Nathan Sharpes | Virginia Tech (original) (raw)

Papers by Nathan Sharpes

Vibration-based energy harvesters using piezoelectric materials have long made use of the cantile... more Vibration-based energy harvesters using piezoelectric materials have long made use of the cantilever beam structure. Surmounting the deficiencies in one-dimensional cantilever-based energy harvesters has been a major focus in the literature. In this work, we demonstrate a strategy of using two-dimensional beam shapes to harvest energy from low frequency excitations. A characteristic Zigzag-shaped beam is created to compare against the two proposed two-dimensional beam shapes, all of which occupy a 25.425.4mm2 area. In addition to maintaining the low-resonance bending frequency, the proposed beam shapes are designed with the goal of realizing a concentrated stress structure, whereby stress in the beam is concentrated in a single area where a piezoelectric
layer may be placed, rather than being distributed throughout the beam. It is shown analytically, numerically, and experimentally that one of the proposed harvesters is able to provide significant increase in power production, when the base acceleration is set equal to 0.1 g, with only a minimal change in the resonant frequency compared to the current state-of-the-art Zigzag shape. This is accomplished by eliminating torsional effects, producing a more pure bending motion that is necessary for high electromechanical coupling. In addition, the proposed harvesters have a large effective beam tip whereby large tip mass may be placed while retaining a low-profile, resulting in a low volume harvester and subsequently large power density.

We propose a technique for increasing the bandwidth of resonant low-frequency (<100 Hz) piezoelec... more We propose a technique for increasing the bandwidth of resonant low-frequency (<100 Hz) piezoelectric energy harvesters based on the modification of the clamped boundary condition of cantilevers, termed here as preloaded freeplay boundary condition. The effects of the preloaded freeplay boundary condition are quantified in terms of the fundamental frequency, frequency response, and power output for two beam configurations, namely, classical cantilevered bimorph piezoelectric energy harvester and zigzag unimorph piezoelectric energy harvester. A comparative analysis was
performed between both the harvesters to empirically establish the advantages of the preloaded freeplay boundary condition. Using this approach, we demonstrate that the coupled degree-of-freedom dynamics results in an approximate 4–7 times increase in half-power bandwidth over the fixed boundary condition case.

We investigate a concept that can reduce the overall power requirement of a smart building throug... more We investigate a concept that can reduce the
overall power requirement of a smart building through
improvements in the real-time control of HVAC and indoor
lighting based on the building occupancy. The increased
number of embedded sensors necessary to realize the
smart building concept results in a complex wiring and
power structure. We demonstrate a floor tile energy harvester
for creating a wireless and self-powered occupancy
sensor. This sensor termed as “Smart Tile Energy
Production Technology (STEP Tech)” can be used to control
automation in smart buildings such as lighting and
climate control based upon the real-time building occupancy
mapping. The sensor comprises of piezoelectric
transducer, energy harvesting circuit and wireless communication.
Modeling and optimization procedure for the
piezoelectric cymbal transducer is described within the
framework of tiles. The design and selection of a packaging
technique and construction of a durable floor tile enclosure
aimed at protecting the bulk piezoceramic is discussed
within the constraint that the deflection of the tile should
be minimal such that it is not readily perceivable by
humans, thus not disturbing their gait. Experimental
results demonstrate that the piezoelectric tile could provide
a promising solution for wireless occupancy sensing.

Energy Harvesting and Systems, 2014

A long-standing encumbrance in the design of low-frequency energy harvesters has been the need of... more A long-standing encumbrance in the design of low-frequency energy harvesters has been the need of substantial beam length and/or large tip mass values to reach the low resonance frequencies where significant energy can be harvested from the ambient vibration sources. This need of large length and tip mass may result in a device that is too large to be practical. The zigzag (meandering) beam structure has emerged as a solution to this problem. In this letter, we provide comparative analysis between the classical one-dimensional cantilever bimorph and the two-dimensional zigzag unimorph piezoelectric energy harvesters. The results demonstrate that depending upon the excitation frequency, the zigzag harvester is significantly better in terms of magnitude of natural frequency, harvested power, and power density, compared to the cantilever configuration. The dimensions were chosen for each design such that the zigzag structure would have 25.4 Â 25.4 mm 2 area, and the cantilever would have the same surface area. The zigzag prototype of 25.4 Â 25.4 mm 2 area was capable of generating 65 μW/cm 3 at 32 Hz when subjected to 0.1 G base acceleration.

APL MATERIALS, 2014

Energy harvesting from ambient low-frequency magnetic field using magneto-mechano-electric compos... more Energy harvesting from ambient low-frequency magnetic field using magneto-mechano-electric composite cantilever Appl. Phys. Lett.

