Piezocomposite Transducers for Adaptive Structures

Abstract

Low profile actuators are a basic technology for smart structures. Bonded on surfaces or embedded in composite structures they work as actuators and sensors to control the structural behaviour. The simplest types are based on thin piezoceramic plates (typical thickness 200 μm) provided with surface electrodes to operate in the lateral d₃₁-mode. This type of actuator is able to generate strains of 500 μm/m. To achieve higher deformations it is necessary to use the d₃₃-effect. The difficulty is to generate the necessary in-plane electrical field. A common solution is the use of interdigitated electrodes consisting of two comb like electrodes with opposite polarity that are placed on the surface of the piezoceramic material. Known as Active Fiber Composites (AFC’s) or Macro Fiber Composites (MFC’s) these kinds of actuators can produce strains of 1,600 μm/m. The drawback of interdigitated surface electrodes is a very high driving voltage of up to 1,500 V. A promising concept to overcome this drawback is presented. It is based on the use of multilayer technology for low profile actuators. Within these actuators the electrodes are incorporated in the piezoelectric material during the sintering process as very thin layers with little impact on the actuator stiffness. This allows a significant reduction of the electrode distance and therefore also a reduction of the driving voltage. To utilize the multilayer technology for low profile actuators, standard multilayer stacks are diced into thin plates. In this configuration the electrodes are not only on the surface of the piezoelectric material but cover the whole cross section. In a second step these plates are embedded into a polymer to build a piezo-composite. Without the mechanical stabilization of the surrounding polymer the handling of the fragile multilayer plate would be extremely difficult or nearly impossible. Several prototypes have been build and achieved an active strain of 1,200 μm/m at a voltage of 200 V. Using other materials an active strain of 1,600 μm/m is possible.