With the extreme strides taken in physics in the early twentieth century, one of the biggest questions on the minds of scientists was what this new branch of quantum physics would be able to be used for. The twentieth century saw the rise of computers as devices that significantly aided in calculations and performing algorithms. Because of the incredible success of computers and all of the groundbreaking possibilities that they afforded, research into using quantum mechanics for these systems was proposed. Although theoretical at the time, it was found that a computer that had the ability to leverage quantum mechanics would be far superior to any classical machine. This sparked a wave of interest in research and funding in this exciting new field. General-use quantum computers have the potential to disrupt countless industries and fields of study, like physics, medicine, engineering, cryptography, finance, meteorology, climatology, and more. The supremacy of quantum computers has not yet been reached, but the continued funding and research into this new technology ensures that one day humanity will be able to unlock the full potential of quantum computing.
The two general categories of structural health monitoring (SHM) systems include passive and active monitoring. Active SHM systems utilize an input of energy to monitor the health of a structure (such as sound waves in ultrasonics), while passive systems do not. As such, passive SHM tends to be more desirable. A system could be permanently fixed to a critical location, passively accepting signals until it records a damage event, then localize and characterize the damage. This is the goal of acoustic emissions testing.
When certain types of damage occur, such as matrix cracking or delamination in composites, the corresponding release of energy creates sound waves, or acoustic emissions, that propagate through the material. Audio sensors fixed to the surface can pick up data from both the time and frequency domains of the wave. With proper data analysis, a time of arrival (TOA) can be calculated for each sensor allowing for localization of the damage event. The frequency data can be used to characterize the damage.
In traditional acoustic emissions testing, the TOA combined with wave velocity and information about signal attenuation in the material is used to localize events. However, in instances of complex geometries or anisotropic materials (such as carbon fibre composites), velocity and attenuation can vary wildly based on the direction of interest. In these cases, localization can be based off of the time of arrival distances for each sensor pair. This technique is called Delta T mapping, and is the main focus of this study.