Sensitive Temperature Sensor Research Articles

Fused filament fabrication of commercial conductive filaments: experimental study on the process parameters aimed at the minimization, repeatability and thermal characterization of electrical resistance

Nowadays, a challenging scenario involving additive manufacturing (AM), or 3D printing, relates to concerns on the manufacturing of electronic devices. In particular, the possibility of using fused filament fabrication (FFF) technology, which is well known for being very widespread and inexpensive, to fabricate structures with embedded sensing elements, is really appealing. Several researchers in this field have highlighted the high electrical resistance values and variability in 3D-printed strain sensors made via FFF. It is important to find a way to minimize the electrical resistance and variability among strain sensors printed under the same conditions for several reasons, such as reducing the measurement noise and better balancing four 3D-printed strain gauges connected to form a Wheatstone bridge to obtain better measurements. In this study, a design of experiment (DoE) on 3D-printed strain gauges, studying the relevance of printing and design parameters, was performed. Three different commercial conductive materials were analyzed, including a total of 105 printed samples. The output of this study is a combination of parameters which allow both the electrical resistance and variability to be minimized; in particular, it was discovered that the “welding effect” due to the layer height and printing orientation is responsible for high values of resistance and variability. After the optimization of printing and design parameters, further experiments were performed to characterize the sensitivity of each specimen to mechanical and thermal stresses, highlighting an interesting aspect. A sensible variation of the electrical resistance at room temperature was observed, even if no stress was applied to the specimen, suggesting the potential of exploiting these materials for the 3D printing of highly sensitive temperature sensors.

High sensitivity temperature sensor based on a PDMS-assisted bow-shaped fiber structure

We experimentally demonstrate a bow-shaped fiber structure (BFS) fabricated by a simple knotting method. Interference transmission spectra of output light is observed due to interference between the core and cladding mode. The extinction ratio (ER) of output transmission spectra can be adjusted by pulling fiber pigtail of the BFS, which indicates the device can be applied to strain or displacement sensor. The temperature sensing performance is investigated with both bare and polydimethylsiloxane (PDMS)-assisted BFS. Compared with the bare structure, the sensitivity is extremely enhanced when the microfiber region is embedded in PDMS layer, which is as large as -1.63 nm/°C when temperature changing from 21.0 °C to 25.0 °C. The PDMS-assisted BFS with excellent characteristics of good mechanical stability, high sensitivity, low cost, easy fabrication and high flexibility is believed to have promising applications in the future.

Optical temperature sensing properties of Tm3+/Yb3+ co-doped LuAG polycrystalline phosphor based on up-conversion luminescence

A series of LuAG: 5 mol%Yb3+/x mol%Tm3+ (x = 0.1, 0.3, 0.5, 1, 2) poly-crystals have been prepared through floating zone method with CO2 laser. The up-conversion luminescence spectra of the samples were recorded under 980 nm excitation. The results tell us that the optimal concentration of Tm3+ ions is around 0.3 mol%. Moreover, the optical temperature sensing properties of the LuAG: 5 mol%Yb3+/0.3 mol%Tm3+ have been investigated by using fluorescence intensity ratio (FIR) method. The FIR data obtained agree well with the fitting curve from 298 K to 1023 K. The absolute and relative sensitivities reach the highest values of 5.55 × 10−3 K−1 at 1023 K and 7.17 × 10−3 K−1 at 555 K, respectively. The results indicate that the Tm3+/Yb3+:LuAG poly-crystalline phosphor is a promising candidate for wide-range and highly sensitive temperature sensor.

Highly sensitive silicon photonic temperature sensor based on liquid crystal filled slot waveguide directional coupler.

