Sensitive Temperature Sensor Research Articles

Highly sensitive temperature sensor using nested hollow-core anti-resonant fibers

A highly sensitive temperature sensor based on composite nested negative curvature hollow-core fiber is proposed. Three resonant tubes are nested inside the cladding tubes to induce a resonant coupling between the fundamental core mode and the dielectric mode of the nested resonant tube. Three glass-sheet conjoined nested tubes are introduced to suppress the comparatively low loss higher-order mode LP02. All the air-holes are filled with temperature-sensitive liquid of ethanol. As the temperature changes, the resonant dip in the transmission spectrum corresponding to the coupling will shift. Numerical simulation results indicate that the temperature sensitivity is 3.36 nm °C−1 in the range of 20 °C–40 °C. Since there is no need of any special post-processing, such as selective infiltration or material coating for the sensors proposed, the sensor provides a promising mechanism for the optical fiber temperature sensing.

An Antisweat Interference and Highly Sensitive Temperature Sensor Based on Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) Fiber Coated with Polyurethane/Graphene for Real-Time Monitoring of Body Temperature.

Body temperature is an important indicator of human health. The traditional mercury and medical electronic thermometers have a slow response (≥1 min) and can not be worn for long to achieve continuous temperature monitoring due to their rigidity. In this work, we prepared a skin-core structure polyurethane (PU)/graphene encapsulated poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) temperature-sensitive fiber in one step by combining wet spinning technology with impregnation technology. The composite fiber has high sensitivity (-1.72%/°C), super-resolution (0.1 °C), fast time response (17 s), antisweat interference, and high linearity (R2 = 0.98) in the temperature sensing range of 30-50 °C. The fiber is strong enough to be braided into the temperature-sensitive fabric with commercial cotton yarns. The fabric with good comfort and durability can be arranged in the armpit position of the cloth to realize real-time body temperature monitoring without interruption during daily activities. Through Bluetooth wireless transmission, body temperature can be monitored in real-time and displayed on mobile phones to the parents or guardians. Overall, the fiber-based temperature sensor will significantly improve the practical applications of wearable temperature sensors in intelligent medical treatment due to its sensing stability, comfort, and durability.

Ultra sensitive temperature sensor based on hybrid fiber optic interferometers and enhanced Vernier effect

An ultra-sensitive temperature sensor with enhanced Vernier effect based on Fabry-Perot interferometer (FPI) and Sagnac interferometer (SI) cascade was proposed and verified through experiments. FPI was made of the thermal sensitive material polydimethylsiloxane. SI was prepared using the panda polarization maintaining fiber. The temperature sensitivity of FPI is positive, while the temperature sensitivity of SI was negative. Therefore, when they were cascaded with similar free spectral ranges, the enhanced Vernier effect was produced, which can further improve the sensitivity magnification factor of traditional Vernier effects. The experimental results showed that the temperature sensitivity of the enhanced Vernier effect sensor was as high as −93.97 nm/°C, which is the highest sensitivity reported in the literature. The temperature sensitivity of traditional Vernier effect sensor is −42.26 nm/°C, and the sensitivity of enhanced Vernier effect sensor has been further improved by 2.22 times. When manufacturing enhanced Vernier effect sensor, there is no need to desensitize the reference interferometer, only the sensitivity symbols of the two interferometers are opposite, so it will not increase the manufacturing cost and difficulty of the sensor. In addition, the sensor has good repeatability and stability.

Electrical conductivity of (Ni,Mn,Fe,Cu)3O4 ceramic semiconductors designed for temperature and magnetic field sensing

This research is focused on designing new ceramic oxides with the spinel structure for a potential application as sensitive temperature and magnetic field sensors. In this respect, the mixtures of ferrimagnetic NiFe2O4 with low-resistive Ni0.66Cu0.41Mn1.93O4 semiconductor (molar coefficient α=1/5 and 1/2) were prepared using the chemical co-precipitation technique followed by a low-temperature sintering of the cold-pressed powders. For the prepared materials, a variation of the electrical conductivity σdc with temperature T (in the range 50 K–400 K) is quantitatively analyzed using different theoretical concepts of the charge carrier hopping transport occurring in disordered materials with strong electron-phonon interaction. It has been shown that an increase in α from 0 to 1/2 causes a step-like change of the dc electrical conductivity and, simultaneously, a gradual change in the magnetization M determined in the saturation state. The temperature coefficient of resistance TCR of the prepared ceramics takes the values from −0.6%/K (at 400 K) to −19.6%/K (below 100 K). The highest absolute value of the magneto-resistance coefficient MR determined at 150 K (and at magnetic field 7 T) registered for ceramic oxide with α=1/2 was found to be 3.4%.

