Positive Temperature Coefficient Thermistors Research Articles

Study on cold start of fuel cell stack combined with liquid heating and fuel cell self-starting

Fuel cell vehicles have been paid more and more attention, while the low temperature cold start capability has become the main reason that hinders their large-scale commercialization, especially for the fuel cell bus. Generally, liquid heating (positive temperature coefficient thermistor (PTC) as the heat source) and fuel cell self-starting heating are the common cold start methods. However, these methods can bring about low start speed and high energy consumption. Therefore, a new cold start method combined with liquid heating and fuel cell self-starting is proposed to solve the problems. Besides, phase change material (PCM) is introduced to reduce energy consumption further. The PCM can absorb the waste heat of the fuel cell stack. Then the heat can be used for stack cold start by circulating liquid. In this study, a fuel cell bus cold start system simulating model is built. Based on this model, the fuel cell temperature and energy consumption during the cold start are analyzed. The results show that the method combined with liquid heating and fuel cell self-starting is superior to the liquid heating method. The cold start time and PTC consumption of the PTC-PCM-self-starting heating mode are 19.0 % and 19.2 % less than that of PTC-PCM heating mode. As for the combined heating method, dropping the self-starting temperature can not only increase the cold start speed but also reduce the proportion of electric heating. For every 1 °C decrease, the start-up time is shortened by 1 % on average, and the waste heat utilization rate is increased by 0.5 %. Although increasing the self-starting current can increase energy consumption, it will save more cold start time and reduce the proportion of electric heating. For every 1 A increase, the start-up time is shortened by 0.3 % on average, and the waste heat utilization rate is increased by 0.1 %. The PTC-PCM-self-starting heating method provides a way for fuel cell stack to start quickly and energy-efficiently in low temperature environment.

Performance evaluation on a novel split thermoelectric system driven by solar energy for electric vehicle seats

This paper proposed a novel split thermoelectric system coupled with a photovoltaic panel for electric vehicle seats. The system separates the hot and cold ends of the thermoelectric device over a long distance with the flexible intermediate conductor, which solves the problem of poor heat dissipation at the hot end resulted from the integration of traditional TEC with the vehicle seats and improves the cooling and heating performance. A three-dimensional heat transfer model was established by COMSOL software to study the temperature field and the comprehensive performance. The results demonstrate that the system can maintain the seat temperatures in 27–30 °C in summer and 18–25 °C in winter, and there exists an optimum input power to maximize the COP. In addition, the seat temperature can be reduced from 60 °C to 31 °C in just 20 min under maximum heating load. The system performance is closely linked to the structure of the middle conductors, heat dissipation, solar radiation intensity, and ambient temperature. In winter, the power consumption of the system is reduced by about 84 % compared to the positive temperature coefficient thermistor with the COP being increased by 5.17. The contribution of the photovoltaic panel based on the studied conditions can save about 215.26 kWh of energy per year, and increase the driving distance of electric vehicles by approximately 1435 km.

Investigation of the Positive Temperature Coefficient Resistivity of Nb-Doped Ba0.55Sr0.45TiO3 Ceramics

The demands of low-Curie-temperature (~−10 °C) positive temperature coefficient (PTC) thermistors are increasing in advanced precision integrated circuits and other industries. In this paper, the Nb-doped Ba0.55Sr0.45TiO3(BST)-based PTC resistivity materials are reported. The effects of the sintering process, especially the cooling rate on the PTC properties of the material, are investigated. The results indicate that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 composition of the prepared PTC ceramics demonstrates promising PTC characteristics. These include a Curie temperature as low as −13 °C, a high temperature coefficient of 0.296 at −3.4 °C, a large enough resistivity change of 3.1 over a narrow phase transition temperature range of approximately 38 °C, and moderate resistivity below the Curie temperature. Such properties suggest that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 ceramics are likely suitable for use in thermal management systems designed for low-temperature control.