A highly sensitive silicon photonic temperature sensor based on silicon-on-insulator (SOI) platform has been proposed and demonstrated. A two-mode nano-slot waveguide device structure cladded with a nematic liquid crystal (LC), E7, was adopted to facilitate strong light-matter interaction and achieve high sensitivity. The fabricated sensor was characterized by measuring the optical transmission spectra at different ambient temperatures. The extracted temperature sensitivities of the E7-filled device are 0.810 nm/°C around room temperature and 1.619 nm/°C near 50°C, which match well with simulation results based on a theoretical analysis. The results obtained represent the highest experimentally demonstrated temperature sensitivity for a silicon-waveguide temperature sensor on SOI platform. The slot waveguide directional coupler device configuration provides submicron one-dimensional spatial resolution and flexible selection in LC materials for designing temperature sensitivity and operational temperature range required by specific applications.

Compact and highly sensitive temperature sensor established with HSC-SPR embedded in a polymer

A surface plasmon resonance fiber sensor on the basis of hollow silica capillary (HSC) is theoretically proposed and experimentally demonstrated. Numerical analysis indicates that the structure of multimode–capillary–multimode fiber (MMF–HSC–MMF) possesses high spectral resolution and sensitivity due to the existence of capillary stomata. A 55-nm-thick gold-coated HSC is experimentally implemented, with an average refractive index (RI) sensitivity of 6352.16 nm/RIU in RI range of 1.396–1.423. Taking advantage of high thermal coefficient of PDMS, the gold-coated section thoroughly covered with PDMS is especially sensitive to temperature changes. When monitoring the temperature variations of 5–80 °C, the sensor shows high sensitivity (− 2.067 nm/°C) and high linearity (R2 = 0.9981).

Strain and temperature discrimination using a fiber Bragg grating concatenated with PANDA polarization-maintaining fiber in a fiber loop mirror

A highly sensitive strain and temperature sensor which is formed by concatenating a fiber Bragg grating (FBG) with a section of PANDA polarization-maintaining fiber (PMF) in a fiber loop mirror (FLM) has been proposed and experimentally demonstrated to perform temperature and strain measurement. The sensing principle of high birefringence fiber loop mirror (HiBi-FLM) and FBG has been analyzed with formula derivation. Due to the different temperature and strain sensitivities of HiBi-FLM resonant dip and FBG resonant peak, the changes in applied strain and ambient temperature can be simultaneously determined by measuring the two resonance wavelengths shifts. High temperature sensitivity of −1.93 nm/℃ and strain sensitivity of 37.5 pm/με have been achieved respectively over the range of 20∼55 ℃ and 0∼789.6 με. The discrimination errors for temperature and strain are measured to be ± 0.5 ℃ and ± 18 με, respectively. The proposed sensor enjoys simple structure, good linearity, high sensitivity and low cost, and thus shows a good application prospects in various fiber-optic sensing applications.

Highly sensitive temperature sensor based on sagnac interferometer using photonic crystal fiber with circular layout

A temperature sensor based on Sagnac interferometer (SI) using photonic crystal fiber (PCF) with circular layout is proposed. Temperature measurement can be realized by filling the temperature sensitive liquid with high thermo-optic coefficient into the air holes. Considering the convenience of the experimental operation, three easy-to-operate liquid filling methods (FMs) were used to investigate the optical transmission characteristics of this sensor by the finite element method (FEM), the results show that two of which exhibit respective detection advantages in different aspects. One of the feasible methods is that all air holes are filled with temperature sensitive liquid. A single sensing interference dip with high detection sensitivity can be achieved, its average sensitivity reaches to 18.27 nm/°C. Another method is that only the large size air holes are filled with the temperature sensitive liquid. Two sensing interference dips with good linearity can be realized simultaneously. The linearity R2 are up to 0.99947 and 0.99877, corresponding average sensitivities are 9.47 and 8.57 nm/°C, respectively. Besides, these two proposed FMs are easier to be completed than FMs of some reported works. The proposed PCF temperature sensor with excellent detection performances, simple FMs and structural design has great application prospects to detect environmental temperature.