Ratiometric optical temperature sensor with wide range and high sensitivity based on the emission of Dy3+ ion-doped Ca5(PO4)2SiO4 phosphor

There is an urgent demand for the development of non-contact optical temperature sensors that possess a wide temperature measurement range and high sensitivity, particularly for extreme environments. In this study, Dy3+-doped Ca5(PO4)2SiO4 phosphors were prepared and comprehensively analyzed. XRD, SEM, EDS, Raman spectrum, as well as excitation and emission spectrum were employed to investigate the structural, photoluminescent, and temperature-dependent properties of the phosphors. Under 349 nm excitation, the luminescence intensity ratio (LIR) of Dy3+ ions at 453 nm (4I15/2) and 480 nm (4F9/2) exhibited a strong correlation with temperature within the range of 296-1073 K. By fitting the FIR of I453 and I480 at different temperatures using Boltzmann equations, we observed a larger energy gap, indicating high relative sensitivity of the synthesized phosphor. Additionally, Ca4.95(PO4)2SiO4: 0.05Dy3+ phosphor shows excellent temperature repetitiveness. These findings highlight the potential applications of Ca5(PO4)2SiO4: Dy3+ phosphors as highly sensitive ratiometric optical temperature sensor over a wide temperature range.

A Highly Stretchable Force Sensitive and Temperature Sensitive Sensor Material with the Sandwich Structure of PDMS + PDMS/GaInSn + PDMS.

Flexible conductive sensor materials have received great attention for their sensitive electrical response to external conditions and their promising applications in flexible wearable and robotic applications. In this work, a highly stretchable force sensitive and temperature sensitive sensor material with a sandwich structure was prepared from the polydimethylsiloxane (PDMS) and the liquid metal (LM) gallium-indium-tin alloy (GaInSn). The sandwich structure (PDMS + PDMS/GaInSn + PDMS) was proven to prevent the "leakage" of LM. The preparation method of the sensing material was simple and time-saving (less than 1.5 h) and can be used for industrial production. The electrical performance analysis results confirmed that the resistance (R) of the material was sensitive to the external force, such as repeated stretching, compressing, bending, and impacting. The ΔR/R changed periodically and stably with the repeated stretching, when the GaInSn/Part A ≥ 0.4, the cyclic tensile strain ≤ 50%, and the cyclic tensile rate ≤ 2.5 mm/min. The R of the sensor materials was also responsive to the temperature, such as hot air and liquid nitrogen. In conclusion, this work provides a method for preparing sensing materials with the sandwich structure, which was confirmed to be sensitive to force and temperature without leaking LM, and it produced different types of R signals under different deformations and different temperatures.

High-Sensitivity Temperature Sensor Based on Fiber Fabry-Pérot Interferometer with UV Glue-Filled Hollow Capillary Fiber.

Optical fiber Fabry-Pérot (FP) interferometer sensors have long been the focus of researchers in sensing applications because of their simple light path, low cost, compact size and convenient manufacturing methods. A miniature and highly sensitive optic fiber temperature sensor using an ultraviolet glue-filled FP cavity in a hollow capillary fiber is proposed. The sensor is fabricated by fusion splicing a single-mode fiber with a hollow capillary fiber, which is filled with ultraviolet glue to form a FP cavity. The sensor has a good linear response in the temperature testing and high-temperature sensitivity, which can be increased with the length of the FP cavity. The experimental results show that the temperature sensitivity reaches 1.174 nm/°C with a high linear response in the range of 30-60 °C. In addition, this sensor is insensitive to pressure and can be highly suitable for real-time water temperature monitoring for ocean research. The proposed ultraviolet glue-filled structure has the advantages of easy fabrication, high-temperature sensitivity, low cost and an arbitrary length of capillary, which has broad application prospects for marine survey technology, biological diagnostics and environmental monitoring.

Improving consistency and performance of graphene-based devices via Al sacrificial layer

Graphene has attracted much attention because of its excellent physical properties and great potential applications in electronic devices. However, traditional lithography process using photoresist masks will inevitably leave some organic matter on the graphene surface, which will reduce the performance and yield of graphene-based devices. In this paper, a new lithography process for the separation of graphene and photoresist using Al sacrificial layer is proposed. ToF-SIMS demonstrated that the process not only avoids photoresist residues, but also significantly reduces PMMA contamination without introducing Al atomic residues. The morphology also shows that the graphene pattern prepared by this process is flatter and cleaner. More importantly, electrical tests show that Al sacrificial layer process can significantly improve the consistency of the resistance (standard deviation reduced by 41.9%) and the sensitivity of the device (temperature sensor sensitivity increased by 54.41%). This work provides a way for the commercial application of graphene electronic devices.

