Full-Field Vibration Measurement by Time-Average Speckle Interferometry and by Doppler Vibrometry - a Comparison

Moreau, Aurélien; Nistea, Ioana; Arghir, Mariana

doi:10.1007/978-1-4020-6239-1_199

Cited by 1 publication

(5 citation statements)

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“…The sign of the Bessel function can be retrieved when a set of steady state measurements, taken under the same conditions as the dynamic one, is available . When this is the case, another set of Equations (3), with J 0 ( φ d ) = 1, can be used to solve the unknowns I B , I M and φ .…”

Section: Linear Regression For True Bessel‐modulated Vibration Amplitmentioning

confidence: 99%

“…Using the steady state data set, the sign of the Bessel function might be retrieved and used to modify the conventional results shown in Figure A. A continuous Bessel‐modulated vibration amplitude map is obtained this way, but the standard deviation for the region selected is not changed; it remains 0.6640 against 0.6259 for the proposed method, which is slightly better.…”

Section: Linear Regression For True Bessel‐modulated Vibration Amplitmentioning

confidence: 99%

“…Furthermore the results at zero crossings of the Bessel function would degrade when applying an averaging filter, because the derivative of its absolute value is not continuous there. Considerable improvements have been reached , also by involving measurements taken under stationary conditions, eliminating most of the noise and producing zero crossings and skeleton lines of a large number of Bessel‐type fringes, allowing local inversion of the Bessel function. Regional inversion requires reliable skeleton indexing in order to be able to identify the correct fringe order for skeleton pairs.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, discontinuities in the vibration field may adversely affect indexing causing inversion errors to propagate. Phase changes between the static and dynamic states are handled by level‐shifting the phase iteratively, supported by histogram analysis . In these references, phase differences within the range of −π to +π are reported but no specific details on the level shifts are given.…”

Section: Introductionmentioning

confidence: 99%

“…Time‐averaged vibration patterns may have much lower quality than the ones presented in Refs. [8] to [10], giving rise to the question whether patterns obtained outside the more or less stable conditions of the laboratory could render indexed skeletons that are reliable enough for regional inversion. In view of this we propose a method that produces reliable results even when the data sets have lower quality.…”

Section: Introductionmentioning

confidence: 99%

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A new Method for Processing Time Averaged Vibration Patterns: Linear Regression

Somers

Bhattacharya

2016

Strain

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Speckle-based interferometry systems are useful tools for measuring vibration patterns at harmonically vibrating objects. The standard method for processing the speckle patterns acquired is to eliminate additive background noise and speckle phase, yielding Bessel-type fringe patterns whose values are proportional to the absolute value of the Bessel function. Fringes are covered by multiplicative speckle intensity noise on the Bessel-modulated vibration amplitude. Sine-cosine filtering is not an option because the Bessel-type fringe pattern is not a phase pattern, and thus, sine-cosine filtering would only degrade the results. Improvements can be reached by involving additional measurements acquired in the stationary state. An alternative method for processing vibration patterns using linear regression is proposed, yielding patterns where the vibration amplitude is an argument of a true Bessel function, not its absolute value. As a result, spatial frequencies of the vibration fringe pattern are only half of those obtained with standard methods, and results can be filtered and normalised conveniently. While other contributions to improve the results rely on determining indexed skeletons for high Bessel fringe densities, the proposed method aims at a very limited number of low-order fringes, allowing demodulation of the Bessel fringe pattern based on the actual Bessel values in the pattern. The method provides an effective alternative for spatial filtering. Phase differences between the stationary and vibrating states have an adverse effect on the results. Two methods, capable of handling phase jumps of 2π in the phase difference distribution, are presented to correct this.

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Section: Linear Regression For True Bessel‐modulated Vibration Amplitmentioning

confidence: 99%

Section: Linear Regression For True Bessel‐modulated Vibration Amplitmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations