Frequency domain thickness measurement approach for microscale multilayered structures

A frequency domain thickness measurement approach for multilayered structures consisting of micrometer-scale viscoelastic thin layers is introduced. The technique presented in present work is based on a transfer matrix formulation and pulse/echo boundary conditions. The algorithms are developed from a first-principle-based analysis of linear elastic wave propagation in layered structures. An experimental procedure is introduced for determining the natural frequencies of a multilayer structure consisting of highly attenuative layers. Extraction of layer thicknesses from a set of natural frequencies is also demonstrated. One unique feature of the current technique is that it requires acoustic equipment operating at relatively low frequency. Specific challenges due to strong frequency-dependent attenuation in viscoelastic materials are discussed and addressed.