• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.341-342
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• 2007

3T MRI system에서 고해상도 영상을 얻기 위해서는 magnetic field를 균일하게 만들어야 한다. 특히 초고속 영상 기법인 Spiral scan 방식과 EPI scan 방식에서는 이미지 영역에서의 magnetic field의 inhomogeneity에 의해 영상의 왜곡이 심해진다. 본 논문에서는 magnetic field의 inhomogeneity를 단시간 내에 측정하기 위해 fast spin echo방식의 pulse sequence 제안하고, magnetic field를 분석하기 위한 field map의 구성과, field pattern의 효과적인 분석을 통하여, magnetic field를 균일하게 만드는 방법을 제안한다.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.621-629
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• 2020

The present paper aims to study the influence of the magnetic field and initial stress on the 2-D problem of generalized thermo-viscoelastic material with voids subject to thermal loading by a laser pulse in the context of the Lord-Shulman and the classical dynamical coupled theories. The analytical expressions for the physical quantities are obtained in the physical domain by using the normal mode analysis. These expressions are calculated numerically for a specific material and explained graphically. Comparisons are made with the results predicted by the Lord-Shulman and the coupled theories in the presence and absence of the initial stress and the magnetic field.

• 한국정밀공학회지
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• 제7권2호
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• pp.14-27
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• 1990

Electromagnetic Pulse Forming is the one of the high velocity forming method. When the electric energy which is charged in the capacitor bank is suddenly discharged into the electromagnetic coil, the high magnetic field occurs at the airgap between the electromagnetic coil and workpiece. Thus we can obtain the high electromagnetic pressure, which is proportional to the square of magnetic flux density. This is the basic principle of the electromagnetic pulse forming. In this paper, the equivalent L-R-C circuit is derived by computing the magnetic field and its loss of the total system. Thus, the values of the magnetic flux density and pressure can be obtained from the equation of this circuit. As a result, the computed and measured values of the maximum magnetic flux density and pressure are compared and the characteristics of the tapered field shaper are further discussed as follows; 1) The strength of magnetic flux density and pressure can be controlled by the charged energy and the size of the airgap between the inner field shaper and the workpiece. 2) During the design of the tapered field shaper, the penetration of the magnetic flux through the sharp edge should be considered.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 G
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• pp.2809-2811
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• 1999

In this paper, we develope an algorithm to calculate field inhomogeneity in MR imaging using a dual fast spin echo pulse sequence. Because phase modulation time can be easily modified with this pulse sequence, high resolution image can be obtained and acquisition time can be reduced compared to gradient echo technique. In the case of phase wrapping in field map, phase corrected using image processing technique. We assume the field pattern to be second order polynomial and apply Pseudo-Inverse equation to calculate second order polynomial coefficients. These coefficients can be used for the shimming of the magnetic field.

• 대한의용생체공학회:의공학회지
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• 제27권6호
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• pp.343-350
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• 2006

Medical magnetic stimulator generates strong magnetic field pulses. Clinical applications of the magnetic pulse are the stimulation of nervous system and the contraction of muscle. The unique source of the strong magnetic pulse is a capacitor-inductor resonator and this inductor generates a strong sinusoidal magnetic pulse by discharging the capacitor with high initial voltage. Continuous muscle contraction needs sequential generation of the magnetic pulses. However, to keep the magnitude of sequential pulses identical, an expensive high-voltage power supply have to support voltage drop of the capacitor between the pulses. A protection circuit between the supply and the resonator is necessary to protect the supply from reverse current caused by capacitor voltage reversal. In this paper, a new circuit structure of the magnetic stimulator adopting a low-frequency fly-back switching is proposed. The new circuit supports sequential pulse generation and allows the reverse current without damage. Performance of the new circuit is examined and a low-cost magnetic stimulator for urinary incontinence therapy is being developed using the presented method.

• Journal of Magnetics
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• 제17권1호
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• pp.27-32
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• 2012

Transcranial magnetic stimulation requires an electric field composed of dozens of V/m to achieve stimulation. The stimulation system is composed of a stimulation coil to form the electric field by charging and discharging a capacitor in order to save energy, thus requiring high-pressure kV. In particular, it is charged and discharged in capacitor to discharge through stimulation coil within a short period of time (hundreds of seconds) to generate current of numerous kA. A pulse-type magnetic field is formed, and eddy currents within the human body are triggered to achieve stimulation. Numerous pulse forms must be generated to initiate eddy currents for stimulating nerves. This study achieved high internal pressure, a high number of repetitions, and rapid switching of elements, and it implemented numerous control techniques via introduction of the half-bridge parallel load method. In addition it applied a quick, accurate, high-efficiency charge/discharge method for transcranial magnetic stimulation to substitute an inexpensive, readily available, commercial frequency condenser for a previously used, expensive, high-frequency condenser. Furthermore, the pulse repetition rate was altered to control energy density, and grafts compact, one-chip processor with simulation to stably control circuit motion and conduct research on motion and output characteristics.

• 한국자기학회지
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• 제7권4호
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• pp.212-216
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• 1997

충전에너지 18 kJ의 커패시터뱅크 및 펄스코일에서 생성되는 주기 10.12 ms의 정현감쇄진동형 펄스자장을 이용하여 최대 인가자장 130 kOe의 펄스마그네토미터를 구성하였다. 자성측정은 펄스자장의 첫 번째와 두 번째 정방향 자장파크 사이의 파형을 이용하여 유도법으로 측정하였다. NdFeB 소결자석의 측정에 있어서 와전류에 의한 측정오차, 즉, 직류특성과의 차이가 직경 5 mm 이하의 시편을 사용할 경우 3% 이내인 펄스자장형 자기이력곡선 측정장치를 제작하였다.

• Journal of Magnetics
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• 제15권4호
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• pp.209-212
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• 2010

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.

• Korean Journal of Acupuncture
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• 제33권4호
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• pp.213-220
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• 2016

Objectives : The aim of this paper is to develop acupuncture needle heating system by utilizing the new method which uses high frequency(HF) time-varying magnetic field. Also, it is possible to make an assessment for reliability and clinical significance of the system. Methods : We designed the system with solenoid coils for generation of HF time-varying magnetic field that oscillates at 150 kHz. Acupuncture needles are quickly magnetized and heated by 150 kHz. We assessed clinical significance of system, such as body temperature, pressure pulse waveform. Results : Temperature of acupuncture needle increased up to 60 degree. In the result for clinical significance of system, in case of manual acupuncture stimulation(MAS), body temperature change was $0.373^{\circ}C{\pm}0.224$(p<0.05), rate of pulse energy change increased about 7.6%. In case of warm acupuncture stimulation(WAS), body temperature change was $0.645^{\circ}C{\pm}0.281$(p<0.05), rate of pulse energy change remarkably increased about 35.9%. Conclusions : We confirm that the system is able to be applied clinically to various warm acupuncture needle therapy in the area of oriental medicine.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 1999년도 추계연구발표회 논문개요집
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• pp.140-141
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• 1999