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Purpose The purpose of this study is to investigate the utility of carbon black containing coating formulations that are conventionally used for pigment printing of textiles in fabricating electrically heated fabrics. Design/methodology/approach Specifically, electrical and thermal characterisation of the coating system was carried out to establish the feasibility of the system for use in the manufacturing of flexible heating elements on textile substrates. The coating formulations were applied via a simple padding technique followed by stitching the electrodes using a conductive yarn. Findings The heating elements of different sizes thus produced showed Ohmic behaviour as a resistor and attained a targeted temperature difference of up to 40°C within the applied voltage range. A prototype heater was also produced, and thermography results showed uniform heating and cooling of the heater that was incorporated into a jacket. Originality/value The proposed method is envisaged to be very practical for the realisation of completely textile-based heating elements of different shapes and sizes. Furthermore, the proposed manufacturing method can be used to convert conventional ready-made articles of clothing into heated textiles for various applications.

peer-reviewed In this work, the digital matched filtering (DMF), a signal processing technique, has been proposed to identify the multiple peak wavelengths, more accurately from reflection spectra of etched few-mode fibre Bragg grating (FM-FBG) sensor. The etched FM-FBG has been fabricated and its intrinsic property of having different sensitivities for different reflection peaks in spectrum has been used for sensing the multiple parameters, such as temperature and refractive index of the ambient environment. The experimental characterization of the fabricated etched FM-FBG sensor has been carried out by using six samples of standard sodium chloride (NaCl(aq)) solutions with refractive indices (RIs) ranging from 1.3159 to 1.3375 at 24 °C temperature. The reflection spectra have been acquired for each sample by varying the temperature from 24 °C to 80 °C. The temperature and RI sensitivities have been investigated from the acquired spectra by using digital matched filter (DMF). The obtained sensor results have been compared with conventional peak detection (CPD) method results for the same spectra. It has been observed that the results obtained by DMF technique are closer to the reference sensor values and has shown more accuracy than the results obtained by CPD technique. It has been shown that the DMF has better performance in terms of the accuracy of measured results than that of CPD. In addition, to eliminate the effect of cross sensitivity issue of the sensor, the 3×3 order characteristic matrix has been used. Hence, the etched FM-FBG can be used as multi-parameter measurements with better performance using DMF technique.

In this paper, the surface roughness characteristic of D-shaped optical fibre sensors with its effects on the sensitivity has been studied. The ULTRAPOL end and edge polishing system was used with some modifications to fabricate the D-shaped sensors with planar sensing zone from the single-mode optical fibres. The mean surface roughness of 343, 96, 25 and 9 nm was estimated at the sensing zone of the D-shaped sensors which were sequentially polished with 30, 9, 3 and 0.5 µm grit size polishing films, respectively. From the experimental results, it has been observed that surface roughness of the sensing zone does not exhibit the significant effects on the output signal strength, whereas the sensitivity of the D-shaped sensors nonlinearly related with the surface roughness of the sensing zone. The designed D-shaped optical fibre sensors have potential applications in biomedical and chemical industries.

The present review provides an overview of the current status and future perspectives of one of the smart manufacturing techniques of Industry 4.0, laser transmission welding (LTW) of semi-crystalline (SC) polymers and their composites. It is one of the most versatile techniques used to join polymeric components with varying thickness and configuration using a laser source. This article focuses on various parameters and phenomena such as inter-diffusion and microstructural changes that occur due to the laser interaction with SC polymers (specifically polypropylene). The effect of carbon black (size, shape, structure, thermal conductivity, dispersion, distribution, etc.) in the laser absorptive part and nucleating agent in the laser transmissive part and its processing conditions impacting the weld strength is discussed in detail. Among the laser parameters, laser power, scanning speed and clamping pressure are considered to be the most critical. This review also highlights innovative ideas such as incorporating metal as an absorber in the laser absorptive part, hybrid carbon black, dual clamping device, and an increasing number of scans and patterns. Finally, there is presented an overview of the essential characterisation techniques that help to determine the weld quality. This review demonstrates that LTW has excellent potential in polymer joining applications and the challenges including the cost-effectiveness, innovative ideas to provide state-of-the-art design and fabrication of complex products in a wide range of applications. This work will be of keen interest to other researchers and practitioners who are involved in the welding of polymers.

peer-reviewed A novel Fabry-Perot sensor, comprised a glass sphere bonded to a capillary and singlemode fiber, is proposed for refractive index sensing. It is characterized in air, water, ethanol, isopropanol, and glycerol. © 2020 The Author(s)

