Flat Photonic Crystal Fiber Plasmonic Sensor for Simultaneous Measurement of Temperature and Refractive Index with High Sensitivity

A compact temperature-refractive index (RI) flat photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is presented in this paper. Sensing of temperature and RI takes place in the x- and y- polarization, respectively, to avoid the sensing crossover, eliminating the need for matrix calculation. Simultaneous detection of dual parameters can be implemented by monitoring the loss spectrum of core modes in two polarizations. Compared with the reported multi-function sensors, the designed PCF sensor provides higher sensitivities for both RI and temperature detection. A maximum wavelength sensitivity of -5 nm/°C is achieved in the temperature range of -30-40 °C. An excellent optimal wavelength sensitivity of 17,000 nm/RIU is accomplished in the RI range of 1.32-1.41. The best amplitude sensitivity of RI is up to 354.39 RIU^-1. The resolution of RI and temperature sensing is 5.88 × 10^-6 RIU and 0.02 °C, respectively. The highest value of the figure of merit (FOM) is 216.74 RIU^-1. In addition, the flat polishing area of the gold layer reduces the manufacturing difficulty. The proposed sensor has the characteristics of high sensitivity, simple structure, good fabrication repeatability, and flexible operation. It has potential in medical diagnosis, chemical inspection, and many other fields.

Temperature-Dependent Photoluminescence of CdS/ZnS Core/Shell Quantum Dots for Temperature Sensors

Exploring the temperature-dependent photoluminescence (PL) properties of quantum dots (QDs) is not only important for understanding the carrier recombination processes in QD-based devices but also critical for expanding their special applications at different temperatures. However, there is still no clear understanding of the optical properties of CdS/ZnS core/shell QDs as a function of temperature. Herein, the temperature-dependent PL spectra of CdS/ZnS core/shell QDs were studied in the temperature range of 77-297 K. It was found that the band-edge emission (BEE) intensity decreases continuously with increasing temperature, while the surface-state emission (SSE) intensity first increases and then decreases. For BEE intensity, in the low temperature range, a small activation energy (29.5 meV) in the nonradiative recombination process led to the decrease of PL intensity of CdS/ZnS core/shell QDs; and at high temperature the PL intensity attenuation was caused by the thermal escape process. On the other hand, the temperature-dependent variation trend of the SSE intensity was determined by the competition of the trapping process of the surface trap states and the effect of thermally activated non-radiative defects. As the temperature increased, the PL spectra showed a certain degree of redshift in the peak energies of both band-edge and surface states and the PL spectrum full width at half-maximum (FWHM) increases, which was mainly due to the coupling of exciton and acoustic phonon. Furthermore, the CIE chromaticity coordinates turned from (0.190, 0.102) to (0.302, 0.194), which changed dramatically with temperature. The results indicated that the CdS/ZnS core/shell QDs are expected to be applied in temperature sensors.

Eye-Resolvable Surface-Plasmon-Enhanced Fluorescence Temperature Sensor

Temperature sensors are widely used in important fields such as daily home, medical care, and aerospace as a commonly used device for measuring temperature. Traditional temperature sensors such as thermocouples, thermal resistances, and infrared sensors are technically mature; however, they have limitations in the application environment, temperature measurement range, and temperature measurement accuracy. An eye-resolvable surface plasmon-enhanced fluorescence temperature sensor based on dual-emission Ag@SiO₂@CdS/ZnS composite nanoparticle film with multiple-parameter detectable signals and high response sensitivity was proposed in this work. The temperature sensor's x-chromaticity coordinate varied from 0.299 to 0.358 in the range of 77-297 K, while the y-chromaticity coordinate varied from 0.288 to 0.440, displaying eye-resolvable surface plasmon-enhanced fluorescence. The ratiometric response of two isolated photoluminescence (PL) peak-integrated areas located around 446 and 592 nm was found to be significantly temperature dependent, with a thermal sensitivity of 1.4% K^-1, which can be used as an additional parameter to measure the precise temperature. Furthermore, the surface state emission peak intensity was linearly related to temperature, with a correlation index Adj. R-Square of 99.8%. Multiple independent temperature estimates can help with self-calibration and improve the measurement accuracy. Our findings show that the designed sensors can detect low temperatures while maintaining stability and reproducibility.

Reverse Offset Printed, Biocompatible Temperature Sensor Based on Dark Muscovado

A reverse-offset printed temperature sensor based on interdigitated electrodes (IDTs) has been investigated in this study. Silver nanoparticles (AgNPs) were printed on a glass slide in an IDT pattern by reverse-offset printer. The sensing layer consisted of a sucrose film obtained by spin coating the sucrose solution on the IDTs. The temperature sensor demonstrated a negative temperature coefficient (NTC) with an exponential decrease in resistance as the temperature increased. This trend is the characteristic of a NTC thermistor. There is an overall change of ~2800 kΩ for the temperature change of 0 °C to 100 °C. The thermistor is based on a unique temperature sensor using a naturally occurring biocompatible material, i.e., sucrose. The active sensing material of the thermistor, i.e., sucrose used in the experiments was obtained from extract of Muscovado. Our temperature sensor has potential in the biomedical and food industries where environmentally friendly and biocompatible materials are more suitable for sensing accurately and reliably.

Use of Chipless RFID as a Passive, Printable Sensor Technology for Aerospace Strain and Temperature Monitoring

This paper was concerned with the current level of progress towards the development of chipless radio frequency identification (RFID) sensors that are capable of sensing strain and temperature. More specifically, it was interested in the possibility that the resulting devices could be used as a passive wireless structural health monitoring (SHM) sensor technology that could be printed in situ. This work contains the development and performance characterization results for both novel strain and novel temperature sensor designs with resulting sensitivities of 9.77 MHz/%ε and 0.88 MHz/°C, respectively. Furthermore, a detailed discussion on the interrogation system required to meet the relevant aerospace sensing requirements was also discussed, and several methods were explored to enhance the multi-sensor support capabilities of this technology.

Temperature Sensor Based on Surface Plasmon Resonance with TiO2-Au-TiO2 Triple Structure

Temperature sensors have been widely applied in daily life and production, but little attention has been paid to the research on temperature sensors based on surface plasmon resonance (SPR) sensors. Therefore, an SPR temperature sensor with a triple structure of titanium dioxide (TiO₂) film, gold (Au) film, and TiO₂ nanorods is proposed in this article. By optimizing the thickness and structure of TiO₂ film and nanorods and Au film, it is found that the sensitivity of the SPR temperature sensor can achieve 6038.53 nm/RIU and the detection temperature sensitivity is -2.40 nm/°C. According to the results, the sensitivity of the optimized sensor is 77.81% higher than that of the sensor with pure Au film, which is attributed to the TiO₂(film)-Au-TiO₂(nanorods) structure. Moreover, there is a good linear correlation (greater than 0.99) between temperature and resonance wavelength in the range from 0 °C to 60 °C, which can ensure the detection resolution. The high sensitivity, FOM, and detection resolution indicate that the proposed SPR sensor has a promising application in temperature monitoring.

