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Instrumentation for Sensing Passive Eye Response due to Head Impact via MEMS IMUs
Keywords: MEMS, Inertial measurement unit, Flexible PCB
Sports-related concussive trauma has received significant attention in recent years. Since 2009, all 50 states and the District of Columbia have passed legislation regulating the treatment of concussions. Concussive trauma has entered public discourse through media including sports, movies, and television. Between 1.6 and 3.8 million instances of concussion occur each year. Thus, the need to better detect and diagnose concussions in real-time has become an effort of national interest. Previous work, such as the Head Impact Telemetry (HIT) System, attempts to solve the problem of real-time diagnosis via an array of accelerometers monitoring head kinematics. Similarly, the work presented here leverages accelerometry while also incorporating gyroscopic angular-rate data by way of an inertial measurement unit (IMU), but seeks to exploit the 20 ms latency period when the extraocular muscles are unable to react. It is hypothesized that the eye moves analogously to the brain as a tissue suspended in fluid, but different with respect to the skull. Our work seeks to expand upon these findings by using MEMS IMUs to obtain angular, acceleration, velocity, and displacement data in a simulated impact test for eye response versus head response. Simulated impact tests using both a 3D-printed skull model and human subjects were conducted. This presentation details the test instrumentation utilized to achieve the aforementioned tasks. Test instrumentation for the acquisition of inertial measurement data utilized two STMicroelectronics LSM6DS3 IMUs. One IMU was placed on the head of the test subject using a breakout board by SparkFun and the other was placed on the left eye to measure relative differences in inertial measurands. Because human subjects were involved in the testing, the IMU measuring eye acceleration had to be custom fabricated to ensure biocompatibility. This IMU was mounted on a flexible ribbon-style PCB made of DuPont Pyralux®, and was coated with silicone conformal coating. Additionally, the PCB was fabricated such that it could be held under the eyelid during impact. Data was logged using a Teensy 3.6 MCU and stored in a micro SD card for further processing. Skull model testing utilized the same sensor configuration but was carried out using a 3D-printed polylactide (PLA) to-scale human skull model and polydimethylsiloxane (PDMS) to-scale eye models. A model gelatin brain was also included in the model. Eye sockets were constructed using gelatin and eyelids were simulated using thin PDMS films. Utilizing this test instrumentation, the technique of using MEMS IMUs to sense passive eye movement during impact was validated. Data demonstrate that displacements of the eye and the head can be estimated. Calculated data from IMUs correspond with measured displacements and, thus, validate the sensing technique.
Brent Bottenfield, Graduate Research Assistant
Auburn University
Auburn, AL

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