Fiber Optic Sensor Array Research Articles

Performance Evaluation of One-dimensional Fiber-optic Radiation Sensor for Measuring High Energy Electron Beam Using a Charge-coupled Device

In this study, we have fabricated one-dimensional fiber-optic radiation sensor array for high energy electron beam therapy dosimetry. Fiber-optic radiation sensor comprises an organic scintillator as a sensing volume, optical fiber as a light guider and photo-detector as a light measuring device. Usually, photomultiplier tube or photodiode is used as a photo-detector however we have tried to use a charge-coupled device as a scintillating light measuring system for one-dimensional fiber-optic radiation sensor array. This system can take an image of the proximal ends of one-dimensional fiber-optic sensor array and can measure light intensities of individual image of optical fibers simultaneously using simple imaging software. Charge-coupled device as a light measuring detector has many advantages which are easy in multi-dimensional measurements, high spatial resolution and relatively low cost. We have measured one-dimensional electron beam distributions in a PMMA phantom with different energies and field sizes of electron beam using a fiber-optic sensor and a charge-coupled device. Also, the percentage depth dose curves for high energy electron beams are obtained.

近年の物理探査の技術動向―時空間スケールの重要性―

Geophysical exploration technologies have been developed through several innovative steps in the history. Data acquisition and processing technologies evolved since 1960s. Since 1980s, these technologies started to be integrated first to reservoir description, then to reservoir modeling (characterization), and recently to reservoir management technologies. These developments have taken place due to the recent tendency to have their target structures in smaller scale or more complex than it used to be. We may summarize these technical developments as follows : a) 3D to 4D data acquisition to realize reservoir management, b) 4-C marine data acquisition (tri-component geophone and pressure gauge), c) single sensor acquisition supported by well-developed multi-channel signal processing techniques for true amplitude recovery without any instrumental spatial filtering, d) new acquisition technologies such as fiber-optic sensor arrays. We believe that further new development would surely be attempted to satisfy the needs to visualize underground structure, to understand what is on-going for the state of natural resources under development, and to enhance our management capabilities to control the production from existing reservoir.

Performance evaluation of a conformal thermal monitoring sheet sensor array for measurement of surface temperature distributions during superficial hyperthermia treatments

Purpose: This paper presents a novel conformal thermal monitoring sheet (TMS) sensor array with differential thermal sensitivity for measuring temperature distributions over large surface areas. Performance of the sensor array is evaluated in terms of thermal accuracy, mechanical stability and conformity to contoured surfaces, probe self-heating under irradiation from microwave and ultrasound hyperthermia sources, and electromagnetic field perturbation.Materials and methods: A prototype with 4 × 4 array of fiber-optic sensors embedded between two flexible and thermally conducting polyimide films was developed as an alternative to the standard 1–2 mm diameter plastic catheter-based probes used in clinical hyperthermia. Computed tomography images and bending tests were performed to evaluate the conformability and mechanical stability respectively. Irradiation and thermal barrier tests were conducted and thermal response of the prototype was compared with round cross-sectional clinical probes.Results: Bending and conformity tests demonstrated higher flexibility, dimensional stability and close conformity to human torso. Minimal perturbation of microwave fields and low probe self-heating was observed when irradiated with 915 MHz microwave and 3.4 MHz ultrasound sources. The transient and steady state thermal responses of the TMS array were superior compared to the clinical probes.Conclusions: A conformal TMS sensor array with improved thermal sensitivity and dimensional stability was investigated for real-time skin temperature monitoring. This fixed-geometry, body-conforming array of thermal sensors allows fast and accurate characterization of two-dimensional temperature distributions over large surface areas. The prototype TMS demonstrates significant advantages over clinical probes for characterizing skin temperature distributions during hyperthermia treatments of superficial tissue disease.

