WHITEPAPER – ULTRASOUND PIEZO ELEMENTS IN MEDICAL TECHNOLOGY
Dipl.-Phys. Frank Moeller

Ultrasound Piezo Elements in Medical Technology
Tool, Therapeutic Device and Sensor

PI Ceramic GmbH_Lindenstrasse_07589_Lederhose_Germany
Tel. +49 36604 882-0, Fax +49 36604 882-4109 EMail info@piceramic.com, www.piceramic.com

WHITEPAPER – ULTRASOUND PIEZO ELEMENTS IN MEDICAL TECHNOLOGY
Dipl.-Phys. Frank Moeller

Ultrasound is sound with frequencies above the range ofWith piezo components, different geometric variants andhuman hearing frequencies starting at around 16 kHz.

resonant frequencies can be realized in addition to theThis range is used for many purposes in medical

material selection for the respective application (Fig. 1);

engineering, but also in industry, and research. The

components such as disc- or plate-shaped transducers

spectrum of applications in medical technology extends

in thickness vibration mode, piezoceramic rings, piezo

from pumping and dosing to diagnostics and therapy.

tubes and shear elements with standard dimensions canPiezoelectric ceramics offer excellent properties forbe delivered on very short notice on the basis of semi-

generating and detecting ultrasonic waves. They can befinished products in stock. Geometries beyond the

manufactured cost-effectively in almost any shape andstandard dimensions are also available upon request.

thus offer tailor-made solutions for different applications.

PI Ceramic furthermore ensures integration in the final

Piezoelectric materials can produce an electric voltage

product. This includes the electrical contacting of thewhen a force is applied to them (piezo effect), and theyelements according to customer specifications as well as

can change their dimensions when an electric field ismounting in third-party components, as well as gluing orapplied (inverse piezo effect). They convert mechanicalpotting of the ultrasonic transducers. To measure thepower into electrical power and vice versa; they are also

flow, filling level and force or acceleration, customized

referred to as piezoelectric transducers. While the direct

sensor components are manufactured that can be easily

piezo effect can be used for sensor applications, theintegrated in the respective application.

inverse piezo effect is used for the manufacture ofactuators. The motion is exclusively based on solid stateeffects, i.e. it is frictionless and wear-free. Piezos also do
not generate any magnetic fields and are not influenced
by them.

Short

ResponseTimes,High

Dynamics and Flexible Designs
The creation and detection of ultrasound, for example, isa classic piezo application because the piezo element
starts to oscillate when an a.c. voltage is applied. The
short response times and the high dynamics of thismotion naturally also benefit ultrasound generation.
The piezo elements from PI Ceramic are suitable for a
multitude of ultrasonic applications. These can beFig. 1 Many variants of piezo elements are possible, e.g.
tubes, disks, benders, shear elements or transducers,which makes it easy to adapt them to the respective
application

generally classified in mainly sensor applications forfrequencies of up to 20 MHz and power ultrasound, inwhich the energy densities are higher.
As a result, the piezo elements accomplish considerable
mechanical work, e. g. in crushing kidney stones orremoving dental plaque. The typical frequencies ofpower ultrasound are between 20 and 800 kHz.

PI Ceramic GmbH_Lindenstrasse_07589_Lederhose_Germany
Tel. +49 36604 882-0, Fax +49 36604 882-4109 EMail info@piceramic.com, www.piceramic.com

WHITEPAPER – ULTRASOUND PIEZO ELEMENTS IN MEDICAL TECHNOLOGY
Dipl.-Phys. Frank Moeller

Aerosol production for respiratory
therapy

Propagation time measurements for bubble-free flow and

There are a wide variety of application areas for

In medical applications it is often necessary to ensure

piezoceramic

there is an undisturbed flow without air or gas bubbles,

Therapeutic

components
devicesinare amedicaltypicalpatient-friendly sonography

technology.

example.

Thee.g. in dialysis, with transfusion pumps. This can bediseasesoften

involves

done with the aid of ultrasonic technology in so-called

appliedwithatomizers.

air-bubble detectors. The piezo elements in these

Conventionally, pressurized air atomizes the inhalation

sensors serve to generate and receive ultrasonic waves.

solution into minute droplets. An alternative method is toThe propagation time of the ultrasound signal isgenerateevaluated (Fig. 3).

treatmentof

respiratory

medication

being

minutedirectly

droplets withtheaidofpiezo

technology. Specially shaped piezo disks act as
ultrasonic transducers and excite a stainless-steel
diaphragm with several thousand holes to executeultrasonic vibrations at 35 kilohertz (Fig. 2). This
produces particularly homogenous aerosols. This isadvantageous for precise dosing – the administration ofhigh-quality drugs can be better targeted allowing accessto new therapeutic concepts. The risk of side effects isalso reduced. Moreover, piezo technology reduces thetime required to atomize medications by up to 50%
compared to conventional systems. For patients withchronic respiratory diseases in particular, this means animprovement in their quality of life.

