Instrumented earplugs were first introduced in 2000 by the Air Force Research Lab as a means of measuring head accelerations in race car drivers after it was shown that instrumented helmets slipped on the head during impact events. A version of these earplugs was adopted by the Indy Racing League and Championship Auto Race Teams (CART) in 2003. In 2006, Begeman, Melvin, Troxel and Mellor reported that signals from earplugs mounted in cadavers showed a phase shift at 50 and 100 Hz vibration indicating less than perfect coupling with the head. A new miniature tri-axial accelerometer has been developed that is small enough to be placed in the ear canal portion of communication earplugs (earpieces) as a way of improving the coupling and thus the reliability of the recordings from drivers undergoing multi-axial crash events.
The first part of the effort involved developing design specifications for the next generation earplugs. These came from Andrew Mellor at the Fédération Internationale de l'Automobile (FIA) Safety Center who developed these specifications with a view toward using the new earplugs in the F1 race series. Endevco/Meggitt proposed to develop this mini-triax which is small enough to fit in the ear canal and secured congressional funding to support the development of a manufacturing process to reliably produce the new sensor. The Air Force Research Laboratory team, who invented the first instrumented earplug, collaborated with Endevco/Meggitt to build the new sensors and provide the validation testing and comparison with the current operational sensors. The new 7273GT sensors were mounted in molded earplugs and subjected to impacts as high as 300g with very short durations in multiple axes. The earplugs were mounted in artificial ears which were mounted on rigid blocks. The sensors showed good correlation with reference sensors and demonstrated improved coupling to the head over the current generation of earplug accelerometers.
