Customizable Acoustic Metamaterial Barrier with Intelligent Sound Insulation

Conventional acoustic metamaterial barriers are usually used to realize sound insulation for a continuous broad bandwidth. In some practical scenes, however, the noise signal from complex noise sources, such as gearboxes and motors, are usually complicated spectra with discrete peaks or valleys, instead of perfect continuous ones. In this case, the broadband design is unnecessary and may increase the thickness of metamaterials if too many frequency components are included. We need only a customized spectrum to achieve sound insulation at desired discrete frequencies, while, at other ones, insulation can be unwanted to preserve an effective signal other than noise. Here, we propose a customizable acoustic metamaterial barrier (CAMB) with intelligent and selective sound insulation. The CAMB is a composite structure consisting of a Helmholtz resonator (HR) and a microperforated panel (MPP) destined to control sound insulation at low frequencies, within 200--1000 Hz, and high-frequencies, within 1000--3000 Hz, respectively. An inverse process is proposed for customizable design. We use analytical and numerical methods to obtain the design libraries for the parameters of the HRs and MPPs. We numerically and experimentally demonstrate an example of a CAMB customized for a practical complex noise source. The sample has a thickness of 48 mm, approximately \ensuremath{\lambda}/11 for the lowest targeted frequency. The proposed customizable concept may pave the way for acoustic insulating metamaterials for complex sound sources with different frequency components.