• Journal of Magnetics
• /
• v.19 no.2
• /
• pp.155-160
• /
• 2014

The heating produced by the absorption of radiofrequency (RF) has been considered a secondary undesirable effect during MRI procedures. In this work, we have measured the power absorbed by distilled water, glycerol and egg-albumin during NMR and non-NMR experiments. The samples are dielectric and examples of different biological materials. The samples were irradiated using the same RF pulse sequence, whilst the magnetic field strength was the variable to be changed in the experiments. The measurements show a smooth increase of the thermal power as the magnetic field grows due to the magnetoresistive effect in the copper antenna, a coil around the probe, which is directly heating the sample. However, in the cases when the magnetic field was the adequate for the NMR to take place, some anomalies in the expected thermal powers were observed: the thermal power was higher in the cases of water and glycerol, and lower in the case of albumin. An ANOVA test demonstrated that the observed differences between the measured power and the expected power are significant.

• Journal of electromagnetic engineering and science
• /
• v.15 no.3
• /
• pp.181-184
• /
• 2015

Evaluation of radiating radiofrequency fields from hand-held and body-mounted wireless communication devices to human bodies are conducted by measuring the specific absorption rate (SAR). The uncertainty of system validation and probe calibration in SAR measurement depend on the variation of RF power used for the validation and calibration. RF input power for system validation or probe calibration is controlled manually during the test process of the existing systems in the laboratories. Consequently, a long time is required to reach the stable power needed for testing that will cause less uncertainty. The standard uncertainty due to this power drift is typically 2.89%, which can be obtained by applying IEC 62209 in a normal operating condition. The principle of the Automatic Input Power Level Control System (AIPLC), which controls the equipment by a program that maintains a stable input power level, is suggested in this paper. The power drift is reduced to less than ${\pm}1.16dB$ by AIPLC, which reduces the standard uncertainty of power drift to 0.67%.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2003.11a
• /
• pp.74-78
• /
• 2003

This paper shows the dosimetric uncertainties of electromagnetic field at in-vivo and in-vitro experiments. For more accurate consequences of these researches, we have tried to find out any correlations among output power, power density and specific absorption rate(SAR) with the results of in-vivo, in-vitro tests and SAR reports of cellular phone and PDA. In the case of in-vivo tests, the power density has close statistical correlations with SAR value and in the event of in-vitro tests, the output power has considerable statistical correlations with SAR containing duty factor. On the other hand, we found that both power density and output power don't have any close correlations with SAR. And, we obtained fitted regression form among frequency, power density and SAR containing duty factor through multiple linear regression analysis.

• Analytical Science and Technology
• /
• v.8 no.1
• /
• pp.69-77
• /
• 1995

The instrumentation and operating characteristics of a gas-jet assisted radio frequency glow discharge atomic absorption spectrometry(RF-GDAAS) are studied. The roles of discharge power, pressure as well as gas flow rate on the sample loss rate and absorbance are described in this paper. Results show that the optimum discharge conditions depend on pressure and discharge power as well as on the gas flow rate. The gas flow rate plays as an important parameter in RF-GDAAS. Absorbance increases as the gas flow rate increase up to 600ml/min., and the optimum absorbance is obtained at the pressure of 3 mbar. The absorbance increases when the discharge power increases as expected, however, the instability of the system due to the heat might be the trade off factor. The linear calibration curves of Ni and Cr in stainless steel(BAS 461-468) and brass (KSS 1121-1126) are obtained with RF-GDAAS.

• Journal of Magnetics
• /
• v.17 no.2
• /
• pp.129-132
• /
• 2012

To evaluate the electromagnetic power absorption in near field, the magnetic composites with the conductive grids were simulated using the typical permeability frequency profiles. The transmission power absorptions of the magnetic composites on microstrip line were extracted by the 3D FEM simulation program of HFSS. The magnitudes of power absorptions were greatly enhanced up to 98% and broadened the absorbing frequency band over 5 GHz by the insertion of a conductive grid in magnetic composite. The initial frequency of the power absorption can controlled by the change of the ferromagnetic resonance frequencies of the magnetic composite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1992.05a
• /
• pp.42-45
• /
• 1992

The poly silicon thin films were prepared by solid phase crystallization at 600$^{\circ}C$ of amorphous silicon films deposited on Corning 7059 glass and (100) silicon wafer with thermally grown SiO$_2$substrate by plasma enhanced chemical vapor deposition with varying rf power, deposition temperature, total flow rate. Crystallization time, microstructure, absorption coefficients were investigated by RAMAN, XRD analysis and UV transmittance measurement. Crystallization time of amorphous silicon films was increased with increasing rf power, decreasing deposition temperature and decreasing total flow rate.