Investigation of the Properties of an All-Fiber Temperature Sensor Created Using the Melting Effect

The temperature sensitivity of an all-fiber temperature sensor created using the melting effect is investigated. In order to study the dependence, a special model was developed and assembled to check the sensitivity of the sensors to temperature changes. During the experiments, the temperature dependences of the spectral shift for the sensor were obtained in the 30–90°С and 20–320°С temperature ranges. During the study, a graph of the dependence of the spectrum on temperature was obtained and a calibration graph was constructed. Thus, the temperature sensitivity of the sensor was determined, which was ≈16 mln–1/°C. The results of the fiber strength in an acrylate coating were obtained before and after tests using the axial tension method. It was found that the ultimate strength of the fiber decreased by more than 2 times when exposed to high temperature.

Epitaxial 4H–SiC based Schottky diode temperature sensors in ultra-low current range

This work reports highly sensitive and linear temperature sensors based on epitaxial silicon carbide (SiC). Circular shaped Ni/4H-nSiC Schottky barrier diode (SBD) temperature sensors of area 3.140 mm2 have been fabricated and characterized in forward current (If) and temperature range from 10 pA to 5 nA and 233 K–473 K, respectively. The highest value of absolute thermal sensitivity |S| has been achieved as 3.425 mV/K at the lowest If = 10 pA. The sensors show best performance at If = 0.1 nA with lowest root mean square error, temperature error and highest coefficient of determination as 5.341 mV, 1.620 K and 99.96%, respectively, with |S| = 3.295 mV/K. Moreover, for If ≤ 20 pA, sensors reach their maximum operating temperature point, i.e., 448 K. The highest value of self-heating in the sensors have been calculated as 1.623 nK. Moreover, asymmetry has been observed between experimental and the theoretical values of |S| which are explained using variation in the barrier height patches (probably caused by defects at the interface) parameter like their effective area, radius, number, barrier height at the saddle point, with the temperature.

Wearable Temperature Sensors with Enhanced Sensitivity by Engineering Microcrack Morphology in PEDOT:PSS-PDMS Sensors.

Wearable temperature sensors with high sensitivity, linearity, and flexibility are required to meet the increasing demands for unobtrusive monitoring of temperature changes indicative of the onset of infections and diseases. Herein, we present a new method for engineering highly sensitive and flexible temperature sensors made by sandwiching a poly(3,4-ethylenedioxythiophene):polystyrene (PEDOT:PSS) sensing film between two poly(dimethylsiloxane) (PDMS) substrates. Pre-stretching the sensor to a certain strain can create stable microcracks in the sensing layer that bestow high senstivity and linearity. The average length and density of the microcracks, which dictate the sensor's temperature sensitivity, can be engineered by controlling three key processing parameters, incuding (a) pre-stretching strain, (b) sulfuric acid treatment time, and (c) surface roughness of the substrate. For a given acid treatment time and surface roughness condition, the density and average length of the microcracks increase pre-stretching strain. A smooth PDMS substrate tends to yield long and straight cracks in the PEDOT:PSS film, compared to shorter microcracks with higher density on rough surfaces. Crack density can be further increased via sulfuric acid treatment with an optimum duration of approximately 3 h. Prolonged treatment would result in weak adhesion between the PEDOT:PSS film and the PDMS substrate, which in turn reduces the microcrack density but increases the crack length. By optimizing the three design parameters we have designed a high performance PEDOT:PSS-PDMS sensor that provides a combined high temperature sensitivity of 0.042 °C-1 with an excellent linearity of 0.998 (from 30 to 55 °C), better than the highest temperature sensitivity of PEDOT:PSS based sensors reported in the literature. With a good optical transparency, high temperature sensitivity, excellent linearity, and high flexibility, this microcrack-based sensor is a very promising wearable temperature-sensing solution.

