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In this paper, a photonic skin sensor based on a balloon-shaped optical fiber structure cascading a Fiber Bragg Grating (FBG) is proposed, which can simultaneously sense pressure and temperature. When the photonic skin feels pressure, the built-in polymer micro-cap is squeezed, causing a change in the radius of the balloon-shaped structure. At the same time, the capillary-enclosed FBG can be used for temperature compensation. The pressure sensitivity of the photon skin sensor can reach 6.556 nm/mN in the range of 0-0.5 mN and the temperature sensitivity can reach -0.192 nm/°C in the range of 30-50 °C. The demodulation of the dual parameter matrix shows that the error rates of pressure and temperature measurements are less than 0.5% and 2.01%, respectively. On this basis, the sensor is applied to robotic arm-assisted puncture experiment detection, and the five states of the puncture process are analyzed. Based on the backpropagation (BP) neural network for repeated training, the results show that its accuracy remains at 98.7%, indicating that the sensor has good robustness. The development of this sensor shows application potential in the field of robotic intelligent skin in the future.

In this work, we demonstrate the usability of a fully-2D-material based device consisting of MoS2/WSe2 heterojunction encapsulated by hBN and contacted by graphene as temperature sensor for linear temperature measurement at cryogenic temperatures. More precisely, temperatures in the range of 10 K up to 300 K were applied to the device while recording the I-V characteristics. In contrast to the classical expectation, the main current flows through the device when it is reversely biased. We ascribe this to a combination of drift-diffusion and band-to-band tunneling, while for very low temperatures (T $ < $ 100 K), variable-range hopping or trap-assisted tunneling seems dominant. In case of forward bias, the Schottky contact on the WSe2-anode hinders the charge transport in the voltage range of interest. Additionally, we obtained the activation energy of the saturation current in reverse direction in an Arrhenius diagram. Depending on the bias level, it varies between 100 meV and 300 meV, which may be related to the energy barrier caused by interface traps, generation centers between both semiconducting 2D materials, and the band-to-band tunneling. Furthermore, we investigated the temperature-sensor performance by applying a constant current to the device and measuring the voltage drop at different temperatures. In the range of 40 K up to 300 K, the sensitivity of the sensor is $\sim 2$ mV/K, which is comparable to Si devices, while the linearity is still lower $(R^{2}~\sim ~0.94$ ). On the other hand, the demonstrated device consists only of 2D materials and is, thus, substrate independent, very thin, and can potentially be fabricated on a fully flexible substrate in a low-cost process.

Sensitivity (${S}$) and drive mode are crucial issues for the vertical metal-oxide-semiconductor (MOS) type diode applied in temperature sensing. In this study, experimentally, we indicated that the ${S}$ values of the ${\mathrm {Ni}}_{(\text {50 nm})}$ - ${\mathrm {Au}}_{(\text {100 nm})}$ /Ga2O3/ ${p}$ -Si vertical MOS type diode, using the measured capacitance–voltage (${C}_{\text {m}}$ – ${V}$) outputs, are obtained with a novel drive mode. We applied the constant capacitance mode to drive the silicon thermo-diodes as well as constant current mode, and constant voltage mode, which are known as two different methods in the literature. Meanwhile, the ${S}$ value is 21.2 mV/K at 1 nF. This value is the highest value proven in the literature excepting the cryogenic temperature region, and near room temperature. This study provided an original structure for the silicon thermo-diodes and a novel way to drive them. [ABSTRACT FROM AUTHOR]

We study the influence of thermal expansion and thermo-optic effect on optical properties of finite 1-D three-periodic photonic crystals (PCs) of structure [(ab) $^{N}$ (cd) $^{M}$ ] $^{K}$ composed of four different nonmagnetic dielectric materials ${a}$ , ${b}$ , ${c}$ , and ${d}$. We calculate temperature dependencies and incidence angle dependencies of the transmittivity of TE- and TM-polarized electromagnetic waves, as well as the distribution of energy within these structures. The optimal adjustment of PC bandgap centers for obtaining the desired transmission characteristics of the temperature-governed photonic bandgap structures is found, and the peculiarities of the energy distributions inside the photonic system are investigated. We propose a sensitive thermal polarization TE/TM switch as well as angular and temperature sensors working at the intraband-mode frequencies exploiting temperature effects. [ABSTRACT FROM AUTHOR]

In this work, the transmission characteristic of a single mode fiber-silica capillary-single mode fiber (SMF-Capillary-SMF) structure is modified by introducing liquids inside and outside the silica capillary. The anti-resonant reflecting guidance mechanism in the silica capillary is influenced by the presence of the liquids. By immersing a section of liquid-filled SMF-Capillary-SMF structure into liquids, both the resonant wavelength and transmission intensity are altered due to a liquid-modified resonant condition. Temperature change will lead to the refractive index (RI) variation of liquids, causing the resonant wavelength to shift. Experimental results indicate that the temperature sensitivity is dependent on the RI value of the liquids, and the liquid temperature sensitivity of 2.99 nm/°C is experimentally achieved in the temperature range of 25 °C-60 °C when the liquid RI is 1.39. On the other hand, the transmission intensity at resonant wavelength, which is determined by the reflectivity at the inner and outer surfaces of the ring cladding, can be affected when the RI of the ambient liquid changes. The intensity at resonant wavelength increases as the ambient RI rises, and the RI sensitivity varies from 240 dB/RIU to 60 dB/RIU in the RI range of 1.31 to 1.39. Such a device is simple and easy to fabricate, which can find wide applications in liquid environments like biochemical and pharmacy industries.

