Embeddable Advanced Sensors for Harsh Environment Sensing Applications

Research and development in advanced sensors with embedded monitoring capability have experienced significant growth in recent years, fueled by their broad applications in real-time measurement of a wide variety of physical, chemical, and biological quantities. Compared with conventional sensors with bulky assemblies, recent progress in 3D manufacturing technologies (e.g., ultrafast laser micromachining and additive manufacturing) has opened up a new avenue in one-step fabrication of assembly-freemicro devices in various materials as well as the development of compact, customized, and intricate smart structures/components. The merits of these advanced manufacturing techniques enable the integration of embeddable advanced sensors into smart structures and components for improved robustness, enriched functionality, enhanced intelligence, and unprecedented performance

Femtosecond laser micro-machined optical fiber based embeddable strain and temperature sensors for structural monitoring

Structural monitoring technology is becoming increasingly important for managing all types of structures. Embedding sensors while constructing new structures or repairing the old ones allows for continual monitoring of structural health thus giving an estimate of remaining utility. Along with being embeddable, miniaturized sensors that are easy to handle are highly sought after in the industry where in-situ monitoring is required in a harsh environment (corrosive atmosphere, high temperatures, high pressure etc.). This dissertation demonstrates the use of femtosecond laser-fabricated Fabry-Perot interferometer (FPI) based optical fiber sensors for embedded applications like structural health monitoring. Two types of Fabry-Perot interferometer sensors, extrinsic FPI and intrinsic FPI, have been designed, developed and demonstrated for strain and temperature monitoring applications. The absence of any movable parts make these sensors easy-to-handle and easy to embed inside a material. These sensors were fabricated using a laboratory integrated femtosecond (fs) laser micromachining system. For the extrinsic Fabry-Perot interferometer (EFPI) design, the fs-laser was used to ablate and remove the material off the fiber end face while for intrinsic Fabry-Perot interferometer (IFPI) design, the laser power was focused inside the fiber on the fiber core to create two microstructures. The scope of the work presented in this dissertation extends to device design, laser based sensor fabrication, sensor performance evaluation and demonstration. Feasibility of using these sensors for embeddable applications was investigated. A new type of material called Bismaleimide (BMI) was used for demonstrating the embeddability of the sensors. Experimental results of strain and temperature testing are presented and discussed. The EFPI sensor has low temperature sensitivity of 0.59 pm/⁰C and a high strain sensitivity of 1.5 pm/µε. The IFPI sensor has the same strain sensitivity as EFPI but is 25 times more sensitive to the temperature. These sensors were tested up to 850 ⁰C in non-embedded condition and they produced a linear response. A hybrid approach combining the EFPI and IFPI sensors was demonstrated for simultaneous measurement of strain and temperature --Abstract, page iii

Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology

INE/AUTC 10.0

NOVEL SENSOR PLATFORMS BASED ON FABRY-PEROT RESONATORS FOR APPLICATIONS IN ENVIRONMENTAL GEOPHYSICS

Fabry-Perot resonator sensors have been widely used for various physical and chemical measurements owing to their unique advantages over traditional sensors such as high measurement resolution, mechanically robust, and distributed sensing capabilities. This dissertation focuses on the development of robust fiber optic microwave sensors based on Fabry-Perot resonator mechanism for real-time applications in environmental geophysics. Firstly, a novel Extrinsic Fabry-Perot Interferometer (EFPI)-based fiber-optic sensor for force measurement using a pre-buckled beam was demonstrated. The axial displacement is transferred and amplified to a horizontal deflection at the middle of the buckled beam, leading to a relatively significant change in the Fabry-Perot cavity length. The force measurement range and the size of the sensor can be easily reconfigured by adjusting the size of the beam, enabling force measurement for different scenarios. Secondly, a self-compensated inclinometer with a wide dynamic range and high measurement resolution based on two hollow coaxial cable Fabry-Perot resonators (HCC-FPRs) was reported. By tracking the shift of the resonance wavelength of the HCC-FPR, two HCC-FPRs are used in the inclinometer design, which enables the inclinometer to achieve self-compensation for variations in environmental factors. Thirdly, a Polyvinyl Alcohol (PVA) film-assisted open-ended hollow coaxial cable Fabry-Perot resonator was proposed for highly sensitive embeddable soil moisture measurements. The invented sensor platform could be reconfigured to detect chemical contaminants in soil by changing the functional films in the active zone of the sensor --Abstract, p. i

Advances in Fiber-Optic Extrinsic Fabry-Perot Interferometric Physical and Mechanical Sensors: A Review

