Investigation of membrane deformation by a fringe projection method.
TL;DR: An optical method has been developed to measure the deformation of a membrane in a microphone with the aid of a phase-shifting technique and signal-demodulating techniques, capable of measuringDeformation of the membrane of the order of as much as submicrometers.
Abstract: An optical method has been developed to measure the deformation of a membrane in a microphone. A fringe projector that consists of an optical fiber and an optical wedge is described and analyzed by geometric optics. A three-step phase-shifting technique that involves the introduction of an arbitrary phase is discussed. The fine fringe patterns projected onto a small test surface are captured by a CCD camera mounted on a long-distance microscope. With the aid of a phase-shifting technique and signal-demodulating techniques, the proposed setup is capable of measuring deformation of the membrane of the order of as much as submicrometers.
Citations
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TL;DR: In this paper, a digital fringe projection technique was used to measure surface topography of the powder bed layers during the fabrication process and observed the types of information that can be extracted from such topographical data.
Abstract: Being able to characterize the process signatures of powder bed based additive manufacturing process is key to improving the product quality. This paper demonstrates the implementation of a digital fringe projection technique to measure surface topography of the powder bed layers during the fabrication. We focus on developing the metrology tool and observing the types of information that can be extracted from such topographical data. The performance of the system is demonstrated with selected in situ measurements. Experimental results show this system is capable of measuring powder bed signatures including the powder layer flatness, surface texture, the average height drop of the fused regions, characteristic length scales on the surface, and splatter drop location and dimension.
104 citations
TL;DR: This article analyzes the measurement performance of a 3D full-field imaging system based on the projection of grating and active triangulation and investigates in detail the influence on the measurement results of the introduction of an inaccuracy into the determination of the system's parameters.
63 citations
TL;DR: Based on speckle projection, a system for deformation measurement is developed with the telecentric lens and an effective calibration method is presented in detail.
42 citations
TL;DR: A laser interferometric system in which two objectives are used to measure surface profile on a connectorized fiber-end surface and the accuracy of the proposed setup is comparable with that of existing white-light interferometers and stylus profilometers.
Abstract: We describe a laser interferometric system in which two objectives are used to measure surface profile on a connectorized fiber-end surface. By the use of the proposed illumination design a He-Ne laser as a point light source is transformed to an extended light source, which is beneficial to localize interference fringe pattern near the test surface. To obtain an optimal contrast of the interference fringe pattern, the flat mirror with an adjustable reflection ratio is used to suit different test surfaces. A piezoelectric transducer attached on the reference mirror can move precisely along the optical axis of the objective and permits implementation of four-step phase-shifting interferometry without changing the relative position between the CCD sensor and the test surface. Therefore, an absolutely constant optical magnification can be accurately kept to capture the interference fringe patterns resulting from a combination of light reflected from both the reference flat mirror and the test surface. The experimental result shows that surface profile on a fiber-end with surface features such as a small fiber diameter of 125 μm and a low reflection ratio of less than 4% are measurable. Measurements on a standard calibration ball show that the accuracy of the proposed setup is comparable with that of existing white-light interferometers and stylus profilometers.
24 citations
TL;DR: In this paper, a DVD optical head was used for the dynamic characterization of the vertical displacement of MEMS structures, and a small silicon cantilever array was designed and fabricated via a commercially available multi-user polysilicon surface micromachining process (PolyMUMPs).
Abstract: Taking advantage of an off-the-shelf, high-quality but inexpensive optical detector, namely a DVD optical head, a system has been developed for the dynamic characterization of the vertical (out-of-plane) displacement of MEMS structures. The novelty of the proposed setup, besides the proposed field of application, lies in the ability of the system to operate both in air and in a liquid environment. In order to give a representative experimental proof of the functionality of the system, a cantilever array was designed and fabricated via a commercially available multi-user polysilicon surface micromachining process (PolyMUMPs). The frequency response of a tiny silicon cantilever beam (150 µm length, 10 µm width and 1.5 µm thickness) was measured, both in air and in deionized water, and compared against theoretical models of the system. Despite the low-cost signal conditioning system used, it was possible to trace a very clear Bode plot, and to obtain good agreement between experimental data and theoretical predictions. The measurements indicate that this displacement sensor performs very well under many circumstances of interest which require continuous monitoring with large bandwidth. This sensor offers a good low-cost measurement solution for the single-point dynamic characterization of the MEMS devices, particularly when the frequencies involved are high and the working environment is unsuitable for other types of detectors.
