Nahm Gyoo Cho

Surface Modification Effect of Wettability on the Performance of PDMS-Based Valveless Micropump

Experimental investigation and numerical simulation on the effect of surface wettability on the performance of a polydimethylsiloxane (PDMS) based diffuser micropump are presented. A valveless micro membrane pump with piezoelectric actuation has been examined. Using a replica molding technique, the valveless micropump was made of PDMS on a Pyrex glass substrate. A thin piezoelectric (PZT) disc was used as an actuator. Poly vinyl alcohol (PVA) and octadecyltrichlorosilane (OTS) coatings, which make the coated surface hydrophilic and hydrophobic, respectively, were used to modify the surface wettability inside the pump. In our experiments, the contact angle of the PDMS surface changed from 96.6 o to 29.1 o and 99.6 o by PVA and OTS coatings, respectively, and the contact angle of glass changed from 33.2 o to 17.5 o and 141.8 o. A self-priming process was numerically simulated in a diffuser element using a computational fluid dynamics program (CFD-ACE+). The results show that fewer gas bubbles were created in the hydrophilic coated pump than in the hydrophobic coated one as time progressed. This agrees well with experimental observations. Steady-state flow rates of the micropump were measured. Compared to the non-coated pump, the flow rate increased slightly with the hydrophobic coating but decreased with the hydrophilic coating. We determine that surface wettability significantly affects the performance of a PDMS-based micropump.

Six-degree-of-freedom Manipulator Displacement Measurement using Stereo Vision

In this paper, six-degree-of-freedom (DoF). Displacement measurement technique using a compact stereo-vision system is proposed. The measuring system consists of a camera, an optical prism, two plane mirrors, and a planar marker on a target. The target was attached on an object so that its six-DoF displacement can be calculated using a proposed coordinates estimating algorithm and stereo images of the marker. A prototype was designed and fabricated for performance test. From the test results, it can be confirmed that the proposed measuring technique can be applied to monitoring and control of various manipulators.

Application of optical force measurement to mode characterization of atomic force microscopy nanomachining

Atomic force microscopy is often used not only to acquire the sample surface topography at the subnanometer scale but also to measure forces on the surface during imaging. This study aims to develop a practical measurement scheme of the actual scratching forces exerted during atomic force microscopy nanoscratching using a simple optical microscope setup. The measurement results are utilized to analyze the mode characteristics of atomic force microscopy nanomachining. Unlike typical atomic force microscopy force measurement methods using position-sensitive detector signal analysis, the optically measured atomic force microscopy cantilever deformation data using varying input (normal) forces along with information on the cantilever stiffness were used to estimate the components of the actual force exerted during nanomachining without using complex data interpolation methods. Scratching experiments were performed on Si(100) workpieces, and the estimated real force values were compared with the experimental data from atomic force microscopy nanomachining for each input force and corresponding scratch depth. Frictional coefficients and in-process acoustic emission monitoring results were also used to conduct an in-depth analysis of the actual force results. It is shown that the estimation results are meaningfully close to both the theoretical evaluations and the scratching experimental data as the scratch depth changes. Moreover, the force data are shown to have the ability to detect mode transitions such as the elastic–plastic and the plowing–cutting transitions during nanomachining, which validates the utility of this approach.

The five-degree of freedom stitching method of areal surface data for high precision and large area measurement

In this research, a five-degree of freedom (5-d.o.f.) stitching method is proposed which is implemented by calculating the 5-d.o.f. relative position and orientation between small areas of 3D profile data acquired with high resolution. The relative position and orientation is calculated from the data of the overlap area for adjacent measured areas by using the least squares method and the cross correlation function. Furthermore, a data synchronizing algorithm is also proposed for the case in which a specimen is measured by different instruments. To verify practical application of the stitching method and the synchronizing algorithm, a multi-probe optical measuring instrument was developed.

The Spatial Synchronization of Areal Measurement Data Sets by Multi-Probes

In this paper, to release this induced errors and improve the accuracy of the measured data, a new spatial synchronization method is proposed to spatially synchronize the three-dimensional surface data sets obtained by variety surface topography measuring instruments. The proposed spatial synchronization method minimizes the geometrical error components using the data interpolation, the least squares method, and the two-dimensional cross correlation function. For verification of the method, it was applied to the measured data sets measured with a chromatic confocal microscopy, a laser scanning confocal microscopy, and an ellipsometer. Based on the experimental results, the accuracy or the proposed method is analyzed and evaluated.

5-D.O.F. Force/moment Sensor using Optical Intensity Modulation in MR-field

A 20 mm diameter of small 5-D.O.F. force sensor has been developed for applications in MR-field Optical intensity modulation was adopted for transducing to miniaturize the sensor structure. For its accurate sensing of 5-D.O.F. force/moment, the elastic detecting module was designed to respond independently to each force or moment component. And for small size, two optical transducing modules of 2-D.O.F. and 3-D.O.F. were designed and integrated with the detecting module where optical fibers were arranged in parallel to make the sensor small. It is confirmed by calibration test that the detecting modules deforms linearly and independently to the input force. The results of evaluating test show that the range and resolution of forces are ±4 N and 0.94~7.1 mN and the range and resolution of moments are ±120 N ·mm and 0.023~0.034 N·mm.

Electric Signal Detection of a Microfilter-Based Biochip for Immunoassay Using Microbead, Nanogold Particle, and Silver Enhancement

This paper presents a microbiochip which can detect an antigen-antibody reaction through an electrical signal in real time with high sensitivity and low sample volume by using nanogold particle and silver enhancement. A filtration method using the microbead is adopted for sample immobilization. The chip is composed of an inexpensive and biocompatible Polydimethylsiloxane (PDMS) layer and Pyrex glass substrate. Platinum microelectrodes for electric signal detection were fabricated on the substrate and microchannel and pillar-type microfilters were formed in the PDMS layer. Successively introducing polystyrene microbeads precoated with protein A, anti-protein A (which was the first antibody) and the second antibody conjugated with nanogold particles into the microchannel, the resulting antigen-antibody complex was fixed on the bead surface. The injection of silver enhancer increased the size of nanogold particles tagged with the second antibody. As a result, microbeads were connected to each other and formed an electrical bridge between microelectrodes. Resistance measured through the electrodes showed a difference of two orders of magnitude between specific and nonspecific immunoreactions. The developed immunoassay chip reduced the time necessary for an antigen-antibody reaction to 10 min, thus shortening the overall analysis time from 3 hours to 50 min. The immunoassay chip reduces analysis time for clinical diagnoses, is simple, and has high sensitivity.

An Electrical Signal Detection System for a Microbiochip with Gold Nanoparticles

In this paper, an electrical signal detection system for microbiochips is proposed to overcome the limitations of conventional optical systems such as bulky system size and high manufacturing cost. An electrical detection system with interdigitated microelectrodes is fabricated using MEMS technology. High conductive nano size gold particles were selected for the system to detect biological reactions between bio materials in the microbiochip. Experiments were performed with variations of particle densities and electrode gaps. In addition, a simulation to predict the electrical resistance of the microbiochip was developed. Both the simulation and experimental data show that the conductivity increases as the gap becomes narrower and the particle density higher.