We report a U-bend plastic optical fiber (POF) sensor for measuring ultralow concentration of ethanol corresponding to the initial bioethanol production rate by cyanobacteria, i.e., 0.1–0.5 gL $^{\mathrm {\mathbf {-1}}}$ day $^{\mathrm {\mathbf {-1}}}$ . This production rate corresponds to 0.00499–0.0499 %wt of ethanol in total solution in terms of weight percent concentration. Refractive indices for these minute ethanol concentration values are not available in the literature hence mathematical estimation of the refractive indices for the ethanol-water solutions in this concentration range is demonstrated. The sensing principle is based on optical fiber-based evanescent wave absorption. Parameters affecting the response of an evanescent wave absorption sensor are analyzed for the intended concentration range of ethanol. Experimental results using the U-bend evanescent wave POF sensor are also presented for ethanol-water solutions having refractive indices corresponding to the bioethanol production rate. The excellent repeatability of the measurement is established and these real-time measurements show that sensor has a sensitivity of 817.76 O.D/RIU (O.D refers to optical density, unit of absorbance) with a 99.76% linearity. The limit of detection of the sensor is $9.2\times 10^{\mathrm {\mathbf {-7}}}$ RIU. It is also proved using refractive index calculations of ethanol-water solutions that the sensor exhibits a resolution of $10^{\mathrm {\mathbf {-7}}}$ RIU. The sensor of this investigation, therefore, represents a potential solution for online and real-time monitoring of the production of biofuels even at the very low-level initial concentration of product.

peer-reviewed This paper explicates the design of an ultra-thin beam splitter based on phase gradient metasurfaces using amorphous silicon hydrogenated (a-Si:H) nano cylinders for the visible frequency of 474 THz. The a-Si:H nano cylinders exhibit low losses in the visible regime compared to standard a-Si, and small size due to reduced aspect ratio compared to other highly efficient materials such as TiO2 and GaN. In the proposed design, incident wave at a single operating frequency of 474 THz in visible regime is split into two different directions according to the generalized Snell’s law of refraction. The angles of refracted waves are controlled by choosing different phase gradients. Based on this concept, three metasurfaces are designed and simulated using finite difference time domain numerical method for various split angles (31.8 , −31.8 , (−44.6 , 31.8 and (−44.6 , 20.5°)

The following presents a comparison of an extrinsic Fabry–Perot interferometer (EFPI)-based temperature sensor, constructed using a novel diaphragm manufacturing technique, with a reference all-glass EFPI temperature sensor. The novel diaphragm was manufactured using polyvinyl alcohol (PVA). The novel sensor fabrication involved fusing a single-mode fibre (SMF) to a length of fused quartz capillary, which has an inner diameter of 132 μm and a 220 μm outer diameter. The capillary was subsequently polished until the distal face of the capillary extended approximately 60 μm beyond that of the single mode fibre. Upon completion of polishing, the assembly is immersed in a solution of PVA. Controlled extraction resulted in creation of a thin diaphragm while simultaneously applying a protective coating to the fusion point of the SMF and capillary. The EFPI sensor is subsequently sealed in a second fluid-filled capillary, thereby creating a novel temperature sensor structure. Both temperature sensors were placed in a thermogravimetric analyser and heated from an indicated 30 °C to 100 °C to qualitatively compare sensitivities. Initial results indicated that the novel manufacturing technique both expedited production and produces a more sensitive sensor when compared to an all-glass construction.

Metasurfaces, the two-dimensional (2D) metamaterials, facilitate the implementation of abrupt phase discontinuities using an array of ultrathin and subwavelength features. These metasurfaces are considered as one of the propitious candidates for realization and development of miniaturized, surface-confined, and flat optical devices. This is because of their unprecedented capabilities to engineer the wavefronts of electromagnetic waves in reflection or transmission mode. The transmission-type metasurfaces are indispensable as the majority of optical devices operate in transmission mode. Along with other innovative applications, previous research has shown that Optical-Vortex (OV) generators based on transmission-type plasmonic metasurfaces overcome the limitations imposed by conventional OV generators. However, significant ohmic losses and the strong dispersion hampered the performance and their integration with state-of-the-art technologies. Therefore, a high contrast all-dielectric metasurface provides a compact and versatile platform to realize the OV generation. The design of this type of metasurfaces relies on the concept of Pancharatnam-Berry (PB) phase aiming to achieve a complete 2π phase control of a spin-inverted transmitted wave. Here, in this paper, we present an ultrathin, highly efficient, all-dielectric metasurface comprising nano-structured silicon on a quartz substrate. With the help of a parameter-sweep optimization, a nanoscale spatial resolution is achieved with a cross-polarized transmission efficiency as high as 95.6% at an operational wavelength of 1.55 µm. Significantly high cross-polarized transmission efficiency has been achieved due to the excitation of electric quadrupole resonances with a very high magnitude. The highly efficient control over the phase has enabled a riveting optical phenomenon. Specifically, the phase profiles of two distinct optical devices, a lens and Spiral-Phase-Plate (SPP), can be merged together, thus producing a highly Focused-Optical-Vortex (FOV) with a maximum focusing efficiency of 75.3%.

