In this work, we present an enhanced design for a Brillouin Ring Laser (BRL) based on a doubly-resonant cavity (DRC) with short fiber length, paired with a heterodyne-based wavelength-locking system, to be employed as pump-probe source in Brillouin sensing applications. The enhanced source is compared with the long-cavity (LC) (~ 2 km) BRL pump-probe source that we have recently demonstrated, showing a significantly lower relative intensity noise (~-145 dB/Hz in the whole 0-800 MHz range), a narrower linewidth (10 kHz), combined with large tunability features and an excellent pumpprobe frequency stability (~200 Hz) which is uncommon for fiber lasers. The measurement of intensity noise on the novel BRL signal yielded an improved signal-to-noise ratio (SNR) of about 22 dB with respect to LC-BRL schemes that is expected to lead to a temperature/strain resolution enhancement in BOTDA applications up to 5.5 dB.
Brillouin distributed optical fiber sensors have proved to be a powerful technology for real-time detection of strain and temperature. In such sensors the optical fiber is interrogated along its full length with a resolution down to decimeters and a frequency-encoding of the measurement data that is not affected by variation of the optical attenuation. The fiber sensing cable plays a key role, since it must provide accurate strain transfer, robustness and durability. In this paper, a novel, suitably designed fiber cable for achieving optimal strain measurement performance is presented. The concept and development phases are illustrated, together with results on the strain transfer capability.
In this work, we present an enhanced design for a Brillouin Ring Laser (BRL) based on a doubly-resonant cavity (DRC) with short fiber length, paired with a heterodyne-based wavelength-locking system, to be employed as pump-probe source in Brillouin sensing applications. The enhanced source is compared with the long-cavity (LC) (~ 2 km) BRL pump-probe source that we recently demonstrated, showing a significantly lower relative intensity noise (~ -145 dB/Hz in the 0-800 MHz range), a narrower linewidth (10 kHz), combined with large tunability features and an excellent pumpprobe frequency stability (~200 Hz) which is uncommon for fiber lasers. The measurement of intensity noise on the novel BRL signal yielded an improved signal-to-noise ratio (SNR) of about 22 dB with respect to LC-BRL schemes that is expected to lead to a temperature/strain resolution enhancement in BOTDA applications up to 5.5 dB.
In this work we report the results of a theoretical and experimental study that we have carried out on a Brillouin optical time domain analysis (BOTDA) sensing scheme using a novel low-noise actively-stabilized fiber Brillouin ring laser (BRL) as probe source. The BRL laser is based on a short-cavity (SC), < 4 meters long, layout achieving double-resonance (DR) operation for both pump and probe signals; an active wavelength-locking circuit is used to stabilize the signal and tune the signal frequency over a range of ̴ 200 MHz range. The wavelength-locked SC-DR BRL shows spectral linewidth of approximately 10 kHz and RIN values of ~-145 dB/Hz across the (0-600) MHz range; pump-probe frequency shift can be efficiently tuned across the entire Brillouin gain spectrum of the sensing fiber with sub-kHz precision (200 Hz) and high temporal stability for timescale of BOTDA measurements (more than 100 ms). A preliminary BOTDA measurement using a wavelength-locked long-cavity (LC) BRL yielded a Brillouin frequency shift (BFS) uncertainty of 1,5 MHz corresponding to temperature and strain sensitivity values of 1 K and 25 με, respectively, and a spatial resolution of 5 m for 50 ns-long pump pulses.
In this paper we show a Brillouin optical time-domain analysis (BOTDA) sensing system experiment employing a tunable narrow-linewidth dual pump-probe source based on modified Brillouin ring laser technology. The developed cost-effective source generates a pump-locked and tunable probe light, with wavelength shift and a large tuning range (~200 MHz), narrow linewidth (<2.5 MHz) and adequate power (~0.5 mW). The developed source was hence employed in BOTDA system experiments providing distributed sensing over ~10 km single mode optical fiber, and attaining strain and temperature resolutions of ~10με and ~0.5 °C respectively, indicating the pump-probe source as an efficient and cost-effective solution for BOTDA avoiding high-frequency signal generators or complex locking techniques.
