• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.63 no.10
• /
• pp.1377-1383
• /
• 2014

This paper deals with eddy current loss of magnetic coupling with radial permanent magnet (PM) using analytical method such as a space harmonic method. Superposition of two kinds analysis model is used to analyze eddy current loss induced in inner PM and outer PM of magnetic coupling. When the eddy current is induced, the environmental temperature increases, and the permanent magnet(PM) characteristics are degraded because the performance of PM is greatly influenced by temperature rise. Hence, the calculation of eddy current loss becomes an important factor in the magnetic coupling. In order to analyze eddy current loss, first, on the basis of the magnetic vector potential and two-dimensional(2-D) polar-coordinate system, the magnetic field solutions of the radial magnetized PM are obtained. And we obtain the analytical solutions for the eddy current density produced by permanent magnet. Lastly, analytical solutions for eddy current loss are derived by using equivalent, electrical resistance calculated from magnet volume and analytical solution for eddy current density. This analytical results are validated by comparing with the 2-D finite element analysis (FEA).

• Progress in Superconductivity and Cryogenics
• /
• v.11 no.3
• /
• pp.1-5
• /
• 2009

It is important to predict AC loss in $Nb_3Sn$ and NbTi cable-in-conduit-conductor (CICC) reliably for the design and operation of large superconducting coils. The hysteresis loss in the superconducting filaments and coupling loss within strands and among strands in a cable or composite are dominant ac losses in superconducting magnets. The coupling loss in a superconductor can be characterized by identifying the coupling constant time $n{\tau}$. To reduce the coupling loss, all the strands (superconductor and Cu) in KSTAR (Korea Superconducting Tokamak Advance Research) are chromium plated with thickness of $l{\pm}0.5{\mu}m$. The ac losses of PF1, PF5 and PF6 coils has been measured by calorimetric method while applying trapezoidal current pulses with various ramp rate from 0.5 kA/s to 2 kA/s. The coupling time constants for $Nb_3Sn$ coils are $25{\sim}55$ ms and the values are not co-related with the coil size, the time constants for NbTi coil is 30 ms.

• Progress in Superconductivity and Cryogenics
• /
• v.13 no.2
• /
• pp.13-16
• /
• 2011

This paper describes the reduction method of eddy current loss generated into a retaining ring installed in wound-field superconducting machine. In order to suggest the reduction method of eddy current loss of the retaining ring, this paper is divided into three parts. Firstly, eddy current loss of prototype model is calculated. Secondly, eddy current loss versus material and shape of the retaining ring is compared. Finally, the material and the shape of the retaining ring to reduce coupling loss generated by a time-varying magnetic field are proposed. In this paper, eddy current loss is calculated by 3-dimensional transient analysis.

• Proceedings of the KIEE Conference
• /
• 1991.07a
• /
• pp.27-30
• /
• 1991

With the recent development of high performance AC superconducting wire of very small ac loss and large current carrying capacity, the possibility of superconducting air core transformer is being studied. The air core transformer has merits of no iron loss, no insulation to the core and no harmonics. But the air core transformer has large exciting current and low magnetic coupling factor. To increase the coupling factor, the transformer of toroidal shape is proposed and designed. (10KVA, 110/220V) Compared with air core transformer of solenoidal shape, the performance is improved. The exciting current occupies about 22% of the rated current.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2002.11a
• /
• pp.9-14
• /
• 2002

Direct-conversion receiver(DCR) architecture has superior advantages in size, cost, and power over superheterodyne receiver architectures. However, the use of direct-conversion receiver architecture has been limited due to the direct-current offset noise. The ac coupling, which is used to overcome the direct-current offset noise, causes an inter-symbol interference(ISI), whose effects can be effectively mitigated using an equalizer. In this paper, the performance of a direct-conversion receiver with ac coupling in the presence of direct-current offset is analyzed via computer simulation. The simulation result shows that by using decision feedback equalizer with LMS(Least Mean Square) algorithm, signal-to-noise ratio loss of the direct-conversion receiver compared to the idea receiver can be reduced to less than 1㏈ for corner frequencies as large as 10% of the symbol rate.

• International Journal of Concrete Structures and Materials
• /
• v.6 no.1
• /
• pp.3-18
• /
• 2012

Observed wall damage in recent earthquakes in Chile and New Zealand, where modern building codes exist, exceeded expectations. In these earthquakes, structural wall damage included boundary crushing, reinforcement fracture, and global wall buckling. Recent laboratory tests also have demonstrated inadequate performance in some cases, indicating a need to review code provisions, identify shortcomings and make necessary revisions. Current modeling approaches used for slender structural walls adequately capture nonlinear flexural behavior; however, strength loss due to buckling of reinforcement and nonlinear and shear-flexure interaction are not adequately captured. Additional research is needed to address these issues. Recent tests of reinforced concrete coupling beams indicate that diagonally-reinforced beams detailed according to ACI 318-$11^1$ can sustain plastic rotations of about 6% prior to significant strength loss and that relatively simple modeling approaches in commercially available computer programs are capable of capturing the observed responses. Tests of conventionally-reinforced beams indicate less energy dissipation capacity and strength loss at approximately 4% rotation.

