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ISSUE 2014
InFocus
Optical Measurement Solutions
Serving Healthcare
Page 5
Extremely Versatile
Page 10
Competence Center for
Laser Doppler Vibrometry
Page 33
Visible Music
Page 36
Fascination of Hearing
Page 40
Big on Small Things
Polytec explores the barely visible
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our Newsletter
now:
www.polytec.com/
newsletter
Editorial
Polytec News
Page 3
Serving Healthcare
Page 5
How do Microstructures Vibrate? –
MSA-100-3D
Page 8
Extremely Versatile
Page 10
Good Vibrations
Page 16
Better Switching
Page 20
Dear Readers,
Just like a Watch – only smaller
The term MEMS is getting more popular, but not everyone knows what it means.
MEMS are mechanical structures as finely engineered as those found in a watch but
way smaller. MEMS dimensions are roughly four times tinier than a human hair.
Technical structures are getting so minute that understanding them with our own
senses is impossible. Without technological help they are invisible. The microphones
in our smartphones are only about 3 to 4 millimeters wide. And this is surely not the
end of this development.
In this edition you will learn how Polytec’s instruments help in different ways to
improve the performance and reliability of these microstructures.
Tailored Modeling of MEMS
Page 23
Developing Biosensors
Page 27
Big Time for Small Singers
Page 30
To Improve Hearing
Page 33
Interview
Page 34
Visible Music
Page 36
Fascination of Hearing
Page 40
Unlimited Possibilities – HSV-100
Page 43
Eric Winkler
Head of Optical Measurement
Systems
2
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Surface Metrology in a
New Dimension
Page 44
Very High Frequency Scanning
Vibrometer – PSV-500-V
Page 46
News
Charity Yoga
Employees exercise for a good cause
Our purchasing manager Thomas Schott offered a beginners
course in traditional Ashtanga Vinyasa Yoga on the 4th of
December. All 15 participants were sweating for a very good
cause. The money collected was donated in full to support
victims of the flooding in the Philippines. Polytec honored the
social commitment by doubling the donations with matching
funds.
Nils Schmid at Polytec
Minister visits world market leader
The Minister of Finance and Economy of Baden-Wurttemberg, Nils Schmid, visited Polytec on the 18th of November.
Employees showed the Minister several measurement technologies. A wrap-up tour of the facility ended with the highlight of
the day – a visit to the RoboVib Test-Center which caused him to
remark: ”Wow, this is really impressive!“
Polytec Promotes Research
Young scientist wins prize
Polytec first honored a young scientist with the ‘Polytec Young
Researcher Award’ in 2013. This award is given to a young
scientist for an outstanding presentation. Taina Conrad from
the University of Ulm won with her presentation: “He’s giving
me good vibrations – The role of vibrations in mason bees”.
She earned the prize during a 2013 entomologist meeting in
Goettingen.
You can find an interesting article about this topic on page 30.
|3
News
Be a Presenter!
MEMS Testing and Metrology Workshop
This international event will take place during SEMICON in
Grenoble, France on the 7th and 8th of October 2014. It deals
with current requirements and trends of MEMS development as
well as measurement technology and testing possibilities.
Learn about the latest ways to characterize MEMS and discuss
Wafer-Level-Test strategies and standardization issues.
Alternatively you can say a few words and share your own results
with everyone.
More information at: www.memunity.org
Sign up now!
Meet at Polytec
13th User meeting in Waldbronn
The largest meeting for users of laser vibrometry will take place
in Waldbronn from the 18th through the 19th of November,
2014.
The main goal of this event is an intensive exchange of ideas and
experience in applications and new developments. Debate with
experienced users and Polytec-Experts.
More information at: www.polytec.de/anwenderkonferenz
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Healthcare
Serving Healthcare
Using acoustic vibrations to manipulate liquids
for handheld diagnostic devices
Advanced diagnostic systems are required in both developed and developing countries
to test patients outside the centralized facilities of hospital laboratories. In the developing world especially, diseases such as Malaria, sleeping sickness (Human African
Trypanosomiasis or HAT), and tuberculosis, still take a significant toll on the population. Professor Jon Cooper’s group at the University of Glasgow has developed
a technology based on ultrasonics and the nanometer vibrations they generate at the
surface of microchips, to manipulate liquid samples and integrate diagnostic tests onto
disposable portable systems. Laser vibrometry critically enables us to characterize the
vibrations on the surfaces with a high spatial resolution and on large scales,
to validate our designs. ►
|5
Healthcare
Only a handful of tests, such as
glucose personal management
for diabetes, have made the transition from centralized facilities
to being performed right next
to the patient. To do that more
widely, we use ultrasound to
perform all of the different functions required to run a complete
diagnostic assay on low cost
disposable devices. A range of
ultrasonic transducers, largely
used in consumer electronics,
have already been developed,
including those using Surface
Acoustic Wave (SAW) devices for
both sensing and microfluidic
manipulations [Friend, J. & Yeo,
L., Rev Mod Phys, 2011, 83, 647],
as shown in Figure 1a.
We have developed a new
platform, in which the ultrasonic waves are coupled into a
phononic lattice, a miniaturized
array of mechanical elements
(Figure 1b-c). In a similar way
that differences in refractive
indices within the elements of a
hologram can ‘shape’ light, the
ultrasonic field is modulated by
the elastic contrast between the
elements in the phononic array
and the matrix surrounding them.
[R. Wilson et al. Lab Chip, 2011,
11, 323].
In one implementation of the
platform, we have applied this
technology to an integrated
nucleic acid based test for the
diagnosis of malaria. This assay is
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targeted at analyzing the genetic
material of the parasite, located
within red blood cells in the blood
of infected patients. Figure 2
shows simulations and vibrometer measurements that illustrate
the use of a phononic device to
shape the waves to perform these
specific functions.
VIBROMETRY
MEASUREMENTS
The measurements were carried
out using a Polytec UHF-120
system at 9.35 MHz excitation.
The originality of these scans lie
with the different scales involved
in the measurements, which
resulted in long scans to cover
sufficient area (a liquid sample of
a few mm) to obtain a valid result
on vertical amplitudes below
1 nm, at resolutions below the
wavelength (100 µm). In some
instances, scans have taken as
long as 10 days to cover cm-wide
areas (see Figure 3).
CONCLUSIONS
Phononic surface acoustic
wave devices have shown great
potential for enabling integrated
point-of-care diagnostics, using
the mechanical energy carried
by sound to manipulate liquid
samples from patients on low-cost
microchips. We have demonstrated the detection of malaria
[Reboud J. et al., PNAS, 2012,
15162-7] from the volume of a
fingerprick of blood using an
acoustic filter. Laser vibrometry is
an essential tool of the development process that permits us to
visualize vibrations on the surface
across the entire microchips, thus
validating our designs. In the
future, more complex assays will
be integrated on the platform to
detect diseases such as tuberculosis. ■
Healthcare
Figure 1: (a) SAW propagating on a piezoelectric substrate transferring mechanical
energy into a liquid sample; (b) an alternative
format where a phononic bandgap structure
is patterned onto a disposable superstrate,
which is placed on the piezoelectric substrate;
(c) Example schematic of a phononic lattice
(holes of 80 µm in diameter).
Figure 2: A phononic filter was (a) simulated (Comsol
Multiphysics) and (b) measured using laser vibrometry (UHF, Polytec) at 9.35 MHz excitation. Results
(vibration amplitude) show the attenuation of the
waves within the structure (represented by the array
of empty holes in the measurement (b)) while they
propagate outside of it. The device is ca. 1.5 cm wide.
Figure 3: Vibrometer scan revealing the amplitude of vibrations
in a phononic cone, able to focus the energy at specific locations.
Scan of ca 190 000 points at 9.35 MHz. [Reboud J., et al, Lab Chip,
2012, 1268-73] – scale bar is 200 µm.
Contact
Julien Reboud, Rab Wilson, Yannyk Bourquin,
Jonathan M Cooper
[email protected]
Glasgow University
|7
Product News
The new
MSA-100-3D
Micro System
Analyzer
How do Microstructures Vibrate?
Optical analysis of
3D mechanical motions of
micro systems with high
displacement resolution
Precise experimental dynamic characterization of micro-devices such as MEMS is
becoming increasingly important in research and development as well as for routine
measurements at the wafer level. Laser Doppler vibrometry is now established as
the essential tool for such measurements, because the entire frequency spectrum is
obtained in real time, non-invasively and phase-resolved. Therefore transient response,
settling characteristics and indeed any vibration waveform, not just periodic motion,
can be investigated very quickly and easily.
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Product News
Laser Doppler vibrometry has
become accepted as a standard
method for studying real-time
in- and out-of-plane 3D mechanical vibration components
of macro-sized objects. On the
other hand, for micro systems,
this approach was restricted until
now to just out-of-plane (OOP)
vibration measurement. Micro
systems and other small objects
with complex motion patterns
however also require simultaneous
acquisition and analysis of three
motion directions. In the past,
in-plane motion of micro systems
was captured using relatively slow
and inefficient methods based on
high-speed image processing such
as stroboscopic video microscopy
with resolution limited to the nm
range. A higher in-plane resolution is often required for qualifying new MEMS devices.
