In-line Fiber Etalon Research Articles

Unbalance and harmonics detection in induction motors using an optical fiber sensor

In this work, a new method for the detection of the negative effects of a particular unbalanced voltage and inverter harmonics on the performance of an induction motor using fiber sensors is proposed. Supplying a three-phase induction motor with unbalanced voltages causes an oscillating electromagnetic torque that generates vibrations, increased losses, efficiency reduction, and an extra temperature rise that leads to a reduction on insulation life of the machine. A new in-line fiber etalon accelerometer has been designed to detect these vibrations in the range DC-500 Hz. The in-line fiber etalon scheme used provides high robustness and stability, giving enough sensitivity to monitor the low-frequency and low-amplitude oscillations in the stator of the machine that exist in a voltage unbalance situation. To prove this claim, a 1.5-kW squirrel cage induction motor is analyzed under different unbalance levels. It is shown that a precise unbalance factor can be detected without accessing to the electric part of the machine and an accurate monitoring can be obtained using the high-resolution analysis proposed

Vibration monitoring in electrical engines using an in-line fiber etalon

In this work a new scheme for condition monitoring of electrical engines using a fiber optic sensor is proposed. The in-line fiber etalon scheme, specifically designed for the detection of damages in large electrical machines, provides high robustness and stability. In general, these large systems are characterized by a low speed operation, and when a new mechanical or electrical fault appears, it can be monitored through the vibration spectrum in the low frequency range, with a maximum bandwidth of 500 Hz. The proposed sensor has been optimized to achieve minimum detectable acceleration amplitude of 0.05 g in the frequency range of interest, although the preliminary scheme can be customized to the specific motion system. The vibration sensor has been tested using laboratory induction motor test-rigs, showing a particularly good performance both in the detection of magnetic and mechanical nature vibrations.

Study on drag forces of the molding flow in IC packaging using optical fiber sensors

The use of optical fiber sensors to study the drag force in molding flow is described. Research has proved that this novel method can be used to study the drag force of the molding flow in IC packaging over a perfectly elastic circular cylinder. The result of this study is found to be useful for characterizing the behavior of the wire sweep in encapsulation of semiconductor chips. An inline fiber etalon (ILFE) as a sensor is designed, constructed, and implemented in the middle of the optical fiber for accurate strain measurement. This is done by first laying an optical fiber in the midplane of a simple rectangular mold cavity, and then measuring the strain at the midspan of the fiber when it is subjected to the flow of a homogeneous fluid. For a given flow field, several dragforce models have been tried to calculate the drag force on the optical fiber, and the resulting strain of the optical fiber has been calculated by finite-element modeling and compared with the experimental results. From the comparison, the Takaisi model to calculate the drag force exerted on the optical fiber by the flow of homogeneous fluid is modified according to the experimental data. This modified model can be applied to study the wire sweep in the encapsulation of semiconductor chips. It is concluded that this measurement system can be used to verify the dragforce model for a molding flow on a perfectly elastic circular cylinder. Even under the more complex conditions in actual molding flow, the proposed sensing system can be used to measure the axial strain accurately. In addition, the transient deformation of the optical fiber characterized by the ILFE sensor provides important information for developing a drag-force model that can be used in IC packaging.

Mathematical modeling of the wall effect on drag forces in molding flow using optical fiber sensing data

This paper studies the wall effect on drag forces in molding flow using optical fiber sensing data. The results indicate that the effect of the wall cavity is significant in the calculation of the drag forces and is required to be considered in molding. The study also shows the effectiveness of the approach in characterizing the behavior of the wire sweep in the encapsulation of semiconductor chips. An in-line fiber etalon (ILFE) sensor is designed and fused in the middle of the optical fiber for accurate strain measurement. This is done by first laying an optical fiber in the mid-plane of a simple rectangular mold cavity, and then measuring the strain at the mid-span of the optical fiber that is subjected to the flow of homogeneous fluid. For a given flow field, several drag force models have been used to calculate the drag forces over the optical fiber. The resulting strain of the optical fiber is estimated analytically first by FEM and then compared with experimental results. To study the wall effect, different sizes of mold cavities are employed for different b/a ratios and used in Takaisi’s model. Subsequently, Takaisi’s model is then modified to comply with the experimental data obtained by using various b/a ratios for comparison with the numerical drag force model computed by Han and Wang. The result indicates that a modified Takaisi model in compliance with the requirement of b/a within the range 20–200 is in good agreement with the numerical model proposed by Han and Wang who had taken effect of the wall cavity into consideration for drag-force calculation. The modified model based on a smaller b/a value is somewhat closer to the numerical model in a higher average cavity velocity. The wall effect of molding flow is concluded to be an important factor for various tests conducted at a greater average cavity velocity or a smaller value of b/a.