Fabry-Perot Interferometers Have Found a Multitude of Scientific and Industrial Applications Ranging from Gravitational Wave Detection, High-Resolution Spectroscopy, and Optical Filters to Quantum Optomechanics. Integrated with Optical Fiber Waveguide Technology, the Fiber-Optic Fabry-Perot Interferometers Have Emerged as a Unique Candidate for High-Sensitivity Sensing and Have Undergone Tremendous Growth and Advancement in the Past Two Decades with their Successful Applications in an Expansive Range of Fields. the Extrinsic Cavity-Based Devices, I.e., the Fiber-Optic Extrinsic Fabry-Perot Interferometers (EFPIs), Enable Great Flexibility in the Design of the Sensitive Fabry-Perot Cavity Combined with State-Of-The-Art Micromachining and Conventional Mechanical Fabrication, Leading to the Development of a Diverse Array of EFPI Sensors Targeting at Different Physical Quantities. Here, We Summarize the Recent Progress of Fiber-Optic EFPI Sensors, Providing an overview of Different Physical and Mechanical Sensors based on the Fabry-Perot Interferometer Principle, with a Special Focus on Displacement-Related Quantities, Such as Strain, Force, Tilt, Vibration and Acceleration, Pressure, and Acoustic. the Working Principle and Signal Demodulation Methods Are Shown in Brief. Perspectives on Further Advancement of EFPI Sensing Technologies Are Also Discussed

A Uniform Strain Transfer Scheme for Accurate Distributed Optical Fiber Strain Measurements in Civil Structures

We report a screw-like package design for an embeddable distributed optical fiber strain sensor for civil engineering applications. The screw-like structure is the exterior support for an optical fiber sensor. The bare optical fiber is embedded and secured in a longitudinal groove of the screw-like package using a rigid adhesive. Our packaging scheme prevents damage to the bare optical fiber and ensures that the packaged sensor is accurately and optimally sensing strain fields in civil structures. Moreover, our screw-like design has an equal area in a cross-section perpendicular to and along the screw axis, so strain field distributions are metered faithfully along the length of the embedded optical fiber. Our novel screw-like package optical fiber sensor, interfaced to a Rayleigh scattering-based optical frequency domain reflectometer system enables undistorted, accurate, robust, and spatially-distributed strain measurements in bridges, tunnels, pipelines, buildings, etc. along structural dimensions extending from centimeters to kilometers

Analysis of Fiber optic sensor embedding in metals by automatic and manual TIG welding

In this paper, the embedding of fiber optic sensors in metals, by using both automatic and manual Tungsten Inert Gas welding (TIG) is discussed for nickel- and copper-coated Fiber Bragg Gratings (FBG) written into an optical fiber, as embedding such sensors in metals provides protection against environmental effects. In the investigation and analysis of the performance of a number of such sensors, copper-coated sensors were seen to lose their temperature and strain sensitivity while being embedded due to damage to the coating, while with a nickel coating the sensors in the fiber were found to withstand the process with a lesser effect on the sensor performance. The research has also shown that the Automatic TIG process used is less invasive than the manual TIG approach, although more expensive to implement

Highway infrastructure health monitoring using micro-electromechanical sensors and systems (MEMS)

The development of novel smart structures by embedding sensing capabilities directly into the construction material during the manufacturing and deployment process has attracted significant attention in autonomous structural health monitoring (SHM). Micro-electromechanical systems (MEMS) provide vast improvements over existing sensing methods in the context of SHM of highway infrastructure systems, including improved system reliability, improved longevity and enhanced system performance, improved safety against natural hazards and vibrations, and a reduction in life cycle cost in both operating and maintaining the infrastructure. Advancements in MEMS technology and wireless sensor networks provide opportunities for long-Term, continuous, real-Time structural health monitoring of pavements and bridges at low cost within the context of sustainable infrastructure systems. Based on a comprehensive review of literature and vendor survey, the latest information available on off-The-shelf MEMS devices, as well as research prototypes, for bridge, pavement, and traffic applications are synthesized in this paper. In addition, the paper discusses the results of a laboratory study as well as a small-scale field study on the use of a wireless concrete monitoring system based on radio-frequency identification (RFID) technology and off-The-shelf MEMS-based temperature and humidity sensors

A Uniform Strain Transfer Scheme for Accurate Distributed Optical Fiber Strain Measurements in Civil Structures

We report a screw-like package design for an embeddable distributed optical fiber strain sensor for civil engineering applications. The screw-like structure is the exterior support for an optical fiber sensor. The bare optical fiber is embedded and secured in a longitudinal groove of the screw-like package using a rigid adhesive. Our packaging scheme prevents damage to the bare optical fiber and ensures that the packaged sensor is accurately and optimally sensing strain fields in civil structures. Moreover, our screw-like design has an equal area in a cross-section perpendicular to and along the screw axis, so strain field distributions are metered faithfully along the length of the embedded optical fiber. Our novel screw-like package optical fiber sensor, interfaced to a Rayleigh scattering-based optical frequency domain reflectometer system enables undistorted, accurate, robust, and spatially-distributed strain measurements in bridges, tunnels, pipelines, buildings, etc. along structural dimensions extending from centimeters to kilometers. Document type: Articl