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In this work, we demonstrate that acoustic waves can achieve extremely flat transmission through a metallic grating under oblique incidence within multiple frequency bands separated by Wood's anomalies. At the low-frequency band, the transmission of acoustic wave is independent of the frequency and presents a flat curve with the transmission efficiency reaching about 100%; while at high-frequency bands, the transmission decreases to be lower flat curves due to the diffraction effect. The transmission efficiency is insensitive to the thickness of the grating. This phenomenon is verified by experiments, numerical simulations, and an analytical model. The broadband high transmission is attributed to the acoustic impedance matching between the air and the grating. This research may open up a field for various potential applications of acoustic gratings, including broadband sonic imaging and screening, grating interferometry, and antireflection cloaking. [ABSTRACT FROM AUTHOR]

In this work, we experimentally and theoretically demonstrate that oblique metal gratings with optimal tilt angles can become transparent for broadband terahertz waves under normal incidence. Direct imaging is applied to intuitively prove this broadband transparency phenomenon of structured metals. The transparency is insensitive to the grating thickness due to the non-resonance mechanism, and the optimal tilt angle is determined only by the strip width and the grating period. The oblique metal gratings with broadband transparence may have many potential applications, such as transparent conducting panels, white-beam polarizers, and stealth objects. [ABSTRACT FROM AUTHOR]