Do Guwn Hwang

Design of Alternating Magnetic Field Stimulator Using Duty Factor

We have developed an alternating magnetic field stimulation system consisting of a switched-mode power supply and a digital control circuit which modulates a duty ratio to maintain a magnetic field intensity of a few mT even while the frequency increases up to 4 kHz with a controllable coil temperature below 30 oC in air. This duty ratio modulation and water circulation are advantageous for cell culture under ac-magnetic field stimulation by preventing the incubator from exceeding a cell-viable temperature of 37 oC. Although the temperature of the coil when subjected to a sinusoidal voltage rapidly increased, that of our system modulated by the duty factor did not change. This is a potentially valuable method to investigate the effects of intermediate frequency magnetic field stimulation on biological entities such as cells, tissues and organs.

Assessment of Pulsed Magnetic Field Stimulus by Using Finger Photoplethysmogram and Pressure Pulse Waveform

Photoplethysmogram (PPG) and pressure pulse waveform (PPW) were compared and evaluated for the efficacy of stimulating knuckles by using the pulsed magnetic field. Both signals were observed simultaneously while the knuckles were exposed for 10 min to the pulsed magnetic field, with maximum field intensity of 0.8 T and transition time of 0.126 msec. After 5 min stimulation of the knuckles, the results showed that the aging indexes calculated from the second derivative of the PPG were increased from ?1.913 to 0.072, and that of the PPW from ?0.063 to 0.387. However, for the relatively long-term stimulation for 10 min, we found that the values of both the aging indexes of the second derivatives and augmentation index of the PPW returned to the starting level. The changes observed in characteristic factors such as the aging indexes of the second derivatives and augmentation index of the PPW indicate the potential of pulsed magnetic field stimulation as a therapeutic method for the treatment of patients with peripheral vascular disease.

Effects of Pulsed Magnetic Field Stimulus on Electroencephalogram Alpha Activity

We investigated the effects of pulsed magnetic field (pMF) stimulus on electroencephalogram alpha activity when applied for various durations at the PC9 and/or HT9 acupoints. The maximum increase in alpha activity occurred after the stimulus was applied to the acupoints for 3 min. It can be concluded that pMF stimulus can be used in an alternative noninvasive acupuncture therapy, in which correct pMF stimulus induces a relaxed mental state.

Partial magnetization reversal in a perpendicular exchange-biased [Pd∕Co]∕FeMn film through laser annealing

Partial magnetization reversal on the perpendicular exchange-bias characteristics in the [Pd∕Co]×5∕FeMn bilayered and [Pd∕Co]×2∕Cu∕Co∕[Pd∕Co]×2∕FeMn spin valve thin films was investigated using laser. The hysteresis loops were measured using the extraordinary Hall effect and magneto-optical Kerr effect (MOKE). By increasing the output intensity of the laser, the exchange-bias fields in the [Pd∕Co]×5∕FeMn bilayered thin film were gradually changed from negative to positive. The distribution of partial magnetization reversal in the vicinity of the laser spot was measured by using MOKE. Although the magnetic moment of the pinned layer was gradually reversed by using laser annealing in the MOKE loops of the [Pd∕Co]×2∕Cu∕Co∕[Pd∕Co]×2∕FeMn spin valves’ structure, that of the free layer was not changed. When the pattern size was decreased to 5×5μm2, the direction of exchange biasing was fully reversed through laser annealing without distorting the hysteresis loop. All the patterned samples below 100×100μm2 have ...

Effects of Co80Fe20 insertion layer on perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films

Effects of Co80Fe20 insertion layer on the perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films have been investigated by changing the Co80Fe20 insertion layer thickness. Hysteresis loops for both in-plane and perpendicular to the film plane were measured by using a vibrating sample magnetometer and an extraordinary Hall effect. It was found that the thin Co80Fe20 insertion layer was very effective in improving the perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films. By increasing Co80Fe20 insertion layer thickness from 0to1.24nm, the exchange bias field was significantly increased up to 332Oe and then decreased down to 60Oe, while the pinned coercivity was monotonically decreased. The effective magnetic anisotropy was kept at positive up to 0.6nm thick of Co80Fe20 insertion layer. It was experimentally confirmed that the perpendicular exchange bias field was promisingly larger than the pinned coercivity when the Co80Fe20 insertion layer had the t...

