Novel design of transducer for bone conduction use

Abstract

Hearing losses are worldwide acknowledged health problems affecting overall life quality of suffering patients. Many different therapeutic prostheses were developed for these hearing traumas. One of the most preferred treatment process are hearing aids. Different types of hearing aids were developed to rehabilitate and treat people suffering from hearing traumas. One such type of hearing aid is the bone conduction (BC) hearing aid, which is helpful for indicated patients. BC has been used for many decades in hearing aids, and there are now several implantable versions. These hearing aids transmit the sound through the skull bones to the inner part of the ear, bypassing the outer and middle parts. BC hearing aids are essentially designed with a transducer principle. The transducers are used to convert energy from one form to another. This process is called as transduction as well. Bone conduction transducers transform incoming audio signals to the vibrations that is transmitted to the cochlea, which transmits converted signals to the brain through auditory nerves. We aim to find a magnetostrictive transducer design with optimized data. The obtained optimized values will be used the possible a transducer prototype design for bone conduction use. This prototype is properly able to perform together with an audio processor, microphones, receiver coil, supermagnet and a battery compartment. We investigated material options to replace piezoelectric ceramics that are frequently used in BC hearing implants. During investigations for material selection, the properties of performing effectiveness and biocompatibility of alloys were watched out. According to the literature review, Terfenol D, Galfenol, and Metglas 2714A® were identified as possible materials for bender in the transducer. The bender component of the simulated transducer is extremely critical for this study. It consists of both magnetostrictive and non-magnetostrictive alloys. Other parts of transducer are counterweight or core, coil, permanent magnet and tape. The material selections for components transducer apart from bender, inspired from other current transducer applications. ANSYS® Mechanical and Electronics environment was chosen for simulations and testing. Some mechanical parameters were determined before starting simulations by reviewing current transducer applications to create a transducer model in ANSYS®. Then, mechanical simulations were performed in the specific ranges of mechanical sizes by using this model. Mechanical dimensions were simulated and optimized regarding size and resonance frequency, similar to existing bone conduction transducers. We determined the reference resonance frequency value as inspired by previous bone conduction transducer studies. For resonance frequency optimization, modal and harmonic analysis were performed. Modal analysis was used to determine specific parameters to create a mathematical model that shows dynamic reaction of the vibrating structure. Meshing adjustments were arranged to have more efficient simulation results. We had specific boundary conditions and, they were applied in the mechanical simulations. The boundary condition adjustment was to show the effect of skull simulator on the connector. Point of mass and cylindirical support parameters were applied to the model as boundary conditions. On the other hand, 1N Force was utilized in the model as the load. As a result of modal and harmonic response analysis, it was found that 0.3 and 0.4 mm for Metglas 2714A®, and 0.4 and 0.5 mm for Galfenol and Terfenol D, were appropriate thicknesses. Furthermore, for all three materials, 20 mm length and 4.8 mm width were evaluated as appropriate in electromagnetic simulations. Electromagnetic simulations were performed by adding different types of super-strong neodymium permanent magnets and turns of the multilayer coil. Also, the optimized mechanical dimensions obtained from mechanical simulatios through ANSYS was utilized in electromagnetic simulations. Besides, mechanical dimesions of electromagnetic components were determined by studies carried out by previous similar studies. Furthermore, resistance, inductance, and the number of turns of the coil were calculated for each simulation. After evaluation, Metglas 2714A® Magnetic alloy and Terfenol D were deemed less suitable for this application because of their size and robustness. Optimized mechanical dimensions and electromagnetic parameters were suggested for ferromagnetic material to construct a bone conduction transducer prototype. It is suggested to use Galfenol alloy with 0.5 mm thickness, 20 mm length, and 4.8 mm for build a magnetostrictive transducer prototype for BC use by using a permanent neodymium magnet with 200-250 turns of the coil.