• Journal of KSNVE
• /
• v.11 no.2
• /
• pp.257-264
• /
• 2001

In this research, piezoelectric smart structures are applied for SEA(Statistical Energy Analysis), which is well known approach for high frequency analysis. A new input power measurement based on piezoelectric electrical power measurement is proposed and compared with the conventional method in SEA. As an example, a simple aluminum beam on which piezoelectric actuator is attached is considered. By measuring the electrical impedance and electrical current of the piezoelectric actuator, the electrical power given on the actuator is found and this is In turn converted into the mechanical energy. From the measured value of the stored energy of the beam, the Internal loss factor is calculated and this value shows a good agreement with that given by the conventional method as well as the theoretical value. To compare the coupling loss factor, L-shape beam system which consists of a aluminum beam subsystem and a steel beam subsystem coupled by three pin is taken as second example. The input power and stored energy of each subsystem are found by the proposed approach. The coupling loss factor found by the electrical input power obtained from the piezoelectric actuator exhibits similar trend to the value found by the conventional method as well as the theoretical value. In conclusion, the use of SEA for high frequency application of piezoelectric smart structures is Possible. Especially, the input power that is essential for SEA can be found accurately by measuring the electrical input power of the piezoelectric actuator.

• Current Optics and Photonics
• /
• v.1 no.1
• /
• pp.65-72
• /
• 2017

We propose a nearly lossless, compact, electrically modulated vertical directional coupler, which is based on the controllable evanescent coupling in a previously proposed graphene-assisted total internal reflection (GA-FTIR) scheme. In the proposed device, two single-mode waveguides are separate by graphene-$SiO_2$-graphene layers. By changing the chemical potential of the graphene layers with a gate voltage, the coupling strength between the waveguides, and hence the coupling length of the directional coupler, is controlled. Therefore, for a properly chosen, fixed device length, when an input wave is launched into one of the waveguides, the ratio of their output powers can be controlled electrically. The operation of the proposed device is analyzed, with the dispersion relations calculated using a model of a one-dimensional slab waveguide. The supermodes in the coupled waveguide are calculated using the finite-element method to estimate the coupling length, realistic devices are designed, and their performance was confirmed using the finite-difference time-domain method. The designed $3{\mu}m$ by $1{\mu}m$ device achieves an insertion loss of less than 0.11 dB, and a 24-dB extinction ratio between bar and cross states. The proposed low-loss device could enable integrated modulation of a strong optical signal, without thermal buildup.

• Current Optics and Photonics
• /
• v.4 no.6
• /
• pp.551-557
• /
• 2020

A mirror-in-slab waveguide is fabricated on a slab waveguide by using the refractive-index contrast between two materials, with the reflection performance depending on the slab waveguide's design. In this research, a slab waveguide design consisting of silicon (Si) as the core and SiO2 as the substrate was designed and developed to determine the coupling, waveguide, and mirror losses. Based on experimental results, coupling loss is dominant and is affected by the design of the slab waveguide. Furthermore, the mirror loss is affected by the design of the mirror, such as the curvature radius and the size of the mirror. TE and TM polarizations of light are used in the measurements. The experimental results show that mirror losses due to reflection by mirrors are 0.011 dB/mirror and 0.007 dB/mirror for TE and TM polarizations respectively. A simulation was performed to confirm whether the size of mirror is sufficient to reflect the input light, and to check the quality of the surfaces of fabricated mirrors.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.11
• /
• pp.589-595
• /
• 2000

In this papre, AC losses of Bi-2223 tapes with different twist pitch of superconducting core were fabricated, measured and analyzed. These samples produced by a powder-in-tube method are multi-filamentary tape with Ag matrix. Also, it's produced by non-twist and different twist pitch(8, 10, 13, 30, 50, 70 mn). The critical current measurement was carried out under the environment in Liquid nitrogen and in zero field by 4-probe method. And the AC loss measurement was carried out under the environment of applied time-varying transport current by transport method. From experiment, the critical current is larger non-twist than twisted filament. And, the AC loss by Norris equation is higher non-twisted tape than 13mm twisted tape. Also, it is confirmed that of AC loss of tape having non-twist pitch larger than those having differnet twist pitch.