The MSA-100-3D is a new measurement system from Polytec
that meets the in-plane measurement requirements for MEMS by
using a revolutionary approach to
laser Doppler vibrometry. Vibration is measured simultaneously
from three different directions to
derive genuine 3D vibration data
in real time with in-plane resolution down to the sub-picometer
(pm) level. For MEMS R&D this
is extremely important since
many MEMS devices have their
dominant motion components in
the plane of the device as is the
case e.g. for gyroscopic sensors
and accelerometers. High spatial
resolution measurements on
devices with small dimensions are
no problem due to the < 4 μm
laser spot size. The large stand-off
distance of the new instrument
facilitates measurements on
deep, structured samples. Two
integrated video cameras provide crisp real-time images that
simplify and accelerate system
set-up. A wide range of hardware
and software options adapt the
instrument to specific needs
of the application. In addition,
full-field measurements of 3D
deflection shapes are easily
achieved with a scanning option.
The MSA-100-3D is available in
different configurations with a
bandwidth of up to 25 MHz.
Figure 2 gives a typical example visualizing the in- and
out-of-plane modes of a
MEMS cantilever device.
This innovative solution facilitates new opportunities for the
development and testing of
MEMS devices and of other tiny
precision mechanical components
such as for example from the
data storage industry or in other
fields such as entomology.
Figure 2: Out-of-plane and in-plane
deflection shapes of a MEMS cantilever
device
The MSA-100-3D is available for
integration into a probe-station
for semi-automated or fully
automated testing of MEMS at
the wafer level. The long working
distance and special shape of
the instrument, together with
a removable compensation
glass render the instrument
ideal for measurements on
a vacuum probe station.
More Info
www.polytec.com/mems
|9
Microstructures
Extremely Versatile
The micro system analyzer
in the MEMS laboratory at
Tohoku University Japan
In this laboratory, and
probably many others
throughout the world,
Polytec Micro System
Analyzers are the most
standard MEMS evaluation
tools for their mechanical characterization.
This article introduces
three examples of MEMS
studies using Polytec
tools in my laboratory.
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HIGH FREQUENCY DISKTYPE MEMS RESONATORS
Mechanical resonance is one of
the most fundamental dynamics
exhibited by MEMS. It is used for
gyroscopes, mass sensors, optical
scanners, clock oscillators etc.
One natural research direction
for MEMS resonators is to pursue
higher resonance frequencies and
find new applications. Electrostatic and piezoelectric transductions
are two major driving principles,
and electrostatic MEMS resonators were more intensively studied
from an early stage. However,
electrostatic transduction suffers
from the critical problem that
electromechanical coupling is
too weak for many applications.
Therefore, we decided to adopt
piezoelectric transduction for
disk-type resonators, which were
based on electrostatic transduction in many previous studies.
Figure 1 shows piezoelectric
disk-type resonators, which are
mechanically connected via
a center silicon disk [1]. Sputter-deposited aluminum nitride
(AlN) was used as a piezoelectric
thin film. Figure 2 shows the
frequency characteristics up to
400 MHz. Each peak corresponds
to a specific resonance mode,
and the (2, 4) mode at 292.8
MHz is the main mode which we
needed. The mode shapes can be
calculated using the finite element
Microstructures
method (FEM), as shown in Figure
3. However, observing the actual
mode shape is not so easy due to
its small size and high frequency.
In this study, we used Polytec’s
UHF-120 to observe the actual
mode shape of the disk-type
resonators [2].
Polytec’s UHF-120 is a high frequency laser Doppler vibro­meter,
which can measure velocity and
integrated displacement up to
1,200 MHz. The displacement
amplitude resolution is 2 pm @
4.88 kHz resolution bandwidth.
Figure 4 shows measured (2, 3)
and (2, 4) mode shapes. The actual mode shapes look somewhat
different from the calculated ones
shown in Figure 3, demonstrating
the necessity to experimentally
characterize and validate modeled data. In addition, a locally
large amplitude is found at the
left upper part, which might
be caused by misalignment of
lithographic patterning. Unfortunately, we concluded that this
type of MEMS resonator was
practically useless for commercial
frequency control applications,
and switched to different acoustic
resonators. However, we demonstrated that Polytec’s UHF-120
was useful for observing high
frequency MEMS resonators.
LATERALLY-DRIVEN
PZT ACTUATOR
Figure 1: Mechanically-coupled piezoelectric disk-type MEMS resonators
(a) (2, 3) mode at 252.6 MHz
Figure 2: Frequency characteristics
of disk-type MEMS resonators
shown in Figure 1
(b) (2, 4) mode at 286.8 MHz
Figure 3: Mode shapes calculated by FEM
(a) (2, 3) mode at 260.1 MHz
(b) (2, 4) mode at 292.9 MHz
Figure 4: Mode shapes observed by scanning laser vibrometry using Polytec
UHF-120
An actuator is often a limiting
factor in MEMS design. Everyone
naturally wants strong forces and ►
| 11
Microstructures
large displacements from a small
actuator, but this is too much to
expect from a MEMS device.
On the other hand, people
expect new MEMS actuators with
better performance and/or new
functions to further extend MEMS
applications. Figure 5 shows a
new type of PZT MEMS actuator,
which we developed recently [3].
Normally, PZT MEMS actuators
move in an out-of-plane direction, i.e. vertically, because the
actuation is based on the bending
motion of a PZT thin film. On
the other hand, our new actuator
moves in the in-plane direction,
i.e. laterally. Figure 6 illustrates the
mechanism of the laterally-driven
PZT actuator. The cantilever is
composed of a laterally-stacked
PZT/silicon/ PZT structure, which
was formed by filling 2 μm wide
deep silicon trenches with sol-gelbased nano-composite PZT. On
both sidewalls of each PZT beam,
thin platinum layers were formed
as driving electrodes by atomic
layer deposition (ALD). The cantilever itself bends with a bimorph
mechanism, and thus our new
actuator is much smaller than
conventional comb-type electrostatic actuators. The fabricated
actuator shown in Figure 5 was
characterized using our standard
MEMS evaluation tool, Polytec’s
MSA-500, serving as a scanning
1
PZT: Lead zirconate titanate (PZT) is an
intermetallic inorganic compound that
consits of lead (Pb), oxygen (O) and titanium(Ti) or zirconium (Zr). It is a ceramic
perovskite material that shows a marked
piezoelectric effect.
12
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Figure 5: Laterally-driven PZT actuator with high aspect ratio PZT/Si/PZT structure
Figure 6: Mechanism of laterally-driven PZT actuator
Microstructures
Figure 7: Decay vibration of laterally-driven PZT actuator measured by stroboscopic video microscopy using Polytec MSA-500
laser Doppler vibrometer, a white
light interferometer and a stroboscopic video microscope.
The latter is suitable for observing
the lateral motion of MEMS actuators. Figure 7 shows a decay vibration of the cantilever measured by
the MSA-500. By Fourier transforming the data in Figure 7, the
fundamental resonance frequency
(f0 ) was found to be 14.26 kHz.
Also, the density of the PZT (ρ PZT )
was measured from the difference
in weight after the selective wet
etching of the PZT. Then, Young’s
modulus of the PZT was calculated from f0 and ρ PZT. The static
tip deflection of the cantilever
was 5 μm and 10 μm at a driving
voltage of 25/0 V (unimorph
actuation) and 25/−5 V (bimorph
actuation), respectively. Finally,
we estimated the d31 piezoelectric constant to be 36 pC/N.
WAFER-LEVEL HERMETIC
PACKAGING WITH
ANODICALLY-BONDABLE LTCC SUBSTRATE
MEMS include very small moving
and/or suspended structures,
which must be sealed hermetically for protection from moisture,
dust and other contamination,
air damping control, thermal
isolation etc. The packaging has a
large impact on the size and cost
of MEMS, and thus wafer-level
packaging is key for their commercialization. To date, the anodic
bonding of a borosilicate glass
lid wafer with a silicon MEMS
wafer has often been used for
wafer-level hermetic packaging.
