Browse Publications Technical Papers 2006-01-3657
2006-12-05

Frequency Response and Coupling of Earpiece Accelerometers in the Human Head 2006-01-3657

Currently, there is great interest in motorsports medicine in measuring driver head impact accelerations by adding small triaxial accelerometers to the communication earpieces worn by drivers. Various studies have attempted to validate the ability of the earpiece accelerometers to accurately measure head accelerations. Those experiments demonstrate success in being able to measure head accelerations on dummies and humans in low severity impacts and non-impact head motion. No study has been performed to ascertain the ability of the earpiece accelerometers to accurately measure rigid body head accelerations of the skull when they are mounted in a human ear canal and subjected to high severity head accelerations.
This research was performed to evaluate the frequency response and coupling of the earpiece accelerometers to the human skull using post mortem human subject (PMHS) heads as the most realistic surrogate for the living human. The heads were fitted with earpiece accelerometers using the same procedures as is done for the Indy Racing League (IRL) drivers. The heads were also instrumented with a 9-accelerometer package rigidly attached to the skull. The heads were subjected to cyclic accelerations up to 100 Hz in the x, y, and z directions and drop tests, helmeted and unhelmeted, at various orientations. During the drop tests the heads experienced over 100 g.
The results of the cyclic tests showed a progressive phase lag in ear accelerometer data compared to the skull, with increasing frequency, as well as increasing acceleration overshoot with increasing frequency. The amount of overshoot varied with direction and ranged between 0% and 70%. Response also depended on how well the earpieces fit and a loose fit exacerbates the overshoot. Drop test results showed mixed responses of undershoot, overshoot and susceptibility to helmet interference.

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