Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications

a technology of fractional bi-spectral and fractional cross-correlation, applied in the field of noise reduction, can solve the problems of inapplicability of techniques, inconvenient use of techniques, and inability to apply techniques,

Inactive Publication Date: 2015-01-22
THE UNIV OF NORTH CAROLINA AT CHAPEL HILL
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Problems solved by technology

Conventionally, there are several techniques to calculate the phase and magnitude of a signal from its computed bi-spectrum, although all of these techniques require huge amount of computation and are very time consuming.
Physically, in order to have a

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  • Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications
  • Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications
  • Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications

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Embodiment Construction

[0043]In various exemplary embodiments, we have developed a novel technique, Fractional Bi-Spectrum Analysis (FBSA), which enables us to apply the concept of bi-spectrum on a linear medium by introducing two known wavelengths to a system. FBSA reduces the noise of the system and recovers the amplitude and phase of the signal. Variously, Fractional bi-spectrum analysis (FBSA) and Fractional cross correlation (FCC) are proposed to enhance signal information in a situation where the signal to noise ratio (SNR) is low. Mathematical models to calculate the fractional bi-spectrum, FBS, and fractional cross correlation, FCC, of an interferometric signal are proposed and verified by both simulation and experiment. FBSA can reconstruct the signal with improved signal to noise ratio. This is supported by simulation and experimental results. FBSA and FCC techniques are compared with themselves and other noise reduction techniques, such as low pass Fast Fourier Transform (FFT) and auto-correlat...

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Abstract

A measurement method and system include illuminating an object to be measured with light at two different wavelengths and an incident angle; capturing an image of the object; detecting a frequency of an interference pattern from the image using Fractional Bi-Spectrum Analysis; and calculating a thickness of the object based on the Fractional Bi-Spectrum Analysis. The thickness is calculated based on a relationship between the thickness and the frequency of the interference pattern. The Fractional Bi-Spectrum Analysis is performed on a linear medium with the two different wavelengths being known.

Description

FIELD OF THE DISCLOSURE[0001]The present invention relates to the field of noise reduction. More specifically, the invention relates to noise reduction, optical measurements, and interferometry.BACKGROUND OF THE DISCLOSURE[0002]Laser interferometry has tremendous applications in several fields including manufacturing and biology. One of the serious limitations of this technique is the inherent speckle noise in laser interferometry of rough surfaces. Waves reflected or transmitted by rough surfaces result in unclear interference pattern. Therefore speckle noise reduction is an important step in laser interferometry of the rough surfaces. Many methods have been proposed over the years to compensate the speckle noise in laser interferometric based technologies such as optical coherent tomography, synthetic aperture radar (SAR), ultrasound, etc. One proposed technique to suppress the speckle noise is moving the aperture of the camera. This technique averages the speckle pattern and redu...

Claims

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Application Information

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IPC IPC(8): G01B9/02G01B11/06
CPCG01B11/06G01B9/02041G01B9/02082G01B11/0633G01B9/02032G01B9/02084G01B11/2441G01B9/02021G01B9/02007A61B3/101
Inventor FARAHI, FARAMARZBABAIE, GELAREHABOLBASHARI, MEHRDAD
Owner THE UNIV OF NORTH CAROLINA AT CHAPEL HILL
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