Natalie Harris ’19 Researches “Skull Resonance” and Acoustics at Central Washington University in Ellensburg, WA

My name is Natalie Harris, I’m majoring in 3-2 Physics/Engineering, class of 2019, and I’m currently working at Central Washington University in the Acoustics Lab with Dr. Andy Piacsek on a project we call “Skull Resonance.” The project started in 2011 when Dr. Piacsek and a team of students started researching the resonance frequencies of spherical objects, skulls, and the correlation between these resonance frequencies and internal pressure of the object. Resonance occurs at an object’s natural frequency. Imagine shaking a typical spring-mass system in the physics lab up and down. If you shake it at a certain speed, the mass begins to uncontrollably bounce up and down, which means you’ve hit a resonance frequency. In the lab, we vibrate objects at many different frequencies–a sweep–to generate a Fast Fourier Transform (FFT) of the response of the objects which shows the resonance frequencies as peaks. This type of research is called modal analysis. The purpose of performing a modal analysis on a human head is to potentially develop a noninvasive method of measuring intracranial pressure (ICP). Currently, the commonly used and accepted method includes drilling into the skull and inserting a catheter, which increases the risk of infection and complications.

While we have a model “skull” setup, another part of the project involves looking at the response of real skulls, which was going to be a sheep skull. Dr. Piacsek subsequently contacted the Biology department at Central and they allowed us access to a full cadaver to test. Not a sheep cadaver, a human cadaver. Needless to say, this caught me by surprise. We had some assistance from a Biology grad student in placing the accelerometers and marking where on the head to tap. Recently, we took some preliminary data that shows the resonance frequencies of this skull. Since the typical ICP measurement requires neurosurgery, we will coordinate further with the Biology department to develop the skills for that procedure, as well as a plan to manually increase/decrease ICP in the cadaver. That extra monitoring and adjustments will mimic our model setup and could show us the accuracy of using our method to monitor ICP.

I spend most of my time in the Acoustics Lab surrounded by all sorts of cool tools, such as a scanning vibrometer, speakers, musical instruments and accelerometers. Though I don’t use it for this project, the anechoic chamber next door is easily my favorite room.  I typically use two accelerometers and a modal impact hammer that connect to LabVIEW to gather data. Our “skull” is an aluminum sphere connected to a hand pump, so we can change the “intracranial” pressure. The hammer produces a wide range of frequencies in one tap to the sphere and the accelerometers glued to the “skull” capture the resulting vibrations. Using this apparatus, we are able to verify the results from Dr. Piacsek’s publication with updated modal analysis tools instead of the loudspeaker that was previously used to generate a frequency sweep. I’m currently working on a program in MATLAB to process the data I’ve collected, and display it to show the effect that changing the pressure has on frequency.

As mentioned, this project allows me to use programs such as LabVIEW and Matlab to collect and analyze data. These are both common tools used in physics and engineering fields, so it will undoubtedly be helpful to know in the future. This project also gave me a crash course in acoustical physics and gave me some time to do some of the traditional acoustics experiments, which were fun and helped me solidify my understanding of the theory. Since the Biology department here does need to operate on the cadaver for their anatomy class, we will not have a chance to take data until they receive new cadavers, which means I will need to pass on my research to future students. As much as the cadaver shocked me at first, knowing that the deceased had previously wished to donate their body for scientific learning and research is really inspiring and highlighted their dedication to hands-on learning. It’s not an experience I will easily forget.

Experiences like Natalie’s are made possible by the Whitman Internship Grant, which provides funding for students to participate in unpaid internships at both for-profit and non-profit organizations. To learn how you could secure a Whitman Internship Grant or host a Whitman intern at your organization, click here or contact Assistant Director for Internship Programs Victoria Wolff

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