Transmission of sound through a gel-filled ear canal: A case study

During function magnetic resonance imaging (fMRI), it would be beneficial to image the brain while sounds are played to the subject. Therefore, there is a need to both block the fMRI machine noise and deliver sound waves to the subject within the machine enclosure. Additionally, the system should also be free of magnetic components, as their presence may disrupt the function of the fMRI machine. In this paper, a method is proposed to address these issues in the form of filling the ear canal with a gel, to block the machine noise, then deliver sound through the gel via a ceramic piezoelectric stack. The piezo actuator is placed against the boundary of the air and the gel. The sound waves traverse through the gel to the tympanic membrane and then further along the auditory chain. There is also some degree of transmission achieved through bone conduction. A case study of this proposed system was performed. It was found that the gel within the ear canal provides adequate hearing protection, and the piezo actuator was capable of transmitting sound to the listener, and sound level was perceived to be higher with the piezo against the gel than against the mastoid.