Papers by Author: Kwang Joon Yoon

Abstract: To address the need for new smart materials, this paper explores the use of carbon nanotubes to develop a nanocomposite smart material having electrochemical impedance properties for sensing and actuation. Fabrication and characterization of the carbon nanocomposite material are discussed in the paper. The issues related to hurdles in the practical manufacturing of commodity level macro size nanocomposite smart materials with prescribed electrical and electrochemical properties are also discussed.

Abstract: The behavior of a circular piezoelectric actuator for volumetric micropump has been investigated by using theoretical and finite element analyses. A modified theoretical model was developed to predict the behavior of a piezoelectric actuator induced by the applied voltage. The theoretical results for the diaphragm deflection were in good agreement with the results from numerical simulation. Based on the theoretical analysis, the effects of several important parameters on actuation performance have been investigated. These parameters include the dimensions and mechanical properties of the piezoelectric disk, bonding layer and elastic diaphragm materials. Consequently, it is thought that above theoretical model might be employed as a tool for design and optimization of the piezoelectric actuator for micropump application.

Abstract: Research on piezoelectric unimorph actuators has been intensively increased during the past decade due to the wide applications of this actuator type in aerospace, vibration control, biomimetic robots, artificial muscles… Most analyses focused on the design performance with load-free actuating condition. Loading performance has not been considered adequately yet though in real application the actuators always work under certain carrying load. This paper introduces the measuring system, the experimental setup and presents the observed loading performance of the actuators with center load. Two typical kinds of piezoelectric unimorph actuator, LIPCA-C3 and THUNDER, are investigated. The numerical analyses are also conducted to illustrate the loading behavior of these devices. Some remarks and suggestions for future research activities are drawn.

Abstract: A smart material actuator is required for a smart structure having multifunctional performance. Among the smart material actuators, piezoelectric actuator is known for its excellent large force generation in broad bandwidth in a compact size. However it needs relatively large actuation voltage requiring a bulky hardware system. This study is mainly concerned to develop a self-powered miniaturized piezoelectric actuator driver (MIPAD) controlled by a radio controller for small sized piezoelectric smart structures. It can receive command from other microprocessors or a remote radio controller. We designed a real hardware and it demonstrated good performances even though the driving system was very small. The MIPAD is expected to minimize the weight and size of the piezoelectric actuator system and it can be easily embedded into mobile smart structures.

Abstract: In this paper, a smart skin, i.e. a conformal load-bearing antenna structure, which is a multi-layer sandwich structure composed of carbon/epoxy, glass/epoxy and dielectric material, designs, analyses, fabrications and tests are conducted. Mechanical properties of each structural layer of the designed smart skin are obtained from experimental tests. Tests and analyses are conducted to study the deformation behavior of the smart skin under compressive loads. The measured data are compared with the numerical results from geometrically linear/nonlinear finite element analyses. Numerical prediction for the buckling load of the smart skin agreed well with the experimental data.

Abstract: This paper introduces a new sensor design based on a carbon nanotube structural neuron for structural health monitoring applications. The carbon nanotube neuron is a thin and narrow polymer film sensor that is bonded or deposited onto a structure. The electrochemical impedance (resistance and capacitance) of the neuron changes due to deterioration of the structure where the neuron is located. A network of the long carbon nanotube neurons can form a structural neural system to provide large area coverage and an assurance of the operational health of a structure without the need for actuators and complex wave propagation analyses that are used with other SHM methods. The neural system can also reduce the cost of health monitoring by using biomimetic signal processing to minimize the number of channels of data acquisition needed to detect damage. The carbon nanotube neuron is lightweight and easily applied to the structural surface, and there is no stress concentration, no piezoelectrics, no amplifier, and no storage of high frequency waveforms. The carbon nanotube neuron is expected to find applications in detecting damage and corrosion in large complex structures including composite and metallic aircraft and rotorcraft, bridges, and almost any type of structure with almost no penalty to the structure.

Abstract: This paper addresses the power consumption of the LIPCA (LIghtweight Piezo-Composite Actuator) device system when electric input was applied at its resonance frequency. The LIPCA device system is composed of a piezoelectric ceramic layer and fiber reinforced lightweight composite layers. Typically, a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. The advantages of the LIPCA design are weight reduction by using the lightweight fiber reinforced plastic layers without compromising the generation of high force and large displacement, and design flexibility by selecting the fiber direction and the size of prepreg layers. An experimental set-up was specially designed to measure the power consumption of the LIPCA. By measuring the capacitance of the PZT ceramic wafer during the test, the electric power that consumed can be determined. Experimental results revealed a significant increase in capacitance of the PZT ceramic wafer with an increase in the frequency of applied voltage around the natural frequency of the actuator.

Abstract: This paper is concerned with the development of stacked ceramic thin actuation layer IDEAL (Inter-Digitated Electrode Actuation Layer) using d33 actuation mechanism of piezoelectric ceramic. Most of the thin piezoelectric actuators are operated with d31 actuation mechanism. Many kinds of piezoelectric ceramic actuators are strived now to improve the actuation performance. One of efforts to improve performance of piezoceramic actuators is the research trying to develop an actuator using the piezoelectric coefficient d33. The piezoelectric coefficient d33 is almost twice larger than piezoelectric coefficient d31. Therefore, the induced strain of PZT thin layer with d33 actuation mechanism is bigger than that with d31 actuation mechanism. The AFC and LaRC-MFC used d33 actuation mechanism with surface interdigitated electrode to enhance its actuation performance. But their actuation mechanism is not perfect d33 actuation mechanism since the interdigitated electrodes are placed at the surface of the actuation layer. In this research, the stacked ceramic thin actuation layer with imbedded inter-digitated electrodes is designed and manufactured. The actuation strain of stacked ceramic thin actuation layer is measured and compared with the actuation strain of the LaRC-MFC. The comparison shows that the developed stacked ceramic thin actuation layer can produce 10% more actuation strain than LaRC-MFC at relatively high electric field.

Abstract: This paper addresses detail design and demonstration of an insect-mimicking flappingwing mechanism composed of LIPCA (Lightweight Piezo-Composite Actuator) and linkage system that can amplify the actuation displacement of LIPCA. The angular amplification of the linkage system can provide various flapping angles by adjusting the actuation point of the LIPCA. The device can generate flapping frequency ranging from 5 to 50 Hz depending on weight of the wing and linkages. Flapping tests using different wing mass, area, and aspect ratio were performed to investigate the flapping performance. The test results were described and compared with the estimation. It was found that changes in wing mass, area, and aspect ratio result in significant variation of natural flapping-frequency.

Abstract: This paper describes design, manufacturing, and wind tunnel test of a motor-driven small-scale expandable wing for MAV class vehicles. The bird-like expandable wing has been developed for investigating the influence of aspect ratio change on the lift and drag of the wing. As a typical bird wing, the wing is separated into inner and outer wings. The wing model consists of the linkage system made of carbon composite strip/rod and the remaining part covered with carbon composite sheet and multiple LIPCAs (Lightweight Piezo-Composite Actuators) mimicking wing feathers. The LIPCA actuator was used to control wing camber, which created additional lift. Wind tunnel tests were conducted to investigate the changes in lift and drag during wing folding and expansion, and to observe the influence of LIPCA actuation on the wing. In the tests, effects of the wing fold/expansion and actuation of LIPCA on changes in lift and drag were quantitatively identified.