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ABSTRACT: We propose a MEMS piezoelectric energy harvester with a wide operating frequency range by incorporating a high-frequency piezoelectric
cantilever and a metal base as the top and bottom stoppers with a low-frequency piezoelectric cantilever. Frequency up-conversion
of the piezoelectric energy harvester is realized when the low-frequency piezoelectric cantilever impacts and scrapes through
the high-frequency piezoelectric cantilever. For an input acceleration of 0.6g, with top and bottom stopper distances of
0.75 and 1.1mm, respectively, the operating frequency ranges from 33 to 43Hz. The output voltage and power up to 95mV and
94 nW can be achieved. Experimental results indicate that the frequency up-conversion mechanism significantly improves the
effective power.
Microsystem Technologies 05/2012; 17(12):1747-1754. · 0.93 Impact Factor
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ABSTRACT: Structured-light profilometry is a powerful tool to reconstruct the three-dimensional (3D) profile of an object. Accurate profile acquisition is often hindered by not only the nonlinear response (i.e., gamma effect) of electronic devices but also the projection-imaging distortion of lens used in the system. In this paper, a flexible 3D profile reconstruction method based on a nonlinear iterative optimization is proposed to correct the errors caused by the lens distortion. It can be easily extended to measurements for which a more complex projection-imaging distortion model is required. Experimental work shows that the root-mean-square (RMS) error is reduced by eight times and highly accurate results with errors of less than 1‰ can be achieved by the proposed method.
Applied Optics 05/2012; 51(13):2419-28. · 1.41 Impact Factor
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ABSTRACT: This paper presents the design, microfabrication, modeling and characterization of a piezoelectric energy harvester (PEH) system with a wide operating bandwidth introduced by mechanical stoppers. The wideband frequency responses of the PEH system with stoppers on one side and two sides are investigated thoroughly. The experimental results show that the operating bandwidth is broadened to 18 Hz (30–48 Hz) and the corresponding optimal power ranges from 34 to 100 nW at the base acceleration of 0.6g and under top- and bottom-stopper distances of 0.75 mm and 1.1 mm, respectively. By adjusting the mechanical stopper distance, the output power and frequency bandwidth can be optimized accordingly.
Smart Materials and Structures 02/2012; 21(3):035005. · 2.09 Impact Factor
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ABSTRACT: A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design.
Journal of Microelectromechanical Systems 11/2011; · 2.10 Impact Factor
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ABSTRACT: White-light scanning interferometry (WLSI) is a useful technique to measure surface profile when a test object contains discontinuous structures or microstructures. A black and white CCD camera is usually utilized to capture interferograms, and a series of corresponding algorithms is used to achieve the profile measurement. However, the color information in the interferograms is lost. A novel profile measurement method that uses phase information in different color channels (red-green-blue) of an interferogram obtained using a three-chip color CCD in WLSI is proposed. The phase values are extracted by a windowed Fourier transform algorithm. Simulation and experimental results are presented to demonstrate the validity of the proposed method.
Applied Optics 05/2011; 50(15):2246-54. · 1.41 Impact Factor
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ABSTRACT: A Michelson-type digital speckle photographic system has been proposed in which one light beam produces a Fourier transform and another beam produces an image at a recording plane, without interfering between themselves. Because the optical Fourier transform is insensitive to translation and the imaging technique is insensitive to tilt, the proposed system is able to simultaneously and independently determine both surface tilt and translation by two separate recordings, one before and another after the surface motion, without the need to obtain solutions for simultaneous equations. Experimental results are presented to verify the theoretical analysis.
Applied Optics 06/2010; 49(18):3573-9. · 1.41 Impact Factor
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ABSTRACT: In this paper, we propose a method for optical image encryption based on fractional Fourier transform (FRFT) and Arnold transform (ART) in phase-shifting digital holography. An input image is first divided into eight bit planes, and each bit plane is encrypted based on double random-phase masks and FRFT. Complex amplitude for the object is retrieved by phase-shifting digital holography in the hologram plane. The real and imaginary parts of the retrieved complex amplitudes for the 0th-7th bit planes are further encrypted using ART algorithm. Numerical results are shown to demonstrate the feasibility and effectiveness of the proposed technique. The sensitivity of security parameters, such as function orders in FRFT and iteration number in ART method, is also analyzed.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
12/2009;
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ABSTRACT: We propose a method to extend the depth of focus in a particle field measurement using a single-shot digital hologram. A focal plane is obtained for each pixel based on an entropy method, and a depth map is subsequently extracted. A synthesized extended focused image is determined correspondingly using the extracted depth map. In addition, a wavelet modulus maxima algorithm and Canny algorithm are further employed to detect the edges of each particle, and the sizes and a three-dimensional localization of the particles are also estimated. Preliminary results are presented to show the feasibility and effectiveness of the proposed technique.
