N121-073 TITLE: Combined Nondestructive Evaluation (NDE) and Electrical Characterization of Missile Radomes

TECHNOLOGY AREAS: Materials/Processes, Weapons

ACQUISITION PROGRAM: PEO IWS 3.0, Standard Missile / SM-6 (ACAT I); FNC: STK-FY09-03

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop a method of characterizing tactical missile radomes that will reveal manufacturing defects that may impair electrical and structural performance and that will provide localized information on dielectric properties which can be used to predict insertion loss and boresight error.

DESCRIPTION: Radomes are a key missile component. Their costs are in the many tens of thousands of dollars. Part of the costs are related to yields, which are a function of the current process used to determine the characterization of the radomes. This process consists of pairing the radome with the seeker in the factory to generate a correction table for seeker target location thus compensating for boresight error.

The Navy is seeking improvements in the process, particularly with respect to electrical characterization without use of actual seekers, through the application of new technology. If extensive electrical characterization could be minimized by use of new technology, the costs of integrating the radome with the seeker would be reduced. If the technology sought in this topic is successful, it would be used to improve manufacturing yield and reduce production costs of radomes in several missile programs. The technology could also reduce costs in the development of future radomes.

Defects in a radome have a significant impact on seeker performance; therefore, radome characterization is key. The current process of characterization in which the radome and seeker must be tested in the factory is costly. Development of the technology under this topic would advance the state of the art in NDE (Non Destructive Evaluation) of composite and ceramic radomes but more importantly would reduce, if not remove, the level of testing of the assembled seeker and radome in the factory.

Radomes on tactical missiles protect the antennas and electronics underneath. Radomes have strict requirements on transmission properties. Transmission through a radome is governed by the thickness, dielectric constant, and loss tangent of the wall material. Local variations of any of these parameters result in distortion of the transmitted signal, which leads to boresight error. Boresight error is the deviation in the apparent signal direction as seen by the seeker antenna when scanning through the field of regard.

The Navy is seeking innovation in technologies such as terhertz radiation that will permit scanning of radomes to generate a map of the local transmission properties of a radome. The instrument needs to be capable of imaging defects such as thickness variations, voids, inclusions, and localized variation in the proportion of constituents (such as fiber/matrix volume fraction in composites). It is envisioned that this instrument would be approximately the size of an office desk. Proposed concept should be capable of detecting defects having length scales of 500 micrometers, and preferably smaller. The current use of sonic techniques cannot give this resolution. The relationship between the instrument scanning wavelength and properties of the missile operating radar should be taken into account. This will involve theoretical physics or experimental measurements. Missile frequencies of interest range from 1 to 100 GHz.

The technique should be capable of characterizing polymer, polymer composite, ceramic, and ceramic composite materials. The output should include an image of the mapped defects including information regarding their character, a map of local transmission characteristics, and an estimated boresight error map.

PHASE I: Conduct analyses and develop concepts and instrument parameters for conducting experiments demonstrating characterization capability on coupons of radome materials. Conduct experiments using breadboard components demonstrating the capability to detect and image defects in coupons of radome materials. Develop understanding (empirical and theoretical) of relationship between proposed instrument measurements and dielectric properties at missile frequencies. Develop a concept to scale the process from coupons to full radomes. Develop a Phase II plan with milestones and testing to verify the feasibility of the technology as well as the concept to meet the Navy need.

PHASE II: Based on the Phase I results and consistent with the Phase II plan, develop a prototype instrument capable of measuring effective electrical thickness (measured at measurement instrument design frequencies and converted to the thickness at the frequency of interest, in X, Ka, or W bands) and mapping defects. Verify performance of the instrument on notional developmental radomes, or actual tactical units, depending on availability. Verify by experiment the correlation between prototype instrument frequencies and Gigahertz properties on radomes. Conduct an analysis showing the cost savings of using this new instrument versus the current process of radome characterization. Prepare a Phase III development plan to transition the technology to Navy and DoD prime contractor use.

PHASE III: There are two possible options to the Phase III. One option is to develop, test, and deliver a fully automated instrument to the Navy that in turn the Navy would provide as GFE to defense prime contractors or radome producers. The second and more likely option is to develop, test and deliver (i.e., sell) the aforementioned instrument directly to defense prime contractors or radome producers.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Although the technology has been described as specific to radomes, the general NDE aspects and the electrical measurement aspects could find use in many commercial applications. The applications of composites are many, including automobiles for example. The NDE techniques could be used on many manufactured materials and components. The electrical measurements could find application in electronics components such as substrates and circuit boards.

REFERENCES:
1. Radome Engineering Handbook, J.D. Walton, Ed.; Marcel Dekker, Inc. 1970

2. Antenna Engineering Handbook, 4th ed. Pp. 53-1 - 56-25. McGraw Hill Publishing, 2007

3. Nature Photonics, Volume 3, pp 630-632 (2009)

KEYWORDS: nondestructive evaluation; terahertz radiation; radomes; dielectric constant; loss tangent; boresight error

** TOPIC AUTHOR (TPOC) **

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