Wide-range soft anisotropic thermistor with a direct wireless radio frequency interface

Temperature sensors are one of the most fundamental sensors and are found in industrial, environmental, and biomedical applications. The traditional approach of reading the resistive response of Positive Temperature Coefficient thermistors at DC hindered their adoption as wide-range temperature sensors. Here, we present a large-area thermistor, based on a flexible and stretchable short carbon fibre incorporated Polydimethylsiloxane composite, enabled by a radio frequency sensing interface. The radio frequency readout overcomes the decades-old sensing range limit of thermistors. The composite exhibits a resistance sensitivity over 1000 °C−1, while maintaining stability against bending (20,000 cycles) and stretching (1000 cycles). Leveraging its large-area processing, the anisotropic composite is used as a substrate for sub-6 GHz radio frequency components, where the thermistor-based microwave resonators achieve a wide temperature sensing range (30 to 205 °C) compared to reported flexible temperature sensors, and high sensitivity (3.2 MHz/°C) compared to radio frequency temperature sensors. Wireless sensing is demonstrated using a microstrip patch antenna based on a thermistor substrate, and a battery-less radio frequency identification tag. This radio frequency-based sensor readout technique could enable functional materials to be directly integrated in wireless sensing applications.

Research and application of heat recovery and automation monitoring system for new energy vehicle motor equipment

In order to improve the energy efficiency of pure electric vehicles, the author proposes a thermal energy recovery and automation monitoring system for motor equipment based on new energy vehicles. Based on the analysis of the battery thermal management model, a series heat exchange model between the motor and the battery was established. An integrated thermal management system control strategy based on motor waste heat recovery was proposed for electric vehicles in low temperature environments, and simulation and validation were conducted at different environmental temperatures (-10~0 ?). The simulation results show that this configuration can shorten the heating time by 111-343 seconds compared to traditional battery thermal management systems during the heating stage. During the insulation stage, frequent activation of positive temperature coefficient thermistor can be avoided and the battery temperature can be maintained around 20?C, which is not only conducive to extending the battery life but also reduces the comprehensive energy consumption by 4.39-7.70%. On the other hand, this configuration can reduce the impact of low temperature on comprehensive energy consumption from 9.77-2.07%. It is proved that heat recovery can effectively alleviate the range anxiety caused by ambient temperature.

Impact of the change in charge compensation mechanism on the electrical, dielectric, and structural properties of La-doped BaTiO3 ceramics

La-doped BaTiO3 ceramics are essential materials in electronic devices, finding applications in multilayer ceramic capacitors and positive temperature coefficient thermistors. While the electrical properties of La-doped BaTiO3 have been investigated, the impact of its room-temperature resistivity anomaly on dielectric properties remains unclear. We synthesized pristine and La-doped BaTiO3 (0.1 – 0.5 mol%) powders via hydrothermal methods, and then sintered bulk samples. Their resistivities (DC and AC), Curie temperature, room-temperature dielectric constant, and lattice volume with varying La doping concentrations were characterized. Beyond 0.3 mol%, the shift from electronic to ionic charge compensation mechanisms resulted in abrupt changes in resistivities, Curie temperature, and dielectric constant near 0.3 mol%. Given minimal changes in average grain size and relative density near 0.3 mol% La, the dominant factor influencing the dielectric constant peaking near this concentration was the shift in charge compensation mechanism.

γ‐irradiation hardness investigations of (PANI)1−x(Bi2Te3)x composites for thermistor applications