Anodic bonding itself is simple,
reliable and of high yield, but
how to electrically access MEMS
hermetically sealed in a cavity,
i.e. electrical feedthrough, is a
critical problem. Nikko Company
(Ishikawa, Japan) and we have
developed the low temperature
co-fired ceramic (LTCC) wafer
which can be anodically bonded
with a silicon wafer [4]. The
LTCC material has a coefficient
of thermal expansion similar
to that of silicon, and contains
sodium ions, which provide ion
conductivity above 300°C. The
anodic bonding characteristic is
identical to that of borosilicate
glass. Like conventional LTCC
wafers, the anodically-bondable
LTCC wafer is produced by
stacking and firing punched green
sheets, and provides screen-printed metal internal wiring, as shown
in Figure 8. As detailed in [5, 6],
the metal vias in the LTCC wafer
and MEMS on a silicon wafer can
be electrically connected using
porous gold bumps in parallel
with anodic bonding. The reliability of hermetic sealing was evaluated using silicon diaphragms. The
LTCC wafer and a silicon wafer
with diaphragms were anodically
bonded in vacuum, and then the
deformation of the diaphragms in
air was measured by white light
interferometry using Polytec’s
MSA- 500. As shown in Figure
9, the deformation of the diaphragms during a thermal cycling
test (40°C × 30 min/125°C × 30
min) was negligible.
High reliability of electrical
interconnection through the
porous gold bumps was also
►
demonstrated from the resistance
| 13
Microstructures
of daisy-chain connections.
Another concern besides the
reliability is pressure in a vacuum-sealed cavity. It is known that
oxygen gas is electrochemically
generated in anodic bonding,
and thus pressure in the sealed
cavity is often higher than that
of bonding environment. The
pressure in the sealed cavity was
measured using the diaphragm
with the zero balance method in
a vacuum chamber. The sealing
pressure was known as the
chamber pressure at which the
diaphragm was flat. The special
optics which compensates the
influence of a vacuum window
was attached to the objective
lens of the MSA-500. Figure 10
shows examples of measured
data. If a thin film non-evaporable
getter (NEG) was used, the
sealing pressure was lower than
the detecting limit, which was
about 80 Pa in this experiment. ■
Figure 8: Cross section of anodically-bondable LTCC wafer
Figure 9: Reliability of hermetic packaging
using anodically-bondable LTCC wafer
Figure 10: Sealing pressure measurement by
zero balance method (Degassing at 400°C for
30 min → Anodic bonding at 400°C and 600
V for 1 min, Cavity volume = 0.26 mm3)
14
|
Microstructures
REFERENCES
[1] Takeshi Matsumura et al., Multi-band radio-frequency
filters fabricated by using polyimide-based membrane
transfer bonding technology, Journal of Micromechanics and Microengineering, 20 (2010) 095027
[2] Takeshi Matsumura et al., Vibration Mode Observation
of Piezoelectric Disk-Type Resonator by High-Frequency Laser Doppler Vibrometer, Electronics and
Communications in Japan, 95 (2012) pp. 33–41
[3] Shinya Yoshida et al., Fabrication and characterization of laterally-driven piezoelectric bimorph
MEMS actuator with sol–gel-based high-aspectratio PZT structure, Journal of Micromechanics
and Microengineering, 23 (2013) 065014
[4] Shuji Tanaka et al., Wafer-Level Hermetic Packaging
Technology for MEMS using Anodically-Bondable
LTCC Wafer, 24th IEEE International Conference
on Micro Electro Mechanical Systems, Cancun,
Mexico, January 23–27, 2011 pp. 376–379
[5] Shuji Tanaka et al., Versatile Wafer-Level Hermetic
Packaging Technology using Anodically-Bondable LTCC Wafer with Compliant Porous Gold
Bumps Spontaneously Formed in Wet-Etched
Cavities, 25th IEEE International Conference on
Micro Electro Mechanical Systems, Paris, France,
January 29–February 2, 2012, pp. 369–372
[6] Shuji Tanaka et al., Electrical Interconnection
in Anodic Bonding of Silicon Wafer to LTCC
Wafer Using Highly Compliant Porous Bumps
Made from Submicron Gold Particles, Sensors
and Actuators A, 188 (2012) pp. 198–202
Acknowledgements
I would like to especially thank Dr. Takeshi Matsumura, Mr. Nan Wang and Mr. Mamoru Mohri for
Examples 1, 2 and 3, respectively. Examples 1
and 2 were supported by the “Funding Program
for World-Leading Innovative R&D on Science
and Technology”, and Example 3 was partially
supported by the “Creation of Innovation Centers
for Advanced Interdisciplinary Research Areas
Program”.
Finally, I would like to thank my friends at Polytec
for giving me the chance to write this article.
Contact
Professor Shuji Tanaka
[email protected]
Department of Bioengineering and Robotics,
Graduate School of Engineering
Tohoku University
| 15
Microstructures
Good Vibrations
Laser vibrometry and its role in micro­
mechanical device development
Microelectromechanical systems (MEMS) devices are fabricated using semiconductorbased micromachining techniques, and use electrostatic, piezoelectric, thermal, or
magnetic methods to control a micron-scale movable component. Billions of MEMS
sensors and transducers have been produced annually since the early 1980s for all
aspects of everyday life and are to be found, for example, in vehicles (inertial and pressure sensors), consumer devices (microphones and accelerometers), and digital projection systems (optical micromirrors).
16
|
Microstructures
Established with a mission to
support industry and academia
in driving research to market, the
Tyndall National Institute is one of
Europe’s leading research centers
in Information and Communications Technology (ICT) research
and development, and the largest
facility of its type in Ireland.
Tyndall has a large R&D activity
focussed on the development
of MEMS devices, primarily for
industries spanning electronics,
medical devices, energy and
communication. As part of this
activity, non-destructive optical
characterization techniques are
routinely used for high-resolution,
static and dynamic characterization of such structures.
pump. The chamber contains
an Olympus V101-RM ultrasonic
transducer for excitation and
an AXL345 accelerometer for
chamber motion sensing, as
well as several feedthroughs
for electrical interfaces. A Falco
Systems WMA-300 voltage amplifier supplies the high voltages
typically required for MEMS
characterization. The system
facilitates complete topographical,
in-plane and out-of-plane analysis
of MEMS structures at pressures
varying from below 0.01 mbar to
atmospheric.
RF-MEMS
RF MEMS components, such as
switches, resonators and varactors, use electrostatic actuation
to change the position of a
micron-scale, mechanical element
suspended over a transmission
line, thereby altering the properties of that line and the circuit in
which it is embedded. RF MEMS
devices exhibit superior RF performance, are small and lightweight
and have a high integration
capability. They are promising
candidates for use in applications
such as phase shifting circuits,
radio front-ends, impedance
matching units and reconfigurable antennas. ►
The article introduces the Polytec
laser vibrometry facility at Tyndall,
and illustrates its use in two applications, namely radio frequency
(RF) MEMS for telecommunications, and piezoelectric MEMS
cantilevers for energy harvesting.
HARDWARE
Our laboratory is equipped with
a 30MHz Polytec MSA-400 with
lenses ranging from 1X to 50X,
mounted on a TS-140 (Table
Stable Ltd.) active anti-vibration
table for high-precision analysis,
Figure 1. The system is also fitted
with a custom-built, 150-mm
diameter vacuum chamber with
a glass lid and interfaced to
an Edwards TY1A12311 turbo
Figure 1:
Left: Polytec MSA-400 at Tyndall, equipped with customized vacuum
chamber, active isolation table and high-voltage amplifier.
Right: close-up view of vacuum chamber. A micromachined energy
harvesting module is under test; a nearby ADXL345 inertial sensor is
used to correlate excitation levels with transducer output.
| 17
Microstructures
A major characteristic of a microswitch is the effective mechanical
stiffness (k) of the movable
electrode, which determines the
voltage required to actuate the
switch. In general, this effective
stiffness is a function of the material properties (Young’s modulus
and material intrinsic stress)
and geometry of the movable
electrode. It may be determined
experimentally by measuring the
mechanical resonance frequency
(f ) of an electrode of mass m, and
using the expression k = (2πf)2m.
Figure 2 illustrates mechanical
resonance frequency data from
100 μm square aluminum electrodes suspended using three
spring types: straight, meander,
and spiral springs. It is clear that
the resonance frequency (and
stiffness) is highly dependent on
the geometry of the suspension
tethers.
The ambient environment (gas
concentration and pressure)
around a MEMS device may seriously affect optimal performance
and reliability. In Figure 3, the
influence of air damping on a
simple MEMS cantilever-based
resonator is illustrated using a plot
of vibration amplitude at various
pressure levels. The results clearly
show that, in order to ensure a
high Q-factor of this resonator,
the ambient pressure level in the
package must be kept below a
certain critical level, which for this
particular device is around 1mbar.
PIEZOELECTRIC ENERGY
HARVESTING
Energy harvesters convert freely
available kinetic environmental
energy into electrical energy that
can be used to power autonomous low power electrical
systems such as wireless sensor
Figure 2: 100 µm square RF-MEMS capacitive switches
featuring three different spring designs, along with the
measured mechanical resonance frequencies.
18
|
nodes (WSNs) in healthcare,
structural or machine health
monitoring applications. The
harvester itself is a mechanical system with a resonance
frequency aligned to a spectral
peak provided by the application
environment. When excited into
resonance by its environment,
therefore, the harvester acts as a
signal amplifier for the external
vibration at that particular
frequency. The harvester must
then be capable of converting
the vibration energy into useful
electrical energy. Piezoelectric
harvesters do this by exploiting
the ability of piezoelectric materials to accumulate charges on
their crystal faces when mechanically stressed.
