Ultrasonic echo technique applied to wood

In practice, decay may present a big problem for timber constructions. Decay can lead to major damage of the whole construction. Tests were made by the Federal Institution for Materials Research and Testing (BAM) and the Technical University of Berlin to detect back walls and covered cavities using ultrasonic echo technique where transmitter and receiver are coupled to the same surface of the specimen. Thus a large variety of applications is possible. Two cylindrical longitudinal wave transducers were used in pulse echo technique and coupled with various coupling media. The ultrasonic centre frequency for pulse excitation was optimised to 100 kHz. Results were represented and evaluated as B-scans. In conclusion, the back walls of specimen without defects can be clearly recognized and cavities could be detected very well.