ST and Micropelt energy harvester
12 Feb 12
Wireless sensor and actuator systems using energy
harvesting have the potential to achieve a huge green impact in future
applications, as they could eliminate the need for battery charging systems,
battery replacement, maintenance and disposal problems. Not only would they
eliminate battery problems, but wiring and connector problems when interfacing
between various sensors, actuators, and other low-power device are eliminated
also. This can save a lot of trouble while being very cost effective, as
wiring, connectors, and batteries can be very expensive and troublesome.
Another huge advantage is that sensors and actuators can now be placed in
previously inaccessible locations.
ST Microelectronics has teamed up with Araymond, a supplier to the automotive and solar industries, and Micropelt GmbH,
of Freiburg, Germany to provide thermal-energy harvesting-based solutions to
power ‘smart sensors’ and ‘smart microsystems’.
Micropelt is known for the development of the
world’s smallest and most effective thermoelectric elements for micro energy
harvesting, thermal sensing, cycling and cooling. Micropelt has developed
chip-sized thermogenerators (TEGs) which converts the waste energy as heat is
transferred from a higher temperature to a lower temperature into electrical
energy, and they have been able to achieve the highest power density available
packed into a few square millimeters of footprint. They accomplish this with a
patented scalable thin film micro-structuring platform technology using the ‘Seebeck
Effect’, which maximizes power density for energy harvesting, cooling or
thermal cycling while minimizing component size. Batteries may now eventually
become obsolete as free electricity from waste heat can power wireless sensor
networks and ultra-low-power systems for their entire life.
ST has focused on providing energy storage
components that would support this new energy harvesting technology. They
supply the rechargeable battery used in the TE-Power NODE kit, which is the
EFL700A39 EnFilm thin film solid state battery, with a 700-microamp-hour
rating. This battery can supply an inrush current up to 10mA. ST also provides
a battery board which contains the EnFilm battery and the electronic circuitry
that controls and monitors both battery charge level and the energy balance.
Their combined efforts resulted in the
development of evaluation system featuring ST’s new long-life EnFilm rechargeable
battery combined with Micropelt’s Thermal Electrical Generator (TEG) chip. This
system is called the TE-Power NODE evaluation kit, and demonstrates a new type
of virtual wireless perpetual-energy solution with long-life and
Micropelt has designed custom power conditioning circuitry
which controls the generated thermoelectric power so that it provides
sufficient power to drive a wireless sensor node and charge a battery using its
excess thermal energy. Within the
TE-Power NODE evaluation kit, the Micropelt TEG MPG-D751 is housed between a
solid Aluminium base plate and a finned heatsink. The base is attached to a
suitable heat source, so the cooling effect of the heat sink creates a
temperature difference which is used to generate electrical power through the
TEG. When the base plate is in contact with a heat source, the TEG provides
power to the system and recharges the EnFilm. When the heat source is removed,
the TEG stops and only the EnFilm battery provides power to the wireless sensor.
The battery is also needed to supply the occasional pulses of higher current.
Micropelt has included a versatile ultra-low
power 2.4 GHz wireless link to its custom designed graphical user interface in the
wireless sensor module. Power management and charge monitoring circuitry in the
TE-Power NODE evaluation kit connect to the included graphical user interface
software using the wireless link. The
software can display and log important thermal and electrical system
parameters, and maintains a continuously measured power balance between the TEG
and the EnFilm battery.
There is a growing trend towards the use of
wireless sensor networks, and they would be useful in applications like process
automation, condition monitoring, and smart buildings. As energy harvesting
becomes more widely used, free electrical energy can be extracted from many
other sources where thermoelectric power isn’t readily available, such as
vibration, light, and RF energy.