At Tyndall we have designed and
developed MEMS harvesters with
a target resonance frequency
below 150 Hz. The devices were
Figure 3: Measured resonance frequency of MEMS resonating cantilever
versus pressure (left) and corresponding characteristics of the resonance
frequency and mechanical quality factor.
Microstructures
Figure 4: Schematic showing the cross-section of a silicon-based piezoelectric energy harvester.
fabricated using a combination
of bulk and surface silicon micromachining technologies. Figure
4 shows, in cross-section, the
profile of a cantilever-type, silicon-based harvester. In order to
achieve resonances below 150 Hz,
the beams, which constitute the
system spring, must be long (~ 8
mm - 10 mm) and thin (<50 μm).
The entire wafer thickness is used
to form the mass.
Two of the major challenges
facing energy harvesters is their
low power output and inherently
narrow bandwidth. One approach
to addressing these limitations
is to combine the output of
multiple harvesters by electrically
connecting the devices. This
can be achieved using series or
parallel (or a combination of
both) configurations. Results for
three cantilever harvesters, with
identical masses but different
beam designs, are shown in
Figure 5. These devices were
designed to resonate at approximately the same frequency.
The resonance frequency of the
cantilever beams was measured
optically using laser vibrometry.
The devices resonate between
115 Hz and 118 Hz with displacements of several micrometers. The
measurements were taken using
the setup shown in Figure 1. ■
Contact
Dr. Conor O’Mahony, Dr. Oskar Olszewski and Dr.
Ruth Houlihan of the Microsystems Centre, Tyndall
National Institute, University College, Cork City,
Ireland
[email protected]
+353 21 2346200
Figure 5: Resonance peaks measured by the vibrometer for
three cantilever structures with slightly varying beam designs.
This research is supported by Enterprise Ireland,
Science Foundation Ireland, the European Space
Agency, and the European Union.
| 19
Microstructures
Better Switching
Characterization and optimization of
BiCMOS-integrated RF-MEMS switches
The monolithic integration of RF-MEMS into a SiGe-BiCMOS technology enables the
development of cost-effective and highly-integrated circuits for future radar and imaging systems. Laser Doppler vibrometry (LDV) and coherence scanning interferometry
(WLI) have enabled the development of RF-MEMS switches with excellent performance and reliability.
20
|
Microstructures
BICMOS RF-MEMS
SWITCH INTEGRATION
SiGe-BiCMOS technologies are
becoming more and more interesting for mm-wave applications
such as WLAN, radar and imaging. These applications frequently
require reconfigurable integrated
circuits (IC) for different frequency bands, switches to control the
signal path between transmitter,
receiver and antenna as well as
phased-array systems, which
can be realized using RF-MEMS
and benefit from their improved
RF-performance (Figure 1).
The capacitive-type RF-MEMS
switch is monolithically integrated
into the backend-of-line (BEOL)
of IHPs SiGe-BiCMOS technology
(Figure 2). Therefore the shortest
interconnections between transistors and MEMS can be achieved,
minimizing or preventing high
frequency parasitic effects.
The switch is realized in the first
three BEOL metallization layers.
The high-voltage electrodes
for electrostatic actuation are
produced in metal 1, metal 2 is
used as the RF-signal line and the
suspended membrane is located
in metal 3. By applying a voltage
to the electrodes, the position of
the membrane can be modified,
hence the capacitive coupling
between the signal line and
suspended membrane changes
leading to efficient switching
of high-frequency signals.
EXPERIMENTAL SETUP
The development of RF-MEMS
switches requires several methods
for mechanical, electrical and
RF-characterization. The analysis
of electromechanical performance
is of utmost importance because
RF-performance is strongly
influenced by this. Optical characterization methods are preferred
because measurements are possible with the highest resolution
and with zero influence on the ►
Figure 1: RF-MEMS switch used as Tx/Rx-switch (left) or phaseshifter (right).
Figure 2: Scanning electron microscopy picture of
RF-MEMS switch.
Figure 3: LDV-measurement shows membrane displacement with different actuation voltages (left) and waferlevel homogenity (right).
| 21
Microstructures
behavior of the device. The
MSA-500’s LDV is used for
automated 200mm wafer-level
electromechanical motion characterization of the RF-MEMS
switches, and WLI for analyzing
the static deformation. LDV is
an outstanding measurement
method for process-control
due to its ability to detect “outof-plane” motions with nmrange displacement resolution
and μm spatial resolution.
RESULTS
Parameters such as pull-in voltage and switching-time can be
extracted by applying different
actuation voltages. Very good
uniformity can be achieved for
the demonstrated RF-MEMS
switch technology (Figure 3).
parallel resulting in fast and very
cost-effective analysis over billions
of switching cycles (Figure 5).
CONCLUSION AND
OUTLOOK
In recent years, the monolithic
integration of RF-MEMS switches
has progressed in terms of performance, process stability, yield
and reliability, not least because of
the application of LDV and WLI.
These characterization methods
provide fast and cost-efficient
detection of electromechanical
performance at the wafer-level
for developing reliable mmwave systems. For example, an
intelligent antenna-array with
integrated RF-MEMS switches has
been developed (Figure 6). ■
Conclusions on the mechanical spring constant and the
influence of residual stress
can be drawn from the membrane displacement. The latter
significantly influences the
mechanical, electrical and RF-performance, therefore requiring
regular detection (Figure 4).
Reliability is a major obstacle
for the successful application
of RF-MEMS because charging
and fatigue can lead to device
failure. LDV can be useful for
reliability detection, leading to
design improvement, because
several switches can be tested in
22
|
Figure 5: RF-MEMS switch reliability
test using LDV
Figure 6: Transceiver
quad-chip for intelligent
antenna-arrays.
Figure 4: WLI of an RF-MEMS switch
shows the influence of residual stress
inside the thin layers.
Contact
Dipl-Ing. (FH) Matthias Wietstruck
IHP – Innovations for High Performance
[email protected]
Microelectronics
Im Technologiepark 25
15236 Frankfurt (Oder), Germany
Microstructures
Tailored Modeling of MEMS
Systematic parameter extraction and model
validation using laser Doppler vibrometry
MEMS transducers are employed in many everyday objects from tire pressure sensors
to mobile phones. For optimal performance and cost savings, their complexity requires
a combination of dedicated modeling and simulation procedures (virtual prototyping), together with experimental characterization, parameter extraction and model
validation. ►
| 23
Microstructures
Microsystem
Divison into subsystems
Derivation of physics-based
subsystem models
Synthesis of full model
(entire system)
Parameter
extraction,
model calibration
and validation:
MSA-500 with
vacuum chamber
Entire system (transducer,
circuitry, environmental
impacts, package)
Figure 2: Micromechanical RF switch. The switch,
and therefore the underlying RF signal path, can be
closed by electrostatic actuation of the sliced, hinged
membrane.
Figure 1: Hierarchical modeling approach for microelectromechanical
devices and systems; parameter extraction, calibration and model validation are carried out by an MSA-500 Laser Doppler Vibrometer, which can
be combined with a vacuum chamber.
Although MEMS are complex,
the computational expense can
often be held in an acceptable
range by applying reduced order
models. We apply the hierarchical
and modular modeling approach
depicted by the flow chart in
Figure 1. Here, the system is
divided into subsystems, for which
we derive dedicated physical
submodels tailored to specific
needs and practicalities. They can
be implemented into a system
simulator by coding them in one
of the standardized hardware
design languages, enabling the
co-simulation of the transducer
and electronic circuitry within a
homogeneous environment.
24
|
One prerequisite for successful,
simulation-based design is a
dedicated parameter extraction,
model calibration and validation
strategy. To achieve this we use
the experimental set-up also
shown in Figure 1. It comprises an
MSA-500 Laser Doppler Vibrometer, which can be combined with
a vacuum chamber to enable pressure- and temperature-dependent
device characterization. A white
light interferometer is used to
determine structural topography
along with supplemental measurement equipment for electrical
characterization.
Figure 3 illustrates the typical
model calibration and validation
procedure for an RF-MEMS switch
(Figure 2). The switch comprises a
sliced membrane hinged by four
beams, which can be actuated
electrostatically to complete an RF
signal path. Initially, the mechanical submodel has to be calibrated.
White light interferometric and
eigenfrequency measurements
deliver the required parameters
such as geometrical dimensions,
mechanical stiffness and deformation caused by fabrication-induced
intrinsic stress (Figures 3a, 3b).
