Low-frequency tunable acoustic absorber based on split tube resonators

We demonstrate a high-efficiency tunable acoustic absorber for low frequencies (<500 Hz) with subwavelength thickness. The acoustic absorber is based on split tube resonators and could reach high-efficiency absorption at tunable resonance frequency with wavelength in air at least 30 times larger than its total thickness in simulations and experiments. The resonance frequency and high-efficiency absorption of the absorber are robust under oblique incidence even at large angles. The absorber could have potential applications for acoustic engineering due to its high structural stability, ease of fabrication, subwavelength thickness, and robust high-efficiency.