Vision-based measurement methods were used to measure bubble sizes in this sonoluminescence experiment. Bubble imaging was accomplished by placing the bubble between a bright light source and a microscope-CCD
camera system. A collimated light-emitting diode was operated in a pulsed mode with an adjustable time delay with respect to the piezo-electric transducer drive signal. The light-emitting diode produced a bubble shadowgraph consisting of a multiple exposure made by numerous light pulses imaged onto a charge-couple device camera. Each image was transferred from the camera to a computer-controlled machine vision system via a frame grabber. The frame grabber was equipped with on-board memory to accommodate sequential image buffering while images were transferred to the host processor and analyzed. This configuration allowed the host computer to perform diameter
measurements, centroid position measurements and shape estimation in "real-time" as the next image was being acquired. Bubble size measurement accuracy with an uncertainty of 3 microns was achieved using standard lenses and machine vision algorithms. Bubble centroid position accuracy was also within the 3 micron tolerance of the
vision system. This uncertainty estimation accounted for the optical spatial resolution, digitization errors and the edge detection algorithm accuracy. The vision algorithms include camera calibration, thresholding, edge detection, edge position determination, distance between two edges computations and centroid position computations.
This paper describes the study of wavelet-based methods employed to de-noise a force transducer signal. This signal was extracted during the extensional deformation of a non-Newtonian polymer fluid. The non-Newtonian polymeric fluid was extensionally deformed with an exponentially increasing velocity profile. This velocity profile corresponded to a specific strain rate. Since the motion was stopped quickly (deceleration time was below 50ms for a complete stop), a serious problem of ringing occurred for approximately one second after the motion has ceased. The ringing manifested itself as a damped harmonic oscillation, which overrides the relaxation characteristics of the molecular structure within the boger fluid. In this paper, our goal was to suppress the damped harmonic oscillatory signal while preserving the relaxation characteristics (decaying exponential signal) of the force data. Several wavelet-based techniques provided acceptable noise suppression while preserving the signal of interest.
In this paper, we describe the design and development of a high sensitivity, large dynamic range force transducer capable of measuring transient force changes in tension and compression. Conventional force transducers typically rely on the deformation of strain gauges, or on servo-mechanical load cells. While strain gauge transducers exhibit a rapid response time, they are subject to electrical noise, and typically have a minimum useful limit of approximately 10-5 N. Servo-mechanical transducers have poor response times and exhibit compliance in the axis of deformation that is unacceptable for many applications. The research objective is to develop a novel force transducer based on the change in optical properties with loading of a pre-stressed polymer. The concept utilizes a pre-stressed polymer material as a linkage to which a force would be applied either in compression or tension. The molecular deformation of the polymer linkage will be analyzed using miniature optical components arranged as a phase-modulated polarimeter capable of birefringence measurements on the order of 10-9. Calibration of the measured birefringence with known loads provides the necessary calibration parameters. The instrument is capable of directional force measurements and is extremely accurate for measuring low-level forces. Since the force transducer is based on optical techniques, it would be resistant to electronic noise, and would allow measurement of rapidly changing loads. The best available force transducers capable of measuring transient responses have a lower resolution of approximately 10-5 N. Research with the rheology of fluids, transient flows of pharmaceuticals in combinatorial research, biological tissue response, and biomimetic adhesive research often require force measurements below this range. Although ultra-microbalances exist that have sensitivities well below this range, the averaging techniques employed that allow these measurements make them unsuitable for transient flows, as does the physical size of the systems.
12 We have assembled and used several different phase-modulated optical polarimeters to measure transient retardance and molecular orientation angle in complex fluids and materials. The main difference in the instrumentation of the polarimeters lies in their modulation technique. Three different phase modulation techniques were used. These included techniques incorporating photoelastic, electro- optic and liquid crystal elements as the modulation source. The precise measurement of a material's retardance and average molecular orientation angle depends on an accurate calibration within the modulation range. In this paper, we address some of the problems associated with phase-modulated polarimeter calibration and techniques used to overcome them.
We have developed an instrument that measures fast transient birefringence and polymer chain orientation angle in complex fluids. This instrument uses a dual-crystal transverse Electro-Optic modulator with second crystal's modulation voltage applied 180 degree(s) out of phase from that of the first crystal. The precise measurement of birefringence using this instrument strictly depends on three separate signals. These are the dc, first and second harmonic voltages. The harmonics are relatively noise-free while the dc signal is subject to appreciable noise. Therefore, wavelet based noise reduction techniques have been used to denoise the measured dc signal. The de-noised signal was recombined with the harmonic signals to obtain retardation and birefringence measurements using a high precision 1/16 wave plate in a rotating mount to simulate a birefringence sample.
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