SAW Response from Acoustically Thin Films

Changes in SAW propagation velocity and attenuation are determined by the mechanical impedances at the substrate/film interface resulting from film translational and strain modes. The impedance associated with each film translation is jtaph, and with each strain mode is where Ef i are taken from Table 

from a perturbation analysis, the change in SAW propagation arising from acoustically thin films is [50]  

Equating real and imaginary parts of Equation 3.58 yields velocity and attenuation changes resulting from the SAW/film interaction. With elastic films, the intrinsic elastic moduli are real, resulting in real 0 and imaginary liy/ko, so that Aa/ko = 0. Substituting the ( expressions written in terms of the Lame constants (A, fi) from Table 3.3 into Equation 3.58 yields the Tiersten formula [52] 

While Equation 3.59 does not apply to viscoelastic films, the velocity and attenuation arising from acoustically thin, viscoelastic films can be determined from Equation 3.58 by inserting complex moduli (e.g., K and G) into the 0 expressions. 

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