23 citations
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TL;DR: One application of phase-shifting techniques to speckle interferometry is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured.
Abstract: Speckle patterns have high frequency phase data, which make it difficult to find the absolute phase of a single speckle pattern; however, the phase of the difference between two correlated speckle patterns can be determined. This is done by applying phase-shifting techniques to speckle interferometry, which will quantitatively determine the phase of double-exposure speckle measurements. The technique uses computer control to take data and calculate phase without an intermediate recording step. The randomness of the speckle causes noisy data points which are removed by data processing routines. One application of this technique is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured. Results of deformations caused by tilt of a metal plate and a disbond in a honeycomb structure brazed to an aluminum plate are shown.
740 citations
TL;DR: In this paper, it was shown that integration of a capacitive microphone and a preamplifier will result in a further reduction of the noise level of the FET microphone.
Abstract: Silicon micromachining has successfully been applied to fabricate piezoelectric, piezoresistive and capactive microphones. The use of silicon has allowed the fabrication of microphones with integrated electronic circuitry and the development of the new FET microphone. The introduction of lithographic techniques has resulted in microphones with very small (1 mm2) diaphragms and with specially shaped backplates. The application of corrugated diaphragms seems a promising future development for silicon microphones. It is concluded from a noise consideration that the FET microphone shows a high noise level, which is mainly due to the small sensor capacitance. From this noise consideration, it can be shown that integration of a capacitive microphone and a preamplifier will result in a further reduction of the noise.
374 citations
TL;DR: Contouring speed, limited only by the frame rate of the camera, can be dramatically increased as compared to that of the traditional phase-shifting techniques.
Abstract: A color-encoded digital fringe projection technique is proposed for high-speed 3-D surface contouring applications. in this technique, a color fringe pattern whose RGB components comprise three phase-shifted fringe patterns is created by software on a computer screen and then projected to an object by a novel computer-controlled digital projection system. The image of the object is captured by a digital camera positioned at an angle different from that of the projection system. The image is then separated into its RGB components, creating three phase-shifted images of the object. These three images are used to retrieve the 3-D surface contour of the object through the use of a phase wrapping and unwrapping algorithm. Only one image of the object is required to obtain the 3-D surface contour of the object. Thus contouring speed, limited only by the frame rate of the camera, can be dramatically increased as compared to that of the traditional phase-shifting techniques. The technique is especially useful in applications where the object being contoured is going through quasi-static or dynamic changes. The principle of the technique is described and some preliminary experimental results are presented.
318 citations
TL;DR: A detailed analysis of the applied phase evaluation algorithm as function of the number of steps, N, is given and the alternating feature of the phase measurement precision ϵ(N), which lead to the obvious choice of seven or five steps, is demonstrated.
282 citations
TL;DR: A new type of moiré and its application to topography are discussed and the fact that a contour line system and a sectional shape of the object are automatically reconstructed and displayed on a color TV monitor is very significant.
Abstract: A new type of moire and its application to topography are discussed. moire fringes are generated by observing a grating projected on an object under test with a scanning imaging device. The general equations of the projection-type moire topography are given. By controlling the phase, the pitch, or the direction of the virtual grating corresponding to the scanning lines of the imaging device, the automatic sign determination of the contour lines is accomplished. By the use of a high precision flying spot scanner with CRT(DD-tube) and a minicomputer system, an experimental measurement system is developed. Very significant is the fact that a contour line system and a sectional shape of the object are automatically reconstructed and displayed on a color TV monitor.
253 citations