Nondestructive Detection of Flaws through Thick Polymers using Electromagnetic Imaging Technologies

Navy SBIR 21.1 - Topic N211-062
NAVSEA - Naval Sea Systems Command - Mr. Dean Putnam -
Opens: January 14, 2021 - Closes: February 18, 2021 (12:00pm EDT)

N211-062 TITLE: Nondestructive Detection of Flaws through Thick Polymers using Electromagnetic Imaging Technologies

RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Materials / Processes

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a wireless nondestructive testing (NDT) capability to inspect hull metal surfaces and assess hull-to-polymer bond health under thick polymer layers without polymer removal.

DESCRIPTION: There is currently no method for nondestructive testing (NDT) of metal health through thick polymers. Current methods for inspections through thick polymers involve destructive removal of sections of the thick polymer. Removal and replacement of these polymer sections involve costly (in labor, time, and materials) operations that generate hazardous waste. An electromagnetic imaging NDT method for inspections through thick polymers is needed to reduce lifecycle costs, improve accuracy of initial maintenance work scoping, and increase operational readiness by reducing emergent maintenance issues in-field that were not discovered during scheduled maintenance. Any solution designed herein must wirelessly transmit data from the electromagnetic imaging sensor unit to a remote device for user-analysis. The electromagnetic imaging sensor unit must weigh 15 pounds or less (including power supply).

The developed NDT system must conform with all Federal Communications Commission (FCC) regulations and deliver a signal-to-noise dynamic range that corresponds to a linear interpolation as a function of frequency between 80dB at 15 GHz and 100 dB at 25 GHz (the frequency range of interest) via either a single frequency, narrowband, broadband, or multi-band solution. The NDT system must detect and classify debonds of any separation distance, corrosion, water intrusion, and surface metal loss (due to damage) of 0.41" diameter or greater on a metal substrate through a thick polymer coating with a refractive index of 1.0.

NDT of a metal substrate through a thick polymer coating while maintaining sub-wavelength resolution has been a long-standing challenge for electromagnetic imaging technologies, such as Terahertz imaging or millimeter-wave imaging, operating at far-field distances from the signal source. At 15 GHz with n = 1.0, the diffraction limit (wavelength size) is 0.79", and at 25 GHz with n = 1.0, the diffraction limit is 0.47". Thus, for the designated frequency band of interest, the given 0.4125" at n = 1.0 feature detection requirement requires sub-wavelength resolution, far-field interrogation of the target. Far-field detection of features smaller than 0.4125" at n = 1.0 is also of interest if possible. Sub-wavelength resolution is possible with geometric super-resolution techniques, such as Multi-spectral Signal Characterization (MUSIC). Far-field super-resolution techniques exist, yet no ruggedized end-user solutions with suitable detector/classifier algorithms are available in the current market. The development of a commercially viable prototype is needed for Navy applications.

Current and near-future Navy preservation applications require fine-resolution detection and classification of metal substrate flaws through thick polymer preservation coatings to perform needed inspections for specific flaws of interest at reduced maintenance cost to the Navy due to repair labor and material from destructive inspection practices. As materials become thicker, they become more attenuating for electromagnetic waves. The materials of interest also become more attenuating with increasing frequency. Thus, to perform needed NDT imaging through the materials of interest, an electromagnetic imaging source is needed that operates along a linear trendline between 15 GHz at 80dB of dynamic range and 25 GHz at 100dB of dynamic range (i.e., 20 GHz at 90dB of dynamic range fits along that linear trendline). Solutions that use performance extrapolations outside of the 15-25 GHz range (along the same dynamic range trendline) are also of interest as long as they meet the required 0.41" minimum flaw detection size, are able to detect "kissing" debonds (defined as when two bonded surfaces break their bond but are still touching), and are in accordance with all FCC regulations.

Any prototype solution developed will also include commercial off-the-shelf (COTS) software tools that provide automated detection and classification of any flaws in the collected data as well as software tools to enable the Navy to incorporate Navy-developed automated detection and classification algorithms. These flaws include debonds ("kissing" and larger debonds), substrate metal corrosion, and water abscessed at the preservation-to-metal interface. The prototype solution should scan for flaws and give processed results as expeditiously as possible. The preferred solution provides results as close to real time as possible, is portable (1-person carry) with supporting equipment, and provides a graphical user interface that is easy to use and understand by a technician with sufficient training. Such training will be developed as part of this topic. The software may be developed in any modern programming language (i.e. Python, R, Rust, Julia, or an appropriate Javascript derivative) and should provide tools for the user to develop and include their own detection/classification algorithms to process the data in real time.

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 DOD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence Security Agency (DCSA). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DCSA and NAVSEA in order 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 IAW DoD 5220.22-M during the advance phases of this contract.

PHASE I: Define and develop a concept for a far-field electromagnetic imaging system with the capacity to meet the operational, frequency, dynamic range, minimum detectible flaw size, and automated detector/classifier requirements specified in the Description. Perform modeling and simulation to provide the initial assessment of concept performance and feasibility. Phase I Option, if exercised, would include the initial layout and capabilities description to build the unit in Phase II.

PHASE II: Develop and deliver a prototype based on the Phase I work and the Phase II Statement of Work (SOW) for demonstration and validation through a field test on a specified, Navy-developed test panel that is equivalent to testing on an in-service Navy asset under field conditions, showing that the prototype meets the performance requirements in the Description. Refine the prototype as required based on the results of the demonstration and validation process. Deliver the final prototype at the end of the Phase II, ready for field use by the Government. Deliver comprehensive instructions and documentation for prototype setup, operation, maintenance, and software SDK development to enable a user to make full use of the prototype.

It is probable that the work under this Phase II effort will be classified (see Description section for details).

PHASE III DUAL USE APPLICATIONS: Assist the Navy in integrating the Phase II prototype into a field-use technology for Navy technicians. Provide a formal training curriculum (Level 1, Level 2, and Level 3) for Navy NDT inspectors to become certified in using this prototype for formal Navy NDT inspections. Update the training based on end-user feedback to the first version of the curriculum. Support Navy personnel to ensure all required software is approved for end-user use as well as testing, validating, certifying, and qualifying the prototype for Navy use.

Dual Use applications include other challenging electromagnetic imaging applications, such as assessing rebar health through concrete in structures, through-wall imaging, and contactless suspected bomb inspection.


  1. "FCC Online Table of Frequency Allocations." Federal Communications Commission Office of Engineering and Technology, 07 May 2019 (revision).
  2. "Radio Frequency Safety." Federal Communications Commission Electromagnetic Compatibility Division, 29 March 2013 (revision).
  3. Liao, Wenjing. "MUSIC for Multidimensional Spectral Estimation: Stability and Super-Resolution." IEEE Transactions on Signal Processing, Vol. 63, No. 23, Dec. 1, 2015.
  4. Ghasr, M.T.; Ying, M.P. and Zoughi, R. "Wideband Millimeter Wave Interferometer for High-Resolution 3D SAR Imaging." IEEE International Instrumentation and Measurement Technology Conference Proc., May 11-14, 2015.

KEYWORDS: Terahertz imaging; electromagnetic imaging; millimeter-wave imaging; mm-wave; nondestructive testing; NDT; nondestructive evaluation; NDE; Multi-spectral Signal Characterization; MUSIC; synthetic aperture radar imaging; geometric super-resolution; SAR


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