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Experiments with the bonding machine Show image information
Quality evaluation of bonded interconnects using a shear tester. Show image information
Reliability analysis of a friction clutch. Show image information
Lab work in teaching. Show image information
Transport of fine powder using ultrasonic vibrations Show image information

Experiments with the bonding machine

Quality evaluation of bonded interconnects using a shear tester.

Reliability analysis of a friction clutch.

Lab work in teaching.

Transport of fine powder using ultrasonic vibrations

Dynamics and Mechatronics (LDM)

Multifunctional materials, actuators and ultrasound technology

Multifunctional materials stand out because they do not only fulfill a single essential function of a system,but several, such as holding, moving, deforming or even altering a structure. This multifunction is controllable and reversible by external variables. Such materials include, but are not limited to, shape memory alloys, piezoelectric materials, and electroactive polymers. These materials are commonly referred to as "functional materials" or "smart materials".

Some of these materials have been developed for several decades and are used industrially (e.g. piezoelectric accelerometers), while others are still under development, particularly in terms of properties optimisation and large-scale manufacturing and application (e.g. shape memory actuators).

Due to the function integration of multifunctional materials, their application in the redesign of existing and the design of new technical systems can reduce the number of components, space and weight of such systems. However, sufficient knowledge of the material and component behavior is a prerequisite for such design. Therefore, we are engaged in research and teaching with the modeling of multifunctional materials, the components based on them and the total resulting systems. We focus our topics on materials that can be used in actuators:

Shape-memory actuators are based on metals or plastics which material structure can be reversibly changed by temperature or magnetic fields. The change in the material structure in turn results in a change in shape and/or a force effect. Actuators with a comparatively high energy density can be constructed in interaction with external loads. The interplay of material conversion and external variables (temperature, magnetic field, force) might be quite complex. We develop models that sufficiently describe the function of components and that can also be employed for control. These models are validated using prototypes and experiments.

As previously mentioned, piezoelectric materials have been used in many areas of technology for decades. Notable examples in the field of actuators are the precision positioning and applications of ultrasound technology. Currently available piezoelectric materials produce strain of about 1 mm and mechanical stresses of some 10 MPa, when energized with electric fields in the kV/mm range. This means that although actuators typically exert high forces by a small cross-section, they can hardly reach strokes of millimeters. If larger strokes are to be attained, then a mechanical displacement amplifier is needed (e.g. levers or hydraulic systems, see "Piezoelectric actuators") or each intermediate step must be added (see "Piezoelectric motors" and "Powder Transport with Ultrasonic Waves"). To successfully design such systems, all dynamic electromechanical interactions up to the feedback on the control electronics have to be considered, which is only achievable with suitable models.

Applications of Ultrasound technology take advantage of the efficient generation of high-frequency mechanical vibrational motions by piezoelectric materials. Although they have a small amplitude (< 100 μm), at high frequencies (> 20 kHz) they generate high velocities, sound pressures (also see "Ultrasonic atomization and -levitation") and accelerations which can be applied to different media (air, water, metals) and can hardly be generated by other technologies. Applications such as cleaning, machining and bonding have also been applied industrially for decades. Nevertheless, there is a need for research, as many of the known processes have only been empirically developed. With modern models, calculation methods and advanced control technologies, efficiency and performance can be increased and new applications can be developed.


Dr. Ing. Tobias Hemsel

Dynamics and Mechatronics (LDM)

Head of Engineering, Team Leader "Multifunctional Materials, Actuators and Utrasound Technology"

Tobias Hemsel
+49 5251 60-1805
+49 5251 60-1803

Office hours:

date by agreement

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