In partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ocean Science & Engineering

In the

School of Civil and Environmental Engineering

BENJAMIN CHAIM HURWITZ

Will defend his dissertation

CT ON A CHIP:

ENABLING HIGH-RESOLUTION POLAR IN-SITU DATA COLLECTION

APRIL 12th, 2024, 10:00 AM

Ford ES&T, Room 3243 (The Ocean Room)

Zoom: https://gatech.zoom.us/j/97140296550

Passcode: 564853

 Thesis Advisor:

Dr. Britney Schmidt

School of Earth and Atmospheric Sciences Georgia Institute of Technology

Committee Members:

Dr. Kevin Haas

School of Civil and Environmental Engineering Georgia Institute of Technology

   Dr. Joe Montoya School of Biological Sciences

 Georgia Institute of Technology

Dr. Alex Robel

School of Earth and Atmospheric Sciences Georgia Institute of Technology

Dr. Norh Asmare

School of Electrical and Computer Engineering Georgia Institute of Technology

The effects of anthropomorphic climate change are being felt globally, but there is still much unknown about the long- term impacts of these changes. Global and regional-scale climate modeling can help us better understand these complex interactions, especially over the long term as the oceans help to buffer much of the response as they take up excess carbon dioxide and heat. Most of this heat is taken up by the Southern Ocean, and then is distributed around the globe through the thermohaline circulatory system via the Antarctic Bottom Water. Melt rates play a major role in generating this cold, fresh water, but these are difficult to measure under hundreds of meters of ice, and parameterization of melt lead to large variations in model estimates, making in situ measurements critical to model and parameterization improvements. Such in-situ measurements are typically done with CTD that measure salinity, from which melt can be calculated, but these are often bulky, heavy, pumped instruments, not conducive to under-ice environments. Microelectromechanical systems offer one alternative to these bulky sensors by taking advantage of microfabrication techniques used for fabricating integrated circuits to shrink measurement volumes for improved accuracy and resolution. However, while work has been done to develop these devices, little has been done to take advantage of their improved abilities. This work looks at addressing that unknown by looking at how changes in the geometry of cell affect the overall response. I developed a set of finite element models to better understand the physics of the system, using COMSOL electro-physical simulations and an algorithm proposed previously in the literature to calculate cell constants for a large number of simulated chips and MATLAB to build a number of variations of linear regression models to help determine which parameters were important. I then fabricated over a hundred chips of various geometries on silicon using standard microfabrication techniques, with a 3μm oxide layer for insulation and 110nm chrome/gold electrodes. Testing and characterization of these devices was done with a Keysight impedance measurement system (LCR E4980A) and demonstrated that the response of the cell was dictated in some part by the width of the driving electrode and the interelectrode spacings, with wider electrodes and spacings leading to weakening responses. Finally, I developed an instrument in a 1000m-rated soda-can-sized housing with a commercial pressure sensor and thermistor to test these chips in the field. Deployments in Antarctica during the 2021/22 austral summer were successful, and demonstrated the potential of the system as a whole, with some post-field debugging and diagnostics discussed with solutions implemented. Future opportunities for continuing this work are provided at the end.