The U.S. Department of the Navy is seeking proposals for the development of second order acoustic vector sensors to enhance the performance of sonobuoys used in air Anti-Submarine Warfare (ASW) operations. The objective is to create advanced sensor configurations that improve tracking and localization of stealthier targets, thereby increasing the effectiveness of naval operations. These sensors are crucial for achieving higher directivity and array gain in complex acoustic environments, which is essential for modern ASW missions. Interested parties should note that the solicitation is set to open on April 23, 2025, with a closing date of May 21, 2025, and must ensure compliance with security requirements for classified work. Further details can be found on the official SBIR website.

## Description

The application of second order acoustic sensors is employed to great effect in commercial acoustic products such as hearing aids. The U.S. Department of the Navy seeks to explore the application of similar second order directional receivers in sonobuoys to increase overall system performance in air Anti-Submarine Warfare (ASW) operations.&nbsp;Historically, sonobuoys utilized a variety of approaches to achieve first order directional channels, including acceleration, pressure gradient, and multi-mode sensors. The main advantage of a higher order directional acoustic channel is increased directivity index, which also results in a more complex beam pattern compared to the conventional first order channel. Together, these attributes provide an opportunity to increase overall array gain in complex real-world acoustic environments.&nbsp;The advantages offered by higher order directional receive channels are fundamentally enabled by increasing the number of receiving channels and then combining them in a beamformer based on the expected acoustic propagation for the sensor configuration. As is true in most acoustic products, sonobuoys must balance these potential performance gains against the targeted unit production cost and limited available volume. Other challenges such as build variances, channel self-noise level, and signal processing power consumption must be addressed to form higher order directional channels. &nbsp;This SBIR topic is interested in developing equally spaced vertical line arrays of second order vector sensors with a center frequency at 1000Hz and a bandwidth of 400 Hz, and with a center frequency at 8kHz and a bandwidth of 1.5kHz. This SBIR topic will determine the number of second order vector sensors that can be packaged in an A-size sonobuoy. The self-noise of each individual second order cardioid will be equal to or less than 30 dB. The array self-noise will be reduced by 10 log of N where N is the number of elements in the array. Approaches must allow for continuous beam steering in in azimuth.&nbsp;Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by 32 U.S.C. § 2004.20 et seq., National Industrial Security Program Executive Agent and Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence and Security Agency (DCSA) formerly Defense Security Service (DSS). The selected contractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances. This will allow contractor personnel to perform on advanced phases of this project as set forth by DCSA and NAVAIR to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material during the advanced phases of this contract IAW the National Industrial Security Program Operating Manual (NISPOM), which can be found at Title 32, Part 2004.20 of the Code of Federal Regulations.

## Objective

Develop and demonstrate an increase in acoustic performance via second order vector sensors for use in advanced sonobuoy arrays to track and localize stealthier targets within a larger search area to increase success in future U.S. naval anti-submarine warfare operations.

## Phase I

Develop, design, and demonstrate feasibility of candidate second order directional sensor configurations and associated beamforming approaches that offer performance advantages for sonobuoys in one or more aspects of the overall air-ASW mission. Predict overall performance and offer mitigations to various design challenges. Compare the candidates and down select to a notional design to build and test in Phase II. Demonstrate that chosen candidates can eventually be scaled to fit into an A-size sonobuoy package with considerable effort.Perform in-depth modelling during the study and identification of possible candidates. Conduct some initial testing to demonstrate the raw material and/or hardware needed to build the candidates for Phase II possess the characteristics used for modeling or that at least the component has the characteristics and performance required for the system to achieve the objectives. The Navy seeks proven candidate(s) that have been demonstrated and validated to meet the objectives and can be scaled down to fit within the A-size constraints. The small business awardee must provide a full report where their models have been performed with sufficient accuracy and depth to produce meaningful results to meet the objectives. In addition, demonstrate that preliminary testing has been performed on the raw material and/or hardware showing that it possesses the characteristics used for modeling, or that at least the component has the characteristics and performance required for the system to achieve the objectives. The small business awardee must also prove the models and results provided in the report were originated by them. The Phase I effort will include prototype plans to be developed under Phase II.

## Phase II

Develop and test prototype(s) of the second order vector sensor to verify Phase I performance predictions. Quantify key performance metrics through a combination of laboratory and open water testing. Extrapolate the expected performance for the intended mission(s).Work in Phase II may become classified. Please see note in Description paragraph.

## Phase III: Dual Use Applications

Integrate the second order vector sensor technology into an A-size sonobuoy, leveraging the prototype fabricated in Phase II. Conduct a demonstration and characterize mission performance under real world conditions.The new approaches developed in this SBIR topic could enhance acoustic sensing technologies for harbor and port security, marine conservation, and other research or monitoring applications.

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