AbstractThe (PANI)1−x(Bi2Te3)x composites were successfully synthesized. These composites have a simple physical combination of intrinsic conducting polymer and nanocrystal topological insulator materials which are promising new materials for unusual applications. The influence of γ‐irradiation (100 kGy doses) on the performance of the (PANI)1−x(Bi2Te3)x composites was described by atypical techniques to assess the radiation hardness of the samples. X‐ray diffraction and Raman spectroscopy measurements show the semi‐crystalline phases, the other structural parameters, and the phonon modes. The compositional analysis and the morphological properties were investigated by energy‐dispersive X‐ray, while transmission electron microscopy imaging confirmed the morphology of the dopants of Bi2Te3 nanoparticles into the polyaniline (PANI) matrix, which shows the accumulation of the particles. Thermogravimetric analysis figured out the degradation behavior of the compositions. The representative electron spin resonance (ESR) signal exhibits a narrow single‐line ESR spectrum for PANI/Bi2Te3 nanoparticle concentrations. (PANI)1−x(Bi2Te3)x illustrates unexpected ferromagnetic behavior that confirms the magnetic performance of the samples without introducing any magnetic dopants. The obtained materials showed promising performance for using such hybrid materials as a positive temperature coefficient thermistor.

Study of Co-Doped K2Ti6O13 Lead-Free Ceramic for Positive Temperature Coefficient Thermistor Applications

Cobalt-doped potassium hexa-titanate (Cox:K2Ti6O13 (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Cox:K2Ti6O13 ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K2Ti6O13 were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K2Ti6O13 ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Cox:K2Ti6O13 and the discovery of positive temperature coefficients of the resistivity of these ceramic samples.

Ultrathin Fiber-Mesh Polymer Thermistors.

Flexible sensors enable on‐skin and in‐body health monitoring, which require flexible thermal protection circuits to prevent overheating and operate the devices safely. Here, ultrathin fiber‐mesh polymer positive temperature coefficient (PTC) thermistors via electrospinning are developed. The fiber‐type thermistors are composed of acrylate polymer and carbon nanofibers. The fibrous composite materials are coated with a parylene to form a core–sheath structure, which improves the repeatability of temperature characteristics. Approximately 5 µm thick fiber‐type thermistors exhibit an increase in the resistance by three orders of magnitude within ≈2 °C and repeatable temperature characteristics for up to 400 cycles. The mesh structure enables the thermistor layer to be ultra‐lightweight and transparent; the mesh‐type thermistor operates with a fiber density of 16.5 µg cm−2, whose fiber layer has a transmittance of more than 90% in the 400–800 nm region. By fabricating the mesh thermistor on a 1.4 µm thick substrate, the thermistor operates without degradation when wrapped around a 280 µm radius needle. Furthermore, the gas‐permeable property is demonstrated by fabricating the fibrous thermistor on a mesh substrate. The proposed ultrathin mesh polymer PTC thermistors form the basis for on‐skin and implantable devices that are equipped with overheat prevention.

Sensing Characteristics of Improved Positive Temperature Coefficient Thermistors with Paint Forms.

The disadvantage of using a typical temperature sensor is limited depending on the shape of the model to be measured. If the shape is curved, it is not easy to check the surface temperature. A smart paint for temperature measurement is proposed to overcome this disadvantage. Polymer solutions were prepared with a dispersion of materials and viscosity with the properties of paint forms. The smart paints showed various sensing characteristics depending on the amount of materials. In addition, it was analyzed through the scanning electron microscopy (SEM) that sliver particles are disposed around the ceramic particles to have electrical conductivity. This study optimized the proportion of ceramics added to smart paints so that they could overcome the limitations of PTC thermistors that can only identify specific temperatures. Therefore, the developed paint-type temperature sensor makes it easy to measure the temperature of various models.

Preparation of chip type negative temperature coefficient thermistor

A thermistor is a class of resistor whose resistance varies with temperature. The two types of thermistors are Negative temperature coefficient (NTC) thermistor and Positive temperature coefficient (PTC) thermistor. NTC thermistors have a negative electrical resistance versus temperature (R/T) relationship. These thermistors are extremely versatile and accurate. This makes them best for a wide variety of applications that measure temperature. They find application in firebrand photographic processing, meteorological, geological, and oceanographic research equipment, as well as in consumer and household appliances. This paper presents the development of a chip-type Mn-Ni based negative temperature coefficient thermistor with varying CuO (Dopant) concentration. The changes in electrical properties are also reported. The expected results indicate an increase in resistivity, material constant and temperature coefficient of resistance (a) with an increase in CuO concentration for all the compositions.

