Perturbations in Acoustic Wave Propagation

Dividing the electrical energy density by the strain energy density yields 

The last term is approximately equal to K when 4 1. Thus, the electromechanical coupling coefficient K ) has a second interpretation is approx- 

This relation can be used to relate changes in wave energy density to changes in wave velocity in a lossless medium, i.e., one in which P is constant Implicitly differentiating Equation 2.47 yields 

Example 2.9 If a plane wave propagates in a medium in which the mass density changes, how is wave velocity effected  

from Equation 2.48, the fractional chan in wave velocity is minus the fractional change in mass density of the medium  

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