We present a tunable narrow-linewidth dual pump-probe optical source based on modified Brillouin ring laser technology aimed at Brillouin-based sensing. The developed source exhibits a narrow linewidth and allows for a large tuning range, attaining <2.5 MHz bandwidth, ~200 MHz tuning range and ~0.5 mW power, thus constituting an efficient and cost-effective solution for sensing interrogators.
In this work a high-performance optical low-coherence reflectometer (OLCR) has been used to estimate the optical
losses in optical fibers and fiber Bragg grating sensors embedded into CFRP material samples. An ASE tunable
narrowband light source coupled to a Michelson interferometer allowed the high spatial resolution localization of both the concentrated and the distributed loss for different fiber coatings and type. In particular, acrylate- and polyimidecoated fibers and bend-insensitive fibers were tested. By using the OLCR it was possible to locate and identify the sources of optical loss introduced by the CFRP manufacturing process, therefore obtaining useful information on the efficiency of the embedding process.
KEYWORDS: Safety, Roads, Telecommunications, Sensors, Bridges, Global system for mobile communications, Data communications, Sensor networks, Structural health monitoring, Databases
This paper describes an autonomous wireless system that generates road safety alerts, in the form of SMS and
email messages, and sends them to motorists subscribed to the service. Drivers who regularly traverse a particular
route are the main beneficiaries of the proposed system, which is intended for sparsely populated rural
areas, where information available to drivers about road safety, especially bridge conditions, is very limited. At
the heart of this system is the SmartBrick, a wireless system for remote structural health monitoring that has
been presented in our previous work. Sensors on the SmartBrick network regularly collect data on water level,
temperature, strain, and other parameters important to safety of a bridge. This information is stored on the
device, and reported to a remote server over the GSM cellular infrastructure. The system generates alerts indicating
hazardous road conditions when the data exceeds thresholds that can be remotely changed. The remote
server and any number of designated authorities can be notified by email, FTP, and SMS. Drivers can view road
conditions and subscribe to SMS and/or email alerts through a web page. The subscription-only form of alert
generation has been deliberately selected to mitigate privacy concerns. The proposed system can significantly
increase the safety of travel through rural areas. Real-time availability of information to transportation authorities
and law enforcement officials facilitates early or proactive reaction to road hazards. Direct notification of
drivers further increases the utility of the system in increasing the safety of the traveling public.
This paper describes the design and testing of a wireless sensor network based on the SmartBrick, a low-power
SHM device developed by the authors. The SmartBrick serves as the base station for the network, which utilizes
additional sensor nodes to periodically evaluate the condition of the structure. Each node measures vibration,
tilt, humidity, and strain, and is designed for easy interfacing of virtually any other analog or digital sensor. The
sensor nodes use Zigbee to transmit their data to the base station, which in turn uses the GSM cellular phone
network to provide long-range communication and support for remote control.
The system has been designed from the outset to minimize power consumption, and is projected to operate
autonomously for up to four years without any on-site maintenance, due largely to the minimal power consumption
and rugged design. Remote calibration over the GSM network further increases the autonomy of the system.
Most importantly, it can perform all requisite actions with no cables for power or communication. The focus of
this paper is the addition of short-range wireless communication over Zigbee. This allows a network of several
devices to be used to monitor larger structures, such as multi-span bridges. Results of laboratory testing are
included and discussed in detail, demonstrating the unique capabilities of the proposed SHM system.
KEYWORDS: Floods, Bridges, Sensors, Structural health monitoring, Telecommunications, Computing systems, Data communications, Global system for mobile communications, Embedded systems, Environmental monitoring
This paper describes an autonomous embedded system for remote monitoring of bridges. Salient features of the
system include ultra-low power consumption, wireless communication of data and alerts, and incorporation of
embedded sensors that monitor various indicators of the structural health of a bridge, while capturing the state
of its surrounding environment. Examples include water level, temperature, vibration, and acoustic emissions.