Simultaneous Measurement of Two Strain Components in Composite Structures Using Embedded Fiber Sensor

This paper uses an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg grating to simultaneously measure axial and transverse strain components inside a cantilever beam fabricated from a graphite/epoxy composite material. The ILFE and Bragg grating sensor signals are demultiplexed using a variation of coherence division multiplexing, and then demodulated using a Pseudo-Heterodyne scheme. Composite cylinders models are developed that allow the optical measurements to be related to the strains in the host composite material. Experimental results show that both of the measurement errors of the two strain components are approximately 5 uE.

Spectrum analysis in cross-talk of series Fabry–Perot sensors in path-matching differential interferometry

The signals between cascaded Fabry–Perot sensors have serious cross-talk problems due to complex phase interactions between sensors. However, cross-talks in cascaded Fabry–Perot sensors for demodulation in a path-matching differential interferometry (PMDI) can be limited by corresponding path-matching read-out systems. This paper presents a method of using spectrum analysis to design the series Fabry–Perot sensors without cross-talk. The spectrum transfer function in a light source and Fabry–Perot cavities are simulated by a Gaussian distribution spectrum and a low-finesse reflectivity, respectively. It shows that two series Fabry–Perot sensors without cross-talk can be designed precisely and following the same procedure, even more series Fabry–Perot sensors without cross-talks in PMDI can be achieved. In-line fiber etalon (ILFE) as a Fabry–Perot cavity is used for multiplexing in the experiment. Experimental data shows that the cross-talk between two series Fabry–Perot sensors is limited. This design in two series Fabry–Perot sensors in PMDI can be applied to a two-parameter optical fiber sensors.

Design of fiber optic sensor systems for low velocity impact detection

This paper describes the design and development of promising optical fiber sensor systems for low velocity impact detection and impact-induced damage assessment. The sensor systems were based on the combination of path-matched differential interferometry (PMDI), in-line fiber etalon (ILFE) sensors and specifically designed analog phase trackers. The four demodulators investigated include: (1) the phase generated carrier (PGC) with differential-cross-multiplier (DCM) implemented electronically; (2) the PGC with DCM but where the final integration in the DCM is carried out numerically; (3) the single-channel phase tracker; and (4) the phase tracker. Careful consideration is given to an impact sensor system design methodology that considers potential optical sensor configurations, dynamic range and bandwidth of demodulation systems, optical phase-strain relationships, and the mechanical interaction of the optical fiber with its host structure. Initial impact tests using aluminium plates with surface-mounted ILFE sensors were performed to investigate the capability of the four given demodulators. The single-channel and phase trackers proved to be most suitable for the present impact application, and therefore they were utilized in the low velocity impact tests using graphite/epoxy composite plates with embedded ILFE sensors.

Embedded In-Line Fiber Etalon/Bragg Grating Hybrid Sensor to Measure Strain and Temperature in a Composite Beam

An optical fiber sensor for simultaneous measurement of axial strain and temperature in composite structures is reported. This sensor configuration consists of an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg grating (BG) and is demultiplexed using a variation of coherence division multiplexing. The strain/temperature sensor is demonstrated by embedding it into a graphite/epoxy composite cantilever beam. Concentric cylinders micromechanics models are developed that enable the optical signals from the embedded sensors to be cast in terms of the composite host strain and temperature without the need for calibration. The fiber optic strain/temperature sensor with a gage length of-1.0 cm is found to agree with traditional strain and temperature sensors to within 5 με and 0.50C, respectively.

Temperature and strain measurement by combining ILFE and bragg grating optical fiber sensors

This paper presents two optical fiber sensor configurations that are capable of simultaneously measuring temperature and strain. These sensor configurations use serial and parallel combinations of in-line fiber etalon (ILFE) and in-fiber Bragg grating sensors, along with wavelength division multiplexing concepts. The results obtained while simultaneously varying the temperature over 130°C and strain field over 1500 μe showed favorable agreement with thermistors and resistance strain gages.

