Temperature Sensor Applications Research Articles

Influence of Chelants and Catalyst on Luminescence of CaAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup> Phosphors for Optical Temperature Sensing Applications

This study synthesized CaAl2O4:Eu2+ blue phosphors using the sol-gel method. The effects of incorporating citric acid, poly (oxyethylene) (PEG), and HCl in the precursor on the luminescent properties of phosphors were investigated. No significant changes were observed in the photoluminescence (PL) spectra of the phosphors when different precursor solutions were used. However, the use of PEG and citric acid led to a noticeable decrease in the PL intensity. Notably, the use of HCl resulted in an increase in PL. In addition, upon heating the phosphors from room temperature to 110 °C, the PL spectrum remained unchanged, whereas the PL intensity decreased linearly with increasing temperature. This indicated the suitability of CaAl2O4:Eu2+ for optical temperature-sensing applications.

Highly durable and conductive Korea traditional paper (Hanji) embedded with Ti3C2Tx MXene for Hanji-based paper electronics

Lightweight, low-cost, eco-friendly, and mechanically flexible Ti3C2Tx (MXene) electrodes require for paper electronics. We develop a highly durable and conductive traditional Korean paper (Hanji) covered with MXene for Hanji-based paper electronics. The effective networking of MXene on the cellulose structure of Hanji leads to a highly conductive and flexible Hanji which acts as a multi-functional paper for Hanji-based paper electronics. Owing to the synergetic combination of Hanji and MXene, the as-prepared Hanji/MXene exhibits a low sheet resistance of 0.62 Ohm square−1, and outstanding mechanical stability without breaking the Hanji fibers. To further evaluate the potential of our Hanji/MXene composite, its performance in electromagnetic interference (EMI) shielding, interconnectors, heaters, supercapacitors, and temperature sensor applications is investigated. Shielding and heater paper samples employing Hanji/MXene-based electrodes show an EMI shielding efficiency (EMI SE) of 43.3 dB and saturation temperature of 76 °C at a low voltage of 3 V. Moreover, the Hanji/MXene-based supercapacitors exhibit a capacitance of 139.6 mF cm−2 at a current density of 1 mA cm−2. Furthermore, the Hanji/MXene-based temperature sensors exhibit an effective sensing performance over a wide temperature range. Overall, the successful operation of Hanji-based EMI shielding devices, interconnectors, heaters, supercapacitors, and temperature sensors indicates that Hanji/MXene serves as a promising conductive paper substrate for multi-functional paper electronics.

Evolution of dielectric properties of SiBCN ceramics and its derived wireless passive temperature sensor application

SiBCN ceramics derived from preceramic polymers are suitable candidates for high-temperature sensors due to their remarkable high-temperature stability and semiconducting properties. However, research into their dielectric performance together with relevant sensors is meaningful but inadequate. In this work, the correlation between dielectric properties and the structure of SiBCN ceramic is identified by studying the evolution trend of the chemical composition, microstructure, and dielectric properties with pyrolysis and environment temperature. SiBCN ceramic was prepared by powder pressing process and pyrolyzed at 1000–1400 °C. As the pyrolysis temperature increased, the dielectric constant and dielectric loss tangent of SiBCN ceramic gradually increased. Within the test temperature range of 500 °C, the dielectric loss was mainly polarization loss. In addition, SiBCN ceramic wireless passive temperature sensors were prepared to test their performance from room temperature to 500 °C. The results showed that the sensitivity increased with the test temperature, and the transmission efficiency of the sensor was closely related to the dielectric properties, indicating that SiBCN ceramic has promising application prospects in the field of high-temperature sensing with good repeatability and stability.

Water-based metamaterial absorber for temperature modulation

In this study, a transmissive all-dielectric metamaterial absorber comprising a photosensitive resin and water layers was proposed. The water layers comprised coin rings, crosses, and fan shapes. The as-obtained absorber achieved >90% absorption of electromagnetic waves within the frequency range of 18.4–41.7 GHz, and the absorption bandwidth covered the Ka-band. Because of the symmetric structure of the designed metamaterial, it was not influenced by polarization. The inherent dispersive properties of water result in a dielectric constant that varies significantly with temperature. This led to fluctuations in the absorption efficiency of the designed metamaterial to different degrees with changes in temperature. The analysis of electric and magnetic fields distributions revealed that the primary absorption physical mechanism of the designed metamaterial originated from magnetic resonances in the water layers. The proposed transmissive metamaterial absorber has potential applications in high-sensitivity thermal and temperature sensors.

