A Method for Reducing Broadband Noise

The plug architecture replaces traditional solid exhaust plugs with an elongated design characterized by a hollow interior and a uniformly porous surface. By positioning the plug's crown inside the nozzle, the exhaust travels through a convergent passage up to the crown and a divergent passage past it. In standard solid plugs, shock waves become unsteady at off-design pressure ratios, causing severe acoustic resonance. The porous skin stabilizes localized flow separation and disrupts unsteady shock formation. By doing so, the technology alters complex aerodynamic interactions providing the noise reduction. Translation of the plug provides variable design condition without requiring heavy, maintenance-intensive mechanisms. Sub-scale acoustic testing demonstrates superior noise suppression without sacrificing aerodynamic efficiency. While existing aerodynamic treatments (such as tabs or boundary layer tripping) only mitigate screech or transonic tones, the porous plug represents a breakthrough by eliminating BBSN and EBBN as well as other aberrant noise. Additionally, thrust measurement data indicates this dramatic noise reduction is achieved with minimal impact on the gross thrust coefficient, preserving engine performance within

The drag penalty incurred by a conventional acoustic liner is dependent, to a large extent, on the perforate open area ratio (porosity) of the perforated facesheet. As the open area ratio is decreased, the facesheet behaves more like a solid surface and the drag is reduced. However, if the open area ratio is too small, the external acoustic field will be isolated from the resonators (in the liner), and the system will not provide noise reduction. The technology is a new type of variable-depth acoustic engine liner, which will reduce the drag and potentially manufacturing cost of this class of engine liner. Individual resonators within a conventional variable-depth liner are effective near resonance, but provide less acoustic benefit at other frequencies. In fact, at anti-resonance, a resonator behaves similar to a hard wall (i.e., the normal component of the particle velocity at the inlet is zero). Therefore, the proposed innovation couples neighboring resonators (tuned for different frequencies) together within the core of the liner. In other words, multiple resonators share a single inlet/port. Sharing inlets reduces the overall number of openings needed to maintain the acoustic performance of the liner by a factor of two or more. Reducing the open area ratio will in turn reduce the liner drag, and will reduce the number of holes that have to be machined into the facesheet, potentially reducing manufacturing cost. The functional operation of the proposed innovation will be identical to conventional engine liners. The innovation enables a reduction of the open area ratio of the perforated facesheet (by a factor of two or more) without degrading the acoustic performance. This will decrease the liner drag, and has the potential to reduce the manufacturing cost of the liner, since fewer holes need to be machined in the facesheet.

This technology uses a layered architecture that couples two complementary mechanisms. Polymer aerogels, with extremely small pores and high surface area, create tortuous pathways that dissipate structure-borne vibration (damping). Open-cell melamine foam captures airborne sound through viscous and elastic losses in the cellular network (absorption). By varying layer order, thickness, and chemistry, the composite becomes a tunable gradient system and can be designed for specific vibro-acoustic signatures, such as targeted frequency bands and mixed noise/vibration environments. Configurations can include melamine foam, compressed melamine, and melamine/aerogel sub-layers to balance absorption and damping in a single, thin envelope. Beyond acoustic performance, the aerogel component contributes low thermal conductivity. This enables insulation that reduces mass and volume while improving thermal management in panels, liners, and enclosure inserts and it integrates readily with existing structures as bonded or mechanically fastened layers. The layers can range from small samples to large panels for system-level installations. The technology has been validated from small test pieces to 8-foot panels where the layered composite can be tuned via stack order, thickness, and compression (melamine, compressed melamine, melamine/aerogel) to target specific frequency bands while retaining low thermal conductivity and low mass. This technology is assessed at TRL 6 and is available for patent licensing.

This water filtration innovation is an acoustically driven molecular sieve embedded with small-diameter carbon nanotubes. First, water enters the device and contacts the filter matrix, which can be made of polymer, ceramic, or metallic compounds. Carbon nanotubes within the matrix allow only water molecules to pass through, leaving behind any larger molecules and contaminants. The unique aspect of the technology is its use of acoustics to help drive water through the filter. An oscillator circuit attached to the filter matrix propagates acoustic vibration, further causing water molecules to de-bond and move through the filter. This use of acoustics also eliminates dependence on gravity (and thus filter orientation) to move water through the device. When water exiting the system diminishes to a pre-determined set point, a cleaning cycle is triggered to clear the sediment from the inlet of the filter, reestablishing the standard system flow rate. Unlike other filtration systems, flushing of the filter system is not required. The combination of acoustics and small-diameter carbon nanotubes in this innovation make it an effective and efficient means of producing contaminant-free, clean water.

A method for predicting the audibility of an arbitrary time-varying noise (signal) in the presence of masking noise is described in "An Algorithm for Statistical Audibility Prediction (SAP) of an Arbitrary Signal in the Presence of Noise" published in the Journal of the Audio Engineering Society (Vo. 69, No. 9, September 2021). The SAP method relies on the specific loudness, or loudness perceived through the individual auditory filters, for accurate statistical estimation of audibility vs. time. As such, this work investigated a new hypothesis that audibility is more accurately discerned within individual auditory filters by a higher-level, decision-making process. Audibility prediction vs. time is intuitive since it captures changes in audibility with time as it occurs, critical for the study of human response to noise. Concurrently, time-frequency prediction of audibility may provide valuable information about the root cause(s) for audibility useful for the design and operation of sources of noise. Empirical data, gathered under a three-alternative forced-choice (3AFC) test paradigm for low-frequency sound, has been used to examine the accuracy of SAPs. Future work should involve additional studies to examine the performance of SAP with realistic ambient noise and signals with higher-frequency content.