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12 Nov 2002
A laser vibrometer finds its first application analyzing the vibrations in a guitar when different strings are plucked.
UK company Ometron has developed a laser Doppler vibrometer (LDV) that measures displacement and vibration speeds at 16 separate points simultaneously.
Ometron business manager Steve Morel and his colleagues unveiled the new instrument, called the XVI, at the recent Leuven Conference on Noise and Vibration Engineering in Belgium.
The key component at the heart of the vibrometer is a diffractive optical element (DOE) that separates a 532 nm beam into 16 different paths. "The optical design is relatively straightforward, but the [DOE] component is very sensitive to environmental change. The challenge has been implementing a design that ensures the system works in real-world applications," said Morel.
He told Optics.org that the XVI instrument offers a "new concept" in vibrometry, as it can measure the rate of phase change at various points of a vibrating object.
Crucially, the XVI preserves the phase relationships between these separate points. "Until now, the biggest drawback of LDV technology has been its inablility to determine the phase relationships between measurements at different points," said the Ometron team.
The first application of the XVI is musical. Morel and colleagues analyzed the vibrations produced in a guitar when its E-string (the fattest string) was plucked.
Analysis of this kind could prove useful for enthusiasts and manufacturers trying to replicate the sound made by old musical instruments in their new designs. "They want to know what made these old instruments sound so good," said Morel.
As with standard LDV, the automotive market offers the greatest potential for applications. With the multipoint instrument, transient effects such as brake squeal and tyre noise should be measurable in a more realistic environment, says Morel.
At the moment, the XVI instrument is an optical bench setup, rather than a fully packaged product. However, Morel says that customized versions can be manufactured within two months.
The current version of the instrument produces a line of 16 points, but Morel says that this can be altered according to the needs of a specific application: "It is neither inherently limited to 16 points, or to a linear pattern." A lens system in the current design also means that the pitch of the pattern can be altered without disturbing the instrument's optical alignment.
Morel says that the XVI is ideal for analyzing transient effects that cannot be repeated under controlled conditions, and he is keen to hear from anybody interested in using the instrument.
Author
Michael Hatcher is technology editor of Opto and Laser Europe magazine.
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