The gap height under the membrane, and switching voltage can
be extracted from quasistatic measurements of the electrostatically
Microstructures
a)
c)
b)
Figure 3: Exemplary data from the parameter extraction and calibration procedure of an energy-coupled simulation model of an RF-MEMS
switch.
a) Initial deformation caused by intrinsic stress obtained by white light interferometry.
b) Eigenfrequency and
c) quasistatic pull-in characteristics of the bridge, both determined by laser Doppler vibrometry.
displaced membrane (“pull-in
characteristics”, Figure 3c). Finally,
the entire model including air
damping can be validated by
recording the dynamic movement
of the bridge. Good agreement
between simulated and measured
data then proves the consistency,
accuracy and validity of the model, which is now ready to be used
for detailed investigations of the
device operation and design tasks,
such as switching time optimization, switching cycles and mechanical contact forces of different
design variants (Figure 4).
Figure 5 shows the membrane
displacement of an alternative
switch design. In order to improve
its robustness during operation,
meander-shaped heaters are
integrated underneath the anchor
regions. In case of stiction, they
are activated by heating the
bridge, exerting shear forces that
are supposed to break up the
sticking contact. Results obtained
from simulation and characterization allow us to investigate the
efficiency and dynamics of this
concept and draw conclusions on
possible improvements.
The last example, depicted in
Figure 6, deals with investigating
the development of novel nano-electromechanical resonators,
where the gap height underneath
the movable structure lies in
the submicron range. For such
devices, the quality factor is of
great interest. Pressure-dependent
Q-factors are shown, extracted
from the 3dB-bandwidth of the
fundamental eigenfrequency.
The challenge when simulating
structures with such small feature
sizes is that the limits of classical
continuum theory are already
reached at room pressure, which
has to be carefully taken into
account inside the models. ■
| 25
Microstructures
Figure 5: Transient vertical deflection of an RF-MEMS switch
induced by heating the bridge. Overlayed are oscillations of
the bridge in its fundamental mechanical eigenmode.
Figure 4: Closing of an RF-MEMS switch. Comparison
between simulation and measurement.
Figure 6: Micromechanical beam with a gap distance to the
substrate in the sub-micron range. Pressure-dependent
quality factor extracted from the 3dB-bandwith of the
fundamental eigenfrequency.
Contact
Gabriele Schrag, Thomas Künzig, Johannes Manz,
Regine Behlert, Martin Nießner*
[email protected]
Research team „Microelectromechanical Systems“
at the Institute for Physics of Electrotechnology,
Munich University of Technology
*now: Infineon Technologies AG, Munich
26
|
Microstructures
Developing Biosensors
Performance characterization of
micro­electromechanical sensors using
laser Doppler vibrometry
The ability to characterize the motion of micro devices at high frequency with
sub-nanometer resolution is key to the development of next generation resonant-based
sensor technology. ►
| 27
Microstructures
Micro fabrication processes herald
a new generation of healthcare
technology where point-ofcare sensors promise increased
sensitivity at low cost, and
readout times within minutes.
The highest sensitivity is gained
from high quality factor resonating devices in which the
addition of mass onto the sensor
causes a shift in the resonant
frequency of the device.
A novel sensing approach being
developed at Newcastle University utilizes degenerate modes
of vibration. For a given sensor
geometry, a pair of degenerate
resonant modes are chosen. In
a perfectly fabricated device,
symmetry in the system dictates
that the frequencies of both
modes are identical (Figure 1).
With functionalization of the
sensor, biomolecules can be
immobilized to specific regions
of the sensor surface, namely
the antinodal position of one
of the modes, thereby breaking
this symmetry and introducing a
split in frequencies between the
modes. This split is proportional
Figure 1: The mode shapes for the (1,0)
vibration of a circular diaphragm. For
a symmetric device, the modes form a
degenerate pair.
28
|
to the mass added to the sensor
but insensitive to non specific
binding events and temperature
fluctuations (Figure 2), making
for a robust technology.
Figure 2: Upon functionalization of
the sensor, degeneracy is broken and
the modal frequencies show a split of
Δf1. Addition of mass to the antinodal
position of the functionalized mode
increase this split to Δf2. For non
specific variations, the split remains
unaltered.
DEVICE DESIGN AND
FABRICATION
Previous incarnations of the
sensor design utilized a 4.5 µm
thick crystalline silicon diaphragm,
capacitively actuated and sensed
through electrodes contained
within a sealed cavity beneath
the device. The drawback of this
approach was complex signal
recovery electronics which ultimately raises the price of what
would be a disposable sensor. The
latest design iteration, funded
through EPSRC (EP/G061394/1),
incorporates a 750 nm thick
piezoelectric (PZT) film deposited
onto the silicon diaphragm. A 200
nm silicon oxide layer provides a
means to define electrode regions
and then by application of voltage
across an electrode, the resulting
induced bending moment
drives the device into motion.
Manufacture of the device utilizes
cleanroom fabrication processes.
The design must account for
fabrication tolerances of ±2 µm.
Two silicon wafers, one of which
is patterned, are bonded together
to form a circular diaphragm resonator. A platinum base electrode
is used as the foundation layer for
the subsequently spun-on PZT
thin film with patterned oxide
and gold layers forming the top
electrodes and immobilization
regions (Figure 3). The wafers
are then diced and individual
devices (Figure 4) packaged.
Figure 3: The
process flow for
fabrication of
the sensor.
Microstructures
Figure 4: Microscope image of a fabricated sensor.
SENSOR CHARACTERIZATION
Ultimately, device motion
is sensed utilizing on-board
electronics, however prior
to development of this electronic solution, sensor performance is characterized using
laser Doppler vibrometry.
Devices are characterized under
vacuum, at atmospheric pressure
and within a liquid. Key measurements are resonant frequencies
and quality factors of the modes.
Results indicate that due to the
high electromechanical coupling
factor of the PZT, performance
between vacuum and atmospheric conditions are comparable however due to the mass
loading of a liquid environment,
the reduction in performance
renders an electronic solution
for this scenario to
be problematic.
Mode shape alignment is a
key issue to sensitivity. As the
designed geometry dictates
where molecules will be immobilized onto the sensor surface,
it is important that this position
corresponds to the antinodal
position of the required mode.
Fabrication inaccuracies lead to
modal misalignment, so an accurate mapping of each mode shape
is required at this stage of development. For a given modal alignment, mass sensitivity is assessed
by electroplating additional
gold onto the sensor surface.
design and development of ultra
high frequency surface acoustic
wave sensors (SAWs). This UHF
vibrometer also acts as an external
user facility and we therefore look
to assist other research groups
and institutes in characterization
of their high frequency devices. ■
RESULTS AND FUTURE WORK
Preliminary results indicate a
device mass sensitivity of 12.0 Hz
pg-1 (full details may be found in J.
Micromech. Microeng. 23 (2013)
125019). Work is in progress
to develop frequency tracking
electronics for the measurement
of biomolecule immobilization
onto the sensor surface.
The preliminary investigation of
the sensor was performed with
a fiber-optic vibrometer from
Polytec giving characterization
up to 20 MHz. Through recent
equipment funding from EPSRC,
a UHF-120 system now extends
the group’s characterization facilities up to 1.2 GHz. With device
sensitivity scaling with operational frequency, this vibrometer
upgrade allows analysis of higher
order modes of the current sensor
Contact
Dr. John Hedley, Dr. Zhongxu Hu, Dr. Barry Gallacher, Dr. Neil Keegan, Julia Spoors, Prof. Calum
McNeil
[email protected], [email protected]
Newcastle University
School of Mechanical and Systems Engineering /
Institute of Cellular Medicine
www.ncl.ac.uk/mech
| 29
Biology
Big Time for Small Singers
Use and benefit of laser vibrometry in
insect research
A planthopper (Hyalesthes obsoletus). This species is
a vector of a plant-disease in vineyards and therefore of scientific and economic interest.
Cicadas, leafhoppers, planthoppers and spittlebugs (also called Auchenorrhyncha) are
a very diverse group of animals within the insect world. Nevertheless, relatively little
is known about their behavior and phylogeny. Vibrational signals play an important
role in species recognition and mating behavior. Here, the use of laser vibrometer is
extremely helpful.
30
|
Biology
Cicadas and their songs are
familiar to many people who live
or vacation in the USA, Mediterranean or tropics. The “true bugs”
(Hemiptera), which not only
include Auchenorrhyncha but also
bugs, aphids and whiteflies, are a
very successful and diverse insect
order. To date, about 42,000
species of Auchenorrhyncha have
been described worldwide. Most
of these species are leafhoppers
or planthoppers (cover picture)
with a body length of less than
5 mm. They play a significant
role as primary consumers and
consequently as a food source
for other animals. Some leafhoppers and planthoppers are
pests, for example in vineyards
or rice fields, and are therefore
of economic importance.
THE PROBLEM
In contrast to cicada songs,
which are easily heard unaided
by humans, leafhoppers and
planthoppers use substrate-born
signals. They produce vibrations
(100 - 3,000 Hz) that can only be
registered on the plant the animal
is sitting on. Substrate-born
signals were ignored for a long
time although they are widespread among insects. The songs,
often sounding like drums, are
produced by so-called tympal organs, plates on the abdomen, set
into vibration by muscles. Duets
can often be observed between
males and females. Because this
communication is mainly used
to find mates, it is believed that
the songs are species specific and
therefore a barrier to other species
(biological species concept).
