In order to monitor the motor vehicle exhaust effectively, a motor vehicle exhaust telemetry device is set up based on differential optical absorption spectroscopy (DOAS) in this paper. The absorption spectrum of NO and 1,3-butadiene are analyzed quickly, meanwhile, qualitative and quantitative analysis are made simultaneously by the Least Square Method. Moreover, the correlation coefficient of absorbance and concentration reaching more than 0.999, which is obtained by non-linear analysis through polynomial fitting method. Additionally, the minimum detection limits of NO and 1,3-butadiene are 3ppm and 0.5ppm respectively. In order to verify the performance of the system, a set of tests were performed for a long time. So the experimental results show that the relative error of NO is not more than 2%, and the relative error of 1,3-butadiene is less than 2%. In addition, the calculation results of the experiment demonstrate that the repeatability error of NO is better than 1%, and the repeatability errors of 1,3-butadiene is lower than 2%. All the results meet the requirement of the application.
A strain sensing element in a high temperature environment is presented and experimentally demonstrated. The proposed strain sensing element consists of polyimide-coated fiber Bragg grating (FBG) and double rhombus metal structure. The polyimide-coated FBG was fabricated on the double rhombus metal structure by a modulated low softening glass process. The double rhombus metal structure was made of high temperature constant modulus alloy. The sensitivity of the strain sensing element is enhanced by two times of strain amplification and could be adjusted by selecting the angle and the dimension of the double rhombus metal structure appropriately. It is experimentally demonstrated that the proposed strain sensing element could be used at the high temperature of 300°C, and the average wavelength sensitivity of the strain sensing element at 300°C is 3.049 and 3.259 pm/μϵ for the compressed and stretched states, respectively.
Fiber Bragg Grating (FBG) sensing technology has many applications, and it’s widely used in detection of temperature, strain and etc. Now the application of FBG sensor is limited to the temperature below 200°C owing to the so called High Temperature Erasing Phenomenon. Strain detection over 200°C is still an engineering challenge since high temperature has a bad influence on the sensor, testing equipment and test data, etc, thus effective measurement apparatus are needed to ensure the accuracy of the measurement over 200°C, but there are no suitable FBG strain experimental apparatus in high temperature to date. In this paper a high temperature FBG strain experimental apparatus has been designed to detect the strain in high temperature. In order to verify working condition of the high temperature FBG strain, an application of FBG strain sensing experiment was given in this paper. The high temperature FBG strain sensor was installed in the apparatus, the internal temperature of experimental apparatus was controlled from -20 to 300°C accurately, and strain loading was given by the counterweight, then the data was recorded through electrical resistance strain measurement and optical sensing interrogator. Experimental data result shows that the high temperature FBG strain experimental apparatus can work properly over 200°C. The design of the high temperature FBG strain experimental apparatus are demonstrated suitable for high temperature strain gauges and FBG strain sensors , etc, which can work under the temperature of -20 ~ 300°C, the strain of -1500 ~ +1500μepsilon and the wavelength resolution of 1pm.
Due to the distinctive merits of FBG, e.g., compact size and immune to electromagnetic, strain sensors based on FBG
have attracted an increasing number of attentions in the field of structural health monitoring. But it is not easy to
fabricate a strain sensor which can survive at high temperature, because normal material can not stand in a strain creep
when the temperature is higher than 200°C. In this paper, a novel strain sensor consisting of a high temperature resistant
FBG and a metal rhombus structure is presented and demonstrated for surface strain measurement. The FBG is bonded
on the metal structure via a low softening point glass and pre-stretched about 2nm before it is bonded, so it can measure
compress and stretch tension. The experimental result shows that the proposed strain sensor can survive at 300°C, and
the average wavelength-strain sensitivity for compress and stretch, are 1.821 pm/μepsilon and 1.814 pm/μepsilon , respectively.
A more insensitive material to temperature and more appropriate adhesive are needed to improve the linear relationship
in the next step.
In the researching field of optical superresolution, a phase or amplitude filter is often utilized. They are easy to build, and
simple to insert to a system. A new idea on design a continuous phase filer is proposed. This type of filter is based on the
law that the focal size is mainly decided by the marginal rays in the aperture. A quadric function consisted of tangent
value is built. Assuming that the radially polarized light incident, passing through a phase filer and being focused by a
lens, the intensity distribution on the focal plane is simulated. The vector diffraction theory is used here. To get a smaller
focus, the parameters in the phase function are optimized in Matlab. The results show the superresolution effects.
Compared with others, the filters maintain higher energy utilization rate. A good prospects for application can be
expected.
