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Average the instantaneous elastic-wave energy flux over one temporal period at fixed position. For complex amplitudes,Write the evanescent P displacement amplitude asFor an isotropic linear elastic material with Lamé parameters $\lambda ,\mu$, its stress and velocity amplitudes areApart from a real common factor,which is purely imaginary. Its real part vanishes, and henceThe converted P-wave is a reactive near-boundary field and transports no time-averaged acoustic energy in the normal direction.