Mechanical and thermal simulations of a microactuator for the Stimulation of the Perilymph

Abstract

Figure I : Conceptual design of the MEMS type inner ear hearing implantThe design goal of the micro actuator is to accomplish a Sound Pressure Level (SPL) of 110 dB in a frequency range from 100 Hz to 6 kHz. The main goal of the i.e. a hearing loss due to damaged hair cells, but still a functional auditory nerve , neither approach described presents a solution. In such a case, a Cochlea Implant (CI) is required. It stimulates the nerve cells electrically [2]. This paper describes the simulations conducted to design an inner ear implant in Micro Electro-mechanical System (MEMS) technology. The system is driven electromagnetically and excites the cochlea's perilymph through the round window. Using mechanical and thermal FEM analyses the microactuator was designed. Using FEM simulations to design a microactuator is a common approach at the Institute for Microtechnology (imt) . Several designs using FEM simulations were carried out at the imt [4,5]. The simulation results of the electromagnetic device were described previously [6]. Figure I depicts the conceptual design of the MEMS type inner ear hearing implant. The system is driven electromagnetically and features a membrane with a boss at its center. The boss carries a plunger. A system excitation results in a vibration of boss and plunger. The plunger penetrates the cochlea through the round window and excites its perilymph. The system's active part contains a coil system , soft magnetic flux guides, and a flux closure located underneath the mechanical system. Due to the absence of hard magnetic materials, the system will vibrate with double the frequency of the exciting signal. Concept and System Requirements Electromagnetic device Spacer AbstractThe design of a microactuator serving as an implantable hearing aid to overcome ambylacousia was conducted by executing mechanical and thermal Finite Element Method (FEM) analyses using the ANSYS® software simulation tool. To do so, the deflection conditions to be fulfilled by the system were determined. The two challenges were to achieve a sufficiently high resonance frequency and to accommodate the physiological restrictions in the middle ear and the cochlea defining the maximal size of the micro actuator. A model of the mechanical system was created and modal analyses were carried out. In the next step, the force required to deflect the membrane in the static case and under damping of the cochlea was simulated. In a last step, a 3-D thermal model of the complete system including the micromagnetics was created to investigate the temperature rise in the system. This is important with respect to the implantation of the actuator into the human body, avoiding a necrosis of the human tissue.

Simulations of an Electromagnetic Microsystem Used in Biomedical Applications

“…This diameter was determined by simulating the mechanical parts of the implant using different diameters of the flux closure until the desired resonant frequency was reached. These simulations are discussed in [8].…”