Distributed Sensing Network Enabled by High-Scattering MgO-Doped Optical Fibers for 3D Temperature Monitoring of Thermal Ablation in Liver Phantom

Thermal ablation is achieved by delivering heat directly to tissue through a minimally invasive applicator. The therapy requires a temperature control between 50–100 °C since the mortality of the tumor is directly connected with the thermal dosimetry. Existing temperature monitoring techniques have limitations such as single-point monitoring, require costly equipment, and expose patients to X-ray radiation. Therefore, it is important to explore an alternative sensing solution, which can accurately monitor temperature over the whole ablated region. The work aims to propose a distributed fiber optic sensor as a potential candidate for this application due to the small size, high resolution, bio-compatibility, and temperature sensitivity of the optical fibers. The working principle is based on spatial multiplexing of optical fibers to achieve 3D temperature monitoring. The multiplexing is achieved by high-scattering, nanoparticle-doped fibers as sensing fibers, which are spatially separated by lower-scattering level of single-mode fibers. The setup, consisting of twelve sensing fibers, monitors tissue of 16 mm × 16 mm × 25 mm in size exposed to a gold nanoparticle-mediated microwave ablation. The results provide real-time 3D thermal maps of the whole ablated region with a high resolution. The setup allows for identification of the asymmetry in the temperature distribution over the tissue and adjustment of the applicator to follow the allowed temperature limits.

An Application of BOTDR to the Measurement of the Curing of a Bored Pile

In order to study the deformation of a bored pile during concrete curing, it is necessary to monitor the strain of the pile. In this paper, Brillouin optical time domain reflectometer (BOTDR) technology is used to monitor the pile strain during concrete curing, and reliable monitoring data are obtained. These data provide a basis for the study of pile deformation and pile–soil interaction during curing of bored cast-in-place piles. Compared with the traditional point strain sensor, the distributed fiber optic sensor is simple in layout and highly accurate; it can fully reflect the strain changes of the pile; the experiment also shows the advantages of distributed fiber optic sensing technology over the traditional point monitoring method.

ANALYTICAL MODEL OF CONVECTIVE TEMPERATURE RECOVERY IN SHUT-IN WELL

Thermometry is the most informative method in the complex of field geophysical research. The method is applied at all stages of the well’s life. Modern technologies for recording the temperature in the well, for example, using a distributed fiber-optic sensor, allow continuous research, and in particular, to carry out temperature probing of the developed formations. Temperature sensing data can be used as an additional (alternative to pressure) independent source of information on reservoir properties. To assess the parametric sensitivity of the temperature field in the well and to solve inverse problems of thermometry, mathematical models are needed to describe the thermohydrodynamic processes both in the reservoir and in the well. This article is devoted to the development of an analytical model describing the change in temperature and pressure in the reservoir after a well shut-in, taking into account some approximations: zero compressibility of the reservoir, fluid and thermal conductivity. The pressure distribution in the reservoir is found from the solution of the piezoconductivity equation. And the temperature distribution from the heat flow equation. The method of characteristics was used for the solution. The results of comparison of analytical and numerical solutions for temperature changes in a shut-in well are presented. It follows from the results obtained that the temperature after well shut-in is sensitive to the size of the near-wellbore zone with altered permeability and to the distribution of permeability in the formation. The proposed analytical solution can be used in thermosimulators to solve inverse problems in order to estimate the parameters of the near-wellbore formation zone based on actual measurements of unsteady temperature in the wellbore of production wells, as well as for planning production geophysical studies using the thermometry method.

Stretchable distributed fiber-optic sensors

Silica-based distributed fiber-optic sensor (DFOS) systems have been a powerful tool for sensing strain, pressure, vibration, acceleration, temperature, and humidity in inextensible structures. DFOS systems, however, are incompatible with the large strains associated with soft robotics and stretchable electronics. We develop a sensor composed of parallel assemblies of elastomeric lightguides that incorporate continuum or discrete chromatic patterns. By exploiting a combination of frustrated total internal reflection and absorption, stretchable DFOSs can distinguish and measure the locations, magnitudes, and modes (stretch, bend, or press) of mechanical deformation. We further demonstrate multilocation decoupling and multimodal deformation decoupling through a stretchable DFOS–integrated wireless glove that can reconfigure all types of finger joint movements and external presses simultaneously, with only a single sensor in real time.

Global Temperature Sensing for an Operating Power Transformer Based on Raman Scattering

Traditional monitoring methods cannot obtain the overall thermal information for power transformers. To solve this problem, a distributed fiber optic sensor (DFOS) was creatively applied inside an operating 35 kV power transformer by highly integrating with the electromagnetic wires. Then, the transformer prototype with totally global sensing capability was successfully developed and it was qualified for power grid application through the strict ex-factory tests. The as designed optical fiber sensor works stably all the time with a temperature accuracy of ±0.2 °C and spatial positioning accuracy of 0.8 m. Based on the obtained internal temperature distribution, Gaussian convolution was further applied for the signal processing and hereby, the hotspots for all the windings and iron cores could be accurately traced. The hottest points were located at 89.1% (55 °C) of the high voltage winding height and 89.7% (77.5 °C) of the low voltage winding height. The actual precise hotspot location corrected the traditional cognition on the transformer windings and it would serve as an essential reference for the manufactures. This new nondestructive internal sensing and condition monitoring method also exhibits a promising future for the DFOS applying in the high-voltage electrical apparatus industry.