An improved sensitivity temperature sensor based on tapered Hollow-core Bragg fiber

A Mach-Zehnder interferometer (MZI) based on tapered Hollow-core Bragg fiber (HCBF) for temperature measurement is proposed and experimentally investigated. The MZI is fabricated by sandwiching the tapered HCBF between two single-mode fibers (SMFs). The tapered HCBF excites strong evanescent wave and forms a sensitive periodic envelope in the spectrum when the ambient temperature changes. Experimental results show that the temperature sensitivity of the sensor is 9.12 pm/°C, 18.90 pm/°C, 24.90 pm/°C, 27.12 pm/°C, and the strain sensitivity is −0.241 pm/με, −0.270 pm/με, −0.427 pm/με, −0.545 pm/με, when the tapered region is not stretched and when it is stretched by 2 mm, 2.4 mm, and 2.8 mm, respectively. The proposed sensor is characterized by high temperature sensitivity and low strain cross-sensitivity as well as simplicity of fabrication. It has good prospects in the field of biochemical and physical sensing.

PDMS-filled micro-spring Fabry-Perot cavity for temperature sensing.

A highly sensitive fiber-tipped temperature sensor based on polydimethylsiloxane (PDMS)-filled spring Fabry-Perot (FP) cavity has been proposed and experimentally demonstrated. The spring FP cavity is first fabricated on the fiber endface by the two-photon polymerization lithography. After that, PDMS is filled into the cavity to drive the elongation of the flexible spring and thus to functionalize high-performance temperature sensing. Benefiting from the large thermal expansion coefficient of PDMS, the proposed sensor exhibits a maximal temperature sensitivity of 704.3 pm/°C with excellent operating repeatability and stability. Besides, by selecting a proper spring constant k, the FP sensitivity can be precisely adjusted in the range of 100-700 pm/°C. Thanks to the advantages of high fabrication accuracy and designable property, the proposed sensor could promote numerous usages for customizable temperature sensing.

A Flexible and Stretchable Temperature Sensor Based on Contact Electrification for Robotic Sensing

With the rapid development of robotic systems, an increasing number of various sensitive sensors are needed to meet the requirement of data collection for unmanned detection and monitoring technology. Among various external stimuli information, temperature sensing is an essential important function that can avoid high-temperature scalding injuries, achieve robot detection of environmental, and human-machine interfaces applications. However, most of the existing temperature sensors for robotic sensing are realized by rigid materials, which have the disadvantage of not being able to adapt to an arbitrarily curved surface. Also, most of the sensors are thermistor-based approaches, which faces challenges in developing a low-cost robotic system since external power is required to obtain the sensing signal. In this work, a self-powered and stretchable temperature sensor based on Triboelectric Nanogenerator (TENG) technology was developed. The principle of TENG is the coupling effect of triboelectric charge transfer and electrostatic induction effects, which can generate different magnitudes of electrical signals when subjected to external stimuli, including temperature. To this end, this study is a pilot effort toward validating the sensitivity of TENG electrical output on different temperature effects. The surface potential of materials is explored under different temperatures by Kelvin probe force microscopy (KPFM), which shows the feasibility of self-powered temperature sensor. The proposed temperature sensor is composed of highly resilient materials physiological saline as liquid electrode encapsulated with Ecoflex as triboelectric layer, which has the advantage of biocompatibility. The temperature sensing performance was successfully maintained at 200% stretch. Owing to its flexible, bendable and stretchable characteristics, the self-powered temperature-sensitive sensor has been successfully demonstrated on a robot hand, which can read the information and respond to different temperatures through the feedback system. Overall, this self-powered temperature-sensitive sensor has great potential to be an emerging tool for human-robot interaction and automatic detection.

Temperature Sensors Integrated with an Electrochromic Readout toward Visual Detection.