High temperature pressure pipes were widely used in the chemical, oil companies and power plants, but the pipe burst incidents occurred from time to time, which had caused some damages on people’s lives and property. Thus, in this paper, with the aim to solve this problem, a FBG (FBG: Fiber Bragg Grating) strain gauge structure which consists of three FBGs is designed and fabricated based on the theoretical strain and stress analysis. The strain gauge can be used for the real-time surface strain monitoring of high temperature pressure pipes. In the strain gauge, the elastic hightemperature alloy(10MoWVNb) is chosen as the substrate. The three FBGs with a similar performance are fabricated on the substrate with the high-temperature glue. Among the three FBGs, FBG1 is used for the horizontal strain sensing of high temperature pressure pipes., FBG2 is used for the longitudinal strain of high temperature pressure pipes, and FGB3 is used for temperature compensation. The strain gauge has a feature of high temperature resistance, temperature compensation and two-dimensional strain measurement. The experiment result shows that : the sensing ranges of temperature is 0~300°C, the transverse strain sensitivity is 1.110nm/με, the temperature sensitivity is 0.0213nm/°C; The longitudinal strain sensitivity is 1.104nm/με, the temperature sensitivity is 0.0212nm/°C; the temperature sensitivity is 0.0103nm/°C. Therefore, the strain gauge can meet the needs of the high temperature and pressure pipes.
The working principle of LPFG(Long-Period Fiber Grating) is based on coupling effect between propagating core-mode
and co-propagating cladding-modes. The effective refractive index of cladding-modes could be obviously influenced by the environmental changes resulting in LPFG more sensitive than FBG (Fiber Bragg Grating) in sensing areas, such as temperature, strain, concentration, bending and etc. LPFG should have more potential in the field of sensors compared with FBG. One of the challenges in using LPFG for environmental sensing is how to interrogate the signal from the LPFG transmission spectrum, due to the large spectral range of the resonant dip. Nowadays the application of LPFG is normally limited in signal interrogation of FBG as optical edge filter. The signal interrogation of LPFG itself needs further research. Presently research on signal interrogation of fiber grating focuses on wavelength interrogation. The aim of wavelength interrogation is to get the wavelength shift caused by environmental change. To solve these problems, a kind of strain sensing interrogation technique for LPFG with low-cost based on tunable FBGs has been developed. Comparing with the method using Fabry-Perot cavity, tunable FBGs can lower the cost with the guarantee of sensing precision. The cost is further lowered without using expensive optical instruments such as optical switch. The problem of temperature cross-sensitivity was solved by using reference gratings. An experiment was performed to demonstrate the interrogation system. And in the experiment, the sensing signal of LPFG applied 0-1300με was successfully interrogated. The results of the interrogation system and OSA are similar.
In this paper, a general scalar model to analyze the diffraction spectrum of holographic variable line space (VLS) plane
grating at oblique incidence is proposed. The analytic expression for the diffraction spectrum of a VLS plane grating at
oblique incidence with a parallel and uniform beam was obtained on the basis of Fraunhofer diffraction theory. And the
applied scope of the analytic expression is that the grating period is much larger than the incident wavelength. Then
some computing examples are given in the condition of single wavelength incident. This oblique incidence model can
provide a theoretical reference for the real distribution of diffraction spectrum of holographic VLS plane grating. In
future work, the diffraction efficiency and polarization state will be considered.
In the application of micro-structural monitoring, one kind of flexible and stretchable sensing elements was urgently
demanded to detect the micro-bending and surface distortions, such as micro-bend sensing elements of medical catheter
or smart skin sensing unit of micro-robots. Here the sensing element must be stretchable and flexible for free operation,
and must be safe enough when used in bio-medical situation. Although the optical fiber grating is very mature and can be
used as sensing element in micro-bending situation, it isn't stretchable enough and flexible enough when used in
bio-medical science and micro- structural monitoring, and when applied in human body, the fiber grating isn't safe
enough for its easily broken character. In this paper a kind of novel flexible and stretchable polymer grating sensing
elements was fabricated by micro-replication process which could be used in micro- structural monitoring, and detailed
processes was presented and discussed.
Soft and flexible grating sensing waveguides is urgently demanded in application of micro-bending sensing and surface
distortion sensing in medical catheter and smart skin sensing unit etc. Based on Nano-imprint Lithography and
micro-replication process, polymer grating waveguides with core size 4μm×20μm and pitch 0.75μm are fabricated
successfully in this paper. This novel grating waveguides is soft and flexible enough for related application and with the
bio-medical safe feature when used in human body catheter. Fabricated processes are presented including the fabrication
of micro mould and UV-replication process, and relative skills are discussed also in this paper.
In this paper, we consider a SPR sensor based on D-type optical fiber with bimetallic combination. In pursuit of both
higher sensitivity and larger operating range, firstly, we separately analyze the influence of parameters such as the length
of coating L, the incident angle θ and the thickness of Au-coating layer d. when the optimum parameters of sensor are
determined, we analyze the performance of the sensor with different bimetallic combination consist of Au, Ag, Cu and
Al. Lastly, we can get a conclusion that the sensor with L=5mm,d=25nm, θ=88° and Au-Ag at x=0.8 can provide the
best performance in terms of the sensitivity and operating range.