Modified sensors open the door to temperature-sensing applications

Changing the design and substrate of a planar resonator adds to its list of uses.

Miniaturized Antenna Design for Wireless and Powerless Surface Acoustic Wave Temperature Sensors.

This paper presents the introduction, design, and experimental validation of two small helical antennae. These antennae are a component of the surface acoustic wave (SAW) sensor interrogation system, which has been miniaturized to operate at 915 MHz and aims to improve the performance of wireless passive SAW temperature-sensing applications. The proposed antenna designs are the normal-mode cylindrical helical antenna (CHA) and the hemispherical helical antenna (HSHA); both designed structures are developed for the ISM band, which ranges from 902 MHz to 928 MHz. The antennae exhibit resonance at 915 MHz with an operational bandwidth of 30 MHz for the CHA and 22 MHz for the HSHA. A notch occurs in the operating band, caused by the characteristics of the SAW sensor. The presence of this notch is crucial for the temperature measurement by aiding in calculating the frequency shifting of that notch. The decrement in the resonance frequency of the SAW sensor is about 66.67 kHz for every 10 °C, which is obtained by conducting the temperature measurement of the system model across temperature environments ranging from 30 °C to 90 °C to validate the variation in system performance.

The probe of current conduction mechanisms, interface states, and the forward bias intersection point of the al/Al2O3/Ge/p-Si heterostructures depending on temperature

The current conduction mechanisms (CCMs), temperature-sensitivities (S), energy-dependent interface traps (Nss), and origin of the intersection points in the forward bias (IF−VF) plots of the Al/Al2O3/Ge/p-Si heterostructure were investigated in wide temperature range of 90–420 K. Firstly, main electrical parameters, including reverse-saturation current (Io), ideality factor (n), zero-bias barrier-height (ΦBo), and series-resistance (Rs) values, were extracted for each temperature. The lnIF-VF curves illustrate two distinct linear regimes at low and intermediate bias voltages. Despite the observed decline in n values as temperature rises, the corresponding ΦBo values exhibit an upward trend. The conventional Richardson plots deviated from linearity at low temperatures, and the Richardson-constants (A*) value obtained from its linear part is quite lower than its theoretical value. Hence, ΦBo−q/2 kT, ΦBo−n, and n(kT)/q−(kT/q) correlations were plotted to seek indications of the Gaussian distribution (GD) of barrier heights (BHs) and tunneling mechanism. Temperate sensitivity (S = dV/dT) for 0.01, 0.10, 0.50, and 1 μA was found as 2.30, 2.33, 2.34, and 2.35 mV/K, which indicated that the fabricated Al/Al₂O₃/Ge/p-Si heterostructure is highly sensitive to temperature, rendering it suitable for use in temperature sensor applications. The observed crossing point at about 2.4V was explained by an increase in the apparent BH with temperature and the presence of Rs.

A Temperature Sensory Leaky Integrate-and-Fire Artificial Neuron Based on Chitosan/PNIPAM Bilayer Volatile Complementary Resistive Switching Memristor.

The presence of neurons is crucial in neuromorphic computing systems as they play a vital role in modulating the strength of synapses through the release of either excitatory or inhibitory stimuli. Hence, the development of sensory neurons plays a pivotal role in broadening the scope of brain-inspired neural computing. The present study introduces an artificial sensory neuron, which is constructed using a temperature-sensitive volatile complementary resistance switch memristor based on the functional layer of the chitosan/PNIPAM bilayer. The resistive switching behavior arises from the formation and ionization of oxygen vacancy filaments, whereby the threshold voltage and low resistive resistance of the device exhibit a temperature-dependent increase within the range of 290-410 K. A functional replication of a neuron with leaky integration and firing has been successfully developed, effectively simulating essential biological functions such as firing triggered by threshold, refractory period implementation, and modulation of spiking frequency. The artificial sensory neuron exhibits characteristics similar to those of leaky integrated firing neurons that receive temperature inputs. It has the potential to control the output frequency and amplitude under varying temperature conditions, making it suitable for temperature-sensing applications. This study presents a potential hardware implementation for developing efficient artificial intelligence systems that can support temperature detections.