Applied Physics Letters 11/2009; 95(20):201103-201103-3. · 3.84 Impact Factor
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ABSTRACT: Measurement of curvature and twist is an important aspect in the study of object deformation. In recent years, several methods have been proposed to determine curvature and twist of a deformed object using digital shearography. Here we propose a novel method to determine the curvature and twist of a deformed object using digital holography and a complex phasor. A sine/cosine transformation method and two-dimensional short time Fourier transform are proposed subsequently to process the wrapped phase maps. It is shown that high-quality phase maps corresponding to curvature and twist can be obtained. An experiment is conducted to demonstrate the validity of the proposed method.
Applied Optics 06/2008; 47(15):2874-81. · 1.41 Impact Factor
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ABSTRACT: A novel method that uses a two-dimensional (2D) digital image correlation (DIC) based on a single CCD camera to measure three-dimensional (3D) displacement and deformation is proposed. Rigid-body displacement in 3D space consists of both in-plane and out-of-plane components. The presence of an in-plane displacement component results in a shift of the center of the image displacement vector, while the slope of the image displacement vector is related to the out-of-plane displacement component. Global DIC is employed to determine the displaced position of each point on an object based on a linear distribution characteristic of the displacement vector. Speckle images with deformation introduced by 3D displacement are generated to demonstrate the feasibility of the proposed method. In the 3D rigid-body displacement, both in-plane and out-of-plane displacement components are separated by determining the intercept and slope of the image displacement vector. In the 3D deformation, a zero order displacement (pure rigid-body displacement) mode is assumed in a small subset of pixels. Simulated and experimental results demonstrate that both in-plane and out-of-plane displacements can be accurately retrieved using the proposed method.
Applied Optics 03/2008; 47(4):583-93. · 1.41 Impact Factor
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ABSTRACT: Recent advances in high-speed networks have made micro-electro-mechanical systems (MEMS) find some niche applications in tunable optical devices. Indium phosphide (InP)-based MEMS have an inherent advantage of being direct band gap as compared to silicon and can thus be used in MEMS structures with light emission/detection capability. In this paper, we report an in-depth study using nanoindentation to determine the mechanical properties of InP free-standing structures that could be incorporated in optical MEMS. The fabrication process for InP-based cantilever beams and membranes is also reported. Young's modulus of the material is determined from both loading and unloading of the InP cantilever beam through a bending test. We also discuss the deformation behaviour of the InP cantilever beam. Indentation on an InP substrate was conducted using a spherical indenter of known radius, in addition to the conventional Berkovich tip. The results were compared with ideal analytical methods. Experiments were also carried out to determine Young's modulus and hardness using continuous stiffness mode (CSM) tests. In addition, as a benchmark, experiments on silicon and sapphire substrates are also discussed. The results show good agreement in the mechanical properties obtained through different experiments.
Journal of Micromechanics and Microengineering 01/2008; 18(2):025015. · 2.11 Impact Factor
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ABSTRACT: We describe a novel method of processing complex phasors in digital holographic interferometry (DHI). Unlike the commonly used digital phase subtraction method that operates on the phase itself, the proposed method operates on the complex phasor instead. Two temporal phase retrieval algorithms are developed in which the complex phasor of each pixel is measured and analyzed as a function of time. The developed algorithms are demonstrated in profile measurement of step heights. Experimental results show that the proposed phase retrieval algorithms for DHI perform well compared with conventional methods.
Optics Letters 07/2007; 32(12):1602-4. · 3.40 Impact Factor
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ABSTRACT: Digital image correlation (DIC) is commonly used to measure specimen displacements by correlating an image of a specimen in an undeformed or reference configuration and a second image under load. To establish the correlation between the images, numerical techniques are used to locate an initially square image subset in a reference image. In this process, choosing appropriate coordinates is of fundamental importance to ensure accurate results. Both global and local coordinates can be used in shape functions. However, large rigid body rotations and deformations are accurately obtained by using global rather than local shape functions. In addition, points located after displacement may not be at an integer pixel distance from the original position. Hence subpixel displacement estimation methods such as interpolation or fitting of correlation coefficients are essential. A solution using the least-squares method is employed by choosing proper coordinates, and the feasibility of using local coordinates is demonstrated and validated with a mathematical model. Both simulated and experimental results show that the proper choice of coordinates does ensure the reliability and improve the accuracy of measurements in DIC.