A dual cross-axis interference polarization-maintaining fiber interferometer (DCAI-PMFI) for simultaneous measurement of strain and temperature is proposed. By using the cross-interference of the fast and slow axes in the polarization-maintaining fiber interferometer with dual axis independent detection, common path dual cross-axis interferometers (DCAIs) are realized. Since the fast and slow axes are different in refractive index and thermo-optic coefficient, the DCAIs have different phase sensitivities to strain and temperature. A sensitivity matrix for simultaneous measurement of temperature and strain is constructed. The temperature phase sensitivities can be adjusted by changing the length ratio of two arms of the DCAI-PMFI to optimize the decoupling performance of temperature and strain. It is found that the temperature sensitivities are opposite signs when the length ratio of two arms is between the ratio of the temperature optical path coefficients of the fast and slow axis and its reciprocal, and the best measurement resolution can be obtained when two arms are equal in length. In the experimental setup of DCAI-PMFI with equal length of two arms, the strain sensitivities are 1.5648 rad/μϵ and 1.5790 rad/μϵ respectively at 0.35m strain sensing fiber, the temperature sensitivities are −25.4990 rad/°C and 24.6000 rad/°C respectively at 10m arm length, the resolutions are 2.4 μϵ in strain and 0.02°C in temperature. The experimental results show that the proposed sensor can solve the crosstalk between strain and temperature of interferometer, and can be applied to various interferometric fiber sensors without changing the topology. [ABSTRACT FROM AUTHOR]

We proposed a simple and compact Fabry-Perot (FP) sensor for simultaneous measurement of water pressure and temperature, composed of a standard fiber ferrule connector/flat contact (FC/FC) connector and aluminum foil attached to a thin metal plate. Two dips in the interference spectrum are selected to illustrate the response of the FP sensor to the water pressure and temperature, we can obtain the simultaneous measurement via a method of sensitivity coefficient matrix. Experimental results show the maximum sensitivity of −2.948 nm/kPa for water pressure sensing in 0~9 kPa and 1.119nm/°C for temperature sensing in 33~45 °C. In addition, the dual-parameter sensor has the advantages of compactness, stability, simple production, small size, and high sensitivity, making it suitable for a wide range of practical applications. [ABSTRACT FROM AUTHOR]

In the field of physical oceanography, the temperature and pressure of seawater are important fundamental parameters. In order to realize the simultaneous measurement of the temperature and pressure in seawater, a reflective optical fiber sensor based on polydimethylsiloxane (PDMS)-sealed optical microfiber coupler combined with a sagnac loop (OMCSL) is proposed. Benefiting from the high thermo-optical coefficient and large elasticity of PDMS, and the large-scale swift field transmission characteristics of optical microfiber coupler (OMC), the sensitivity and structural stability of our sensor is largely improved. The response performance of the sensor is further analyzed by numerical simulation calculations and theoretical modeling. Experimental results show that the temperature and pressure sensitivity of the sensor could reach −2.133 nm/°C and 3.416 nm/Mpa, respectively, about one order higher than that of bare fiber OMCSL. Furthermore, via inversely calculating the cross-sensitivity matrix, the temperature and pressure sensing can be demodulated simultaneously, and the average errors of the preliminary experimental settlements are 1.61% and 5.02%, respectively. Due to the merits of compact structure, easy fabrication, high sensitivity, fast response speed and high stability, the basic performance of this dual parametric sensor is comparable to the existing electrical temperature-depth (TD) sensor, which is expected to meet the practical application requirements of marine environmental monitoring and ocean dynamics research. [ABSTRACT FROM AUTHOR]

A distributed temperature monitoring inside a cavity of ytterbium DFB and holmium fiber lasers has been demonstrated with a spatial resolution of 1 and 5 mm, respectively, for the first time to the best of our knowledge. For this, we use an optical backscatter reflectometer, which measures intracore temperature, and compare it with the data of an IR thermographic camera, which measures temperature from the surface of a fiber. In the case of holmium fiber laser pumped at a wavelength of 1125 nm with a power of 6 W, the maximum temperature variation along the ∼3-m active fiber reaches ∼60 °C. In the case of ytterbium DFB laser, we observe a strong inhomogeneity of the temperature along the DFB cavity, which leads to a significant decrease in the lasing efficiency. When pumped by a single-mode laser diode at a wavelength of 976 nm with a power of up to 526 mW, the maximum temperature difference reaches 37 °C for the 37-mm DBF cavity. [ABSTRACT FROM AUTHOR]

A twin-core sensor with high birefringence employing a photonic crystal fiber (PCF) is presented for simulated temperature measurements based on surface plasmon resonance (SPR). The internal wall of the central hole of the PCF is plated with gold and coated with graphene oxide (Au-GO) to develop an SPR sensing channel. The results of a numerical analysis with COMSOL Multiphysics show that the birefringence of this sensing structure can reach 0.0052. In addition, an average sensitivity of -12.695 nm/ °C can be achieved in the range of 0 °C~80 °C. Compared with uncoated GO sensors and existing sensing units, this sensor shows improved stability, sensitivity and birefringence.

