Study on wave propagation in the modulation structure with gradually changing impedance according to specific waveform based on magneto-rheological fluid

This work proposes a novel hierarchical modulation structure with gradually-changed impedance built by magneto-rheological (MR) fluid and investigates its wave propagation characteristics theoretically and experimentally. Based on the impedance tunable property of the MR fluid, applying multiple magnetic fields to MR fluid realizes the modulation of this proposed structure, and regulating its magnetic field distribution law can effectively change the impedance variation forms in the structure. Establish the elastic wave propagation model of this modulated structure, and analyze the variation trends of its elastic wave propagation characteristics with different impedance distribution patterns, taking the vibration level difference as an indicator. Subsequently, conduct experimental testing for the transmissibility of elastic waves. The results show that the elastic wave transmission characteristics of the proposed modulation structure mainly depend on its impedance variation rate and the frequency of external excitation. On a broader band of the frequency range (20–300 Hz) studied in this paper, the gradual impedance distribution of MR fluid enhances the transmission loss of elastic waves compared to a uniform distribution of its impedance. Moreover, in the lower frequency range (40–125 Hz), the layered modulation structure with a non-monotonic variation of impedance following a wave-like waveform presents more significant attenuation on elastic waves than the structure whose impedance varies monotonously in a gradient waveform. This work contributes to expanding the design thoughts of the structure with gradually changing impedance and providing new ideas and means for the control of elastic waves.