Ultrasonic Rainbow: A Meta‐Transducer for Frequency‐Selective Elastic Wave Control via Dithering‐Based Wavenumber Tuning

Elastic wave control underpins numerous technologies, from structural health monitoring and biomedical imaging to wireless communications and energy harvesting. Conventional phased arrays enable dynamic beamforming but are bulky, power-intensive, and complex, limiting their integration into compact or distributed systems. Here, we present a meta-transducer design that embeds wavenumber-domain filtering directly into the electrode geometry, enabling frequency-controlled unidirectional generation of ultrasonic guided waves without active phasing networks. A key innovation is the use of error-diffused spatial dithering to approximate continuous 2D filters with binary patterns by shaping the transducer electrodes, suppressing sidelobes and enhancing angular resolution. Finite element simulations and experimental validation with a scanning laser Doppler vibrometer confirm that the Frequency-Steerable Acoustic Transducer (FSAT) achieves sharp, frequency-tunable beam steering across a 180° sector with over 80% reduction in sidelobe energy compared with conventional designs. This approach enables ultra-compact, energy-efficient ultrasonic devices with wavefront control, offering a pathway to advanced applications in guided wave imaging, IoT-enabled sensing networks, and ultrasonic communications.