Characteristics of a Type of NTC Thermistors for Cryogenic Applications

A new type of miniature negative temperature coefficient (NTC) thermistors has been developed and manufactured with Mn-Ni-Cu-Fe oxides. The prepared NTC thermistors were calibrated in the temperature range from 77 K to 300 K with 1 μA exciting currents. The automatic calibration apparatus as well as thermometric characteristics, stability, calibration equations and interchangeability of the manufactured thermistors were investigated. A mean fit equation was obtained: 1/T = 8.60 × 10−4 + 6.54 × 10−4 ln(R/Rref) + 2.46 × 10−5 ln(R/Rref)2 + 9.48 × 10−7 ln(R/Rref)3 − 2.16 × 10−8 ln(R/Rref)4. All the prepared NTC thermistors agreed with this fit with an error of 1.5 K. If the greater accuracy is required, a calibration is necessary, and the calibration accuracy is estimated to be ±10 mK.

Enhanced thermal constant B of diamond films for ultrahigh sensitivity negative temperature coefficient thermistors

Negative temperature coefficient(NTC)thermistor plays a crucial role in science research and engineering applications for precise temperature monitoring.Although great progress has been achieved in NTC materials,enhancing sensitivity and maintaining this high sensitivity along with linearity across extensive temperature ranges remain a significant challenge.In this study,we introduce a diamondbased thermistor(DT)characterized by its outstanding sensitivity,swift response time,and broad temperature monitoring capabilities.The temperature constant B for this DT,measured from 30 to 300°C(B30/300),achieves an exceptional value of 8012 K,which notably exceeds the temperature sensing capabilities of previously reported NTC thermistors within this extensive range.Moreover,diamond’s unique thermal conductivity and stability significantly boost the response speed and durability of the DT,offering substantial advantages over traditional ceramic thermistors.The enhanced temperature-sensitive properties of the DT are attributed to the presence of impurity elements in polycrystalline diamond.Impedance analysis indicates a hopping conduction mechanism,likely involving C-H or C-N dipoles at the diamond grain boundaries.This study marks a significant leap forward in diamond thermistor technology and sheds light on the mechanisms of thermal active conduction in diamond materials.

Characterization of new negative temperature coefficient thermistors based on Zn-Ni-O system

Y2O3-doped Zn1-xNixO (x=0,0.3,0.4,0.5,0.6,0.7,and 0.9) powders were prepared by a wet chemical synthesis method,and the related ceramics were obtained by the traditional ceramic sintering technology.The phases and related electrical properties of the ceramics were investigated.The analysis of X-ray diffraction (XRD) indicates that the prepared ceramics with Ni substitution have a cubic crystalline structure.The resistance-temperature feature indicates that all the ceramics show a typical effect of negative temperature coefficient (NTC) of resistivity with the thermal constants between 3998 and 5464 K,and have high cyclical stability in a temperature range from 25 to 300 ℃.The impedance analysis reveals that both grain effect and grain boundary effect contribute collectively to the NTC effect.The electron hopping and band conduction models are proposed for the grain (bulk) conduction,and the thermally activated charge carrier transport overcoming the energy barrier is suggested for the grain boundary conduction.

Fabrication of nano-grained negative temperature coefficient thermistors with high electrical stability

Dense nano-grained Ni_(0.7)Mn_(2.3O4) negative temperature coefficient(NTC) thermistors were fabricated by a novel two-step sintering approach that combines rapid sintering and principle of conventional two-step sintering technique.Samples were sintered at 1042℃ for 30 s in the first rapid step and then at 850-950℃ for 20 h in the second soaking step.Crystal phase,microstructure and electrical properties of sintered samples were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),resistance temperature relationship and aging performance.Sintered samples show a single-phase cubic spinel structure and indicate a high relative density ranging from 84% to 91% of the theoretical density.Moreover,average grain sizes of sintered samples under SEM are distributed between 254 and 570 nm.Meanwhile,the resistivity and the aging coefficient significantly decrease when soaking sintering temperature rises.In addition,the obtained material constant(B) ranges from 3931 to 3981 K.Ni_(0.7)Mn_(2.3)O_(4)-3(soaking at 900℃) and Ni_(0.7)Mn_(2.3O4)-4(soaking at 950℃) present little aging behavior,implying great electrical stability.

