Multipoint Fiber Loop Ringdown Sensors for Large Strain Measurement Using Frequency-Shifted Interferometry
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A novel multipoint fiber loop ringdown (FLRD) strain sensing system using frequency-shifted interferometry (FSI) is proposed and experimentally validated. Compared to conventional multipoint FLRD techniques, this scheme measures the decay rate of the continuous wave (CW) light in the space domain and thus greatly reduces the cost without the requirement of expensive devices. A serial dual-point strain sensing system was experimentally constructed and a biconical tapered multimode fiber (MMF) as the sensor head was used for obtaining the large measuring range. By applying different strains on the sensor heads through translation stages, a linear response between strain and additional loss induced by strain sensor was obtained, and the static strain sensitivities of 0.13676 dB/mε and 0.19665 dB/mε were achieved, corresponding to the detection limit of 0.0123 dB and 0.0360 dB, respectively. Moreover, a large measuring range of approximately 6 mε was achieved for both strain sensors. The experimental results indicate that our proposed method offers a promising multipoint strain sensor which has the advantages of low cost, a simple sensing structure and a large measuring range.Keywords:
Strain (injury)
Various aspects of time domain and frequency domain analysis of the dielectric response function have been discussed in detail. Time domain results of several alcohols have been found to be in reasonably good agreement with the frequency domain results. The accuracy of the experimental results in the high frequency region is considerably improved by the application of successive synchronized sampling for drift reduction.
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In this paper, the shielding effectiveness of planar material was calculated by time and frequency domain simulation. The time domain method is to calculate time domain response of the material under the electromagnetic pulse; the frequency domain method is to calculate frequency domain response of the material under the continuous wave. By comparing time domain and frequency domain results, it is found that SE calculated by transient method is consistent with frequency domain SE, so the shielding characteristics of materials can be analyzed by narrowband pulse test. The conclusions can help us to study the EMC and EM protection of electronic devices and systems.
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Electromagnetic Compatibility
Transient (computer programming)
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The article describes the operation's rule of the fiber optic sensor in the modalmetric configuration. This type of sensor is described by comparatively simple construction, while retaining other features of fiber-optic sensors such as high sensitivity. A modalmetric fiber optic sensor [1], whose scheme is shown in Fig. 1, comprises a multimode sensor fiber, a light source for launching light into the multimode fiber to produce a multimode speckle pattern of light at an end of the fiber, a single mode fiber to receive light from the multimode speckle pattern and a detector connected to the single mode fiber to detect the received a partial light from the multimode speckle pattern. Any disturbance to the fiber which can cause a change in any one of the phase, polarization and distribution of the modes, will cause the speckle pattern to change. By measuring this change, a physical perturbation to the fiber such as a vibration or strain can be detected. This gives a very high potential application. In the paper presents, for example, possible application of the modalmetric sensor to protection of works of art and museum collections. The advantage of its use is the ability to tie the fiber in structure of material. Moreover, the advantage of such type a sensor compared to existing solutions of security sensors is the reaction for vibration and touch. The paper presents the concept and results of the system optimization.
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An approach of generating synthetic time domain data from frequency domain simulations in complex environments is presented in this paper. As a result, pulse forms scattered by wind turbines can be studied and compared with measurements. For large scenarios such as electromagnetic scattering from wind farms, only high-frequency methods, e.g., ray tracing can be applied. However, these methods generally operate in frequency domain, whereas measurements show the scattered pulses in time domain. The methodology presented in this paper first transfers the time domain signal to frequency domain, so the frequency-dependent scattering coefficients obtained from ray tracing can be applied. Then the data is transformed back to time domain, yielding the scattered pulse in time domain.
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A low-cost fiber optic sensor system based on multimode fiber and an LED light source is presented. A multimode fiber Bragg grating (MMFBG) element is used as a strain sensor. In a matched grating scheme, a MMFBG similar to the sensing one was used as a reference in the receiving unit. For detection of large wavelength shift we demonstrated the feasibility of MMFBG wavelength detection using a single mode fiber fused coupler edge filter. The high cost normally associated with wavelength interrogators for single mode fiber FBG sensors was overcome by the utilization of a low cost multimode fiber pigtailed LED light source. The multimode fiber sensing system has the potential of maintaining much of the advantages of its single mode FBG sensor system counterparts. The MMFBG sensing schemes could be used for short distance, high sensitivity, high speed, strain, temperature and acoustic sensing applications
Fiber Bragg Grating
Long-period fiber grating
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The generation and propagation of an electromagnetic pulse (EMP) in real time, can be visualized in time domain because of its transient nature. The coupling of an EMP with different systems can be assessed by analyzing the frequency spectrum and can be very well understood in the frequency-domain through the lowest frequency, the highest frequency, and the energy content. This chapter presents the mathematical waveforms representing the nuclear electromagnetic pulse (NEMP) for simulating the electromagnetic environment in the event of nuclear explosion. It discusses most commonly used waveforms of a high-altitude electromagnetic pulse. The characteristics of a NEMP waveform in time-domain can be understood through the following parameters: rise time, pulse duration, and peak characteristics. The transient nature of an EMP is revealed by the time-domain analysis. The frequency domain analysis helps us to understand how does an EMP couples with different systems.
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Transient (computer programming)
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Current trends of fiber optic sensor technology are in a direction of a broadening scope of sensor innovation based on a few basic concepts. Both single-mode and multimode fibers have their proponents: single mode for primarily interferometric sensors and multimode for primarily amplitude-modulated sensors. This paper illustrates four unique and innovative multimode sensor designs and also discusses the basic inhibition to more rapid utilization of optical fiber sensors. A case is made for more effort in standardization of optical fiber sensor interface design and integration requirements. To benefit the optical fiber sensor R & D and small business community, attention to system level requirements is necessary to encourage greater utilization and achieve greater exploitation of the benefits offered by optical fiber sensors.
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Current sensor
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Novel optical fiber sensor architecture has been developed. The actual element of the sensor is highly curved multimode fiber. However, the feed to the multimode fiber is through a single mode fiber to ensure that only the lowest order spatial mode is launched. Similarly the receiver is also coupled to the sensing element through a single mode fiber. The fundamental mode within graded index multimode fiber proves to be very insensitive to macrobends, if bend radius is larger than certain critical value. If bend radius is reduced below critical value the loss increases very rapidly and this allows for construction of relatively sensitive macrobend fiber optic sensor. In this paper we describe a quantitative theoretical model and a corresponding experimental investigation of the proposed structure. A proposal for simple and practical sensor design based on the proposed structure is presented. It is consisted of a miniature fiber optic coil that is deformed proportionally to the measured environmental parameter. We practically demonstrated sensitivities in the range of ΔI/Δx=130%/N and ΔI/ΔF= 1.1%/μm. Even higher sensitivities are possible by proper mechanical construction of the sensor element. The proposed structure can configured in variety of different distributed and quasi-distributed architectures and is suitable for embedding into the composite materials.
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In the optimization or parametric analyses of risers, several configurations must be analyzed. It is laborious to perform time domain solutions for the dynamic analysis, since they are time-consuming tasks. So, frequency domain solutions appear to be a possible alternative, mainly in the early stages of a riser design. However, frequency domain analysis is linear and requires that nonlinear effects are treated. The aim of this paper is to present a possible way to treat some of these nonlinearities, using an iterative process together with an analytical correction, and compare the results of a frequency domain analysis with the those of a full nonlinear analysis.
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Frequency analysis
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