Theoretical model and optimization of a novel optical fiber current sensor is presented, and the principle of this sensor is based on Fabry-Perot cavity multi-light interference theory and magnetostrictive effect of Tb-Dy-Fe material. This optical fiber current sensor is specially suitable in application of the hazardous high-voltage environments due to their characteristics including a dielectric nature, immunity to electro-magnetic interference, high sensitivity, non-contacted measurement feature, small size, light weight and capability of remote measurement and control. In practical application, it can be hung on a high-voltage wire and its range of measurement and sensitivity can be adjusted through modulating the distance between the sensor and the high-voltage wire. Static electromagnetic analysis is presented by means of ANSYS software, and the distribution of the magnetic field in the sensor can be gotten, which offers an effective reference for further calculation. In order to achieve a well-distributed magnetic field on capillary of Tb-Dy-Fe material, the distance between the sensor and the high-voltage wire was optimized by the finite element analysis software. The result of theoretical simulation obtained is as follows, the sensitivity is 13nw / A, while the distance between the center of high-voltage wire and transducer head is 20mm, the range of the measured current is 1000A to 8000A.
A novel micro-mechanical temperature sensor is presented theoretically and experimentally. The working principle of this sensor is based on Optical interference theory of Fabry-Perot cavity that is formed between a polished optical fiber end and micro-mechanical Bi-layered membranes. When ambient temperature is changing, Bi-layered membranes will be deflected based on 'Bi-coating effect', and then the length of Fabry-Perot cavity will be changed correspondingly. By detecting the optical output of Fabry-Perot cavity resulted from the change of Fabry-Perot cavity length, the ambient temperature can be measured. First, using finite element software ANSYS, the structures of this sensor was designed and corresponding theoretical model was set up based on theoretical analysis; Second, the sensor structure was optimized based on Fabry-Perot optical Interference theory and Bi-layered membranes dimensions selection, and theoretical characteristics was given by simulation; Third, using optical fiber 2×2 coupler and photo-electrical detector, the fabricated sample sensor was tested successfully by experiment that demonstrating above theoretical analysis and simulation results. This sensor has some favorable features, such as: micro size owing to its micro-mechanical structure, high sensitivity owing to its working Fabry-Perot interference cavity structure, and optical integration character by using optical fiber techniques.
Grating waveguides were fabricated based on Nano-imprint lithography (NIL) and silicon mould replication techniques in this paper. Using a silicon mould repeatedly, low-cost grating waveguides can be fabricated in batches. The proposed grating waveguide is soft enough to be an optical sensing element for catheter, smart skin sensing unit of micro-robots, and etc. Further, these grating waveguides were coupled with optical fibers for its convenient applications. There are two main parts in this paper, the first is to fabricate a suitable silicon mould for replication of grating waveguides, and the second is to reprint grating waveguides by using the fabricated silicon mould. Basing on NIL technology proposed in 1995 by Professor Stephen Y Chou, silicon moulds of grating waveguides with pitch 0.75μm were fabricated on (100) silicon wafer. There are several methods to carry out the replication process, such as Hot embossing, Injection moulding, UV-replication and Casting moulding method. In this work, UV-replication and Casting moulding method was selected to fabricate the grating waveguide structures for its easy control and high fidelity. There are two associated challenging issues in the replicating process; one is to prevent the replicated materials from sticking to the mould for easily peeling off the replicated structure, the other is to find matching materials for the waveguide core and cladding to guarantee the optical characteristics of the grating waveguide. Grating waveguides with core size 4μm×20μm were fabricated successfully in this paper that demonstrated the novel idea of this paper.
Silicon micro-cantilever resonators are typical elements in micro-electro-mechanical systems. Basing on the photothermally excited micro-cantilever resonators, many optical microsystems can be realized, such as micro-swichtes,mciro-modulators and microsensors etc. In this paper, mechanism and experiment study is given on photo-thermally excited bi-layered silicon micro-cantilever resonators, and relative results can be served as the basis of further applications. When coating is put on the surface of micro-cantilever to increase the optically exciting efficiency, the whole resonator becomes bi-layered structure, and the mechanism of this bi-layered resonator is very different from those of single material resonators. In this paper, photo-thermally excited mechanism of bi-layered silicon micro-cantilever was presented and a corresponding photo-thermal theoretical model was set up based on the photo-thermal effect. The first three resonant modes of the silicon micro-cantilever were detected successfully by using piezoelectric resistors fabricated as a Wheat-stone sensing bridge on the micro-cantilever. A novel method was presented to excite and detect the microresonator at the same time by using only one optical source , and this novel method was demonstrated by detecting the first resonant mode of the micro-cantilever.
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