Many structural systems, such as aircraft, orbital infrastructure, and energy harvesting devices, experience dynamic forces along with changing structural boundary conditions. Collecting and analyzing data on these systems provides useful insight that aids design, evaluation, and function. For real-time decision-making on systems experiencing high-rate changes, completing assessments quickly enough to be relevant poses a unique set of challenges. In systems sufficiently understood and well defined, determining a system's state that experiences high-rate structural boundary condition changes can be accomplished by monitoring its frequency response. In this work, methods of frequency detection applicable to real-time state estimation of structures experiencing high-rate boundary changes were investigated; progress and findings in extracting the frequency response of a structure in real-time are presented here. A novel Delayed Comparison Error Minimization technique is presented and experimentally validated using the DROPBEAR experimental testbed at the Air Force Research Laboratory. This testbench consists of an oscillating beam with one end fixed and roller support that can move along the beam's length. Real-time estimation of pin location through the measurement of beam motion was performed using the novel Delayed Comparison Error Minimization technique. Results are compared against an FFT-based method with a variety of window lengths. The latency and precision of this method are analyzed, and the results from each method are compared, with a discussion on the applicability of each method.
In elastic dielectrics, piezoelectricity is the polarization response to applied mechanical strain, and vice versa. Piezoelectric coupling is controlled by a third-rank tensor and is allowed only in materials that are non-centrosymmetric. Flexoelectricity, however, is the generation of electric polarization by the application of a non-uniform mechanical strain field, i.e. a strain gradient, and is expected to be pronounced at submicron thickness levels, especially at the nanoscale. Flexoelectricity is controlled by a fourth-rank tensor and is therefore allowed in materials of any symmetry. In this work, we explore the effects of varying crosssection and axial strain gradient on bending vibrations on flexoelectric cantilevers. The focus is placed on the development of governing electroelastodynamic flexoelectric equations for a cantilever with varying cross-sectional widths for energy harvesting. The coupled governing equations are analyzed to obtain the frequency response and study the effects of various axial geometry profiles on the electromechanical coupling. The effect of axial strain gradient was also studied and found to be negligible for the geometries and various cross-sections studied here. Varying cross-section profile (with a reduced tip width) yields increased flexoelectric coupling.
In elastic dielectrics, piezoelectricity is the response of polarization to applied mechanical strain,
and vice versa. Piezoelectric coupling is controlled by a third-rank tensor and is allowed only in materials
that are non-centrosymmetric. Flexoelectricity, however, is the generation of electric polarization by the
application of a non-uniform mechanical strain field, i.e. a strain gradient, and is expected to be pronounced
at submicron thickness levels, especially at the nano-scale. Flexoelectricity is controlled by a fourth-rank
tensor and is therefore allowed in materials of any symmetry. As a gradient effect, flexoelectricity is size
dependent, while piezoelectric coupling has no size dependence. Any ordinary piezoelectric cantilever
model developed for devices above micron-level thickness has to be modified for nano-scale piezoelectric
devices since the effect of flexoelectric coupling will change the electroelastic dynamics at such small
scales. In this work, we establish and explore a complete analytical framework by accounting for both the
piezoelectric and flexoelectric effects. The focus is placed on the development of governing electroelastodynamic
piezoelectric-flexoelectric equations for the problems of energy harvesting, sensing, and
actuation. The coupled governing equations are analyzed to obtain the frequency response. The coupling
coefficient for the bimorph configuration is identified and its size dependence is explored.
Intentionally designed nonlinearities have been employed by several research groups to enhance the frequency bandwidth of vibration energy harvesters. Another type of nonlinear resonance behavior emerges from the piezoelectric constitutive behavior for high excitation levels and is manifested in the form of softening stiffness. This material nonlinearity does not result in the jump phenomenon in soft piezoelectric ceramics, e.g. PZT-5A and PZT-5H, due to their large internal dissipation. This paper explores the potential for wideband energy harvesting using a hard (relatively high quality factor) PZT-8 bimorph by exploiting its material softening. A wide range of base excitation experiments conducted for a set of resistive electrical loads confirms the frequency bandwidth enhancement.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.