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Author: search.filters.author.Chevasuvit, F.

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    Low cost hot embossing process for plastics microfluidic chips fabrication
    (2009-10-22)
    Lomas, T.
    ;
    Mongpraneet, S.
    ;
    Wisitsoraat, A.
    ;
    Jaruwongrungsee, K.
    ;
    Sappat, A.
    In this work, we develop plastic microfluidic chips based on low cost hot embossing process with metal micromold. Metal micromold was formed on aluminum substrates by CNC milling machine and high precision micromachine. The hot embossing system is in-house made with computer aid design by Solid Work program. The system consists of four main parts, structural body, heating system, compressive system and control electronics. The compressive system consists of two top hydraulic single-stage pistons and four middle-stage pistons. Polymethyl methacrylate (PMMA) microfluidic chips were then produced by hot embossing under different applied temperatures and time. It was found that optimum temperature and time for minimum contraction and depth error were 80 degree C and 2-5 minutes. The developed technique offer advantages for microfluidic chip fabrication in term of quality, complexity and cost. ©2009 IEEE.
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    A precision hot embossing mold fabricated by high-resolution powder blasting with polydimethylsiloxane and SU-8 masking technology
    (2009-03-16)
    Lomas, T.
    ;
    Wisitsoraat, A.
    ;
    Chevasuvit, F.
    ;
    Tuantranont, A.
    In this paper, we applied a three-dimensional micromold by using micropowder and micropattern masking technology. High-resolution powder blasting with polydimethylsiloxane (PDMS) and SU-8 masking is developed for the fabrication of a precision microfluidic mold for hot embossing fabrication. The PDMS is a suitable masking material for powder blasting due to its high erosion resistance. First, a 100 νm SU-8 negative pattern was developed on a stainless steel substrate by standard photolithography. A PDMS solution was then applied to the substrate, mainly filling recessed regions. Excess of PDMS was then physically removed by a blade. The PDMS/SU-8 structure was then cured. Next, silicon carbine (SiC) powder with an average diameter of 50 νm was blasted on a PDMS/SU-8 coated stainless sheet at a constant pressure between 4 and 6 bar and a PDMS mask was removed by ultrasonic cleaning in isopropanol. The three-dimensional structure was examined by an optical microscope, optical white light interferometer and scanning electron microscope. The PDMS pattern is found to be 50 νm wide, and the maximum etched depth at this thickness is around 150 νm at a blasting pressure of 6.2 bar; thus, an aspect ratio of 3 is easily obtained. In principle, the low-cost micromachining hot embossing mold developed can be improved to yield submicrometer- and nanometer-scale resolution. © 2009 IOP Publishing Ltd.
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    Experimental results of using rough sets for printed Thai characters recognition
    (2001-12-01)
    Mitatha, S.
    ;
    Dejharn, K.
    ;
    Chevasuvit, F.
    ;
    Chankuang, B.
    ;
    Kasemsiri, W.
    This paper proposes the experimental results of using a Rough sets for the recognition of printed Thai characters. In our experiment, we segment each character into 32 pieces sized 4×4 pixels, and then find the distribution of pixels that match a value of "1" (black dot) in each section Following this, we use the resulting 32 values as the attributes for each given object. Afterwards, we create 3 sets of decision making rules from 3 different training sets and use those 3 set of rules to classify each member of the unknown set. This set is composed of 42 Thai characters, excluding the two that are very rarely used, with 7 fonts and 7 sizes, for a total of 2058. The results are 46.20%, 63.15%, 73.12% for the first set of rules, the second set of rules and the third set of rules respectively. And the results when apply the set of rule to the unknown which related to each set of rules's training sets are 100% for all three set of rules.