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me.postech.ac.kr ● Faculty of the Department of Mechanical Engineering

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Vibration and Acoustic Transducers (VATrans) LaboratorySearch for Active Applications of Vibration and Acoustic Phenomena

Won Kyu Moon

Education Ph.D. 1995 Univ. of Texas, Austin (ME)M.S. 1986 KAIST (ME)B.S. 1984 Seoul Nat'l Univ. (ME)

Experience 1998~ present Professor, Pohang University of

Science and Technology1996~1998 Member of Research Staff,

Samsung Adv. Inst. of Tech.1986~1990 Researcher, KAERI

Contact Tel : +82-54-279-2184Fax: +82-54-279-5899E-mail: wkmoon@postech.ac.kr

Many studies have been done on the vibration and acoustic phenomena. The usual purpose of engineers for these studiesis to reduce vibration itself and its effects or unwanted sounds (noise). The research works in this laboratory are, however,focused on the applications of vibrations and sounds.

One good example among the applications of vibrations and sounds is the loudspeaker. As can be seen in a loudspeaker, atransducer may be found in such active applications of vibrations and sounds. For this reason, the research area of thislaboratory includes modeling of transducers as well as analyses and measurements of vibrations and sounds.

Transducers are defined as devices or machines that convert one form of energy into another form. Hence, in order toanalyze and design transducers, the coupling phenomena between various forms of energies should be understood.Electromechanical coupling phenomena such as piezoelectricity and electromagnetic forces are focused to study here inVATrans Lab.

The following show the more-detailed research areas studied in the laboratory:

● Analysis and Modeling of Transducers and Ambient Components- Modeling of transduction materials and their applications- Dynamic simulations of systems with transducers

● Nonlinear Acoustics and Ultrasonic Loudspeakers- Nonlinear acoustic phenomena and their numerical simulations for designing acoustic transducers- Radiation theory and design of ultrasonic loudspeakers- Ultrasonic radiation/imaging devices

● Sensors for Bio-Objects- Protein/DNA sensors based on the mass micro-balancing- Measurement system for bonding forces of adhesive bio-materials- Sensors and applications of micro/nano scale physics

● Machines/Devices to Manipulate Micro/Nano Objects- Long-range nano-precision displacement Sensors- Ultra-precision actuators- Machines/Equipments with Grippers for manipulating nano-objects

Major Publications■Sangkyu Lee, Yeolho Lee, Haksue Lee and Wonkyu Moon, “Improvements in electrical properties of piezoelectric microcantilever

sensors by reducing parasitic effects”, Journal of micromechanics and microengineering, Vol. 21, 085015■ Sungjoon Choi, Haksue Lee, and Wonkyu Moon, “A micro-machined piezoelectric flexural-mode hydrophone with air backing:

Benefit of air backing for enhancing sensitivity”, Journal of the Acoustical Society of America, Vol.128, No.3, pp.1033-1044, 2010.■ Yonghwan Hwang, Yub Je, Dawnielle Farrar, James E. West, S. Michael Yu, Wonky Moon, “Piezoelectric properties of

polypoptide-PMMA molecular composites fabricated by contact charging”, Polymer, Vol 52, Issue 13, pp.2723-2728■ Sangkyu Lee, Jinam Kim, wonkyu moon, Jinhwan Choi, Ilhan Park, Daesung Bae, “A Multi-body-Based Dynamic Simulation

Method for Electrostatic Actuators”, Nonlinear Dynamics, Vol.54, No.1-2, pp.53-68, 2008■ Haksue Lee, Daesil Kang, Wonkyu Moon, “A micro-machined source transducer for a parametric array in air”, JASA2009,

Vol.125, No.4, pp.1879-1893, 2009■ Sungjoo Kim, Wonkyu Moon, “A Micro-Pull-Off Test Machine for Reliable Measurement of Adhesive Forces on Micro/Nano-

Scale Areas”, The Journal of Adhesion, Vol.87, No.2, pp.139-153

Micro structures and Reliability Lab.

This laboratory has carried out researches on the Micro/Nano-mechanics, mechanical properties of the materials in smallscale and its applications. Objectives are : improvement of the reliability for the MEMS/NEMS devices by evaluatingmechanical properties accurately, and design of the micro-sensor by making use of the AAO structure. The lab is directed byHyunchul Park, Professor in Mechanical Engineering.On going recent research activities are in the following areas:

● Measurement of Mechanical Properties and Size EffectMicro-electro-mechanical systems (MEMS) consist of various thin films the thickness of which ranges from sub-micron to

tens of microns. But, the mechanical properties of such thin films are different from those of bulk materials and difficult tobe identified.

We measured the mechanical property of films using the bulge test and the nano-indentation test are powerful techniquesfor measuring the mechanical properties of thin films. Bulge test of free standing membrane was found to be a promisingmethod of determination of mechanical properties without being influenced by the mechanical properties of the substrate.And nano-indentation test is technique for measuring the elastic modulus and hardness of thin films and small volumes.Using the these methods, we investigate the effect of specimen size, grain size, fabrication condition and annealing on themechanical property of films.

