Fabry-Perot Interferometric Strain Sensors Research Articles

Fiber-optic extrinsic Fabry–Perot interferometer sensors with three-wavelength digital phase demodulation

A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry-Perot interferometer vibration, acoustic, and strain sensors. This scheme uses a superluminescent diode light source with interference filters in front of the photodiodes and real-time arctan calculation. Quasi-static strain and dynamic vibration sensing with up to an 80-kHz sampling rate is demonstrated. Periodic nonlinearities owing to dephasing with increasing fringe number are corrected for with a suitable algorithm, resulting in significant improvement of the linearity of the sensor characteristics.

An Embedded Fiber Optic Sensor Method for Determining Residual Stresses in Fiber-Reinforced Composite Materials

A method to determine process-induced residual stress in fiber-reinforced composite materials using strain measurements from embedded fiber optic sensors is presented. This method allows non-destructive, real-time determination of residual macrostress in these materials and may be useful for both process monitoring and control. Extrinsic Fabry-Perot interferometer strain sensors were embedded in Hercules AS4/3501-6 graphite/epoxy composite specimens prior to cure. The specimens were cured in a press, and the internal strains and temperatures developed during processing were monitored and recorded. Residual macrostresses were computed from these measurements using a viscoelastic model of the material. The results compare favorably with analytical predictions, previous experimental measurements from a destructive technique, and with measurements of warpage of a non-symmetric laminate.

Intelligent Material and Fluid Systems. Real-Time Measurement of Internal Strain in FRP Laminates with Optical Fiber Sensors in Autoclave Molding.

In the present study, real-time measurement of internal and residual strains in GFRP laminates with an optical fiber strain sensor was performed in an autoclave molding. An Extrinsic Fabry-Perot Interferometric (EFPI) type optical fiber strain sensor was embedded into prepreg sheets before the molding. The ion viscosity and the temperature of the epoxy resin matrix were also measured simultaneously with the internal strain measurement. The results of the experiments showed that the internal and residual strain of GFRP laminates during the molding could be monitored by the optical fiber sensor embedded in the parallel direction to the reinforcing fibers. It was also found that the circumstances around the embedded optical fiber strain sensor should be taken into account for the interpretation of the measured internal and residual strain.

Recent developments in optical-fiber-based extrinsic Fabry-Perot interferometric strain sensing technology

Progress in the performance and reliability of the fiber-optic-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor is reported. The developments include refined fabrication techniques and improved quality of constituent elements for enhanced durability and greater temperature sustenance, higher strain sensitivity using using high-finesse cavities, a modified sensor-head for complete strain-field characterization, absolute, real-time and inexpensive measurements employing white light interferometry and multipoint, distributed sensing using CDMA and path matching multiplexing techniques. It is shown that these improvements have assisted in overcoming the limitations of the conventional EFPI sensor and made possible the large-scale commercialization of the state-of-the-art EFPI-based strain sensing system.

Multiple strain state measurements using conventional and absolute optical fiber-based extrinsic Fabry-Perot interferometric strain sensors

A modified design of the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor to allow complete characterization of multicomponent strain fields is proposed. The novel EFPI includes a sensor head with two input fibers such that the respective interference pattern from the end face of the output multimode fiber are in quadrature. Any strain field possessing a component along the line joining the axes of the two fibers causes the initial phase difference to be modulated. The measured change in phase difference is employed to determine this transverse component of the strain field. Absolute, rather than differential measurements of strain are possible using the absolute EFPI sensing system. Applications of the modified sensor-head to smart materials and structures are discussed.

Intelligent Process Monitoring of Multilayer Ceramic Actuators Using High Temperature Optical Fiber Displacement Sensors

The Fiber & Electro-Optics Research Center (FEORC) has developed a sensing technique for the intelligent processing of a multilayer ceramic actuator (MCA) elements manufactured by the AVX Corporation in Conway, South Carolina. Presented are the results of the fiber optic strain sensor used to monitor the burnout of organic binders from a green actuator sam ple. The results establish the operation of the short gage length, low finesse Fabry-Perot interferometric strain sensor as a tool for intelligent processing of such ceramic actuator elements. Also pre sented is the method of sensor operation, and post-processing results using the same sensor for tracking actuator performance and hysteresis.

Neural Network Processing of Optical Fiber Sensor Signals for Impact Location

AbstractA system to detect and locate impacts by foreign bodies on a surface was developed and tested. Fiber optic extrinsic Fabry-Perot interferometer (EFPI) strain sensors were attached to or embedded in the surface, so that stress waves emanating from an impact could be detected. By employing an artificial neural network to process the sensor outputs, the impact location could be inferred to centimeter range accuracy directly from the arrival time data. In particular, the network could be trained to determine impact location regardless of material anisotropy. Results demonstrate that a back-propagation network identifiesimpact location for an anisotropic graphite/bismaleimide plate with the same accuracy as that for an isotropic aluminum plate.

Fiber optic Fabry-Perot strain gauge

A local all-fiber Fabry-Perot interferometric strain sensor is reported. The device makes use of a simple semireflective fusion splice technique and is operated in reflection mode. Five sensors of gauge lengths of approximately 10 mm were fabricated and adhered to the surface of a cantilever beam. The phase-strain sensitivity, Delta phi / Delta L, was measured to be 2.24+or-0.07*10/sup 7/ m/sup -1/ ( lambda =632.8 nm) and found to be symmetric with respect to tension and compression. >