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Electronics circuit for analog processing.
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A Michelson interferometer based sensor, to monitor the displacement and vibration of a surface, is presented. The interference signals detected in quadrature are processed using analog electronics to find the direction of the motion of a vibrating surface in real-time. The complete instrumentation and signal processing are implemented for the inte...
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... output of the interferometer would be about 2 kHz. Figure 4(a) shows that the gain of the differentiator is about 10 dB, and Fig. 4(b) shows that the phase difference is less than 30° (90°-60°) at 2 kHz which is tolerable for analog processing proposed in our technique. The complete circuit used for analog processing in our technique is shown in Fig. 5. The integrator introduces a delay in processing after the output of the multiplier changes its polarity. Simple analysis reveals that the time delay introduced by the integrator is about 1 ms at the frequency of 2 kHz. This delay is equal for each half cycle, therefore, it does not produce error in the measurement. The effects of the ...
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Citations
... It worth mentioning that, already the N-point SPS method has been used for the detection and compensation of the environmental vibrational noise but the vibration characteristics has not been investigated [9]. Also, in two other works, two different arrangements of the two-point SPS method [10,11], were proposed for the reconstruction of the motion. These arrangements can be only applied when the visibility of fringes is very close to one. ...
In this work, a three-point spatial phase shifting (SPS) method is implemented for chasing of the moving interference fringes in the homodyne laser Doppler vibrometry (HoLDV). By the use of SPS method, we remove disability of the HoLDV in the discrimination of the motion direction for long-range displacements. From the phase increments histogram, phase unwrapping tolerance value is selected, and adequacy of the data acquisition rate and required bandwidth limit are determined. Also in this paper, a detailed investigation on the effect of detectors positioning errors and influence of the Gaussian profile of the interfering beams on the measurements are presented. Performance of the method is verified by measuring a given harmonic vibration produced by a loudspeaker. Also, by the proposed method, vibration of mounting system of a disk laser gain medium is characterized.
... Interferometry is one of the most established techniques of measurement that dates back to Michelson-Morley experiment [1]. Applications of optical interferometry include interference lithography for the fabrication of large area variable period gratings [2], surface metrology [3], vibration analysis [4][5][6], astronomical optical interferometry e.g. space interferometry mission, 2009 [7] etc. Thickness and refractive index of thin films can also be measured by interferometry with higher accuracy than that in other optical techniques [8,9]. ...
... Previously, we have reported two electronic processing techniques for fringe analysis to be used in displacement/vibration sensors [5,6]. In this paper, we report a comparison of different image processing techniques for interference based fringe analysis. ...
We present a comparison of different techniques for the analysis of the shift and tilt in optical interference fringes. Fringe center, Radon transform, and Gaussian approximation methods are used for fringe analysis. We have measured the tilt and shift between two relevant fringe patterns. The error in tilt measurement was about 2%, and the displacement of the order of few nanometers was measured by the fringe shift analysis. The comparison between the techniques is analyzed with respect to percentage error.
... Recently, we reported an analog processing based vibration measurement technique [16]. In this paper, we demonstrate a vibration detection technique in which signal processing can be performed without using an ADC, therefore, real time information about a vibrating surface can be obtained at a much faster rate as compared to other techniques. ...
An interferometer based optical sensor for displacement measurement is reported. This method requires quite simple signal processing as well as least electronic components. Referring to this technique, two photodiodes spatially shifted by 90 degrees were used. The output of photodiodes was converted into rectangular signals which were extracted in LabVIEW using the data acquisition card without using an analog to digital converters (ADC). We have also processed the signals in C++ after acquiring via parallel port. A Michelson interferometer configuration was used to produce linear fringes for the detection of displacements. The displacement less than 100 nm could be measured using this technique.
To improve the accuracy of the mover position detection with longer measurement range, a linear motor displacement measurement method is proposed based on digital image measurement and temporal sinusoidal fringe pattern phase retrieval. A simple computer-generated sinusoidal fringe pattern is designed as the target image, and sequences of fringe signals are recorded by a line scan camera that moves with the linear motor. Fourier phase analysis is employed to extract the initial phase of each signal curve, and then temporal phase unwrapping is applied to reconstruct the mover displacement evolution according to the system magnification parameter and fringe width. The method removes the phase ambiguity problem of traditional temporal phase analysis, and can be used in complex motion of permanent magnet synchronous linear motors (PMSLM). To suppress the spectrum leakage of fast Fourier transform (FFT), all-phase FFT (ApFFT) with double Hanning windows is used to improve the detection accuracy of initial phase and fringe width. Simulation and experimental results demonstrate that the proposed method can estimate the mover position with longer measurement range precisely and robustly under different working conditions.
We have proposed a novel micro-vibration measurement systems which we call Robust Optical Interferometer (ROI). ROI is consisted of a laser, optical and electronic systems. Optical system has the beam displacing prism which is a birefringence element. The prism can split a beam of linear polarization with 45° azimuth angle into two beams of linear polarizations with 0° and 90° azimuth angle. One of two beams becomes a signal beam reflected from micro-vibration object and another one is reference beam. These two beams pass through near same path, so effect of ambient noises are canceled efficiently. Accordingly, this systems are very robust for external noise. Reflected wave from a micro-vibrating object and reference wave generates an optical interference signal which is frequency modulated-periodic signal. Wave peak number N per period is proportional to vibration amplitude parameter a/λ. (a: object vibration amplitude, λ:wave length of laser), whose relationship is independent from object vibration frequency. We have developed the electronic system which detects vibration frequency from the interference signal and shows the output voltage proportional to a/λ. We have measured relationship between output voltage and a/λ at the object vibration frequency. And we have confirmed that we can measure the amplitude range from 0.3λ to 3.5λ with vibration frequency range between 100 and 900 Hz.
The orthogonal interferometer based on 1/8 wave plate generates orthogonal signals by optical configuration. It is widely applied to interference system because of simple optical path and passive demodulation scheme for easy operation. But in the process of demodulation, the DC component of the signal needs to be eliminated. Because of the instability of light source and optical structure, the DC component of the signal may change over time. Therefore the circuit subtracting a constant can not thoroughly eliminate the DC component, causing the demodulation results are inaccurate. A improved demodulation algorithm is proposed in this paper. Theoretical analysis and experimental results show that, the demodulation method is almost not affected by the size of the DC component. When small deviation in DC component occurs, the demodulation results keep stable and accurate.
