This invention has applications in the development of wearable passive hearing protection devices that filter out hazardous noise while allowing communicative sounds such as speech and audible alarms to be heard. These hearing protection devices can be used in the military as well as a wide range of civilian industries such as manufacturing and construction.
Hearing loss is a major cause of disability among military personnel who are routinely exposed to a wide range of acoustic threats ranging from machinery noise to ordnance detonation. Currently, utilization of hearing protection devices (HPDs) in the field is limited. Passive HPDs such as earplugs indiscriminately attenuate sounds over a wide frequency band, leading to reduced situational awareness. This limitation contributes to low utilization rates of currently issued passive HPDs. Active HPDs rely on digital processing circuitry to selectively attenuate hazardous noise. However, their fragility and prohibitively high cost has thus far prevented widespread use. This invention addresses these limitations with a new class of passive frequency-selective hearing protection devices.
This invention describes a passive acoustic filter made up of a periodic array of shaped unit cells. These unit cells collectively make up a phononic crystal whose internal topology allows sound waves of some frequencies to propagate through with less attenuation than others. In fact, the Inventors have devised a design capable of filtering noise over a wide normalized gap size of 117% while retaining a completely passive design. The performance of this phononic filter is primarily dependent on its geometric design rather than material properties. This affords significant design freedom in selecting materials and manufacturing processes for affordable production at large scale. For example, the phononic filter may be fabricated in a highly scalable single-material “mold-and-release” process. Finally, the design described in this invention is capable of reducing system size by approximately three times compared to existing phononic filters. This compactness allows the phononic filters to be incorporated into easily wearable HPDs.
Effective attenuation over a wide range of frequencies (normalized gap size of 117%) while allowing propagation of sounds necessary for communication
Reduces form factor by ~3x compared to existing phononic filters
Acoustic performance decoupled from material characteristics
- Significantly lower cost and higher robustness compared to active HPDs