Inkjet-Printed Temperature Sensors Characterized according to Standards

This paper describes the characterization of inkjet-printed resistive temperature sensors according to the international standard IEC 61928-2. The goal is to evaluate such sensors comprehensively, to identify important manufacturing processes, and to generate data for inkjet-printed temperature sensors according to the mentioned standard for the first time, which will enable future comparisons across different publications. Temperature sensors were printed with a silver nanoparticle ink on injection-molded parts. After printing, the sensors were sintered with different parameters to investigate their influences on the performance. Temperature sensors were characterized in a temperature range from 10 °C to 85 °C at 60% RH. It turned out that the highest tested sintering temperature of 200 °C, the longest dwell time of 24 h, and a coating with fluoropolymer resulted in the best sensor properties, which are a high temperature coefficient of resistance, low hysteresis, low non-repeatability, and low maximum error. The determined hysteresis, non-repeatability, and maximum error are below 1.4% of the full-scale output (FSO), and the temperature coefficient of resistance is 1.23-1.31 × 10^-3 K^-1. These results show that inkjet printing is a capable technology for the manufacturing of temperature sensors for applications up to 85 °C, such as lab-on-a-chip devices.

Experimental and Numerical Validation of Whispering Gallery Resonators as Optical Temperature Sensors

This study experimentally and numerically validates the commonly employed technique of laser-induced heating of a material in optical temperature sensing studies. Furthermore, the Er3+-doped glass microspheres studied in this work can be employed as remote optical temperature sensors. Laser-induced self-heating is a useful technique commonly employed in optical temperature sensing research when two temperature-dependent parameters can be correlated, such as in fluorescence intensity ratio vs. interferometric calibration, allowing straightforward sensor characterization. A frequent assumption in such experiments is that thermal homogeneity within the sensor volume, that is, a sound hypothesis when dealing with small volume to surface area ratio devices such as microresonators, but has never been validated. In order to address this issue, we performed a series of experiments and simulations on a microsphere supporting whispering gallery mode resonances, laser heating it at ambient pressure and medium vacuum while tracking the resonance wavelength shift and comparing it to the shift rate observed in a thermal bath. The simulations were done starting only from the material properties of the bulk glass to simulate the physical phenomena of laser heating and resonance of the microsphere glass. Despite the simplicity of the model, both measurements and simulations are in good agreement with a highly homogeneous temperature within the resonator, thus validating the laser heating technique.

Plasmonic Refractive Index and Temperature Sensor Based on Graphene and LiNbO3

A high-efficiency dual-purpose plasmonic perfect absorber sensor based on LiNbO₃ and graphene layers was investigated in this paper for the refractive index and thermal sensing. The sensor design was kept simple for easy fabrication, comprising a LiNbO₃ substrate with a quartz layer, thin layer of graphene, four gold nanorods, and a nanocavity in each unit cell. The nanocavity is located in the middle of the cell to facilitate the penetration of EM energy to the subsurface layers. The proposed sensor design achieved an output response of 99.9% reflection, which was easy to detect without having any specialized conditions for operability. The performance of the device was numerically investigated for the biomedical refractive index range of 1.33 to 1.40, yielding a sensitivity value of 981 nm/RIU with a figure-of-merit of 61.31 RIU^-1. By including an additional polydimethylsiloxane polymer functional layer on the top, the device was also tested as a thermal sensor, which yielded a sensitivity level of -0.23 nm/°C.

Temperature dependent studies on centimeter-scale MoS2and vdW heterostructures

Transition metal dichalcogenides is an emerging 2D semiconducting material group which has excellent physical properties in the ultimately scaled thickness dimension. Specifically, van der Waals heterostructures hold the great promise in further advancing both the fundamental scientific knowledge and practical technological applications of 2D materials. Although 2D materials have been extensively studied for various sensing applications, temperature sensing still remains relatively unexplored. In this work, we experimentally study the temperature-dependent Raman spectroscopy and electrical conductivity of molybdenum disulfide (MoS₂) and its heterostructures with platinum dichalcogenides (PtSe₂and PtTe₂) to explore their potential to become the next-generation temperature sensor. It is found that the MoS₂-PtX₂heterostructure shows the great promise as the high-sensitivity temperature sensor.

Position Measurements Using Magnetic Sensors for a Shape Memory Alloy Linear Actuator

This article presents the design and implementation of a linear actuator based on NiTi Shape Memory Alloys with temperature and position measurements based on a magnetic sensor array and a set of thermistors. The position instrumentation is contact free to avoid friction perturbations; the position signal conditioning is carried out through the calculation of the response of each magnetic sensor, selecting the closest sensor to ensure accurate results on the full range of movement. Experimental results validate the accuracy of the position sensing with a competitive behaviour.

Upconversion Emission Studies in Er3+/Yb3+ Doped/Co-Doped NaGdF4 Phosphor Particles for Intense Cathodoluminescence and Wide Temperature-Sensing Applications

Er³⁺/Yb³⁺ doped/co-doped NaGdF₄ upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The α-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands at 520 nm, 540 nm, and 655 nm were obtained. The sample was also examined for cathodoluminescence (CL) analysis at different filament currents of an electron beam. Through CL analysis, different emission bands of 526 nm, 550 nm, 664 nm, and 848 nm were obtained. The suitability of the present sample for temperature-sensing applications at a wide range of temperatures, from room temperature to 1173 K, was successfully demonstrated.

Hyperbolic-Metamaterials-Based SPR Temperature Sensor Enhanced by a Nanodiamond-PDMS Hybrid for High Sensitivity and Fast Response

A high-performance surface plasmon resonance (SPR) fiber sensor is proposed with hyperbolic metamaterials (HMMs), nanodiamonds (NDs), and polydimethylsiloxane (PDMS) to enhance the temperature sensitivity and response time. The HMM with tunable dispersion can break through the structural limitations of the optical fiber to improve the refractive index (RI) sensitivity, while NDs and PDMS with large thermo-optic coefficients enable to induce significant RI change under varied thermal fields. The ternary composite endows the sensor with a high temperature sensitivity of -9.021 nm/°C, which is 28.6 times higher than that of the conventional gold film-based SPR sensor. Furthermore, NDs with high thermal conductivity (2200 W/mK) effectively expedite the thermal response of PDMS, which reduces the response time from 80 to 6 s. It is believed that the proposed sensors with high sensitivity, fast response time, and compact size have great potential for applications in industrial production, healthcare, environmental monitoring, etc.

A Surface Plasmon Resonance-Based Photonic Crystal Fiber Sensor for Simultaneously Measuring the Refractive Index and Temperature

In this paper, a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) sensor is proposed for simultaneously measuring the refractive index (RI) and temperature. In the design, the central air hole and external surface of the proposed PCF are coated with gold films, and an air hole is filled with the temperature-sensitive material (TSM). By introducing the inner and outer gold films and TSM, the RI and temperature can be measured simultaneously at different wavelength regions. The simulation results show that the average wavelength sensitivities of the proposed SPR-based PCF sensor can reach 4520 nm/RIU and 4.83 nm/°C in the RI range of 1.35~1.40 and a temperature range of 20~60 °C, respectively. Moreover, because of using the different wavelength regions for sensing, the RI and temperature detections of the proposed SPR-based PCF sensor can be achieved independently. It is believed that the proposed SPR-based PCF RI and temperature sensor has important applications in biomedicine and in environmental science.

