Thermoelectric Sensitivity Research Articles

Ultimate Charge Transport Regimes in Doping-Controlled Graphene Laminates: Phonon-Assisted Processes Revealed by the Linear Magnetoresistance.

Understanding and controlling the electrical properties of solution-processed 2D materials is key to further printed electronics progress. Here, we demonstrate that the thermolysis of the aromatic intercalants utilized in nanosheet exfoliation for graphene laminates allows for high intrinsic mobility and the simultaneous control of doping type (n- and p-) and concentration over a wide range. We establish that the intraflake mobility is high by observing a linear magnetoresistance of such solution-processed graphene laminates and using it to devolve the interflake tunneling and intralayer magnetotransport. Consequently, we determine the temperature dependencies of the inter- and intralayer characteristics. The intraflake transport appears to be dominated by electron-phonon scattering processes at temperatures T > 20 K, while the interflake transport is governed by phonon-assisted tunneling. In particular, we identify the efficiency of phonon-assisted tunneling as the main limiting factor for electrical conductivity in graphene laminates at room temperature. We also demonstrate a thermoelectric sensitivity of around 50 μV·K-1 in a solution-processed metal-free graphene-based thermocouple.

Thermoelectric Sensor with CuI Supported on Rough Glass.

Thermoelectric generators convert heat into a potential difference with arrays of p- and n-type materials, a process that allows thermal energy harvesting and temperature detection. Thermoelectric sensors have attracted interest in relation to the creation of temperature and combustible gas sensors due to their simple operation principle and self-powering ability. CuI is an efficient p-type thermoelectric material that can be readily produced from a Cu layer by an iodination method. However, the vapor iodination of Cu has the disadvantage of weak adhesion on a bare glass substrate due to stress caused by crystal growth, limiting microfabrication applications of this process. This work presents a rough soda-lime glass substrate with nanoscale cavities to support the growth of a CuI layer, showing good adhesion and enhanced thermoelectric sensitivity. A rough glass sample with nanocavities is developed by reactive ion etching of a photoresist-coated glass sample in which aggregates of carbon residuals and the accumulation of NaF catalyze variable etching rates to produce local isotropic etching and roughening. A thermoelectric sensor consists of 41 CuI/In-CoSb3 thermoelectric leg pairs with gold electrodes for electrical interconnection. A thermoelectric leg has a width of 25 μm, a length of 3 mm, and a thickness of 1 μm. The thermoelectric response results in an open-circuit voltage of 13.7 mV/K on rough glass and 0.9 mV/K on bare glass under ambient conditions. Rough glass provides good mechanical interlocking and introduces important variations of the crystallinity and composition in the supported thermoelectric layers, leading to enhanced thermopower.

Thermo Electric Sensitivity Fractal Dimension for Characterizing Shajara Reservoirs of the Permo-Carboniferous Shajara Formation, Saudi Arabia

The quality and assessment of a reservoir can be documented in details by the application of thermo electric sensitivity. This research aims to calculate fractal dimension from the relationship among thermo electric sensitivity, maximum thermo electric sensitivity and wetting phase saturation and to approve it by the fractal dimension derived from the relationship among capillary pressure and wetting phase saturation. Two equations for calculating the fractal dimensions have been employed. The first one describes the functional relationship between wetting phase saturation, thermo electric sensitivity, maximum Thermo electric sensitivity and fractal dimension. The second equation implies to the wetting phase saturation as a function of capillary pressure and the fractal dimension. Two procedures for obtaining the fractal dimension have been utilized. The first procedure was done by plotting the logarithm of the ratio between thermo electric sensitivity and maximum thermo electric sensitivity versus logarithm wetting phase saturation. The slope of the first procedure = 3- Df (fractal dimension). The second procedure for obtaining the fractal dimension was determined by plotting the logarithm of capillary pressure versus the logarithm of wetting phase saturation. The slope of the second procedure = Df -3. On the basis of the obtained results of the fabricated stratigraphic column and the attained values of the fractal dimension, the sandstones of the Shajara reservoirs of the Shajara Formation were divided here into three units.

