Optical fiber detection of ultrasonic vibration and acoustic emission

Several techniques for measuring high frequency vibrations are presented. The goal of the study is to develop a sensor for detecting acoustic emissions (AE) inside composite structures. The basics of wave propagation inside of materials has been presented along with an overview of typical acoustic emission testing. Surface acoustic waves (SAWs) were studied first and a novel, noncontact optical interferometric technique for measuring absolute amplitudes is presented. This technique has the added advantages in that it does not require that the interferometer be stabilized or phase biased. It is insensitive to laser fluctuations, random phase drifts, polarization changes and changes in mixing efficiency of the interferometer. SAW amplitudes between 7 and 2.5 angstroms were measured with the described technique. An intrinsic Fabry-Perot type interferometer was demonstrated for detecting SAW's and was then embedded into carbon fiber composite panels which were then put through tensile tests. AE's were captured, centered around 300 KHz, as is expected of a composite. These tests were repeatable and indicate that qualitative measurements of AE can be made. This sensor configuration was also used for detecting a variety of taps on the composite panel as well as pencil lead breaks, a standard calibration procedure for AE testing.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Electrical Engineering

Department dc:contributor.department

Electrical Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1992

Author dc:creator

• Nau, Gregory Merrill

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-09292009-020053

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/44910