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The energy around us

March 1st, 2014 / By: / Technical

Energy harvesting researcher Dr. Shashank Priya, Virginia Tech, responds to questions about the status of kinetic energy harvesting technology.

What is your assessment of the commercial viability of kinetic energy harvesting?

Kinetic energy harvesting prototypes have been demonstrated by several research laboratories and large companies, such as Exelis Inc. There are a variety of platforms where this technology is being targeted, such as trains, aircrafts and buildings for powering the wireless sensor nodes, surveillance components and health monitoring systems. A lot of progress has also been made on water flow energy harvesting systems, and they should find deployment for remote monitoring applications.

What markets and applications are
most likely to be (or will continue to be)
early adopters?

Wireless sensor nodes, surveillance components, and health monitoring systems are the prime applications for platforms, such as buildings, automobiles, trains, aircraft and ships.

What could happen in the research
(what would be “breakthrough”) that
could change the picture?

There are two main metrics that need to be improved: power density and bandwidth. In order to do so, more research needs to be conducted on improving the material performance and implementation of these material architectures on the desired substrates. In addition, research is required to further the design of low-frequency structures, non-linear concepts and
efficient circuits.

For kinetic energy harvesting, “There are only certain places where you will get stress, which you have to have,” you said. Explain how research is addressing this challenge.

For maximum power transfer, the harvester needs to operate at the resonance. However, as we scale down the size of harvester the resonance frequency continues to increase. Thus, the challenge has been to design structures on the size of a few mm in diameter exhibiting resonance frequency in the range of 10–100 Hz. This is the desired frequency range for most of the kinetic energy harvesters.

The second factor that controls the magnitude of power is volume of the active material. Maximizing the active material volume while meeting the other structural criteria, such as mechanical strength, resonance frequency and volume of the device, has been another challenge. Depending upon the mechanism, such as piezoelectric, electromagnetic or electrostatic, the operation mode and structure of the harvester is critical in gaining higher efficiencies.

How are textile substrates (or textiles, generally, because there are conductive fibers that can be woven into e-textiles) figuring into the research?

Kinetic energy harvesting from textiles is a bit more complicated as one has to develop harvesting architectures within the conformal package. Mostly these architectures are off-resonance devices that rely on simple bending or stress pulses. This presents a challenge in designing circuits that can efficiently transfer the generated electric energy into storage components, such as a capacitor or battery. Macrofiber composites and metal–MEMS (micro-electro-mechanical systems) are some approaches that have been experimented with. However, going forward, more research is required on developing nanoscale-based approaches, such as core-shell magnetoelectric fibers, self-poled structures and on developing flexible energy harvesting circuits with high efficiency.

There’s quite a lot of interest in the fashion and design world in kinetic energy harvesting. How might this world and the world of industrial applications intersect? Is there much sharing of research?

Kinetic energy harvesting refers to the conversion of dynamic stresses into electric signal. Kinetic energy harvesters mostly utilize the same principles on smaller or larger scales. However, most of the large-scale systems are based upon electromagnetics and use either a moving magnet-coil arrangement or an electromagnetic generator. At small scales we have many choices for kinetic energy harvesting, such as piezoelectric, electrostatic, electrets, elastomers and electromagnetics.

This research area is continuously growing and organizations such as the National Science Foundation Industry – University Collaborative Research Center “Center for Energy Harvesting Materials and Systems” (CEHMS) are providing avenues for transition from laboratory development into industry.

Shashank Priya, Ph.D., is professor in the Department of Mechanical
Engineering and Turner Fellow in the College of Engineering at Virginia Tech. His research is focused on energy harvesting and bio-inspired
materials and devices. He is editor-in-chief of the journal Energy
Harvesting and Systems and founding chair of the conference in
“Energy Harvesting Workshop.”

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