Elastic complementary meta-layer for ultrasound penetration through solid/liquid/gas barriers

•The “first elastic complementary metamaterial” for canceling barriers spanning from solid to liquid and even gas is presented.•A novel meta-atom is proposed where dipolar and monopolar resonators are deliberately configured in a transverse manner to enable independent tunability of effective negative properties.•Explicit theoretical backgrounds to evaluate the effective properties (including impedance and phase change) are presented.•Our complementary metamaterial in a monolayer form enhances the ultrasound transmission by 593%, 1426%, and 3280% by “cancelling out” the polymer, water, and air barriers, respectively.