| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | April 7, 2015 |
| Latest Amendment Date: | April 7, 2015 |
| Award Number: | 1463339 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Robert Landers
CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | June 1, 2015 |
| End Date: | May 31, 2019 (Estimated) |
| Total Intended Award Amount: | $377,829.00 |
| Total Awarded Amount to Date: | $377,829.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
926 DALNEY ST NW ATLANTA GA US 30318-6395 (404)894-4819 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
225 North Ave NW Atlanta GA US 30332-0002 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Dynamics, Control and System D |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
Small sensors -- at the micro or nanoscale -- promise to extend human perception to extreme and previously inaccessible environments. How will these next-generation stand-alone sensor systems be powered? Many existing solutions use piezoelectric materials to convert mechanical vibration into electricity. However, only a small class of materials exhibits practically useful levels of this form of electromechanical coupling, and those typically lose their piezoelectricity at higher temperatures. This precludes their use in precisely the environments where the new classes of sensors are needed most. Furthermore, the highest performing piezoelectric materials contain lead, which creates manufacturing and disposal hazards. This project investigates generation of electricity by an entirely different phenomenon, called flexoelectricity. Unlike piezoelectricity, flexoelectricity is present in all dielectric solids, and thus offers an environmentally compatible alternative to piezoelectrics. This project combines complementary computational and experimental research studies to explore and understand flexoelectricity from atomistic scales to the device level. This work will enable a novel framework for the dramatically enhanced performance of energy harvesting devices.
This collaborative research program combines atomistic and continuum electroelastic modeling, nonlinear dynamic phenomena, nanofabrication, multi-scale experiments, and device characterization to facilitate the establishment of a novel class of revolutionary self-powered sensors and sensing systems at small scales. By bridging the atomistic and continuum theories with rigorous experiments, a fully coupled flexoelectric energy harvester framework will be established to explore the scaling laws for conversion efficiency and power density. For high excitation levels, nonlinear elastic, electroelastic, and dissipative effects in flexoelectric energy harvesting will also be characterized. Based on this fundamentally transformative approach to electromechanical energy harvesting, atomistic modeling of flexoelectricity and continuum-based energy harvesting models will be synergistically coupled with experiments to establish next-generation energy harvesters. Both linear and nonlinear broadband architectures will be explored for harvesting deterministic and stochastic vibrational energy. This research will also establish a framework and thorough understanding of the electroelastic dynamics of nanostructures for use in a variety of other problems involving two-way electromechanical coupling (e.g. sensing, actuation, control) at submicron scales.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
- An analytical framework was developed and analyzed for flexoelectric and flexoelectric-piezoelectric energy harvesting from bending vibrations, by accounting for the presence of a finite electrical load across the surface electrodes as well as two-way coupling, yielding closed-form frequency response equations of the fully coupled system.
- Beyond energy harvesting, the framework was also modified to implement for resonant actuation, and the relevant electromechanical frequency response functions have been identified (vibration and electromechanical admittance).
- The flexoelectric energy conversion (coupling coefficient) and harvesting become significant only for nm thickness levels (<100nm, especially <10nm) for typical flexoelectric coefficients obtained from atomistic simulations of STO.
- Based on coupling coefficient (k) arguments, it was suggested that flexoelectric constants reported for experiments on certain mm-thick samples (by Ma and Cross) are unlikely to be bulk flexoelectricity and are not valid at other scales.
- In the case of a piezoelectric material (e.g. BTO), flexoelectricity enhances the overall electromechanical coupling again for thickness levels below 100nm such that the bulk piezoelectric constant of k ~ 0.0652 at the mm-scale increases to k ~ 0.365 at nm thickness level.
- An approximate analytical modeling framework (using Hamilton's principle and Lagrange's equations via assumed-modes method) for flexoelectric and combined flexoelectric-piezoelectric effects was developed for varying cross-section thin beams under bending vibration.
- It was shown that the cross-section variation/geometry can be used to tailor the strain gradient distribution to increase electromechanical coupling; tapered beam geometry results in a coupling coefficient 10-20% more than that of the uniform case.
- An approximate analytical modeling framework for geometrically nonlinear beam accounting for flexoelectric effects was developed and the jump phenomenon was captured.
- The analytical framework for flexoelectric and flexoelectric-piezoelectric beams for energy harvesting and actuation was extend to 2D configurations (Kirchhoff plates) and coupling was increased for a simply supported plate to k ~ 0.34 in nm thickness.
- An approximate analytical modeling framework for axial flexoelectric effect (accounting for Poisson effect) via Rayleigh and Bishop theories was developed for truncated cones under longitudinal vibrations and size dependent electromechanical coupling was observed.
- It was shown that the flexoelectric coupling in the cone can be enhanced with changing the cone angle such that it increases from k ~ 0.00397 to k ~ 0.0351 as the cone angle is changed from 1.8 degrees to 10 degrees.
Last Modified: 08/29/2019
Modified by: Alper Erturk
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