Tay Cho Jui
Email Address
mpetaycj@nus.edu.sg
Organizational Units
260 results
Publication Search Results
Now showing 1 - 10 of 260
Publication A parametric study on surface roughness evaluation of semi-conductor wafers by laser scattering(2003) Tay, C.J.; Quan, C.; MECHANICAL ENGINEERINGA technique for measuring surface roughness of semi-conductor wafers in the nanometer range has been developed. The principle of the method is based on laser scattering from a rough surface. A tele-centric optical set-up is constructed to illuminate the test specimens and the scattered light field is recorded with a photo-diode sensor connected to a digital amplifier. A parametric method is proposed for the evaluation technique and results obtained are compared with those obtained using a conventional Taylor Hobson mechanical stylus profilometer. A set of roughness standards fabricated in accordance with BS 2634 and ISO 2632 is employed in the calibration process.Publication Micro-components evaluation using laser interferometry(2008) Tay, C.J.; MECHANICAL ENGINEERINGThis work describes the use of optical interferometry techniques for non-destructive evaluation of micro-components. Various techniques using coherent interferometry techniques are developed. The techniques include, Optical Wedge Fringe Projection, Modified Michelson Interference, Laser Scattering Technique and Newton's Rings. In the optical wedge fringe projection technique a method for determining the deformation of a membrane in a miniature microphone is described. Using an optical fiber and an optical wedge a sinusoidal fringe pattern with a pitch of the order of microns can be readily generated. Subsequent image processing is carried out using a four frame phase-shifting technique. Results obtained suggest that the proposed setup is capable of measuring deformations on a miniature microphone in the sub-micron range. In the modified Michelson interference technique an optical method for the measurement of angular rotation of a micromirror driven by an electrostatic force is developed. To detect the rotation of the micromirror, a He-Ne laser probe with a collimated light beam of less than 50 μm in diameter is directed onto a micromirror with an achromatic lens. The laser beam reflected off the micromirror falls on the achromatic lens and is combined with another laser beam from a fixed reference mirror. The resulting interference fringe pattern is recorded and the angular rotation of the micromirror is determined from the change in pitch of the fringe pattern. In the laser scattering technique detection of cracks on the surface of a micro-chip solderball is carried out by capturing scattered light of a laser probe directed at the solderball. The technique is based on light scattering theory and uses conventional optical components to focus light beams emitted from a low-power He-Ne laser. The laser beam scans a test surface and when it encounters a surface defect, the scattered light intensity distribution is altered the scattering characteristic is dependent on the defect size. Test results on specimens with crack size ranging from 4 μm to 60 μm show that the proposed technique is suitable for crack detection of solderballs on a micro-chip. In the Newton's rings technique a collimated monochromatic light is directed onto an airwedge consisting of a reference surface (e.g. an optical flat or thin membrane) and an object. A long-working distance microscope with a CCD camera is utilized to capture the interference fringe pattern that results from a recombination of two beams reflected from the reference and the object. The resulting fringe patterns are analyzed by the use of Fast Fourier Transform (FFT) and deflections of the object are obtained and subsequently used to calculate the Young's modulus and deformation. By the use of monochromatic lights with different wavelengths, a method called multiple-wavelength interferometry is also developed to measure the deformation of an object. Different micro-components are used to validate the proposed technique. Experimental results show good agreement with that of the proposed technique. © 2008 by Nova Science Publishers, Inc. All rights reserved.Publication Scanning moiré and phase shifting with time delay and integration imaging(1997-09-01) Sajan, M.R.; Tay, C.J.; Shang, H.M.; Asundi, A.; MECHANICAL & PRODUCTION ENGINEERINGScanning moiré is generated by undersampling of a phase-modulated grating pattern. In projection profilometry the scanning moiré pattern represents equal height and depth contours on a test object. By use of time delay and integration (TDI) imaging, it is possible to generate an on-line scanning moiré pattern from the complete periphery of a rotating cylindrical object. For automated phase and profile unwrapping from scanning moiré fringes, phase-shifting interferometry techniques are most desirable. However, lack of spatial information in the undersampled scanning moiré fringes introduces serious errors in phase unwrapping. We report a method that uses oversupply of data to balance the effect of undersampling. This oversupply is achieved with a TDI feature that permits programmable image magnification in the scanning direction. © 1997 Optical Society of America.Publication Measurements of surface coordinates and slopes by shearography(1992-08) Tay, C.J.; Shang, H.M.; Poo, A.N.; Luo, M.; MECHANICAL & PRODUCTION ENGINEERINGThis paper represents an optical method which is based on speckle-shearing interferometry for the measurement of surface coordinates and slopes. The technique enables generation of carrier fringes which measure surface coordinates, or displacement derivative fringes which measure surface slope. The theory of the method as well as some experimental results are presented. © 1992.Publication CONTACT PRESSURE SENSOR AND METHOD FOR MANUFACTURING THE SAME(2005-01-13) AKKIPEDDI, RAMAM; SPERRING, CHRISTOPHER