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iSYS R&D(Intelligent SYStem Reliability & Design Laboratory) |
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Research Prognosis & Health Management(PHM) |
(Click
the image above to see the movie) Motivation: The continual
advances in wireless technology and low power electronics have enabled the
deployment of remote sensor networks for various applications including
environmental monitoring, gas and chemical sensors, motion detectors,
structural health monitoring, and explosive detection. Current wireless
sensor nodes are mainly powered by electrochemical batteries, which is
problematic due to their limited lifespan and continual replacement.
According to the Department of Energy (DOE), battery replacement in wireless
sensors costs $80-$500 per replacement including labor, which exceeds a
sensor cost. Energy harvesting technology has been motivated to overcome such
difficulties, which captures the ambient, otherwise wasted, energy sources
(e.g., vibration, heat, solar, wind) and converts into a usable electrical
energy. Vibration energy is one of widely available ambient energy sources
which can be converted into electrical energy using a piezoelectric material.
The harvester we developed makes use of the piezoelectricity and is
especially designed to utilize multiple vibration frequencies. Challenges and resolutions: • Cancellation effect in electric energy:
Other than a pure bending mode of a cantilever, electric energy can be
cancelled during a vibration. This phenomenon is called “cancellation
effect”. A PZT plate is segmented to minimize the cancellation. In addition
to the proof mass at the tip of the PZT plate, another proof mass is placed
at the separating point to generate greater strain energy. This design platform
is entitled as “segment-type energy harvester (EH).” • FE model validation: FE model
validation is an essential step for optimizing the segment-type EH design.
The validation study involved the comparison between observed and predicted
distributions of an open-circuit voltage over an operating frequency domain. • Stochastic nature of the vibration energy:
Ambient vibration energy has random nature in terms of amplitudes,
frequencies, and bandwidths at harmonic frequencies. In order to overcome
this challenge, a sustainable harvester design problem is formulated as a
stochastic design optimization. • Structural and environmental durability:
The stochastic design optimization was formulated with a structural
durability constraint, in which the maximum tensile strength exceeds the
dynamic tensile strength of the PZT. In addition, manufacturability was also
considered in the design process by defining every edge of the structure with
straight lines. The
optimization maximizes the power generation subject to the following
constraints as structural durability, manufacturability, and random frequency
matching between operational and EH frequencies. The
optimal design is displayed below together with its
prototype (about 4 inch long).
Optimized FE model of energy harvester and its
prototype Performance verification Its
performance is verified by the test with a shaker. The table below shows the
power estimation for 5 multimodal excitation cases. By comparing case (a) to
(c), we can confirm that the power generation is significantly increased as
the amplitude at 110Hz increases, which shows the excellent performance of
the segment-type harvester by showing its ability to utilize multiple
resonant frequencies. The comparison through case (c) to (e) shows that the
EH effectively utilizes the second resonant frequency (110Hz) rather than
other frequencies (80, 140Hz). Power estimation of segment-type
harvester
Case study: HVAC vibration utilization for building
automation The prototype
was successfully integrated into a wireless sensor and transceiver, which is
the first-ever self-powered wireless sensor/transceiver system for the
building automation in the world. In the field test, the harvester unit was
attached to an HVAC system in the Engineering Laboratory (089), as shown at the
top of this page. This sensor system transmits temperature data in every 6
to 7 seconds, showing great feasibility of the sustainable EH for wireless
sensors. Relevant Publications: 1. Lee S and
Youn B D 2008 Computer model calibration and design
comparison on piezoelectric energy harvester Proc. 12th AIAA/ISSMO Multidisciplinary Analysis and Optimization
Conference (Victoria, Canada) 2. Youn B D and Lee S, inventor; 3. Youn B D, Lee S and Jung B C, inventor; 4. Lee S,
Youn B D and Jung B C 2009 Robust Segment-Type
Energy Harvester and Its Application to Wireless Sensor Smart Mater. Struct. Vol.18 doi:10.1088/ |
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