The first design step of a MEMS (Micro Electro Mechanics System) for a new implantable audioprosthesis has been developed. The device is designed to substitute the human tympanic-ossicular system and to be implanted in patients with the ossicular chain damaged or surgically eliminated in order to restore hearing. The piezoelectric transductor is directly coupled to the oval window to convert electrical energy into vibrational energy. Basically, the actuator is formed by a passive membrane and a sandwich-like structure of one piezoelectric film between two electrode layers. In the design process two contradictory conditions must be balanced in order to obtain a correct dimension of the MEMS, on the one hand the static response is increased by the global flexibility of the vibratory device; on the other hand dynamic properties are penalized with this characteristic. The first natural frequency should stay above 20 KHz (outside the human hearing range); while a displacement close to 1 μm (micron) should be achieved with a limited voltage (1 V). In this paper a parametric study of different configurations is made in order to balance both constraints. Two typologies of actuator (with one or two piezoelectric layers) have been considered and numerical studies have been carried out by means of a finite element approach. Aspect as different combinations of materials (piezoelectric and passive layer), the diameter of the passive membrane and the piezoelectric layer and the thicknesses of the different layers have been studied in terms of the static and dynamic response. Results and conclusions obtained provided a great deal of information to take the proper decisions in the next step of the design process.
展开▼