Dynamics and coherence resonance in a thermosensitive neuron driven by photocurrent

A feasible neuron model can be effective to estimate the mode transition in neural activities in a complex electromagnetic environment.When neurons are exposed to electromagnetic field,the continuous magnetization and polarization can generate nonlinear effect on the exchange and propagation of ions in the cell,and then the firing patterns can be regulated completely.The conductivity of ion channels can be affected by the temperature and the channel current is adjusted for regulating the excitability of neurons.In this paper,a phototube and a thermistor are used to the functions of neural circuit.The phototube is used to capture external illumination for energy injection,and a continuous signal source is obtained.The thermistor is used to percept the changes of temperature,and the channel current is changed to adjust the excitability of neuron.This functional neural circuit can encode the external heat(temperature)and illumination excitation,and the dynamics of neural activities is investigated in detail.The photocurrent generated in the phototube can be used as a signal source for the neural circuit,and the thermistor is used to estimate the conduction dependence on the temperature for neurons under heat effect.Bifurcation analysis and Hamilton energy are calculated to explore the mode selection.It is found that complete dynamical properties of biological neurons can be reproduced in spiking,bursting,and chaotic firing when the phototube is activated as voltage source.The functional neural circuit mainly presents spiking states when the photocurrent is handled as a stable current source.Gaussian white noise is imposed to detect the occurrence of coherence resonance.This neural circuit can provide possible guidance for investigating dynamics of neural networks and potential application in designing sensitive sensors.

Characterization of the BaBiO_3-doped BaTiO_3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with T_c=155℃

BaBiO3-doped BaTiO3 （BB-BT） ceramic, as a candidate for lead-free positive temperature coefficient of resistivity （PTCR） materials with a higher Curie temperature, has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature, Tc = 155℃, which is higher than that of BaTiO3 （≤ 130 ℃）. Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current （AC） resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data, the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature, indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency, the conduction mechanism is also discussed for a BB-BT ceramic system.

AN APPARATUS FOR MEASURING THERMAL CONDUCTIVITY OF LIQUIDS UNDER HIGH PRESSURE

We have reported a method for measuring the thermal conductivity of liguids un-der high pressure previously [1,2].Such data are necessary for improving thetechnologies such like processing as acidity,pressure cracking,thermal exploitation ofpetroleum,etc. An apparatus has thus been constructed,as shown schematically in Fig.1,tomeasure the thermal conductivity of liquids under pressure up to 25 MPa and temperatureranging from 150 to 250℃.The thermal conductivity cell is cylindrical in from,35mmin length and 25mm in inner diameter.The sample is poured into the cell through

The Printing and Firing Process of Al Paste in PTC Ohmic Contact Electrodes

Al electrodes are well known as ohmic contact electrodes for the PTC component , the influence of their thickness on final component properties was investigated by comparing their ohmic characteristics with the ones of InGa electrodes . After observing the Al paste physical and chemical behaviors during rising temperature by thermal analysis (DTA), the firing operation of Al electrodes could be divided into three main subsections: the temperature rising time (t-r), the peak firing temperature (T-p) and the hold time at peak firing temperature (t-h). The effects of these three parameters on final component properties were discussed in detail.

Modified Function Transformation Method for Linearizing Thermistor Characteristics

A mathematical method called Modifled Function Transformation Method(MFTM) for linearizing thermistors is proposed.Theoretically,the method has unified many schemes of linearizing thermistors into a mathematical rational frame,and explained the reason of different circuits having the same capabilities for linearizing the thermistor characteristics.

A Simulation of the Response of a Sounding Temperature Sensor Based on the Combination of a Genetic Algorithm and Computational Fluid Dynamics

The present study aims at improving the accuracy of weather forecast by providing useful information on the behavior and response of a sounding temperature sensor.A hybrid approach relying on Computational Fluid Dynamics and a genetic algorithm(GA)is used to simulate the system represented by the bead thermistor and the surrounding air.In particular,the influence of different lead angles,sensor lead length,and lead number is considered.The results have shown that when the length of the lead wire of the bead thermistor is increased,the radiation temperature rise is reduced;when the number of lead wire is four and the angle between the lead wires is 180°,the solar radiation angle has a scarce influence on the radiation temperature rise of the sounding temperature sensor.

