Siemens_CN120 pages

Multiphysics
Siemens Corporate Technology, Munich, Germany

Modeling Optimizes a Piezoelectric Energy Harvester
Used in Car Tires
Siemens is using fluid-structure interaction simulation to ensure the cost-effective optimization
of a cantilever in a MEMS generator designed to power a tire pressure monitoring system.
By Jennifer Hand
Co-Authored by Dr. Ingo Kuehne and Dr. Alexander Frey, Siemens AG

T

he desire to get rid of batteries and
power lines motivates a wide range
of research. In the quest for systems that
are energy autonomous, the concept of energy harvesting attracts much attention.
Combine this idea with operation at the
micro level and the ‘what if ’ scenarios become even more enticing.

“Our ultimate goal is
to design the MEMS
generator to be as small,
light and strong as
possible with enough
energy to power a
system under a range
of conditions.”
For researchers at Siemens Corporate
Technology in Munich, there was a strong
attraction for exploring the potential of an
energy harvesting MEMS (Micro ElectroMechanical System) generator. Dr. Ingo
Kuehne explains, “Our remit is broad.

We are looking to develop
platform technologies for
tomorrow rather than specific products; however,
it makes sense to demonstrate the value of our research. Together with our
partner Continental AG
we decided to focus on an
application with clear commercial potential. Our ultimate goal is to design the
MEMS generator to be as Figure 2. Schematic of the piezoelectric MEMS generator energy
small, light and strong as harvester. The cantilever is made of two materials and electrical
possible with enough en- energy is transferred through the circuit from the cantilever.
ergy to power a system uning and engine control; and convey all this
der a range of conditions.” They chose to
design a microgenerator for an innovative critical information wirelessly. It would also
Tire Pressure Monitoring System (TPMS) be maintenance free, low cost and environmentally friendly.
driven by motion.
Yet, locating the device within the tire
Because TPMS are traditionally powrequires that the assembly be extremely
ered by batteries, they tend to be mounted
on the wheel rim. With no reliance on a robust and able to withstand gravitabattery, such a system could be placed in- tional acceleration up to 2,500 g. Moreside the tire and would be in a position to over, in order to avoid tire imbalance it
measure much more than pressure (Figure would have to be very light, and in terms
of operational life it would need to match
1). It could monitor temperature, friction,
that of a tire, a minimum of 8 years.
wear and torque; assist with optimal track-

From Mechanical Stress into
Electrical Energy

Figure 1. TPMS mounting options — on the rim or on the inner lining of the tire.
1 2 // C o ms o l

N E W S

2 0 1 2

Mounted to one spot on the inside of a
tire, a piezoelectric microgenerator would
be able to harvest energy from the compression created each time that particular area
of the tire touched the ground. The cantilever was designed to incorporate a thin
film of self-polarized piezoelectric ceramic
material with a silicon carrier layer, which
provides mechanical stability and stores
harvested mechanical energy (Figure 2).
The team had settled on a triangular
design for the spring-loaded piezoelectric cantilever, as such a shape enables a