|
Laser vibrometry became a well-established method for vibration detection of solids. By the means of laser Doppler interferometry it is possible to obtain information about displacement and velocity of the system under test. This approach allows the non-contact measurement of small vibrations, and is therefore capable of investigating vibration response of the middle ear ossicles or tympanic membrane due to sound simulation. There have been investigated 20 fresh human temporal bone specimens. Various components related to the sound transmission due to acoustic or mechanic stimulation have been measured by a commercial laser vibrometer (OFV3000 + OFV302/Polytec). Data acquisition, signal processing and test signal generation have been provided by a signal analyzer B&K3550/Bruel&Kjaer or integrated into a Notebook PC. The samples became prepared to allow laser beam access to the regions of interest. Generally our experiments show the capability of laser vibration measurements of the temporal bone specimen for middle ear sound transmission investigations. But the complexity is limiting that method unfortunately. 1D detection could represent insufficient information about the acoustic transmission characteristics only. The request of possibly 3D scanning is limited by anatomic conditions, e.g., according to the narrowness of the tympanic cavity. Nevertheless, for specific problems, e.g., investigation of spatially resolved tympanic membrane vibration characteristics, laser vibrometry performs a unique and high-sensitive approach. After removing the external ear canal different, well-defined points of the tympanic membrane surface have been manually scanned by the open laser beam. Particular care has been taken of the problem of perpendicular beam incidence, in order to detect identical vector components of the vibration amplitude. Laser vibrometry becomes suitable for functional investigation of the vibrating system `ear' influenced by boundary condition changes too. Vibration measurements of the umbo corresponding to manipulations of the ossicular chain allow conclusions regarding its sound transmission characteristics.
|
