We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33–1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10⁻³ refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41–1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost.

A theoretical analysis for a new high-sensitivity pressure sensor based on the surface plasmon resonance (SPR) phenomenon is presented. The device consists a thin metal film deposited on the cladding of a U-shaped optical fiber probe embedded in a silicon rubber block. When the block is under pressure, the bending radius will vary and consequently a shift on the SPR wavelength can be noticed and converted to pressure units. Theoretical simulations using the transfer matrix formalism and the N-layer U-shaped fiber model were developed and implemented for three different metals: gold, copper, and silver. A resolution of 5.9 × 10 ^-4 , 6.3 × 10 ^-4 , and 1.3 × 10 ^-3 kPa can be expected for gold, copper, and silver, respectively for a working range up to 0.12 MPa. The proposed structure reveals to be suitable to high-sensitivity pressure measurements, including industrial operating machinery and R&D applications.

The last few years have seen a great number of announcements and projections on cities of the future, where technological interconnected metering infrastructure is the main smart-grid unit, promoting higher sustainability due to its more efficient management capability. The water supply network is one of the grids that has been given additional attention due to the problem of waste caused by water leakage, usually requiring rapid detection for fast intervention to prevent high costs. With centralised information coming from the grid, like the measurement of pressure and flow, it is revealed that anomaly detection could be an important tool for quick automatic detection without needing permanent analysis by a human operator. However, there is a need for a more robust approach, especially when noisy data are present. In this paper, we propose the implementation of a new approach based on a hybrid expectation maximization (EM) Gaussian model combined with a t -distribution mixture. This approach is compared to both a pure EM Gaussian mixture model and a t -distribution mixture model that can use labelled data or not. Each EM algorithm was applied to real data acquired from a water supply grid with the aim of automatically detecting water leaks. Using the newly developed approach, the results show that detection is both possible and more accurate for this type of database.

An in-line and real time chromatic sensor for liquids based on plastic optical fiber was developed. It uses an air gap, fiber to fiber, transmission principle. Its dependency to turbidity and refractive index is studied and characterized. This information will provide the necessary knowledge for future implementation of more complex auto-compensations routines. Due to the predictable behavior of the sensor to variations of turbidity and refractive index, it is shown that a posterior compensation could be applied for the discrimination of color. The real-time color sensor can be used in different turbid liquids and contain different refractive indices.