PHILIP; TOH, SIEW LOK; TAY, CHO JUI; RAHMAN, MUSTAFIZUR; CHUA, SOO JIN; ELECTRICAL & COMPUTER ENGINEERING; MECHANICAL ENGINEERINGA contact pressure sensor (10) and method for manufacturing a contact pressure sensor for detecting contact pressure between two surfaces is disclosed. The contact pressure sensor disclosed comprises a substrate (40) for supporting the sensor and a contact pressure sensitive layer (26) sensitive to pressure applied to the contact pressure sensor. The method disclosed also comprises transferring a process post structure (8) that is formed on a first process support substrate (20) from the first process support substrate to a second contact pressure sensor support substrate (40).Publication Effect of phase-shifting error on deformation evaluation using phase-shifting digital holography(2006) Xin, K.; Xiaoyuan, H.; Tay, C.J.; Quan, C.; MECHANICAL ENGINEERINGPhase-shifting technique is an effect way to suppress the zero order diffraction and the conjugate term in digital holography. However the phase-shifting error will influence inevitably the evaluation precision in practice operation. In this paper, the deformation evaluation errors by means of two kinds of four-step phase-shifting algorithms, which are in common use in digital holography, are analyzed and compared by computer simulation. In addition, the phase-shifting errors may cumulate or not according to different phase-shifting techniques, and both cases are considered in this paper. The results based on the digital in-line holography show that the two four-step phase-shifting algorithms possess different sensitivity to the phase-shifting errors, and the preferable one, which is more immune to the phase-shifting errors, is educed in conclusion.Publication The use of carrier fringes and FFT in holographic nondestructive testing(2001-07) Quan, C.; Tay, C.J.; Shang, H.M.; MECHANICAL ENGINEERINGThe carrier fringe technique for holographic interferometry was discussed. The use of fast Fourier transforms (FFT) in the method enabled phase measurement from fringe patterns caused due to interference of tilted wavefronts. The FFT approach was used to extract deformation information automatically from complex interferograms and was shown to have considerable potential for solving images in its ability to extract data in the presence of pixel noise.Publication Measurement of transparent coating thickness by the use of white light interferometry(2005) Li, M.; Quan, C.; Tay, C.J.; Reading, I.; Wang, S.; MECHANICAL ENGINEERINGWhite light interferometry is widely used to measure surface profiles in order to overcome the phase ambiguity problem, which is inevitable in the monochromatic light interferometry. In this paper, we describe a white light interferometric technique to determine the thickness of transparent coating on a silicon substrate. The layer thickness is obtained by a straightforward subtraction of two surfaces in the coated layer. The surface information is extracted by the white light interferometric surface profiler developed in the proposed system. In the surface extraction, a digital filtering technique based on fast Fourier transform (FFT) is used to retrieve the envelopes of the interferograms, and then differential operation is implemented to determine the peaks of the envelopes. Experimental work conducted on a flat mirror surface demonstrates the feasibility of the proposed method with a measuring accuracy in the order of nanometers. Results also show that by the use of the proposed method the coating thickness in the order of micrometers can be extracted satisfactorily without phase ambiguity problem.Publication A new method for phase extraction from a single fringe pattern(2004-09-15) Tay, C.J.; Quan, C.; Yang, F.J.; He, X.Y.; MECHANICAL ENGINEERINGA new technique for phase extraction from a single fringe-pattern image is presented. The algorithm locates the fringe maxima (assigned value 1) and minima (assigned value - 1), and converts the intermediate gray-values into values between - 1 and 1 using linear interpolation. A wrapped phase map is demodulated from a single fringe-pattern and the phase values are computed using an atan mode rather than an atan2 mode. Using the new algorithm wrapped phase values can be efficiently extracted from a single fringe pattern without the need for phase-shifting or carrier fringes. Phase extraction is carried out without the need for assigning fringe orders and distinction for a peak and a trough. The method can be applied to the study of transient events. Experimental results are presented to demonstrate the validity of the method. © 2004 Elsevier B.V. All rights reserved.Publication Phase extraction from electronic speckle patterns by statistical analysis(2004-06-15) Tay, C.J.; Quan, C.; Chen, L.; Fu, Y.; MECHANICAL ENGINEERINGIn electronic speckle pattern interferometry (ESPI), speckles are information carriers as well as noise that hinders the extraction of high quality phase. This paper presents a phase extraction method based on the statistical property of speckles. Assuming that speckle related phase is a random variable having a uniform distribution, the grey level variance of a number of pixels is found to be related to the modulation intensity of a speckle pattern. The relation is used to establish a connection between the phase to be measured and the variance of grey level difference between two speckle patterns. Subsequently, a phase map wrapped in [0,π) is extracted. In order to obtain a standard 2π wrapped phase map, an initial one step phase shift is introduced. The phase value of a pixel under consideration is obtained from the grey levels of its N × N neighbouring pixels. The optimal value of N is obtained based on a qualitative analysis of the initial results. With an appropriate value of N, an accuracy of 1% can be achieved. © 2004 Elsevier B.V. All rights reserved.