SUCCESS STORY – Piezoelectric All-Rounder-- Birgit Schulze --Piezoelectric All-RounderSensor, Actuator or Both?

PI Ceramic GmbH, Lindenstraße, 07589 Lederhose, Germany
Phone +49 36604 882-0, Fax +49 36604 882-4109,Email info@piceramic.com

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SUCCESS STORY – Piezoelectric All-Rounder-- Birgit Schulze --The Piezo Effect
By the end of the 19th century Jacques und Pierre Curie hadalready discovered that an electrical potential could begenerated by exerting force on a quartz crystal. They named
this phenomenon the “piezoelectric effect” from the Greek
word “piezo” meaning "to press". Later they realized thatelectric fields cause deformation of piezoelectric materials.
This is known as the “inverse piezo effect”.
The direct piezo effect can be used in sensing applications,while the inverse effect is employed in actuators. In thecorrect combinations, piezoelectric materials can thus be
used to create the most versatile of devices.
With the DuraAct Patch Transducer (Fig. 1), a very versatile
piezoelectric device which will find wide application both inindustry and in research is now commercially available. This
compact unit can be used either as sensor or actuator: its
uses range from energy harvesting to self-regulating
adaptronic systems (see Adaptronics: New Technology with aBright Future on p.4).

Fig. 1

Fig. 2

Schematic design: at the heart of the transducer is apiezoceramic film with an electrically conductive layer applied toeach side. This construction is then embedded in a flexible
polymer strip

At the heart of the transducer is a piezoceramic film with anelectrically conductive layer applied to each side. Thisconstruction is then embedded in a flexible polymer strip. The
advantages of this design are multiple: the piezoceramic iselectrically insulated, mechanically preloaded, and, out of thebasically brittle ceramic, a unit is created which is so robustthat it can be affixed to surfaces with curvature radii as low as
12 mm (Fig. 3).

Sensor, actuator or both: multi-talented piezo-electric elements

Design and Working Principle
DuraAct patch transducers are based on a patented
development by the German Aerospace Center (DLR). The
transducers are fabricated by INVENT GmbH in Braunschweig,
the piezoceramics used are provided by PI Ceramic.
The finished devices are marketed exclusively by PI Ceramicfrom their headquarters in Lederhose. Despite theirversatility, the design and working principle of thepiezoelectric patch transducers is easy to understand (Fig. 2).

PI Ceramic GmbH, Lindenstraße, 07589 Lederhose, Germany
Phone +49 36604 882-0, Fax +49 36604 882-4109,Email info@piceramic.com

Fig. 3

Curvatures with radii as low as 20 mm are easily accommodated

The transducers can simply be glued to a surface, or they canbe integrated directly into a structure or structural material.
Custom transducer geometries are also possible, as iscustomization of the curvature, dimensions and thickness ofthe ceramic, to fit the specific application. The same is true
for the properties of the ceramic depending on the operating
temperature and the configuration of the electricalconnections.

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SUCCESS STORY – Piezoelectric All-Rounder-- Birgit Schulze --Actuators Exploit the Inverse Piezo
Effect...
The electrical design is basically that of a plate capacitor. Theceramic serves as dielectric between the two metalized
surfaces which act as the plates. When an electric potential isapplied, a field with lines running through the ceramic
perpendicular to the plates is created. This causes acontraction of the ceramics at 90° to the field lines, i. e. thepiezo ceramic contracts evenly in the plane. This deformation
can be transmitted to structural elements, where, when
attached to only plane, it causes the structure to bend (Fig. 4).
The force is transmitted over a surface, not just at discrete
points as with conventional actuators, making reinforced
force transmission points superfluous.

Fig. 4

Because of their high bandwidth, reaching into the kilohertz
range, patch transducers together with the appropriate
control electronics, can be used as precision, high-dynamics
positioning elements with submicrometer accuracies.

… While Sensors Use the Direct
Piezo EffectConversely, when the transducer is subjected to deformation,
an electric potential is generated, making it possible to use
the element as a sensor (Fig. 5). The changes in electric fieldin reaction to deformations of the piezoceramic are extremely
rapid, allowing measurement of vibrations in the kilohertz
range.

For actuators the inverse piezo effect is employed; theway these piezo actuators are affixed to the substrate
makes them operate as benders

The patch transducers can also operate well under highdynamic loads. Because the transducer motion depends onsolid-state crystalline effects and involves no sliding or
rotating parts to cause wear, failure rates are very low. Their
10life expectancy is over 10 cycles, giving them an excellent
fatigue resistance rating.
DuraAct patch transducers are currently available in standard
sizes with ceramic thicknesses of 0.1 mm, 0.5 mm and0.8 mm.
The contractions obtained with the maximum operating
voltage is 400 µm/m, 650 µm/m or 800 µm/m, respectively.
The operating temperature range goes from -20°C to +120°C(-4°F to +248°F).

