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A four-tether silicon microthermocycler for point-of-care PCR analytical systems is proposed. Substituting the commonly employed platinum with titanium in the fabrication of thin film resistance temperature detectors and heaters enabled the realization of a smaller device without compromising temperature accuracy or increasing heater lead power losses. The device was extensively analyzed through analytical modeling and FEM numerical simulations using a 3-D thermo-mechanical simulation model in COMSOL. Numerical simulations revealed that the four-tether design provides a 460% improvement in mechanical strength and a 57% reduction in the thermal time constant compared with a similar three-tether design, with a trade-off of a 22% increase in heat losses. Detailed structural and thermal analyses of crucial design parameters guided the optimization of the final geometry, leading to the successful fabrication of prototypes. It was shown that the current of 60 mA was sufficient to heat the fabricated solid and hollow silicon structure to 132 °C and 134 °C in 10 s for an applied heater power of 510 mW and 525 mW, respectively. [ABSTRACT FROM AUTHOR]

A four-tether silicon microthermocycler for point-of-care PCR analytical systems is proposed. Substituting the commonly employed platinum with titanium in the fabrication of thin film resistance temperature detectors and heaters enabled the realization of a smaller device without compromising temperature accuracy or increasing heater lead power losses. The device was extensively analyzed through analytical modeling and FEM numerical simulations using a 3-D thermo-mechanical simulation model in COMSOL. Numerical simulations revealed that the four-tether design provides a 460% improvement in mechanical strength and a 57% reduction in the thermal time constant compared with a similar three-tether design, with a trade-off of a 22% increase in heat losses. Detailed structural and thermal analyses of crucial design parameters guided the optimization of the final geometry, leading to the successful fabrication of prototypes. It was shown that the current of 60 mA was sufficient to heat the fabricated solid and hollow silicon structure to 132 °C and 134 °C in 10 s for an applied heater power of 510 mW and 525 mW, respectively.

Graphene resonant sensors have shown strong competitiveness with respect to sensitivity and size. To advance the applications of graphene resonant sensors, the damage behaviors of graphene harmonic oscillators after thermal annealing and laser irradiation were investigated by morphology analysis and frequency domain vibration characteristics. The interface stress was proven to be the key factor that directly affected the yield of resonators. The resulting phenomenon could be improved by appropriately controlling the annealing temperature and size of resonators, thereby achieving membrane intactness of up to 96.4%. However, micro-cracks were found on the graphene sheets when continuous wave (CW) laser power was more than 4 mW. Moreover, the fluctuating light energy would also cause mechanical fatigue in addition to the photothermal effect, and the threshold damage power for the sinusoidally modulated laser was merely 2 mW. In this way, based on the amplitude-frequency surface morphology of the graphene resonator, the thermal time constant of the order of a few microseconds was confirmed to evaluate the damage of the graphene oscillator in situ and in real time, which could be further extended for those resonators using other 2D materials. [ABSTRACT FROM AUTHOR]

Radiant system design standards and guidebooks classify radiant systems as a function of their structure and geometry. We assume that design approaches, testing methods, and control strategies of radiant systems can be more clearly described and classified based on thermal parameters. We calculated using computational fluid dynamics method the thermal time con-stants for 66 radiant system cases. We found pipe spacing, thickness and material properties of structural layer have a significant impact on time constant, while operative temperature, water temperature and water flow regime do not. We found time constants of radiant ceiling panels vary between 30-91 s; for embedded surface systems between 0.25-3.5 h; for thermally activated building systems with pipes embedded in the massive concrete slabs, between 2.4-7.7 h; and for capillary pipes embedded in a layer at the inner surface, between 0.1-0.6 h. A preliminary radiant system classification scheme based on thermal time constant is proposed.

