Research On The Acoustic Absorption Characteristic Of EMRF Based On Biot Theory

Electro/Magneto-rheological fluid is a class of important intelligent soft material. The suspended particles in EMRF form orderly microstructures along the direction of the field which is applied, resulting in the dramatic changes of rheological property which is reversible. Not only have that, a lot of physical properties, such as optical properties, acoustic properties, of EMRF showed the outfield controllable property, which indicate its great potential in various fields. In the dissertation, EMRF is proposed as an acoustic medium based on the internal microstructure of EMRF. Focus on the sound propagation mechanism, composite structure and match layer of EMRF, the theoretical modeling, numerical calculation and experiment are done. The main work in the dissertation is as follows:EMRF is proposed as an acoustic medium which property is controllable, providing a theoretical foundation for a new type of underwater sound-absorbing materials. In the present of external field, the Biot theory is used to describe the sound field of EMRF, while suspension scattering theory is used when the external field is zero. The microstructure of the EMRF is equivalent to saturated porous structure. The full frequency band dynamic shear modulus equivalent method is established based on the test results and the discrete relaxation spectrum theory. The absorption performances of EMRF layer are compared under different strength of outfield. It is show that the microstructure in EMRF is facilitating the absorption and illustrates the feasibility of EMRF as an acoustic absorption medium.The propagation of acoustic waves in poroelastic structure is investigated. The configuration of the porous materials with different flow resistance is discussed and global absorption optimization by the resonance effect of the porous materials is proposed. The acoustic model of the composite structure comprising an EMRF layer is established. The double layer structure’s underwater absorption composed of an MRF layer and a porous metal layer is investigated through numerical simulation. The influences of the liquid filled in, the configuration of materials and the strength of the outfield are also discussed. The results show that the microstructure of EMRF and the viscosity of the liquid filled in are helpful for the acoustic energy absorption.Due to the controllable of the impedance of EMRF, it can be used as a match layer with continuously changed impedance with designed outfield. The acoustic model of EMRF with continuously changed impedance is established based on the wave equations with variable parameters and transfer matrix method. Several impedance distribution forms are numerically discussed and the exponent type whose impedance change slowly at first and fast at end with sound propagating shows the best absorption performance. On this basis, the match layer whose characteristics impedance does not match with the incident medium and the transmission medium at the interfaces are investigated. The efficiency of the materials can be effectively improved by removing both ends of the original match layer.Based on the theory research, a impedance tube for the MRF testing is designed which can be used to testing the acoustic impedance of MRF underwater. Some experiment of the acoustic property of MRF is implemented. The results show that the acoustic impedance of MRF is changing with the external magnetic field, which is consistent with the theoretical calculation.