All-angle wideband acoustic self-collimation by Helmholtz resonators

Phononic crystals and acoustic metamaterials have transformed acoustic wave control over the past three decades, enabling unprecedented manipulation of sound through tailored structural periodicity and local resonances. In this study, we demonstrate how Helmholtz resonators (HRs) embedded in square-lattice sonic crystals (SCs) achieve all-angle self-collimation (AASC) of acoustic waves across wide frequency ranges—a phenomenon previously attainable only with rectangular lattices or elliptical scatterers. Through finite element simulations, we analyze two types of Locally Resonant SCs (LRSCs) with different HR embedded scatterers: One with resonant frequency in the wavelength regime, classified as H R − T 2 and another with a lower local resonance frequency, termed as H R − T 1 . The H R − T 2 case exhibits wideband All-Angle Self-Collimation(AASC) in the third band, covering 66.5% of its bandwidth (520 Hz), while H R − T 1 shows frequency-sensitive super-collimation (FSSC) and AASC in the fourth band (22.86% bandwidth, 190 Hz). Frequency response analysis of finite supercell arrays validate robust collimation for incident angles up to 85°. Our findings highlight the unique ability of HRs to induce AASC in symmetric lattices, unlocking applications in directional sound control, low-loss acoustic waveguides, non-diffractive beam shaping, and high-resolution acoustic imaging systems. • All-Angle Self-Collimation (AASC) is demonstrated in square-lattice sonic crystals using Helmholtz resonators, without lattice anisotropy. • Frequency-Sensitive Super-Collimation (FSSC) is explained for the first time in acoustics, enabled by totally flat Equi-Frequency Contours. • Finite-size simulations validate broadband angular robustness of self-collimation up to 85°incidence, suitable for directional wave control.