Thermosonics: Electrostatic transducer based air-coupled ultrasonics and thermography for NDE of carbon fibre reinforced polymer materials

Custom made electrostatic transducers were used for ultrasonic investigations of damaged CFRP. These investigations resulted in identification of non-linear ultrasonic responses due to the presence of damage. The broadband nature of electrostatic transducers is essential for this work to scan a wide range of frequencies to identify non-linear responses. These non-linear response frequencies were used with an electrostatic transducer to induce thermosonic heating at the damage which was measured with an IR camera. The use of non-linear response frequencies reduces the power required to produce thermosonic heating. Travelling guided waves (Lamb waves) allow excitation of the damage at a distance from the excitation source allowing large samples to be studied. This provides a completely non-contact measurement for NDE which shows promise for future composite inspection systems.