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Passive wireless sensor for strain and crack characterization Wireless strain sensors are becoming more and more popular for SHM systems. These sensors, equipped with embedded microprocessors and wireless communication capabilities, have the potential to reduce the installation and maintenance costs of distributed sensor networks. Passive wireless sensors are particularly attractive because they do not require any electric wiring for power supply or data communication. ASTL has proved the feasibility of using patch antenna for strain measurement. With integrated sensing and data transmitting capabilities, these antenna sensors are small in size, have a low profile, conform to any surface, and are inexpensive to fabricate. The goal of this project is to expand the antenna sensor technology to form distributed, passive, wireless sensor networks. These sensor networks will be characterized in terms of full-field strain measurement and crack characterization.
Video Demo (this video demonstrates how the antenna resonant frequency is shifted by applied loads)
LPFG-based optical fiber distance sensor Optical fiber sensors have been widely exploited for displacement measurement, temperature sensing, medical diagnosis, and confocal microscopy, due to their compact size, light weight, remote operation, capability to operate in harsh environment, and immunity to electro-magnetic interference. Among different measurement schemes, distance measurement is one of the most common and widely applied techniques that often serve as the basis for the sensing of other physical parameters such as pressure, strain, vibration, and acceleration. Optical fiber whitelight interferometers for distance measurement have attracted a lot of attentions recently because they offer ultrahigh accuracy, large dynamic range, and robustness. We are developing an in-fiber whitelight Michelson interferometer using long period fiber grating for absolute distance measurement. The advantages of the proposed distance sensor include ultra-precise absolute distance measurement, large dynamic range, simultaneous distance and temperature measurement, and self-calibrated high-speed data interrogation. We have developed a simple sensor fabrication technique to fabricate the sensor in house. Experimental results demonstrate that the sensor is capable of measuring arbitrary small distances. We are interested in applying this novel distance sensor for near-field surface profiling of nanoscale structures and mechanical testing of MEMS thin film materials. In addition, it could have broad applications for damage detection of composite materials, real-time monitoring of manufacturing processes, and in-situ measurement of crack-tip plasticity.
Laser reflectance sensor for material damage detection Changes in surface reflectivity can serve as an excellent indicator for material damages that are difficult to detect using other sensing techniques, such as corrosion, fatigue, and recystallization under elevated temperature. We have developed an optical fiber reflectance senor that is sensitive to these material damages. A flexible fabrication technique has been developed to package the sensor system into a compact format that is suitable for field test. Preliminary experimental results demonstrated the feasibility of applying the laser reflectance sensor for corrosion, fatigue, and grain growth detection.
Hybrid silica/polymer sensor for large strain measurement Silica-based optical fiber sensors are widely used in structural health monitoring systems for strain and deflection measurement. One drawback of silica-based optical fiber sensors is their low strain toughness. In general, silica-based optical fiber sensors can only reliably measure strains up to 2%. Recently, polymer optical fiber sensors have been employed to measure large strain and deflection. Due to their high optical losses, the length of the polymer optical fibers is limited to 100 meters. We have developed a novel economical technique to fabricate a polymer fiber core between two silica optical fibers. The hybrid silica/polymer optical fiber strain sensors are under evaluation for large strain measurement. Preliminary experiments demonstrated that the silica/polymer strain sensor can measure strains as high as 52%.
Tapered optical fiber for bio-chemical sensing Bio-chemical sensing using evanescent wave requires the access of the core of an optical fiber. Conventional techniques for exposing the fiber core include removing the fiber cladding by chemical etching or tapering the optical fiber. Both techniques result in very fragile optical fiber sensors. We have developed a technique to fabricate a tapered polymer tip on the cleaved end of an optical fiber. The nature of the fabrication process guarantees that the tapered polymer tip has the same size as the fiber core and is automatically aligned with the fiber core. Experimental results confirmed that the tapered optical fiber sensor is sensitive to refractive index changes in the surrounding medium.
Study of elastic wave generation using piezoelectric patches Lamb wave is a special type of elastic wave that is widely employed in structural health monitoring systems for damage detection. Recently, piezoelectric (piezo) patches are becoming popular for Lamb wave excitation and sensing because it can be utilized as an actuator and a sensor. All published work assumed that the Lamb wave displacement field generated by a piezo patch actuator is axi-symmetric. However, we have observed that piezo sensors placed at equal distances from the piezo patch actuator may have different responses. In order to understand this phenomenon, we used a Laser vibrometer to measure the full-field displacements around a piezo actuator non-contactly. Contrary to common believes, the displacement fields excited by the piezo patch actuator are found to be directional and frequency dependent. Based on the evolution of the displacement fields with excitation frequency increases, we concluded that the directional and frequency dependent nature of the displacement fields is governed by the out-of-plane deformation of the piezo actuator. A simulation model that incorporates the bending deformation of the piezo patch into the calculations of the Lamb wave displacement field has been developed. The simulation results matched with the experiment measurements very well.
Video Demo 3D laser vibrometer view of the Lamb wave displacement field at different excitation frequencies Simulated Lamb wave displacement fields
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With gratitude and recognition to our fine sponsors:
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500 W. First Street, Arlington, TX 76019, Tel: 817-272-0563, Fax: 817-272-5010, Email: huang@uta.edu
Copyright @2006-2008, University of Texas at Arlington. All rights reserved. Last Updated 08/18/2008.
