Vibrating structures radiate acoustic waves into the fluid media which surround them at the structure-fluid interface. Fundamentally, the interfacing structural surface topology governs the amplitude and frequency sensitivities of acoustic energy propagation away from the surface, a characteristic known as directivity. Assembling many planar acoustic transducer elements into arrays is one way to greatly enhance the far-field energy propagation directional sensitivities. Due to the spatially distributed transducers, the travelling waves combine uniquely in phase at an observation point in the far field where large energy focusing or suppressing occurs as a function of the spatial coordinates. The conventional approach to tune planar array directivity for a different purpose or new spectral sensitivity is to actively adjust each array input signal with a controlled phase delay which requires accessory hardware and computational burden. From a different standpoint, structures created from foldable, tessellated architectures, such as origami patterns, can yield enormous topological variation from the simple, kinematic motions of connected planar facets. This observation has inspired recent efforts to develop innovative, adaptable engineering systems using origami tessellations as an architectural basis for design. Considering together the topological sensitivities of planar acoustic arrays and the multifunctionality engendered by folding origami-based structures having planar facets, this research seeks to surmount the limitations of conventional acoustic arrays and explore a new idea for adaptable acoustic systems by integrating principles from acoustics and origami-inspired design. Upon the new idea, this research studies a tessellated acoustic transducer array able to drastically adapt energy guiding capabilities through simple topological folding. An array based on the Miura-ori folding pattern is examined in a new structural-acoustic model to assess the capability of folding to tune the magnitude and spatial variations of acoustic energy propagated to the far field. The acoustic directivity of the array is found to exhibit massive sensitivities based on the excitation frequency and fold angle, giving rise to large amplitude and spatial adaptation of the energy guiding to the far field point. An experimental tessellated acoustic array is fabricated and evaluated to verify the trends predicted by the model. From the measurements, it is conclusively seen that the topological change of the origami-inspired acoustic array empowers straightforward and reversible means for orders of magnitude in change in acoustic energy transmission and steering. Upon this basis, future compact, deployable, and kinematically-adaptable wave energy transmission systems may be developed for applications including field imaging, communications, and long range force projection.
Experimental Study of a Broadband Parametric Acoustic Array for Sub-Bottom Profiling in Shallow Water