• Smart Structures and Systems
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• 제18권3호
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• pp.449-470
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• 2016

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

• Smart Structures and Systems
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• 제24권1호
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• pp.83-94
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• 2019

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.

• 한국전자파학회논문지
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• 제30권2호
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• pp.173-176
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• 2019

본 논문에서는 밀리미터파 탐색기에 적용 가능한 Ka-대역 도파관 로터리조인트를 설계 및 제작하였다. 제안된 로터리 조인트는 낮은 정재파 비와 저손실 특성을 유지하며, 방위각과 고각 회전이 가능하도록 하는 두 개의 회전축으로 설계되어 있다. 또한 구형 도파관과 원형 도파관 사이에 전파 모드를 정합하기 위한 리지 도파관 형태의 모드 변환기와 ${\lambda}/4$ 길이의 초크 구조로 로터리 조인트를 설계하였다. 제작된 로터리 조인트의 성능은 회로망 분석기와 고출력 송신기를 이용하여 확인하였으며, 진동/충격 시험을 통해 신뢰성 검사를 수행하였다. 그 결과, 중심 주파수$(F_C){\pm}500MHz$의 대역에서 최대 정재파비 1.19 : 1 이하, 삽입손실 0.80 dB 이하의 우수한 특성을 갖는 것을 확인하였다.

• 대한기계학회논문집A
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• 제39권4호
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• pp.415-421
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• 2015

본 연구는 햅틱 진동자의 개발과정에 있어 성능인자의 단계별 설정절차와 성능 및 소형화를 위한 자석의 착자방법에 대한 연구를 수행하였다. 착자방법에 대한 연구는 수평착자와 수직착자의 구성방법에 따른 전자기력을 비교분석하여 수행하였으며, 수행결과 수평착자가 우수한 것으로 나타났다. 시스템적 설계 절차로는 제품의 특성으로부터 설계 인자를 설정하는 단계적 절차를 구성하여 시작품을 제작하고 시험을 통하여 검증하였다. 해석적 방법에서는 진동응답 특성 해석과 전기장의 해석을 독립적으로 수행하였으며, 시험결과와의 검증을 통해 잘 일치하는 결과를 도출하였다. 제품신뢰성 확보를 위한 신뢰성 기반 설계인자는 스프링 높이, 용접 위치, 코일의 위치로 선정하였다. 그리고 설계 인자에 따른 전자기장 민감도 및 성능 변화를 분석하였고 이를 바탕으로 신뢰성 기반의 고성능 햅틱 진동자를 구현할 수 있도록 설계방법을 제시하였다.

• 대한의용생체공학회:의공학회지
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• 제23권3호
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• pp.217-225
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• 2002

이식형 인공중이는 일반적인 공기전도형 보청기가 가지는 난점인 고이득에서의 왜곡과 음향 피이드백에 의한 링잉 현상을 해결할 수 있는 동시에 음질과 주파수 특성 및 청음명료도가 우수하다 본 논문에서는 마이크로머시닝 기술을 이용하여 차동 전자 트랜스듀서를 제작한 후 이를 사용하여 이식형 인공중이 시스템을 구현하였다. 제작된 시스템을 이용하여 무부하 진동실험. 사체를 이용한 부하진동실험 및 살아있는 개를 이용하여 동물이식실험을 실시함으로써 이의 성능을 확인하였다. 무부하 진동실험을 통하여 제작된 트랜스듀서는 입력되는 소리신호와 같은 형태의 진동을 일으킴을 확인하였고, 사체의 이소골에 트랜스듀서를 이식하고 부하실험을 실시함으로써 트랜스듀서의 이소골 구동능력과 진동특성을 조사하였다. 그리고 개를 이용하여 동물이식실험을 실시한 후 뇌간 유발 반응검사를 실시함으로써 생체 내에서의 이식형 인공중이의 동작을 확인하였다. 이를 통하여 제작된 차동 전자 트랜스듀서를 이용한 이식형 인공중이 시스템의 성능을 검증하였고 난청자에게 적용할 경우에도 잘 동작할 수 있음을 증명함으로써 임상실험을 실시할 수 있는 근거를 마련하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.678-684
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• 2011

