Papers by Author: Nam Seo Goo

Abstract: In this study, a high performance peristaltic micropump has been developed and investigated. The micropump has three cylinder chambers which are connected through microchannels and two normally closing active membrane valves at inlet/outlet for high pumping pressure performance. A circular shaped miniature LIPCA has been developed and manufactured for actuating diaphragms. In this LIPCA, a 0.1mm thickness PZT ceramic is used as an active layer. As a result, the actuator has shown to produce large out-of-plane deflection and consumed low power. During the design process, a coupled field analysis was conducted to predict the actuating behavior of a diaphragm. The actuator behavior was investigated both theoretically and experimentally. In addition, MEMS technique was used to fabricate the peristaltic micropump. Judging from experimental flow rate and pumping pressure results, the present peristaltic micropump has higher performance than the same kind of micropump developed elsewhere.

Abstract: In this article, the flexural displacement of plate-type piezoelectric composite actuators (PCA) with various lay-up configurations has been evaluated considering the thermal deformations induced by a temperature drop using a three-dimensional finite element simulation. The results reveal that the flexural displacement of PCA subjected to electrical loadings is significantly affected by their lay-up configurations, the thickness of constituent PZT ceramic and applied boundary conditions, which is associated with the location of the neutral plane by moment equilibrium and the bending stiffness of PCA. For the displacement performance of PCA, an adequate choice of layup configuration together with the proper thickness of PZT ceramic is required.

Abstract: In this paper, the pumping performance of a piezoelectric micropump is simulated with commercial finite element analysis (FEA) software COMSOL Multiphysics 3.2a. The micropump is composed of a 4-layer piezo-composite actuator (LIPCA), a polydimethylsiloxane (PDMS) pump chamber, and two diffusers. The piezoelectric domain, structural domain and fluid domain are coupled in the simulation. Water flow rates are numerically predicted for geometric parameters of the micropump. Based on this study, the micropump is optimally designed to obtain its better pumping performance.

Abstract: This paper presents a mechanical design of biomimetic fish robot using the Lightweight Piezo-Composite Actuator (LIPCA). We have designed a mechanism for converting actuation of the LIPCA into caudal fin movement. The linkage mechanism consists of rack-pinion and four-bar linkage systems. Two kinds of caudal fins are fabricated such that the shapes resemble subcarangiform and ostraciiform caudal fin shape, respectively, and then attached to the linkage system. The swimming test using 300 Vpp input with 1 Hz to 3 Hz frequency was conducted to investigate the effect of tail beat frequency and shape of caudal fin on the swimming speed. The maximum swimming speed was reached when the device was operated at its natural swimming frequency. At the natural swimming frequency of 1.016 Hz, maximum swimming speeds were 1.267 cm/s and 1.041 cm/s for ostraciiform and subcarangiform caudal fin, respectively. The Strouhal numbers, which are a measure of thrust efficiency, were also calculated in order to examine thrust performance of the present biomimetic fish robot.

Abstract: In this work, behavior of a unimorph piezoceramic actuator, LIPCA (Lightweight Piezo- Composite Actuator) has been numerically and experimentally investigated. By measuring the lateral displacement created by the compressive load, the buckling load of the LIPCA was determined. Under simply supported configuration, the measured buckling load agreed well with the geometrically nonlinear buckling load from the finite element analysis. The measured data shows that the lateral displacement of the LIPCA is significantly increased when the electric field is prescribed to the LIPCA in addition to the compressive load. The measured data was compared with the computed results from the geometrically nonlinear finite element analysis. The numerical simulation agreed well with the measurement for low compressive load and low electric field.

Abstract: Characteristics during the fracture process of a plate-type piezoelectric composite actuator (PCA) using acoustic emission (AE) monitoring were investigated under a bending load. The fracturing of a monolithic PZT ceramic shows typically brittle behavior; furthermore, the AE signal at the maximum load, which corresponds to the final fracture, has a high amplitude and long duration. Analysis of dominant frequency bands by a fast Fourier transform (FFT) in conjunction with AE parametric analysis expressed the characteristic changes of the fracture process in the PCA. For the PCA, a brittle fracture in a PZT ceramic layer induces the local delamination between the PZT ceramic and adjacent fiber composite layers. Based on the AE analysis and damage observations through optical microscopy, the features of AE associated with fracture process can be elucidated for the PCA.

Abstract: A performance evaluation of plate-type piezoelectric composite actuators (PCA) having different lay-up sequences was experimentally carried out at simply supported and fixed-free boundary conditions. The actuating displacement of the manufactured PCAs was measured using a non-contact laser displacement measurement system. It was shown that the actuating displacement with increasing applied electric field at a drive frequency of 1 Hz increased nonlinearly at the simply supported boundary condition whereas it almost linearly increased at the fixed-free boundary condition. In contrast, the actuating displacement of the PCAs depended on the applied electric fields in a drive frequency range from 1 Hz to 10 Hz. However, the displacement behavior of PCAs varied significantly at a higher range of drive frequency, i.e., beyond 15 Hz, due to the occurrence of resonance. On the basis of these experimental results, the bending characteristics of PCAs in relation to applied electric field, drive frequency, and boundary conditions were elucidated.

Abstract: This paper presents a design and performance evaluation of a valveless micropump fabricated from polydimethylsiloxane (PDMS) based on molding techniques. A circular lightweight piezo-composite actuator (LIPCA) was successfully developed for the actuating diaphragm of the micropump. The LIPCA is a composite actuator designed and fabricated with piezoceramics in combination with carbon fabric and glass epoxy. Numerical and experimental methods were used to investigate the performance of the circular LIPCA. The LIPCA was glued to a PDMS membrane to form the diaphragm of the micropump. The diaphragm has several advantages, such as high displacement, dome-shaped deformation and geometrically independent actuation profile. The diaphragm based on a LIPCA 9 mm in diameter produces a deflection of 27 μm at the applied voltage of ± 200 V and a frequency of 1 Hz. The micropump has a maximum water flow rate of 0.95 ml/min and a maximum backpressure of 3.8 kPa. The merits of the present micropump are low cost, ease of manufacturing and high level of effectiveness. The proposed LIPCA is proven to be a promising alternative to the conventional piezoelectric actuator used in micropumps.

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 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.