Characterization of On-Foil Sensors and Ultra-Thin Chips for HySiF Integration

The characterization of multiple mechanically flexible passive and active electronic components, namely on-foil temperature sensor, relative humidity sensor, and ultra-thin microcontroller unit (MCU) integrated circuit (IC) is presented. These components are readily available for Hybrid System-in-Foil (HySiF) integration, which combines the merits of the high-performance silicon chips with the large-area electronics. The 60-nm thin-film resistance temperature detector (RTD) is fabricated on different substrates and the extracted temperature coefficient ranges from 0.002 to 0.003( $\Omega/\Omega$ )/°C. Furthermore, the capacitive relative humidity sensor is fabricated by utilizing a polymeric sensing dielectric material that is compatible with those polyimides used in ultra-thin chip embedding. The $1-\mu \text {m}$ thick sensor achieves a fast adsorption rise time of $\text {54 ms}$ and a spontaneous desorption fall time of $\text {750 ms}$ . For flexible ICs packaging and HySiF integration, microcontroller chips are back-thinned to a thickness of about ${30}~\mu \text {m}$ . The characterization of the MCU after the thinning process step showed undegraded performance of the integrated analog-to-digital converter in terms of linearity. However, a drop in the on-chip temperature sensor sensitivity is observed for the thin chips and significant degradation in the period jitter of the high-frequency RC oscillator is measured. Finally, continuity tests are performed to validate the functionality of the ultra-thin MCUs when embedded using the Chip-Film Patch (CFP) flexible package.

High sensitivity flexible paper temperature sensor and body-attachable patch for thermometers

A highly sensitive, flexible, and wearable paper-based temperature sensor is fabricated using printing paper and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) solution. It exhibits a negative temperature coefficient and is implemented in a new band-like body-attachable thermometer. Compared to the polymer substrate, the use of hydrophilic and flexible paper substrate facilitates significantly superior sensitivity and simple fabrication. The paper sensor is fabricated by depositing PEDOT:PSS onto the paper with an 80 g base weight for 40 s, which is covered with a 50 μm film to protect it from humidity. This is followed by a heat treatment at 150 °C for 10 min. The paper sensor exhibited an electrical conductivity of 0.48 Ωcm−1 at room temperature with a linearity of 99.86 %. Remarkably, its sensitivity is 658.5 Ω/°C, which is 14 times higher than that of sensor with polyimide substrate (46 Ω/°C), for the body temperature range of 30–42 °C. The paper-based temperature sensor is implemented in a body-attachable patch for a wearable thermometer, which is simply connected with a circuit part for signal processing and the results are transferred to a phone via Bluetooth. The proposed inexpensive sensor is potentially useful for a wide range of flexible electronics and healthcare applications.

Detection of groundwater flux changes in response to two large earthquakes using long-term bedrock temperature time series

Heat as a groundwater tracer has potential application in identifying earthquake-induced changes in fluid flow. Since convective heat transport modifies the phase and amplitude of periodic oscillations under pure heat conduction condition, temporal variation of groundwater flux can thus be derived from multi-depth periodic temperature signals. Here we present groundwater flux changes after two large earthquakes nearby, determined from in situ bedrock temperature measurements in the Xianshuihe fault zone, at the eastern margin of the Tibetan Plateau. Five-year temperature time series at six different locations are recorded by high sensitivity temperature sensors (10−4 K) installed at various depths ranging from 0 to 20 m. Groundwater fluxes are estimated through time-varying amplitudes and phases of the annual oscillations, extracted from the Dynamic Harmonic Regression technique. Results show different hydrological responses to these two earthquakes. After the 2013 Ms 7.0 Lushan earthquake, sustained rise in upward flux was revealed at all locations in the intermediate-field, contradicting to the modeled coseismic static dilatational strains. However, groundwater flux patterns after the 2014 Ms 6.3 Kangding earthquake are consistent with the coseismic volumetric strain distribution of a quadrantal pattern of this event. We propose that enhanced hydraulic permeability by dynamic stress might cause the increased upward fluid flux after the Lushan earthquake in the intermediate-field, while coseismic static volumetric strain may account for the hydrological changes after the Kangding earthquake in the near-field. This is the first time that temperature–time series are used to quantify continuous earthquake-related changes in groundwater fluxes. In situ temperature monitoring can provide insights into earthquake-driven hydrologic responses, and also offer additional information to identify temporal changes in crustal strain or hydraulic properties.