(Invited) Use of Supercritical Solvents for Electrodeposition of Thermoelectric Materials

Background: Thermoelectric materials (TEMs) are of interest for both cooling (Peltier effect) and voltage generation applications (Seebeck effect). Thermoelectric generators (TEGs) convert heat energy into electrical voltage via the Seebeck effect. In a typical TEG the thermoelectric elements, usually alternating p-type and n-type semiconductors, are arranged electrically in series and thermally in parallel. The power that can be generated depends on many factors: geometrical design of the module, thermal coupling to the heat exchangers, thermal and electrical conductivity of the materials supporting and separating the TEM elements and fundamentally the thermal and electrical conductivity of the TEM itself. The latter is summed up by the materials dimensionless “figure of merit”: zT = S2σT/κ. Where: S = Seebeck coefficient (thermoelectric sensitivity often given in μV/K); σ = electrical conductivity and κ = thermal conductivity (usually in W/mK). The current consensus is that, to be truly competitive for power generation, TEMs should have zT of 2-3[1]; although there are plenty of cases where this is less important. For instance where waste heat can be used on a large scale for power generation; here the conversion efficiency and the cost of the TEM is far more important. For certain niche applications requiring low to moderate power and low maintenance (e.g. for remote, standalone power supplies) cost is less important and there are a range of exotic materials with zT on the order of 1. One such material that has been widely studied is bismuth Telluride (Bi2Te3) which has a figure of merit typically between 0.7 and 0.8. This can be doped (often with antimony to produce p-type or selenium to produce n-type) to give zT >1.4[2, 3]. Modifying the carrier concentration to improve electrical conductivity (σ) is one way of improving zT but as can be seen from the equation above the figure of merit is also inversely proportional to the thermal conductivity (κ). Unfortunately σ and κ tend to vary likewise and good electrical conductivity usually goes hand in hand with good thermal conductivity. One strategy for reducing the thermal conductivity of a TEM, with minimal impact on the electrical conductivity, is nanostructuring[4, 5]. In in bidimensional or monodimensional structures (i.e. very thin films or nanowires) as the critical dimension is reduced it approaches the same scale as the mean free path of the phonons and their propagation is limited by surface scattering. Thus by tuning the size of the TE elements along with surface roughness and grain boundaries it should be possible to optimise both the thermal and electrical conductivities and produce superior TEGs. In this work: Previously we have demonstrated that, through judicious choice of electrolyte and design of precursor complex, supercritical solvents such as CO2 and difluoromethane (R32) may be used to electroplate a range of metal and semiconductor elements[6]. Furthermore supercritical fluid electrodeposition (SCFED) has distinct advantages over electroplating from conventional solvents: the broad potential window offered by R32 and CO2 allowing for electrodeposition of elements such as germanium; an ability to operate at high temperatures (since the reaction cells are all sealed); tunability of solvent properties (such as density and viscosity) and the absence of surface tension and very high rates of diffusion. The latter is a particular advantage when trying to electrodeposit into high aspect ratio nanopores and we have shown that filling of pores of 2-3 nm is viable by SCFED[7]. Here we demonstrate electrodeposition from binary solutions in supercritical R32 to produce bismuth telluride and antimony telluride films and nanowires of 13-55 nm diameter. We also demonstrate deposition of bismuth-tellurium and antimony-tellurium heterojunction nanowires. It is thought that Bi2Te3nanowires with a diameter <30 nm would offer a significant improvement in thermoelectric figure of merit[8, 9]. This work is conducted as part of the ADEPT project funded by EPSRC (EP/N035437/1).

Characterization of fiber-optic light delivery and light-induced temperature changes in a rodent brain for precise optogenetic neuromodulation.

