hus the word efficiency is not appropriate to describe coupling coefficients. It is also important to note that the electromechan-ical coupling factor only concerns the ratio between input and stored energy; thus, it does not represent the actual working efficiency of the material when utilized in transducer applications.Simply put, not all of the energy stored can be transferred to the mechanical output signal due to mechanical and electricallosses.123,124The normally quoted electromechanical couplingcoefficients are the theoretical maximum values usually deter-mined at the resonance frequency