The emergence of planar metamaterials (PrMMs) has opened a gateway to unprecedented electromagnetic (EM) properties and functionality unattainable from naturally occurring materials, thus enabling a family of PrMM based devices. In this paper, a novel class of superconducting (SC) PrMM is presented and a series of THz reflectance spectral responses simulations reveals that these SC PrMM structures portend applications in a variety of temperature sensors, thermo-optical modulators, and magnetic switch devices. [ABSTRACT FROM AUTHOR]

In this paper, we proposed an in-fiber Mach-Zehnder temperature sensor based on a dual-core fiber (DCF) in which one core, working as the sensing arm, is suspended in an embedded fluidic channel filled with silicone oil, while the other one, working as the reference arm, locates eccentrically in the DCF. Temperature variations would change the refractive index of silicone oil infiltrated as well as the effective index of the guided mode in the suspended core, thus shifting the interference spectra. Both experiments and numerical simulations were carried out to characterize the sensor. The spectrum shifts measured experimentally agreed well with the theoretical results. Experimental sensitivity of the sensor using a DCF infiltrated with ~20 cm-long silicone oil was found to be as high as −1.42 nm/°, comparable to those of the SPR fiber sensors and other interferometric sensors. The measuring range of the sensor was more than 120°. The proposed sensor could be easily fabricated with good robustness and stability, which makes the sensor promising for applications such as environment and architecture monitoring. [ABSTRACT FROM AUTHOR]

This article presents a new methodology for monitoring next generation SiC mosfet-based converters. The methodology uses the spectral distribution of electroluminescence that is emitted by the body diodes of SiC mosfets and includes information on device current as well as the junction temperature. Intelligent estimation algorithms based on artificial neural networks allow processing the extracted information to separately estimate device current and junction temperature with high bandwidth. The resulting unified monitoring of device current and junction temperature galvanically isolates the sensors via optical guides from the power module. Thus, it can be effectively integrated into future power electronic modules to replace external temperature and current sensors and enable monitoring for safe and reliable long-term operation. Previous publications successfully investigated how either temperature or current information can be extracted from the intensity of the emitted light if the other variable is known. However, they did not aim to extract both variables at the same time from one measurement. This work presents how multiple optical sensors with different wavelength sensitivities and artificial-intelligence techniques can separately extract both variables. The proposed technology is evaluated using an automotive-grade SiC power module. Its utilization for monitoring future SiC-based converters allows reducing converter size and cost while increasing reliability. [ABSTRACT FROM AUTHOR]

Due to the unique optical properties and good thermal stability, GeAsSeTe microstructured optical fiber (MOF) offers tremendous opportunity for applications in mid-infrared range (MIR). In this article, we design a CS2-filled GeAsSeTe MOF whose core, inner and outer cladding adopt Ge15As25Se15Te45, Ge20As20Se17Te43 and Ge20As20Se15Te45 glass, respectively. Highly efficient four-wave mixing (FWM) is realized and ultrabroadband optical parametric gain is obtained. By analyzing the central parametric gain bandwidth change with the temperature variation, this CS2-filled GeAsSeTe MOF is proved to be highly sensitive concerning temperature sensing, the sensitivity being as high as 2.32nm/°C from −80°C to 45°C. Such high temperature sensing property have key prominence for developing optical fiber temperature sensor in MIR region based on FWM. To the best of our knowledge, this is the first study to propose temperature sensing in the MIR by drawing on central parametric gain bandwidth of FWM change in a GeAsSeTe MOF. [ABSTRACT FROM AUTHOR]

Economical sensing and recording of temperature are important in the transportation and management of fragile goods such as medicine, fish/poultry, and other temperature-sensitive items. Existing approaches measure the entire temperature profile using electronic devices running on a continuous power source. This letter presents a simple, intelligent, and battery-free solution for capturing interesting temperature events using the natural thermo-mechanical state of a shape memory alloy (SMA). Our approach utilizes the temperature variation induced irreversible configuration of SMA, which provides a natural ability to capture the temperature history without the need for electronic data logging. In this letter, SMA is used to record the threshold temperature violation event. A prototype antenna is shown to monitor the temperature at 30  $^\circ$ C with a $\pm$ 1  $^\circ$ C error. A difference of 17 dB in frequency response was observed with and without temperature violation. Detailed design and experimental studies have been performed to validate the proposed approach. [ABSTRACT FROM AUTHOR]

