Sensitive Thermistor Research Articles

The development and characterisation of 3D-printed multi-material thermistor

This paper introduces a multi-material, low-cost, and highly sensitive thermistor concept developed for body temperature monitoring. The designed thermistor utilises poly(3,4-ethylenedioxythophene):poly(4-styrenesulfonate) (PEDOT:PSS) for the temperature sensing layer, silver (Ag) for the contact electrodes, and polycarbonate (PC) as the substrate. In contrast to traditional printed electronics substrates used in thermistor development, the utilisation of Material Extrusion via Fused Deposition Modelling (FDM) for the manufacture of PC substrates is the distinct feature of the work. For the manufacture of multi-material thermistors, two different Additive Manufacturing (AM) methods, FDM for substrates and micro dispensing for PEDOT:PSS sensing layer and Ag electrodes, were employed. Two thermistors with varying sensing areas, namely D1 and D2, were designed and fabricated. The thermistors demonstrated a high degree of linearity and repeatability within the temperature range of 25–45°C with a viable hysteresis maximum around 3 %. The measurement sensitivity of thermistors was assessed based on Temperature Coefficient of Resistance (TCR) values, which were –0.68 ±0.057 % and –0.49 ±0.078 % per °C for the D1 design and –0.53 ±0.078 % and –0.40 ±0.069 % per °C for the D2 design, during heating and cooling, respectively. Comparable average response and recovery times to those reported in the literature were also acquired, which were 31.47 ±1.02 and 54.42 ±0.70 seconds for the D1 design and 27.38 ±0.96 and 48.45 ±1.69 seconds for the D2 design, during heating and cooling, respectively. It was evident that the sensing area had an impact on thermistor TCR as well as response and recovery times, where higher TCR and faster response and recovery times were recorded with the small sensing area. It was also observed that humidity had a significant impact on thermistor reliability, exhibiting a normalised resistance change of ∼12 % and ∼9 % of the initial measurement at 50 % and 75 % RH, respectively. When compared to PEDOT:PSS-based thermistors reported in the literature, the obtained results in this research have demonstrated that our multi-material thermistor concept is a promising candidate for the low-cost and highly sensitive multi-material thermistor that can be manufactured in a fully additive manner using AM technologies.

A Prosthetic Hand with Integrated Sensing Elements for Selective Detection of Mechanical and Thermal Stimuli

Flexible electronics have gained popularity because of their capability to combine softness and functionality. Soft resistive sensors are susceptible to mechanical stimuli and detecting temperature selectively remains a challenge. In this study, soft flexible thermistors are developed for detecting temperature changes based on the positive temperature coefficient (PTC) effect, selectively. By thermomechanical analysis and differential scanning calorimetry, it is observed that thermoplastic elastomers with higher thermal expansion and semicrystalline morphology result in a sensitive thermistor response. To achieve a high sensitivity in temperature and low sensitivity in the detection of mechanical stimulus, a low‐carbon filler content is required. The opposite trend is seen for the piezoresistive sensors for mechanical strain detection. Both sensory material types are compatible with thermoplastic material extrusion‐based additive manufacturing. The method is used for the fabrication of the sensing elements and an open‐source prosthetic hand. The strain sensor detects the bending of the fingers and the temperature sensor detects the temperature when in contact with a heated surface, successfully. In addition, the temperature sensor is used as a tactile sensor to detect contact with a non‐heated surface. Combining selective multisensory capabilities will significantly affect the future development of sensorized prosthetic devices and wearable electronics.

