Phononic crystals (PnCs) have emerged as promising structures for manipulating elastic waves, finding applications in various engineering domains such as vibration isolation and frequency filtering[1]. This study delves into the design of PnCs based on the p4gm plane group, leveraging its nonsymmorphic properties to induce the band-sticking phenomenon, resulting in wider bandgaps. Through extensive parametric studies using finite element software COMSOL Multiphysics 6.1, we investigate the impact of different geometric features on PnC bandgaps. Employing eigenfrequency analysis, we calculate the phononic band structure using the Bloch-Floquet approach and identify bandgaps by scanning the Irreducible Brillouin Zone (IBZ) contour. The high symmetry of the PnC unit cell allows the IBZ alone to provide a comprehensive description of wave vectors corresponding to allowed propagation frequencies. Additionally, we perform transmission loss simulations for finite PnCs and compare them with the experiments on a custom-built ultrasonic set-up. We conduct a comparative analysis with PnCs based on p4mm and p4gm plane groups, revealing that the latter exhibit superior ultrasonic attenuation within the bandgap region. Our results demonstrate that PnCs based on the p4gm group exhibit significantly larger bandgaps and higher ultrasonic attenuation within these gaps for both transverse and longitudinal waves[2]. This research enhances our understanding of PnC design principles, showcasing the potential of nonsymmorphic symmetries for advanced bandgap engineering. The findings serve as a guide for developing innovative PnCs with improved performance, particularly in the realms of vibration control and frequency filtering. REFERENCES [1] Krushynska AO, Torrent D, Aragón AM, Ardito R, Bilal OR, Bonello B, et al. Emerging topics in nanophononics and elastic, acoustic, and mechanical metamaterials: an overview. Nanophotonics 2023;12:659–86. [2] Nadejde I, Thomas EL, Galich PI. Pushing the limits of complete omnidirectional bandgaps in 2D nonsymmorphic single-phase phononic crystals. Appl Phys Lett 2023;123.