The ignition process of a hypergolic hybrid rocket fuel presents a significant challenge due to its complex and interconnected nature. However, understanding its underlying physics is crucial for accurately estimating the delay time and ignition performance. In this study, we employed an approximate analytical method to directly address the transient conduction problem with nonlinear surface heat generation. By using the Arrhenius equation and considering dual heat flux directions in both the liquid and solid domains, we propose a model for determining the delay time of heterogeneous hypergolic ignition. Our solution is straightforward and computationally efficient. Notably, when subjected to identical initial conditions and property settings, our results exhibit similarity with the solutions derived from other models. Moreover, we advance our approach by developing a particle packing model through the utilization of a well-established algorithm. By simulating the particle arrangement within the pellet, the surface layer properties and the thermal time constant of certain fuel designs can be modeled. This simulation serves the purpose of incorporating the particle size effect of the fuel pellet into our ignition model. The results generated by our heterogeneous hypergolic ignition model, in conjunction with the particle packing model, demonstrated impressive agreement with the experimental data derived from droplet tests. This study utilized a novel solving method to address a transient conduction problem with non-linear heat generation on the surface during a heterogeneous hypergolic ignition process. The study successfully derived an analytical solution, providing a simpler method for calculating ignition delay times. A scenario involving different initial temperatures was also examined. Additionally, the research integrated particle packing model data and thermal time constants to assess the effect of particle size. The model results were in agreement with the experimental data, confirming its accuracy and offering a reliable method for estimating the heterogeneous hypergolic ignition delay time. [ABSTRACT FROM AUTHOR]

The decentralized feed-ins from distributed energy resources (DER) represent a significant change in the manner in which the power grid is used. If this leads to high loads on electrical equipment, its aging can be accelerated. This applies in particular with regard to the thermal aging of older generations of power cables, namely paper insulated lead covered (PILC) cables. This type of power cable can still be found frequently in medium voltage (MV) networks. If aging of these cables is significantly accelerated in the presence of DER, distribution system operators (DSO) could face unplanned premature cable failures and a high replacement demand and costs. Therefore, this paper investigates the thermal aging of PILC cables in a MV distribution network benchmark for different load scenarios, using standardized load profiles and representative expansion scenarios for wind power and photovoltaics plants in particularly affected network areas in Germany. A main objective of this paper is to present a methodology for estimating the thermal degradation of PILC cables. An approach is used to draw simplified conclusions from the loading of cables to their conductor or insulation temperature. For this purpose, mainly Joule losses are considered. In addition, thermal time constants are used for the heating and cooling processes. Based on the insulation temperature, thermal aging is determined using the Arrhenius law or the Montsinger rule. However, it is important to note that there is an urgent need for research on reference data in this area. For this reason, the results of the lifetime estimation presented in this paper should only be considered as an approximation if the selected reference data from the literature for the aging model are actually applicable. The lifetime assessment is performed for a highly utilized line segment of the network benchmark. Accordingly, extreme values are examined. Different operational control strategies of DSO to limit cable utilization are investigated. The results show that the expansion of DER can lead to a short but high cable utilization, although the average utilization does not increase or increases only slightly. This can lead to significantly lower cable lifetimes. The possible influence of these temporarily high loads is shown by comparing the resulting cable lifetime with previous situations without DER. It is also shown that DSO could already reduce excessive aging of PILC cables by preventing overloads in a few hours of a year. In addition to these specific results, general findings on the network load due to the influence of DER are obtained, which are of interest for congestion management.

Thermal-based germination models are widely used to predict germination rate and germination timing of plants. However, comparison of model parameters between large numbers of species is rare. In this study, seeds of 27 species including 12 C4 and 15 C3 species were germinated at a range of constant temperatures from 5 °C to 40 °C. We used a modified thermal time model to calculate germination parameters at suboptimal temperatures. Generally, the optimal germination temperature was higher for C4 species than for C3 species. The thermal time constant for the 50% germination percentile was significantly higher for C3 than C4 species. The thermal time constant of perennials was significantly higher than that of annuals. However, differences in base temperatures were not significant between C3 and C4, or annuals and perennial species. The relationship between germination rate and seed mass depended on plant functional type and temperature, while the base temperature and thermal time constant of C3 and C4 species exhibited no significant relationship with seed mass. The results illustrate differences in germination characteristics between C3 and C4 species. Seed mass does not affect germination parameters, plant life cycle matters, however.

Abstract Mn 1.2 Co 1.5 Ni 0.3 O 4 ceramic chips with 90, 100, 110 and 120 µm thickness were developed using the tape casting method. The structure, electrical properties and thermal time constant have been investigated as a function of the thickness of the miniature NTC chip thermistors. The ρ 25 increased from 127 to 449.7 Ω cm and the thermal constant B 25/50 increased from 52.8 to 180.5 K as the thickness increased. This could be a result of the increased grain boundary resistance and Mn3+/Mn4+ ratio (0.7–1.02) from the increased thickness. The thermal time constants were 0.83, 0.89, 1.05 and 1.10 s for chip thermistors with thicknesses from 90 to 120 µm, respectively. This reveals that the thickness of chips could affect the thermal time constant, a result of significantly different dissipation constants and heat capacities in MCN thermistors. The proposed sensors demonstrated a superior temporal response. [ABSTRACT FROM AUTHOR]

