Wide-band transducers and higher-order spectral characterization of low-level ultrasounds in wood

Two high-sensitivity ultrasonic transducers have been used to perform the higher-order characterization of vibratory events, in order to get the tracks of low-level transients produced when wood fibres are broken. Although the power spectral density is a valid tool for a prior characterization, third and fourth-order spectra slices exhibit more distinctive shapes, because they content a few number of frequency components, which have been enhanced over the thermal noise, which comes from the sensor and the equipment, and the external sources of interference. The wide-band transducer exhibits better performance due to the expanded spectral pattern it outlines. Fourth-order slices can be used as a complement to third-order ones, when the resolution in the bi-spectrum is not as much satisfactory.