Metamaterial Acoustic Absorber with Magnetic Negative Stiffness

In collaboration with our customer, we worked on applying academic research to develop a manufacturable prototype of an acoustic absorber capable of resonating at lower frequencies than its cavity size would typically allow. This is achieved by prestressing the membrane using a static magnetic field, reducing its effective stiffness, and shifting the resonance to lower frequencies. The absorber operates within an external acoustic field ranging from 100 to 1500 Hz.

The simulation model employs harmonic perturbation analysis to account for both static deformation and dynamic acoustic loading. It integrates three physics interfaces across two distinct study steps.

1. Static Preloading: The first step calculates the static deformation of the membrane. The Magnetic Fields, No Currents interface solves for the magnetic flux conservation equation, while the Shell interface determines the membrane's stress and deformation. The model captures the magnetic force exerted by a soft iron plate bonded to the membrane, which is pulled toward the permanent magnet.
   

2. Acoustic Interaction: The second step couples the Shell interface with the Acoustic Pressure, Frequency Domain interface via the Acoustic-Structure Boundary multiphysics interaction. Here, an external acoustic source induces harmonic perturbations on the prestressed membrane.
   

The model's simulation results showed excellent agreement with experimental data, validating the effectiveness of the design.