Helmut W. Zaglauer

Integrated wireless piezoelectric sensors

Piezoelectric sensor arrays and sensor networks have been suggested as a means to monitor the integrity of composite structures throughout the service life for instance of an aircraft. Complex sensor systems will require significant additional expenditures with respect to cabling and electronics, with the added weight and effort possibly outweighing any benefits. Sensor positions in remote locations of an aircraft will often necessitate accessibility to these locations for maintenance purposes. For these reasons wireless, integrated sensors have recently become an object of increasing interest. Within the framework of a feasibility study various aspects of integrated wireless sensor system were investigated in detail. Particular emphasis was thereby laid on issues that are essential form a practical point of view, but that have not been discussed in the literature extensively. As a starting point a trade-off study between different sensor network configurations was conducted, form passive, remotely queried senors without power supply to fully functional active sensor pads with integrated power supply and electronics. Various concepts for the on-board energy supply of remotely queried sensor pads were studied and a comparison between rechargeable, and single-use batteries was performed. The suitability of different electronic components for integration into carbon fiber composites was investigated with particular emphasis on their survivability under typical temperature cycles experienced in autoclave runs. Finally, a crackwire sensor as an example of a passive remotely queried sensor system was pursued further in order to show the feasibility of such a wireless system for composite health monitoring purposes.

On the Integration of Piezoceramic Actuators in Composite Structures for Aerospace Applications

Up to now experimental and theoretical research on active structures for aerospace applications has put the focus mainly on surface bonded actuators. Simultaneously piezoceramics became the major type of actuating device being investigated for smart structures. In this context various techniques of insulating, bonding and operating these actuators have been developed. However, especially with regard to actuators, only a few investigations have dealt with embedding of these components into the load bearing structure so far. With increasing shares of fibre-reinforced plastics applied in aerospace products the option of integrating the actuation capability into the components should be reconsidered during the design process. This paper deals with different aspects related to the integration of piezoceramic actuators into fibre reinforced aerospace structures. An outline of the basic possibilities of either bonding an actuator to the structures surface or embedding it into the composite is given while the emphasis is put on different aspects related to the latter technology. Subsequently, recent efforts at DaimlerChrysler Aerospace Dornier concerning aircraft components with surface bonded actuators are presented. Design considerations regarding embedded piezoceramic actuators are discussed. Finally, some techniques of nondestructive testing applicable to structures with surface bonded as well as embedded piezoelectric actuators are described.

Fin-buffet alleviation via distributed piezoelectric actuators: full-scale demonstrator tests

Structural fin or wing vibrations are observed on high performance aircraft when flying at high angles of attach. The severity of the so-called buffeting vibration depends on the aircraft configuration and aerodynamic optimization of the configuration. The vibrations are caused by flow fluctuations resulting from flow separation at wings or from bursting of wing leading edge and front fuselage vortices. The resulting dynamic loads with maneuver loads lead to increased material fatigue and may require an augmented effort in aircraft maintenance.

Fin-buffet alleviation via distributed piezoelectric actuators: materials qualification program

One of the most innovative concepts for active fin-buffet alleviation in vertical tail aircraft is the use of piezoelectric patch actuators distributed across the tail surface to actively induce a counter-strain into the structure. This concept involves the development of a novel material compound structure consisting of a fiber-composite aircraft skin, a ceramic patch actuator and the bonding layer between both components. This actively controllable structure has to provide enough authority to dampen the fin- buffet vibrations. It also has to function reliably during long-term aircraft operation under severe mechanical and environmental load conditions.

Adaptronics applications in satellite mirrors

Up to now all mirrors verified and flown in interferometric optical and IR astronomic instruments on space missions documented in the literature have been passive systems. Preliminary investigations have shown that requirements of future systems like a significant reduction in mass while maintaining optical quality or an increase of optical quality at constant mass, as well as realization of mirrors with several meters in diameter while meeting all requirements for modern satellite systems can only be achieved by active shape control of the optical surface.