Impact-Induced Damage of Laminated Graphite/Epoxy Composites Monitored Using Embedded In-Line Fiber Etalon Optic Sensors

This paper describes the use of fiber optic sensors embedded into laminated graphite/epoxy composites for low velocity impact-induced damage assessment. The sensor system uses in-line fiber etalon (ILFE) sensors interrogated with path-matched differential interferometry (PMDI) and demodulated with a "single channel phase tracker." Uncoated and coated copper ILFE sensors were embedded at the mid-plane of [902/04/OF(O)/04/902] composite plates subjected to transverse impact (The OF(0) denotes an optical fiber orientation of zero degree). The ILFE sensor response was compared to a resistance strain gage bonded to the back side of the specimen and to the load cell mounted on the impactor. The strain measured with the metal coated ILFE sensor and the load cell response were used to plot a hysteresis strain-load curve to assess the impact-induced damage. The result shows that the-1 J impact energy starts to initiate the composite damage, and that the area contained within the hysteresis loop area is approximately proportional to the delamination area evaluated by X-ray radiographs. X-ray NDE indicates that the embedded ILFE sensor does not alter the structural integrity based on the macro-scale observations. In addition, the impact test showed that the sensor embedded in the middle layer had higher survivability than the resistance strain gage bonded to the rear surface of the plate.

Simultaneously measuring temperature and strain using optical fiber microcavities

Presents an optical fiber sensor capable of simultaneously measuring both axial strain and temperature. The sensor configuration is composed of a 70 /spl mu/m in-line fiber etalon (ILFE) cascaded with a 170 /spl mu/m intrinsic Fabry-Perot (IFP) sensor to form a lead in-sensitive, localized, 240 /spl mu/m gauge-length dual parameter sensor. The sensor response from this configuration is interrogated using coherence division multiplexing based on white light interferometry, and using pseudoheterodyning demodulation. The results obtained in a simultaneously varying temperature and strain field by the fiber sensor are compared with a semiconductor temperature gauge and a resistance strain gauge. The correlation is very good.

Passive signal processing of in-line fiber etalon sensors for high strain-rate loading

This paper describes the development of a passively demodulated optical fiber sensor system capable of accommodating the high strain-rate events commonly encountered in applications involving stress wave propagation. This sensor system, which is based on in-line fiber etalon (ILFE) sensors and path-matched differential interferometry (PMDI), was tested experimentally at low frequency and strain-rates (time derivative of strain) up to (/spl sim/10/sup 7/ /spl mu//spl epsiv//s). For the present system, this strain-rate corresponds to a sensor phase bandwidth of approximately 100 kHz. Characterization tests using sensor gauge lengths ranging from 260 to 350 /spl mu/m showed that the sensor system had a minimum detectable phase of /spl sim/2 microrad//spl radic/HZ rms at 2 kHz which corresponds to /spl sim/0.8 n/spl epsiv///spl radic/Hz rms for 260 /spl mu/m-gauge length sensor.

Development of an optical fiber strain sensor for explosively generated stress wave propagation applications

Abstract A passive optical signal processing scheme for in-line fiber etalon (ILFE) fiber optic strain sensors is developed, and demonstrated, in an explosively generated shock environment. The signal processing system is based on interpreting two out-of-phase optical intensity signals. Verification tests were implemented using one-dimensional stress wave propagation where good general agreement with resistance strain gages was obtained.

Multiplexed optical fiber sensors for air frame repair patch monitoring

This paper describes the use of two multiplexed in-line fiber etalon (ILFE) sensors for air frame repair patch monitoring. The ILFE sensors are multiplexed using a combination of coherence division and frequency division multiplexing. Cantilever beam tests are used to verify the ILFE strain sensor performance and to measure multiplexing cross talk. The multiplexed ILFE sensors are then used to monitor the load transfer in a boron/epoxy patch utilized to repair cracks that occur in aging aircraft. The experiments show a clear relationship between a normalized measure of the strain inside the repair patch and crack extension in an aluminum single-edge notch specimen.

Evaluation of integrated optic modulator-based detection schemes for in-line fiber etalon sensors

This paper compares three classes of demodulation schemes for interpreting the static and dynamic response of in-line fiber etalon (ILFE) sensors. Each demodulation scheme employs path matched differential interferometry and an unbalanced integrated optic Mach-Zehnder interferometer as a readout interferometer. Active homodyne, synthetic-heterodyne and two types of pseudo-heterodyne based demodulators are evaluated. In the results presented here, signals generated by the ILFE ranging from quasistatic to about 100 Hz were recorded and compared with the signals generated by a resistance strain gauge, and were found to be in good agreement. >