Fraunhofer Adaptronics Alliance

Adaptive Vibration Reduction

Today the implementing of adaptive structural functions which facilitate an adaptation to varying operational conditions by continuous intervention in the structural-dynamic qualities, can be recognized as an outstanding method to reduce vibrations. Additionally, transducer materials are switched in the structure´s mechanical load paths and their sensory and actuator functionality is linked with a ´regulation-technical‚ Intelligence´. The active manipulations of the disturbing or disturbed systems as well as the interference into the transmission circuit between these constitute the fundamental attempts of vibration reduction. After detection of disturbance and suitable signal processing, actuator signals are introduced into the structure corresponding to the frequency, amplitude and phase, according to the vibrations´ character. The active manipulation of the system as well as the interference into the transmission circuit can cause a damping or decoupling of the source, i.e. a vibration cancellation.

Adaptive Noise Reduction

Contrary to passive structural measures of noise reduction that concentrate on the strong increase of structure mechanical impedance and structure damping by adding material, adaptive noise reduction is based on the principle of replacing passive structure components with active, multi-functional components, to control these adequately and thus counteract the spreading structure-borne sound and the propagation of interference energy and not only the consequences of the interference.

This means that ideally the sound energy's interfering radiation is not only reduced by active countermeasures, but rather prevent such noise disturbance. This approach of active structure influence is summarized under the term of the Active Structural Acoustic Control (ASAC).

In contrast, the manipulation of active noise according to the well-known principle of Active Noise Control (ANC) pursues the goal of weakening primary acoustic sources and their emitted sound by superimposing artificially produced sound fields and destructive interference. To accomplish this, secondary sources (loudspeakers) are electronically controlled.



Active shape control / special actuator systems

By integrating and controlling suitable multifunctional materials in structural components (e.g. reflectors), it is possible to actively control their shape or properties. Compared with conventional approaches, this enables continuous control of the elastic shape state, as well as compact lightweight construction and the implementation of new actuator approaches to optimally extend the functionality at the same time.

Sample application: SMA actuators as the basis of a sensorless drive and control concept for exoprosthetics.

Actuatory use of thermal shape memory alloys (SMAs) is increasingly taking centre stage in application-oriented research due to significant improvements to material properties. In addition to the possibilities of using actuators such as these in machine tools and in the field of vehicle technology, the shape memory materials can also be used for medical applications. Thermal SMAs are currently being examined with respect to their applicability as actuators for exoprosthetics. The main objective here is to develop a sensorless drive and control concept to complement existing drive systems for external power prostheses.

Structural Health Monitoring

The Structural Health Monitoring (SHM) technology permits damage in structure dynamic components and systems to be detected while these are in operation or being installed. Contrary to conventional procedures of non-destructive component testing, actuators and sensors are integrated into the system in order to evaluate the current condition of the structure. Damages generally change characteristic properties of a structure. For example, resonance frequencies of certain oscillation modes or the propagation characteristics of high frequency waves are damage symptoms.

This change can be detected by the Health Monitoring System. With the help of suitable analysis algorithms, for example on the basis of neural nets, a classification of these damage symptoms is subsequently made to determine the exact location and severity of the damage. On the basis of this analysis, condition-dependent maintenance of the structure is possible on the one hand while a life span forecast can be derived on the other hand.

Energy Harvesting

To use energy from the environment (energy harvesting) enables the supply of wireless systems and their integration into surroundings, in which big or frequently changed batteries or the supply via cables are not possible. This means that this technology is an enabler for innovative applications of the Internet of Things, especially for wireless sensors.

One challenge during the implementation is the low amount of available energy from the usually used sources like for example light, temperature differences or vibrations. This is the reason why the power efficiency of electrical loads and an ideal design of the generators are so important for developing.

The source availability represents another challenge. Depending on applications, the availability is subjected to temporal fluctuations. Examples: solar cells often depend on the time of day, the weather and the pollution degree; vibration transducers (e.g. in freight wagons) provide a different amount of energy according to driving conditions and track characteristics; the energy output of thermogenerators depends on temperature differences and therefore also on airstream and light irradiation. All these fluctuations may conflict with the demand of wireless sensors.

For that reason, our services include initially the consulting in design and concept of energy-harvesting-systems, to decide which appropriate energy source and dimensioning of components suit the particular task best. Naturally we also assist you with new and adjustment development of the systems. Our offer ranges from the conception to the implementation of prototypes and realization of laboratory and field tests up to hedging the reliability for operating in industrial environments.