PI Ceramic GmbH, Lindenstraße, 07589 Lederhose, Germany
Phone +49 36604 882-0, Fax +49 36604 882-4109,Email info@piceramic.com

Fig. 5Classical application of the direct piezoelectric effect in a sensor:
the smallest motion of the substrate is transferred to thetransducer where it produces an electric signal proportional tothe displacement

When integrated in a servo-control loop, patch transducers
give very good results in applications like vibration control.
There, a sensor signal from the transducer is used to control aseparate damping system.
Patch transducers can also be used in the area known as
structural health monitoring (Fig. 6). In those applications,they are integrated in the structure to be monitored, e.g. partof a machine or an airplane wing, where they detect possible
degradation.

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SUCCESS STORY – Piezoelectric All-Rounder-- Birgit Schulze --For the applications described so far, the transducers are
made with a single piezoceramic layer. It is equally possible,
however, to fabricate multilayer elements, which in turn open
up new and interesting possibilities. In actuators, multiplelayers operated in parallel can increase the force generated
for the same operating voltage. If the layers are operated
independently, then the transducer can be operated as asensor and actuator at the same time, i.e. without the delayinherent in switching a single-layer device from one mode tothe other.
Fig. 6

Wide areas can be monitored when an array of modules isaffixed to the surface; some act as actuators and some as
sensors to pick up auto-resonance effects. Comparison to areference signal made under ideal conditions then provides
information about the current condition of the part

With appropriate electronics, an adaptive system can be built
which detects mechanical shock or vibration and also damps
it out. Compatible control electronics can be found in theextensive product palette of Physik Instrumente (PI). In
addition, customized versions can be provided at any time.

Energy Autonomy and Adaptive
Systems

Adaptronics: New Technology witha Bright Future

Another interesting application area is energy harvesting. The
conversion of up to kilohertz mechanical vibrations into
electricity can yield power in the milliwatt range, sufficient for
running small circuits for LEDs, sensors or micro-powertransmitters. In such constellations, the patch transducers act
as tiny generators (Fig. 7).

The young technology of adaptronics has been attributed thebrightest of prospects. With adaptronics systems, undesired
noise and vibrations can be suppressed, and material flaws in
structures from machine parts to bridges can be detected
before they become dangerous cracks.
Intelligent, adaptive, “smart” materials with integrated
actuators and sensors open new horizons for designers andproduct developers. The concept of adaptronic materials ismodeled on the behavior of biological systems, which arecapable of reacting intelligently to changing environments.
Possible applications range from automotive, industrial
engineering, medical technology, metrology to aeronauticsand aerospace. In this context, piezoelectric patch
transducers like the DuraAct described here can expect wide
application.

Fig. 7

The absorbed mechanical energy is converted to electricalenergy; this makes the patch transducer into a mini-generator
with which energy-autonomous systems can be built

For structural health monitoring, for example, this could makefor a totally wireless system made up of simple elements. The
transducer acts as a deformation sensor and at the same time
supplies power to a mini-transmitter which sends the data toa nearby structure-monitoring station.
This is the better part of an energy-autonomous monitoring
and warning system, in which external power and batteries
are unnecessary.

PI Ceramic GmbH, Lindenstraße, 07589 Lederhose, Germany
Phone +49 36604 882-0, Fax +49 36604 882-4109,Email info@piceramic.com

Conclusion
DuraAct patch transducers are very versatile piezoelectricelements which can be used as both sensors and actuators.
When used as actuators the transducers change shape, whena voltage is applied, and generate useful forces. Used theother way they convert mechanical deformation intomeasurable electric charge and thus act as sensors. In bothcases the transducers consist basically of a piezoceramic film,
which can be adapted to meet application-specificrequirements such as bending radius, nature of the ceramicand design of the electrical connections.

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SUCCESS STORY – Piezoelectric All-Rounder-- Birgit Schulze --The patch transducers can also cope with high dynamic loads
for an average lifetime of more than 10 billion cycles.
They have low susceptibility to wear and faults because thetransducer operates on the basis of crystalline solid stateeffects, i.e. they do not contain moving parts. In addition totheir use as sensors or actuators, DuraAct patch transducers
can also serve as mini-generators. For the so-called “energyharvesting” the transducers convert mechanical oscillations
into electric voltage and thus provide a self-sustaining
monitoring and warning system.
More information on DuraAct piezoelectric patch transducers
is available at:
http://www.piceramic.com

Author

Dipl.-Phys. Birgit Schulze, Market & Products at PI (PhysikInstrumente)

PI Ceramic in Brief
PI Ceramic is considered a global leading player in the field ofpiezo actuators and sensors. The broad range of expertise in
the complex development and manufacturing process offunctional ceramic components combined with state-of-theart production equipment ensure high quality, flexibility andadherence to supply deadlines.
Prototypes and small production runs of custom-engineered
piezo components are available after short processing times.
PI Ceramic also has the capacity to manufacture mediumsized to large series in automated lines. PI Ceramic, asubsidiary of Physik Instrumente (PI) GmbH & Co. KG, islocated in the city of Lederhose, Thuringia, Germany.

PI Ceramic GmbH, Lindenstraße, 07589 Lederhose, Germany
Phone +49 36604 882-0, Fax +49 36604 882-4109,Email info@piceramic.com

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