Growth and pre-cooling doping of semiconducting C-doped hBN as a sensitive thermistor

This letter describes the growth of hexagonal boron nitride (hBN) on plateau and terrace regions of nickel foil by tuning the V/III ratio of NH3 and B2H6, followed by pre-cooling carbon doping with CH4. The V/III ratio = 120 with a growth duration of 30 min is good to grow ∼ 14 nm-thick hBN for the application requiring it as an insulator. Pre-cooling doping by CH4 is possible because crystallizing BN prevents carbon from diffusing into bulk nickel and allows the substitution of nitrogen atoms. The C-doped hBN is having a lowered bandgap of 5.79/5.47 eV, sub-bandgap of 2.86 eV, narrowed Raman E2g peak on plateau and terrace regions, a slight decrease in nitrogen atomic%, and reduced thickness. These convert hBN from an insulator into a semiconductor. The C-doped hBN is a very sensitive thermistor with a temperature coefficient of resistance up to –0.037 K−1.

Cost-Effective Sensor for Flow Monitoring in Biologic Microreactors

Continuous nutrient supply of cell cultures in perfused bioreactors requires reliable flow monitoring. This work presents an approach for the flow rate measurement based on low temperature ceramic technology, which allows the direct integration of temperature sensors in the center of fluid channels. Thick film thermistors detect the flow rate in two different operation modes: the calorimetric addresses flow rates from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{l}$ </tex-math></inline-formula> /min to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu \text{l}$ </tex-math></inline-formula> /min and the time of flight flow such as up to 1.5 ml/min. The design takes advantage of highly sensitive thermistors with negative temperature coefficient, and optimized heat exchange due to the direct thermal contact between fluid and temperature probe. In addition to calorimetric evaluation, the temperature course as a function of time is used to detect the time of flight. This allows the tracking of the flow rate independent from the thermistor’s temperature characteristic using the temperature maximum as marker. Cross-correlation applied to this temperature problem significantly improves the detection accuracy for the time of flight. Based on temperature and flow measurement data, it was proven that a fit function could replicate the flow rate as a function of the difference in time of flight between two thermistor positions with a deviation less than 4 %. The evaluation of time of flight data can extend the operation range of the sensor by two orders of magnitude. Applying this signal processing, the same method can be applied even for low flow rates, with a measurement range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$30~\mu \text{l}$ </tex-math></inline-formula> /min to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1500~\mu \text{l}$ </tex-math></inline-formula> /min.

Fast and sensitive bolometric terahertz detection at room temperature through thermomechanical transduction

Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

High Precision Temperature Control System for an Oven-Controlled Crystal Oscillator

Environmental temperature is a highly influential factor regarding the stability of the crystal oscillator frequen- cy. Thus, a high precision temperature control system is critical for improving the frequency stabilization of crystal oscil- lators. This paper proposes a temperature control system, including a high sensitive thermistor, precision reference voltage source and an instrumentation amplifier for the temperature measurement and preamplifier. System level MCU— MSC1210 acts as a main controller, and a novel way of the interrupt + ribbon strategy is adopted to realize real-time task scheduling. The PID controller program is crafted with the help of the anti-integral saturated and bumpless trans- fer algorithms. The cascade control system with the heating current of negative feedback is then realized using the triode tube consumption heating style. The results show that the temperature and fluctuation of heat voltage have almost no ef- fect on the heating current when the heating system voltage fluctuates between 2.2 ~ 8V. Within those parameters, the temperature deviation remains within 0.01 degrees. Thus it can be seen that the high-performance temperature control sys- tem has a high anti-interference capability and a similarly high level of accuracy.

Planar electrical-substitution carbon nanotube cryogenic radiometer**Contribution of an agency of the US government; not subject to copyright

We have developed a fully-lithographic electrical-substitution planar bolometric-radiometer (PBR) that employs multiwall vertically-aligned carbon nanotubes (VACNT) as the absorber and thermistor, micro-machined Si as the weak thermal link and thin-film Mo as the electrical heater. The near-unity absorption of the VACNT over a broad wavelength range permits a planar geometry, compatible with lithographic fabrication. We present performance results on a PBR with an absorption of 0.999 35 at 1550 nm, a thermal conductance of 456 µW K−1 at 4 K and a time constant (1/e) of 7.7 ms. A single measurement of approximately 100 µW optical power at 1550 nm achieved in less than 100 s yields an expanded uncertainty of 0.14% (k = 2). We also observe an elevated superconducting transition temperature of 3.884 K for the Mo heater, which opens the possibility of future devices incorporating more sensitive thermistors and superconducting thin-film wiring.