Robust Carbazole-Based Rare-Earth MOFs: Tunable White-Light Emission for Temperature and DMF Sensing

Rare-earth metal-organic frameworks (RE-MOFs) are an attractive platform to construct luminescent materials for practical applications in lighting, optoelectronics, and sensing. By adjusting the metal composition in mixed RE-MOFs, one can not only realize tunable emission but also construct ratiometric luminescent sensors. As such, it is highly desirable to prepare robust RE-MOFs that display efficient, multifunctional sensing capability. In this work, we designed and synthesized a series of RE-MOFs that exhibit both excellent thermal and chemical stability due to the incorporation of a bulky tert-butyl group on a new carbazole-based ligand. By rationally tuning the molar ratio of Eu³⁺/Tb³⁺/Y³⁺, a white-light-emitting MOF was developed as an excellent thermal sensor that exhibits a temperature-induced ratiometric luminescence response between 278 and 378 K. After removing the coordinated solvent molecules via thermal treatment, the desolvated MOF materials exhibit excellent turn-on or color change sensitivity to recognize dimethylformamide (DMF) molecules. Such high sensitivity is attributed to the DMF coordination that induces the framework structure change and shifts the ligand's excited-state energy level to facilitate the ligand-to-metal energy transfer process. Taking together, NPF-700-RE represents a new class of robust, tunable luminescent materials that have great potential in white-light emission and thermal- and DMF-sensing applications.

Temperature controllable Goos-Hänchen shift and high reflectance of monolayer graphene induced by BK7 glass grating

BK7 glass has an unusual temperature-dependent refractive index and thickness, which provides a promising platform for uncovering the temperature-related optical phenomena and applications. Here, we theoretically demonstrate that monolayer graphene based BK7 glass grating structure has two Goos-Hänchen (GH) peaks with respective magnitudes of2564λand1993λ,and their corresponding reflectances are also high. The electromagnetic field distribution in this structure directly reveals that the enhanced GH shifts can be ascribed to the excitation of the guide mode resonances in the waveguide dielectric layer below BK7 glass grating structure and their high reflectances are granted by the constructive interferences between the reflected waves. In addition, the magnitudes of the GH peaks can be controlled by the temperature of BK7 glass as well as the chemical potential of monolayer graphene. We also evaluate the temperature sensing property of this structure based on the GH shifts and find that its maximum temperature sensitivity can be up to5.0017×104μm°C-1.The enhanced and controlled GH shift presented in monolayer graphene based BK7 glass grating structure shows promise for the applications, such as, optical sensors, temperature sensors, and optoelectronic detectors.

Wireless LC Conformal Temperature Sensor Based on Ag Film (9912-K FL) for Bearing Temperature Measurement

As the key component of aero-engines and industrial gas turbines, a bearing’s working temperature at high speed is close to 300 ℃. The measurement of an engine bearing’s temperature is of great significance to ensure flight safety. In this study, we present a wireless LC conformal temperature sensor for bearing temperatures, which integrates silver on the bearing surface in situ through a screen-printing process. This process makes Ag film (9912-K FL) firmly adhere to the bearing surface and realizes wireless measurements for bearing temperatures in situ. A high-temperature holding experiment of the prepared sensor was conducted, and the results showed that the sensor can work stably for 10 h at 300 ℃. We tested the designed wireless LC conformal temperature sensor at 20−270 ℃. The results showed that the proposed temperature sensor attained as good accuracy and stability in the temperature range 20−270 ℃. The sensitivity of the temperature measurements was 20.81 KHz/℃ when the bearing rotateds, the maximum repeatability was 0.039%, the maximum uncertainty was 0.081%, and the relative error was stable within 0.08%.

Colorful Conductive Threads for Wearable Electronics: Transparent Cu-Ag Nanonets

Electronic textiles have been regarded as the basic building blocks for constructing a new generation of wearable electronics. However, the electronization of textiles often changes their original properties such as color, softness, glossiness, or flexibility. Here a rapid room-temperature fabrication method toward conductive colorful threads and fabrics with Ag-coated Cu (Cu-Ag) nanonets is demonstrated. Cu-Ag core-shell nanowires are produced through a one-pot synthesis followed by electroless deposition. According to the balance of draining and entraining forces, a fast dip-withdraw process in a volatile solution is developed to tightly wrap Cu-Ag nanonets onto the fibers of thread. The modified threads are not only conductive, but they also retain their original features with enhanced mechanical stability and dry-wash durability. Furthermore, various e-textile devices are fabricated such as a fabric heater, touch screen gloves, a wearable real-time temperature sensor, and warm fabrics against infrared thermal dissipation. These high quality and colorful conductive textiles will provide powerful materials for promoting next-generation applications in wearable electronics.

Novel Surface Acoustic Wave Temperature-Strain Sensor Based on LiNbO3 for Structural Health Monitoring

In this paper, we present the design of an integrated temperature and strain dual-parameter sensor based on surface acoustic waves (SAWs). First, the COMSOL Multiphysics simulation software is used to determine separate frequencies for multiple sensors to avoid interference from their frequency offsets caused by external physical quantity changes. The sensor consists of two parts, a temperature-sensitive unit and strain-sensitive unit, with frequencies of 94.97 MHz and 90.05 MHz, respectively. We use standard photolithography and ion beam etching technology to fabricate the SAW temperature-strain dual-parameter sensor. The sensing performance is tested in the ranges 0-250 °C and 0-700 μԑ. The temperature sensor monitors the ambient temperature in real time, and the strain sensor detects both strain and temperature. By testing the response of the strain sensor at different temperatures, the strain and temperature are decoupled through the polynomial fitting of the intercept and slope. The relationship between the strain and the frequency of the strain-sensitive unit is linear, the linear correlation is 0.98842, and the sensitivity is 100 Hz/μԑ at room temperature in the range of 0-700 μԑ. The relationship between the temperature and the frequency of the temperature-sensitive unit is linear, the linearity of the fitting curve is 0.99716, and the sensitivity is 7.62 kHz/°C in the range of 25-250 °C. This sensor has potential for use in closed environments such as natural gas or oil pipelines.

Temperature-Responsive Ionic Conductive Hydrogel for Strain and Temperature Sensors

Flexible wearable devices have achieved remarkable applications in health monitoring because of the advantages of multisignal collecting and real-time wireless transmission of information. However, the integration of bulky sensing elements and rigid metal circuit components in traditional wearable devices may lead to a mechanical and signal-conducting mismatch between wearable devices and biological tissues, thus restricting their wide applications in the human body. The excellent mechanical properties, conductivity, and high tissue resemblance of conductive hydrogel contribute to its application in flexible electronic sensors to monitor human health. In this work, a dual-network, temperature-responsive ionic conductive hydrogel with excellent stretchability, fast temperature responsiveness, and good conductivity was developed by introducing a polyvinylpyrrolidone (PVP)/ tannic acid (TA)/ Fe3+ cross-linked network into the N,N-methylene diacrylamide (MBAA) cross-linked poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAAm-co-AM)) network. Furthermore, the introduction of the PVP/TA/Fe3+ cross-linked network endowed the hydrogel with excellent stretchability and conductivity. By adjusting the molar ratio of TA and Fe3+ to 3:5, a hydrogel with a maximal stretching ratio of 720% and sensitive strain response (GF = 3.61) was achieved, showing a promising application in wearable strain sensors to monitor both large and fine human motions. Moreover, by introducing PNIPAAm with a lower critical solution temperature (LCST), the hydrogel may be used to monitor the environmental temperature through the temperature-conductivity responsiveness, which can be applied as a wearable temperature sensor to detect fever or tissue hyperthermia in the human body.