Electrical Properties of Textured Bismuth Layer-Structured Ferroelectric Ceramics with Large Number of Layers (m = 5)

Bismuth layer-structured ferroelectrics (BLSF) ceramics are attractive materials for high temperature sensor applications, because of their high Curie temperature Tc (300–900 °C), and the large anisotropy of their electromechanical coupling factor kt/kp or k33/k31. In this study, BLSF ceramics with a large number of layers, namely, (K0.5Bi0.5)2Bi4Ti5O18 + MnCO3 0.3 wt%+ Bi2O3 0.025 wt% (KBT5) and Sr0.75Ca0.25Na0.5Bi4.5Ti5O18 + CeO2 1 wt% [(SC)NBT5] ceramics, were prepared by ordinary firing (OF) and hot forging (HF) methods, and their electrical and piezoelectric properties were examined. Both KBT5 and (SC) NBT5 ceramics showed high Tc values of 545 and 424 °C, respectively. The OF-KBT5 ceramic had an electromechanical coupling factor k33 of 0.14 and a piezoelectric constant d33 of 20 pC/N, whereas the HF-KBT5 ceramic had k33 of 0.17 and d33 of 31 pC/N. On the other hand, the OF-(SC) NBT5 ceramic had k33 of 0.13 and d33 of 17 pC/N, whereas the HF-(SC) NBT5 ceramic had k33 that increased to 0.32 and d33 to 41 pC/N. The k33 and d33 of the HF ceramics were improved compared with those of the OF ceramics. Thus, the KBT5 and (SC) NBT5 ceramics with oriented grains were shown to have good piezoelectric properties with high Tc.

Tuning of power factor in bismuth selenide through Sn/Te co doping for low temperature thermoelectric applications

The physical parameters of solid-state produced tin and tellurium co-doped bismuth selenide polycrystalline crystals were described. Powder X-ray diffraction revealed the hexagonal structure in the samples’ phase domination. A field emission scanning electron microscope was used to analyze the surface microstructure. Thermoelectric properties such as Seebeck coefficient, electrical resistivity, and thermal conductivity were analyzed in the temperature range 10–350 K. The electrical resistivity of (Bi0.96Sn0.04)2Se2.7Te0.3 was found to be four times lower than that of pure Bi2Se3. Due to donor-like effects and antisite defects, the Seebeck coefficient demonstrates a p- to n-type semiconducting transition. When compared to pure Bi2Se3, power factor and thermoelectric figure of merit of (Bi0.96Sn0.04)2Se2.7Te0.3 is found to increase by 15 and 9 times respectively. Tellurium excess boosts tin vacancies, promoting the p to n-type transition in (Bi0.96Sn0.04)2Se2.7Te0.3, making it a good option for low temperature thermoelectric and sensor applications.

A novel fluorapatite-type deep-red CsSr3La(PO4)3F:Eu3+ phosphor with intense 5D0-7F4 transition for temperature sensors, plant growth lighting, and w-LEDs

