Amplitude Behavior of AO Mode Transduced Using Circumferentially Misaligned Air-Coupled Transducers

Air-coupled transducers are successfully employed for selective excitation and reception of Lamb waves in both orthotropic and isotropic plates. While using air-coupled transducers for Lamb wave applications, the transducers are to be set at (1) proper orientation and also (2) they have to satisfy the "co-planarity condition.'' Fulfilling these two conditions will result in transmission and reception of high amplitude Lamb wave in the plate. In the present work, one of the misalignments, termed "circumferential misalignment,'' is introduced between the air-coupled transmitter and receiver in such a way that the coplanarity condition is violated. In the misaligned configuration, the fundamental antisymmetric Lamb mode (A(o)) was transmitted and received. Interestingly, it was found from experiments that, with the increase in severity of the misalignment, amplitude of the A(o) mode decreases, and the normalized amplitude of the A(o) mode follow the double and the single Gaussian curves in the orthotropic and isotropic plates, respectively.