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AF083-264 TITLE: MOBILE LOW-POWER MULTIPOINT LASER DOPPLER VIBROMETER TECHNOLOGY AREAS: Sensors OBJECTIVE: Research and develop an alternative mobile, low-power, human eye safe, matrix laser beam Doppler vibrometer. DESCRIPTION: Vibration diagnostics and predictive structural health analysis plays an important role in the flight testing of airframe structures and avionic sub-systems. AFFTC has a need to test structural integrity and predictive response/failure analysis of control surfaces, relative response of doors, storehangers, articulating surfaces, pods, and fins. The predictive analysis of structural-behavior to airflow, propulsion, ionic gases, shock waves, in low/high atmosphere, under normal or extreme operating conditions, provides a key metric for evaluating design integrity and structural health of flying vehicle and its avionics. It links actual system behavior to design specifications. Measurements of structural response to forced excitation are traditionally obtained from a distributed network of surface mounted accelerometer load cells, which are time consuming to set up and dismantle. More recently, there have been some publications in alternative methods, employing non-contact optical measurements made possible by the laser Doppler vibrometer (LDV). It measures vibration at the point where the laser beam is incident on the surface. The instrument is, however, costly (typ. $250,000), and the measurement cycle can still be very time consuming on large structures which require many hundreds of point measurements. With existing LDV instruments, this information must be inferred from multiple time-sequential measurements based on the assumption that steady-state conditions prevail between the first and final measurement. The research is needed to devise an alternative low power human eye safe Multiple Beam Laser Doppler Vibrometer to facilitate the single-shot capability of simultaneous measurement of structural integrity of airframe structures. Electro-optic, acoustic, or multi-channel diffraction optics are preferred to be used to achieve the multipoint measurement capability (2-D matrix including at least 256 points) without any moving parts. This will also ensure minimum power consumption and eye safety. Other approaches which offer the capability of providing these measurements without extensive use of accelerometers will also be given appropriate consideration. Other factors that can be considered are developing an intelligent data processing system that can process the measurement data and plot the whole field, time resolved vibration data into engineering parameters commonly used in test, evaluation and design. PHASE I: Perform a feasibility study and develop a conceptual design for mobile low-power multipoint laser Doppler vibrometer. PHASE II: Develop and demonstrate a prototype system based on the Phase I design. PHASE III / DUAL USE: Military application: There exists a continuing need to measure and evaluate the response to vibrations in military aircraft and components which could be greatly improved by new non contact measurement technology. Commercial application: There exists a continuing need to measure and evaluate the response to vibrations in civilian aircraft and components which could be greatly improved by new non contact measurement technology. REFERENCES: 1. A. Chattopadhyay, M. J. Schulz, R. Thornburgh, K. Waldron and A. Ghoshal “Experimental of Damage Detection in Composite Material Structures Using a Laser Vibrometer and Piezoelectric Actuators” Journal of Intelligent Material Systems and Structures, Vol. 14, No. 8, 521-537 (2003). 2. E. Peter Carden and Paul Fanning, Vibration Based Condition Monitoring: A Review, Structural Health Monitoring, Vol. 3, No. 4, 355-377 (2004). 3. JA Oliver and JB Kosmatka , “Evaluation of modal-based damage detection techniques for composite aircraft sandwich structures”, Proceedings of SPIE,Volume 5767, Nondestructive Evaluation and Health Monitoring of Aerospace Materials, Composites, and Civil Infrastructure IV, May 2005, pp. 264-273. 4. Damage identification and health monitoring of Structural and mechanical systems from changes in their vibration characteristics: A literature review. S. W. Doebling, C. R. Farrar, M. B. Prime, and D. W. Shevitz. Technical Report LA-13070-MS, Los Alamos National Laboratory, Los Alamos, NM, 1996. 5. Cawley, P. et al. “The Location of Defects in Structures from Measurements of Natural Frequencies,” Journal of Strain Analysis, Vol.14, No.2, p.49-56, 1979. KEYWORDS: Matrix Laser Beam Doppler Vibrometer, control surfaces, relative response of doors, storehangers, articulating surfaces, pods, fins