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Energy Harvesting Efforts Are Picking Up Steam
(Power Electronics Technology Via Acquire Media NewsEdge) Energy harvesting devices are making steady
improvements in performance and their manufacturers are seeking
greater market acceptance of their devices. They’re being
encouraged by major semiconductor IC manufacturers who are joining
forces with them by offering supporting products like sensors,
microcontrollers, power supplies, DSPs and solid state batteries,
as well as development kits and application notes. These IC
manufacturers realize there’s a large market potential for
these efforts as ICs downscale in size and are called upon to
operate at lower and lower power levels.
The market for energy harvesters in 2011 reached $700 million,
with the majority market value going into consumer electronics
according to IDTechEx, a market research and consulting services
firm. It forecasts this market to grow to over $1.4 billion by
2017, with two of the leading growth segments being the wireless
sensor network and military/aerospace segments (Fig. 1).
Shrinking semiconductor IC chip line geometries and lower power
consumption levels come at a time when energy harvesting devices
are becoming more effective and practical (Fig. 2). For example, thermoelectric energy
harvesting is now possible with only a few degrees of temperature
difference.
This was demonstrated by Schneider Electric for wireless
communications applications using the ZigBee communications
protocol. The company used a thin-film thermoelectric generator
where only 3ºC of temperature difference generated 126 µW (at 210
mV), and a standard dc-dc converter with about 70% efficiency (100
µW at 2.4 V). In a star architecture, measurement and data
transmission could be achieved every 5 susing ZigBee.
We don’t have to look very far when it comes to
lower-power future IC chips. Intel Corp., for example, recently
demonstrated an experimental IA microprocessor core capable of
unprecedented low-power operation, the product of many years of
research. Codenamed Claremont, it can operate at a near threshold
voltage (NTV) so low that it can be powered by a small solar cell
(Fig. 3). Intel’s Chief Technology Officer
Justin Rattner showed this last September at the Intel Developer
Forum as an example of how to develop NTV computing and to
demonstrate the energy benefits of NTV designs, which promise
better energy efficiency.
The Claremont, designed for high-performance computing, is a
heat-sink-free processor core that can be placed in the NTV mode
that dissipates less than 10 mW with minimum energy and provides
five times better energy efficiency than what is possible today. It
also provides a wide dynamic operational range and can run at
higher frequencies (about 10 times higher) when performance is
needed. “It might not be a commercial product, but the
research could be integrated into future processors and other
circuitry,” says Rattner.
A common form of energy harvesting comes from the piezoelectric
effect. Materials like certain ceramics and crystals can generate
electricity in response to an applied strain, a behavior that is
reversible wherein an applied electric field can produce mechanical
motion of the material.
One notable player in piezoelectric-based products is
MicroStrain Inc., a leading provider of inertial measurement
systems, displacement transducers, and sensing networks used in
health monitoring of civil structures and military/aerospace
aircraft. The company’s patented temperature-compensated
differential variable-reluctance transducers provide extremely
small size and high-accuracy attributes and the ability to
withstand high-temperature gradients, saline solutions, and
pressurized environments.
France-based Arveni s.a.s. has already demonstrated the first
infra-red (IR) Philips TV remote control that requires no batteries
(Fig. 4). The remote control, developed for
Franceís IP TV provider SFR, contains a standard pulse
microgenerator consisting of a sensor, microprocessor and an RF
output stage. It accepts electrical inputs from the click of the
remote’s buttons that produce a piezoelectric output.
Arveni’s AR01 microgenerator produces 2.1 mJ of energy (31.6
V) in response to 3.4 N of force.
AdaptivEnergy is another company that capitalizes on the
piezoelectric effect. Their Joule-Thief dc power device harnesses
energy from vibrations and impact forces, and converts it to usable
electrical power.
The technology of piezoelectric energy harvesting is improving.
At last November’s Energy Harvesting 2011 meeting in Boston,
MA, researchers from the National Institute of Aeronautics (NIA)
showed how piezoelectric devices could be made to produce
high-energy efficiencies and output levels. They demonstrated that
piezoelectric crystals in the <33> longitudinal mode can be
made to produce three times higher energy harvesting efficiency
than those in the <31> transversal mode, using a hybrid
piezoelectric energy harvesting transducer, and can harvest four
times more energy.
