Difference between electromechanical coupling coefficient and effective electromechanical coefficient

The electromechanical coupling coefficient is a parameter that describes the efficiency of energy conversion in piezoelectric materials, which reflects the efficiency of piezoelectric materials in the interconversion of electrical energy and mechanical energy.

The effective electromechanical coupling coefficient, on the other hand, is a parameter that describes the efficiency of energy conversion in a piezoelectric resonator, which is largely influenced by the properties of the piezoelectric material (i.e., the piezoelectric coupling coefficient), as well as by the performance of the resonator itself.