Study on Low Resistance PTC Ceramic Material

The low resistance PTC ceramic thermistor material with excellent eleectricalproperties are successfully fabricated by raw materials at industrial range made in our country onthe study of its composition expression and fabrication process by using the addition of Nb, La, Y,Ta , microstructure regulator BN and ASTL phase . The composition and its fabrication method arestudied. The relation of electrical properties of the PTC ceramic material to its compositionexpression and its related electrical properties are discussed

Ovulation detection mechanism—a microcomputer based approach

This paper presents a real-time microcomputer-based logger for measuring basal body temperature (BBT). BBT is the normal resting body temperature of a healthy person immediately upon waking in the morning. The temperature for women normally rises after ovulation due to hormonal changes. The temperature is logged real-time into the computer over a period and the BBT chart produced is used to predict ovulation. There is high correlation between the approach developed by this study and other standard measuring equipments—correlation of 0.9945with standard thermistor, and correlation of 0.9977 with standard thermocouple. This development enables privacy of use, allowing women to predict their ovulation status at a personal level.

A novel(Sm_(0.2)Eu_(0.2)Gd_(0.2)Ho_(0.2)Yb_(0.2))CrO_(3)high-entropy ceramic nanofiber as a negative temperature coefficient thermistor

The electrical properties of high-entropy ceramics(HECs)have been extensively studied in recent years due to their unique structural characteristics and fascinating functional properties induced by entropy engineering.Novel high-entropy(Sm_(0.2)Eu_(0.2)Gd_(0.2)Ho_(0.2)Yb_(0.2))CrO_(3)(HE-RECrO_(3))nanofibers were prepared by electro spinning.This work demonstrates that HE-RECrO_(3)nanofibe rs were successfully synthesized at a low temperature(800℃),which is approximately 400℃lower than the temperatures at which chromate ceramics were synthesized via the sol-gel method and the solid-state reaction method.The resistivity of HE-RECrO_(3)nanofibers decreases exponentially with increasing temperature from 25 to600℃.The logarithm of the resistivity is linearly related to the inverse of the temperature,confirming the negative temperature coefficient property of HE-RECrO_(3)nanofibers.The B_(25/50)value of the HERECrO_(3)nanofibers reaches 4072 K.In conclusion,HE-RECrO_(3)nanofibers are expected to be potential candidates for negative-temperature-coefficient(NTC)thermistors.

Frequency and temperature dependent electrical characteristics of CaTiO_(3) nano-ceramic prepared by high-energy ball milling

Nanocrystalline calcium titanate(CT)ceramic has been synthesized by a combination of solid-state reaction and high-energy ball milling.This nano-ceramic is characterized by X-ray diffraction(XRD),dielectric study and impedance spectroscopy.The XRD pattern shows single phase ceramic of orthorhombic symmetry.The frequency-dependent dielectric study shows that the dielectric constant is maximized at low frequencies and decreases with an increase in frequency.Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon.A significant shift in impedance loss peaks toward the higher-frequency side indicates conduction in the material favoring the long-range motion of mobile charge carriers.The grain conduction effect is observed from the complex impedance spectrum by the appearance of one semicircular arc in Nyquist plot.It is also observed that the resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance(NTCR).Various thermistor parameters have been calculated by fitting with Steinhart-Hart equation.The modulus plots represent the presence of temperature-dependent electrical relaxation phenomenon with the material.The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated.The activation energy has been calculated from an Arrhenius plot of DC conductivity and relaxation frequency.

Enhanced time response and temperature sensing behavior of thermistor using Zn-doped CaTiO_3 nanoparticles

In the present study, Zn-doped CaTiO_3 nanocrystalline was synthesized to study the thermistor behavior with temperature. The X-ray powder diffraction analysis showed the formation of a single-phase orthorhombic structure at room temperature. The electrical resistance of the Zn-doped CaTiO_3 increased with increasing doping concentration and decreased at higher measuring temperature, showing a negative temperature coefficient of resistance(NTCR) behavior. Different thermistor parameters were calculated using Steinhart–Hart equations, whilst time domain analysis confirmed faster response towards applied voltage.