Development of One-dimensional Fiber-Optic Radiation Sensor for Measuring Dose Distributions of High Energy Photon Beams

The purpose of this study was to develop a method for measuring the one-dimensional dose distribution of a high-energy photon beam using a miniaturized high-resolution fiber-optic radiation sensor array. The measurements were made by thin plastic optical fibers with organic scintillating fiber sensor probes that emit the visible wavelength of light. The scintillating light is guided to a silicon photodiode array by plastic optical fibers in order to convert light output to an electrical signal. The one-dimensional spatial dependence of photon beam is measured by a one-dimensional fiberoptic sensor array in a poly(methyl methacrylate) (PMMA) phantom. It is shown that this fiber-optic radiation sensor has better spatial resolution than a conventional ionization chamber and much less time is required to measure one-dimensional dose distribution in the high radiation fields. The real-time and the high spatial resolution measurements due to the small detector volume make this system suitable for dosimetry in radiation therapy.

Twin multiplexing strain sensing array based on a low-coherence fiber optic Mach–Zehnder interferometer

A twin multiplexed white light interferometric fiber optic strain sensor array was designed and demonstrated. In this sensing system, based on a low-coherence fiber optic Mach–Zehnder interferometer, an optical path matching technique is used to demodulate each sensor. The strain sensor array consists of 2 × N sensing elements linked by N 3 dB couplers. When one of the fiber sensors has been used to measure the strain, the variation caused by the temperature can be compensated by the other sensor. The multiplexing capacity of the sensing scheme has been analyzed. The results shown that it is depend on the light source power. The maximum number of the twin fiber sensor size is 4 for light source with 35 μW, and 7 for light source with 3 mW, respectively. The experimental result with a two-coupler sensor array was conducted and demonstrated which confirm this. It is useful for temperature compensation of distributed strain measurement in smart materials or structures health monitoring.

Frequency-shifted Mach-Zehnder interferometer for locating multiple weak reflections along a fiber link

We propose and demonstrate a novel technique for measuring fiber lengths and locating multiple weak reflections along the fiber using a low-cost continuous wave source, a folded Mach-Zehnder interferometer (MZI), and a frequency shifter. By sweeping the frequency of the shifter, which is located in one path of the MZI, the optical length of the test fiber can be determined precisely from the interference pattern constructed by the reflected signals from the fiber end. Experimentally, for fibers shorter than 10 km, the standard deviations are less than 1 mm. Furthermore, by incorporating lock-in detection and fast Fourier transform techniques, both the locations and the reflectance of multiple reflection sites along one fiber can be resolved with a spatial resolution of about 5 m and a sensitivity better than -67dB. This could be a powerful interrogating technique for optical fiber sensor arrays.

Schemes of a fiber-optic multiplexing sensor array based on a 3×3 star coupler

A Michelson-based fiber-optic low-coherence interferometric quasi-distributed sensing system permitting absolute length measurement in a sensor array is proposed. The main part of the sensing system is a fiberoptic 3 x 3 star coupler. The architecture of fiber-optic sensors can be easily realized as a linear sensor array, twin sensor arrays, or a loop sensor array. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application could be deformation sensing in smart structures. A six-sensor array is demonstrated experimentally.

Progress toward the determination of Sr2+ in highly basic solutions using imaging optical fiber sensor arrays

This manuscript describes initial progress toward the development of an imaging optical fiber microsphere sensor array for real-time monitoring of Sr2+ in process streams from high-level radioactive waste (HLW) remediation. Fura-2, a fluorescent molecular recognition compound, which displays increased fluorescence intensity upon complexation with divalent cations, was employed as a probe to quantify Sr2+. The solution-based detection of Sr2+ using Fura-2 was investigated in the presence of low Ca2+ concentrations and at high pH and ionic strength. A linear range of 6.7 × 10−7 M to 6.7 × 10−4 M was obtained for Sr2+ in neutral solutions containing trace Ca2+ and 6.7 × 10−8 M and 6.7 × 10−4 M for Sr2+ in high pH, high ionic strength solutions. Additionally, the stability of imaging optical fibers to harsh, high pH conditions was examined. These experiments suggest the fiber surface may need to be modified so that they are stable during the anticipated measurement times required for HLW.