And researchers at Belgium’s IMEC have produced a MEMS
chip that can harvest energy from vibrations inside a car to power
tire-pressure monitoring systems (TPMSs) without the need for
battery power. The chip’s maximum output was just under 500
µW at its natural frequency of 1 kHz. Energy generation dropped to
a little over 40 µW when a car’s tire was traveling at 40
miles/hour, which is still enough to qualify the part for TPMS and
wireless communications circuitry.
The chip consists of cantilever beam with an aluminum-nitride
piezoelectric layer sandwiched between metallic electrodes that
form a capacitor. A mass attached to one end of the cantilever beam
enables to act as a transducer, converting vibrations into
electricity as the piezoelectric layer flexes. The voltage across
the capacitor is harvested to drive wireless transmissions.
One of the largest suppliers of energy harvesting product from
vibration is United Kingdom’s Perpetuum Ltd. It makes use of
electromagnetic vibration harvested energy to power wireless sensor
nodes in the monitoring of railroad wheel bearings, wheel
conditions, derailments, hazardous cargo, braking systems and GPS
stationary locations.
Perpetuum’s PMG FSH tranducers work on Faraday’s law
principle. A magnet vibrates up and down relative to a coil, both
of which are housed in a case with springs (Fig. 5). The transducer produces an ac current
that is rectified to dc. A PMG FSH delivers at least 0.5 mA at 3.6
V, indefinitely. As such, it replaces a typical and more costly
battery (in the long term) and provides “fit and forget
it” life-cycle independence.
Thermal energy is another good source for harvesting electrical
power. Germany’s Micropelt GmbH’s TGP651/751
thermoelectric generators (TEGs) produce electricity from
temperature differences of 5ºC or more and output power ranging
from 100 µW to over 10 mW. This is sufficient to offset most
batteries in wireless sensor networks.
The TEG modules use an aluminum oxide substrate on which
multiple thermocouples are laid thermally in parallel and
electrically in series. Up to 128 thermocouples can be laid on a
1600-mm2 substrate to produce about 50 mV/K.
Another German manufacturer, EnOcean GmbH, offers the Dolphin
platform of energy harvesting modules that can create electricity
from thermal as well as solar and motion sources. Modules like the
STM300 868-MHz wireless sensor transceiver feature the
industry’s lowest sleep-mode current of just 200 nA and
consume one-tenth the power of conventional modules.
Kits, Development Tools
Evergen thermoelectric kits from Marlowe offer a range of
thermal energy harvesting for evaluation and testing purposes (see
Power Electronics Technology, Feb. 2012, p. 24). The kits allow
solid-to-air, liquid-to-liquid and liquid-to-air thermal energy
harvesting evaluation and testing for powering sensors, actuators,
valve solenoids and other small devices. They operate from
temperature-difference outputs of 0.3 and 0.5 mW that can be
converted to outputs of 2.3 and 5.1 W.
Energy harvesting kits are available with all sorts of devices
that include not the only the energy harvesting source, but also
solid-state storage devices (to store the energy charge) as well as
electronic ICs like microprocessor development tools. For example,
Cymbet Corp. has teamed up with Texas Instruments (TI) to offer
Cymbet’s EnerChip solid-state battery with TI’s MSP430
Value Line LaunchPad development kit.
TI also offers the TPS62120 75-mA dc-dc step-down converter for
energy harvesting and low-power applications. It supports inputs of
2 to 15 V and consumes a mere 11 µA of quiescent current. The part
is 96% efficient and can operate from 9-V and 12-V dc or a
battery.
Others also offer components for energy harvesting. For example,
Advanced Linear Devices recently introduced the EH4200 family of
micropower step-up low-voltage booster modules that boost the
output of some TEGs, electro-magnetic coils, and single
photovoltaic and infrared emitters for effective energy harvesting.
And, Linear Technology Corp. offers the LTC3105 and LTC3108 step-up
dc-dc converters for boosting purposes as well.