Bio-Based Solar Energy Harvesting for Onsite Mobile Optical Temperature Sensing in Smart Cities

The Internet of Things (IoT) fosters the development of smart city systems for sustainable living and increases comfort for people. One of the current challenges for sustainable buildings is the optimization of energy management. Temperature monitoring in buildings is of prime importance, as heating account for a great part of the total energy consumption. Here, a solar optical temperature sensor is presented with a thermal sensitivity of up to 1.23% °C-1 based on sustainable aqueous solutions of enhanced green fluorescent protein and C-phycocyanin from biological feedstocks. These photonic sensors are presented under the configuration of luminescent solar concentrators widely proposed as a solution to integrate energy-generating devices in buildings, as windows or façades. The developed mobile sensor is inserted in IoT context through the development of a self-powered system able to measure, record, and send data to a user-friendly website.

Carbonized Silk Nanofibers in Biodegradable, Flexible Temperature Sensors for Extracellular Environments

Temperature is one of the key parameters for activity of cells. The trade-off between sensitivity and biocompatibility of cell temperature measurement is a challenge for temperature sensor development. Herein, a highly sensitive, biocompatible, and degradable temperature sensor was proposed to detect the living cell extracellular environments. Biocompatible silk materials were applied as sensing and packing layers, which endow the device with biocompatibility, biodegradability, and flexibility. The silk-based temperature sensor presented a sensitivity of 1.75%/°C and a working range of 35-63 °C with the capability to measure the extracellular environments. At the bending state, this sensor worked at promising response of cells at different temperatures. The applications of this developed silk material-based temperature sensor include biological electronic devices for cell manipulation, cell culture, and cellular metabolism.

Wireless Passive Microwave Antenna-Integrated Temperature Sensor Based on CSRR

A novel, wireless, passive substrate-integrated waveguide (SIW) temperature sensor based on a complementary split-ring resonator (CSRR) is presented for ultra-high-temperature applications. The temperature sensor model was established by using the software of HFSS (ANSYS, Canonsburg, PA, USA) to optimize the performance. This sensor can monitor temperature wirelessly using the microwave backscatter principle, which uses a robust high-temperature co-fired ceramic (HTCC) as the substrate for harsh environments. The results are experimentally verified by measuring the S (1,1) parameter of the interrogator antenna without contact. The resonant frequency of the sensor decreases with the increasing temperature using the dielectric perturbation method, which changes from 2.5808 to 2.35941 GHz as the temperature increases from 25 to 1200 °C. The sensitivity of the sensor is 126.74 kHz/°C in the range of 25-400 °C and 217.33 kHz/°C in the range of 400-1200 °C. The sensor described in this study has the advantages of simple structure, higher quality and sensitivity, and lower environmental interference, and has the potential for utilization in multi-site temperature testing or multi-parameter testing (temperature, pressure, gas) in high-temperature environments.

An Ultra-High-Resolution Bending Temperature Decoupled Measurement Sensor Based on a Novel Core Refractive Index-like Linear Distribution Doped Fiber

A high-resolution and high-sensitivity fiber optic sensor based on the quasi-linear distribution of the core refractive index is designed and fabricated, which enables decouple measurement of bending and of temperature. First, single-mode fiber doped with Al₂O₃, Y₂O₃, and P₂O₅ was drawn through a fiber drawing tower. The fiber grating was engraved on the fiber by a femtosecond laser. Modeling analysis was conducted from quantum theory. Experimental results show that the bending sensitivity of the grating can reach 21.85 dB/m⁻¹, which is larger than the reported sensitivity of similar sensors. In the high temperature range from room temperature to 1000 °C, the temperature sensitivity was 14.1 pm/°C. The doped grating sensor can achieve high temperature measurement without annealing, and it has a distinguished linear response from low temperature to high temperature. The bending resolution can reach 0.0004 m⁻¹, and the temperature resolution can reach 0.007 °C. Two-parameter decoupling measurement can be realized according to the distinctive characteristic trends of the spectrum. What’s more, the sensor exhibits excellent stability and a fast response time.

Ultrasensitive Multimodal Tactile Sensors with Skin-Inspired Microstructures through Localized Ferroelectric Polarization

Multifunctional electronic skins have attracted considerable attention for soft electronics including humanoid robots, wearable devices, and health monitoring systems. Simultaneous detection of multiple stimuli in a single self-powered device is desired to simplify artificial somatosensory systems. Here, inspired by the structure and function of human skin, an ultrasensitive self-powered multimodal sensor is demonstrated based on an interlocked ferroelectric copolymer microstructure. The triboelectric and pyroelectric effects of ferroelectric microstructures enable the simultaneous detection of mechanical and thermal stimuli in a spacer-free single device, overcoming the drawbacks of conventional devices, including complex fabrication, structural complexity, and high-power consumption. Furthermore, the interlocked microstructure induces electric field localization during ferroelectric polarization, leading to enhanced output performance. The multimodal tactile sensor provides ultrasensitive pressure and temperature detection capability (2.2 V kPa^-1 , 0.27 nA °C^-1 ) over a broad range (0.1-98 kPa, -20 °C < ΔT < 30 °C). Furthermore, multiple simultaneous stimuli can be distinguished based on different response times of triboelectric and pyroelectric effects. The remarkable performance of this sensor enables real-time monitoring of pulse pressure, acoustic wave detection, surface texture analysis, and profiling of multiple stimuli.

Orbital Angular Momentum Mode Sensing Technology Based on Intensity Interrogation

A novel optical fiber sensing technology based on intensity distribution change in orbital angular momentum (OAM) mode is proposed and implemented herein. The technology utilizes a chiral long-period fiber grating (CLPFG) to directly excite the 1st-order OAM (OAM₁) mode. The intensity changes in the coherent superposition state between the fundamental mode and the OAM₁ mode at the non-resonant wavelength of the CLPFG is tracked in order to sense the external parameters applied to the grating area. Applying this technology to temperature measurement, the intensity distribution change has a good linear relationship with respect to temperature in the range of 30 °C to 100 °C. When the intensity was denoted by the number of pixels with a gray value of one after binarization of collected images, the sensitivity was 103 px/°C and the corresponding resolution was 0.0097 °C. Meanwhile, theoretical and experimental results show that the sensitivity and resolution can be further improved via changing the area of the collected image. Compared with sensing methods based on spiral interference pattern rotation in previous work, this sensing technology has the advantage of exquisite structure, easy realization, and good stability, thus making it a potential application in practices.

Putting Temperature into the Equation: Development and Validation of Algorithms to Distinguish Non-Wearing from Inactivity and Sleep in Wearable Sensors

Long-term monitoring of real-life physical activity (PA) using wearable devices is increasingly used in clinical and epidemiological studies. The quality of the recorded data is an important issue, as unreliable data may negatively affect the outcome measures. A potential source of bias in PA assessment is the non-wearing of a device during the expected monitoring period. Identification of non-wear time is usually performed as a pre-processing step using data recorded by the accelerometer, which is the most common sensor used for PA analysis algorithms. The main issue is the correct differentiation between non-wear time, sleep time, and sedentary wake time, especially in frail older adults or patient groups. Based on the current state of the art, the objectives of this study were to (1) develop robust non-wearing detection algorithms based on data recorded with a wearable device that integrates acceleration and temperature sensors; (2) validate the algorithms using real-world data recorded according to an appropriate measurement protocol. A comparative evaluation of the implemented algorithms indicated better performances (99%, 97%, 99%, and 98% for sensitivity, specificity, accuracy, and negative predictive value, respectively) for an event-based detection algorithm, where the temperature sensor signal was appropriately processed to identify the timing of device removal/non-wear.

