Hierarchical particles and tunable acoustics soft film

The thick films and the devices composed of thick films with muti-function haveattracted considerable attention for their outstanding properties in pratical application. Inthis chapter, we introduce a kind of electrorheological (ER) soft film which can tuneacoustics properties by the applied electric fields. The typical ER soft film with thicknessabout 1 mm is composed of two sheets of conductive electrodes, ER fluid, and a PMMAspacer. The ER fluid, which is also referred as smart fluid consisting of micrometre ornanometre scale dielectric particles dispersed in insulating carrier oils, is important to theresulted properties of soft film. Because the properties of the ER fluid are furtherinfluenced by the nature of dispersed particles in the fluid, such as the component, size,morphology, and crystallinity, herein we firstly introduce several kinds of ER particleswith hierarchical structure and their electrorheological properties. Then we describe twokinds of ER soft films including the ER soft film with flat electrodes and the ER soft filmwith grating electrodes. The sound transmission through the flexible ER soft films ispresented under the applied electric field.