Simultaneous measurement of pressure and temperature in seawater is realized based on polydimethylsiloxane (PDMS) sealed microfiber Mach–Zehnder interferometer (MZI). Benefitting from the high thermal-optic coefficient and large elasticity of PDMS, high sensitivity and robust structure can be obtained. In theoretical modeling, significant enhanced pressure response in fiber is observed clearly, and pressure or temperature sensitivities are calculated theoretically. In experiment, PDMS sealed MZI is fabricated by a two-step sealing method. Using this MZI, sensitivity of 13.31 nm/MPa for pressure sensing and −7.41 nm/°C for temperature sensing are demonstrated, respectively, which are about one order higher than bare fiber MZIs (without PDMS sealing). To verify the accuracy of sensor, several tests under arbitrarily pressure and temperature are performed with average errors of 4.38% and 1.44%, respectively. In addition, effects of encapsulation on avoiding cross-sensitivity with salinity, PDMS thickness on pressure sensitivity, response time, repeatability, time stability, and polarization of the sensor are also evaluated by experiment. Sensors demonstrated here show advantages of low cost, simple fabrication, robust and compact structure, high-pressure resistance, high sensitivity, good repeatability, and long-term stability. [ABSTRACT FROM AUTHOR]

Thermal issues seriously restrict the quality, reliability, and lifetime of semiconductor chips. To prevent thermal runaway situations, modern processors deploy numerous on-die thermal sensors to collect temperature information, which is then used to guide dynamic thermal management (DTM) mechanisms. Accurate on-chip temperature information is critical for DTM as temperature overestimation will degrade the performance by an unnecessary invocation of thermal control mechanisms, and underestimation will result in the reliability issues of the systems. In this article, two effective techniques are proposed to achieve an accurate on-chip temperature sensing. The first technique is a synergistic calibration method for forecasting the actual temperatures of noisy thermal sensors. Second, we propose a full thermal characterization technique based on convolutional neural networks (CNNs) to accurately recover the entire thermal maps by using a limited number of thermal sensors. In a realistic scenario, these two techniques can be used in combination to provide a more accurate thermal monitoring. By utilizing the sophisticated infrared imaging setup, the effectiveness of the proposed techniques is validated on a real 45-nm AMD quad-core chip. The simulation results show that the methods achieve significant improvements compared with existing techniques in the literature. The successful implementation of the proposed methods will significantly improve the efficiency of DTM. [ABSTRACT FROM AUTHOR]

A twin-core sensor with high birefringence employing a photonic crystal fiber (PCF) is presented for simulated temperature measurements based on surface plasmon resonance (SPR). The internal wall of the central hole of the PCF is plated with gold and coated with graphene oxide (Au-GO) to develop an SPR sensing channel. The results of a numerical analysis with COMSOL Multiphysics show that the birefringence of this sensing structure can reach 0.0052. In addition, an average sensitivity of −12.695 nm/ °C can be achieved in the range of 0 °C∼80 °C. Compared with uncoated GO sensors and existing sensing units, this sensor shows improved stability, sensitivity and birefringence. [ABSTRACT FROM AUTHOR]

Bond-wire liftoff caused by mechanical stress due to thermal cycling is one of the major failures in power electronic systems. Condition monitoring concepts which allow prediction of these failures are often based on voltage-drop detection and thermal monitoring. However, solutions to determine the junction temperature and semiconductor voltage drop during operation often require additional effort and lead to increased cost. In this article, a direct semiconductor temperature detection method is proposed which is based on instantaneous semiconductor voltage-drop monitoring. A mosfet inverter system, equipped with a digital integration-based instantaneous output voltage measuring circuit, is extended by software to enable instantaneous semiconductor voltage-drop detection. Experimental results demonstrate that the proposed method is feasible for online temperature measurement and detection of increased resistance due to bond-wire faults. The voltage measurement resolution is sufficient for dynamic temperature monitoring, including fundamental frequency temperature cycles at very low frequency. [ABSTRACT FROM AUTHOR]

A compact U-shaped interferometer with high refractive index (RI) sensitivity based on bent single-mode fiber is proposed and demonstrated experimentally. The sensor is fabricated by roasting a balloon-shaped single-mode optical fiber to form a U-shaped modal interferometer. Since the spectral dips show different sensitivities to both the surrounding RI and temperature, simultaneous measurement of RI and temperature can be achieved by demodulating the shifts of the different resonance dips without cascading additional components. The sensitivity of RI reaches up to −1705.66 nm/RIU in the range of 1.3330-1.3581, which is about 10 times as the reported arts. The proposed compact U-shaped interferometer is a potentially effective sensor for chemical and biological applications where an accurate RI measurement of a temperature-changing liquid is required. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the need for real-time temperature monitoring in battery packs used in automotive applications so to have an accurate estimation of battery life and performances. Advanced energy storage management systems should sense operating and ambient temperature of battery packs in order to implement proper strategies to improve the efficiency of charge and discharge processes and to extend battery life. The proposed evaluation technique is based on an innovative and dynamic circuital model, which allows to accurately represent the functioning of a battery pack (in charge and discharge) in the various operating conditions. Each circuital parameter of the model has a well-defined function which highlights its dependence on temperature, state of charge, state of health and number of cells. The model characterization has been made through tests on different battery sets. A climatic chamber has been used to simulate different operating conditions of ambient temperature. The analysis of the parameters evolution in time has led to the identification of an ideal ambient temperature range for the type of batteries under examination in order to improve their performances over time in terms of energy efficiency and extension of useful life. [ABSTRACT FROM AUTHOR]