Development of a semi-adiabatic isoperibol solution calorimeter.

A semi-adiabatic isoperibol solution calorimeter has been indigenously developed. The measurement system comprises modules for sensitive temperature measurement probe, signal processing, data collection, and joule calibration. The sensitivity of the temperature measurement module was enhanced by using a sensitive thermistor coupled with a lock-in amplifier based signal processor. A microcontroller coordinates the operation and control of these modules. The latter in turn is controlled through personal computer (PC) based custom made software developed with LabView. An innovative summing amplifier concept was used to cancel out the base resistance of the thermistor. The latter was placed in the dewar. The temperature calibration was carried out with a standard platinum resistance (PT100) sensor coupled with an 8½ digit multimeter. The water equivalent of this calorimeter was determined by using electrical calibration with the joule calibrator. The experimentally measured values of the quantum of heat were validated by measuring heats of dissolution of pure KCl (for endotherm) and tris (hydroxyl methyl) amino-methane (for exotherm). The uncertainity in the measurements was found to be within ±3%.

SU-E-I-45: Measurement of CT Dose to An HDPE Phantom Using Calorimetry: A Feasibility Study.

Radiation dose in CT is traditionally evaluated using an ionization chamber calibrated in terms of air kerma in a phantom of specific dimensions. The radiation absorbed dose, J/kg, can also be realized directly by measuring the temperature rise in the medium. We investigate using this primary method to determine the CT dose at a point (a few mm), using the recently proposed (APMM TG220) high density polyethylene (HDPE) phantom as a medium. The calorimeter detection scheme is adapted from the second generation NIST water calorimeter using sensitive thermistors in a Wheatstone bridge powered by a lock-in amplifier. The temperature sensitivity is about 3 microK. The expected temperature rise in PE is about 0.6 mK per Gy. The thermistor sensors were placed inside a 26 cm dia. × 10 cm HDPE phantom. Two preliminary tests were made: at a linear accelerator with a 6 MV photon beam, and at a 16-slice CT scanner with a 120 kV beam, each with the thermal sensor and with a calibrated ionization chamber. The 6 MV photon beam with 10 on/off cycles at 60 s each yielded the (uncorrected) run-to-run average dose of 3.06 Gy per cycle (sdm 0.3%), about 8% higher than the Result from the ionization chamber (calibrated in terms of absorbed to water). The CT measurements were also made in the middle section of the TG200 30 cm phantom. Twenty consecutive axial scans at 250 mA, which delivers a nominal accumulated dose (CTDIvol) of 705 mGy in 50 s at three axial and three radial locations were measured. The accumulated dose measured by the ionization chamber at the center of the smaller phantom was 347 mGy. The calorimeter data show qualitative tracking of the chamber measurements. Detailed thermal and electrical analysis of the system are planned to obtain quantitative results.

Silicon hot-electron bolometers with single-electron transistor readout

With the goal of making high-sensitivity bolometers for low-background measurements in the far-infrared or submillimeter, we have made small silicon thermistors, which act as hot-electron bolometers, with integrated single-electron transistors for readout amplifiers. Semiconductors doped just below a metal–insulator transition can make highly sensitive thermistors that have been used as thermometers in X-ray microcalorimeters and FIR bolometer arrays. In such arrays, thermal isolation is engineered by supporting the absorber and thermometer on a membrane. However, electron–phonon decoupling in doped silicon can be made the dominant thermal isolation by reducing device volume, potentially allowing a smaller thermal conductance and a more sensitive bolometer. A key feature is that, while its DC resistance is very high, the thermistor's surface impedance at terahertz frequencies is conveniently low, making feasible efficient antenna coupling of radiation into the electron system. Radio-frequency single-electron transistors integrated with the thermistors have sufficiently low input capacitance to offer high-speed readout of the high impedance detectors.