In 2013, Korea will become the world's second country to operate the urban Maglev system with the inauguration of demonstration line at Incheon International Airport. A prototype Maglev is under the test at KIMM's(Korea Institute of Machinery & Materials, Daejeon) track. This Maglev is an EMS(Electromagnetic suspension)-type vehicle of controlled $8{\pm}3mm$ air gap. The air gap between electromagnet and the guiderail in an EMS-type Maglev must be maintained within an allowable deviation by controlling the magnet. The air gap response is strongly dependent on the structural characteristics of the elevated guideway. For this reason, the interaction between the vehicle with electromagnets and the elevated guideway must be understood to ensure safe running. The purpose of this paper is to compare vibration characteristics of the vehicle on the switching system and other sections when the full weight condition of urban maglev vehicle that 26.5 tons per car(empty car weight 19 tons + passenger condition 7.5 tons), is applied. Through such results, Maglev vehicles and switching system can be established and the levitation stability can be improved.

• 한국소음진동공학회논문집
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• 제20권8호
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• pp.717-726
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• 2010

For the application into a 1 kWh flywheel energy storage system(FESS), this paper presents the design scheme of radial and axial hybrid magnetic bearings which use bias fluxes generated by permanent magnets. In particular, the axial hybrid magnetic bearing is newly proposed in this paper, in which a permanent magnet is arranged in axial direction so that it can support the rotor weight as well as provide a bias flux for axial magnetic bearing. Such hybrid magnetic bearings consume very low power, compared with conventional electromagnetic bearings. In this paper, to stably support a 140 kg flywheel rotor without contact, design process is explained in detail, and magnetic circuit analysis and three-dimensional finite element analysis are carried out to determine the design parameters and predict the performance of the magnetic bearings.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1033-1036
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• 2007

The optical disc drive has used a high NA objective lens and a shorter wavelength laser diode for high recording density. But high NA and shorter wavelength cause several margins to become short. Focusing and tracking servo has to be more accurate and active tilt compensation mechanism is also needed for coma aberration compensation. In this paper, we proposed 3-axis moving magnet type actuator. For 3-DOF motion, moving coil actuator has to equip 6 wires for supplying 3 independent signals. However, moving magnet type actuator doesn't need to change the configuration of wires because coils are in stator. So, we added tilting mechanism to 2-axis moving magnet actuator which is designed in previous research. Addition of the tilting mechanism cuts down the focusing sensitivity. So, maximization the tilting sensitivity and securing the focusing sensitivity are objectivities of this research. DOE (design of experiments) procedures of electromagnetic circuit are performed for parameter study and the optimization is also performed to maximize the tilt sensitivity. And then the final design is suggested and its performance is verified by FE simulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.848-851
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• 2007

Recently, as the demand of the information storage devices with large storage capacity such as BD(Blu-ray Disk) and HDTV(high-definition television) is increased, the optical storage devices are also required to have fast data transfer rate and large storage capacity. To satisfy these requirements, the actuator for optical disk drive should have high flexible mode frequencies for system stability. In this paper, we suggested a moving magnet type actuator having high flexible mode frequency. However, the moving magnet type actuator does not have sufficient driving sensitivities due to the weight of its moving part. To improve driving sensitivities, we designed the model with the closed electromagnetic circuit for tracking direction. In addition, driving sensitivities and flexible mode frequencies were improved by using DOE(Design of Experiments) for magnetic circuit and modifying the lens holder. Consequently, it is confirmed that the designed model is satisfied with the desired specifications.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.359-367
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• 2008

The maximum sound pressure level in a ship is restricted by the international standard such as MIL-Std. 740-1 in order to protect hearing ability for the crew on a ship. Especially, the noise of a fan system is restricted by the maximum level of the sound power according to the military specification such as MIL-F-1900A. In this paper, the reduction of tonal noise for the fan-motor system on a ship is described related to the electrical as well as structural problems. For the electrical problems, the difference of the magnetic flux caused by the variation of the air-gap is described related to the bad concentricity of the motor housing and the shaft-bearing. And for the structural problem, the resonance of the fan motor system is described.