An optical fiber strain sensor based on sandwiched long-period fiber gratings (OFSS-SLPFG) with a surface bonding layer is proposed. The proposed OFSS-SLPFG is an etched optical fiber that is sandwiched between two thick photoresists with a periodic structure. To prevent the glue effect in the surface bonding process, where glue flows into the SLPFG structure, reducing the coupling strength, a surface bonding layer (thickness: 16 μm) is used as the base layer on the bottom of the OFSS-SLPFG. The OFSS-SLPFG is, therefore, more effective for use as a strain sensor. When external strain loading is applied, the resonant dip loss of the OFSS-SLPFG is reflected linearly. A bending strain calibration experiment is demonstrated by the four-point bending test. The results show an average linearity (R2) of 0.980, with a sensitivity of 0.00788 dB/με. This phenomenon suggests that the OFSS-SLPFG can be utilized as a sensitive strain transducer.
This study presents a novel type of optically driven lever-based micro-actuator fabricated using two-photon
polymerization 3D-microfabrication technique. The lever is composed of a beam, an arch, and a sphere. First, optical
tweezers is applied on the spheres to demonstrate the actuation of the lever. A spring is jointed at the lever for verifying
the induced forces. Under the dragging by laser focusing, the lever simultaneously turns and results a torque like a
mechanical arm. Then, the demonstration of a photo-driven micro-transducer with a mechanical arm and a gear is
preformed. The experimental result indicates that our design enables precise manipulation of the mirco-actuator by
optical tweezers at micron scale. This study provides a possibility for driving micron-sized structured mechanisms, such
as connecting rods, valves. It is expected to contribute on the investigation of "Lab-on-a-chip".
The Gr/Epoxy laminated composite materials have high specific stiffness and strength for applications in the aerospace
and industries. It is important to monitor the curing residual stress to ensure the reliability of composite materials. Fiber
Bragg Grating (FBG) sensors are small and compatible with polymeric materials so that they can be easily embedded
into the internal sensing site of a composite structure without introducing significant defections. This study embedded 4
FBGs into different laminae of composite materials to monitor the internal residual strain during the curing process. The
curing residual strain was assessed via changes in the shape of the optical spectra, intensity attenuation and shifts in
wavelengths of FBGs. Utilizing this approach we can monitor curing residual strains in different layers of the composite
during the curing process.
Current study utilizes the corrugated long period fiber grating (CLPFG) edge filter and fiber Bragg grating (FBG) strain sensor to configure the high speed strain sensing system by intensity modulation. For static calibration, the FBG wavelength shift is linear with the modulated intensity by CLPFG while the linearity (R2) of the FBG intensity and strain is 0.994. For dynamic strain sensing, the performance of this system is good as the strain gage at 500Hz under the various strain fields. Experimental results also indicate that the optimal sensitivity is 11.08 mV/με.
A novel fabrication method for corrugated long-period fiber gratings (CLPFG) is presented in this study. The patterned SU-8 photoresist is used as a double-side stopper layer for a wet-etching process to fabricate the CLPFG. Presented in this research are four types of CLPFG with periods of 660, 670, 680, and 690 µm and resonant wavelengths of 1531, 1539, 1550, and 1558 nm, respectively. The maximum resonance loss of the CLPFG with a 680-µm period is 23 dB. The CLPFG fabricated in this study is demonstrated for temperature sensing, and the results illustrate that the fabricated CLPFG with a 680-µm period has a temperature sensitivity of 58.4 pm/°C, a wavelength-shifting linearity of R2=0.994, and a 0.856 °C resolution.
This study presents a novel fabrication method of corrugated long-period fiber gratings (CLPFG). The chemical
wet etching process is used to fabricate the CLPFG, and the patterned SU-8 50 photoresist is used as etch mask. Since the
CLPFG fabricated by the novel method reduces the complication and cost, it is suitable for mass production. In this study,
the period of the CLPFG is 690 μm and the resonant-attenuation wavelength is 1558 nm. The maximum
resonance-attenuation of the CLPFG is 23 dB. Eventually, the CLPFG in this study has demonstrated a high temperature
sensitivity (60 pm/ °C), wavelength-shifting linearity (R2=0.99), and 1°C of resolution.
The curing monitoring of polymeric composite materials has attracted wide interests recently. Monitoring the
curing process is necessary to improve the performance of Gr/Epoxy composites, especially for the
characterization of residual strains after manufacture. This paper aimed on exploring the use of embedded fiber
Bragg grating (FBG) to monitor the characterizations of the curing process in a Graphite/Epoxy composite. The
curing development and residual stress measurement were assessed through changes in the shape of the optical
spectra, intensity attenuation and shifts in wavelengths in the optical fiber sensors. The curing caused residual
stress was presented and analyzed systematically in this paper.
In this study, we proposed a new approach to make a low-cost, high-pressure and easy-to-made fiber optic pressure
sensor for human disc pressure measurement. The principle of this sensor is based on Fresnel reflection equations. The
sensor is sealed in a 25G needle (500 micron outer diameter), and coated with a thin film on the tip of the sensor. The
developed system is capable of measuring pressure up to 10 bar.
A fast responding interrogation system based on intensity modulation using fiber Bragg gratings (FBG) has been developed to interrogate long period fiber grating (LPFG) sensor. Temperature and dynamic strain monitoring using this system have been successfully demonstrated. The performance of long period fiber grating (LPFG) sensors written in single cladding (SC) and double cladding (DC) fibers have been compared. This system is capable of resolving strain to 0.2με and 0.4με at a loading frequency of 20 Hz, and temperature resolution to 0.02°C and 0.19°C, by using LPFG in the single cladding (SC-LPFG) and double cladding (DC-LPFG) respectively.
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