Understanding light intensity and temperature increase is of considerable importance in designing or performing in vivo optogenetic experiments. Our study describes the optimal light power at target depth in the rodent brain that would maximize activation of light-gated ion channels while minimizing temperature increase. Monte Carlo (MC) simulations of light delivery were used to provide a guideline for suitable light power at a target depth. In addition, MC simulations with the Pennes bio-heat model using data obtained from measurements with a temperature-measuring cannula having 12.3 mV/°C of thermoelectric sensitivity enabled us to predict tissue heating of 0.116 °C/mW on average at target depth of 563 μm and specifically, a maximum mean plateau temperature increase of 0.25 °C/mW at 100 μm depth for 473 nm light. Our study will help to improve the design and performance of optogenetic experiments while avoiding potential over- and under-illumination.

Neutronics analysis for ITER cable looms

This paper briefly presents the results of neutronics analysis performed in support for the design development of the ITER diagnostics cabling system including its cable looms. The cable looms are distributed all around the ITER device and attached to the inner wall of the Vacuum Vessel (VV) and under the divertor cassettes. The results include distributions of neutronics characteristics calculated with the MCNP5 3D Monte Carlo code assuming ITER operation with 0.54 Full Power Years on 500MW fusion power of DT neutron source defined in the standard ITER B-lite neutronics model. Neutron and photon fluxes, neutron energy group fluences, nuclear heating, neutron damage, and neutron-induced transmutation of the cable looms’ materials have been analyzed in this paper. This work provides data for more comprehensive integral analysis of the cabling system with consideration of thermo-mechanical, electromagnetic, and structural aspects. The temperature gradients along the cable looms and nuclear transmutation of copper could result in formation of thermocouples due to the Radiation-Induced Thermoelectric Sensitivity (RITES) effect, which should be reduced in order to enhance the performance of the magnetic sensors. Therefore, reliable thermal contact should be established in the places of attachments of cable looms to the VV inner wall and the divertor cassette body.

Optimized thermoelectric sensitivity measurement for differential thermometry with thermopiles

A novel approach to calibrate the sensitivity of a differential thermometer, consisting of several thermocouples connected in series (thermopile), has been developed. The goal of this method is to increase the accuracy of small temperature difference measurements (ΔT⩽1K), without invoking higher sensor complexity. To this end, a method to determine the optimal temperature difference employed during the differential measurement of thermoelectric sensitivities has been developed. This calibration temperature difference is found at the minimum of combined measurement and linearization error for a given mean temperature. The developed procedure is demonstrated in an illustrative example calibration of a nine-junction thermopile. For mean temperatures between −10°C and +15°C, the thermoelectric sensitivity was measured with an uncertainty of less than ±2%. Subsequently, temperature differences as low as 0.01K can be resolved, while the thermometer used for the example calibration was accurate only to ±0.3K. This and higher degrees of accuracy are required in certain research applications, for example to detect heat flux modulations in bifurcating fluidic systems.

근골격계 통증질환의 진단과 치료를 위한 주사바늘형 복합온도 프로브의 개발

This paper describes the development of needle type probe that measures temperature and injects medicine for both diagnosis and treatment of musculoskeletal pain syndrome (MPS). The size of trigger points is from several micrometers to millimeter. Therefore, it is required to develop a medical device that is capable of not only finding the trigger points by temperature measurement, but also injecting medicine at the exact location for treatment. To challenge these difficulties, thermocouple was fabricated on the surface of a needle using metal deposition process. Special type of stainless-constantan thermocouple was achieved from the stainless body of a needle itself and deposited constantan metal film. In particular, parylene coating enables to limit the temperature sensitive area to the end of the needle tip. Fabricated needle type probe produces 3.25 mV/℃ of thermoelectric sensitivity and compared its performance with commercial T-type thermocouple in animal muscle sample.