Species differentiation is difficult
for many groups of Auchenorrhyncha, and until now the
identification is mainly based on
anatomical characteristics. However these are often very small,
so other features are needed for
identification. Aside from molecular methods, it turns out that
bioacoustics is a helpful solution.
EXPERIMENTAL SETUP
In the past, vibration signals were
recorded using very simple methods. The vibrations were made audible by touching the host plant
with a gramophone stylus. More
recently, piezoelectric transducers
were used. The signals could then
be recorded on magnetic tape or
later on computers. The biggest
disadvantage of these methods
was that the pickup system had ►
Figure 1: Experimental setup for recording planthopper songs. The vibrations are registered with a
PDV-100 laser vibrometer either directly on the animal or on its host plant.
| 31
Biology
to either be in direct contact with
the host plant, or at least so close
to the animal that it could possibly disturb its natural behavior.
Laser vibrometers offer incomparable advantages by measuring
vibrations directly on the animal
or the plant without direct contact (Figure 1). In addition, the
measurement recording locations
are more precisely defined and
therefore more easily reproduced.
Figure 2: Laser vibrometer and microphone measurements compared.
Above: The clear vibrational signal
from a male planthopper (Hyalesthes
obsoletus).
Below: Simultaneously recorded
airborne sound close to the animal.
32
|
OUTLOOK
Additional questions can be
addressed with laser vibrometer
measurements. It is unclear for
example if only structure-borne
vibrational signals are important
or, at least in close-up range, if
airborne sound also plays a role in
planthopper communication. Our
initial experiments have shown
that a feeble airborne sound
can be measured, but the signal
is weaker and noisier (Figure
2). The flow of the vibrational
sound into the host plant and
its vibrational behavior can be
studied thanks to the scanning
laser vibrometer (Figure 3).
Important considerations are the
position of the insect during the
diffusion and the characteristics
of the plant material as well as the
relation between the generated
frequency and resonance of the
plant. Further studies will reveal
possible evolutionary adaptations
of insects to their host plants,
which will lead to a better
understanding of speciation
processes in Auchenorrhyncha. ■
Figure 3: Deflection shape of a plant
leaf (nettle) induced by a artificial
signal (170 Hz) and the corresponding
frequency spectrum.
Authors
Dr. Roland Mühlethaler, Dr. Andreas Wessel,
Prof. Dr. Hannelore Hoch
[email protected]
Museum für Naturkunde
Leibniz Institute for Evolution and Biodiversity
Science of Humboldt-University Berlin
www.naturkundemuseum-berlin.de
Photo
Title: E. Wachmann, Berlin.
Figure 1: S. Grube/V. Hartung, Berlin.
Acknowledgements
We are very grateful to Dr Reinhard Behrendt and
Samy Monsched from Polytec for their intellectual
and technical support.
Cooperation
To Improve Hearing
Polytec and the University of Stuttgart open competence
center for laser Doppler vibrometry in biomechanics
In November 2013, the University of Stuttgart opened a
new competence center for laser Doppler vibrometry at
the Institute of Engineering and Computational Mechanics where mechanical engineering measurement technologies are being transferred to biomechanics. Some of
the results from Polytec‘s cooperation with the center are
reported here.
Hearing impaired people are
especially benefiting from this
research. “Laser measurement
technology is the basis for excellent research and solid education“
says Prof. Peter Eberhard, Head
of the Institute. Dr. Stefan König,
sales engineer at Polytec adds:
“The new competence center
promotes interesting applications
as well as fundamental analysis.“
Laser Doppler vibrometry
measures the tiniest nanometer
movements and shows highly
dynamic processes without
affecting the measured object.
“Laser vibrometry is a basic
method to measure and understand vibrations. Therefore it can
also be applied to biomechanical
processes such as the transmission
of sound through the middle
ear to the inner ear“ explains
Dr. Albrecht Eiber who is the
deputy head of the institute and
uses methods such as computer
simulation to investigate implants
that allow the reconstruction of
ears damaged by age, illness or
accident.
aids that can be grafted without
major surgery, offering maximum
comfort and safety to the patient.
Because the middle and inner
ear region is very narrow, it was
difficult in the past to painlessly
figure out how hearing prostheses
respond to different sounds and
how well the patient hears after
surgery. With the help of laser
Doppler vibrometry such examinations are now possible. The
instruments make a major contribution to the design of passive,
efficient and well-priced hearing
| 33
Cooperation
“In continuous
use since 1991“
We talked to Prof. Dr.-Ing. Peter
Eberhard, Head of the new competence
center for laser Doppler vibrometry
in biomechanics at the University
of Stuttgart, Germany, about his
research and experience with Polytec
instruments.
Prof. Eberhard, you are Head
of the new competence center
for laser Doppler vibrometry in
biomechanics at the University
of Stuttgart. What questions are
being answered at the center?
We are exploring several fields of
research together with Polytec.
First, we are investigating the
human hearing process. We are
designing and testing passive
and active prostheses. Besides
highly precise measurements we
therefore need reliable simulations.
Secondly, we educate students at
an early stage about the relevant
measurement technology so that
they can use it independently for
their studies. Additionally we investigate the vibration behavior of
different components and systems.
34
|
„We have been working
with Polytec’s laser
Doppler vibrometers
for more than 20
years.“
How and when did you first
get in contact with Polytec?
We have been working with
Polytec’s laser Doppler vibro­
meters for more than 20 years.
Determining factors for the decision were their ease of operation
and that objects can be measured
without contact and without
needing long preparation.
Which Polytec instruments are you using?
At the moment we are using
the four 1D vibrometer types
OFV-300, OFV-3001, OFV-5000
and PDV-100, the two 3D vibro­
meters: CLV-3D and MSA-050-3D
as well as PSV-500 model scanning vibrometers. It’s worth
noting that our oldest vibrometer
is from 1991. It’s been in continuous use for those 23 years!
Could you describe
one application?
At the competence center
we measure the behavior of
biological structures inside the
human ear. We therefore detect
the movement of the smallest
Cooperation
structures, where very small shifts
and forces are taking place.
Where do you see the
benefits of the measurement tools from Polytec?
It works without contact, so
the measurement doesn’t influence the measured object. The
result is not distorted. Other
important attributes are the
precise measure­ment of small
signals and the possibility to
detect high frequency vibrations.
This is not possible with mechanical measurement methods.
„... but when you
reach physical
extremes optical
methods demonstrate
their strengths.“
What advantages do our
measurement instruments have over other
measurement methods?
Mechanical measurement
methods, e.g. accelerometers,
can also deliver reliable results,
but when you reach physical
extremes, optical methods
demonstrate their strengths.
Simple operation is also key. In
many cases we combine different
measurement methods, e.g.
during the reproducible excitation of biological structures
through micro adjustable tables
and the simultaneous measurement of displacement along
with forces from force sensors.
What is your general
impression of Polytec?
We have shared our development
ideas with Polytec for many years
and are delighted with the innovative improvements that have
transpired. For us it is important
that there are new developments
both for simple instruments for
standard measurements and for
high-end applications for difficult
situations. Also important to us
are Polytec’s highly competent
sales engineers who understand
our requirements and help us
to find the best solution.
tools are in continuous use and
colleagues like to use them for
different purposes you know that
you made the right decision.
Besides that, we, together with
Polytec, face some challenges
for future Polytec instruments as
experts for mechanical vibration
technology and dynamics.
Mr. Eberhard, we thank
you for this interview.
What are future questions
that you want so solve
with Polytec’s vibration
measurement tech­nology?
For me as head of the institute
it is always interesting to see the
broad span of applications for
the vibrometers in our lab. In
many cases the instruments are
used in experiments for which
optical methods weren’t scheduled. The instruments can also
be found in tests where you just
want to try something. When
Prof. Dr.-Ing. Prof.E.h. Peter Eberhard
[email protected]
Head of Institute of Engineering and Computational Mechanics, University of Stuttgart,
Germany
| 35
Acoustics
Visible Music
Scanning vibrometer measures
vibration behavior of instruments
The history of musical instruments dates back nearly as long as the humanity itself.
During the last centuries, the development of the quality as well as of the play of
musical instruments has been pushed empirically and experimentally by instrument
makers and players. This development can hardly be surpassed. Therefore, at first
sight, the scientific study of instruments does not seem to allow any further significant improvement. It is, however, very important to gain an understanding for these
complex systems and to provide numerical models to illustrate the behavior of sound.
36
|
Acoustics
The initial topic of this research
project is the investigation of
two triangle instruments. At first
sight, the instruments differ in
form, see Figure 1, and for the
listener their sound is also clearly
dissimilar. The aim of the study
is to investigate the influence of
special geometrical properties
of a high-quality triangle on
the radiated sound, primarily
to gain experience in numerical
modeling and experimental
analysis of musical instruments.
