Smart Materials and Structures National Physical Laboratory

1
Smart Materials and Structures National Physical
Laboratory
The National Physical Laboratory carries out
Research and Development into the Measurement and
the Characterisation of functional materials,
including piezoelectrics.
The United Kingdoms Department of Trade and
Industry support our RD in industrially relevant
metrology.
Displacement mapping techniques are also being
used to evaluate the performance of multilayer
actuators.
In this work the focus has been not so much on
accuracy and traceablity but on developing
techniques for the point-to-point scanning of
actuators. This means that the piezoelectric
displacement is measured on a small region of the
sample and then either the sample or the
measuring probe is scanned in order to build up a
map of displacement behaviour.
Piezoelectric materials are often used as
actuators in order to make small precise
movements. It can be difficult to measure these
displacements in an industrial environment.
Consequently, simpler methods have been sought to
measure piezoelectric activity, such as resonance
methods, and measurement of the piezoelectric
coefficient d33 using what is commonly referred
to as the Berlincourt method. Various factors,
such as loading configuration, frequency, sample
geometry etc. complicate the measurement process.
At NPL, we have been studying these factors.
NPL is the UKs National Standards Laboratory for
physical measurements
Sample Geometry FEA shows changes in stress with
point contact loading. This leads to changes in
measured d33.
Set-up for scanning, and special sample with 5
well defined defects
Laser Triangulation Sensor
Laser Vibrometer
The methods were able to determine differences in
the displacement behaviour which related well
with the electrode configuration of the
multilayer. The resolution of the laser
vibrometer would appear to be more suited to this
application but the laser triangulation sensor
offers a cost effective alternative.
Static Loading Higher stresses are produced on
point loading. So thinner samples have higher
d33. But, as area of contact increases, then so
does constraint on sample movement. This leads to
a decrease in d33.
Dr Markys G Cain Dr Mark Stewart Mr Will Battrick