Ease of installation, physical robustness, remote maintenance and calibration, and autonomous data communication
make the device a self-contained solution for remote monitoring of structural health. The system
addresses shortcomings present in centralized structural health monitoring systems, particularly their reliance
on a laptop or handheld computer. The system has been field-tested to verify the accuracy of the collected data
and dependability of communication. The sheer volume of data collected, and the regularity of its collection can
enable accurate and precise assessment of the health of a bridge, guiding maintenance efforts and providing early
warning of potentially dangerous events. In this paper, we present a detailed breakdown of the system's power
requirements and the results of the initial field test.
Brillouin fiber optic sensing is a promising technology for Structural Health Monitoring (SHM) whose diffusion is however at present reduced by the unavailability of proper sensor products and established installation techniques specifically aimed at the building industry.
Due to its intrinsic distributed sensing capability, Brillouin systems can individually measure the deformation of any single segment of considerable lengths of single-mode fiber. In addition, Brillouin retains all the other typical advantages of Fiber Optic Sensors (FOS), such as harsh environment durability and electro-magnetic interference rejection.
These advantages, especially considering that the required sensors are really low cost, make the system particularly attractive for periodical ("discontinuous") strain monitoring of unattended infrastructures that might be exposed to ageing and vandalism damages. Despite the high equipment cost, the technique can become economically convenient when the same initial investment can be amortized over a number of applications that can be monitored periodically using the same device.
This work presents a comparison between two different Brillouin sensor installation techniques: Near-to-Surface Fiber (NSF) embedding and smart-FRP sensor bonding. Both systems have been experimented in the field on small Reinforced Concrete (RC) bridges subject to a diagnostic load test. The obtained results clearly highlight the advantages of the smart-FRP system, in terms of performance enhancements, installation cost, and time reduction.
Strain and temperature sensing obtained through frequency shift evaluation of Brillouin scattered light is a technology that seems extremely promising for Structural Health Monitoring (SHM). Due to the intrinsic distributed sensing capability, Brillouin can measure the deformation of any individual segment of huge lengths of inexpensive single-mode fiber. In addition, Brillouin retains other typical advantages of Fiber Optic Sensors (FOS), such as harsh environment durability and interference rejection. Despite these advantages, the diffusion of Brillouin for SHM is constrained by different factors, such as the high equipment cost, the commercial unavailability of specific SHM oriented fiber products and even some prejudices on the required sensitivity performances.
In the present work, a complete SHM pilot application was developed, installed and successfully operated during a diagnostic load test on the High Performance Steel (HPS) bridge A6358 located at the Lake of the Ozarks (Miller County, MO, USA). Four out of five girders were extensively instrumented with a "smart" Glass Fiber Reinforced Polymer (GFRP) tape having embedded fibers for strain sensing and thermal compensation. Data collected during a diagnostic load test were elaborated through a specific post-processing software, and the strain profiles retrieved were compared to traditional strain gauges and theoretical results based on the AASHTO LRFD Bridge Design Specifications for structural assessment purposes. The excellent results obtained confirm the effectiveness of Brillouin SHM systems for the monitoring of real applications.
Composite materials based on glass, carbon and aramid fibers have many advantages such as fast application, lightweight and corrosion resistance, and are widely diffused for manufacturing of tanks, pipings and for restoration, upgrade and seismic retrofit of structures and historical heritage. As several questions regarding long term durability of composite strengthenings remains still unsolved, monitoring of strain and temperature is strongly recommended, respectively to assess proper load transfer and no glass phase transition of the polymeric matrix. In this research work strain and temperature distributed sensing trough Brillouin scattering in single-mode optical fibers was used in different tests in order to understand the influence of different fiber coatings and embedding techniques. Pressure tests were performed on a GFRP piping with inhomogeneous strengthening layout and Brillouin strain data were compared with conventional strain gages. A smart CFRP material has been also developed and evaluated in a seismic retrofit application on an historical building dated 1500 that was seriously damaged in the earthquake of 1997. The developed embedding technique has been demonstrated successful to obtain fiber-optic smart composites with low optical losses, and the data comparison between Brillouin and resistive strain gauges confirms Brillouin technique is very effective for composite monitoring.
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