F R A U N H O F E R I N S T I T U T E F O R I N T E G R AT E D C I R C U I T S I I S
INTEGRATION OF ENERGY
HARVESTING SYSTEMS
Figure 1: Installation of tracking
modules with energy harvesting
power supply on railway containers
OVERVIEW
E le c t ronic c irc u i ts a n d s y s te m s h a ve to b e powered wi th el ec tri c al energy . Thi s energy i s us ual ly provided
w it h a pow e r c o rd fro m th e g ri d o r i s s to red i n batteri es i n the dev i c e, whi c h hav e to be rec ha r ged f rom
t im e t o t im e . T h i s l i mi ts th e mo b i l i ty o f the us er or c aus es i ns tal l ati on or mai ntenanc e c os ts . The t echnology of e ne rg y h a rve s ti n g c o n v e rts a mbi ent energy l i ke heat, l i ght or moti on i nto el ec tri c al e ner gy t o
supply e le c t ro n i c d e vi ce s . T h i s wa y , o p e r ati on and s tandby ti mes c an be i nc reas ed or ev en be unlim it ed.
S hr ink ing t he b a tte ry s i ze o r e v e n re m o vi ng i t c ompl etel y i s a further c os t-s av i ng benefi t of en er gy harv e st ing pow e r s u p p l i e s . Us i n g typ i ca l e n ergy s ourc es whi c h are pres ent i n the natural env i ronm ent , seve r a l hundre d m i c ro wa tts u p to s o me m i l li watts of el ec tri c al energy c an be c onv erted from one cubic
c e nt im e t e r size o f a n e n e rg y h a rve s ti n g trans duc er.
Ty pic a l a pplic a ti o n d e vi ce s fo r th i s k i n d of power s uppl i es are l ow-power s ens ors , ac tuators , m icro cont rolle r s a nd w i re l e s s tra n s c e i v e rs . Ap p l i c ati on fi el ds are bui l di ng automati on, s truc tural heal th and condit ion m onit o ri n g , l o g i s ti c s , c o n s u me r p roduc ts and hous ehol d appl i anc es .
System Architecture
vibration to provide electrical energy. Due to the specific form
of energy, they produce pulse currents and need a rectifier
Figure 2 shows the block diagram of a generic energy harvest-
circuit.
ing powered device. Important functional components of
self-powered systems are the energy transducer, energy stor-
Power Management
age element (like a battery or capacitor), power management
unit and application module, represented by e.g. a sensor, an
One major challenge in energy harvesting arises from the
actuator and a wireless communication module.
very low output power delivered by the energy harvesting
transducers. The power management unit adapts the electrical
Energy Transducer
energy obtained to the requirements of the application device
or the energy storage element. This often means converting
Different kinds of transducers that are able to convert ambient
the voltage level or rectifying and filtering pulse currents.
energy into electrical energy became popular in recent years.
The specific energy transducer to be used depends on the
given application and the ambient energy available. Solar cells
convert light into electrical energy. Plane areas with sufficient
illumination and a proper orientation are required to achieve
RADIO
MODULE
POWER
MANAGEMENT
best performance. They are already available in flexible designs
and at different prices and efficiencies. Thermoelectric generators use thermal gradients to provide electrical energy. Based
on the Seebeck effect, they produce constant currents at very
small voltages, depending on the temperature differences
ENERGY
TRANSDUCER
ENERGY
STORAGE
SENSOR,
ACTUATOR
applied. Often heat sinks are required to maintain the thermal
gradients. Kinetic harvesters based on the electrodynamic,
electrostatic and piezoelectric principle use motion and
Figure 2: Block diagram of a generic energy harvesting device
Figure 3: Wristband with
Bluetooth module and thermoelectric power supply
Special care must be taken in matching the internal resistance
Sophisticated systems employ GPS modules or displays. Special
of the transducer and the power management or the load
attention must be given to the power consumption, which
to maximize the harvested electrical energy. Besides passive
can be reduced with the appropriate power management,
matching, active techniques like maximum power point
shutting off the sensors or actuators in inactive times.
tracking (MPPT) and non-linear circuits can be used to achieve
this goal with maximum efficiency. A major obstacle is the
Application Areas
power consumption and start-up of the power management
unit itself. It must not consume a significant part of the overall
– Condition monitoring
power consumption and save enough for the main application
– Structural health monitoring
of the self-powered system. With maximum efficiency of
– Home automation
the power management unit, the energy transducer can be
– Logistics and security
minimized allowing an optimized design in terms of volume
– Smart wearables
and cost.
– Consumer products
– Industrie 4.0
Energy Storage
– Internet of Things
An energy storage element – battery or capacitor – is usually
Advantages of Energy Harvesting Power Supplies
required in the implementation of energy harvesting power
supplies since ambient energy is variable and not always pres-
– Unlimited operation and standby times
ent. It permanently accumulates the available energy to power
– Shrinking or replacement of batteries
the application device, even if the device is powered-off for a
– No cable or connectors for power supply
given time period. Furthermore, if excessive power bursts are
– No installation or maintenance effort
required, e.g. during application start-up or during transmis-
– Supply of electronic system in inaccessible, remote locations
sion time-slots, they can be drawn out of this energy buffer.
Numerous communication devices – like wireless transmitters
– operate in time-division multiplex mode. Thus, high currents
SERVICES
are required only for small periods of time and for the remaining longer standby periods power in the order of micro- or
Fraunhofer IIS has many years of expertise in various
nanowatts is required to supply microcontrollers or timers.
technologies related to energy harvesting. We analyze
the application and suggest the appropriate energy
Radio Module, Sensors and Actuators
transducer. Our application-specific power management
circuits are optimized for different energy transducers.
Depending on the application and the sensors or actuators,
Our recommendations allow you to find the best suited
various communication principles and standards are ap-
energy storage and communication module. We com-
plicable. They differ in data rates, transmission range, and
bine the different modules concerning various optimiza-
power consumption. Also, various sensors and actuators can
tion goals like price, volume, weight or required opera-
be powered with energy harvesting. Typical examples measure
tion conditions. From various research and development
temperature, light, oxide, gas, acceleration or moisture.
projects carried out in the past, we provide demonstra-
Applications with actuators are door locks or heating valves.
tors and prototypes.
For more information please visit
WWW.IIS.FRAUNHOFER.DE/ENERGYHARVESTING
Fraunhofer Institute for
Integrated Circuits IIS
Director
Prof. Dr.-Ing. Albert Heuberger
Am Wolfsmantel 33
91 058 Erlangen, Germany
Contact
Integrated Energy Supplies
Dr.-Ing. Peter Spies
Nordostpark 84
90411 Nürnberg, Germany
Phone +49 911 58061-6363
Fax +49 911 58061-6398
peter.spies@iis.fraunhofer.de
www.iis.fraunhofer.de