Temperature sensors have attracted great attention for personal health care and disease diagnosis in recent years. However, it is still a great challenge to fabricate reliable and highly sensitive temperature sensors that can convert physiological signals into easily readable signals in a convenient way. Herein, an integrated smart temperature sensor system based on a traditional temperature sensor and electrochromic display is proposed for real-time visual detection of temperature. Significantly, a voltage-regulated electrochromic device (ECD) based on tungsten oxide (WO3) and polyaniline (PANI) as the real-time visualization window was integrated into the platform to provide feedback on the temperature change. The ECD would change its color from green to blue based on the electrical signal of the temperature sensor, resulting in a visualized readout that can be monitored through our naked eye. Additionally, the smart temperature sensor system possesses an extremely durable property and cycle stability, remaining around 90% of the initial value even after 15,000 s continuous cycle. Thus, the novel design and low power consumption advantages make it a good candidate to pave the way for developing interactive wearable electronics and intelligent robots as real-time temperature feedback systems.

Polymer-coated fiber-optic Fabry-Perot interferometer-based temperature sensor with high sensitivity

In this paper, a highly sensitive temperature sensor based on polymer-coated Fabry-Perot interferometer (FPI) is proposed and demonstrated. The FPI temperature sensor consists of the end face of single-mode fiber (SMF) and the Polydimethylsiloxane (PDMS) cap on the end face. By varying the number of coatings, the thickness of the PDMS cap can be flexibly controlled to obtain FPI sensors with different cavity lengths. The temperature sensitivity is studied experimentally from −30 °C to 85 °C, and it is found that the sensor shows different sensitivity in different temperature intervals, up to 0.698 nm/°C. Compared to similarly constructed sensors, the sensor in this paper has a large temperature range while maintaining a high sensitivity. In addition, the performance of the sensor is tested by experiments and the results show that the sensor possesses the advantages of good stability, fast response time and good repeatability.

Highly sensitive fiber-optic temperature sensor based on Lyot filter cascaded with Fabry-Perot interferometer

A highly sensitive fiber-optic temperature sensor based on a Lyot filter cascaded with a Fabry-Perot interferometer (FPI) is proposed and demonstrated in this study. The FPI consists of a segment of hollow-core photonic crystal fiber (HCPCF) spliced between two single-mode fibers (SMFs), which is insensitive to temperature and strain and is an ideal reference interferometer. The Lyot filter is composed of two polarizers with an uiltra-fine polarization maintaining fiber (UFPMF) of a certain length for temperature sensing. By adjusting the length of the UFPMF, the free spectral range (FSR) of the Lyot filter is close to FPI, resulting in an optical Vernier effect and improved sensitivity. Experimental results show that with the Vernier effect, the temperature sensitivity is enhanced from −1.145 nm/℃ to −59.31 nm/℃, and the sensitivity amplification factor is about 51.8. The proposed sensor with the Vernier effect has good performance in temperature sensing and is suitable for applications fields where high sensitivity temperature measurement is required.

Evaluation of the Curing Process Effects on the TCR of Temperature Sensors Printed by Aerosol Jet Printing

Temperature sensors have been widely developed to control the course of diseases, improve haptic feelings, and in multi-sensing systems to compensate for the output of other temperature-sensitive sensors. The use of additive manufacturing to produce resistive temperature detectors (RTDs) with reduced dimensions and bulkiness is attracting great interest. Among the relevant process parameters and design choices, the curing process must be considered. In this work, two different commercial metallic-based materials are cured at various temperatures to evaluate the differences in their microscopic and macroscopic behavior. The sensors were designed, developed, and evaluated for their temperature coefficient of resistance (TCR) at different curing temperatures using a programmable climatic chamber. A scanning electron microscope has been used to microscopically inspect the sensing structures with respect to the different curing temperatures. The results show insightful correlations between the macroscopic and microscopic behavior of the used inks as well as the performance of the sensors. In particular, increasing the curing temperature decreased the room-temperature resistance in all the samples by up to 70% and increased the sensitivity by up to 95%. These findings will help propose better processes as well as design choices for the development of printed resistive temperature sensors.

Estimation of mixing efficiency of a small dimictic lake due to surface cooling

The paper presents the results of studying the mixing of the water mass of a small forest dimictic lake at the stage of summer heating. The wind effect is limited by the small area of the mirror (the size of the lake is 80–110 by 400 m) and the forested shores, so in summer the convective mixing mechanism prevails when the lake surface cools at night. Evaluation of the mixing efficiency η was carried out by the integral energy method, based on the calculations of energy pumping and changes in the background potential energy according to the temperature profile transformation. For this purpose, a chain with 13 highly sensitive temperature sensors was used; the measurements were carried out in the middle of summer 2022 for 35 days with a time interval of one minute. Acoustic current profiler’s data were used to estimate turbulent velocity fluctuations and calculate the energy dissipation rate, which made it possible to make an alternative assessment of the mixing efficiency. The value of η ~0,4 was obtained, which significantly exceeds the “canonical” value of 0,17 for the case of wind mixing.

