Finite Element Approximation of the Acoustic Impedance in Transducer Layers Comprising Silver Coated Monodisperse Polymer Spheres in a Polymer Adhesive
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In this work, we study the acoustic impedance of Isotropic Conductive Adhesives (ICAs) consisting of silver coated monodisperse polymer spheres. These ICAs are intended to be used as thermal conductive isolation and matching layers in dual frequency ultrasound transducers because of their low acoustic impedance. In order to design the transducer layers, it is necessary to understand how the geometric parameters (such as particle size, coating thickness and particle density) alter the acoustic impedance. As far as the author know, there are no studies of the acoustic impedance of these ICAs. We use the Finite Element Method (FEM) and the Three Phase Model (TPM) (also known as the Generalized Self-Consistent Method) to approximate the effective acoustic impedance of composites and compare our results to experimentally measured acoustic impedances. Finally, we use the models to do numerical experiments in design. In conclusion, the TPM is just as good as the FE model at approximating the homogeneous properties. However, we show that the composite used as a transducer layer may be too thin to be assumed homogeneous at a macroscopic level. Large particles seem favourable to use in thermal conductive transducer layers, and polystyrene is more favourable than PMMA as the core material.