In this paper, the tilted fiber Bragg grating is proposed as a corrosion sensor and experimentally demonstrated for measuring and evaluating corrosion of steel rebars in wet conditions. To expedite the corrosion process, the impressed current technique was used to achieve a 28.9% mass loss in the rebar for a total time of 24 h. It is observed that the cladding resonant wavelengths red-shift during the corrosion process and the wavelength shifts are greater for higher order resonances. The proposed technique can be used for monitoring steel corrosion.

In this paper, we propose a Photonic Crystal Fiber (PCF)-cavity fiber Bragg grating (FBG) Fabry-Perot resonator for simultaneous sensing of temperature and pressure. The proposed device is constructed by splicing a 1.5-mm long PCF segment between two identical saturated FBGs written in SMF-28 forming an FBG-PCF-FBG configuration. As a result, a resonance dip is created within the Bragg reflection curve. Taking advantage of the difference in pressure sensitivities between the two types of fiber, the discriminative measurement of pressure and temperature can be achieved from the shifts of the resonance wavelength and band-edge wavelength. In addition, the same temperature sensitivity of PCF and SMF-28 provides the convenience of eliminating the temperature variable and achieving temperature insensitive pressure measurement.

Biofuel processing applications require concentration measurement of bio-ethanol during its evolution by algae in a proprietary chemical process to optimize the chemical parameters and the resulting yield of bio-ethanol. The production rate of bio-ethanol is initially very low with correspondingly minute concentration changes. This study presents a highly sensitive U-bend evanescent wave plastic optical fibre sensor for ethanol concentration measurement in water corresponding to the production rate limit of bio-ethanol by algae (cyanobacteria) i.e. 0.1–0.5g per liter per day or 0.0126%v/v–0.0633%v/v in terms of percent volume concentration of a solution or %volume/volume concentration. The sensor was fabricated using low cost, large core (1000μm diameter) plastic optical fibre (POF) and investigated in the broadband visible light spectrum (VIS) and specifically at 630nm wavelength. Real-time measurements show that the sensor provides a significant response in the range of 0.00633%v/v to 0.0633%v/v concentration of ethanol in water which corresponds to detection of change in refractive index as low as 10−7. Moreover, sensitivity of sensor was derived for the above range as 0.6448 O.D/%v/v with 97.14% of linearity in results at 630nm wavelength, here O.D refers to optical density — unit of absorbance. It indicates that the proposed sensor represents a viable solution for real time and very low level concentration sensing in biofuel processing applications.

An optimized study of biconical tapered multi-mode plastic optical fiber sensor for concentration sensing of ethanol (C2H5OH) is presented. The sensitivity is enhanced through V-number matching as well as by optimizing the taper radius and taper length. The ray-tracing method is used to analyze the evanescent wave penetration depth (EWPD). The theoretical analysis and experimental results are used to optimize the taper ratio and taper length for the achievement of high EWPD and high sensitivity. The analysis indicates that the sensitivity of tapered fiber sensor can be improved by decreasing the taper ratio with simultaneous increase in the taper length. The highest sensitivity of 1.527 mV/% is achieved from the tapered fiber with a taper ratio of 0.27 and taper length of 8 cm. The proposed parametric optimized tapered fiber sensor can detect the change in concentration of C2H5OH as small as 6.55 × 10-3.

Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed.

This paper proposes an approach based on an optical imaging technique for the period measurement of fiber Bragg gratings (FBG). The simple, direct technique involves a differential interface contrast (DIC) microscope and a high-resolution CCD camera. Image processing is performed on the microscope images to obtain low-noise grating profiles and then the grating periods. Adopting a large image sample size in the image processing can reduce uncertainty. During the investigation, FBGs of different grating periods are fabricated by prestraining the photosensitive fibers during the UV-writing process. A good linearity between the measured Bragg wavelengths and grating periods is observed and the measured strain—optics coefficient was found to be in agreement with reported literature.

In this study, a technique for measuring the grating visibility of the fiber Bragg grating (FBG) based on bent-spectral analysis is proposed. From varying ac and dc coupling coefficients at different bending radii, the grating visibility is estimated with the aid of a simple mathematical model. The investigation begins with the estimation of the grating visibility from the transmission spectra of the FBG during the inscription process. After that, the FBGs are subjected to a bending test with reducing radii, and again the transmission spectra are recorded. It is shown that the estimated grating visibility is in agreement with the result determined from the earlier inscription process.

This Letter presents a simple mathematical model developed from coupled-mode theory to describe the relationship between Bragg transmission loss (BTL), grating length, coupling coefficients, and bending loss in a bent fiber Bragg grating. In our investigation, the finding indicates that the decrement of BTL can be attributed to the increasing bending loss and degradation of both dc and ac coupling coefficients as the bending radius decreases. Besides, the center wavelength shifts as a result of coupling coefficients degradation. The validity of the proposed model is supported by experimental result.