Integrated Fiber Ring Laser Temperature Sensor Based on Vernier Effect with Lyot-Sagnac Interferometer.

The Vernier effect created using an incorporated Lyot-Sagnac loop is used to create an ultra-high sensitivity temperature sensor based on a ring laser cavity. Unlike standard double Sagnac loop systems, the proposed sensor is fused into a single Sagnac loop by adjusting the welding angle between two polarization-maintaining fibers (PMFs) to achieve effective temperature sensitivity amplification. The PMFs are separated into two arms of 0.8 m and 1 m in length, with a 45° angle difference between the fast axes. The sensor's performance is examined both theoretically and experimentally. The experimental results reveal that the Vernier amplification effect can be achieved via PMF rotating shaft welding. The temperature sensitivity in the laser cavity can reach 2.391 nm/°C, which is increased by a factor of more than eight times compared with a single Sagnac loop structure (0.298 nm/°C) with a length of 0.8 m without the Vernier effect at temperatures ranging from 20 °C to 30 °C. Furthermore, unlike traditional optical fiber sensing that uses a broadband light source (BBS) for detection, which causes issues such as low signal-to-noise ratio and broad bandwidth, the Sagnac loop can be employed as a filter by inserting itself into the fiber ring laser (FRL) cavity. When the external parameters change, the laser is offset by the interference general modulation, allowing the external temperature to be monitored. The superior performance of signal-to-noise ratios of up to 50 dB and bandwidths of less than 0.2 nm is achieved. The proposed sensor has a simple structure and high sensitivity and is expected to play a role in biological cell activity monitoring.

Highly Sensitive Temperature and Gas Pressure Sensor Based on Long-Period Fiber Grating Inscribed in Tapered Two-Mode Fiber and PDMS

Highly Sensitive Temperature and Gas Pressure Sensor Based on Long-Period Fiber Grating Inscribed in Tapered Two-Mode Fiber and PDMS

Highly sensitive temperature and curvature sensor based on seven-core fiber

A high sensitivity temperature and curvature micro-fiber Mach-Zehnder interferometer (MMZI) sensor is proposed and demonstrated. A peanut structure is fused by a section of seven-core fiber (SCF) and a section of single-mode fiber (SMF). Then the SCF is connected to another SMF and tapered. Finally, the composite structure with the tapered SCF and the SCF-SMF peanut structure is fabricated. The coupling efficiency can be significantly improved, and more high-order modes can be stimulated via the new sensor structure. The experimental results demonstrated that the maximum temperature sensitivity is 836.67 pm/ °C in the range of 35 °C to 40 °C, which is the highest temperature sensitivity of the peanut-shaped MMZI sensor to the best of our knowledge. Furthermore, the sensor can be used for curvature measurement. When the curvature changes from 0 m−1 to 0.0522449 m−1, the sensitivity can achieve 93.33664 nm/m−1. The proposed sensor not only provides a novel method to fabricate a high-sensitivity sensor by combining different types of fibers, but it also has a meaningful application prospect in the fields of biological detection and environmental monitoring.

Highly sensitive surface plasmon resonance temperature sensor based on a hollow core fiber multilayer structure.

A surface plasmon resonance (SPR) temperature sensor based on a hollow core fiber (HCF) is designed in this paper. The sensor is composed of a multi-mode fiber (MMF)-HCF-MMF structure, and the self-made HCF is deposited successively with a thin layer of Au film (50 nm in thickness), gold nanoparticles (10 nm in diameter) and polydimethylsiloxane (PDMS). A series of theoretical and experimental investiagtions are conducted, and the results are as follows: the proposed sensing structure only with Au film can effectively excite the SPR effect, with a sensitivity of (2200 ± 100) nm / RIU in the refractive index (RI) range of 1.3334-1.3811; after adding AuNPS, the sensitivity of the sensor is effectively improved, the sensitivity can be increased to (3100 ± 100) nm / RIU, and after the PDMS coating, temperature sensing can be realized due to its unique temperature-sensitive characteristics, a linear sensitivity of (-2.1 ± 0.1) nm / °C is realized in the temperature range of 25 °C to 100 °C. The sensor has the advantages of simple structure, wide application, large measurement range, high sensitivity, good stability and repeatability. Meanwhile, the internal air hole of HCF leaves a preparation channel for dual-parameter measurement. It has broad application prospect in medical treatment, environmental monitoring and manufacturing industry.