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Scanning Laser Vibrometry

Scanning Laser Vibrometry

  Mode Shape
Mode ShapeThe application of effective noise and vibration treatment often requires a precise knowledge of the spatial and temporal distribution of the source vibration. Researchers at ARL have developed considerable expertise in the use of a laser technique, scanning laser vibrometry, which is sensitive, robust, and greatly facilitates solving vibration problems since it measures the full-field surface vibration. Structural acousticians are able to couple this information with special post-processing techniques to reveal optimum areas for damping or structural changes to bring about effective noise and vibration reduction.


System Description

  Water Scan of Rotor Blade
In Water Scan of Rotor BladeThe ARL Penn State system has recently been upgraded with a PC-based scanning system that greatly accelerates the process of data acquisition and interpretation. Vibration problems can be quickly assessed by way of full-field animated vibration shapes or specially processed images of vibrational energy flow. The entire system is portable and, like similar laser systems, has the ability to take data in areas not readily accessible to other sensors. Despite the low power of the laser (less than one milliwatt for safety purposes) the vibrometry system is capable of obtaining quality data at offsets of up to 60 meters. Conversely, the laser beam can be specially focused down to measure the vibrations of human tympanic membranes. The system covers a frequency range of DC to 250 kilohertz and can be extended into the megahertz range.


Expertise

Considerable research in experimental structural acoustics as well as laser vibrometry is conducted at ARL Penn State. Numerous publications in these fields (the most recent includes a vibrometry article in the April 1997 Review of Scientific Instruments) attest to the extensive use of these systems in research at ARL Penn State. Expertise in computational acoustics complements this technology by providing predictions of radiated sound from the laser vibrometer data.

Supporting facilities
ARL Penn State has well-maintained support facilities and can adapt these systems for laser vibration studies in special conditions, such as in water tunnels, wind tunnels, anechoic chambers, or reverberant tanks.

Research Interests
ARL is actively pursuing new applications and extensions of this growing technology such as: wave decomposition techniques for computing in-plane and out-of-plane structure-borne intensity; methods for extracting three-dimensional vibration fields from nonplanar surfaces; nondestructive evaluation; and measurement of the vibration of rotating machinery.