Tissue heating of the skin flap in cochlear implant users

The relative temperature of the skin directly over the implant was measured in three patients. An impedance bridge with a pair of sensitive thermistors (each about 0.12 inches in diameter) was attached to the skin, one underneath the transmitter and one some distance away. Good contact was established with conductive paste and plastic tape. After an initial settling phase (‘No trans’, see Figure 1), the transmitter was applied (‘RF off ’) resulting in a rapid heating of about 2oC. In patient JV, the transmitter itself was cooler than room temperature when it was applied. Powering up the implant (‘RF on’) further increased the temperature by about 1.8oC (subject JdeW), but after 10 to 15 minutes a cooling became visible (patients CG and JV), resulting in an effective heating of about 1oC. After switching the processor off (‘RF off 2’) temperature returned to baseline, except in patient JV. In two patients, time allowed a last phase without transmitter (‘No trans 2’). The baseline temperature was not reached within the time window considered. Especially in JV a long-lasting residual effect seemed to be present.

Sol–gel based thermal biosensor for glucose

A sol–gel (SG) based glucose biosensor using thermometric measurement is reported. The enzymes (glucose oxidase, GOD and catalase, CAT) were entrapped on the surface of reticulated vitreous carbon cylinder (RVC cartridge) using SG as a binder. This ‘RVC cartridge’ was placed within the column of an enzyme thermistor (ET) device. Injection of various d-glucose concentrations resulted in changing the heat content of the circulating buffer, recorded as a thermometric peak by a sensitive thermistor. Independent calibration curves between 10 and 50 mM and between 0.2 and 1 mM d-glucose was obtained by plotting the d-glucose concentration versus the thermometric peak height. The sensitivity of the response was optimized to 1 ml min −1 flow rate of the buffer. The stability of the entrapped GOD/CAT stored at room temperature (25°C) or 4–10°C was 3 or 6 months, respectively. The effect of dissolved oxygen and other interferents such as acetaminophen, ascorbic acid, aspartic acid, glutamic acid, urea and uric acid, on the catalytic activity of the enzyme was also investigated. This system was employed to detect glucose in samples of fruit juice, coca cola and human blood serum.

Highly sensitive thermistors based on high-purity polycrystalline cubic silicon carbide

It is possible to fabricate highly sensitive thermistors using polycrystalline, intentionally undoped, chemical vapor deposition cubic SiC wafers. Resistance–temperature characteristics described by thermistor equations with thermistor constants around 7000 K from 25°C to 200°C and around 5000 K from 200°C to 400°C are presented (temperature coefficient of resistance at 25°C=−7.9%/K). The influence of the fabrication process on thermistor characteristics as well as conduction mechanisms are discussed.

Measurement of heat evolution and correlation with oxygen consumption during microbial growth. Reprinted from Biotechnology and Bioengineering, Vol. XI, Issue 3, Pages 269-281 (1968).

A procedure for measuring the rate of heat production from a fermentation has been developed. The method is based on measuring the rate of temperature rise of the fermentation broth resulting from metabolism, when the temperature controller is turned off. The heat accumulation measured in this manner is then corrected for heat losses and gains. A sensitive thermistor is used to follow the temperature rise with time. This procedure is shown to be as accurate as previous methods but much simpler in execution. Using this technique, the rate of heat production during metabolism was found to correlate with the rate of oxygen consumption. Experiments were performed using bacteria (E. coli and B. subtilis), a yeast (C. intermedia), and a mold (A. niger). The substrates investigated included glucose, molasses, and soy bean meal. The proportionality constant for the correlation is independent of the growth rate, slightly dependent on the substrate, and possibly dependent on the type of organism growth. This correlation has considerable potential for predicting heat evolution from the metabolism of microorganisms on simple or complex substrates and providing quantitative parameters necessary for heat removal calculations.