Highly sensitive temperature sensor based on cascaded HiBi-FLMs with the Vernier effect

We propose and experimentally demonstrate a highly sensitive temperature sensor based on cascaded high birefringence fiber loop mirrors (HiBi-FLMs) with the Vernier effect. The two HiBi-FLMs have almost the same free spectrum range (FSR), which can be regarded as two scales of different periods of an optical Vernier-scale, and act as the fixed part and the sliding part, respectively. A Gauss fitting algorithm is introduced to fit the Vernier spectrum envelope to accurately trace the spectral shift of the envelope. The temperature sensitivity and temperature resolution of the cascaded configuration are much larger than those of the individual HiBi-FLMs due to the Vernier effect. The experimental result shows that the temperature sensitivity of the proposed sensor can be improved from − 1.723 n m / ∘ C (single HiBi-FLM) to − 43 n m / ∘ C (cascaded configuration) by employing the Vernier effect, and the temperature resolution is enhanced from ± 0.029 ∘ C to ± 0.001162 ∘ C . The amplification factors for temperature sensitivity and temperature resolution are both 24.96, which shows good agreement with the theoretical predictions. The proposed sensor with huge temperature sensitivity, high resolution, and simple configuration may be a promising candidate for some applications that need precise temperature control.

ZnO composite graphene as sensing coating for interferometric temperature sensor

A simple and reliable temperature sensing method with high sensitivity is proposed. ZnO composite graphene sensitive materials with different shapes are successfully prepared by hydrothermal method and characterized by scanning electron microscpoy. The sensor is fabricated by coating the singlemode-taper multimode-singlemode with ZnO composite graphene. The effects of different shapes of ZnO composite graphene on the sensitivity of temperature sensors are further investigated. The electron migration rate of ZnO composite graphene is changed by temperature change. Furthermore, the surface refractive index of the optical microfiber changes. The results show that the sensor with floriated ZnO composite graphene exhibits a high sensitivity of 282.48 pm °C for temperature ranging from 30 °C to 48 °C, which provides a novel and convenient platform for temperature sensing.

Realization of a highly sensitive multimode interference effect-based fiber-optic temperature sensor by radiating with a Vortex beam

In this research, an ultra-high sensitive multimode interference-based fiber-optic temperature sensor is unveiled by radiating with a Vortex beam. The efficient excitation of several high-order modes within the waveguide structure has been affirmed by using the classical wave-optic model. By exploiting the advantages of Vortex beam, the difference in transmitted output power is determined for various surrounding temperatures, ranging from 28 °C–100 °C. To corroborate our theoretical study, an Eigenmode expansion solver (EME) propagation analysis has been carried out in commercially offered Mode solution software (Lumerical Inc.) to investigate the propagation characteristics of Vortex beam inside the waveguide structure. Our simulation outcome reflects a maximal temperature sensitivity of 0.14 dB/°C with a commendable sensing resolution of ∼0.07 °C. When compared to the conventional Gaussian beam-based sensor, such sensitivity of the proposed temperature sensor was found to be enhanced by a factor of about 3.5. Finally, we presented the systematic study describing the impact of fiber radius, order of Vortex beam, and waist size of input field on the sensor response. On account of such superior sensing performance, the proposed idea expedites new possibilities in any sort of physical, chemical or biological sensing needs.