Correlation Between the Degradation of Perpendicular Anisotropy and the Double Hysteresis Behavior in [Pd/Co]

We clearly detected double hysteresis by increasing Co layer thickness and decreasing the number of bilayers in perpendicular exchange biased [Pd(0.6)/Co(t)] n/FeMn(11.6 nm) thin films. In-plane tensile stress calculations confirmed that the appearance of double hysteresis is closely related to the degradation of stress-induced perpendicular anisotropy in the [Pd/Co] multilayers. Furthermore, annealing at the magnetic field applied perpendicular to the film plane directly verified that the enhancement of thermally induced perpendicular anisotropy, K eff-induced, in the [Pd/Co] multilayers is the main physical reason for removal of the double hysteresis. All our experimental and theoretical results demonstrated that perpendicular anisotropy is the dominant factor in controlling the double hysteresis behavior of perpendicularly magnetized [Pd/Co]n/FeMn exchange biased thin films.

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We have investigated the changes of electroencephalography (EEG) and electrocardiography (ECG) under pulsed magnetic field (PMF) and acupuncture stimulus on acupoint PC9. In order to compare quantitatively the effect of PMF and acupuncture stimulus, the difference of alpha activities are calculated from EEG spectra, and the spectrum curves of ECG were analyzed in the frequency domain of heart rate variability (HRV). The increase of alpha activities after both stimuli could be explained that the impulse of stimulus on PC9 might pass through sensory nerve following meridian and approach the cerebral cortex, causing the central nervous system (CNS) to be activated for pacifying emotion and calming the mind. The decrease in sympathovagal activity of HRV after both stimuli indicates that parasympathetic nerves were activated and the sympathetic nerves were in constrained condition. These findings suggest that PMF could be patient-friendly alternative non-invasive medical treatment for influencing human physiology, in comparison with acupuncture inserting the needle and inducing nervous and anxious state to subject.

/FeMn Exchange Biased Thin Films

The purpose of this study was to investigate the effect of pulsed magnetic field (PMF) and low frequency low level laser (LFLLL) stimuli on acupoint LI4 (Hegu) using photoplethysmography (PPG). Our PMF system was designed to generate maximum intensity of 0.20 T at a transition time of 0.16 ms, with pulse intervals of 1 Hz. The diode laser with wavelength of 650 nm and power of 5 mW was also employed. It was observed the change of the pulsating blood volume through measuring PPG signals from both hands. These results imply that stimulating acupoint LI4 with PMF and LFLLL improves the circulation of peripheral vascular system. In particular, PMF stimulation brings a big improvement of the blood flow even with short term stimulation of 3-4 minutes compared to LFLLL stimulus.

An Analytical Comparison in Electoencephalography and Electrocardiography under Pulsed Magnetic Field and Acupuncture Stimulus on Acupoint PC9

We have investigated the effects of pulsed magnetic field (PMF) stimulus on acupoint KI1 using electroencephalography (EEG) analysis. Compared with the control group, the PMF stimulus group showed a decrease of SEF-50, an increase of relative theta power, and activation of alpha power in brain map. This means the impulse of stimulus on acupoint KI1 might pass through the sensory nerve following meridian and approach the cerebral cortex, causing the autonomic nervous system to be activated for relaxed mental state. The percentage (PCT) showing asymmetry pattern and correlation coefficient among channels calculated from EEG data also showed proper PMF stimulus to induce the relaxation. Therefore, PMF stimulus on appropriate acupoint is thought to be one of the candidates for alternative non-invasive acupuncture therapy.

Comparative Analysis of Photoplethysmography under Pulsed Magnetic Field and Low Level Laser Stimulus: Motivation for Blood Flow Increase using Stimulus on Acupoint LI4 (Hegu)

To investigate the effects of alternating magnetic field intensity and stimulation time on the proliferation of human breast cancer cells (BT-20), we cultured the cells under a magnetic field with a saw tooth waveform of 2 kHz. The field intensities varied from 3 to 7 mT, and the stimulation time varied from 24 to 72 hours. Cell proliferation decreased dramatically to 40% during magnetic stimulation for 72 hours at 5 mT. However, the cells were not affected by a strong magnetic field of 7 mT. The p-values obtained using statistical package for social science software were below 0.05 for 5-7 mT. This means that the results have statistical significance. However, it is difficult to explain our results based on the physiology of cell membranes, which have various ionic flows at ion channels.