A Coaxial Cable Fabry-Perot Interferometer for Sensing Applications

This paper reports a novel coaxial cable Fabry-Perot interferometer for sensing applications. The sensor is fabricated by drilling two holes half-way into a coaxial cable. The device physics was described. The temperature and strain responses of the sensor were tested. The measurement error was calculated and analyzed

Coaxial Cable Sensors Based on Fabry-Perot Interferometers and Their Applications in Distributed Sensing

Aging civic infrastructures in the world has put tremendous pressure in their maintenances because potential failure of the large size civil structures will be catastrophic. Structure health monitoring (SHM) has been proven effective to prevent these failures, and distributed sensing technologies are preferred in SHM as they are effective to provide comprehensive evaluation of the structures. Fiber optic sensors are well developed in the past two decades for distributed sensing, but the lack of robustness and the limited deformability of silica make them not suitable for heavy duty and large deformation applications, which is very common in SHM. To address the above limitation of optical fiber sensors, we change the sensing platform from optical fibers to coaxial cable. Inspired by optical FPI, we created two reflectors on a coaxial cable to form a coaxial cable Fabry-Perot interferometer (CCFPI). The reflectors are commonly made by drilling half way holes or crimp on the cable, which introduce impedance discontinuity and hence partial reflection of EM wave in the cable. The two reflectors can produce interference patterns with multiple resonant frequencies which can be tracked to indicate changes in physical parameters such as temperature and strain. To realize distributed sensing, multiple reflectors are implemented along a coaxial cable, where every two consecutive reflectors will form a low finesse CCFPI. A specific signal process technique is used to reconstruct each individual CCFPI interferogram from the complex frequency domain signal. As examples of the distributed sensing capability of the coaxial cable platform, distributed torsion sensing and 3D beam shape estimation system are demonstrated in this thesis. By modifying the cable material and structure, we can achieve other special function for CC-FPI sensors. By fabricating the cable with ceramics as dielectric material and implanting built in reflectors, a high temperature CC-FPI sensor is developed and tested. Another example is a magnetic field sensor made by filling a cavity in a semi-rigid cable with ferrofluid. When external magnetic field change, the property of the ferrofluid will also change, resulting in spectrum shift of the FPI. The coaxial cable FPI sensors have many potentials to measure different physical parameters in distributed sensing form, which makes it a very good sensing platform for long distance and distributed sensing in harsh environment and heavy duty applications

Fiber-optic and coaxial-cable extrinsic Fabry-Perot interferometers for sensing applications

”The fiber-optic extrinsic Fabry-Perot interferometer (EFPI) is one of the simplest sensing configurations and is widely used in various applications due to its prominent features, such as high sensitivity, immunity to electromagnetic interference, and remote operation capability. In this research, a novel one-dimensional wide-range displacement sensor and a three-dimensional displacement sensor based on fiber-optic EFPIs are demonstrated. These two robust and easy-to-manufacture sensors expand the application scope of the fiber-optic EFPI sensor devices, and have great potential in structural health monitoring, the construction industry, oil well monitoring, and geo-technology. Furthermore, inspired by the fiber-optic EFPI, a novel and universal ultra-sensitive microwave sensing platform based on an open-ended hollow coaxial cable resonator (OE-HCCR, i.e., the coaxial cable EFPI) is developed. Both the theoretical predictions and experimental results demonstrate the ultra-high sensitivity of the OE-HCCR device to variations of the gap distance between the endface of the coaxial cable and an external metal plate. Additionally, combining the chemical-specific adsorption properties of metal-organic framework (MOF) materials with the dielectric sensitivity of the OE-HCCR, a mechanically robust and portable gas sensor device (OE-HCCR-MOF) with high chemical selectivity and sensitivity is proposed and experimentally demonstrated. Due to its low cost, high sensitivity, all-metal structure, robustness, and ease of signal demodulation, it is envisioned that the proposed OE-HCCR device will advance EFPI sensing technologies, revolutionize the sensing field, and enable many important sensing applications that take place in harsh environments”--Abstract, page iv

A Hollow Coaxial Cable Fabry-Perot Resonator for Liquid Dielectric Constant Measurement

We report, for the first time, a low-cost and robust homemade hollow coaxial cable Fabry-Pérot resonator (HCC-FPR) for measuring liquid dielectric constant. In the HCC design, the traditional dielectric insulating layer is replaced by air. A metal disk is welded onto the end of the HCC serving as a highly reflective reflector, and an open cavity is engineered on the HCC. After the open cavity is filled with the liquid analyte (e.g., water), the air-liquid interface acts as a highly reflective reflector due to large impedance mismatch. As a result, an HCC-FPR is formed by the two highly reflective reflectors, i.e., the air-liquid interface and the metal disk. We measured the room temperature dielectric constant for ethanol/water mixtures with different concentrations using this homemade HCC-FPR. Monitoring the evaporation of ethanol in ethanol/water mixtures was also conducted to demonstrate the ability of the sensor for continuously monitoring the change in dielectric constant. The results revealed that the HCC-FPR could be a promising evaporation rate detection platform with high performance. Due to its great advantages, such as high robustness, simple configuration, and ease of fabrication, the novel HCC-FPR based liquid dielectric constant sensor is believed to be of high interest in various fields