The mechanism based strain gradient (MSG) plasticity is one of the methods to analyze non-uniform deformation behaviorin micro/nano scale. In this theory, a multiscale, hierarchical framework to facilitate such a marriage between plasticity anddislocation theory were proposed. A mesoscale cell with linear variation of strain field is considered. Each point within thecell is considered as a microscale sub cell within which dislocation interaction is assumed to obey the Taylor relation so thatthe strain gradient law applies.

We propose a modified strain gradient plasticity theory, which is based on MSG theory using the concept of GNDs on thegrain boundaries in order to explain the size effect for polycrystalline materials. To validate the proposed model, variousexperimental results for polycrystalline materials such as micro tension test, bulge test and bending test were employed. Theproposed model can predict the size effect in deformation for polycrystalline material which can not explain using theclassical mechanics and original strain gradient plasticity theory.

● Multibody dynamic analysis of the cold rolling millChatter is the phenomenon caused by vibration between the workpiece and

the manufacturing machine. Because the chatter reduces the quality ofproducts in the grinding and milling operation, it constitutes a majorproblem. The chatter vibration of the rolling process also has a significanteffect on the surface and thickness of the metal strips.

We investigated the dynamic behavior of the cold rolling mill in theGwangyang Works of POSCO. For the experimental study, the acceleration ofthe roll, rolling force and speed of the work roll were measured byaccelerometer, load cell and tachometer, respectively. The numerical modelof the rolling mill including the driving system was built for multibodydynamic analysis. The model was validated by experiment. The effects of therolling parameters such as rolling force and speed on chatter vibration wereinvestigated.

● Design and analysis of offshore wind turbine foundationWith the development of offshore wind energy, several types of foundation

can be used to support offshore wind turbine. According to differentenvironmental conditions, various fixed-bottom foundations, such as,monopile, tripod, jacket, and multipile are designed and analyzed to studythe dynamic response of wind turbine for Korean Western Sea, where the firstoffshore demonstration project will be located. The influence of differentissues, such as, joint can, overlapping, X-brace stress concentration, marinegrowth, soil-structure interaction, are investigated for specific foundations.

Major Publications■ D. Kim, W. Hwang, H.C. Park, K.H. Lee, “Superhydrophobic nanostructures based on porous alumina”, Physics, Volume 8, Issue

6, October 2008, Pages 770-773.■ Donghyun Kim, Hyun Chul Park, Kun-Hong Lee, Ki-Bae Park, Kangduk Choi, Woonbong Hwang, “Overcoming of nanoscale

adhesion by electrostatic induction”, CURRENT APPLIED PHYSICS, vol.9, No.3, pp.703-706, 2009.05.■ Youngdeuk Kim, Bongbu Jung, Hunkee Lee, Hyejin Kim, Kunhong Lee, Hyunchul Park, “Capacitive humidity sensor design based

on anodic aluminum oxide”, Sensors & Actuators: B. Chemical, vol.141, No.2, pp.441-446, 2009.9.■ Hun-kee Lee, Bong-bu Jung, Young-deuk Kim, Woon-bong Hwang, Hyun-chul Park, “Analysis of flow stress and size effect on polycrystalline

metallic materials in tension”, MATERIALS SCIENCE & ENGINEERING, in press, vol.527, Issues 1-2,pp.339-343, 2009.12.■W. Hwang, K. H. Lee, H. Park, J. Kim, J. Park, J. H. Cho, J. H. Jeon, D. Choi, D. Kim, D. Kim, S. Kim, K. Lee, T. Jing, and S. Lee

“Some aspects of the design and applications of nanohoneycomb and nanofiber array structures” Mechanics of CompositeMaterials, Vol. 47, No. 1, (2011.3), pp.11~36.

■ Hunkee Lee, Bongbu Jung, Dongseob Kim, Hyunchul Park “On the size effect for micro-scale structures under the plane bulge test usingthe modified strain gradient theory” International journal of precision engineering and manufacturing, Vol.12, No.5(2011.10) pp.865-870.

Nane Indentation and UTM

Bulge Test

Hyun Chul Park

Education Ph.D. 1985 Mechanical Engineering, Univ.

of IowaM.S. 1981 Mechanical Engineering, Univ.

of IowaB.S. 1974 Mechanical Engineering, Seoul

National Univ.

Experience 1986~ Dept. of Mechanical

Engineering, Postech,Professor

1985~1986 University of Iowa, VisitingAssistant Professor

1985~ University of Iowa , Lecturer1974~1979 Agency for Defense

Researcher

Contact Tel: 82-54-279-2167Fax: 82-54-279-5899E-mail: hcpark@postech.ac.kr