Description:
TECHNOLOGY AREA(S): Weapons
OBJECTIVE: Reduce or change the sound signature, in terms of magnitude, frequency, and/or duration, of a small caliber projectile as it travels downrange through the use of Active Noise Reduction, Active Noise Control, or similar methods. Overall control of weapon signature at the muzzle is a secondary objective.
DESCRIPTION: Active Noise Control (ANC), or Active Noise Reduction (ANR), is a method for reducing unwanted sound by introducing additional sound waves which are specifically tuned to cancel out the first. The added waves combine to form a new wave, in a process called destructive interference. The Army is seeking innovative approaches that apply these super position techniques to small caliber systems without degrading the performance of current weapon platforms at all ranges of military interest. Performance in this context refers to accuracy and the spread of impact momentum values for selected projectiles. Firearm sound is generated by a number of sources. The sudden release of hot, high pressure, high velocity gas from a gun barrel bore is an example. The sound of the bullet as it pushes through the air in flight is another. Bullets traveling near or greater than the speed of sound generate a ballistic crack or sonic boom. This is the sound which is generated outside of the weapon and cannot be addressed by a simple weapon suppressor. The ballistic crack of a projectile or “sonic boom” is the result of air flow traveling at or over the local speed of sound (approximately 1,126 ft/s, or 768 mph depending upon conditions). Current 5.56x45mm NATO rifle rounds are launched at speeds between 2,970 ft/s and 3,100 ft/s depending upon the specifics of the weapon/munition design, and 7.62x51mm rifle rounds have muzzle velocities that are between 2,580 ft/s and 2,733 ft/s. This is obviously faster than the local speed of sound. Subsonic projectiles and pistol bullets in general are not currently of interest. The non-suppressed sound of a 5.56mm or 7.62mm supersonic rifle bullet when measured 1 meter to the left or right of the weapon is often around 164 dB. This has a direct impact on training, effectiveness, and survivability. Projectile sound is a consideration in tactical effectiveness, as it identifies type, range, and intensity of oncoming fire. Traveling projectiles undergo the Doppler effect. This changes the frequency (or pitch) of the sound depending upon whether the projectile is getting closer or receding. The magnitude (or loudness) of the sound diminishes by the inverse-square law as the receiver (of the sound) moves away from the source. Each doubling of distance reduces the volume by a significant amount. For example, for a 164 dB source, a doubling of distance might reduce the sound level by 6 dB. The science behind this rudimentary discussion of wave behavior has been well understood for centuries. What has changed is the ability to measure, process, and use the information collected by sensors in practical time increments. What has changed is the ability to mitigate these waves, at least to a degree, and at least under certain conditions. The question for this SBIR topic is are we at a point where this technology can have a meaningful impact on marksmanship training (safety), small unit command and control (issuing/receiving orders in high noise environments), weapon/projectile launch (enabling high velocity solutions which would have previously been prohibited for sound reasons), survivability (how far does the sound of fire travel), cover fire effectiveness (how close does the round sound), fire control (does the sound generated by the projectile enable a better fire solution once the sound has been processed), and other applications. The Government is not currently interested in technology solutions which are not part of the weapon or the munition; ear muffs and similar safety gear are outside of this topic. Technical challenges: • Determination of the performance tradespace which is associated with reasonable application of this technology for the field of small arms. • Ability to induce a meaningful noise-canceling/shift in the sound as the projectile is fired. • Ability to induce a meaningful noise-canceling/shift in the sound signature as the projectile flies. • Ability to put robust electronics on projectiles which will withstand the high g-forces and other stresses which are associated with launch. • Powering of electronics on ammunition/weapon hardware. • Determination of the suitability of this approach for a man-portable small arm, crew served weapon, or remote weapon system platform employing small arms such as CROWS. • Determination of the impact of this in practical situations of military interest. • Ability to do all of the above without overtly affecting the usefulness of the system.
PHASE I: The offeror will explore and determine the feasibility/approach for the development and application of ANC/ANR technology to mask or shift the noise of a rifle in a way in which the source and direction of fire will be difficult to determine. The tasks will include a technology analysis to guide the application and trade-off of key components, approaches, and subsystems; research conducted to ensure that ballistic performance and impact characteristics required to produce lethal effects are maintained. The phase will result in a study and report on the current state of the art of ANC/ANR technology with discussion of that technology for small arm development. The report will also cover performance metrics/goals, an experiment test design for use in a modeling and simulation environment, any notable spin off applications of the technology that can be applied to the commercial sector, and a detailed research plan to develop and demonstrate a Phase II proof-of-concept/prototype.
PHASE II: The offeror will develop, demonstrate, and validate the rifle findings developed during Phase I to produce a prototype of the ANC/ANR technology for use in a small caliber system. The offeror will conduct a statistically relevant set of experiments using the design and performance metrics developed in Phase I to evaluate source location/direction phase shift and below Mach 1 sound masking. The Phase II final report shall include: (1) full system design and specifications detailing the electronics and proof-of-concept components to be integrated; (2) expected performance specifications of the proposed components; (3) expected improvements which are achievable through continued refinement of the design; and (4) data and analysis of the experiments and modelling and simulation work which was done.
PHASE III: The offeror will work with available funding sources to transition capability into practical use within Army/DoD programs of record and production lines, while considering options for dual-use applications in broader domains including state/local governments, and commercial. Potential opportunities may exist to produce technologies which will reduce hearing loss in high intensity sound environments.
REFERENCES:
1: MIL-STD-1474E: Department of Defense Design Criteria Standard: Noise Limits, 15 Apr 2015.
2: Maher, Robert C., "Acoustical Characterization of Gunshots," 44th Annual SAFE Symposium, Washington DC, April 2007.
3: Dater, Philip H. "Firearm Sound Suppression: Nature and Measuring of Firearm Sounds." 2014.
4: Kuo, S. M. and Morgan, D. M., "Active Noise Control: A Tutorial Review," Proc. of IEEE Signal Processing Society, Vol. 87, No. 6, June 1999.
KEYWORDS: Active Noise Control, Active Noise Reduction, Adaptive Noise Cancellation, Digital Signal Processing (DSP) Applications, Weapon Signature, Muzzle Pressure, Suppressor, Hearing Protection