Applied Optics 04/2007; 46(7):1050-6. · 1.41 Impact Factor
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ABSTRACT: In fringe projection profilometry, an object shape is evaluated through phase distribution extracted from a projected fringe pattern. For parallel illumination geometry, the carrier phase component introduced by the fringes is spatially linear, whereas nonparallel illumination would lead to a nonlinear carrier. In this study, a general approach for the removal of a nonlinear-carrier phase component is proposed. A series expansion technique is used to approximate the carrier phase function, and a least-squares method is developed to estimate the unknown coefficients of the series. The theoretical analysis is given on the basis of a divergent illumination geometry with carrier fringes in the x direction. The method is also extended to include a curved surface-fitting approach, which is applicable to various measurement system geometries.
Journal of the Optical Society of America A 03/2006; 23(2):435-43. · 1.56 Impact Factor
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ABSTRACT: A new technique based on digital shearography for determining the transient curvature and twist of a continuously deforming object from a series of speckle patterns is presented. The intensity variation of each pixel is analyzed along the time axis by using a complex Morlet wavelet transform. The absolute sign of the phase variation is determined by introduction of a temporal carrier when the speckle patterns are captured by a high-speed camera. A high-quality spatial distribution of the deflection derivative is extracted at any instant without the need for temporal or spatial phase unwrapping. The continuous Haar wavelet transform is subsequently processed as a differentiation operator to reconstruct the instantaneous curvature and twist of a continuously deforming object.
Optics Letters 12/2005; 30(21):2873-5. · 3.40 Impact Factor
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ABSTRACT: A method for automatic phase extraction from a single fringe pattern based on the guidance of an extreme map is introduced. The method uses an adaptive weighted filter to reduce noise and enhance contrast and to locate the fringe extremes. Wrapped phase values are calculated by use of an arccosine function obtained from the extreme map. With this method, wrapped phase values can be efficiently demodulated from a single fringe pattern without the need for assigning fringe order or interpolating fractional fringe order. The validity of the method is demonstrated by use of closed-fringe patterns generated by digital speckle interferometry.
Applied Optics 09/2005; 44(23):4814-21. · 1.41 Impact Factor
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ABSTRACT: A temporal wavelet analysis algorithm is proposed for shadow-moiré-based three-dimensional surface profiling on objects having discontinuous height steps. A grating is positioned close to an object, and its shadow is observed through the grating. The moiré fringe patterns vary when the grating is in-plane rotating. A series of fringe patterns are captured by a CCD camera at different rotating angles. Phase values are evaluated point by point with the continuous wavelet transform. From the phase values of each point on the object, the distance between the object and the grating can be retrieved. The surface profile is obtained without temporal or spatial phase unwrapping. This technique is applicable to objects with discontinuous height steps, which are impossible to measure with conventional shadow moiré topography. Two specimens are tested to demonstrate the validity of the method: One is an object with a height step of 1.6 mm, and another is a small coin with unevenness of less than 0.2 mm. The experimental results are compared with test results by use of the mechanical stylus method.
Applied Optics 07/2005; 44(16):3284-90. · 1.41 Impact Factor
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ABSTRACT: Talbot interferometry is used to study the surface profile of a transparent object. Periodic patterns are produced by illuminating a grating with a collimated laser beam. The object is placed on the self-image plane of the grating. The deformed grating image, which interferes with another grating, results in the Talbot interferometric fringes. The fringe pattern is recorded on a CCD camera for subsequent analysis, and the phase variation is achieved by a linear translation stage. In this application two specimens are tested to demonstrate the validity of the method; one is a transparent object with a spherical shape with a height of less than 350 microm, and the other is a transparent object with an uneven surface of 50-microm average height. The experimental results are compared with the test results obtained with the mechanical stylus method.
Applied Optics 06/2005; 44(13):2541-5. · 1.41 Impact Factor
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ABSTRACT: For many phase extraction algorithms, a priori knowledge of a fringe-pattern density distribution is beneficial for later processing. A fringe-density estimation method based on a continuous wavelet transform (CWT) is proposed. For a one-dimensional signal the instantaneous frequency detected at the CWT ridge is directly adopted as a measure of the local fringe density. For a two-dimensional signal the instantaneous frequency components in both the x and the y directions are detected. Their reliability is evaluated by the CWT coefficient magnitude, based on which an approximate density value is given. The capability for noise reduction and the accuracy of the method are discussed.
Applied Optics 05/2005; 44(12):2359-65. · 1.41 Impact Factor
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ABSTRACT: A grating projection system is a low-cost surface contour measurement technique that can be applied to a wide range of applications. There has been a resurgence of interest in the technique in recent years because of developments in computer hardware and image processing algorithms. We describe a method that projects a phase-shifted grating through a lens on an object surface. The deformed grating image on the object surface is captured by a CCD camera for subsequent analysis. Phase variation is achieved by a linear translation stage on which the grating is mounted. We compare the experimental results with the test results using a mechanical stylus method.
Applied Optics 04/2005; 44(8):1393-400. · 1.41 Impact Factor