The synthesis of CsSr3La(PO4)3F:xEu3+ phosphors (x = 1, 2, 5, 10, 20, 30, 40, and 50 mol%) with fluorapatite-type structure was successfully accomplished through a direct solid-state reaction in this work. A systematic characterization was carried out, encompassing the crystal structure, phase composition, morphology, optical properties, and diverse applications of the samples. The crystalline structure of CsSr3La(PO4)3F belongs to the hexagonal system with space group P63/m (176), displaying two polyhedral structures [AⅠO9] and [AⅡO6F]. The band gap (Eg) of the material CsSr3La(PO4)3F is 5.823 eV. At the excitation of 393 nm, CsSr3La(PO4)3F:30 mol%Eu3+ phosphor exhibits a primarily significant emission peak at 703 nm, referring to the 5D0→7F4 transition due to a highly polarizable chemical environment and a distorted coordination polyhedron around Eu3+ ions. The concentration quenching process is attributed to the quadrupole-quadrupole interaction between Eu3+ ions, with the maximum luminescence intensity achieved at a doping content of 30 mol%. At 420 K, the emission intensity of the CsSr3La(PO4)3F:30 mol%Eu3+ phosphor can still maintain 75.04 % of the emission intensity observed at 300 K. The value of activation energy is 0.18 eV. The maximum absolute and relative thermal sensitivities (Sa and Sr) for the temperature sensor can reach 5.25 × 10−4 K−1 and 7.71 % K−1, respectively. The made-up red LED is well-suited to meet the light requirements for the growth and development of plants. The fabricated white light-emitting diode (w-LED) has a relatively high color rendering index (Ra) of 89 and a suitable correlated color temperature (CCT) of 4392 K. The phosphors have applications in temperature sensors, plant growth lighting, and w-LEDs.

Piezoelectric temperature acoustic sensor of LiNbO3 crystal fibers operating at radio frequencies

This study focuses on the growth and characterization of crystalline LiNbO3 (LN) piezoelectric fibers pulled by the Laser Heated Pedestal Growth (LHPG) technique. The electrical properties of the fibers were investigated using an impedance analyzer, which yielded values for resonance frequency, anti-resonance frequency, and phase angle. Subsequently, elastic constants and coupling factor were determined through calculations based on thickness resonance modes. The accuracy of the resonance method was validated through numerical simulations utilizing COMSOL software, demonstrating a close agreement between experimental and simulated results. Additionally, a temperature sensing was conducted, subjecting the fibers to a wide temperature range from 30 °C to 236 °C to assess their sensitivity to temperature variations. The coupling factors of K = 0.37 for LN-1 and K = 0.35 for LN-2 demonstrated efficient performance of the crystalline fibers. Furthermore, the numerical simulations exhibited strong correlation between simulated and experimental data. The sensitivity analysis revealed the potential of LN fibers for temperature sensor applications, exhibiting a sensitivity of −87 Hz.°C−1. These findings underscore the promise of LN piezoelectric fibers in advanced sensing technologies.

Temperature/Component‐Dependent Luminescence in Lead‐Free Hybrid Metal Halides for Temperature Sensor and Anti‐Counterfeiting

AbstractHybrid metal halides (HMHs) have emerged as a promising platform for optically functional crystalline materials, but it is extremely challenging to thoroughly elucidate the electron transition coupled to additional ligand emission. Herein, to discover sequences of lead‐free HMHs with distinct optically active metal cations are aimed, that is, Sb3+ (5s2) with the lone‐pair electron configuration and In3+ (4d10) with the fully‐filled electron configuration. (Me2NH2)4MCl6·Cl (Me = −CH3, M = Sb, In) exhibits the superior temperature/component‐dependent luminescence behaviors resulting from the competition transition between triplet‐states (Tn‐S0) self‐trapped excitons (STEs) of inorganic units and singlet‐state (S1‐S0) of organic cations, which is manipulated by the optical activity levels of [SbCl6]3− and [InCl6]3−. The bonding differences between Sb3+/In3+ and Cl− in terms of electronic excitation and hybridization are emphasized, and the different electron‐transition mechanisms are established according to the PL spectra at the extreme temperature of 5 to 305 K and theoretical calculations. By fine‐tuning the B‐site Sb3+/In3+ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb3+. This research sheds light on the rules governing PL behaviors of HMHs, as well as exploring the optical‐functional application of aviation temperature sensors and access‐control systems.

Toward Humidity-Independent Sensitive and Fast Response Temperature Sensors Based on Reduced Graphene Oxide/Poly(vinyl alcohol) Nanocomposites.

