A double-stage impedance matching mechanism with quasi-arbitrary materials

In wave propagation between two media, a perfect impedance matching eliminates reflection and enables 100% energy transmission. Traditional matching mechanisms, with either single or multiple matching stages, require a specific impedance and dimension of each material, which is impossible to satisfy in many cases due to material unavailability or fabrication constraints. Consequently, many current systems are imperfectly matched with compromised performance. Here we show a universal impedance matching mechanism that realizes ∼100% energy transmission by double stages of quasi-arbitrary materials. The impedance of either matching material ranges from almost zero to almost infinity, as long as the impedance pair satisfies one of the four criteria. We validate the proposed mechanism with acoustic waves based on finite element modeling and experimental characterization. This work relaxes the requirement of matching materials and enables the universal matching of multiple waves with quasi-arbitrary materials.