Papers by Author: Dong Weon Lee

Abstract: In this paper, thermal postbuckling of a beam-like structure subjected to a uniform thermal loading is studied both theoretically and experimentally. In theory aspect, the equations governing the axial and transverse deformations of beams are derived. The two equations are reduced to a single nonlinear fourth-order integral-differential equation governing the transverse deformations. The analytical method presented here offers a simple yet efficient solution approach to analyze the bistable behavior of microbeam or beam-like structures under thermal loading. Then, microfabricated double-clamped beams are chosen as experimental object due to its precise dimensions and easy loading method. The lab-made HF vapor system was used to release the suspended structures with satisfactory results. After the fabrication and measurement, by comparing the theoretical results with experimental results, an excellent agreement is gotten. It proves not only the validity of the solution obtained here, on the other hand, importantly, it also demonstrates a new field for MEMS as another easy and accurate tool to investigate mechanics problems. With the accurate solutions for posbuckling beams, we apply it into new electrothermal postbuckling actuators, a big deflection promising the possibility of a new kind of actuator.

Abstract: A micro grooved finger has smaller bending stiffness and can be used to improve the performance of some micro cantilever devices. The deflection and bending stiffness of a micro grooved finger are discussed in this paper. An analytical model of the deflection is built up to study the effect of the groove sizes on the bending stiffness and the deflection of the grooved finger. The calculation of the analytical model is consistent with the simulation and experiment results. When the grooves depth is 0.5 μm, the spring constant of grooved micro finger is 19.8% smaller than that of flat finger without groove patterns. The spring constant of the finger decreases with the increasing of the width and depth of the groove. A novel micro electric-thermal gripper is introduced based on the grooved finger. It consists of four sub-cantilever beams arranged at the diagonal lines of the square frame in the end of the main cantilever structure suspended from the silicon substrate, which guarantees an effective contact by the four-point contact area on the top surface to grab object of importance. The thermal expansion induced deflection makes the fingers moving vertically from an ‘open’ position to a working one. The grooved fingers help to decrease the bending stiffness of the finger and increase the deflection and the initial gap. The simple fabrication process has a feasibility of compatible and mass production.

Abstract:
In order to control the IPMC (Ionic Polymer Metal Composite) actuators, it is necessary to use a vision sensing system and a reduced order model from the vision sensing data. In this study, the MROVS (Modal Reduced Order Vision Sensing) model using the least square method has been developed for implementation of the biomimetic motion generation. The simulated transverse displacement is approximated with a sum of the lower mode shapes of the cantilever beam. The NIPXI 1409 image acquisition board and CCD camera (XC-HR50) are used in the experimental setup. Present results show that the MROVS model can efficiently process the vision sensing of the biomimetic IPMC actuator with cost-effective computational time.

Abstract: This paper describes an integrated tunneling sensor for applications of an electronic nose and a scanning probe microscope. Ultra-thin silicon dioxide having a thickness of ~2 nm is used as a material of the tunneling sensor. It provides much higher sensitivity in comparison with others sensing methods. The tunneling sensor is placed on a fixed edge where the maximum strain arises. As additional masses or forces are added to the surface of the cantilever, the thickness of the thin silicon dioxide layer is slightly decreased. By using exponential nature of electron tunneling dominated by the thickness of the silicon dioxide it can be used as an ultra-high sensitive sensor. The thin dioxide is fabricated by dry oxidation using a vertical furnace. The cantilever structures are defined by conventional MEMS technologies. Current density of the tunneling sensor is evaluated as a function of voltage and is compared with numerical analysis based on direct tunneling phenomena.