EXPERIMENTAL SET-UP AND
MEASUREMENT PROCEDURE
The experimental analysis is
divided into two parts. The
experimental modal analysis,
using a Polytec PSV-400 Scanning
Laser Doppler Vibrometer, provides the eigenfrequencies and
mode shapes of the structure. The
measurement is then repeated
using a microphone to obtain
information related to the transmission behavior from the structural vibration to what the listener
hears. For music, the triangle is
Figure 1: Special geometrical properties of the high-quality triangle
instrument.
suspended by one string and excited by a small metal stick. In the
experiment the triangle has to be
suspended at two points to avoid
a twist and large motion during
the measurement, see Figure 2.
Because of the softness of the
suspension, the triangle can be
decoupled from the experimental
rig. Furthermore, this suspension
facilitates the comparison between measurement and numerical analysis, as the structure can
be assumed as free. Similar to
when played, the excitation in
the experiment is performed by
an impact hammer. The sound
does not differ significantly from
when excited with the metal stick.
Figure 3 shows the mounting of
the impact hammer, ensuring that
every strike is at the same place,
in the same direction and with
approximately the same energy.
In the experiment, the excitation
of the triangle is performed in
two directions. The first is in the
triangle plane (Figure 2 green)
and the other is orthogonal to this
(Figure 2 blue). In contrast to alternative measuring methods with ►
| 37
Acoustics
RESULTS AND CONCLUSIONS
Figure 2: Suspension and excitation
directions of the triangle.
accelerometers, the contactless
measurement using laser Doppler
vibrometry has some advantages.
Firstly, vibration properties of the
structure are not influenced by
additional masses. Secondly, the
optical approach of the PSV-400
greatly simplifies the setup of the
scan grid. To achieve good signal
quality, dots of retroreflective tape
are applied to the chrome-plated
surface of the triangle to ensure a
strong backscattered light level.
The microphone is placed at
a distance of 40 cm from the
triangle. The distance is limited by
the spatial dimensions of the test
rig, and yet it must be far enough
away to measure outside the
acoustic near-field. The suspension geometry and structural
excitation remain unchanged.
To analyze the influence of the
high-quality triangle’s special
geometric features in the numerical simulation, it’s important to
know the real material properties.
38
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These parameters are obtained
by an indication procedure. The
criterion for having chosen the
right parameters is the agreement
of the eigenfrequencies between
measurement and simulation.
Figure 3: Mounting of the impact
hammer.
Fundamentally, acoustic instruments radiate sound that represents a superposition of many
harmonic oscillations of different
frequencies. These frequencies
correspond to the natural
frequen­cies of the structure.
A typical sound usually comprises
one fundamental tone along with
harmonic overtones. The sense for
a beautiful tone is highly dependent on the musical experience
and talents of the listener. There
are objective criteria which can
be found to explain consonance
or dissonance of two frequencies,
or harmonic correlation of all
occurring frequencies. How­
ever, the triangle is a percussion
instrument that can be played
without regard to the tonality.
Therefore, the series of frequencies should not exhibit one
fundamental tone. That is why
the criterion of harmoniousness
cannot be applied. The sound of
the triangle is highly dependent
on the direction of excitation. The
microphone measurement shows
that it is not possible to ensure
that only one direction is excited.
Therefore, it is not identifiable
which natural frequencies belong
to which excitation direction. The
advantage of the PSV-400 is that
the direction of measurement
can be set in only one direction.
Here, the eigenfrequencies can
be assigned to the corresponding
excitation direction.
Acoustics
From these results and the
criterion for consonance it can
be seen why the higher-quality
triangle instrument sounds better.
The first five eigenfrequencies
are responsible for that. For a
good sound it is necessary that
the corresponding tones are not
dissonant to each other. The
next step will be to optimize the
triangle’s shape such that the
sound quality is optimized. ■
Contact
Figure 4: Comparison of mode shapes between simulation and
experimental test.
Dipl.-Ing. Pascal Bestle,
Prof. Dr.-Ing. Prof. E.h. Peter Eberhard,
Prof. Dr.-Ing. Michael Hanss
[email protected]
Institute of Engineering and Computational
Mechanics, University of Stuttgart, Germany
| 39
Medicines
Fascination of Hearing
Vibration patterns of the
smallest bone in the human body
According to the WHO, 360 million people worldwide suffer from hearing loss, often
caused by damage to middle-ear structures from disease or accidents. The University
Hospital Zurich has measured vibration patterns of the impaired structures in order to
select appropriate prostheses and related surgical techniques. The goals of the research
are optimal coordination of hearing aids, improved interpretations in clinical diagnostics and further development of current diagnostic procedures.
40
|
Medicines
The ear is an important sensory
organ for protection as well as
communication. It warns us
about approaching dangers –
even during sleep! So, how do
we perceive sounds and alert
signals? Acoustic sound waves are
nothing more than fluctuations of
air pressure. The acoustic sound
waves collected by the pinna
travel through the ear canal and
cause vibration of the ear drum.
The vibration of the ear drum is
transmitted via the ossicular chain
of the middle-ear into the inner
ear, where hair cell movement
causes nerve impulses generating
perception of hearing in the brain.
Our research project focuses on
the ossicular chain consisting
of the hammer, the anvil, and
the stirrup which is the smallest
bone in the human body.
A middle-ear sound transmission
line that is broken or damaged
will reduce hearing ability. To
assess changes in middle-ear
sound transmission caused by a
damaged middle-ear and assess
related surgical treatments, the
University Hospital of Zurich has
investigated the differences in
vibration patterns of damaged
middle-ears compared with
those of normal intact ears, using
instrumentation from Polytec. The
sound transmission mechanisms
in normal and damaged middle
ears could be revealed from the
measurement results. The measurements were also used to find
optimal choice of hearing aids,
improve interpretations in clinical
diagnostics and further develop
current diagnostic procedures.
The impaired sound transmission
line in the damaged middle-ear
can be surgically treated bypassing
the damaged middle-ear structure
using implantable middle-ear
prostheses. Such surgical treatments with middle-ear prostheses
include replacement of the entire
ossicular chain and replacement
of a part of the ossicular chain,
for example, the stirrup (stirrup
prostheses). Analysis of the
measurement results has provided
information on development and
optimization of the middle-ear
prostheses and related surgical
techniques. Our current project
with such measurements focuses
on functional roles of the joint
between the hammer and the
anvil (hammer-anvil joint).
EXPERIMENTAL SETUP
The ossicular chain is made up of
temporal bones. The eardrum is
stimulated with a loudspeaker, and
the ossicular chain vibrates. The
loudness of the stimulation level
is monitored with a microphone
inside the ear canal. Vibrations
of the stirrup are measured
simultaneously with a scanning
laser vibrometer system. ►
Figure 1:
The human ear: Sound waves travel via the
eardrum
, the hammer
, the anvil
and the stirrup
to the inner ear
.
| 41
Medicines
Figure 2: Experimental setup: the robot arm enables control of the desired position
of the scanning-laser-vibrometer so that vibration of the stirrup can be measured
as well as vibrations of the temporal bone.
The desired position of the
scanning laser vibrometer is
controlled by a robot arm (KUKA
KR-16, position repeatability
<± 0.05 mm), and a video
camera (VCT 24) captures
the area to be scanned.
The reflection of the laser beam
is optimized with retro-reflective
glass beads (50 μm diameter).
Vibration measurements of
the stirrup are made at several
frequencies, and repeated for
the immobilized hammeranvil-joint. From differences in
the stirrup vibration between
functioning and immobilized
hammer-anvil joints, we can
deduce the role of the hammeranvil joint in sound transmission
through the middle-ear.
RESULTS AND APPLICATIONS
Figure 3: Example of a middle-ear prosthesis: stirrup-prosthesis (NiTiBOND®):
the immobilized stirrup is replaced by a
mobile prosthesis. Thanks to the prosthesis, sound transmission is restored
and hearing capacity improved. .
42
|
What influence does the hammeranvil joint have on sound
transmission in the middle-ear?
Preliminary data suggest that the
hammer-anvil joint influences the
frequency content of vibrations in
the stirrup. These determinations
will serve as the basis for
modelling the dynamic behavior
of a virtual middle-ear. It may
also help to explain the influence
of the hammer-anvil joint on
age-related hearing loss and a
potential damping function of the
hammer-anvil joint for protection
against sudden exposure to high
intensity sounds or air pressure.
Moreover, middle-ear prostheses
that bypass conductive hearing
loss and therefore improve hearing
will be developed and continually
optimized.
A new kind of stirrup prosthesis
(NiTiBOND®) has already been
developed and brought to
market by KURZ® together with
the Institute of Engineering and
Computational Mechanics at
the University of Stuttgart. ■
Contact
Rahel Gerig
PhD candidate, M.Sc. biomedical sciences
[email protected]
Group ‚Biomechanics of Hearing’ Prof. Dr. med.
