Knock on wood

 作者:阳忪追     |      日期:2019-03-08 07:13:03
By Andy York AN ELECTRONIC woodpecker that can identify trees with hidden rot could save healthy trees from being damaged or felled. Foresters looking for rot normally have to drill a hole in the trunk and take a core sample. This damages the tree, so Geoff Lawday of Buckinghamshire Chilterns University College near London wanted to find a less invasive and harmful method. Woodpeckers search for grubs and nesting sites by tapping a tree trunk and assessing the sound it makes—and Lawday’s technique works in a similar way. It involves hitting a tree with an ordinary hammer and then analysing the stress waves that emerge from the opposite side. A piezoelectric crystal sensor picks up these waves and converts them into an electrical signal that can be downloaded onto a PC to be analysed. “Rotting and healthy wood have different moisture contents, affecting the vibrations of the waves differently,” says Lawday. Tree analysis is often complicated by the presence of bark or damaged wood which has repaired itself. With current methods, these are often mistaken for rot, so healthy trees are cut down as a result. “Using our technique a clear signature for rot can be obtained, and these are distinguishable from the other abnormalities,