Applications

Non-contact Wood Products Testing
As previously noted, the timber industry was among the first that employed air coupled ultrasound commercially. Applications of air-coupled ultrasound fall into four main groups:

-    Assessment of bulk timber for internal decay and voids prior to processing. This requires extremely high penetration. Currently fully air-coupled inspection has not provided adequate signal to noise ratio, although the technology has been applied with soon success in conjunction with dry pressure coupling.

-    Detection of delaminations and cracking in composite or processed wood products such as particleboard and pressed wood. This normally involves some form of scanning, although a single line test is sometimes acceptable. By using a lamb wave it may be possible to test the entire width of a board, allowing effectively 100% inspection.

-    Assessment of wood quality by measuring sound transmission velocity. This has been quite successful, although the tone burst limits accuracy of timing measurement.

-    In-service Inspection of wood products for internal decay and cracking, for example structural beams and utility poles.

Many different configurations are used, with thin wood panels high frequencies can be used, and extremely good imaging can be obtained, as shown in Figure 8.

Fig. 8: Comparison of photograph and C-scan in wood

Equipment for Non-Contact Ultrasonic Testing of Wood
16 channel non/contact system for inspection of boards LSL 13. The system evaluates defects in real time using cluster analysis algorithms.