Potential of High-purity Polycrystalline Silicon Carbide for Thermistor Applications

This report concerns with a new material for thermistors, which consists of an undoped, polycrystalline, ultrahigh-purity chemical vapor deposition silicon carbide wafer. The resistance-temperature characteristic was measured from 25°C to 365°C. A good fit to the thermistor equation was observed and the thermistor B constant was 4845 K. These wafers are thermally and chemically stable, homogeneous and pure. They might be useful for fabrication of sensitive thermistors with stability and reproducibility of characteristics.

A highly sensitive thermistor bolometer for a clinical tympanic thermometer

A newly designed infrared radiation sensor for a clinical tympanic thermometer has been developed. A very small packaging size (2.2 mm × 2.3 mm × 0.8 mm) is achieved so that the sensor can be used in the human auricle. To realize high sensitivity, infrared sensing regions in the shape of a pair of micro-air-bridges are encapsulated in a vacuum microchamber through a successive silicon batch process using micromachining techniques. The sensor shows a sensitivity R v of 5000 V W −1 and a noise equivalent temperature difference (NETD) of 0.062 °C at a d.c. bias voltage of 1.56 V.

Photothermal spectroscopy of CdInGaS4 and related compound

Photothermal spectroscopy using high sensitive thermistor is applied to study the heat generation of multinary compounds CdxInGaS3+x system (x=1, 2 , 3) together with the optical absorption. There are differences between the photothermal spectra and optical energy absorption (1-T-R) in CdxInGaSa+x system and it depends on the composition x.

A multipurpose scanning apparatus for automatic analyses of soft magnetic materials and circuits (abstract)

Proper techniques for simultaneous evaluation of both global properties of magnetic circuits and local magnetic parameters of single grains or domains are an important prerequisite for optimal application and future improvement of ferromagnetic materials. The paper presents a test equipment designed to accommodate magnetic circuits up to outer dimensions of about 1 m×1 m×0.5 m. The box is thermally isolated for most sensitive thermistor applications such as local loss measurements. By means of a stepper-motor-driven sensing head which can pick up one or more sensors simultaneously, the scanning resolution and area can be freely chosen in a wide range from minimum scanning width of 10 μm to a maximum area of about 0.9 m×0.9 m. Geometrically highly resolving Hall sensors have been prepared for normal stray field analysis, thus visualizing local domain configurations.1 Tangential Hall sensors and differential field plates can be mounted for field measurements during magnetization process. Optionally, all sensors can be coupled with thermistors for local loss measurements. Reference elements in bridge connection ensure results considerably free from ambient disturbances. The apparatus is fully automated by a PC controlling scanning procedures as well as data acquisition and managing to storage disks and graphic devices.

Milk temperature fluctuations during milking in cows with subclinical mastitis

Observations on fluctuations of milk temperature during milking were carried out on 114 cows. A sensitive thermistor mounted in the short milk tube was used to measure milk temperature; fluctuations were very frequent in cows with subclinical mastitis as diagnosed by the presence of mastitis pathogens, high cell count, increased electrical conductivity and chloride content. Similar fluctuations were found in experimentally infected quarters of some cows. The fluctuations seem to indicate disorders in milk ejection and the automated measuring technique may be used as a tool in the early diagnosis of mastitis.

Study on Work Function of the {0001} Faces of CdS Crystal. III. Effect of the Irradiation with Red Light

By means of a highly sensitive thermistor (sensitivity: 10-3°C) as well as a Kelvin electrode of NESA glass with a detection sensitivity of several mV, the contact potential difference and the temperature of a crystal were measured with respect to CdS polar surfaces. It was confirmed that when a photoconducting crystal is irradiated at room temperature by weak light with bulk excitation for a certain time and then interrupted, the temperature drop and rapid decrease in the electric conductivity of the crystal suggests a pyroelectric charge on the polar surface.