The electromechanical coupling coefficient is a numerical measure of the conversion efficiency between electrical and acoustic energy in piezoelectric materials. Qualitatively the electromechanical coupling coefficient, k, can be described as:
k − 2 = 1 energy converted per input energy {\displaystyle k^{-2}={\frac {1}{\mbox{ energy converted per input energy}}}}
References "Electromechanical coupling coefficient". Medcyclopaedia. GE.{{cite web}}: CS1 maint: deprecated archival service (link) Vilnius University, Laboratory of Physical Acoustics