UHF RFID Temperature Sensor Tag Integrated into a Textile Yarn

This paper presents the design of an ultra high-frequency (UHF) radio frequency identification (RFID) sensor tag integrated into a textile yarn and manufactured using the E-Thread^® technology. The temperature detection concept is based on the modification of the impedance matching between RFID tag’s antenna and the chip. This modification is created by the change in the resistance of a thermistor integrated within the tag system due to a temperature variation. Moreover, in order to obtain an environment independent detection, a differential approach is proposed that avoids the use of a pre-calibration phase by the use of a reference tag. Experimental characterization demonstrates the RFID sensor’s potential of detecting a temperature variation or a temperature threshold between 25 and 70 °C through the variation of the transmitted differential activation power.

Flexible and Transparent Pressure/Temperature Sensors Based on Ionogels with Bioinspired Interlocked Microstructures

Bioinspired by the interlocked geometry between the epidermal-dermal layers of natural skin, here we design a flexible and transparent (94.2%) skin-like sensor with an interlocked hexagonal microcolumn array structure based on ionogels of ionic liquids (ILs) and thermoplastic polyurethane (TPU) assisted by laser-etched silicon wafers. Attributed to the bioinspired microstructure, the resulting interlocked TPU@IL ionogel sensor exhibits outstanding pressure-sensing properties, which has an ultralow detection limit (∼10 Pa) and ultrafast responsiveness (∼24 ms). Interestingly, it is worth noting that the interlocked TPU@IL ionogel sensor also has high temperature-sensing performance because of the dependence of the ionic conductivity of ILs on the temperature, which can accurately detect a slight temperature change (0.1 °C). Moreover, the interlocked TPU@IL ionogel sensor can also serve as the strain sensor in the strain range of 0.1-10%. Attributed to the intrinsically antibacterial effect of ILs, the interlocked TPU@IL ionogel sensor possesses an antibacterial function, which is a desired merit of wearable electronics and devices. The current study provides a novel strategy to manufacture transparent, flexible, and antimicrobial e-skin sensors with multiple sensing capabilities, which may inspire more future research studies for e-skins.

Meal-Monitoring Systems Using Weight and Temperature Sensors for Elder Residents in Long-Term Care Facilities

This paper presents a few meal-monitoring systems for elder residents (especially patients) in LTCFs by using electronic weight and temperature sensors. These monitoring systems enable to convey the information of the amount of meal taken by the patients in real-time via wireless communication networks onto the mobile phones of their nurses in charge or families. Thereby, the nurses can easily spot the most patients who need immediate assistance, while the families can have relief in seeing the crucial information for the well-being of their parents at least three times a day. Meanwhile, the patients tend to suffer burns of their tongues because they can hardly recognize the temperature of hot meals served. This situation can be avoided by utilizing the meal temperature-monitoring system, which displays an alarm to the patients when the meal temperature is above the reference. These meal-monitoring systems can be easily implemented by utilizing low-cost sensor chips and Arduino NANO boards so that elder-care hospitals and nursing homes can afford to exploit them with no additional cost. Hence, we believe that the proposed monitoring systems would be a potential solution to provide a great help and relief for the professional nurses working in elder-care hospitals and nursing homes.

An Experimental and Theoretical Study of Impact of Device Parameters on Performance of AlN/Sapphire-Based SAW Temperature Sensors

The impact of device parameters, including AlN film thickness (h_AlN), number of interdigital transducers (N_IDT), and acoustic propagation direction, on the performance of c-plane AlN/sapphire-based SAW temperature sensors with an acoustic wavelength (λ) of 8 μm, was investigated. The results showed that resonant frequency (f_r) decreased linearly, the quality factor (Q) decreased and the electromechanical coupling coefficient (Kt2) increased for all the sensors with temperature increasing from −50 to 250 °C. The temperature coefficients of frequency (TCFs) of sensors on AlN films with thicknesses of 0.8 and 1.2 μm were −65.57 and −62.49 ppm/°C, respectively, indicating that a reduction in h_AlN/λ favored the improvement of TCF. The acoustic propagation direction and N_IDT did not obviously impact the TCF of sensors, but they significantly influenced the Q and Kt2 of the sensors. At all temperatures measured, sensors along the a-direction exhibited higher f_r, Q and Kt2 than those along the m-direction, and sensors with N_IDT of 300 showed higher Q and Kt2 values than those with N_IDT of 100 and 180. Moreover, the elastic stiffness of AlN was extracted by fitting coupling of modes (COM) model simulation to the experimental results of sensors along different directions considering Euler transformation of material parameter-tensors. The higher f_r of the sensor along the a-direction than that along the m-direction can be attributed to its larger elastic stiffness c₁₁, c₂₂, c₄₄, and c₅₅ values.

Assessment of Sensitivity and Profitability of an Intravaginal Sensor for Remote Calving Prediction in Dairy Cattle

One critical point of dairy farm management is calving and neonatal first care. Timely calving assistance is associated with the reduction of calf mortality and postpartum uterine disease, and with improved fertility in dairy cattle. This study aimed to evaluate the performance and profitability of an intravaginal sensor for the prediction of stage II of labor in dairy farms, thus allowing proper calving assistance. Seventy-three late-gestating Italian Holstein cows were submitted to the insertion of an intravaginal device, equipped with light and temperature sensors, connected with a Central Unit for the commutation of a radio-signal into a cell phone alert. The remote calving alarm correctly identified the beginning of the expulsive phase of labor in 86.3% of the monitored cows. The mean interval from alarm to complete expulsion of the fetus was 71.56 ± 52.98 min, with a greater range in cows with dystocia (p = 0.012). The sensor worked correctly in both cold and warm weather conditions, and during day- or night-time. The intravaginal probe was well tolerated, as any cow showed lesions to the vaginal mucosa after calving. Using sex-sorted semen in heifers and beef bull semen in cows at their last lactation, the economic estimation performed through PrecisionTree™ software led to an income improvement of 119 € and 123 €/monitored delivery in primiparous and pluriparous cows, respectively. Remote calving alarm devices are key components of "precision farming" management and proven to improve animal welfare, to reduce calf losses and to increase farm incomes.

Temperature Sensor Based on Periodically Tapered Optical Fibers

In this paper, the fabrication and characterization of a temperature sensor based on periodically tapered optical fibers (PTOF) are presented. The relation between the geometry of the sensors and sensing ability was investigated in order to find the relatively simple structure of a sensor. Four types of PTOF structures with two, four, six and eight waists were manufactured with the fusion splicer. For each PTOF type, the theoretical free spectral range (FSR) was calculated and compared with measurements. The experiments were conducted for a temperature range of 20–70 °C. The results proved that the number of the tapered regions in PTOF is crucial, because some of the investigated structures did not exhibit the temperature response. The interference occurring inside the structures with two and four waists was found be too weak and, therefore, the transmission dip was hardly visible. We proved that sensors with a low number of tapered regions cannot be considered as a temperature sensor. Sufficiently more valuable results were obtained for the last two types of PTOF, where the sensor’s sensitivity was equal to 0.07 dB/°C with an excellent linear fitting (R² > 0.99). The transmission dip shift can be described by a linear function (R² > 0.97) with a slope α > 0.39 nm/°C.