Infinite Power Solutions has teamed up with Maxim Integrated
Products to offer a development kit that contains Infinite Power
Solutions’ ThinEnergy MEC101 solid-state rechargeable
thin-film battery and Maxim’s 17710 power-management IC to
develop and evaluate self-sustaining “green” power
solutions. The IPS-EVAL-EH-01 kit efficiently accepts charge less
than 1µA.
Wireless Sensor Networks
A large number of energy harvesting applications involves their
use in wireless sensing applications. Many of these applications
serve consumer electronics, building and industrial automation,
automotive uses, military/aerospace, and medical body area networks
for monitoring.
According to the aforementioned IDTechEx forecast for energy
harvesting, approximately 1.6 million energy harvesting devices
were used in wireless sensing in 2011, resulting in $13.75 million
being spent on this market segment. The study forecasts that the
market for wireless sensors in industrial automation will reach
$140 million, and $210 million for military/aerospace applications
by 2017.
Many companies are offering starter kits and components
specifically designed for wireless sensor networks. EnOcean, for
example, is offering its ESK 300 starter kit, which consists of a
switch module for building services, components for different
switch applications, a temperature sensor module, a USB gateway, PC
software for visualization, and a sample case for industrial
switching applications.
Powercast Corp. is offering a licensable RF power chip-set and
reference design for embedded low-power wireless charging (Fig. 6). These enable OEMs to directly embed
the same functionality provide by Powercast’s P1110 or P2110
Powerharvester receivers.
TI offers the BQ25505 IC, a booster charger that can be used in
wireless sensor networks. It maximizes the energy harvested from
solar and TEG sources with an industry low quiescent current of
just 330 nA.
Dust Networks Inc. has demonstrated a self-powered IPV6
intelligent wireless sensor network using MicroPelt’s
TE-Power TEG as well as Cymbetís EnerChip solid-state battery
rechargeable solid-state battery. The SmartMesh IP 6LoWPAN network
runs entirely on harvested energy and does not require conventional
batteries.
An important development has emerged from IMEC’s Host
Centre in the form of a record low-power 2.3/2.4-GHz transmitter
for wireless sensor applications compliant with four wireless
standards: the IEEE802.15/15.6/4/4g and Bluetooth Low Energy.
Fabricated on a 90-nm CMOS process, the transceiver consumes only
5.4 mW from a 1.2-V supply (2.7 nJ of energy) at a 0 dBm output.
This is said to be three to five times more efficient than current
state-of-the-art Bluetooth Low Energy solutions.
Energy limitations
One of the impediments to wider-scale adoption of wireless
sensor networks is the fact that there is no universally available
source of energy available to harvest at all times. Solar energy
harvesting is not possible in dark areas (near machines, in
warehouses, etc.), and thermal gradients and vibrations cannot be
harvested in situations where there are no such sources of
energy.
These observations have been pointed out by researchers at
Franceís CEA-Leti in an article entitled “Energy Harvesting,
Wireless Sensor Networks & Opportunities for Industrial
Applications”
(http://www.eetimes.com/design/smart-energy-design/4237022/Energy-harvesting--wireless-sensor-networks---opportunities-for-industrial-applications).
They emphasize that because different power densities characterize
different energy sources, the source of energy to be harvested for
wireless sensor networks must be carefully chosen according to the
local environment (Fig. 7).
The idea that present-day renewable energy sources such as
solar, wind, geothermal and hydropower cannot be easily adopted due
to their intermittency and storage difficulties is shared by others
like Professor Jeongmin Ahn at Syracuse University. He also points
out that despite significant advances in battery technologies,
their power densities cannot meet the demands for powering future
wireless sensor networks. He believes that combustion devices are
the answer to powering wireless networks where electrical energy is
created from chemical energy available in various hydrocarbon
fuels.
Ahn believes the such devices are needed due to limitations of
present-day power generation systems that require moving parts and
need parasitic power. Such devices would impose no parasitic
electrical power requirements; use fuel, not electrical power, as
the energy feedback for pumping; produce electrical power with no
moving parts; and do not require high-precision fabrication. Ahn is
trying to develop power solutions that meet these stringent
requirements.
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Harvesting Investigation
© 2012 Penton Media
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