CSEM Scientific and Technical Report 2008

Towards Integrated Hybrid Microsystems: Flexible Distributed Pressure Sensing Strips
N. Schmid, M. Fretz, H. F. Knapp, T. Burch, S. Bitterli, C. Bosshard, F. Zimmermann • , P. Sollberger • , T. G. Harvey ••
The pressure sensing strip to measure pressure profiles for rapid aerodynamic testing developed last year was further optimized and successfully
tested in a wind tunnel.
A non-intrusive pressure sensing strip to measure pressure
profiles for rapid aerodynamic testing [1] was further developed
and tested. The novel pressure sensor combines microfluidics
with traditional pressure transducer arrays. A film with
integrated micro-channels guides pressure signals from
arbitrary points on the surface to the sensor. The strip delivers
a non-invasive, accurate pressure distribution measurement
on any surface. It can be used to determine fluid flow
distribution, to detect flow separation, to determine drag, lift
and down-force on an airfoil.
The processing electronics was fabricated using standard
PCB manufacturing processes. To get rid of electrical cables a
wireless signal processing module was developed and
included in the system. The sensor integration and the
assembly of the pressure sensor strip contain the following
steps:
• Integration of sensor using die and wire bonding
• Application of a lid to protect the sensors
• Manufacturing of 200 micron thick strips with integrated
microchannels
• Assembly of sensor module onto polymer strip (Figure 1)
Figure 1: Manufactured pressure sensing strip.
A number of experiments were carried out to validate the
performance of the pressure strip. Table 1 summarizes the
main specifications that were achieved.
Table 1: Achieved specifications of the pressure strip.
All specifications can be modified depending on the application.
Pressure range 6000 Pa
Pressure accuracy 30 Pa
Pressure resolution 3 Pa
Strip thickness (at measuring points) < 0.2 mm
Strip length 20 to 500 mm
Temperature range 0 to 60°C
Measuring speed per sensor 300 Hz
In addition, the pressure strip was validated through a wind
tunnel test performed at the Institute of Fluid Dynamics (IFD)
of the Swiss Institute of Technology in Zürich (Eidgenössische
Technische Hochschule, ETH). The tests were carried out by
RUAG Aerospace, a specialist in Aviation and Space. The
measurement data were transmitted wirelessly. For certain
applications, e.g. wind turbines, wireless signal processing
can be of great importance.
During the wind tunnel test session the pressure strip proved
to be reliable and provided results which are in good
agreement (both in absolute values and uncertainty) to those
obtained by conventional methods (Figure 2). This
demonstrates that the pressure strip is a valuable new method
with the potential to complement more classical methods.
Figure 2: Comparison of standard pressure tap readings (o) and
pressure strip measurements (+) (for different angles of attack of the
wing alpha of 0°, 4°, 8°, 12°). An excellent agreement is obtained.
Potential markets include testing environments (e.g. wind
tunnels) in automotive, aerospace, wind turbines, urban goods,
and watercrafts industries. In addition, the developed
integration processes are generic and can have a major
impact on application domains including diagnostics and life
sciences, safety and automation pressure sensing in e.g.
pneumatics / power plants / ships and acoustic measurements.
This work was supported by the Sixth Framework Programme
of the European Commission (project IST-FP6-027540,
INTEGRAMplus) and the MCCS Micro Center Central
Switzerland. CSEM thanks them for their support.
•
Hochschule Luzern Technik & Architektur, Horw
••
Epigem Ltd, Redcar
[1] N. Schmid, et al., “Pressure Sensing Strip for Rapid
Aerodynamic Testing”, CSEM Scientic Report 2007, page 97
109