With more than three decades of development, three-dimensional optical measurement technology has reached a mature
stage in commercial applications, meanwhile new ones have continually arisen. Due to the development of Charge
Coupled Device (CCD) array camera and digital projection technology, the applications of Phase Measurement
Profilometry (PMP) become more and more broad. Among these, dual-frequency grating method has drawn many
attentions because of its simplicity in principle and optical path, low requirement of equipment, high accuracy and level
of automation comparing with other methods. The phase calculation is one of the key technologies in PMP. However,
phase unwrapping algorithm in PMP is a difficult issue. A lot of new algorithm have been proposed, but neither one can
solve all the problems, so how to set up new phase unwrapping algorithm becomes urgent. In this chapter, we
systematically investigate the phase unwrapping method in dual-frequency grating method, and experimentally set up the
system. To verify our method, we experimentally measure a three dimensional object which possesses complicated stair
shapes on its surface. The results show that our dual-frequency grating method could achieve phase unwrapping without
doing conventional phase unwrapping calculations, and it could also detect the detailed stair shapes on the surface of this
three dimensional object automatically.
A type of Michelson interferometer with two optical fiber loop reflectors acoustic emission sensor is proposed in the
article to detect the vibrations produced by ultrasonic waves propagating in a solid body. Two optical fiber loop reflectors
are equivalent to the sensing arm and the reference arm instead of traditional Michelson interferometer end reflecter
Theoretical analyses indicate that the sensitivity of the system has been remarkably increased because of the decrease of
the losses of light energy. The best operating point of optical fiber sensor is fixed by theoretical derivation and simulation
of computer, and the signal frequency which is detected by the sensor is the frequency of input signal. PZT (Piezoelectric
Ceramic) is powered by signal generator as known ultrasonic source, The Polarization controller is used to make the
reflected light interference,The fiber length is changed by adjusting the DC voltage on the PZT with the fiber loop to
make the sensor system response that ΔΦ is closed to π/2. the signal basis frequency detected by the sensor is the
frequency of the input signal. Then impacts the surface of the marble slab with home-made mechanical acoustic emission
source. And detect it. and then the frequency characteristic of acoustic emission signal is obtained by Fourier technique.
The experimental results indicate that the system can identify the frequency characteristic of acoustic emission signal,
and it can be also used to detect the surface feeble vibration which is generated by ultrasonic waves propagating in
material structure.
The property of polarization is a nature of light. In this paper, the polarization of optical fiber sensor is mainly studied
and the control of optical fiber polarization is achieved by using a controller of optical torsion polarization instead of coil
type polarization controller. A novel combined optimum type of single-mode fiber interferometer is designed and the
expression of output waveform is acquired through theoretical derivation. Accordingly, with MATLAB simulation, it can
be analyzed and obtained that while the phase difference between the two arms of the interferometer is Δφ = 90°, the output light is not under the influence of the frequency doubling and it is the most sensitive at this moment . The
performance of the developed optical fiber sensor system which is composed by the combined interferometer is verified
by a preliminary test that we generate the AE (acoustic emission )signals by knocking a piece of marble slab, then the AE
signals could be detected by the system. The test results demonstrate that the developed fiber-optic sensors have emerged
as effective means of detecting AE signals, which solves the polarization fade-out problem using a controller of optical
torsion polarization, then the output signals could be achieved with higher visibility.
A novel open loop Sagnac optical fiber sensing system for detecting AE(acoustic emission) has been proposed and
demonstrated. The fiber loop of the Sagnac interferometer was cut off and formed two fiber ports, they were bound and
made into the fiber probe. It was placed in the front of the reflector attached to the measured solid. The light from one
port was reflected by the reflector and injected into the other fiber port. On the basis of the output optical field
distribution function, the position of maximum reflected light intensity was theoretically analyzed. The best work region
between the fiber probe and the reflector was ascertained by the experiment. Phase modulation property of the optical
fiber sensor was discussed and the optimal working state was obtained by the computer simulation. The optical phase
was modulated by the vibration of the reflector generated by the AE. The AE signals were obtained though the
optoelectronic conversion, and the frequency of the AE were acquired by using Fourier transform. The experiment
results show that the system could be used to detect the ultrasonic waves that propagating on the surface of the solid. The
open loop Sagnac optical fiber interferometer sensor has potential for the structural integrity monitoring and NDT
applications.
The sensor array is structured by the ring optical fiber Sagnac interferometers by way of point sensors to detect and
locate the analog source of the acoustic emission (AE). The principle of the ring optical fiber Sagnac interferometer is
used to detect ultrasonic waves and locate the AE source is given. One method based on microcomputer intelligent
detection is proposed. A steel plate is used as the medium of the acoustic wave propagation, and four sensors are
respectively placed on the steel plate to structure a sensor array with point sensors. The home-made analog source of the
acoustic emission is applied to do the experiment. When the ultrasonic signal is generated by driving the analog source
of the acoustic emission at any position of the steel plate, the ultrasonic signal will be received by the four sensors at the
different time. The microcomputer will count the position of the AE source with the time differences of the four received
signals and set value of the velocity at which the ultrasonic waves propagating in a solid plate, and then the coordinates
of the AE source are displayed by LED.
A theoretical analysis model of fiber-optic sliding sensor is presented. The sliding sensor is designed for robot hands or intelligent mechanical clamping apparatuses. In the sliding sensor designing, a sliding ball has been used as sliding transfer device of the sensor. In the center of the in side sliding ball, a 4-face-prismoid reflective mirror has been fixed with the ball to determine the 2D rotation angles, and the angles were measured by a five-fiber-optic probe. The theoretical characteristic functions of the sliding sensor are deduced and simulated.
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