A Preliminary Investigation of an Active Membrane-type Acoustic Metamaterial

Abstract

One of the most promising features of membrane-type acoustic metamaterials (MAM) is their anti-resonance at low frequencies, which typically exhibits sound transmission loss values that can significantly exceed the corresponding mass-law values. The bandwidth of this anti-resonance, however, is usually very small, which limits the applicability of MAM in practical noise control problems. In previous research it has been shown that different types of actuators (e.g. magnets, electrodes, or pressurized air) can be used to adjust the anti-resonance frequency of MAM, for example to adapt to changing tonal frequencies. However, these actuation principles require additional components to be added to the otherwise lightweight MAM. To overcome these limitations, this paper will present preliminary results from an experimental study of a smart MAM which has the sensors and actuators compactly embedded within the added mass located at the center of the membrane of the unit cell. A small accelerometer is used to measure the vibration of the added mass and this signal is fed back to a controller, which is used to actuate the MAM using a small electrodynamic exciter. An impedance tube is used to measure the sound transmission through the smart MAM and different control algorithms are compared.