Rayleigh backscattering-based distributed fiber optic sensing technology is well known and widely used for large-scale structural health monitoring. Inspired by the Rayleigh backscattering-based sensing methodology on an optical fiber, in this paper, we present a sensing concept based on the random inhomogeneities on a coaxial cable. As an analogy of Rayleigh backscattering along an optical fiber length, “backscattering” also exists from a commercial coaxial cable due to its inherent defects along a cable length which induce a local variation (i.e., impedance mismatch). This is because of the irregular microscopic structures of the inner/outer conductors, and the inhomogeneous density or permittivity of the inner dielectrics after the cables are manufactured. The accumulated backscattered signals along the coaxial cable can be obtained using frequency-domain reflectometry. By analyzing the shift in the local backscattered signal, the local environmental perturbations (e.g., local strain or temperature) can be determined, so that truly distributed sensing capability using a coaxial cable can be achieved. To verify the proposed concept, an intact and commercial coaxial cable was demonstrated for distributed temperature sensing. Compared with the existing coaxial cable-based distributed sensing technologies, the proposed sensing concept does not need extra modifications to the coaxial cable and offers a truly distributed sensing capability. [ABSTRACT FROM AUTHOR]

We demonstrate a novel fiber Bragg grating (FBG) temperature sensor based on lead sulfide (PbS)-doped silica optical fiber, prepared by atomic layer deposition (ALD) doping technique. The FBGs are fabricated using the phase mask method, without hydrogen loading. The temperature sensitivity of the FBG-PbS is found to be $\sim$ 19 pm/ $^\circ$ C within 20–150 $^\circ$ C, showing great linearity and repeatability. It is increased by approximately 60% compared to the temperature sensitivity of FBG in standard single mode fiber (SMF). Furthermore, the temperature characteristics of PbS-doped silica optical fiber are investigated. The thermal expansion coefficient and thermal-optic coefficient of PbS-doped silica fiber are 6.3 $\times\; 10^{-7}$ and 1.23 $\times\; 10^{-5}$ / $^\circ$ C, respectively. Moreover, the thermal-optic coefficient value of the PbS-doped silica optical fiber is nearly one order of magnitude higher than that of SMF. Therefore, the FBG based on PbS-doped silica optical fiber appears to be very attractive for the temperature sensing fields. [ABSTRACT FROM AUTHOR]

In this paper, we present the results for thermal gradient measurements using constant period UV written long-period gratings (LPGs) in photosensitive and SMF-28 fibers. We have studied theoretically and experimentally the effect of thermal gradients on the spectrum of LPGs. It has been shown theoretically and confirmed experimentally that thermal gradients lead to changes of the depth of the grating spectrum while changes of the mean temperature cause shifts of the resonance wavelength. Thus, thermal gradients and average temperature can be independently measured using a single LPG. Sensitivities to temperature difference and to average temperature for LPGs in air have been found to be higher than in water. [ABSTRACT FROM AUTHOR]

A dual parameter optical fiber sensor for temperature and pressure discrimination has been proposed and experimentally realized. A tapered fiber Bragg grating (tapered-FBG) and an extrinsic Fabry–Perot interferometer with a ball shape (ball-EFPI) are the two main sensing structures. The taper is fabricated by elongating it during an arc-discharge provided by the fusion splicer. Then, the femtosecond laser is used to inscribe a first-order Bragg grating in the taper region, adopting the point-by-point direct-writing technique. The ball-EFPI is fabricated using the chemical etching and arc-discharge enlargement method. The test temperature range is 40 °–400°, and the test pressure range is 0–2 MPa on the basis of ambient pressure. Experimental results show that the tapered-FBG has good temperature response while the ball-EFPI is sensitive to pressure. By analyzing the sensitivity matrix, the temperature and pressure discrimination can be achieved using the proposed hybrid sensor. [ABSTRACT FROM AUTHOR]

Though the strain characteristics of fiber Bragg gratings (FBGs) inscribed in perfluorinated graded-index (PFGI) polymer optical fibers (POFs) have been reported, their temperature characteristics have not yet been detailed. In this paper, we experimentally investigate the temperature dependence of the Bragg wavelength of a PFGI-POF-FBG. With the increasing temperature, each peak of the FBG-reflected spectrum shifted to longer wavelength with different coefficients. The temperature coefficient of one of the clearest peaks was 0.09 nm/°C, which was eight times larger than those of FBGs in silica single-mode fibers and almost the same as those of FBGs in polymethyl methacrylate POFs. A temperature-independent but strain-dependent peak was also observed, which indicates the potential of discriminative sensing of strain and temperature. [ABSTRACT FROM AUTHOR]