Alexander Huber
University Hospital of Zurich
Department of Otorhinolaryngology, Head and
Neck Surgery
Nord 2, B
Frauenklinikstrasse 24
CH 8091 Zurich
Acknowledgements
This study is supported by the Swiss National
Science Foundation (SNSF) Nr. 138726 and
the German Research Foundation (DFG) within the
EI-231-6/1 Grant.
The author is grateful to Prof. Dr. med. Alex Huber,
Dr. Jae Hoon Sim and Dr. med.
Christof Röösli for their valuable advice and
support.
Product News
Unlimited
Possibilities
HSV-100 High Speed Vibrometer
High resolution vibration
measurement at high speeds
of up to 40 m/s is a key feature
of the HSV-100 High Speed
Vibrometer. Applications such as
the measurement of valve train
dynamics in high power engines,
resonance testing of turbine
blades or analysis of pyroshock
events are handled reliably
by HSV-100, which outputs
velocity and displacement signals
simultaneously. The HSV-100 is
available in a single-channel as
well as a dual-channel version,
which features differential vibration measurement with respect
to a reference surface. For valve
trains, motions of the valve and
the engine block can be measured
and subtracted from each other,
revealing the true valve motion,
closing velocity and bounce
characteristics. A novel HSV-100
feature is the ability to interconnect several controllers, allowing
vibration measurements with an
arbitrary number of channels.
More Info
www.polytec.com/highspeed
| 43
Product News
Surface Metrology
in a New Dimension
High production quantities and
low costs are important economic factors these days. Therefore it
is absolutely essential to identify
errors in production at an early
stage. The TMS-500 TopMap
optical measurement system
is not only used for quick and
precise 3D surface structure
characterization, it can also
check flatness, parallelism and
step height tolerances reliably
and with high repeatability.
The TMS-500 TopMap takes only
a few seconds to scan nearly 2
million points, covering an area
of 43 mm x 32 mm. A high lateral
resolution of up to 13 μm ensures
that important details are not
missed. A broad vertical scan
range of 70 mm combined with
the white light interferometric
measuring principle allows precise
and traceable characterization
of huge step heights and hard
to reach areas (inside deep
holes). The measurement results
are always reliable, no matter
if the surface is shiny or dull.
The TMS-500 TopMap software
user interface can be adapted to
customer needs and can therefore
be individually configured to most
different requirements of the user.
The easy-to-use measuring and
analysis software comes standard, offering a wide variety of
evaluation options. Included is
areal step height analysis as well
44
|
as profile step height analysis
according to DIN ISO 5436-1.
The TMS-500 TopMap system
comprises a sensor head,
controller and data management system. A broad range
of accessories such as vibration
damping and motorized stages
are available. TMS-500 performs
routine automated measurements
quickly with the help of a software user interface that can be
easily adapted to customer needs.
For example the software user
interface can be adjusted to the
special requirements of the precision watch industry. Here there
is a particular need for the fast
and simple teach-in procedure
of new components due to the
high variety of component types.
Most of the time several parts will
be scanned with a large field of
view and afterwards automatically
checked with regard to defined
tolerances. TMS software is able
to identify, position and align the
measured objects and adapt the
tolerance evaluation accordingly.
Easy-to-use and automated
operation ensures that different
TMS-500 users achieve identical
measurement results. This is
an important condition for the
automotive or watch industry for
example where the reliable testing
of components with demanding
tolerance requirements is essential. TMS software allows the
transfer of measurement data
to common statistics software
packages such as qs-STAT.
The system can be tailored
to customer needs with
trouble-free integration. It
is perfectly suited for applications where quality assurance is an important issue:
In the lab, pre-production
or directly in the production line.
More Info
www.polytec.com/tms500
| 45
Product News
Very High Frequency
Scanning Vibrometer
PSV-500-V
High spatial resolution is required for characterizing
deflection shapes of transducers at ultrasonic frequencies. A new version of Polytec Laser Doppler Vibrometers
is released providing excellent resolution for easy transducer characterization or in situ non-destructive testing.
The 25 MHz bandwidth V-series (very high frequency; VHF)
PSV-500 Scanning Vibrometer
uses digital decoding to achieve
for the first time the low noise
required to resolve minute
vibrations of medical or sonar
transducers and transducer arrays.
Timing, cross-talk and amplitude
distribution are assessed with
ease, providing high fidelity data
for finite element model validation
and performance verification.
PSV-500 digital scanning
technology provides excellent
measurement density and precision with mm2 to a m2 size fields
of view. The PSV-500-V includes
a full workstation with a built in
VHF signal generator, low jitter
46
|
trigger and 3 acquisition channels for additional high dynamic
signals.
Polytec also developed for the
first time a high-MHz full 3D
vibration mapping system for
VHF ultrasonic vibrations. The
latest development extends the
available 3D bandwidth by an
order of magnitude, using 3 independently scanning laser beams
and a machine vision system for
perfect beam intersection thereby
achieving excellent spatial resolution. PSV-500-3D-V is the flexible
solution for material characterization, non-destructive evaluation
and transducer qualification.
Researchers
from all over the
world have already
achieved innovations in diagnostics and treatment with the
PSV-500-V’s predecessors. The V
again promises to play a major
role in future breakthroughs.
More Info
www.polytec.com/psv3d
Leave it to the
Commander
Scanning Vibrometer
Software 9.1
Sensors are useless without a brain. PSV software provides a powerful user interface to the Laser Vibrometer
sensor. New machine vision support and a full 64-bit
environment provides even better usability, and speeds
up the measurement and analysis process.
Designed to be
an open platform,
users can control and
analyze data with third party
tools such as MatLab®, LabView®
or Microsoft™ Excel. Users of 3D
versions of PSV Scanning Vibro­
meters benefit from the machine
vision supported semi-automatic
3D alignment procedure, which
quickly and precisely matches
imported Finite Element Geometry models to the object under
test.
Modal Analysis experts can now
use the technical data stored in an
accelerometer with TEDS (Transducer Electronic Data Sheet).
Sensitivity data is unambiguously
read from the transducer and
stored in the acquisition settings
of the software. Extended
damping values are available in
the analyzers for a first assessment of the validity of simulation
results.
MEMS and microsystems
researchers using the software
with the Micro System Analyzer
(MSA) or Ultra High Frequency
(UHF) scanning systems will
benefit from the Q-factor feature
for damping evaluations, as well
as extended grid definition tools
to allow a precise adjustment
of the spatial resolution of the
measurement grid to the acoustic
wavelength of the sample.
Research groups in universities
and colleges that are part of
Polytec’s University Program
benefit from these new features
automatically. New attractive
pricing for the desktop version of
the software, which allows offline
analysis of the measurement data,
provides access to a larger group
of users in R&D departments
and e.g. simulations service
companies.
More Info
www.polytec.com/software
| 47
Events
Advancing Measurements by Light
Polytec GmbH (Germany)
Polytec-Platz 1-7
76337 Waldbronn
Tel. + 49 7243 604-0
[email protected]
Events
Date
Event
Location
Oct 28 - 30, 2014
Automotive Testing Expo 2014
Novi, MI
Oct 29 - 30, 2014
International Automotive Body Congress
Troy, MI
Nov 17 - 19, 2014
Eastern Analytical Symposium & Exposition
Somerset, NJ
Dec 4, 2014
MBL: Workshop on “Quality control, condition
monitoring and predictive maintenance“
Brussels, Netherlands
Expertise for Rent
Technical specifications are subject to change without notice. OM_InFocus_2014_08_2000_E_42332
Systems and Engineering Services
Whether your measurement task
involves general vibration testing,
structural dynamics characterization,
acoustic localization, finite element
model validation or surface metrology
– our experienced PolyXperts are
always happy to take care of your
needs, be they occasional or long
term. Address your individual
measurement tasks cost-effectively
and productively by using our
advanced systems and engineering
services.
■■
Access to the latest in non-contact
measurement technology
Short term or occasional measurement
Polytec Japan
Arena Tower, 13th floor
3-1-9, Shinyokohama
Kohoku-ku, Yokohama-shi
Kanagawa, 222-0033
Tel. +81 45 478-6980
[email protected]
Central Office
1046 Baker Road
Dexter, MI 48130
Tel. +1 734 253-9428
■■
■■
Improved data quality
Fast response to critical characterization
requirements
Tests can be performed in one of our state-of-the-art engineering centers and test
facilities or at the convenience of your facility. Please contact us at 949-943-3033 or send us
an email at [email protected].
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Imprint
Polytec InFocus · Optical Measurement Solutions
Issue 2014 – ISSN 1864-9203 · Copyright © Polytec GmbH, 2014
Polytec GmbH · Polytec-Platz 1 - 7 · 76337 Waldbronn · Germany
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(Great Britain)
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Images courtesy of the authors unless otherwise
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