Definition of electromechanical coupling coefficient of bulk acoustic waves from energy consideration

As is well known electromechanical coupling coefficient is extraordinarily important parameter, which defines the measure of acoustic wave piezoactivity and allows comparison of various types of waves from united consideration. Traditionally this coefficient is defined as fractional change in square of wave velocity due to total or partial "turning off" of piezoeffect. However, recently there appear publications showing that use of such approach to definition of electromechanical coupling coefficient in some cases becomes unacceptable or inadequate and this fact leads to necessity of more precise definition. At present in spite of its traditional estimation there exist at least two different definitions from energy consideration. In this paper having basically the methodological meaning on example of plane bulk acoustic waves we first carried out the comparative analysis of different definitions of the electromechanical coupling coefficient.