To develop effective control optimization strategies for managing residential electricity consumption in a smart grid environment, predictive algorithms are needed that are simple to implement, minimize custom configuration, and provide sufficient accuracy to enable meaningful control decisions. This paper presents a self‐learning algorithm for predicting indoor temperature in a single-family residence using a first-order lumped capacitance (1R1C) model that can be used to evaluate the consequences of energy saving or load shifting strategies on thermal comfort. The algorithm is formulated in such a way that key design details such as window size/configuration, thermal insulation, and airtightness (all major factors that affect heat loss and solar heat gain) are combined into effective parameters that can be learned from observation. This approach eliminates the need for a custom configuration for each residence. The model was validated using experimental data from the National Institute of Standards and Technology (NIST) Net-Zero Energy Residential Test Facility. It was found that with a simple temperature decay test to determine a thermal time constant and a seven-day sliding window of training data to account for seasonal variations in other parameters, the algorithm can reliably predict indoor temperatures for a 24 h period using a solar irradiance forecast, an outdoor air temperature forecast, and heat pump output. The average root mean square temperature prediction error was found to be 2.2%. [ABSTRACT FROM AUTHOR]

Bolometer detector is one of thermal detectors. In this research the essential concepts and parameters are included which cover the main types of bolometer detectors. But the actual values of parameters used here in simulation are adopted from [7] for semiconductor bolometer. This detector operates for all optical wavelengths of different sources. From analysis and results obtained, it is shown that minimum and maximum values of specific Detectivity D* for cryogenic temperatures from 0.5 K to 10 K are 0.25~10 / and 5 ~ 10 / , respectively and the values between them when the incident radiation frequency is 100 Hz.. It is seen that for frequency greater than 1Hz, the specific Detectivity increases rapidly which means that the bolometer detector will respond for high frequencies in a manner more speed than that of low frequencies. It is found that as the value of Ąth is increased, the temperature change in detector sensor is decreased. That is decreasing Ąth enhance the performance of bolometer detector. It is found that the responsivity of this detector follow its output voltage which in turn follow the bolometer temperature change.

A new technique for characterizing the thermal properties of heat-assisted magnetic recording media (HAMR) using pulsed near-field heating recording with a static tester is reported. It has the advantage over traditional recording techniques of enabling studies of the 1–100 ns transient thermal configurations rather than only thermal steady states. The technique is applied to HAMR media with different heatsink thicknesses. While each media has a different steady-state temperature profile, the heatsinking differences are eliminated or enhanced by tuning the pulse duration for each media. The technique is used to extract thermal properties of the media. [ABSTRACT FROM PUBLISHER]

This paper presents an accurate thermal characterization of thin-film heaters manufactured on glass substrates. The characterization has been performed on Cr/Al/Cr meandered heaters. Techniques commonly adopted for measuring the temperature coefficient of resistance, the thermal resistance and thermal capacitance in the case of Si-based microheaters have been conveniently modified to consider the fundamentally different thermal parameters of a heater manufactured on glass. To reduce power consumption and thermal capacitance, a grating of 250- $\mu $ m wide trenches, stopped at $80~\mu $ m from the opposite metalized front surface, was manufactured on the back side of the heaters, obtaining an increase of the thermal resistance of about 110% and a decrease of the thermal capacitance of about 65% when the glass is in good thermal contact with a heat sink. The measured values of thermal resistance and time constants on a heat sink and in air have been justified starting from realistic physical considerations. Finally, a novel thermal model suitable for microheaters on glass immersed in air was presented and validated by comparing its predictions with the experimental cooling behavior of the microheater and with the predictions of an exponential model. [ABSTRACT FROM PUBLISHER]

Infrared neural stimulation (INS) is becoming an important complementary tool to electrical stimulation. Since the mechanism of INS is photothermal, describing the laser-induced heat distribution is fundamental to determining the relationship between stimulation pulses and neural responses. This work developed both a framework describing the time evolution of the heat distribution induced by optical fluence and a new method to extract thermal criteria (e.g., temperature change and rate of change) for neural activation. To solve the general problem of describing the temperature distribution, a Green's function solution to the heat diffusion equation was determined and convolved with the optical fluence. This provided a solution in the form of a single integral over time, from which closed-form solutions can be determined for special cases. This work also yielded an expression for thermal relaxation time, which provides a rigorous description of thermal confinement for INS. The developed framework was then applied to experimental data from the cochlea to extract the minimum temperature increase and rate of that increase to stimulate the cochlear spiral ganglion. This result, and similar analyses applied to other neural systems, can then shed light on the fundamental mechanism for INS and aid the development of optical neuroprostheses. [ABSTRACT FROM AUTHOR]

