Frequency-Angle Acoustic Beam Steering via Nearly Dispersionless Gradient Metasurfaces

Gradient metasurfaces provide a powerful platform for wavefront and dynamic beam steering of electromagnetic and acoustic waves by introducing the phase-gradient degree of freedom, but they still suffer from narrow steering angles and low efficiency due to inherent dispersion. Here, we theoretically propose and experimentally demonstrate a dispersionless gradient metasurface approach that offers a practical yet powerful route to wide-angle, near-perfect beam steering, overcoming the longstanding trade-off between bandwidth and efficiency in metasurface design. As a proof of concept, we design and fabricate an acoustic metasurface operating at 3430 Hz, which exhibits near-perfect anomalous refraction with an efficiency exceeding 85% over an unprecedented bandwidth of 44.4% (2800-4400 Hz). This performance enables continuous frequency-driven beam steering from 46.5° to 15.8°, covering a 30.7° field of view. Serving as a critical transition between anomalous and normal dispersion, the concept of dispersionless gradient metasurfaces provides a criterion for evaluating the bandwidth limitations of various dispersive counterparts, and establishes a new paradigm for high-performance, frequency-driven dynamic wavefront manipulation.