Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer
Vibration measurement is important to high prec1s10n machining and structural health monitoring. Techniques for vibration measurement are classified in two categories: contact mode and · non-contact mode. Non-contact mode measurement, such as that using Laser Doppler vibrometer (LDV), is pr...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
2013
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| Online Access: | http://hdl.handle.net/10356/54770 |
| _version_ | 1826113716236582912 |
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| author | Chen, Guofei. |
| author2 | School of Mechanical and Aerospace Engineering |
| author_facet | School of Mechanical and Aerospace Engineering Chen, Guofei. |
| author_sort | Chen, Guofei. |
| collection | NTU |
| description | Vibration measurement is important to high prec1s10n machining and
structural health monitoring. Techniques for vibration measurement are classified in
two categories: contact mode and · non-contact mode. Non-contact mode
measurement, such as that using Laser Doppler vibrometer (LDV), is preferred
because it offers high measurement accuracy and does not load the vibrating target.
Laser Doppler vibrometer (LDV) can accurately measure vibration amplitude and
frequency of a vibrating target by shining single laser beam on a point on the target.
It can be extended to measure vibration mode shapes on multiple points using
multiple laser beams. Such extended system is named as multi-point LDV and it
makes use of acousto-optic modulator (AOM), a key component, to generate
multiple laser beams. The acoustic-optic modulator works on the principle of
optical diffraction that happened in the medium with periodic refractive index.
A major problem with the multi-point LDV is non-uniformity optical powers
among the multiple laser beams. As a result, some laser channels of the multi-point
LDV are weak in optical power while some channels are stronger. The channel with
weak optical power has a very poor accuracy of measurement, because the scattered
back signal is too weak and buried in noise. This channel will lower down overall
measurement accuracy of mode shape using multi-point LDV. Therefore,
optimization of power distribution of diffracted laser beams is required. In this
dissertation, a Raman-Nath AOM will be studied to get a uniform power
distribution. The optimized results will thereafter be used in a 4-point LDV to
measure vibrations and mode shape of a clamped-clamped beam. Measurement
results show that the optimization improves the measurement accuracy.
Keywords: Multi-point LDV, vibration, Doppler effect, diffraction, grating,
acousto-optic modulator, power distribution, transient events. |
| first_indexed | 2024-10-01T03:27:46Z |
| format | Thesis |
| id | ntu-10356/54770 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T03:27:46Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | ntu-10356/547702023-03-11T17:13:36Z Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer Chen, Guofei. School of Mechanical and Aerospace Engineering Lau Gih Keong DRNTU::Engineering::Mechanical engineering Vibration measurement is important to high prec1s10n machining and structural health monitoring. Techniques for vibration measurement are classified in two categories: contact mode and · non-contact mode. Non-contact mode measurement, such as that using Laser Doppler vibrometer (LDV), is preferred because it offers high measurement accuracy and does not load the vibrating target. Laser Doppler vibrometer (LDV) can accurately measure vibration amplitude and frequency of a vibrating target by shining single laser beam on a point on the target. It can be extended to measure vibration mode shapes on multiple points using multiple laser beams. Such extended system is named as multi-point LDV and it makes use of acousto-optic modulator (AOM), a key component, to generate multiple laser beams. The acoustic-optic modulator works on the principle of optical diffraction that happened in the medium with periodic refractive index. A major problem with the multi-point LDV is non-uniformity optical powers among the multiple laser beams. As a result, some laser channels of the multi-point LDV are weak in optical power while some channels are stronger. The channel with weak optical power has a very poor accuracy of measurement, because the scattered back signal is too weak and buried in noise. This channel will lower down overall measurement accuracy of mode shape using multi-point LDV. Therefore, optimization of power distribution of diffracted laser beams is required. In this dissertation, a Raman-Nath AOM will be studied to get a uniform power distribution. The optimized results will thereafter be used in a 4-point LDV to measure vibrations and mode shape of a clamped-clamped beam. Measurement results show that the optimization improves the measurement accuracy. Keywords: Multi-point LDV, vibration, Doppler effect, diffraction, grating, acousto-optic modulator, power distribution, transient events. Master of Science (Precision Engineering) 2013-08-13T01:28:45Z 2013-08-13T01:28:45Z 2013 2013 Thesis http://hdl.handle.net/10356/54770 en 66 p. application/pdf |
| spellingShingle | DRNTU::Engineering::Mechanical engineering Chen, Guofei. Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title | Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title_full | Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title_fullStr | Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title_full_unstemmed | Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title_short | Optimization of power distribution of diffracted laser beams in multi-point laser doppler vibrometer |
| title_sort | optimization of power distribution of diffracted laser beams in multi point laser doppler vibrometer |
| topic | DRNTU::Engineering::Mechanical engineering |
| url | http://hdl.handle.net/10356/54770 |
| work_keys_str_mv | AT chenguofei optimizationofpowerdistributionofdiffractedlaserbeamsinmultipointlaserdopplervibrometer |