A simple, high-sensitivity, and low-cost optical sensor for the measurement of temperature and salinity in seawater is demonstrated based on a microfiber directional coupler. The shifts of sensing dips are highly sensitive to the change of salinity and temperature in seawater with highest sensitivities at 930 pm/% and -160 pm/°C for coupler assembled by 3.79and 2.20-μm-diameter fibers. The temperature sensitivity can be further improved to -1130 pm/°C for smaller fibers with diameters of 3.50 and 1.35 μm. To keep the stable structure in liquid, a methodology of coating using ethyl cellulose ethoce film is proposed. By ethyl cellulose ethoce solvent coating on the coupling area, the coupler can be operated stably in seawater. The sensor demonstrated here is easy to construct, is low cost, is high sensitivity, and is compatible with the optical fiber system, which may find applications in developing miniature and multifunction optical sensors used in seawater and other liquid surroundings.

This paper presents the development of a wireless low power reconfigurable self-calibrated multi-sensing platform for gas sensing applications. The proposed electronic nose (EN) system monitors gas temperatures, concentrations, and mixtures wirelessly using the radio-frequency identification (RFID) technology. The EN takes the form of a set of gas and temperature sensors and multiple pattern recognition algorithms implemented on the Zynq system on chip (SoC) platform. The gas and temperature sensors are integrated on a semi-passive RFID tag to reduce the consumed power. Various gas sensors are tested, including an in-house fabricated $4\times 4$ SnO2based sensor and seven commercial Figaro sensors. The data is transmitted to the Zynq based processing unit using a RFID reader, where it is processed using multiple pattern recognition algorithms for dimensionality reduction and classification. Multiple algorithms are explored for optimum performance, including principal component analysis (PCA) and linear discriminant analysis (LDA) for dimensionality reduction while decision tree (DT) and k-nearest neighbors (KNN) are assessed for classification purpose. Different gases are targeted at diverse concentration, including carbon monoxide (CO), ethanol (C2H6O), carbon dioxide (CO2), propane (C3H8), ammonia (NH3), and hydrogen (H2). An accuracy of 100% is achieved in many cases with an overall accuracy above 90% in most scenarios. Finally, the hardware/software heterogeneous solution to implementation PCA, LDA, DT, and KNN on the Zynq SoC shows promising results in terms of resources usage, power consumption, and processing time. [ABSTRACT FROM PUBLISHER]

The switching transient properties from the switching power semiconductor gate side are sensitive to the device's junction temperature (Tj). Real-time Tj sensing methods based on gate drive switching transient properties have been investigated on silicon MOSFET and silicon IGBT, with a conventional push–pull-type gate drive, under fixed dc-bus voltage. In this paper, this method is applied to silicon-carbide (SiC) MOSFET. The Tj sensing methods are evaluated with different types of gate drive topologies. By implementing the SiC MOSFETs into an H-bridge inverter, the effect of dc-bus voltage for the Tj sensing method is investigated. Different “gate drive−semiconductor” dynamic models are built, including gate drive output power stage, gate drive parasitics, SiC MOSFET intrinsic parameters, and PCB parasitics. Experimental results are compared with circuit LTSpice model simulation. The device vertical temperature contours are evaluated. Suitable circuitry for Tj sensitivity extraction is provided. [ABSTRACT FROM PUBLISHER]

In this paper, a new sensor system for simultaneous and independent multipoint strain and temperature measurements is presented. The interrogation of the sensing heads has been carried out by monitoring their fast Fourier transform phase variations. In particular, two of each microstructured optical fiber cavity interference frequencies were used for the measures. This method is independent of the signal amplitude and also avoids the necessity of tracking the wavelength evolution in the spectrum, which can be a handicap when there are multiple interference frequency components with different sensitivities. The sensing heads present birefringent and multimodal properties, and therefore, both characteristics lead to their own interference with different properties and sensitivities. The multiplexing capability of the sensing heads and the interrogator method has also been tested and validated. Sensors were operated within a range of temperature 30 °C-80 °C and a deformation of ~450 με was applied. Crosstalk between measurements can be corrected through simple math operations leading to independent and crosstalk-free multipoint and multiparameter sensors. [ABSTRACT FROM AUTHOR]

We develop a simple and cost-efficient configuration of Brillouin optical correlation-domain reflectometry (BOCDR), the setup of which does not include an additional reference path used in standard BOCDR systems. The Fresnel-reflected light from an open end of a sensing fiber is used as reference light. The limitations of spatial resolution, measurement range, and their ratio are theoretically clarified, and then, a distributed strain measurement with a

A temperature estimation method is proposed which utilizes the ratio of two emitter-to-base voltages of bipolar transistors. This removes the need for a precision reference voltage from the digitization step by implicitly implementing the reference in the digital backend. Using measurement data for p-n-p transistors in a 65-nm CMOS technology, we show that the proposed scheme is tolerant to tens of millivolt of offset and up to ±50% gain errors without the need for any calibration. The designed sensor core, incorporating the new estimation scheme, reports room-temperature trim accuracy of ±1 °C ( $3\sigma )$ , and an area and power of 0.009 mm2 and 200~\mu \text{W} , respectively. [ABSTRACT FROM AUTHOR]