CaTiO_(3) nano ceramic for NTCR thermistor based sensor application

It is possible to fabricate highly sensitive NTCR(negative temperature coefficient of resistance)thermistor using nano crystalline CaTiO_(3) synthesized by high energy ball milling.Disc shaped green pellets were prepared and effects of sintering on the disc pellets were studied as thermistor by sintering the samples at 1000℃,1100℃and 1200℃.The as-prepared samples were characterized by X-ray diffraction(XRD),impedance analysis and electrical measurement.The resistivity of the prepared samples varies predictably with temperature:this makes them promising material for temperature sensor.The experimental results prove that nano crystalline CaTiO_(3) ceramic is one kind of thermistor with exponential negative temperature coefficient of resistance in the temperature range of 300-500℃.The samples have the advantages of rapid response,high sensitivity and capability to withstand thermal surges over the temperature range of 300-500℃.Resistance-temperature characteristics are described by thermistor equation with thermistor constant around 4003 K to 10795 K and thermal coefficient of resistanceαaround-1%/℃to-13%/℃.The activation energy is in the range of 0.34-0.93 eV.The observed thermistor parameters are found to be comparable with many of the known thermistor materials.This suggests that the electrical properties can be adjusted to desirable values by controlling the temperature parameter.The influence of fabrication process of disc thermistor and electrical properties are discussed.The study shows the potential of nano crystalline CaTiO_(3) to act as an NTCR material for thermistor applications.

Electronic and magnetic stability in correlated transportations of rare-earth nickelate perovskites

Although the thermistor and metal to insulator transition bi-functionalities were discovered for rareearth nickelates(RENiO3),the electronic stability in their correlated transports under impulse voltage or magnetic field remain as open questions.Herein,we demonstrate the thermistor transportations of the electron correlated rare-earth nickelates under impulse direct current voltage and in magnetic environment.The insulating phase of RENiO3 shows zero crossing linear I-V characters,indicating their stable electronic resistance is independent of the imparted voltage up to 10 V and pulse width down to1 us,in spite of their sensitive electronic structures to polarizations.In addition,the high electronic stability associated with the thermistor transportation of RENiO3 is also demonstrated in magnetic fields up to 9 T(i.e.,MR<0.2%).The high electronic stability further paves the way to applying RENiO3 as a broad temperature range thermistor in temperature sensing or circuit protections for correlated electronics.

NUMERICAL ANALYSIS OF NONSTATIONARY THERMISTOR PROBLEM

The thermistor problem is a coupled system of nonlinear PDEs which consists of the heat equation with the Joule heating as a source, and the current conservation equation with temperature dependent electrical conductivity. In this paper we make a numerical analysis of the nonsteady thermistor problem. L(infinity)(OMEGA), W1,infinity(OMEGA) stability and error bounds for a piecewise linear finite element approximation are given.

PTC Effect and Its Mechanism in a Novel Thermistor Material —— Hot-pressed SiC/SiO_2 Multiphase Ceramic

As functional materials, PTC thermistor ceramics characterized by a drastic increase in resistivity at its transition temperature have been widely used in high-technology areas such as temperature measurement and indication, temperature control, protective switches and so on. At present, the PTC thermistors are fabricated by means of doping BaTiO3 and their PTC effects result from the existence of acceptor state or electronic trap on grain boundary. But the fabrication process

Correlation of Spherical Thermistor for the Measurement of Low Velocity Air Flow

A spherical thermistor, an accurate temperature sensor, is employed as an air velocity sensor in this work. The measuring principle is derived and the effects of the insulation layer, air temperature, natural convection and thermal radiation are discussed. Two different correlation relations for velocity measurements are proposed based on theoretical analyses and experimental calibrations. Experiments have shown that spherical thermistor is a good velocity sensor for speed between 0.1-2.5 m/s at room temperature and the insulation layer hardly influences the accuracy of the thermistor used in the present work. Modification on correlation can even further improve measurement accuracy. Since the thermistor is small and cheap, it is possible to apply this method to multi-point velocity measurement with a low disturbance to the flow field.