Lamb and shear-horizontal wave production by interdigital transducers deposited on both sides of a piezoelectric plate

Interdigital transducers (IDT) deposited on one side of a sample are commonly used to generate and detect acoustic plate modes. The electromechanical coupling coefficient can be calculated to find the relative efficiency of mode generation by TDT. However, experimental observations have shown that some modes are difficult to excite with IDT deposited on only one side of the plate. In this paper it is shown that the shape of the tranducer and its electrical connections can be adjusted for each mode, A(0), S-0, and SH0. in order to achieve an electromechanical conversion in good agreement with theoretical predictions. Some experiments have been performed on quartz plates with different kinds of transducers in order to check the validity of this approach. The electrostatic potential generated by these transducers has been compared with the electrical potential associated with a plate mode already excited. It appears that when the electrostatic field generated by the excitation device has the same symmetry as the electric field associated with a piezoelectrically coupled plate mode, excitation and detection of this particular mode are possible. (C) 1996 Acoustical Society of America.