In the engineering realm of micro-electromechanical devices MEMs), high-efficiency/high output, wire-less energy harvesters are the holy grail. To be sure, various energy harvesting devices have been developed and have found applications in several industries, but these have been limited in bandwidth, efficiency, capacitance and output.
Recently, electrical engineers at the University of Michigan, have perfected a device that can harness ambient, mechanical vibrations and convert these into electricity at 5 to 10 times the efficiency and power output than previous devices of this type. At 27 cubic millimeters, a single such system fits — with room to spare — on a penny.
“In a tiny amount of space, we’ve been able to make a device that generates more power for a given input than anything else out there on the market,” said Khalil Najafi, one of the system’s developers and chair of Electrical and Computer Engineering (source: U of Michigan News Service).
The devices actually “scavenge” energy from their local environs in the form of cyclic vibrations from the factory machines they touch. The devices make use of the piezoelectric effect which is produced by crystalline structures that generate an electrical charge when subjected to mechanical strain or pressure.
In many automated factory environments, constant monitoring/sensing of machine performance (e.g., possible malfunction) is vital to keeping production moving. Networks of sensors are needed to accomplish this, preferably wireless ones.
Some earlier devices have been called “wireless” because the sensors can transmit data, wirelessly, to computers but which also require tiny batteries to keep them operable. According to the engineers, the replacing of batteries and/or wires in sensors is responsible for up to 80% of the maintenance and installation costs for what’s known as pervasive information-gathering sensor networks.
Thus “scavenging energy already present in the environment is an effective solution.” says engineering team member Erkan Aktakka. What’s more, the integrated system has an “ultacapacitor” that does not need to start out charged.
With previous devices of this type, there has been a trade-off between frequency and bandwidth (typically, either very high frequency or very narrow band width). The new harvester has a relatively large bandwidth of 14 Hertz and operates at a vibration frequency of 155 Hertz (about the vibrational frequency of your microwave oven). And, when exposed to only a 1.5g vibration amplitude (1g is the gravitational acceleration that all objects experience by Earth’s gravity) the device can generate 200 microwatts. An integrated circuit then processes the harvested energy to charge the ultracapacitor to its working capacitance of 1.85 volts)
For such sensor networks, long-lasting power is key. According to the engineers, the wireless/battery-less devices can be installed and left alone for 10 to 20 years, essentially a “limitless shelf time”.
Other applications for these new generation MEMs include use as a power source for medical implants, and, in heat sensors for motor vehicles
The market for power sources for wireless sensor networks in industrial settings is expected to reach $450 million by 2015.
The university is currently pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.
I wonder to what extent these devices can be scaled up (capacitance and output) to power, say, household appliances, or portable digital devices/smart phones. I believe MIT engineers had created a wireless (ambient) power source technology just a few years ago (anyone?).
Also: is this technically “clean technica”, or is it (post manufacture) only as “clean” as the machine to which it is attached? At least, it doesn’t seem to add to the energy usage of the factory.
Then there is the manufacturing of the devices themselves…
Environmentally, piezoelectric crystals are fairly abundant (e.g., quart) and cheap (extraction locales/impacts also vary), but would need to be assessed for contamination potential and sustainability. But just imagine, no more need for millions more metallo-toxic batteries leaching out of our landfills…
To read the full press release, check out : Most powerful millimeter-scale energy harvester generates electricity from vibrations
Top photo: U of Michigan News Service
GIF animation (piezoelectric effect): Mael Guennou – Titzeff; CC – By – SA – 3.0