
• /
• v.18 no.1
• /
• pp.16-22
• /
• 2005

Application fields on structural health monitoring of fiber Bragg gratings (FBGs) are gradually expanded even to a primary structure as well as a secondary structure and a specimen. For the reason, verification for the reliability of FBGs such as signal characteristics and mechanical strength becomes much more important. In this study, mechanical strength characteristics of FBGs with their fabrication process and reflectivity are investigated with various grating lengths. From the results of tension tests, it is shown that the mechanical strength of optical fibers decreases about $50\%$ just by jacket stripping and the amount of decrease is dependent on stripping methods. About $55\%$ of mechanical strength of stripped optical fibers decreases if gratings are formed in the core and it is regardless of grating lengths and reflectivity. However, the width of strength distribution increases relative to increases in reflectivity.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.5
• /
• pp.565-570
• /
• 2017

The various techniques proposed previously to obtain a good antireflection(AR) coating induce a scattering of incident light by nanoparticles or control the refractive index by using different materials. This paper compares a suggested graded index profile with the quintic index profile previously suggested for producing an index profile that gives good performance from an AR coating. We assume the structure of the AR coating has three, six, and nine layers with 180 nm total thickness. The wavelength of incident light ranges from 300 nm to 1100 nm. We use the transfer matrix theory for a single layer to obtain the reflectivity of three, six, and nine layers. The reflectivity of two different index profiles with three, six, and nine layers is compared. As a result, the suggested graded index profile shows lower reflectivity than the quintic index profile with three layers, especially in the wavelength range from about 600 nm to 1100 nm. Therefore, we expect that these results can be applied to optical devices and filters in the range from visible(red) to near infrared.

• The Korean Journal of Malacology
• /
• v.25 no.1
• /
• pp.81-89
• /
• 2009

In this study, we conducted heat-treatment on freshwater cultured pearls at various conditions in other to improve their color. Also, after heat treatment, we used the UV-Vis, ED-XRF and SEM to investigate changes freshwater cultured pearls' color, composition and internal structure. UV-Vis analysis showed the reflectivity of samples increased at most heat-treatment conditions although the reflectivity decreased at a certain temperature and duration. At $100^{\circ}c$/8 h, $120^{\circ}c$/6 h and $140^{\circ}c$/4 h, the reflectivity increased highest. In proportion to reflectivity increase, freshwater cultured pearls' color was improved. Ca, Mn, Sr and other micro elements were found from ED-XRF analysis. However, changes in composition of elements were not detected. It was found that the content of Mn in freshwater cultured pearl is higher than other micro elements. From SEM analysis, aragonite's shape was shown in narce and some of the narce were condensed after heat treatment.

• Smart Structures and Systems
• /
• v.19 no.3
• /
• pp.335-340
• /
• 2017

Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of $-20^{\circ}C$ to $60^{\circ}C$, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from $-20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM.

• Korean Journal of Materials Research
• /
• v.9 no.7
• /
• pp.707-714
• /
• 1999

To save electrical energy as much as 40 % for fluorescent lighting, the reflectors coated with silver reflective thin films recently became popular with higher reflectivities and long life. The thin films fabricated by using sputtering techniques are produced mainly in U.S.A. On the other hand, some silver films deposited by using evaporation methods show low adhesion in general, although the reflectivity is no problem. We have studied various PVD methods to obtain thin films with high reflectivity and adhesion on a substrate of polyester, for a couple of years. Silver films manufactured byusing evaporation showed the reflectivity of 96.4 % and the adhesion of $12 kg/\textrm{cm}^2$. while samples manufactured by using sputtering depicted the adhesion as much as $20 Kg/\textrm{cm}^2$ that is almost double, although their reflectivity was not much different. X-ray diffraction spectra for the sputtered films demonstrated a preferential growth on (111) plane and the cross-sections of the specimens revealed a dense columnar structure to result in the enhanced adhesion.