In this paper, we report on the successful fabrication and comprehensive optical and electrothermal characterization of a silicon-based tunable optical filter. Of particular interest here are the static and transient electrothermal characteristics of the filter membrane. The filter is configured as a Fabry-Pérot resonator with dielectric Bragg reflectors and is fabricated as a stress-compensated multilayer of dielectric thin-films. Tunability is achieved by changing the refractive index of the solid-state cavity material through thermal modulation, accomplished by Joule heating in metal thin-film resistors. The filter layers are configured as a membrane to provide good thermal isolation and its electrothermal behavior was characterized in steady-state and dynamically. A maximum stable temperature difference of 450 K and a heating efficiency of 13.4 K mW-1 were measured with a thermal time constant for the filter hotplate of 3 ms. The filter's spectral width is 0.28 nm at a wavelength of 1550 nm and through thermal modulation it was possible to shift the filter peak over more than 29 nm. [ABSTRACT FROM AUTHOR]

A technique for significantly reducing the time of al ternating to direct current (ac-dc) transfer measurements is proposed in which a thermal converter is synchronously switched with the ac input signal. The technique facilitates the use of thermal converters in routine ac-dc transfer calibrations making them less time consuming and more attractive in calibration laboratories. A fast ac-dc transfer measurement system using this technique and a synchronous sampling system will be presented. [ABSTRACT FROM AUTHOR]

This paper described a comparison between a numerical Finite Element Analysis (FEA) and an analytical approach in order to extract the thermal time constants and the thermal resistances of simple but realistic structures. Understanding the complex contribution of multidimensional thermal spreading, the effect of multiple layers, and the correlation with the heat source length is mandatory due to the severe mismatch of thermal expansion in different epitaxial layers and high operating temperatures. This is especially true on GaN HEMT (High Electron Mobility Transistor) with the continuous decrease of the gate length and the increase of the power density. Moreover, in this paper, we extracted the time constants with a Model Order Reduction (MOR) technique based on the Ritz vector approach with inputs coming from the FE matrices. It was found that the time constants obtained by an analytical solution and a model order extraction from FEA were exactly the same. This result validated the idea that our MOR technique provides the real time constants and resistances for our device structures and in this case unified the analytical world with the numerical one. [ABSTRACT FROM AUTHOR]

As the technology nodes of semiconductor devices have become finer and more complex, progressive scaling down has been implemented to achieve higher densities for electronic devices. Thus, three-dimensional (3D) channel field-effect transistors (FETs), such as fin-shaped FETs (FinFETs) and gate-all-around FETs (GAAFETs), have become popular as they have increased effective surface areas for the channels (Weff), owing to the scaling down strategy. These 3D channel FETs, which have completely covered channel structures with gate oxide and metal, are prone to the self-heating effect (SHE). The SHE is generally known to degrade the on-state drain current; however, when AC pulsed inputs are applied to these devices, the SHE also degrades the off-state leakage current during the off-phase of the pulse. In this study, an optimization methodology to minimize leakage current generation by the SHE is examined. [ABSTRACT FROM AUTHOR]

