WHITEPAPER – DRIVES AND TESTING AIDS FOR INHALATION DEVICES
Dipl.-Phys. Steffen Arnold & Dipl.-Ing. Elmar Uhlitzsch

Piezo Actuators: Drives and Testing Aidsfor Inhalation Devices
Creating Oscillations – Measuring Oscillations

Physik Instrumente (PI) GmbH & Co. KG • Auf der Roemerstrasse 1 • 76228 Karlsruhe
Germany • Tel. +49 721 4846-0 • Fax +49 721 4846-1019 • info@pi.ws • www.pi.ws

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WHITEPAPER – DRIVES AND TESTING AIDS FOR INHALATION DEVICES
Dipl.-Phys. Steffen Arnold & Dipl.-Ing. Elmar Uhlitzsch

Piezoelectric materials convert electrical energy directly
into mechanical energy and vice versa. This presentsinteresting possibilities: the motion that results when an
electric a.c. voltage is applied to a piezoelectric material
is very important for creating oscillations, for example.
Actuators

exploiting

thispiezoeffectmovewithresolutions in the sub-nanometer range, with highdynamics and frequencies of up to several thousand
hertz.
In the application described in the following, this is of
double advantage: in inhalation devices, piezoelectricelements ensure an even aerosolization of medicine,and the piezos are the driving force in function testing of
the aerosol heads as well.

Fig. 2 A piezo element excites the diaphragm of thenebulizer to execute ultrasonic oscillations. The fluid ispressed through the roughly 3000 fine holes in thediaphragm and thereby aerosolized (Image: PariPharma)
The reservoir of the inhalation device is first filled withthe desired dose of medicine, and the aerosol is thencreated in the nebulizer (figure 2) using a perforated
steeldiaphragm.

"Apiezoelementexcites

thismembrane to execute ultrasonic oscillations at approx.
120 kHz," is how Phillip Holzmann (figure 3), Head of theMicrosystems Development Group at Pari Pharma
explains the functioning of the nebulizer. "Due to theresulting pressure changes at the diaphragm, the fluid is®

Fig. 1 The inhalation system eFlow rapid works very
efficiently with comparatively short inhalation times andthus meets the needs of patients very well (Image: PariPharma)pressed through the holes in the diaphragm and thereby
aerosolized. The approximately 3000 holes in thediaphragm have a diameter of roughly 2 µm. Thisguarantees a defined droplet size distribution."

Oscillations manifest themselves in different ways: they
can be disturbing or even destructive, e.g. in the case of
imbalance, noise, friction or impact. On the other hand,
they also have a positive effect, e.g. as music or intherapeutic applications, for example to treat respiratory
disorders. During inhalation, liquid medication has to be
aerosolized in very fine droplets, and the drug mist has
to be mixed into the respiratory air as homogeneously aspossible. For this purpose, Pari Pharma GmbH has®

developed the inhalation system eFlow rapid (figure 1),
an innovative device that works very efficiently withcomparatively short inhalation times.

Fig. 3 Philipp Holzmann, Head of the Microsystems
Development Group at Pari Pharma (Image: PariPharma)

Physik Instrumente (PI) GmbH & Co. KG • Auf der Roemerstrasse 1 • 76228 Karlsruhe
Germany • Tel. +49 721 4846-0 • Fax +49 721 4846-1019 • info@pi.ws • www.pi.ws

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WHITEPAPER – DRIVES AND TESTING AIDS FOR INHALATION DEVICES
Dipl.-Phys. Steffen Arnold & Dipl.-Ing. Elmar Uhlitzsch

Convincing Arguments for the Piezo
Element"We have also found an established and competent

There were simultaneously several reasons for selecting

manufacturer in PI Ceramic (figure 5), which modifies

a piezo element as the driving force in the aerosol

and produces the piezo elements specifically for ourgeneration. The creation of vibrations, for example, isapplication conditions", adds Holzmann.

virtually a classic piezo application because the piezo
element starts to oscillate when an a.c. voltage isapplied. Since the annular piezo (figure 4) is directly
glued to the metal ring of the diaphragm, the diaphragm
oscillates along with it. The amplitude is in the range of afew µm. "The oscillation generated by the piezo element
thus perfectly suits the application in respect tofrequency as well as displacement", Holzmann explains.
The short response times of the piezos and the highdynamics of the motion naturally also benefit theapplication as a diaphragm drive.

Fig. 5 Many variants of the basic structure of piezo
elements are possible, for example piezo tubes, disks,
shears or translators, which makes it easy to adapt themto the actual application

Quality Assurance of theDiaphragms Directly in theManufacturing Process
For patients to benefit from the new inhalation system,
the nebulizer system must function flawlessly. For thisreason, the manufacturer relies on 100% testing.
Fig. 4 The annular piezo is directly glued to the metalring of the diaphragm. When the a.c. voltage is applied,the piezo element oscillates with a frequency of 120 kHz(Image: Pari Pharma/PI)"In principle, an electrical impedance test that can detect
particular oscillation characteristics of the component(figure 6) would also be possible" continues Holzmann.
"In the end, however, we did not believe that this method

However, there are further arguments that speak for thewas precise and reliable enough. Since the oscillation

use of piezos in aerosol nebulizers: Since the motion isbehavior had already been optimized with a scanning

based on crystalline solid-state effects, there is novibrometer during the development phase, we were abledanger of abrasion with this technology and there are noto use the knowledge gained from this to determine

cogwheels, bearings or other mechanical parts subject tomeasuring points that yield quality-relevant results inwear. Piezos do not generate any magnetic fields andoscillation

aretherefore decided to use a laser vibrometer in quality

notinfluencedbythem.

