While SNCF has to control exterior railway noise emissions for regulatory and public health reasons, reducing noise inside trains constitutes another major consideration for SNCF to improve passenger experience and comfort. In both cases, the use of vibro-acoustic metamaterials appears to be a promising solution due to their excellent absorption properties, low weight, and minimal spatial requirements. However, designing and optimizing these metamaterials for industrial applications requires simulating their response under real operating conditions over a wide frequency range. In this context, conventional methods such as the finite element method (FEM) become very costly and are not compatible with the design process. Alternatively, the variational theory of complex rays (VTCR), which is part of Trefftz's methods, approximates the solution by a sum of plane waves satisfying the boundary conditions in a weak sense. Therefore, VTCR is highly effective for problems in the mid-to-high frequency range because it does not require domain discretization; however, its effectiveness is limited in cases involving complex geometries due to the necessity of partitioning the domain into star-shaped subdomains. That is why we propose using a hybrid method that combines FEM and the VTCR here to leverage the advantages of both methods. FEM enables us to simulate the complex geometry of the metamaterials studied, while VTCR allows us to simulate wave propagation in the surrounding environment without incurring high computational costs. The two methods are coupled by imposing the continuity between the pressure and velocity at the interface. After presenting the implementation choices for the hybrid method, we will compare it to FEM for the study of the vibro-acoustic behavior of metamaterials, such as an assembly of Helmholtz resonators.