Field Demonstration of Heat Technology to Mitigate Heat Sinks for Drywood Termite (Blattodea: Kalotermitidae) Management

Simple Summary

The West Indian drywood termite, Cryptotermes brevis poses a significant economic threat in Hawaii, the southeast portion of continental United States, and throughout tropical and subtropical regions worldwide. Heat treatment is among the nonchemical options to manage them. A typical heat treatment may not be able to provide a complete kill of drywood termites due to the presence of difficult-to-heat areas. To mitigate this effect, studies were conducted in drywood termite-infested condominiums in Honolulu, Hawaii, where either a standard heat treatment performed by a heat remediation company or improved heat treatment methods were used. For improved treatments, heated air was directed into the drilled bases of infested cabinets for better heat penetration. Eight temperature sensors showed that sufficiently high heat was recorded at difficult-to-heat areas, including inside thick wooden cubes, for 120 min, with target temperatures of above 46 °C or 50 °C capable of killing drywood termites. A pre-treatment and a 6-month posttreatment inspection were performed to monitor termite inactivity using visual observations and by recording the numbers of spiked peaks on a termite detection device. The data showed no termite activity in improved heat treatment condominiums at 6-month posttreatment. Guidelines for the improved heat treatment are proposed.

Abstract

With heat treatments to control drywood termites (Blattodea: Kalotermitidae), the presence of heat sinks causes heat to be distributed unevenly throughout the treatment areas. Drywood termites may move to galleries in heat sink areas to avoid exposure to lethal temperatures. Our studies were conducted in Crytotermes brevis-infested condominiums in Honolulu, Hawaii to reflect real-world condominium scenarios; either a standard heat treatment performed by a heat remediation company, or an improved heat treatment was used. For improved treatments, heated air was directed into the toe-kick voids of C. brevis infested cabinets to reduce heat sink effects and increase heat penetration into these difficult-to-heat areas. Eight thermistor sensors placed inside the toe-kick voids, treatment zone, embedded inside cabinets’ sidewalls, and in a wooden cube recorded target temperatures of above 46 °C or 50 °C for 120 min. Pre-treatment and follow-up inspections were performed at 6 months posttreatment to monitor termite inactivity using visual observations and by recording the numbers of spiked peaks on a microwave technology termite detection device (Termatrac). In improved treatment condominiums, significantly higher numbers of spiked peaks were recorded at pre-treatment as compared to 6 months posttreatment. Efficacious heat treatment protocols using the improved methods are proposed.

Micrometer Sized Hexagonal Chromium Selenide Flakes for Cryogenic Temperature Sensors

Nanoscale thermometers with high sensitivity are needed in domains which study quantum and classical effects at cryogenic temperatures. Here, we present a micrometer sized and nanometer thick chromium selenide cryogenic temperature sensor capable of measuring a large domain of cryogenic temperatures down to tenths of K. Hexagonal Cr-Se flakes were obtained by a simple physical vapor transport method and investigated using scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy measurements. The flakes were transferred onto Au contacts using a dry transfer method and resistivity measurements were performed in a temperature range from 7 K to 300 K. The collected data have been fitted by exponential functions. The excellent fit quality allowed for the further extrapolation of resistivity values down to tenths of K. It has been shown that the logarithmic sensitivity of the sensor computed over a large domain of cryogenic temperature is higher than the sensitivity of thermometers commonly used in industry and research. This study opens the way to produce Cr-Se sensors for classical and quantum cryogenic measurements.

Body Temperature Monitoring for Regular COVID-19 Prevention Based on Human Daily Activity Recognition

Existing wearable systems that use G-sensors to identify daily activities have been widely applied for medical, sports and military applications, while body temperature as an obvious physical characteristic that has rarely been considered in the system design and relative applications of HAR. In the context of the normalization of COVID-19, the prevention and control of the epidemic has become a top priority. Temperature monitoring plays an important role in the preliminary screening of the population for fever. Therefore, this paper proposes a wearable device embedded with inertial and temperature sensors that is used to apply human behavior recognition (HAR) to body surface temperature detection for body temperature monitoring and adjustment by evaluating recognition algorithms. The sensing system consists of an STM 32-based microcontroller, a 6-axis (accelerometer and gyroscope) sensor, and a temperature sensor to capture the original data from 10 individual participants under 4 different daily activity scenarios. Then, the collected raw data are pre-processed by signal standardization, data stacking and resampling. For HAR, several machine learning (ML) and deep learning (DL) algorithms are implemented to classify the activities. To compare the performance of different classifiers on the seven-dimensional dataset with temperature sensing signals, evaluation metrics and the algorithm running time are considered, and random forest (RF) is found to be the best-performing classifier with 88.78% recognition accuracy, which is higher than the case of the absence of temperature data (<78%). In addition, the experimental results show that participants' body surface temperature in dynamic activities was lower compared to sitting, which can be associated with the possible missing fever population due to temperature deviations in COVID-19 prevention. According to different individual activities, epidemic prevention workers are supposed to infer the corresponding standard normal body temperature of a patient by referring to the specific values of the mean expectation and variance in the normal distribution curve provided in this paper.

A temperature-dependent gain compensation technique for positron emission tomography detectors based on a silicon photomultiplier

In this study, we propose a simple gain compensation technique for silicon photomultiplier (SiPM)-based positron emission tomography detectors, using a temperature sensor that automatically controls the bias voltage of the SiPM depending upon the ambient temperature. The temperature sensor output, for which the temperature coefficient can be controlled by the input voltage, is used as one end of the bias voltage. By adjusting the temperature coefficient, the proposed gain compensation method can be applied to various SiPMs with different breakdown voltages. As a proof of concept, the proposed method was evaluated for two scintillation detector setups. Applying the proposed method to a single-channel SiPM (ASD-NUV3S-P; AdvanSiD, Italy) coupled with a 3 mm × 3 mm × 20 mm LGSO crystal, the 511 keV photopeak position in the energy histogram changed by only 1.52% per 10 °C while, without gain compensation, it changed by 13.27% per 10 °C between 10 °C and 30 °C. On a 4 × 4 array MPPC (S14161-3050HS-04; Hamamatsu, Japan), coupled with a 3.12 mm × 3.12 mm × 15 mm 4 × 4 LSO array, the photopeak changes with and without gain compensation were 2.34% and 20.53% per 10 °C between 10 °C and 30 °C, respectively. On the wider range of temperature, between 0 °C and 40 °C, the photopeak changes with and without gain compensation were 3.09% and 20.89%, respectively. The energy resolution degradation of SiPM-based scintillation detectors operating at temperatures was negligible when the proposed gain compensation method was applied.

