The estimate and measurement of longitudinal wave intensity

Abstract

Quasi-longitudinal waves are one type of structural waves, which areimportant at high frequencies. This paper studies the estimate theory and measure-ment technique of quasi-longitudinal waves, analyzes the bias error due to the effectof bending waves. In a two-dimensional quasi-longitudinal wave field, the intensityvector is the sum of the effective intensity vector and the intensity variation vector.Its axial component is proportional to two imaginary parts of cross spectral densitiesand in the measurement, it is measured by a pair of two-transducer arrays. In a one-dimensional quasi-longitudinal wave field, the intensity variation is zero, the intensityis proportional to only one imaginary part of a cross spectral density and it can bemeasured using a two-transducer array. If bending and quasi-longitudinal waves co-ekist and the contribution from bending waves cannot be eliminated or reduced toa certain extent, the measured quasi-longitudinal wave intensity will contain a largeerror. The results measured on the three-beam structure show that quasi-longitudinalwave intensity can be accurately measured using the intensity technique when bendingwaves are negligible in comparison with quasi-longitudinal waves.