A new microbent in-line microfiber interferometer (MI–MI) is proposed and demonstrated as a compact temperature and current sensor. The MI–MI is capable of generating interference fringes with a high extinction ratio of about 12.0 dB and a free spectral range of 1.9 nm at a wavelength of 1545 nm. When employed as a temperature sensor, a copper wire carrying a direct current is placed against the MI–MI sensor, and the interference fringes of the MI–MI sensor shifts toward the longer wavelength as the heat generated by the copper wire increases. As the temperature increase corresponds linearly to the current, thus the measurement of the current can be extrapolated as well. The sensor has a temperature responsivity of 33.0 pm/°C with a linearity of more than 0.97 as well as a current responsitivity of 1.46 °C/A2, and has significant potential for application as a health and warning sensor for electricity generation and distribution grids. [ABSTRACT FROM PUBLISHER]

In this paper, a fiber-optic sensing interrogation system for simultaneous measurement of temperature and transversal loading based on a single-passband RF filter has been proposed and experimentally demonstrated. This sensing interrogation system consists of a fiber Mach–Zehnder interferometer (FMZI) as the sensing device and a dispersive medium. The FMZI also acts as the spectrum slicer to induce continuous sampling, which results in the single-passband frequency response together with the dispersive medium. Two arms of the FMZI are used to measure the temperature and transversal loading respectively. The temperature change on one arm introduces the variation of fiber refractive index, which will change the central frequency of the RF filter’s passband, while the transversal loading induces the change of polarization state of the light, and thus, the amplitude of the RF filter’s passband will be changed accordingly. By tracking the central frequency and amplitude changes of the passband, temperature, and transversal loading can be monitored simultaneously. With the proposed fiber-optic sensing interrogation system, the temperature and transversal loading variation-induced optical spectra changes can be converted to the variation of frequency and amplitude of the RF filter’s passband in electronic domain, which greatly facilitates the measurement. [ABSTRACT FROM PUBLISHER]

This paper explores the near infrared (NIR) to visible frequency upconversion emissions in the Er3+−Tm3+−Yb3+ tri-doped Gd2O3 phosphors prepared by the combustion technique. The cubic phase formation and crystalline structure of the prepared materials has been examined with the help of X-ray diffraction study. The multicolour upconversion emission capability of the prepared materials has been confirmed under the excitation with 980-nm NIR laser source. The relative intensity variation corresponding to the transitions from the thermally coupled energy levels ( ^2\textH11/2 , ^4\textS3/2 ) to the ground level ( ^4\textI15/2 ) of Er3+ ions with pump power and temperature has been studied to investigate the optical temperature sensing ability of the prepared material. The maximum sensor sensitivity of the synthesized material reaches the value 0.0073 \textK^-1 at 443 K. The laser-induced heating capacity of the prepared material caused by laser excitation at different pump powers has been analyzed. The observed results support the utility of the prepared materials in optical temperature sensing and laser-induced heating along with additional capability for being used in making NIR to visible upconverter. [ABSTRACT FROM PUBLISHER]

A novel temperature sensor based on up-taper and single mode–multimode fiber has been presented and demonstrated in this letter. The sensor is fabricated by fusing an up-taper in a single mode fiber (SMF) and splicing the SMF with a section of multimode fiber. In the taper region, a part of light is propagated from the fiber core into the cladding and a series of high-order modes are excited. The reflected light will be coupled back into the core to interfere with the residual core mode when passing through the taper again. Compared with the conventional single mode–multimode–single mode (SMS) fiber sensor, temperature sensitivity of the sensing probe, which consists of SMS and up-taper structure, is improved greatly. According to the experimental results, the temperature sensitivity of 89.42 pm/°C in the temperature range of 20 ^\circ \textC\sim 80~^\circ \textC can be achieved. The sensor has a series of advantages, such as high sensitivity, low cost, compact size, and reflective measurement. [ABSTRACT FROM PUBLISHER]

A method to extend the operation of traditional single-frequency phase-sensitive optical time-domain reflectometry ( $\Phi $ OTDR) to the monitoring of distributed temperature gradients along an optical fiber is proposed and experimentally validated. The measurement principle is derived from the perturbation response of a single-wavelength $\Phi $ OTDR signal, which is analyzed as a unidimensional speckle pattern. The method could be implemented in parallel to standard $\Phi $ OTDR systems used for distributed vibration sensing with a close to zero cost and without affecting its operation, as it only requires a low computational cost post-processing of the traces which are already acquired. Frequency scanning of the laser, heterodyning or additional hardware are not required. The distributed detection of a temperature gradient of 2.5 °C over 10 min is demonstrated. [ABSTRACT FROM PUBLISHER]