Temperature and Pressure Wireless Ceramic Sensor (Distance = 0.5 Meter) for Extreme Environment Applications

This paper presents a design for temperature and pressure wireless sensors made of polymer-derived ceramics for extreme environment applications. The wireless sensors were designed and fabricated with conductive carbon paste on an 18.24 mm diameter with 2.4 mm thickness polymer-derived ceramic silicon carbon nitride (PDC-SiCN) disk substrate for the temperature sensor and an 18 × 18 × 2.6 mm silicon carbide ceramic substrate for the pressure sensor. In the experiment, a horn antenna interrogated the patch antenna sensor on a standard muffle furnace and a Shimadzu AGS-J universal test machine (UTM) at a wireless sensing distance of 0.5 m. The monotonic relationship between the dielectric constant of the ceramic substrate and ambient temperature is the fundamental principle for wireless temperature sensing. The temperature measurement has been demonstrated from 600 °C to 900 °C. The result closely matches the thermocouple measurement with a mean absolute difference of 2.63 °C. For the pressure sensor, the patch antenna was designed to resonate at 4.7 GHz at the no-loading case. The sensing mechanism is based on the piezo-dielectric property of the silicon carbon nitride. The developed temperature/pressure sensing system provides a feasible solution for wireless measurement for extreme environment applications.

Modified Thermocouple Sensor and External Reference Junction Enhance Accuracy in Indoor Air Temperature Measurements

Indoor air temperature belongs to the most important climatic variables in indoor climate research, affecting thermal comfort, energy balance, and air movement in buildings. This paper focuses on measurement errors when using thermocouples in indoor temperature measurements, with special attention on measurements of air temperature. We briefly discuss errors in thermocouple measurements, noting that, for temperatures restricted to indoor temperature ranges, a thermocouple Type T performs much better than stated in "standards". When thermocouples are described in the literature, industrial applications are primarily considered, involving temperatures up to several hundred degrees and with moderate demands on accuracy. In indoor applications, the temperature difference between the measuring and the reference junction is often only a few degrees. Thus, the error contribution from the thermocouple itself is almost immeasurable, while the dominant error source is in the internal reference temperature compensation in the measuring instrument. It was shown that using an external reference junction can decrease the measurement error substantially (i.e., down to a few hundredths of a degree) in room temperature measurements. One example of how such a device may be assembled is provided. A special application of room temperature measurements involves measuring indoor air temperature. Here, errors, due to radiation influence on the sensor from surrounding surfaces, were surprisingly high. The means to estimate the radiative influence on typical thermocouples are presented, along with suggestions for modification of thermocouple sensors to lower the radiation impact and thereby improve the measurement accuracy.

A Numerical Investigation of a Plasmonic Sensor Based on a Metal-Insulator-Metal Waveguide for Simultaneous Detection of Biological Analytes and Ambient Temperature

A multipurpose plasmonic sensor design based on a metal-insulator-metal (MIM) waveguide is numerically investigated in this paper. The proposed design can be instantaneously employed for biosensing and temperature sensing applications. The sensor consists of two simple resonant cavities having a square and circular shape, with the side coupled to an MIM bus waveguide. For biosensing operation, the analytes can be injected into the square cavity while a thermo-optic polymer is deposited in the circular cavity, which provides a shift in resonance wavelength according to the variation in ambient temperature. Both sensing processes work independently. Each cavity provides a resonance dip at a distinct position in the transmission spectrum of the sensor, which does not obscure the analysis process. Such a simple configuration embedded in the single-chip can potentially provide a sensitivity of 700 nm/RIU and -0.35 nm/°C for biosensing and temperature sensing, respectively. Furthermore, the figure of merit (FOM) for the biosensing module and temperature sensing module is around 21.9 and 0.008, respectively. FOM is the ratio between the sensitivity of the device and width of the resonance dip. We suppose that the suggested sensor design can be valuable in twofold ways: (i) in the scenarios where the testing of the biological analytes should be conducted in a controlled temperature environment and (ii) for reducing the influence on ambient temperature fluctuations on refractometric measurements in real-time mode.

Temperature-Sensing Inks Using Electrohydrodynamic Inkjet Printing Technology

Temperature measurement is very important for thermal control, which is required for the advancement of mechanical and electronic devices. However, current temperature sensors are limited by their inability to measure curved surfaces. To overcome this problem, several methods for printing flexible substrates were proposed. Among them, electrohydrodynamic (EHD) inkjet printing technology was adopted because it has the highest resolution. Since EHD inkjet printing technology is limited by the type of ink used, an ink with temperature-sensing properties was manufactured for use in this printer. To confirm the applicability of the prepared ink, its resistance characteristics were investigated, and the arrangement and characteristics of the particles were observed. Then, the ink was printed using the EHD inkjet approach. In addition, studies of the meniscus shapes and line widths of the printed results under various conditions confirmed the applicability of the ink to the EHD inkjet printing technology and the change in its resistance with temperature.

A novel temperature sensor based on three-dimensional buried-gate graphene field effect transistor

Temperature sensor is one of the primarily developed and most proverbially utilized sensors. Owing to the limitations of their characteristics (stability, thermal conductivity, and thermal contact area), traditional temperature sensors may exhibit drawbacks of high production cost and large volume. In this paper, a three-dimensional (3D) buried-gate graphene field effect transistors (GFETs) are proposed as a novel sensor for temperature detection, which possess a 3D microtube structure by self-rolled-up technology. Compared to conventional two-dimensional (2D) devices, the 3D devices would have tinier area and higher integration. Two main reasons that would affect the resistance of the graphene are the graphene electro-phonon coupling and the thermal expansion effect. In addition, by applying the COMSOL Multiphysics software, it has been demonstrated that the microtube would deform to a certain extent when the temperature increases. And the strain on the 3D devices is proved to be greater than that of the 2D devices. Experimental results show that 3D GFETs could realize temperature detection between 30 °C and 150 °C, and its resistance increases with temperature rising. Furthermore, the maximum achieved temperature coefficient of resistance (TCR) is 0.41% °C^-1and the hysteresis error is only 3.85%. By virtue of the 3D microtube, not only more superior temperature detection could be achieved, but also more devices are integrated in unit area. The 3D temperature sensor possesses superior sensitivity, repeatability and stability, which contributes a new approach to develop the high-performance temperature sensor.

Modelling of carbon nanotube film based temperature sensor: thermal emission and gas discharge

The carbon nanotube (CNT) film based ionized temperature sensor is sensitive to gas temperature, and shows good sensitivity compared with other temperature sensors. But it is still unclear about the effect of CNT film on thermal emission and gas discharge at different temperatures. In this article, we established a gas discharge model of the CNT film temperature sensor. Field assisted thermal emission is simulated at the tip of CNTs by analysing the field enhancement effect and effective work function. Ionization collision, excitation, recombination collision, Penning ionization and quenching of argon are considered in order to obtain the interaction of various particles at different temperature. The current density-temperature characteristic of the temperature sensor was obtained at 24-80 V. The increase of the working voltage is helpful to improve the output current and sensitivity of the temperature sensor. Response time of the sensor will not change in the temperature range of 293-373 K. However, the change of temperature will affect the current density, secondary electron emission and reaction rate. In addition, the sensor has different temperature sensitivity in argon and helium. The above simulation results are helpful to understand the role of CNT film and temperature sensitivity of the ionized sensor. It can also be used to study and improve the sensitivity of this type of sensor.

