Air-coupled ferroelectret ultrasonic transducers for nondestructive testing of wood-based materials
Air-coupled ultrasound (ACU) is used in through transmission to detect delamination, rot, and cracks in wood without altering the structure permanently. Novel ferroelectret transducers with a high signal-to-noise ratio enable high-precision structure recognition. Transducers made of cellular polypropylene are quite suitable for ACU testing due to their extremely low Young’s modulus and low density resulting in a favorable acoustic impedance for the transmission of ultrasonic waves between the transducer and air. Thus, structures with great dimensions, with a thickness of up to 300 mm and material densities below 500 kg/m3, can be inspected. Promising results were obtained under laboratory conditions with frequencies ranging from 90 to 200 kHz. The advantage of ACU transducers is that they do not require contact to the sample; they are accurate and cost-effective. Ultrasonic quality assurance for wood is an important avenue to increase the acceptance of wooden structures and toward sustainability in civil engineering in general.
The research work was subsidized by the Cusanuswerk, Episcopal Study Sponsorship.
- Buckley J (2000) Air-coupled ultrasound—a millennial review. In: Paper presented at the 15th world conference on NDT, RomeGoogle Scholar
- Bucur V (2005) Acoustics of wood. Springer series in wood science. Springer, BerlinGoogle Scholar
- Gaal M, Caldeira R, Bartusch J, Schadow F, Vössing K, Kupnik M (2018) Air-coupled ultrasonic ferroelectret receiver with additional bias voltage. IEEE Trans Ultrason Ferroelectr Freq Control (under review)Google Scholar
- Hasenstab A (2006) Integritätsprüfung von Holz mit dem zerstörungsfreien Ultraschallechoverfahren. (Integrity testing of wood with the nondestructive ultrasonic echo technique). Dissertation, Technische Universität BerlinGoogle Scholar
- Hughes M (2015) Wood composites. In: Ansell MP (ed) Woodhead publishing series in composites science and engineering, vol 2. Elsevier, Amsterdam, pp 69–89Google Scholar
- Kunkle J, Vun RY, Eischeild T, Langron M, Bhardwaj N, Bhardwaj M (2006) Phenomenal advancements in transducers and piezoelectric composites for non-contact ultrasound and other applications. In: Paper presented at the european conference on non-destructive testing (ECNDT). Germany, BerlinGoogle Scholar
- Ross RJ, Pellerin RF (2002) Nondestructive evaluation of wood. Forest Products Society, MadisonGoogle Scholar
- Sanabria SJ (2012) Air-coupled ultrasound propagation and novel non-destructive bonding quality assessment of timber composites. Dissertation, ETHGoogle Scholar
- White RH, Ross RJ (2014) Wood and timber condition assessment manual, vol 2. United States Department of Agriculture, WashingtonGoogle Scholar