Examiner: Sabine Reinfeldt, Dept of Electrical Engineering
Supervisor: Henrik Fyrlund, Cochlear Bone Anchored Solutions AB
Hearing loss is a major health issue throughout the world and reduces the quality of life for people. Various types of hearing implants have been developed to support people with such an impairment. One such type of hearing aid is the bone conductio hearing implants, which facilitate sound transmission to the inner ear via the skull bone, thereby bypassing the outer and middle ears. They are intended for patients with the conductive hearing loss (problems with outer or middle ear), mixed hearing loss (combination of conductive loss and sensorineural loss in cochlea or auditory nerve) and single sided deafness (loss of hearing perception in one of the ears). For research and development purposes in the bone conduction business, there are some subjective measurements involving human subjects for parameters such as mechanical point impedance, transcranial attenuation, skin attenuation and acoustic feedback. These parameter values are relevant during testing, calibration, product development and quality control phases for bone conduction hearing implants.
However, involving human subjects for testing is a challenge, as these are patients, who are surgically implanted with hearing implants, which makes the whole process impractical and cumbersome on a long term basis. Hence there exists a need to develop an alternative, which is the objective measurements of the above mentioned parameters. One option among the objective measurements could be testing on cadavers or post-mortem human surrogates. However, these options have their own pitfalls, in the sense that they change in nature after death, leading to variability in results and there are also ethical issues, which makes this an undesirable option. We could accomplish these objective measurements through development of an artificial
or synthetic head, which can illicit the same or similar mechanical and acoustic response as a live human subject would.
This thesis work, which was done in collaboration with Cochlear Bone Anchored Solutions AB (CBAS), focuses on building an artificial head prototype (which consists of an artificial skull, skin and brain assembled together) to be used for testing the bone conduction hearing implants developed by Cochlear. An extensive literature
study was conducted to identify materials which could mimic the mechanical properties of the skull, the skin and the brain. These materials/prototypes have been sourced from various facilities throughout the world and they are assembled at CBAS, Mölnlycke, Sweden.
Different brain surrogate materials on spheres were tested and the spheres mechanical point impedance were measured. The obtained results were plotted, compared with the clinical reference and an existing artificial head values. From the results, Permagel was identified as the most suitable brain surrogate material from the test results, which is to be later used on an anatomically correct artificial head for testing all the relevant parameters mentioned before.
Student project presentation
23 April, 2021, 10:00
23 April, 2021, 11:00