Protection Devices in Commercial 18650 Lithium-Ion Batteries

18650 Lithium-ion batteries are wildly used as power sources for portable electronics because of the standardized format and economical manufacturing cost. However, commercial 18650 cells come in various designs due to the implementation of different protection devices. The current interrupt device and top vent are mandatory protection devices for all commercial 18650 Li-ion batteries. In contrast, the positive temperature coefficient thermistor, bottom vent, and protection circuit are optional protection devices that can be non-installed, installed separately, or combined in commercial 18650 batteries. Four representative commercial 18650 Li-ion batteries were disassembled and compared in terms of the similarities and differences of the protection devices. This paper overviews the working mechanism, advantages, and drawbacks of each protection device. Recommendations on battery selection and potential future trends are then provided.

Fabrication of Ferroelectric Liquid Crystal Thermistor

Thermistor is fabricated using thermotropic ferroelectric liquid crystalline material. The design, performance, and characteristics of this fabricated liquid crystal (LC) device are demonstrated in this article. As a representative case, the characteristics of two ferroelectric LCs (FLCs), which exhibit positive and negative temperature coefficients of resistance, are detailed. An ambient temperature ferroelectric mesogen (S)-1-[4’-(octyloxy carbonyl) phenyl]-4-[2-chloro-(4-benzamido acetyl) phenyl propionato]-Benzoate yielded negative temperature coefficient thermistor, while dextro tartaric acid with p-n decyloxy benzoic acid ferroelectric mesogen was used as a positive temperature coefficient (PTC) thermistor. This endeavor was not reported in the literature, where thermotropic mesogens are being used for thermistor [PTC and negative temperature coefficient (NTC)] application. This thermistor possesses a wide temperature range (~69° C) with a resolution of $0.05~\mu $ AV−1 and accuracy of ±0.1 °C which is more competent than its conventional counterpart. Furthermore, the heat capacity of the LC-based thermistor device is 0.2 Jg−1 K−1 for PTC and 0.4 Jg−1 K−1 for NTC.

Free standing tapes of donor doped BaTiO3 for multilayer positive temperature coefficient thermistors

A disruptive method of fabricating free-standing tapes of La-doped (BaCaSrPb)TiO 3 thermistors is demonstrated. The greatest advantage is that the free-standing tapes do not require high temperature co-firing of electrodes or reduced environment cofiring — soft oxidation cycle to obtain thermal sensitivity. The approach thus solves the long-standing problem with the ceramic thermistor technology that eluded its compatibility with surface mount technology (SMT) and miniaturization. Stencil printing is employed that can fabricate up to 500 μm thick tapes in a single step, saving huge cost and processing steps for application requiring thicker films. The pastes suitable for freestanding tapes are reported. The method provides a novel route to integrate PTC elements into the chips of passive components and would lead to a massive reduction in cold resistivity when developed in multilayer laminated stacks.

Free standing tapes of donor doped BaTiO3 for multilayer positive temperature coefficient thermistors

A disruptive method of fabricating free-standing tapes of La-doped (BaCaSrPb)TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> thermistors is demonstrated. The greatest advantage is that the free-standing tapes do not require high temperature co-firing of electrodes or reduced environment cofiring — soft oxidation cycle to obtain thermal sensitivity. The approach thus solves the long-standing problem with the ceramic thermistor technology that eluded its compatibility with surface mount technology (SMT) and miniaturization. Stencil printing is employed that can fabricate up to 500 μm thick tapes in a single step, saving huge cost and processing steps for application requiring thicker films. The pastes suitable for freestanding tapes are reported. The method provides a novel route to integrate PTC elements into the chips of passive components and would lead to a massive reduction in cold resistivity when developed in multilayer laminated stacks.