Magnetic Fluid-Injected Ring-Core-Based Micro-structured Optical Fiber for Temperature Sensing in Broad Wavelength Spectrum

A highly sensitive temperature sensor of magnetic fluid (ethanol) using a ring-core-based microstructured optical fiber (MOF) with two large elliptical air holes beside the ring core has been suggested by the finite element method. Highly sensitive magnetic fluid ethanol is injected into the ring core to improve its high sensitivity response. The maximum sensitivity response of 25,641.025 nm/RIU and 10 nm/°C are obtained for the broad operating wavelength of 6500–7000 nm where the temperature range is 10–60°C and the applied magnetic field strength range is 50–200 Oe. Various parameters such as high birefringence, coupling length, power spectrum, transmission, and loss spectra were studied and 14 modes were analyzed in our work. The proposed structure can be further modified and applied in various applications, such as magneto-optic modulators, optical fiber gyroscopes, and switches. The reported MOF structure can easily be fabricated owing to its simplified structure and easy filling of functional materials.

A Low Loss Quantum-Dot-Doped Optical Fiber Temperature Sensor Based on Flexible Print Technology

A quantum dots optical fiber (QDOF) sensor is proposed for temperature sensing in this paper. The sensor is fabricated by the drop-on-demand inkjet printing technology. By controlling the diameter of droplet, the spacing between droplets and the number of printed layers, the QDOF is printed on the polymer substrate. The loss of QDOF is less than 0.35 dB·mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at the fluorescence wavelength. The experimental results show that the temperature sensitivity of sensor is 109 pm/ °C. As far as we know, this is the first time that a QDOF sensor is manufactured by the inkjet printing technology to realize the temperature measurement.

Development of highly sensitive temperature sensor made of graphene monolayers doped P(VDF-TrFE) nanocomposites

New series of nanocomposites composed of graphene and P(VDF-TrFE) have been developed for the manufacturing of ultrasensitive and flexible temperature sensor for the first time. Monolayer graphene sheets were synthesized via sonochemical approach. This graphene embedded into the P(VDF-TrFE) at various concentrations (0−0.09 wt%). The developed nanocomposites were characterized via SEM, XRD, and FTIR. The P-E hysteresis and pyroelectricity measurements were carried out. The thermal stability was emphasized using TG-TDA measurements. The electrical conductivity was investigated under different temperatures. The activation energy and the positive temperature coefficient of conductivity were determined. The developed nanocomposites were examined as temperature sensor at low temperatures (-20−0 °C) and at high temperatures (0−300 °C). Among all prepared nanocomposites, it was found that the inclusion of 0.05 wt% of graphene in the P(VDF-TrFE) resulted in a highly sensitive temperature sensor along the temperature range from -20 °C to 300 °C with sensitivity of 0.025 °C−1. This sample exhibited fast detection of temperature within 4 s and fast recovery time of 3 s. This nanocomposite exhibited high repeatability, stability and reproducibility. Therefore, the developed nanocomposite may be served as efficient, low price, light weight and ultra-sensitive flexible temperature sensor for daily life use.

Size-dependent dynamics of a FG Nanobeam near nonlinear resonances induced by heat

This study explores heat-induced nonlinear vibration of a functionally graded (FG) capacitive nanobeam within the framework of nonlocal strain gradient theory (NLSGT). The elastic FG beam, which is firstly deflected by a DC voltage, is driven to vibrate about its deflected position by a periodic heat load. The nano-structure, which consists of a clamped-clamped nanobeam, is modeled assuming Euler–Bernoulli beam assumption which accounts for the nonlinear von-Karman strain and the electrostatic and intermolecular forcing. To simulate the static and dynamic responses, a model reduction procedure is carried out by employing the Galerkin method. The method of Averaging as a regular semi-analytic perturbation method is applied to obtain governing equations of the steady-state responses. With the purpose of establishing the validity of the solution, a Shooting technique in conjunction with the Floquet theory is used to capture the periodic motions and then examine their stability. The nonlinear resonance frequency of the FG nanobeam near its fundamental natural frequency (primary resonance) and near principal parametric resonance is investigated while the emphasis is placed on studying the effect of various parameters including DC voltage, amplitude of the periodic heat source, material index, damping ratio, and small scale parameters. The main objective of this study is to model a miniature structure which can be used as either a sensitive remote temperature sensor or a high-efficiency thermal energy harvester.