SBIR-STTR Award

Laser Fare-Advanced Technology Group (LF-ATG) has teamed with Triton Systems, Inc. (Triton), and Molecular Geodesics, Inc. (MGI), to propose an innovative method for producing multi-material structures that arrest the propagation of acoustic or vibrational energy. The approach forms scattering centers using Laser Engineered Net Shaping (LENS). The scattering elements will be intrinsically periodic due to their layered build format and geometric structure. With proper choice of material densities and elastic moduli, destructive interference of longitudinal and transverse acoustic waves over a specific frequency range has been demonstrated in simple periodic structures (Refs. 1-3). LF-ATG and Triton have applied the LENS solid freeform (SFF) method to generate titanium matrix composites (Ref. 4). We anticipate adapting LENS to provide a more diverse range of materials and periodic geometries in the design, fabrication and test of composite devices that are opaque to mechanical vibrations over a significant range of frequencies. As shown in this proposal, our approach can achieve precise tailoring of the spatial distribution of the scattering / phase shifting materials in millimeter to tens of centimeter-scale structures. This will potentially enable acoustic and vibration isolation in multiple directions at frequencies ranging from the audible to the ultrasonic.

Keywords:
Solid Freeform Fabrication; Acoustic Band Gap; Stereolithographer

Laser Fare, working with Triton Systems, the Naval Undersea Weapons Center, and the Electric Boat Division of General Dynamics, recently completed the DARPA "Acoustic Band Gap Materials and Devices" Phase I program. During this work we repeatedly demonstrated that periodic arrangements of various structural elements could establish acoustic band gaps or "ABG's". Comparison with existing 2-dimensional theoretical work from relevant references showed that the fundamental band gap center frequency was well predicted. However, a fundamental and potentially important result was the detection and verification of "sub-harmonic" ABG center frequencies. These ABG's were not predicted by existing theory, and are potentially important to a number of military and commercial applications where attenuation of lower frequency sound has proved very difficult. Further, it was found that structures involving aluminum rods in hexagonal arrays, coupled with interstitial open-celled foam, produced ABG's much wider than any reported in the literature. Funding limitations on the Phase I program precluded extensive modeling. However, with additional analytical and Finite Element modeling on a Phase II program, specific structures tailored to attenuate certain acoustic frequencies will be modeled, iterated, optimized, fabricated, tested, and utilized as the basis for military and commercial applications described in this proposal.

Keywords:
Acoustic; Band Gap; Sound Suppression; Destructive Interference; Acoustic FEA