Fiber optic sensor arrays: a new method to improve multiplexing capability with a low complexity approach

In this paper, we show some preliminary numerical results in order to increase the multiplexing capability of a multipoint fiber Bragg grating (FBG) sensor network without increase the system complexity. We base the new approach on the possibility of exploiting the chirped-pulsed frequency modulation technique (C-PFM). This technique, extensively used in radar applications, is based on the amplitude modulation of the emitted signal (pulsed) by a chirped frequency signal and on the demodulation of the reflected signal by means of adaptive filter. FBG sensors are instrumental to obtain cheap and easy handling multipoint sensing arrays.

Large-scale remotely pumped and interrogated fiber-optic interferometric sensor array

We report a demonstration of a large-scale remotely interrogated remotely pumped fiber-optic, interferometric sensor array. The system is designed primarily for underwater acoustic applications where each sensor is configured as a hydrophone and a large number of sensors (i.e., up to /spl sim/500) are required to be interrogated through link lengths of several tens of kilometers. A system comprising of 96 sensors combined using time and dense wavelength-division multiplexing and interrogated through a 40-km fiber link is demonstrated. A remotely pumped erbium-doped fiber amplifier is incorporated into the array to increase the distance between the array and interrogation electronics. We describe the performance of our system and validate a previously published model.

Fiber-Optic Sensor Arrays for Permanent Offshore Applications

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 15072, "Requirements, Constraints, and Advantages of Fiber-Optic Sensor Arrays for Permanent Offshore Applications," by M.H. Houston, SPE, Northrop Grumman, originally presented at the 2003 Offshore Technology Conference, Houston, 5-8 May.

Large-scale remotely interrogated arrays of fiber-optic interferometric sensors for underwater acoustic applications

The fiber-optic interferometric acoustic sensor array has established itself as a potential alternative to the conventional sonar array based on electroceramic transducers. In this paper, we discuss all the aspects of a large-scale fiber-optic interferometric sensor array. We review the basic operating principles of the fiber-optic interferometric sensor, signal processing, and multiplexing techniques, we present results from a noise model for a full size system, and we determine the benefit of incorporating a remotely-pumped optical amplifier in the array. As a practical example we describe the design and construction of a prototype array with 96 hydrophones incorporating a remotely pumped erbium-doped fiber amplifier, called the fiber-optic bottom mounted array, which is based on a dense wavelength division and time division multiplexed architecture. These arrays have applications in military sonar and seismic surveying.

Fiber-Optic Sensor Technology and Combinatorial Chemistry

ABSTRACTOur recently introduced “Fiber-Optic Combinatorial Chemistry” technique combines combinatorial synthetic methods and optical fiber sensor technologies. Our one-dimensional combinatorial chemistry method allows for synthesis of large compound libraries in a linear format, for example in the cladding of optical fibers. Subjecting these libraries to assays that indicate positive identification of a library member by the binding of a fluorescent group, produces, in effect, an optical fiber sensor array. The location of a particular fluorescent region along the optical fiber can be determined through the optical time-of-flight technique, in which laser pulses propagating through the fiber core probe through their evanescent fields the fluorescent properties of the compounds located in the fiber cladding. It is a virtue of our combinatorial synthetic procedure that with the location of a compound on the fiber, its synthetic history is immediately known. We demonstrated that limitations on the spatial resolution of compounds along the fiber due to the excited state lifetimes of the fluorescent marker molecules can be overcome by the use of a second fiber - evanescently coupled to the first one - as an optical delay.The existing claddings of optical fibers severely restrict the range of chemistries for the synthesis of combinatorial libraries. Therefore, in order to make our method more generally applicable, the existing fiber cladding has to be replaced by a porous material that can act as solid support for reactions and at the same time preserve the optical guiding conditions of the fiber. In this contribution we discuss the requirements for such a replacement cladding and evaluate the general suitability of a functionalized candidate material.

Intrinsic fiber-optic ultrasonic sensor array using multiplexed two-wave mixing interferometry.

