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Line-Distributed Hoop Strain Sensor




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: The objective of this task would be to research, develop, and demonstrate a strain gage (sensor) capable of measuring axisymmetric hoop strain of a large diameter shell. The sensor must be accurate over a broad frequency range, down to and including zero Hz.

DESCRIPTION: Large structures acted upon by external forces exhibit complex vibrations. A complex vibration pattern consists of a superposition of many simpler vibration patterns (modes), each of which has a characteristic wavelength. Often the impact on the overall health of a structure depends more heavily on the vibration of modes with long wavelengths. For cylindrical shells, hoop strain is a key indicator of structural health. The current method of estimating the hoop strain is to place a large number of point sensors (accelerometers) around the circumference of the structure and apply geometrical weighting to the sensor signals. Many sensors are needed to filter out the shorter wavelength vibration content that can dominate the signals of the individual sensors. Each point sensor requires a cable to provide electric power and to transmit the measured signal to a centralized signal processing unit. Thus, to extract the single measure of axisymmetric hoop strain can require a significant amount of hardware and signal processing.

This proposal is looking for an innovative and cost reducing method that can measure the required strain over a long line or large area.  Such a sensor must operate with minimal signal processing and low electrical power. It must operate over a range of environmental conditions (temperature, humidity, noise, and vibration). It must be capable of installation, operation, and maintenance by trained personnel. It should provide a significant signal-to-noise (SNR) improvement over current technology.  Such a technology could intrinsically eliminate the need for spatial filtering, thereby radically reducing the signal processing and cabling demands and greatly reducing installation, operational, and servicing cost.

PHASE I: Develop concepts for a field of distributed sensor technology and propose a candidate set of technologies to test and evaluate in Phase II. The contractor will develop distributed hoop strain sensor concepts to address the requirements mentioned above.  Criteria for assessing the technology will include accuracy, latency, linearity, ease of calibration, durability, fragility, electrical power/voltage/current requirements, and electro-magnetic interference.

PHASE II: The contractor will expand upon the Phase I work to develop a representative prototype of selected sensor concepts.  The prototypes will then be demonstrated and tested under a number of operating conditions (temperature, humidity, noise and vibration level) that the government will specify.

PHASE III: The contractor will support the government in field testing the distributed strain sensor. The contractor will acquire the capability to manufacture the distributed strain sensor and the capability to provide technical support to the government in installation, operation, and maintenance of the strain sensors.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The benefits from a distributed strain sensor in reducing installation and servicing cost can be adopted by the private sector for commercial purposes.  Such applications include installation of distributed strain sensors on pressure tanks and in the aircraft industry.

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