Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
This article presents experimental characterization and numerical simulation techniques\nused to create large amplitude and high frequency surface waves with the help of a metal/ceramic\ncomposite transducer array. Four piezoelectric bimorph transducers are cascaded and operated in\na nonlinear regime, creating broad band resonant vibrations. The used metallic plate itself resembles\na movable wall which can align perfectly with an airfoil surface. A phase-shifted operation of\nthe actuators results in local displacements that generate a surface wave in the boundary layer\nfor an active turbulence control application. The primary focus of this article is actuator design\nand a systematic parameter variation experiment which helped optimize its nonlinear dynamics.\nFinite Element Model (FEM) simulations were performed for different design variants, with a primary\nfocus in particular on the minimization of bending stress seen directly on the piezo elements while\nachieving the highest possible deflection of the vibrating metallic plate. Large output force and\na small yield stress (leading to a relatively small output stoke) are characteristics intrinsic to the\nstiff piezo-ceramics. Optimized piezo thickness and its spatial distribution on the bending surface\nresulted in an efficient stress management within the bimorph design. Thus, our proposed resonant\ntransduction array achieved surface vibrations with a maximum peak-to-peak amplitude of 500 �¼m\nin a frequency range around 1200 Hz....
Rubberââ?¬â??steel-layered structures are used in many engineering applications. Laminated\nrubberââ?¬â??steel bearing, as a type of seismic isolation device, is one of the most important applications\nof the rubberââ?¬â??steel-layered structures. Interfacial debonding in rubberââ?¬â??steel-layered structures is a\ntypical failure mode, which can severely reduce their load-bearing capacity. In this paper, the authors\ndeveloped a simple but effective active sensing approach using embedded piezoceramic transducers\nto provide an in-situ detection of the interfacial debonding between the rubber layers and steel plates.\nA sandwiched rubberââ?¬â??steel-layered specimen, consisting of one rubber layer and two steel plates,\nwas fabricated as the test specimen. A novel installation technique, which allows the piezoceramic\ntransducers to be fully embedded into the steel plates without changing the geometry and the surface\nconditions of the plates, was also developed in this research. The active sensing approach, in which\ndesigned stress waves can propagate between a pair of the embedded piezoceramic transducers (one\nas an actuator and the other one as a sensor), was employed to detect the steelââ?¬â??rubber debonding.\nWhen the rubberââ?¬â??steel debonding occurs, the debonded interfaces will attenuate the propagating\nstress wave, so that the amplitude of the received signal will decrease. The rubberââ?¬â??steel debonding\nwas generated by pulling the two steel plates in opposite directions in a material-testing machine.\nThe changes of the received signal before and after the debonding were characterized in a time\ndomain and further quantified by using a wavelet packet-based energy index. Experiments on\nthe healthy rubberââ?¬â??steel-layered specimen reveal that the piezoceramic-induced stress wave can\npropagate through the rubber layer. The destructive test on the specimen demonstrates that the\npiezoceramic-based active sensing approach can effectively detect the rubberââ?¬â??steel debonding failure\nin real time. The active sensing approach is often used in structures with ââ?¬Å?hardââ?¬Â materials, such as\nsteel, concrete, and carbon fiber composites. This research lays a foundation for extending the active\nsensing approach to damage detection of structures involving ââ?¬Å?softââ?¬Â materials, such as rubber....
Cracks in oil and gas pipelines cause leakage which results in property damage,\nenvironmental pollution, and even personal injury or loss of lives. In this paper, an active-sensing\napproach was conducted to identify the crack damage in pipeline structure using a stress wave\npropagation approach with piezoceramic transducers. A pipeline segment instrumented with five\ndistributed piezoceramic transducers was used as the testing specimen in this research. Four cracks\nwere artificially cut on the specimen, and each crack had six damage cases corresponding to different\ncrack depths. In this way, cracks at different locations with different damage degrees were simulated.\nIn each damage case, one piezoceramic transducer was used as an actuator to generate a stress wave\nto propagate along the pipeline specimen, and the other piezoceramic transducers were used as\nsensors to detect the wave responses. To quantitatively evaluate the crack damage status, a wavelet\npacket-based damage index matrix was developed. Experimental results show that the proposed\nmethod can evaluate the crack severity and estimate the crack location in the pipeline structure\nbased on the proposed damage index matrix. The sensitivity of the proposed method decreases with\nincreasing distance between the crack and the mounted piezoceramic transducers....
Circular piezoelectric transducers with axial polarization are proposed as low frequency acoustic sensors for dark matter bubble\nchamber detectors.The axial vibration behaviour of the transducer is studied by three different methods: analytical models, FEM\nsimulation, and experimental setup. To optimize disk geometry for this application, the dependence of the vibrational modes\nin function of the diameter-to-thickness ratio from 0.5 (a tall cylinder) to 20.0 (a thin disk) has been studied. Resonant and\nantiresonant frequencies for each of the lowest modes are determined and electromechanical coupling coefficients are calculated.\nFrom this analysis, due to the requirements of radiopurity and little volume, optimal diameter-to-thickness ratios for good\ntransducer performance are discussed...
This article presents design, fabrication and characterization of lead zirconate titanate\n(PZT)-actuated micromirrors, which enable extremely large scan angle of up to 106ââ??¦ and high\nfrequency of 45 kHz simultaneously. Besides the high driving torque delivered by PZT actuators,\nmechanical leverage amplification has been applied for the micromirrors in this work to reach large\ndisplacements consuming low power. Additionally, fracture strength and failure behavior of poly-Si,\nwhich is the basic material of the micromirrors, have been studied to optimize the designs and\nprevent the device from breaking due to high mechanical stress. Since comparing to using biaxial\nmicromirror, realization of biaxial scanning using two independent single-axial micromirrors shows\nconsiderable advantages, a setup combining two single-axial micromirrors for biaxial scanning and\nthe results will also be presented in this work. Moreover, integrated piezoelectric position sensors\nare implemented within the micromirrors, based on which closed-loop control has been developed\nand studied....
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