Asynchronous sliding mode control of singularly perturbed semi-Markovian jump systems: Application to an operational amplifier circuit

This paper gives a new systematic framework to solve the asynchronous sliding mode control (SMC) problem for the semi-Markovian jump systems with singular perturbations, which can effectively remove the dependence on the unavailable system mode of SMC controller in some existing works. By considering the effect of the singular perturbation, this paper introduces a novel ε-dependent common sliding function, and then an asynchronous SMC law is developed by just using the detected mode signal. In order to overcome the difficulties in analyzing the stability of the sliding mode dynamics and the reachability of the specified sliding surface, a novel matrix decoupling technique and a novel semi-Markovian Lyapunov function method are introduced. Besides, genetic algorithm (GA) is employed to solve two meaningful optimization problems arising from designing a desired asynchronous SMC scheme. Finally, an operational amplifier circuit with a switching positive temperature coefficient thermistor is simulated to show the practicability of the proposed asynchronous SMC approach via GA.

Piezoresponse force microscopy and electron backscattering diffraction of 90° ferroelectric twins in BaTiO3 positive temperature co-efficient thermistors

The positive temperature co-efficient (PTC) of resistivity in BaTiO3 is a grain boundary effect, where the resistivity increases by several orders of magnitude near the transition temperature from ferroelectric (tetragonal) to paraelectric (cubic) phase. We combine electron backscatter diffraction (EBSD) and piezoresponse force microscopy (PFM) to investigate the crystallographic orientation, topography, and intergranular polarization in polycrystalline PTC BaTiO3 ceramics leading to PTC effect. EBSD study showed that while macroscale BaTiO3 displayed no overall preferential crystallographic orientation, individual grains had preferred orientations at a localized level. Twinning patterns were revealed by EBSD and PFM images showing classical 90° ferroelectric domain patterns.

Gamma radiation induced fabrication of styrene butadiene rubber/ magnetite nanocomposites for positive temperature coefficient thermistors application

A new positive temperature coefficient resistor (PTCR) thermistor based on styrene butadiene rubber/nanomagnetite (SBR/Fe3O4) nanocomposite was successfully fabricated by conventional roll milling technique.XRD, FT-IR,TEM and EDX techniques were utilized to elucidate the developed of magnetite nanoparticles the analyses revealed a diameter of 9–11 nm.The (SBR/Fe3O4) nanocomposite was examined via the XRD patterns and SEM micro images before and after gamma irradiation. The mechanical properties of the developed nanocomposites: tensile strength, elongation at break and elastic modulus were investigated, whilst the thermal stability was analyzed by TGA. Explicit improvement was been noticed by elevation of the nano load and radiation dose within the cited range. The electrical conductivity examination and the derived thermistor constant, sensitivity and stability of irradiated nanocomposite, 10% Fe3O4 at 100 kGy ensured typical PTCR.

The Thermistor Problem with Hyperbolic Electrical Conductivity

This paper presents the one-dimensional, positive temperature coefficient (PTC) thermistor equation, using the hyperbolic-tangent function as an approximation to the electrical conductivity of the device. The hyperbolic-tangent function describes the qualitative behaviour of the evolving solution of the thermistor in the entire domain. The steady state solution using the new approximation yielded a distribution of device temperature over the spatial dimension and all the phases of the temperature distribution of the device without having to look for a moving boundary. The analysis of the steady state solution and the numerical solution of the unsteady state is presented in the paper.

Wind direction sensor based on thermal anemometer for olfactory mobile robot

A wind direction sensor has been implemented for many applications, such as navigation, weather, and air pollution monitoring. In an odor tracking system, the wind plays the important role to carry gas from its source. Therefore, the precise, low-cost, and effective wind direction sensor is required to trace the gas source. In this study, a new design of wind direction sensor has been developed using thermal anemometer principle with the main component of the positive temperature coefficient thermistor. Three anemometers each of which has different directions are used as inputs for the neural network to determine the direction of the wind automatically.The experimental results show that the wind sensor system is able to detect twelve wind directions. A mobile robot equipped with this sensor system can navigate to a wind source in the open air with a success rate of 80%.This system is expected to increase the success rate of the mobile robot in searching for dangerous leaking gas in the open air.