Most commercially available cochlear implants and hearing aids use microphones as sensors for capturing the external sound field. These microphones are in general located in an external element, which is also responsible for processing the sound signal. However, the presence of the external element is the cause of several problems such as discomfort, impossibility of being used during physical activities and sleeping, and social stigma. These limitations have driven studies with the goal of developing totally implantable hearing devices, and the design of an implantable sensor has been one of the main challenges to be overcome. Different designs of implantable sensors can be found in the literature and in some commercial implantable hearing aids, including different transduction mechanisms (capacitive, piezoelectric, electromagnetic, etc), configurations microphones, accelerometers, force sensor, etc) and locations (subcutaneous or middle ear). In this work, a detailed technical review of such designs is presented and a general classification is proposed. The technical characteristics of each sensors are presented and discussed in view of the main requirements for an implantable sensor for hearing devices, including sensitivity, internal noise, frequency bandwidth and energy consumption. The feasibility of implantation of each sensor is also evaluated and compared.

In order to improve the productivity and quality of machining operations, chatter should be monitored and strategies for its reduction should be considered and evaluated. Previous works demonstrated that structural damping has a proportional relationship with stability limit. In this way, chatter instability can be reduced by increasing damping passively or actively. In this work, an availability study on the use of piezoelectric layers embedded in the tool-holder during turning/boring operations to modify the system damping is numerically performed. Two strategies are evaluated: 1) the passive one which shunt damping circuits are employed; 2) the active one which position and velocity feedback control algorithms are considered. It can be concluded that both strategies can be good alternatives for chatter reduction in turning/boring operations, but some practical issues should be overcome for a proper experimental implementation.

El comportamiento vibratorio de un sistema de transmisión de potencia permite caracterizar las señales, a fin de detectar posibles fallas en los componentes del sistema. Esta estrategia de mantenimiento predictivo contribuye a la estimación de la vida útil de los sistemas rotatorios, lo cual disminuye el tiempo y los costos de mantenimiento. Esta caracterización se realiza considerando modelos de diferentes grados de libertad de sistemas rotodinámicos, en los cuales es posible simular fallas comunes en los sistemas de transmisión —desgaste, roturas, sobrecarga—. Teniendo en cuenta lo anterior, este trabajo consiste en modelar un sistema de transmisión de potencia de dos etapas: la primera, engranajes helicoidales, y la segunda con engranajes hipoidales, usando como base el modelo de Jeffcott. Además, se implementa el acoplamiento de los ejes de transmisión a través de los engranajes, donde también es simulado el comportamiento de las fallas. La ejecución del modelo y la obtención de resultados es realizada usando el software MATLAB®. Así, fue posible completar un modelo matemático de múltiples grados de libertad que permite evaluar el comportamiento de la dinámica del sistema por etapas y, finalmente, acoplar cada una de ellas en un sistema completo. Para ello se consideraron varios factores para lograr similitudes con respecto a la realidad. Las especificaciones de algunos materiales —revisión de catálogos, entre otros— permitieron suponer valores que representaran de manera adecuada todas las partes del sistema, y, de esta forma, estar en capacidad de simular para las etapas del desarrollo del proyecto.