Flexible temperature sensors are becoming increasingly important these days. In this work, we explore graphene oxide (GO)/poly(vinyl alcohol) (PVA) nanocomposites for potential application in temperature sensors. The influence of the mixing ratio of both materials, the reduction temperature, and passivation on the sensing performance has been investigated. Various spectroscopic techniques revealed the composite structure and atomic composition. These were complemented by semiempirical quantum chemical calculations to investigate rGO and PVA interaction. Scanning electron and atomic force microscopy measurements were carried out to evaluate dispersion and coated film quality. The temperature sensitivity has been evaluated for several composite materials with different compositions in the range from 10 to 80 °C. The results show that a linear temperature behavior can be realized based on rGO/PVA composites with temperature coefficients of resistance (TCR) larger than 1.8% K-1 and a fast response time of 0.3 s with minimal hysteresis. Furthermore, humidity influence has been investigated in the range from 10% to 80%, and a minor effect is shown. Therefore, we can conclude that rGO/PVA composites have a high potential for excellent passivation-free, humidity-independent, sensitive, and fast response temperature sensors for various applications. The GO reduction is tunable, and PVA improves the rGO/PVA sensor performance by increasing the tunneling effect and band gap energy, consequently improving temperature sensitivity. Additionally, PVA exhibits minimal water absorption, reducing the humidity sensitivity. rGO/PVA maintains its temperature sensitivity during and after several mechanical deformations.

Tunable multicolor-emission in Eu3+ and Tb3+ codoped Cs2NaInCl6:Sb3+ double perovskite nanocrystals and its dual-model anti-counterfeiting and temperature-sensing applications

Lead-free metal halide double perovskites with non-toxicity and stable self-trapped excitons (STEs) have received considerable attention in the field of photoelectric applications. However, it is difficult to achieve independent control of its photoluminescence performance to meet the requirements of multi-band emission. Herein, a doping strategy was employed to introduce lanthanide ions (Ln3+) into Cs2NaInCl6:Sb3+ nanocrystals (NCs), enabling the multicolor emission modulation ranging from blue to red and even white light. Benefiting from the efficient energy transfer from Sb-related self-trapped excitons to Ln3+ ions, green and red emissions originate from the 5D0→7FJ (J = 1, 2, 3, 4) transition of Eu3+ ions and 5D4-7FJ (J = 6, 5, 4, 3) transition of Tb3+ ions, respectively. According to the tunable polychromatic photoluminescence characteristics of doped NCs, the dual-mode fluorescent anti-counterfeiting applications were exhibited. Furthermore, the distinct temperature sensitivities exhibited by blue (453 nm) and red (617 nm) emission in Cs2NaInCl6:Sb3+/Eu3+ NCs provide the opportunity for the optical thermometry, which demonstrates the maximum absolute and relative sensitivity are 0.0018 and 0.43 % K−1, respectively. These results indicate that the synthesized codoped NCs have the potential applications in multifunctional fields, such as optical thermometer, fluorescence anti-counterfeiting, and multicolor-LEDs.

Upconversion Emission and Dual-Mode Sensing Characteristics of NaYF4:Yb3+/Er3+ Microcrystals at High and Ultralow Temperatures.

In this study, we investigate micrometer-sized NaYF4 crystals double-doped with Yb3+/Er3+ lanthanide ions, designed for temperature-sensing applications. In contrast to previous studies, which focused predominantly on the high-temperature regime, our investigation spans a comprehensive range of both high and ultralow temperatures. We explore the relationship between temperature and the upconversion luminescence (UCL) spectra in both frequency and time domains. Our findings highlight the strong dependence of these spectral characteristics of lanthanide-doped NaYF4 crystals on temperature. Furthermore, we introduce a dual-mode luminescence temperature measurement technique, leveraging the upconversion emission intensity ratio for both green and red emissions. This study also examines the correlation between temperature sensing, energy level disparities, and thermal coupling in Er3+ ions across various temperature scales. Our research contributes to advancing the understanding and application of lanthanide-doped materials, setting a foundation for future innovations in temperature sensing across diverse fields.

Evaluation of isothermal and isofield designs of a temperature sensor using magnetic phase transition

Digitalisation and related concepts such as cyber-physical systems and Industry 4.0 have gained focus in the past few decades with the increasing need for real-time data acquisition methods for large-scale use. This study investigates the magnetic flux change throughout a magnetic phase transition and the potential of changing the magnetic moment in a temperature sensor. Magnetothermal properties are experimentally measured using gadolinium to examine characteristics that have strong implications for the proposed temperature sensor. The results are used to propose different device designs for changing magnetic flux. The magnetothermal characteristics identified in the previous investigation are also reconsidered under the scope of these device designs. The results show that while certain characteristics need to be carefully considered throughout material development and the actual device designing process, the magnetic flux behaviour shows potential for temperature sensor application.

