Squid Speed

Abstract

The Woods Hole Oceanographic Institution is interested in studying the ethology of longfin squid because of their importance in the ocean ecosystem. For this purpose, they have previously developed the iTag, a reusable biologging sensor tag with an integrated inertial measurement unit and magnetometer which record the squid’s motion as it swims. Our team was assigned the task of integrating a dedicated speed sensor into the existing iTag, which would allow the tag to more accurately measure the swimming speed of the animal. Our selected tag design was required to accurately measure the flow speed around the squid while also having minimal impact on both the existing sensors and the squid’s natural behavior. Based on our sponsors’ suggestions, the team selected a speed sensor design that had previously been explored on another sensor tag, which consisted of a magnetic Hall-effect sensor and rotating turbine element. At present, we have successfully integrated the new speed sensor onto the existing iTag PCB without significant interference to the magnetometer, and have confirmed that the addition of the impeller to the exterior of the current sensor package will not significantly increase the drag of the iTag. Due to time limitations and a reduced capacity for in-person work, we have not yet been able to create a prototype of the updated iTag with a functioning impeller. However, our separate analysis of the iTag internals and external package suggest that our design would fulfil the specified requirements. We recommend that future teams interested in this subject prioritize finishing the integration of the iTag system and performing physical validation of the redesigned iTag, which we were not able to achieve during this semester. In order to physically validate the redesign, we suggest programming the Hall effect sensor switch reading, calibrating the sensor to eliminate directional bias, and using the magnetometer to determine the general direction the squid is swimming. Additionally, we also suggest waterproofing the sensors and testing the tag in water for more accurate measurements than extrapolating air readings to water. Finally, the team has identified several potential design changes to the prototype iTag, including moving the Hall sensor cavity nearer to the impeller in order to improve reading accuracy, and elongating the tag body to mitigate magnetic interference. Implementing these changes will improve the functionality of the tag to make it more suitable for our sponsor’s needs.