• Journal of the Korean institute of surface engineering
• /
• v.25 no.5
• /
• pp.271-281
• /
• 1992

Amorphous hydrogenated silicon carbide(a-Si1-xCx : H) films have been prepared by the rf sputtering using a silicon target in a gas mixture of Argon and methane with varying methane gas flow rate(fCH) in the range of 1.5 to 3.5 sccm at constant Argon flow rate of 30sccm and rf power in the range of 3 to 6 W/$\textrm{cm}^2$. The effects of methane flow rate and rf power on the structure and optical properties of a-Si1-xCx : H films have been analysed by measuring both the IR absorption spectrum and the UV transmittance for the films. With increasing the methane flow rate, the optical band gap(Eg) of a-Si1-xCx : H films increases gradually from 1.6eV to the maximum value of 2.42eV at rf power of 4 W/$\textrm{cm}^2$, which is due to an increases in C/Si ratio in the films by an significant increase in the number of C-Hn bonds. As the rf power increases, the number of Si-C and Si-Hn bonds increases rapidly with simultaneous reduction in the number of C-Hn bonds, which is associated with an increase in both degree of methane decomposition and sputtering of silicon. The effects of rf power on the Eg of films are considerably influenced by the methane flow rate. At low methane flow rate, the Eg of films decreased from 2.3eV to 1.8eV with the rf power. On the other hand, at high methane flow rate, that of films increased slowly to 2.4eV.

• Korean Chemical Engineering Research
• /
• v.47 no.1
• /
• pp.105-110
• /
• 2009

IZO thin films have been deposited on poly(ethylene terephthalate) flexible substrate under varying radio frequency (rf) power, process pressure and thickness of IZO films using rf magnetron sputtering under $Ar/O_2$ gas mix. As the process pressure increased, the deposition rate was slightly increased and the transmittance showed little change, but the resistivity was increased. With increasing rf power, the great increase in deposition rate was observed but the transmittance showed a slight change only, and the resistivity was decreased. In addition, an attempt was made to find the optimal thickness of IZO films under varying the thickness of IZO films at the process conditions of 1 mTorr pressure and 90 W rf power, which showed lowest resistivity. IZO thin films with the thickness of $1,500{\AA}$ showed lowest resistivity and also showed highest transmittance around the wavelength zone of the maximum absorption. The power conversion efficiency of solar cells fabricated using various transparent electrodes with different thicknesses were measured and the solar cell with IZO electrode of $1,500{\AA}$ showed the maximum conversion-efficiency of 2.88 %.

• Journal of Magnetics
• /
• v.11 no.3
• /
• pp.130-134
• /
• 2006

The microwave power absorption for the patterned CoNbZr magnetic film has been investigated by coplanar waveguide method. The power absorption peaks of the patterned CoNbZr film (50 ${\mu}m$ ${\times}$ 2 mm ${\times}$ 2 ${\mu}m$), were observed at around 5.7 GHz. The observed resonance peak was in good agreement with calculated ferromagnetic resonance frequency including magnetic shape anisotropy effects. Compared with the coplanar waveguide without a magnetic film, the characteristic impedance of patterned film was shown to be increased. This resulted from the large increment of inductance up to 33 % without any significant changes of the capacitance.

• Korean Journal of Materials Research
• /
• v.13 no.10
• /
• pp.640-644
• /
• 2003

NiCr thin films were fabricated by rf magnetron sputtering for applying to both the top electrode and absorption layer on Pb(Zr, Ti)O$_3$(PZT) thin films for infrared sensors. The rms roughness and resistivity of NiCr films prepared with Ni power of 80 W and Cr power of 50 W showed the most stable oxidation resistance after annealing at $600^{\circ}C$ for 5 min in oxygen ambient. The rms roughness and resistivity of NiCr films annealed at $V^{\circ}C$ in oxygen ambient were about 2$0\AA$ and $70 \mu$Ω-cm, respectively. As-deposited Ni/PZT/Pt and NiCr (Ni 80 W, Cr 50 W)/PZT/Pt structures showed well saturated hysteresis loops. However, in case of the samples annealed at $500^{\circ}C$ in oxygen ambient, only NiCr/PZT/Pt showed saturated loops having a remanent polarization of 20$\mu$C/$\textrm{cm}^2$. Ultra-thin NiCr films showed a possibility as a top electrode for infrared sensors.