"Effective" electromechanical coupling coefficient for IPMC by equivalent bimorph beam model is studied. The
collective effect of the membrane thickness and operating voltage is demonstrated by using a design of experiment of
three and four levels of the two factors, respectively. Experiments and finite element analyses using MSC.NASTRAN
are used to evaluate the tip displacement and the coupling coefficient for which approximations as function of the
thickness and voltage are constructed. Initial curvature of the strips before electrical excitation is also shown to be a
factor in "effective" coupling coefficient. A correction factor approach is proposed to include the effect of the preimposed
curvature.
This work aimed at fabrication and electromechanical characterization of a smart material system composed of
electroactive polymer and ceramic materials. The idea of composite material system is on account of complementary
characteristics of the polymer and ceramic for flexibility and piezoelectric activity. Our preliminary work included
Polyvinylidene Fluoride (PVDF) as the flexible piezoelectric polymer, and Zinc Oxide (ZnO) as the piezoelectric
ceramic brittle, but capable to respond strains without poling. Two alternative processes were investigated. The first
process makes use of ZnO fibrous formation achieved by sintering PVA/zinc acetate precursor fibers via
electrospinning. Highly brittle fibrous ZnO mat was dipped into a PVDF polymer solution and then pressed to form
pellets. The second process employed commercial ZnO nanopowder material. The powder was mixed into a
PVDF/acetone polymer solution, and the resultant paste was pressed to form pellets. The free standing composite pellets
with electrodes on the top and bottom surfaces were then subjected to sinusoidal electric excitation and response was
recorded using a fotonic sensor. An earlier work on electrospun PVDF fiber mats was also summarized here and the
electromechanical characterization is reported.
This paper presents the modeling and design optimization of a micromachined floating element piezoresistive shear stress sensor for the time-resolved, direct measurement of fluctuating wall shear stress in a turbulent flow. The sensor structure integrates side-implanted diffused resistors into the silicon tethers for piezoresistive detection. A theoretical nonlinear mechanical model is combined with a piezoresistive model to determine the electromechanical sensitivity. Lumped element modeling (LEM) is used to estimate the resonant frequency. Finite element modeling is employed to verify the mechanical models and LEM results. Two dominant noise sources, 1/f noise and thermal noise, were considered to determine the noise floor. These models were then leveraged to obtain optimal sensor designs for several sets of specifications. The cost function is the minimum detectable shear stress that is formulated in terms of sensitivity and noise floor. This cost function is subjected to the constraints of geometry, linearity, bandwidth, power and resistance. The results indicate the possibility of designs possessing dynamic ranges of greater than 85dB.
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