A simple, high-sensitivity, and low-cost optical sensor for the measurement of temperature and salinity in seawater is demonstrated based on a microfiber directional coupler. The shifts of sensing dips are highly sensitive to the change of salinity and temperature in seawater with highest sensitivities at 930 pm/‰ and -160 pm/ ^{\circ}C for coupler assembled by 3.79- and 2.20- \mu\text{m}- diameter fibers. The temperature sensitivity can be further improved to -1130 pm/ ^{\circ}C for smaller fibers with diameters of 3.50 and 1.35 \mu\text{m}$. To keep the stable structure in liquid, a methodology of coating using ethyl cellulose ethoce film is proposed. By ethyl cellulose ethoce solvent coating on the coupling area, the coupler can be operated stably in seawater. The sensor demonstrated here is easy to construct, is low cost, is high sensitivity, and is compatible with the optical fiber system, which may find applications in developing miniature and multifunction optical sensors used in seawater and other liquid surroundings. [ABSTRACT FROM PUBLISHER]

Chip-based microheaters have been widely used in many applications, including gas sensors, flow meters, mass sensors, and polymerase chain reaction chambers, where accurate monitoring of temperature is critical. The temperature measurement is conventionally done with the aid of a separate sensor, which may add to the cost and inaccuracy. In this paper, a built-in temperature sensing method is provided for the microheaters. The resistor-based microheater relies on Joule heating mechanism and its resistance is dependent upon its own body temperature, implying that the microheater has an inherent temperature sensing mechanism. It is found that an intermittent temperature sampling in the middle of the heating cycle does not disturb the body temperature if the temperature sampling voltage and pulsewidth are sufficiently low and short, respectively. The built-in temperature sensing is attributed to the electrical time constant being few orders of magnitude smaller than the thermal time constant. The temperature estimation results using the built-in method show excellent agreement with the benchmark measurements from an infrared pyrometer. [ABSTRACT FROM PUBLISHER]

An all-fiber high-sensitivity modal interferometer formed by a bent standard single-mode fiber (SMF) has been presented and demonstrated, which can be used to measure refractive indexes (RIs) of solutions and temperature. The interferometer has a simple and compact structure built with a bent bare SMF mimicking a balloon shape. Because of the curvature of bent fiber sensor, modal interference effect would occur when light propagates from the fiber core into the cladding. The measurement is achieved by monitoring the spectral shift of the modal interference. The performances of the interferometers with different bending diameters and sensitive lengths are experimentally investigated concluding the optimal bending radius as 4 mm and sensitive length 16 mm. In the RI range of 1.3493–1.3822, the corresponding sensitivity and detection limit are 225.95 nm/RIU (refractive index unit) and 3.2\times 10^-4 , respectively. The temperature sensitivity and detection limit of 0.418 nm/°C and 0.173 °C are achieved, respectively. [ABSTRACT FROM PUBLISHER]

A novel low cost and simple temperature sensor based on multimode interference (MMI) is formed by a successive singlemode fiber (SMF)-bent multimode fiber (MMF)-SMF structure. Due to the small curvature radius of bent MMF section mimicking a balloon shape, MMI effect from the core is spreading into coating. The high temperature sensitivity is mainly due to the large thermo-optical coefficient of the existing acrylate coating of the MMF fiber. A temperature sensitivity of up to −2060 pm/°C and −25.1 nW/°C for wavelength- and intensity-based interrogation, respectively, have been achieved in the range between 27 °C and 31 °C. This sensor is most suitable in high sensitivity and low-temperature application such as the measurement of human body temperature. [ABSTRACT FROM PUBLISHER]

The basic properties of a thermal memory effect of polymer optical fibers (POFs) are experimentally investigated. We measure the thermally induced loss as a function of time at several high temperatures, and find that the loss becomes almost constant after heating for $\sim 200$ s. The loss remains unchanged even after the heated section is cooled to room temperature. We subsequently measure the optical time-domain reflectometry traces under three different conditions: 1) before a POF section is heated; 2) shortly after the POF section is heated at high temperature; and 3) after the heated section is cooled to room temperature. The traces measured under 2) and 3) are moderately identical, which indicates that the thermal memory effect can be exploited in developing excess-heat detecting system in future. [ABSTRACT FROM PUBLISHER]

To perform distributed strain and temperature measurement, we have recently developed simplified Brillouin optical correlation-domain reflectometry (S-BOCDR), in which the light that is Fresnel reflected at the ends of the fiber under test (FUT) is used as a reference light. Here, we implement S-BOCDR using a polymer optical fiber (POF) as an FUT, which provides the following advantages over S-BOCDR using a standard silica single-mode fiber (SMF): 1) The beat signal of the Stokes light and the Fresnel-reflected light that is obtained at the interface between the POF and the SMF (the pigtail of an optical circulator) can be stabilized, and 2) the effect of the zeroth correlation peak can be easily and effectively suppressed by exploiting a so-called Brillouin frequency shift-hopping phenomenon. We then experimentally demonstrate a distributed measurement and detect a 0.46-m-long heated POF section. [ABSTRACT FROM AUTHOR]