Progress in ZnO Nanosensors

Developing various nanosensors with superior performance for accurate and sensitive detection of some physical signals is essential for advances in electronic systems. Zinc oxide (ZnO) is a unique semiconductor material with wide bandgap (3.37 eV) and high exciton binding energy (60 meV) at room temperature. ZnO nanostructures have been investigated extensively for possible use as high-performance sensors, due to their excellent optical, piezoelectric and electrochemical properties, as well as the large surface area. In this review, we primarily introduce the morphology and major synthetic methods of ZnO nanomaterials, with a brief discussion of the advantages and weaknesses of each method. Then, we mainly focus on the recent progress in ZnO nanosensors according to the functional classification, including pressure sensor, gas sensor, photoelectric sensor, biosensor and temperature sensor. We provide a comprehensive analysis of the research status and constraints for the development of ZnO nanosensor in each category. Finally, the challenges and future research directions of nanosensors based on ZnO are prospected and summarized. It is of profound significance to research ZnO nanosensors in depth, which will promote the development of artificial intelligence, medical and health, as well as industrial, production.

High-Performance Temperature Sensor by Employing Screen Printing Technology

In the present study, a high-performance n-type temperature sensor was developed by a new and facile synthesis approach, which could apply to ambient temperature applications. As impacted by the low sintering temperature of flexible polyimide substrates, a screen printing technology-based method to prepare thermoelectric materials and a low-temperature heat treatment process applying to polymer substrates were proposed and achieved. By regulating the preparation parameters of the high-performance n-type indium oxide material, the optimal proportioning method and the post-treatment process method were developed. The sensors based on thermoelectric effects exhibited a sensitivity of 162.5 μV/°C, as well as a wide range of temperature measurement from ambient temperature to 223.6 °C. Furthermore, it is expected to conduct temperature monitoring in different scenarios through a sensor prepared in masks and mechanical hands, laying a foundation for the large-scale manufacturing and widespread application of flexible electronic skin and devices.

Optical-Fiber Microsphere-Based Temperature Sensors with ZnO ALD Coating-Comparative Study

This study presents the microsphere-based fiber-optic sensor with the ZnO Atomic Layer Deposition coating thickness of 100 nm and 200 nm for temperature measurements. Metrological properties of the sensor were investigated over the temperature range from 100 °C to 300 °C, with a 10 °C step. The interferometric signal was used to monitor the integrity of the microsphere and its attachment to the connecting fiber. For the sensor with a 100 nm coating, a spectrum shift of the reflected signal and the optical power of the reflected signal were used to measure temperature, while only the optical power of the reflected signal was used in the sensor with a 200 nm coating. The R² coefficient of the discussed sensors indicates a linear fit of over 0.99 to the obtained data. The sensitivity of the sensors, investigated in this study, equals 103.5 nW/°C and 19 pm/°C or 11.4 nW/°C for ZnO thickness of 200 nm and 100 nm, respectively.

A Thermal Skin Model for Comparing Contact Skin Temperature Sensors and Assessing Measurement Errors

To improve the measurement and subsequent use of human skin temperature (Tsk) data, there is a need for practical methods to compare Tsk sensors and to quantify and better understand measurement error. We sought to develop, evaluate, and utilize a skin model with skin-like thermal properties as a tool for benchtop Tsk sensor comparisons and assessments of local temperature disturbance and sensor bias over a range of surface temperatures. Inter-sensor comparisons performed on the model were compared to measurements performed in vivo, where 14 adult males completed an experimental session involving rest and cycling exercise. Three types of Tsk sensors (two of them commercially available and one custom made) were investigated. Skin-model-derived inter-sensor differences were similar (within ±0.4 °C) to the human trial when comparing the two commercial Tsk sensors, but not for the custom Tsk sensor. Using the skin model, all surface Tsk sensors caused a local temperature disturbance with the magnitude and direction dependent upon the sensor and attachment and linearly related to the surface-to-environment temperature gradient. Likewise, surface Tsk sensors also showed bias from both the underlying disturbed surface temperature and that same surface in its otherwise undisturbed state. This work supports the development and use of increasingly realistic benchtop skin models for practical Tsk sensor comparisons and for identifying potential measurement errors, both of which are important for future Tsk sensor design, characterization, correction, and end use.

FBG-Based Temperature Sensors for Liquid Identification and Liquid Level Estimation via Random Forest

This paper proposed a liquid level measurement and classification system based on a fiber Bragg grating (FBG) temperature sensor array. For the oil classification, the fluids were dichotomized into oil and nonoil, i.e., water and emulsion. Due to the low variability of the classes, the random forest (RF) algorithm was chosen for the classification. Three different fluids, namely water, mineral oil, and silicone oil (Kryo 51), were identified by three FBGs located at 21.5 cm, 10.5 cm, and 3 cm from the bottom. The fluids were heated by a Peltier device placed at the bottom of the beaker and maintained at a temperature of 318.15 K during the entire experiment. The fluid identification by the RF algorithm achieved an accuracy of 100%. An average root mean squared error (RMSE) of 0.2603 cm, with a maximum RMSE lower than 0.4 cm, was obtained in the fluid level measurement also using the RF algorithm. Thus, the proposed method is a feasible tool for fluid identification and level estimation under temperature variation conditions and provides important benefits in practical applications due to its easy assembly and straightforward operation.

Synthesis, Characterization, and Applications of Silver Nano Fibers in Humidity, Ammonia, and Temperature Sensing

The promising chemical, mechanical, and electrical properties of silver from nano scale to bulk level make it useful to be used in a variety of applications in the biomedical and electronic fields. Recently, several methods have been proposed and applied for the small-scale and mass production of silver in the form of nanoparticles, nanowires, and nanofibers. In this research, we have proposed a novel method for the fabrication of silver nano fibers (AgNFs) that is environmentally friendly and can be easily deployed for large-scale production. Moreover, the proposed technique is easy for device fabrication in different applications. To validate the properties, the synthesized silver nanofibers have been examined through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Further, the synthesized silver nanofibers have been deposited over sensors for Relative humidity (RH), Ammonia (NH3), and temperature sensing applications. The sensor was of a resistive type, and found 4.3 kΩ for relative humidity (RH %) 30-90%, 400 kΩ for NH3 (40,000 ppm), and 5 MΩ for temperature sensing (69 °C). The durability and speed of the sensor verified through repetitive, response, and recovery tests of the sensor in a humidity and gas chamber. It was observed that the sensor took 13 s to respond, 27 s to measure the maximum value, and took 33 s to regain its minimum value. Furthermore, it was observed that at lower frequencies and higher concentration of NH3, the response of the device was excellent. Furthermore, the device has linear and repetitive responses, is cost-effective, and is easy to fabricate.

Ultrabright Fluorescent Silica Nanoparticles for Dual pH and Temperature Measurements

The mesoporous nature of silica nanoparticles provides a novel platform for the development of ultrabright fluorescent particles, which have organic molecular fluorescent dyes physically encapsulated inside the silica pores. The close proximity of the dye molecules, which is possible without fluorescence quenching, gives an advantage of building sensors using FRET coupling between the encapsulated dye molecules. Here we present the use of this approach to demonstrate the assembly of ultrabright fluorescent ratiometric sensors capable of simultaneous acidity (pH) and temperature measurements. FRET pairs of the temperature-responsive, pH-sensitive and reference dyes are physically encapsulated inside the silica matrix of ~50 nm particles. We demonstrate that the particles can be used to measure both the temperature in the biologically relevant range (20 to 50 °C) and pH within 4 to 7 range with the error (mean absolute deviation) of 0.54 °C and 0.09, respectively. Stability of the sensor is demonstrated. The sensitivity of the sensor ranges within 0.2-3% °C-1 for the measurements of temperature and 2-6% pH-1 for acidity.