Coaxial cable ring resonator based on pair sided coaxial cable Bragg grating coupler for sensing appllication

“Coaxial cable based devices, such as coaxial cable Bragg grating (CCBG), coiled coaxial cable resonator have been demonstrated for sensing applications to address the challenges faced by fiber optic sensors (e.g., large strain survivability, installation). Inspired by the fiber ring resonator (FRR), coaxial cable based ring resonator (CCRR) is reported in this thesis. The device mainly formed by a homemade coaxial cable Bragg grating (CCBG) pair based side coupler. Comparing to the commercial coupler, CCBG-SC improves the flexibility of the device for sensing applications. The coupling frequency of the CCBG-based coupler can be modified by changing the grating length and period of the CCBG, providing a more convenient method to realize critical coupling in the CCRR. Resonances were observed at discrete frequencies in transmission spectrum. A high Q-factor could be achieved by varying the length of the loop. The basic principles were investigated to understand the device physics. The S-parameter of CCBG was calculated using finite element method. Full wave electromagnetic software was employed to simulate and demonstrate the concept. S-parameters of CCRR is calculated by an estimated algorithm. The device was tested for its potentially large strain application. The temperature responses were also investigated to study the influence of their crosstalk. CCRR sensing system offers improvements of performance and largely reduces costs by minimizing the requirements for insulation”—Abstract, page iv

Development and evaluation of a coaxial cable sensing system for CO₂ sequestration wellbore integrity monitoring

Downhole monitoring plays a crucial part in geological carbon dioxide (2) sequestration. Various downhole monitoring technologies have been explored and applied, but they are either expensive or have system longevity issues. To address this issue, a robust and cost-effective downhole sensing system based on distributed coaxial cable sensors is developed and evaluated in laboratory, and a numerical simulation with staged finite element model is conducted to study the feasibility of using the coaxial cable sensing system for monitoring and evaluation of wellbore stability during CO2 injection. The real-time distributed sensing system is composed of Fabry-Perot interferometer based coaxial cable temperature and strain sensors. A high pressure high temperature (HPHT) sensor testing system is developed to study the temperature sensor accuracy, sensitivity, stability, hysteresis, and crosstalk effect under simulated downhole conditions. A lab-scale prototype of the casing imager based on strain sensors is developed and tested in laboratory to prove its real-time monitoring ability in casing axial compression, radial expansion, bending, and ovalization. A parametric study with staged finite element analysis is conducted to study the feasibility of using the casing imager in wellbore stability monitoring and evaluation during CO2 injection in the Weyburn field. The system is proved to perform under 1,000 psiaand 110 ⁰C, with real-time monitoring ability in casing axial compression, radial expansion, bending, and ovalization. And the parametric study with finite element model not only proved the feasibility of using the system for wellbore stability monitoring and evaluation during CO2 injection in the Weyburn field, but also provided insight into the best cementing practice and injection conditions as guidance to avoid leakage risks in a geologic CO2 sequestration project --Abstract, page 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

Evaluation and Application of a High-Resolution Fiber-Optic Strain Sensor

We evaluated the measuring capabilities of a high-resolution fiber-optic strain sensor based on a miniaturized Fabry-Perot interferometer (FPI). We designed an opto-mechanical setup to experimentally evaluate theoretical analyses and verify its reliability. High-resolutions are needed to testing performance of new designs. Sensors must not alter design intent and be immune to electromagnetic interference. After calibration, results indicate a gage factor on the order of 40mV/236229, proving the capabilities of the fiber FPI for high-resolution measurements of strain. The fiber FPI has been proven to provide high-resolution measurements in conditions where conventional strain sensors may fail to provide reliable results

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described

Evaluation of ceramic coaxial cable sensors for long-term in-situ monitoring of geologic CO₂ injection and storage

Monitoring is an essential component of CO₂ injection and storage projects in order to manage the injection process, identify leakage risks, provide early failure warnings, determine the movement of CO₂ plume and provide input into reservoir models. In-situ monitoring provides critical and direct data points that can be used to fulfill the above objectives. However, downhole sensors that can withstand the harsh conditions and run over decades of the project life cycle remain unavailable. A new idea of ceramic coaxial cable temperature, pressure and strain sensor has recently been put forward and the sensors are under development. A high pressure high temperature (HPHT) testing system was developed in order to characterize the novel ceramic coaxial cable sensors under combined temperature, pressure and strain conditions with water, oil, brine, CO₂ and CO₂ brine mixture. Tests were conducted on a semi-rigid coaxial cable temperature sensor under combined temperature and pressure conditions with water. Besides, a preliminary test was conducted on the ceramic coaxial cable pressure sensor model to help with the design of the sensor. The semi-rigid coaxial cable temperature sensor showed an excellent ability of recording the actual temperature of hydraulic water with a constant resolution of ± 1 ºC. The preliminary test on ceramic coaxial cable pressure sensor model decided stainless steel as the proper material for sensor jacket. --Abstract, page iii