Changing

ambient

temperatures do not interfere with the piezo effect either.

measurements

duringcontrol as well."

Physik Instrumente (PI) GmbH & Co. KG • Auf der Roemerstrasse 1 • 76228 KarlsruheGermany • Tel. +49 721 4846-0 • Fax +49 721 4846-1019 • info@pi.ws • www.pi.ws

Page 3 of 5production.

We

WHITEPAPER – DRIVES AND TESTING AIDS FOR INHALATION DEVICES
Dipl.-Phys. Steffen Arnold & Dipl.-Ing. Elmar Uhlitzsch

Deviations in the diaphragm quality, e.g. due todeformations during assembly or errors in the adhesion
process, can be reliably detected with the opticaloscillation analysis.

Fig. 7 Quality control with the laser vibrometer: exampleof the frequency spectrum of a diaphragm (Image: PariPharma)"To evaluate the quality of a measurement, the signal-to-Fig. 6 View of the test items (Image: Pari Pharma)
A semiautomatic measuring station was developed for
quality control in production. The main item is a laser
vibrometer from the product range of Polytec, which
consists of a control unit and a compact measuring headwith a flexible fiber optic cable. As part of quality control,
the oscillation behavior of the diaphragm is measured
contact-free at each aerosol head and the frequency

noise ratio is calculated as well." In order to ensure thatthe laser hits a level position between the holes of thediaphragm on each test item, the measurement isevaluated on the basis of the intensity of the reflectedlight. If the laser intensity is too low, the measuring point
is moved by a few micrometers with a deflection unit until
the full intensity is reached (figure 8).

spectrum is determined for each diaphragm. The
important measuring points for this were alreadyobtained with the scanning vibrometer during thedevelopment phase.

Piezo as the Driving Force during
Testing
The piezo also assumes a key role as the driving force
during function testing: It is electrically excited in afrequency

spectrumbetween30and300kHz.

Measurements of the oscillation amplitudes within thisfrequency band and the position of the resonances makeit possible to draw conclusions about the diaphragm
quality (figure 7).
"The analysis is performed with the testing software
QuickCheck from Polytec, which was adapted very wellto our requirements and reliably separates good partsand rejects", adds Holzmann.

.
Fig. 8 Integration of the laser vibrometer in the a bench(Image: Pari Pharma/Polytec)

Physik Instrumente (PI) GmbH & Co. KG • Auf der Roemerstrasse 1 • 76228 Karlsruhe
Germany • Tel. +49 721 4846-0 • Fax +49 721 4846-1019 • info@pi.ws • www.pi.ws

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WHITEPAPER – DRIVES AND TESTING AIDS FOR INHALATION DEVICES
Dipl.-Phys. Steffen Arnold & Dipl.-Ing. Elmar Uhlitzsch

The 100 percent testing with the laser vibrometer thus
ensures that the inhalation systems reliably function
during practical use with patients. The piezo elements
used also significantly contribute to this because they
are the driving force in the aerosol generation as well as

About Polytec
As an innovative high-tech company, Polytec has beendeveloping,producinganddistributing

laser-based

measurement technology solutions for research andin the oscillation testing

industry for over 40 years. Building on their success withAuthors

manufacturing

distribution business, Polytec began developing andSteffen Arnold, Head of Marketing & Products at Physik
Instrumente (PI) GmbH & Co. KG, Elmar Uhlitzsch,
Vibrometer Product Manager at Polytec GmbHtheirown

laser-based

measuring

instruments in the 1970's. Today, the company withheadquartersinWaldbronn

nearKarlsruhe

isaworldwide leader in the field of optical oscillation
measurement with laser vibrometers. Systems forsurface

About the PI GroupOver the last four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany, has developed into
the leading manufacturer of positioning systems withaccuracies in the range of only a few nanometers.
With four company sites in Germany and ten sales andmeasuring

technology,

analytic

measuring

technology as well as velocity and length measurement
also belong to their now wide range of innovative
products.

About Pari Pharma
For over 100 years, PARI has made a name for itself asservice offices abroad, the privately managed company

a company specializing in treating respiratory disease,operates globally. More than 700 highly qualified

with an international reputation. Today, PARI Pharma is

employees all over the world enable the PI Group todeveloping modern devices for inhalation treatment. Withfulfill almost any requirement from the area of innovative

their own research and production, the company has

precision positioning technology.

repeatabily

All key technologies are developed in-house. This allows

standards in aerosol technology. Careful selection of

the company to control every step of the process, frommaterials, production at their own manufacturing plants

design right down to shipment: precision mechanics andand the strictest quality controls guarantee the reliability

electronics as well as position sensors. The requiredof their products, the purpose of which is to make life

piezoceramiceasier for people who suffer from respiratory diseases

elements

aremanufactured

byoursubsidiary PI Ceramic in Lederhose, Germany, one ofsucceeded

inestablishingand those who care for them.

the global leaders for piezo actuator and sensor
products.
The PI miCos GmbH in Eschbach near Freiburg,
Germany, is a specialist for positioning systems forultrahigh vacuum applications and parallel-kinematic
positioning systems with six degrees of freedom andcustom-made designs.

Physik Instrumente (PI) GmbH & Co. KG • Auf der Roemerstrasse 1 • 76228 Karlsruhe
Germany • Tel. +49 721 4846-0 • Fax +49 721 4846-1019 • info@pi.ws • www.pi.ws

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