Wireless Temperature Measurement for Curved Surfaces Based on AlN Surface Acoustic Wave Resonators.

In this paper, we propose a novel method for temperature measurement using surface acoustic wave (SAW) temperature sensors on curved or irregular surfaces. We integrate SAW resonators onto flexible printed circuit boards (FPCBs) to ensure better conformity of the temperature sensor with the surface of the object under test. Compared to traditional rigid PCBs, FPCBs offer greater dynamic flexibility, lighter weight, and thinner thickness, which make them an ideal choice for making SAW devices working for temperature measurements under curved surfaces. We design a temperature sensor array consisting of three devices with different operating frequencies to measure the temperature at multiple points on the surface of the object. To distinguish between different target points in the sensor array, each sensor operates at a different frequency, and the operating frequency bands do not overlap. This differentiation is achieved using Frequency Division Multiple Access (FDMA) technology. Experimental results indicate that the frequency temperature coefficients of these sensors are -30.248 ppm/°C, -30.195 ppm/°C, and -30.115 ppm/°C, respectively. In addition, the sensor array enables wireless communication via antenna and transceiver circuits. This innovation heralds enhanced adaptability and applicability for SAW temperature sensor applications.

Breakthrough Boost of Stokes Fluorescence from Er3+ in Perovskites for Flexible Temperature Sensing

AbstractPerovskites with ultra‐low phonon energy have excellent radiation properties, while the population distribution of its luminescent initial state needs to be facilitated to further optimize the stokes fluorescence of Er3+ under high‐energy photons excitation. Herein, UV excitability of Er3+ is remodeled by building an energy transfer channel from Sb3+ to Er3+ in Cs2NaInCl6 (CNIC) microcrystal to realize the enhancement of stokes fluorescence of Er3+. Under UV excitation, the breakthrough boost of Er3+ is observed in Cs2NaInCl6:Sb3+‐Er3+ (CNIC:Sb‐Er), and the sensitization coefficient from Sb3+ to Er3+ in CNIC is derived to be as high as 112. Moreover, CNIC:Sb‐Er is embedded into functional fibers to enhance the crystal stability and the composite flexibility, which form fluorescence fibers with strong radiation transition probability. Finally, a high‐precision temperature sensing is achieved based on FIR (fluorescence intensity ratios) technology, and the maximum relative sensitivities of CNIC:Sb‐Er phosphors and CNIC:Sb‐Er/PAN fibers reach 1.13 and 1.10% K−1, respectively, indicating that CNIC:Sb‐Er and CNIC:Sb‐Er/PAN fibers have potential applications in optical temperature sensors.

3D-Printed Smartwatch Fabricated via Vat Photopolymerization for UV and Temperature Sensing Applications.

Ultraviolet (UV) exposure overdose can cause health issues such as skin burns or other skin damage. In this work, a UV and temperature sensor smartwatch is developed, utilizing a multimaterial 3D printing approach via a vat photopolymerization-digital light processing technique. Photochromic (PC) pigments with different UV sensitivities, UVA (315-400 nm) and UVB (315-280 nm), were utilized to cover a wider range of UV exposure and were mixed in transparent resin, whereas the smartwatch was printed with controlled thickness gradients. A multifunctional sensor was next fabricated by adding a thermochromic (TC) material to PC, which is capable of sensing UV and temperature change. Colorimetric measurements assisted by a smartphone-based application provided instantaneous as well as cumulative UV exposure from sunlight. The mechanical properties of the device were also measured to determine its durability. The prototype of the wearable watch was prepared by fixing the 3D-printed dial to a commercially available silicon wristband suitable for all age groups. The 3D-printed watch is water-resistant and easily removable, allowing for its utilization in multiple outdoor activities. Thus, the developed wearable UV sensor alerts the user to the extent of their UV exposure, which can help protect them against overexposure.