The decentralized feed-ins from distributed energy resources (DER) represent a significant change in the manner in which the power grid is used. If this leads to high loads on electrical equipment, its aging can be accelerated. This applies in particular with regard to the thermal aging of older generations of power cables, namely paper insulated lead covered (PILC) cables. This type of power cable can still be found frequently in medium voltage (MV) networks. If aging of these cables is significantly accelerated in the presence of DER, distribution system operators (DSO) could face unplanned premature cable failures and a high replacement demand and costs. Therefore, this paper investigates the thermal aging of PILC cables in a MV distribution network benchmark for different load scenarios, using standardized load profiles and representative expansion scenarios for wind power and photovoltaics plants in particularly affected network areas in Germany. A main objective of this paper is to present a methodology for estimating the thermal degradation of PILC cables. An approach is used to draw simplified conclusions from the loading of cables to their conductor or insulation temperature. For this purpose, mainly Joule losses are considered. In addition, thermal time constants are used for the heating and cooling processes. Based on the insulation temperature, thermal aging is determined using the Arrhenius law or the Montsinger rule. However, it is important to note that there is an urgent need for research on reference data in this area. For this reason, the results of the lifetime estimation presented in this paper should only be considered as an approximation if the selected reference data from the literature for the aging model are actually applicable. The lifetime assessment is performed for a highly utilized line segment of the network benchmark. Accordingly, extreme values are examined. Different operational control strategies of DSO to limit cable utilization are investigated. The results show that the expansion of DER can lead to a short but high cable utilization, although the average utilization does not increase or increases only slightly. This can lead to significantly lower cable lifetimes. The possible influence of these temporarily high loads is shown by comparing the resulting cable lifetime with previous situations without DER. It is also shown that DSO could already reduce excessive aging of PILC cables by preventing overloads in a few hours of a year. In addition to these specific results, general findings on the network load due to the influence of DER are obtained, which are of interest for congestion management. [ABSTRACT FROM AUTHOR]

Thermal characterization of modern microwave power transistors such as high electron-mobility transistors based on gallium nitride (GaN-based HEMTs) is a critical challenge for the development of high-performance new generation wireless communication systems (LTE-A, 5G) and advanced radars (active electronically scanned array (AESA)). This is especially true for systems operating with variable-envelope signals where accurate determination of self-heating effects resulting from strong- and fast-changing power dissipated inside transistor is crucial. In this work, we have developed an advanced measurement system based on DeltaVGS method with implemented software enabling accurate determination of device channel temperature and thermal resistance. The methodology accounts for MIL-STD-750-3 standard but takes into account appropriate specific bias and timing conditions. Three types of GaN-based HEMTs were taken into consideration, namely commercially available GaN-on-SiC (CGH27015F and TGF2023-2-01) and GaN-on-Si (NPT2022) devices, as well as model GaN-on-GaN HEMT (T8). Their characteristics of thermal impedance, thermal time constants and thermal equivalent circuits were presented. Knowledge of thermal equivalent circuits and electro–thermal models can lead to improved design of GaN HEMT high-power amplifiers with account of instantaneous temperature variations for systems using variable-envelope signals. It can also expand their range of application. [ABSTRACT FROM AUTHOR]

In the international guidelines/standards for human protection against electromagnetic fields, the specific absorption rate (SAR) is used as a metric for radio-frequency field exposure. For radio-frequency near-field exposure, the peak value of the SAR averaged over 10 g of tissue is treated as a surrogate of the local temperature elevation for frequencies up to 3⁻10 GHz. The limit of 10-g SAR is derived by extrapolating the thermal damage in animal experiments. However, no reports discussed the difference between the time constant of temperature elevation in small animals and humans for local exposure. This study computationally estimated the thermal time constants of temperature elevation in human head and rat models exposed to dipole antennas at 3⁻10 GHz. The peak temperature elevation in the human brain was lower than that in the rat model, mainly because of difference in depth from the scalp. Consequently, the thermal time constant of the rat brain was smaller than that of the human brain. Additionally, the thermal time constant in human skin decreased with increasing frequency, which was mainly characterized by the effective SAR volume, whereas it was almost frequency-independent in the human brain. These findings should be helpful for extrapolating animal studies to humans., Competing Interests: The authors declare no conflicts of interest.

Elevated skin temperature at the body/device interface of lower-limb prostheses is one of the major factors that affect tissue health. The heat dissipation in prosthetic sockets is greatly influenced by the thermal conductive properties of the hard socket and liner material employed. However, monitoring of the interface temperature at skin level in lower-limb prosthesis is notoriously complicated. This is due to the flexible nature of the interface liners used which requires consistent positioning of sensors during donning and doffing. Predicting the residual limb temperature by monitoring the temperature between socket and liner rather than skin and liner could be an important step in alleviating complaints on increased temperature and perspiration in prosthetic sockets. To predict the residual limb temperature, a machine learning algorithm - Gaussian processes is employed, which utilizes the thermal time constant values of commonly used socket and liner materials. This Letter highlights the relevance of thermal time constant of prosthetic materials in Gaussian processes technique which would be useful in addressing the challenge of non-invasively monitoring the residual limb skin temperature. With the introduction of thermal time constant, the model can be optimised and generalised for a given prosthetic setup, thereby making the predictions more reliable.