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Prepared by Sandia National Laboratories Albuquerque, New Mexlco 87185 and Livermore, California 94550 for the United States Department of Energy under Contract DE-AC04-94AL85000 Approved for public release; distribution is unlimited.

One of our primary goals was to determine how well a laser Doppler vibrometer (LDV) could measure the structural d p m i c response of a wind turbine that was parked in thc field. We performed a series of preliminary tests in the lab to determine the basic limitations of the LDV for this application. We then instrumented an installed parked horizontal axis wind turbine with accelerometers to determine the natural frequencies. damping, and mode shapes of the wind turbine and rotor as a baseline for the LDV and our other tests. We also wanted to determine if LDV modal information could be obtained from a naturally (wind) excited hind turbine. We compared concurrently obtained ric:elerometer and LDV data in an attempt to assess the quality of the LDV data. Our test results indicate the LDV can be successfully used in the field environment of an installed wind turbine, but with a few restrictions. We were successful in obtaining modal information from a naturally (wind) excited wind turbine in the field. but the data analysis requires a large number of averaged data sets to obtain reasonable results. An ultimate goal of this continuing project is to develop a technique that will monitor the health of a structure, detect damage, and hopefully predict an impending component failure.

A quad-phase-only filter (QPOF) is introduced. It is shown that the QPOF can have improved correlation response and signal-to-noise ratio with respect to the Hartley binary phase-only filter for some objects.

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Some of the fastest commercially available coherent spatial light modulators are binary. This fact has motivated research on the binary phase-only filter, which is unfortunately unable to represent a complex filter function. A technique is introduced here with which a single binary device can be used to represent a complex filter with independent binary representation of real and imaginary parts. The technique is analyzed theoretically, and simulation and laboratory results are presented.

A microchannel plate is demonstrated as both an optical lowpass filter and a heterodyning modulator. The frequency response function of the microchannel plate indicates it behaves as a low-pass filter. Antialiasing with the microchannel plate is demonstrated using a twotone amplitude modulated laser beam, with the higher tone above the cutoff frequency being successfully suppressed while the frequency within the bandwidth of the filter is passed through. Selection of different commercially available phosphors controls the filtering and frequency response characteristics of the optical filter, effectively moving the cutoff frequency. By gating the microchannel plate at different frequencies, the microchannel plate can also be used analogously to a heterodyning spectrum analyzer, supplying all of the required functions of a local oscillator, mixer, and filter.

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