Designing Active Acoustic Metamaterials

In recent years metamaterials gained a lot of interest from the research community in acoustics. One potential benefit of acoustic metamaterials lies in the ability to design compact absorber systems that are efficient at low frequencies. For this case resonators can be used as building blocks of the metamaterial. From that follows, that the effective frequency bandwidth of metamaterials is narrow by nature. To design metamaterials that are also effective for broadband or time variant scenarios, incorporating active components is a promising way. To develop an active metamaterial it is advantageous to combine methods from different disciplines such as acoustics and electronics. This article will show a way to systematically design active acoustic metamaterials making use of the transfer-matrix-method. We focus ourselves on metamaterials made of periodically arranged locally resonant structures referred to as unit cells that are applied to one-dimensional waveguides. Here, the active components are realized as electro dynamic loudspeakers. The designs are simulated with the proposed methods and evaluated by measurements with the transmission tube.