MERGE - Cluster of Excellence

Germany funds Excellence Initiatives for Cutting-Edge Research at Institutions of Higher Education. On June 15, 2012, the grants committee decided about the proposals of the third round of the excellence initiative. All selected proposals will be funded over a time period of five years starting from November 2012. Fraunhofer ENAS and the Center for Microtechologies of the Technische Universität Chemnitz and Fraunhofer ENAS work in two of these clusters of excellence, which have been accepted in June 2012, cfaed and MERGE. The Cluster of Excellence of the TU Chemnitz "Merge Technologies for Multifunctional Lightweight Structures - MERGE" is coordinated by Prof. Kroll, Director of the Institute of Lightweight Structures of the Faculty of Mechanical Engineering. The main object of the cluster is the fusion of fundamental technologies suitable for the resource-efficient massproduction of lightweight structures of high-performance and functional density. In order to make the structures much more intelligent, microsystems, smart sensors, actuators and electronics will be integrated. ZfM and Fraunhofer ENAS are mainly working in research area D - Micro- and nanosystems integration.
For more information please visit: http://www.tu-chemnitz.de/MERGE/

Domain D -
Micro- and nanosystems integration for hybrid structures

The next generation technologies and products will be measured by the increase of resource and energy efficiency as well as by securing the competitiveness, taking into account an effective climate and environmental protection. For the combination of diverse material groups, such as metals or plastics respectively, and the integration of active components like sensors and actuators, currently separated manufacturing processes have to be combined by fusion and linkage to integrated mass-oriented technologies for the production of high-performance structures. Such a technology consolidation is characterized by substantial energy and material savings and by the increase of functional density. The integration of microelectronic and micromechanical components in hybrid structures enables the functionalizing by sensors, actuators and electronics and therefore a further improvement of performance and functional density of hybrid components. In the sphere of the integrated research domain D Micro- and nanosystems integration in composite structures new approaches for microelectronic components in hybrid structures are developed.

Integration concept for fluidic actuators

Fluidic actuators such as Synthetic Jet Actuators (SJA) or Pulsed Jet Actuators are fluidic elements that are known to be suitable for the uses in active flow control applications e.g. for high lift devices in aircrafts or in wind turbines. Modern wind turbines are manufactured using composite materials. Consequently, the integration of such fluidic devices must fit the manufacturing process and the material properties of the composite structure. The challenge is to integrate temperature-sensitive active elements and to realize fluidic cavities at the same time. The design concept of the actuators as well as the integration concept is based on the MuCell® technology. MuCell® allows combining the advantages of a closed surface and low density in the center of the injection molded part. Since low process forces are necessary, the inserted actuator elements are less stressed compared to classical injection molding technologies.

Figure 1: 3D images of devices are created by using computer tomography at the Fraunhofer ENAS. Failures or damages inside the devices are analyzed on the basis of these images. (photo @ Hendrik Schmidt)

Foil based sensors

The focus of integrating polymeric foils in lightweight structures is to design and manufacture energy self-sufficient sensor systems, which allow the detection, storage and visualization of mechanical overloads. These loads generate electrical charges within the piezo material, which are then transferred to the quantum dot layer leading to fluorescence quenching. Thus component areas which faced a mechanical overload exhibit lower fluorescence intensity or a color change, depending on system design. This optical information can be stored for a certain time within the material as signature of possible damage. Mechanical loads can be visualized spatially-resolved directly on the component. Key feature of the sensor is a double layer consisting of a piezoelectric and a quantum-dot-based foil, that can be integrated by laminating or injection molding. The emphasis here is on mass producible processes, such as printing and injection molding processes. A first appropriate multilayer sensor design was carried out and it could be shown, that layers can be manufactured and the main important material properties of the respective layers and the general cross-sectional profiles were discussed and preliminary defined.

Metamaterials for communication and energy transmission

The integration of multiple wirelessly communicating electronic sensor nodes into lightweight structures will open the way for distributed sensing and for structural health monitoring. Future electronics and even some recent developments exhibit very low energy consumption, so microwaves become a reasonable way of powering. The major benefit will be a completely wireless sensor system. The integration of metamaterials in planar lightweight structures will allow communication and energy transmission.

Figure 2: Within the Federal Cluster of Excellence EXC 1075 "MERGE Technologies for Multifunctional Lightweight Structures", integration opportunities are investigated for functional elements of active flow control systems, here for a metallic segment of a wing structure. (photo @ Hendrik Schmidt)

Metamaterials enable the production of efficient antennas by focusing or diverting electromagnetic waves. Thereby, electrical performance and information can be absorbed into the work piece and allocated without additional cabling. Integrated sensors, microcontroller or energy storages would be conceivable, being supplied with energy and able to communicate by incident microwave radiation. It is expected that printing of conductive patterns on dielectric substrate, application of embroidery technology for mounting of conductive sequins on isolating fabric, both in combination with moulding will generate lightweight material component parts with integrated antenna functionality. A second objective of the integration of metamaterials is to enable material integrated sensing. The behavior of metamaterials at high frequency is changed by environmental impacts, such as crack formation and resulting water climbing. Suitable measuring instruments detect these modifications and conclusions can be drawn about the condition of a component.

Silicon-based sensor integration

The monitoring of the condition and health of composite structures can be done by the use of well-known microtechnology based sensors such as stress sensors. The main challenges are, on the one hand, integration as well as the supply with energy and enabling to communicate. On the other hand, reliability aspects have to be taken into account especially during the manufacturing process. For this reason, silicon based sensors in composite structures shall be analyzed, in this context giving special attention to organize the manufacturing process of sensor-integrated semi-finished products mass producible. Therefore, a textile based preform with integrated conductive wires for energy and data transmission is developed. This smart textile can be made of materials, which are usual for reinforcing thermosetting plastic lightweight structures. The conductive wires consist of carbon fibers, which are also strengthening the favored structural element. By means of the micro injection molding technology, a printed circuit board, the so-called interposer, is fixed and electrically contacted with electrically conductive thermoplastics that need to be adjusted to the specific application. This interposer is the interface between the smart textile and the silicon-based sensor. For guarding the sensor and to finish the fixation, an encapsulation is the last step prior to integrate the overall system for different purposes like structural health monitoring.