Material’s internal structure knowledge is highly relevant to improve quality indexes [1]. For example, the exact information of the internal structure of a wood log or lumber such as density and internal defects is an important economic advantage (see [2]). Internal characteristics of materials have been studied with different non-destructive techniques, including ultrasound [3], microwaves [4...

In this paper, we perform the first study of noncontact internal structure sensing based on mechanical resonance mode excitation of an elastic object. The vibration is excited by airborne ultrasound acoustic radiation pressure. It is confirmed by using the noncontact sensing system that the lowest resonance frequency of the measured displacement amplitude frequency response decreases as the inc...

Abstract In vibrating structures, nonlinear effects can play a decisive role. For example, stiffening responses occur in integral components with low damping, but softening shift of the resonance to lower values by an increase vibration energy be observed. Often these systems are considered only characteristic mode, allowing well‐known phenomena investigated. However, it may case that more than...