Acousto-Electromagnetic Interaction in Materials for Aerospace Composites

Sammanfattning: Non-destructive testing (NDT) is a vital part of aerospace manufacturing due to high demands for quality and safety. Advances in materials science have given rise to aerospace composites with highly improved properties compared to traditional materials. To ensure that materials can be used safely, NDT techniques are continuously improved to follow advances in materials. This has also spurred development of new NDT techniques. One suggestion for improving NDT techniques is based on combining several phenomena. One such combination is acoustics and electromagnetics, such as ultrasound and mm-waves. This work explores interaction between acoustic and electromagnetic waves and attempts to connect this with possibilities for novel NDT techniques. The focus is on photoelastic interaction, meaning that an acoustic wave alters dielectric properties of a medium which in turn scatters electromagnetic waves. Existing techniques such as acousto-optics and Radio Acoustic Sounding System are used as a starting point for exploring this interaction mechanism. Analytical models for photoelastic interaction are developed from basic electromagnetism and photoelasticity theory. Two important results are a phase matching condition for maximum scattering and a frequency shift of scattered waves, both of which are also present in acousto-optics. Numerical simulations are used to verify the phase matching condition and compare scattering power with analytical models. Defects with electric or acoustic contrast are simulated to explore NDT possibilities. Both types of contrast are shown to affect the interaction, which could be an advantage over some existing NDT techniques. However, more work is required to determine the utility for NDT.