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Acoustic metamaterials are being considered for periodic structures where specific microscopic material properties can be tailored to alter macroscopic acoustic fields. One type of acoustic metamaterial being considered is an active fluid known as magnetorheological (MR) fluids. MR fluids contain magnetic particles dispersed within a host fluid where its viscoelastic behavior is controllable by varying the magnetic field intensity. A series of acoustic experiments has recently been conducted at the National High Magnetic Field Laboratory in Tallahassee, Florida. The acoustic sound speed of MR fluids was measured as functions of applied magnetic field strength, normal and orthogonal field orientations, and acoustic frequency. This presentation will discuss MR fluids, measurement methodology, and preliminary results. [Work supported by NAVSEA Division Newport ILIR.]

Magnetorheological (MR) fluids contain magnetic particles dispersed within a host fluid. These materials are considered a type of “smart” fluid in that their viscoelastic properties can be controlled by varying the magnetic field intensity. MR fluids have found favor in high-end automobile applications such as the General Motors dynamic MR suspension system which has been in Corvettes (and other GM products) since 2005. Recently there has been interest in understanding the acoustic properties of MR fluids. In particular, the ability to control the radial and orthogonal bulk moduli suggests that MR fluids are a potential candidate for acoustic metamaterial applications. This presentation will discuss MR fluids and a method for the acoustic characterization of these fluids as functions of frequency and magnetic drive levels. [Work supported by the Office of Naval Research.]