Fig. 3 The propagation time measurement is based on
the alternate transmission and receiving of ultrasonicpulses in and against the direction of flow
The sensors are mounted on the outside of flexible tubes
and operate without coming into contact with the medium
to be transported; they therefore do not interfere with theflow rate, nor is there any danger of contamination. The
nonmagnetic piezo technology means that, when theelectronics are shielded appropriately, it is even possible
to operate in an extreme environment, such as in thevicinity of magnetic resonance tomographs.

Fig. 2 The piezo ring is directly glued to the metal ring of
the diaphragm. When an a.c. voltage is applied, thepiezo element oscillates with a frequency of approx.
35 kHz (Image: Pari Pharma/PI)

Sonography, whose advantages derive mainly from theEven the special hygiene requirements which come withgenerates ultrasonic waves and also detects them again.

medical engineering applications are mastered by piezo

It emits short, directional sound wave pulses which areceramics; the aerosol generators can be professionallyreflected and scattered by the tissue layers to different

sterilized in autoclaves. The ultrasonic operation isdegrees. By measuring the propagation time and thenoiseless for humans, and the low power consumption ofmagnitude of the reflection an image of the structure

the piezo component also allows battery operation.

under investigation can be produced.

harmlessness of sound waves, is likewise based on theprincipleofpropagation

timemeasurement.

Theultrasonic transmitter contains a piezo element, which

PI Ceramic GmbH_Lindenstrasse_07589_Lederhose_Germany
Tel. +49 36604 882-0, Fax +49 36604 882-4109 EMail info@piceramic.com, www.piceramic.com

WHITEPAPER – ULTRASOUND PIEZO ELEMENTS IN MEDICAL TECHNOLOGY
Dipl.-Phys. Frank Moeller

In addition to propagation time measurements, typical

Therapeutic methods working with ultrasound methods

applications for piezo elements are in pumping andinvolve irradiating the tissue with ultrasonic waves bydosing (Figure 4). The dosing amounts range from themeans

microliter and nanoliter range to the picoliter range.

longitudinal waves generate mechanical vibrations in theHere, piezo-based microdosing systems stand out due totissue, which can promote healing processes, for

theirexample.

very

small

dimensions,

their

low

energyconsumption and low costs.

of

anA

ultrasonicpartofthetransmitter.

ultrasoundMechanicalenergyissimultaneously converted into heat. Typical working
frequencies for the piezo elements are in the range 0.8
to over 3 MHz, both continuous wave and pulsed wave
ultrasonic techniques being used in the application.
Different effects can be achieved depending on theenergy of the waves. High-energy shock waves are used
to destroy kidney stones, for example. Low-energy shockwaves effect a type of micro-massage, and are used forthe treatment of bones and tissue in physiotherapy
among other things.

Fig. 4 In addition to propagation time measurements,
typical applications for piezo elements are in pumping
and dosing; the picture shows a tube pump

In cosmetic applications ultrasonophoresis, i.e. theTools and therapy methods withultrasoundelements in medical technology is thus constantly

Further interesting applications are found in the area ofpower ultrasound. Nowadays, instruments with ultrasonicintroduction of drugs into the skin, is becoming
increasingly important.The field of applications for piezo
expanding.

Authordrives allow minimally invasive surgical techniques in
eye and oral surgery. Devices based on ultrasound are
frequently used for liposuction and removing dental
plaque (Fig. 5) and they have been using piezo elements
as sound generators for quite some time.

Dipl.-Physiker Frank Moeller, Sales at PI Ceramic GmbH

Fig. 5 Instrument for ultrasonic plaque removal (OEMproduct); the piezo disks can be clearly seen

PI Ceramic GmbH_Lindenstrasse_07589_Lederhose_Germany
Tel. +49 36604 882-0, Fax +49 36604 882-4109 EMail info@piceramic.com, www.piceramic.com

WHITEPAPER – ULTRASOUND PIEZO ELEMENTS IN MEDICAL TECHNOLOGY
Dipl.-Phys. Frank Moeller

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 andservice offices abroad, the privately managed company
operates globally. More than 700 highly qualified
employees all over the world enable the PI Group to
fulfill almost any requirement from the area of innovative
precision positioning technology.
All key technologies are developed in-house. This allows
the company to control every step of the process, fromdesign right down to shipment: precision mechanics andelectronics as well as position sensors. The requiredpiezoceramicelements

aremanufactured

byoursubsidiary PI Ceramic in Lederhose, Germany, one of
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.

PI headquarters in Karlsruhe, Germany: More than 350
employees work on high-resolution drive systems andpositioning systems

PI Ceramic GmbH_Lindenstrasse_07589_Lederhose_Germany
Tel. +49 36604 882-0, Fax +49 36604 882-4109 EMail info@piceramic.com, www.piceramic.com