The geometric model around the middle ear which includes the tympanic membrane, tympanic cavity, auditory ossicles, several ligaments, and tensor was constructed using SolidWorks. The auditory ossicles consist of malleus, incus and stapes. The computerized tomography (CT) scan data around the middle ear was converted into DICOM (Digital Imaging and Communication in Medicine) data, then into STL data. This STL data was imported to SolidWorks in order to generate the geometric model. The sound pressure through the tympanic membrane was applied to this model in a three-dimensional finite element analysis using COSMOSWorks. Then, the mechanical influence of the sound pressure upon the middle ear was analyzed. The deformation of the middle ear and the displacement of the stapes under the sound pressure of 120 dB were clarified. The displacement of the bottom of the stapes in the direction of the axis is about 3.1 nanometers which becomes a standard value of the hearing ability evaluation. In the internal ear, the stapes vibration is transmitted to the labyrinthine fluid in the cochlea where electrical signals are generated. Finally, it is recognized in the brain as sound. For example, in the case that the medical device is substituted for the deficient auditory ossicles, it is possible to estimate hearing ability by comparing to what degree the displacement of stapes changes. This kind of approach makes it possible to propose a new medical treatment for the recovery of conductive hearing loss.
We show that microjoining of LSI chips on a film made of poly(ethylene naphthalate) (PEN), whose glass transition temperature is 155 °C, can be realized by using a cone-shaped compliant bump for flexible electronics. A 20-µm-pitch area array of cone-shaped Au bumps was fabricated on a Si wafer by photolithography and electroplating. The counter electrode on the PEN film was composed of a Au (top)/Ni/Al (bottom) layered structure, where Ni and Au layers were deposited by electroless plating on patterned Al. The bonding was carried out at 150 °C. More than 10,000 connections with 108 mΩ/bump were achieved. Mechanical analysis using finite element method indicates that the joining is due to deformation of the cone-shaped Au bumps.
When the middle ear is damaged by various ear diseases, the linkage of the auditory ossicles may be reconstructed using the column article called the columella, or artificial stapes. In tympanoplasty, operations are carried out based on the workmanship and experience of the surgeon. We have proposed a new method for estimating the hearing restoration effect prior to the tympanoplasty operation. In this method, a geometric model of the human middle ear is constructed using SolidWorks based on CT scanning data. Then, frequency response characteristics of the stapes displacement in sound conduction are calculated using finite element harmonic vibration analysis. The hearing restoration effect can be estimated by a comparison of the differences in the stapes displacement between the reconstruction model and a healthy subject. Through the study of our method, it has been clarified that a maximum displacement of 5.0 nm of a III-i type operation model for chronic otitis media achieves a response of about 98% compared to a healthy subject.Furthermore, several models in which an annular ligament becomes more rigid through otosclerosis and related operation models using artificial stapes are constructed and analyzed. As much as the annular ligament stiffened, it followed that sound conduction efficiency decreased. Frequency characteristics of the conductive hearing loss due to otosclerosis thus could be reproduced. According to operation models using artificial stapes, it is possible that the stapes displacement increases, that is, the sound conduction efficiency is improved, more than the result in which an annular ligament becomes highly rigid.From the vibration analysis of these models, our proposed estimation method for reconstruction of the auditory ossicles was verified. Through this study, the optimization of structures and materials for columella and artificial stapes becomes possible. Finally, the efficacy of predicting the hearing restoration effect prior to an operation was verified.
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