An intrinsic multiplexed laser interferometer is presented that allows for the simultaneous detection of acoustic waves by an array of fiber-optic sensors. The phase-modulated signals from each sensor are demodulated by use of an adaptive two-wave mixing setup. The light from each sensing fiber in the array is mixed with a reference beam in a single photorefractive crystal (PRC), and the output beams from the PRC are imaged onto separate photodetectors to create a multiplexed two-wave mixing (MTWM) system. The sensing fibers are embedded in graphite-epoxy composite panels, and detection of both acoustic emission and ultrasonic signals in these materials is demonstrated. The intrinsic MTWM system is an effective tool for the simultaneous demodulation of signals from a large fiber sensor array. Also, the adaptive nature of the MTWM setup obviates the need for active stabilization against ambient noise.

Folded Sagnac sensor array

A folded Sagnac fiber optic acoustic sensor array (1200) operates in a manner similar to a Sagnac Interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor (716) is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on the operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors (718(N)) can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Optical multibead arrays for simple and complex odor discrimination.

A fiber optic bead-based sensor array platform has been employed to discriminate between six different odors and air carrier gas. Six different bead sensor types, with over 250 replicates of each, were monitored before, during, and after odor exposure to produce time-dependent fluorescence response patterns that were unique for each sensor-analyte combination. A total of 2,683 sensors were analyzed with respect to changes in their fluorescence, and signals from identical sensor beads were averaged to improve signal-to-noise ratios. Analyte classification rates of 100% were achieved for three complex (coffee bean) odors and three pure (simple) odors (toluene, acetone, 1,3-dinitrotoluene) measured at their highest relative concentrations. When lower odor concentrations were employed, the system exhibited better than 85% classification rates for analyte discrimination. Sensor response repeatability to these odor stimuli has also been quantified statistically, which is vital in defining the detection limit of the overall system. These results demonstrate, for the first time, the utility of our bead array technology for discriminating between different odor types at various dilution levels.

Fiber-optic sensor array based on Sagnac interferometer with stable phase bias

We propose and experimentally demonstrate a novel fiber sensor array based on a Sagnac interferometer with very simple electronic signal processing. A stable quadrature phase bias was obtained using a phase modulator, and the polarization-induced signal fading was suppressed by using a depolarizer and a broad-band source. A phase sensitivity of about 4.0 /spl mu/rad/sub rms///spl radic/Hz at 5 kHz was obtained using a two-sensor array.

Quasi-distributed strain sensing with white-light interferometry: a novel approach

An optical fiber ring is used to generate multiple reference waves in a multiplexed fiber-optic Michelson-type sensor array. The array consists of N sensing segments connected in series along a single optical fiber path and is interrogated with a white-light interferometric technique. Experimental results with a two-sensor array are presented.

Spatially continuous six degree of freedom position and orientation sensor

This paper describes SHAPE TAPE™, a thin array of fiber optic curvature sensors laminated on a ribbon substrate, arranged to sense bend and twist. The resulting signals are used to build a three dimensional computer model containing six degree of freedom position and orientation information for any location along the ribbon. The tape can be used to derive dynamic or static shape information from objects to which it is attached or scanned over. This is particularly useful where attachment is only partial, since shape tape “knows where it is” relative to a starting location. Measurements can be performed where cameras cannot see, without the use of magnetic fields. Applications include simulation, film animation, computer aided design, robotics, biomechanics, and crash testing.

A novel fiber-optic sensor array based on the Sagnac interferometer

We propose a novel design for a fiber-optic acoustic sensor array that is based on the Sagnac interferometer. The performance of this Sagnac sensor array (SSA) design is analyzed and compared to acoustic sensor arrays based on the Mach-Zehnder (MZ) interferometer. It is found that the SSA exhibits several decisive advantages, including a stable bias point, a reduced conversion of source phase noise into intensity noise, and a frequency response that matches the ambient ocean noise. It is also shown that the SSA can be easily designed to have a much larger dynamic range than an MZ-based sensor array. Potential noise sources are analyzed and shown to be manageable. A means for eliminating polarization-induced signal fading is presented. The applicability of time-division, frequency-division, and code-division multiplexing schemes for the proposed design is presented.