Chin-Tu Lu

Simulation of a carbon graphite brush with distributed metal particles

The electric and thermal fields within a metal graphite brush in sliding electrical contact with a fast moving rotor are simulated. The composite nature of the brush, a carbon graphite matrix with randomly distributed metal (silver) particles, is treated via finite elements in an inner zone about the brush-rotor contact, and composite mixture theory in an outer zone away from the contact. In the inner zone, individual elements are randomly assigned metal or carbon properties in a manner consistent with the volume fraction. Computations are three dimensional. Electrical and frictional heatings are considered. Simulations of thermal and electric fields are performed over ten different specific distributions of metal particles; averages are then taken over this ten-member ensemble. Simulation results indicate and verify the existence of a critical volume fraction of silver for good brush performance. At this critical volume fraction, individual silver particles link into networks and encourage efficient transfer of electrically and frictionally generated heat away from the contact region. Temperatures remain moderate with this critical volume fraction (even at extreme heatings), and a hot zone does not form. >

Development of a micro-CMM with scanning touch probe and high-precision coplanar platform

This study develops a micro-CMM incorporating a scanning touch probe and a high-precision coplanar platform. The measurement performance of the proposed system was enhanced through the use of a rigid aluminum double-arch-bridge structure to support the scanning touch probe. For the working stage, a linear motor was used for long-stroke positioning and a piezoelectric actuator was then employed to fine-tune the positioning so as to achieve a requirement of highprecision. The platform has two characteristics: (i) the driving and measuring axes are designed along the same line so that Abbe error of the stage can be eliminated; (ii) the coplanar design makes the X and Y axes reach a goal of two-axis concurrent. The aforementioned two designs can reduce the error of the platform so that the micro-CMM reaches a positioning accuracy of ±0.1μm for a working volume of 80×80×40 mm3. Furthermore, the reliability of the probe mechanism of three degrees of freedom was analyzed and validated. The sensor coordinates a laser diode with Position Sensor Detectors (PSD) working with an optical path to measure placement of Z-axis and angle placement of XY-axis. By validation through an experiment, the three dimensional scanning touch probe developed by this study has a measuring range of ±1mm × ±1mm × 1mm with a unidirectional repeatability of 0.6μm.

The Study of Microfluidic Chip with Micro Cylindrical Post Array for Separating Particles

This study presents the design, simulation, fabrication and measurement of a microfluidic chip with micro cylindrical post array for separating particles. The structure of microfluidic chip is consisted of top glass, a micro channel with cylindrical post array, two Au end electrodes and bottom glass. Both in-line and staggered arrays of micro cylindrical posts were designed and made of SU-8 inside the micro channel by MEMS technology. The simulated results showed that the applied DC voltage at the end electrodes would generate a non-uniform electric field within the array of cylindrical posts, and particles would be attracted there. From the results of experiment, the minimum required DC voltages to drive micro particles flowing into the micro channel by electrokinetic effect were 15V and 30V, respectively, at the electrode spacing of 8mm and 25mm for both array types. Under the dielectrophoretic effect created by the non-uniform electric field, the latex particles could be concentrated around micro cylindrical posts with electric field intensity minima and separated from flowing fluid. This phenomenon is in agreement with the simulation.

Development of a 3D touch trigger probe using micro spherical stylus machining by micro-EDM for micro-CMM

This study develops a low-cost three-dimensional touch trigger probe for micro-CMM using micro spherical stylus machining by micro-EDM. The tip ball of the stylus, with a diameter smaller than 100 μm, is made by a micro electro discharge machine with the method of wire electro discharge grinding (WEDG). The current study uses tungsten carbide (WC) as the material for the stylus. Experimental results show that, the tip ball roundness could amount to 2 μm. Since the tip ball is not easily observable by naked eyes, we designed a micro imaging system to observe the probing in real time. This system is created with modified commercial webcam and microscope. The general design of the touch trigger probe is combined the stylus and suspension structure. When the stylus touches workpiece, it can be determined the time of probe trigger by measuring the motion of suspension structure. The stylus machined by micro-EDM was very fragile and the stylus handle of the tip ball was very thin. Therefore, the stylus handle bends easily that would result in the large measurement error or stylus break when the stylus touched workpiece. In this study we designed a measuring probe using a small chuck and an electrical circuit to measure the probe trigger. When the stylus touches the workpiece, the parallel circuit will switch on immediately and pick up the voltage variation of the resistor. Because the transistor always turns ON, it can avoid the problems of excessive energy and electrical noise.

Analysis of Photoelectric Property and Surface Morphology of Amorphous TiO2 at Different Substrate Temperatures by Sputtering

This paper reports the photoelectric property and surface morphology of amorphous titanium dioxide (TiO2) made at the different substrate temperatures by RF- sputtering on the glass. Five different temperatures (room temperature, 100degC, 200degC, 300degC and 400degC) are set on the substrate holder. The thicknesses of the film are 100 nm, 300 nm and 500 nm. After preparing amorphous TiO2 thin film, the surface morphology and the light absorption were examined by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and UV-VIS spectrometer respectively. The amorphous phase starts to transform into clustered morphology at temperature of 200degC that was examined by XRD. The thicker film showed several advantages: (i) the amorphous phase of TiO2 was easy to form cluster morphology, (ii) the light absorption was increased, (iii) the band gap energy of TiO2 was lowered (from 3.30 eV to 3.28 eV).

Dielectrophoretic Frequency Effect on Purification and Field Emission of Carbon Nanotubes

This paper presents the design, fabrication and test of a field emission chip with carbon nanotubes (CNTs). The objective of this study was to utilize positive dielectrophoresis (DEP) to purify CNTs on parallel microelectrodes and then to perform a field emission test on the CNT film. Study parameters include the electrode width and gap, and the frequency of DEP. To understand the locations where the CNTs might be accumulated, a computer simulation was used to analyze the distribution of gradient of the square of electric field, VE, around the electrodes under the electric field. Three combinations of parallel electrodes, with various width and gap, were designed for the purification and field emission of CNTs. A test chip consisting of three parallel micro electrodes and a micro channel, formed by polydimethyl siloxane (PDMS), was manufactured by photolithography. The medium, also served as cathode surfactant and dispersant, was prepared by sodium dodecyl sulfate (SDS), and the medium with CNTs was fulfilled into the micro channel by syringe pump. By applying different DEP frequencies on the electrodes, the experiment on trapping and purification of CNTs was observed and analyzed. The results showed the CNTs would be accumulated around the edges of electrodes where higher values of VE existed. This trend was in good agreement with the simulation. After the CNTs were purified, Raman spectroscopy showed that the relative intensity ratio of G-band to D-band increased from 0.36 to 0.56 for the samples prepared by DEP at frequencies from 1 to 25 MHz, while the value of non-purified CNTs was 0.29. Therefore, higher frequency of DEP resulted in better purification of CNTs. Followed by the field emission test on the CNT film under voltage ranging from 0 to 1100 V. Results revealed that the CNT film prepared at higher frequency of DEP had a lower threshold of electric field for field emission.