Vibration-based energy harvesters using piezoelectric materials have long made use of the cantile... more Vibration-based energy harvesters using piezoelectric materials have long made use of the cantilever beam structure. Surmounting the deficiencies in one-dimensional cantilever-based energy harvesters has been a major focus in the literature. In this work, we demonstrate a strategy of using two-dimensional beam shapes to harvest energy from low frequency excitations. A characteristic Zigzag-shaped beam is created to compare against the two proposed two-dimensional beam shapes, all of which occupy a 25.425.4mm2 area. In addition to maintaining the low-resonance bending frequency, the proposed beam shapes are designed with the goal of realizing a concentrated stress structure, whereby stress in the beam is concentrated in a single area where a piezoelectric
layer may be placed, rather than being distributed throughout the beam. It is shown analytically, numerically, and experimentally that one of the proposed harvesters is able to provide significant increase in power production, when the base acceleration is set equal to 0.1 g, with only a minimal change in the resonant frequency compared to the current state-of-the-art Zigzag shape. This is accomplished by eliminating torsional effects, producing a more pure bending motion that is necessary for high electromechanical coupling. In addition, the proposed harvesters have a large effective beam tip whereby large tip mass may be placed while retaining a low-profile, resulting in a low volume harvester and subsequently large power density.

We propose a technique for increasing the bandwidth of resonant low-frequency (<100 Hz) piezoelec... more We propose a technique for increasing the bandwidth of resonant low-frequency (<100 Hz) piezoelectric energy harvesters based on the modification of the clamped boundary condition of cantilevers, termed here as preloaded freeplay boundary condition. The effects of the preloaded freeplay boundary condition are quantified in terms of the fundamental frequency, frequency response, and power output for two beam configurations, namely, classical cantilevered bimorph piezoelectric energy harvester and zigzag unimorph piezoelectric energy harvester. A comparative analysis was
performed between both the harvesters to empirically establish the advantages of the preloaded freeplay boundary condition. Using this approach, we demonstrate that the coupled degree-of-freedom dynamics results in an approximate 4–7 times increase in half-power bandwidth over the fixed boundary condition case.

We investigate a concept that can reduce the overall power requirement of a smart building throug... more We investigate a concept that can reduce the
overall power requirement of a smart building through
improvements in the real-time control of HVAC and indoor
lighting based on the building occupancy. The increased
number of embedded sensors necessary to realize the
smart building concept results in a complex wiring and
power structure. We demonstrate a floor tile energy harvester
for creating a wireless and self-powered occupancy
sensor. This sensor termed as “Smart Tile Energy
Production Technology (STEP Tech)” can be used to control
automation in smart buildings such as lighting and
climate control based upon the real-time building occupancy
mapping. The sensor comprises of piezoelectric
transducer, energy harvesting circuit and wireless communication.
Modeling and optimization procedure for the
piezoelectric cymbal transducer is described within the
framework of tiles. The design and selection of a packaging
technique and construction of a durable floor tile enclosure
aimed at protecting the bulk piezoceramic is discussed
within the constraint that the deflection of the tile should
be minimal such that it is not readily perceivable by
humans, thus not disturbing their gait. Experimental
results demonstrate that the piezoelectric tile could provide
a promising solution for wireless occupancy sensing.

Energy Harvesting and Systems, 2014

A long-standing encumbrance in the design of low-frequency energy harvesters has been the need of... more A long-standing encumbrance in the design of low-frequency energy harvesters has been the need of substantial beam length and/or large tip mass values to reach the low resonance frequencies where significant energy can be harvested from the ambient vibration sources. This need of large length and tip mass may result in a device that is too large to be practical. The zigzag (meandering) beam structure has emerged as a solution to this problem. In this letter, we provide comparative analysis between the classical one-dimensional cantilever bimorph and the two-dimensional zigzag unimorph piezoelectric energy harvesters. The results demonstrate that depending upon the excitation frequency, the zigzag harvester is significantly better in terms of magnitude of natural frequency, harvested power, and power density, compared to the cantilever configuration. The dimensions were chosen for each design such that the zigzag structure would have 25.4 Â 25.4 mm 2 area, and the cantilever would have the same surface area. The zigzag prototype of 25.4 Â 25.4 mm 2 area was capable of generating 65 μW/cm 3 at 32 Hz when subjected to 0.1 G base acceleration.

APL MATERIALS, 2014

Energy harvesting from ambient low-frequency magnetic field using magneto-mechano-electric compos... more Energy harvesting from ambient low-frequency magnetic field using magneto-mechano-electric composite cantilever Appl. Phys. Lett.