|
|
|
|
|
|
|
|
|
|
|
·
Passive
wireless sensors for strain sensing and crack characterization ·
LPFG-based
optical fiber distance sensor development ·
Laser
reflectance sensor for material damage detection ·
Hybrid
silica/polymer sensor for large strain measurement ·
Tapered
optical fiber sensor for bio/chemical sensing ·
Study of elastic wave
generation using piezoelectric patches 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
|
|
With
gratitude and recognition to our fine sponsors:
|
|
|
|
|
|
|
500 W.
First Street, Arlington, TX 76019, Tel: 817-272-0563, Fax: 817-272-5010, Email: huang@uta.edu
Copyright
@2006-2009, University of Texas at Arlington. All rights reserved. Last Updated
08/18/2008.