Flexible Heat Flux Sensor for Firefighters Garment Integration

The interest in using optimal equipment to face unknown hazards is growing, as it ultimately save lives. This holds especially true for fire-fighters which are confronted with other hazards during the course of operations. Improvement of their security by an integrated sensory clothing system was the main objective of the European project ProeTEX. In this context, the integration of commercial heat flux sensors into fire-fighters garment has proved the interest of such measurements. However, low flexibility and high cost remain major disadvantages of these sensors. The objective of this work is to develop an innovative heat flux sensor based on a low cost technology. Heat flux sensors have been realized using printable thermoelectric materials and present high sensitivity (146 mV/ (W/cm2)). Their flexibility is compatible with integration in clothes and three specific integrations are proposed and compared. Proof of concept of flexible heat flux sensor is also presented in this paper.

Neutron irradiation and temperature effects on induced voltages in various mineral insulated cables and ceramic-coated wires

U-shaped single copper and stainless steel core mineral insulated cables (with outer diameter 1.0 and 1.5 mm), dual core mineral insulated cables (also with copper and stainless steel cores) and three types of ceramic-coated wires have been irradiated in the BR2 research reactor up to a maximum thermal neutron fluence of 10 20 n/cm 2. The cables were guided through a 25 cm long double wall tube to create significant temperature gradients during the irradiation or during reference measurements in zero radiation field using electrical heating. The induced core-to-core voltages, which were continuously measured, scale with the temperature gradients. For all single-core cables and for the wires they increased significantly during the irradiation, while for the dual core cables the thermoelectrical effects from the two legs of the core wires cancel almost completely. No significant effect of the core wire diameter was observed. The increase in thermoelectric sensitivity of the copper core cables was found to scale with the thermal neutron fluence and could be attributed unambiguously to partial transmutation from copper to nickel. The stainless steel core cables showed a fast sensitivity increase at low fluences, but saturating at a moderate level, depending on the local irradiation temperature.

Design optimisation of the ITER divertor magnetic probes using FEM analyses

This paper is focused on the design, simulation and optimisation of the ITER divertor magnetic tangential coils. The most critical issue for the divertor coils is to minimise RITES [G. Vayakis, et al., Radiation-induced thermoelectric sensitivity (RITES) in ITER prototype magnetic sensors, Rev. Sci. Instrum. 75 (10) (2004) 4324–4327] and TIEMF [R. Vila, E.R. Hodson, Thermally induced EMF in unirradiated MI cables, J. Nucl. Mater. 367–370 (Part 2) (2007) 1044–1047] by combining a proper choice of conductor with low temperature variation in the coil. Instead of mineral insulated cable (MIC), which was foreseen as the preferred winding, a winding made of ceramic-coated steel wire was recently proposed [G. Chitarin, L. Grando, S. Peruzzo, C. Tacconet, Design developments for the ITER in-vessel equilibrium Halo current sensors, 24th SOFT Conference, Warsaw, Poland, September 2006, Fusion Eng. Design, in press]. It is thought that, for this wire, maintaining a temperature variation in the wiring below 10 K will be sufficient to allow long-pulse operation. Variations of the divertor coil design have been simulated with the help of ANSYS. The aim was to keep the temperature variation in the winding pack within this limit. The optimisation of the coil based only on a cooling by conduction was not sufficient to meet the 10 K target. Therefore, an actively water-cooled coil was designed which finally met these requirements.

Radiation-induced thermoelectric sensitivity (RITES) in ITER prototype magnetic sensors

This report summarizes the results of in situ measurements of noninductive voltages developed across prototype International Thermonuclear Experimental Reactor (ITER) magnetic coils performed at the Japan Materials Test Reactor. The voltages appear to be mainly thermoelectric in origin, with the thermal sensitivity developing gradually through irradiation and the thermal gradients supplied by nuclear heating. Possible mechanisms and circuits within the coils that can contribute to this radiation-induced thermoelectric sensitivity are described, and schemes to improve the ITER coil design are outlined.

Radiation-induced thermoelectric sensitivity in the mineral-insulated cable of magnetic diagnostic coils for ITER

Magnetic coils are indispensable for plasma position control in tokamaks. For ITER, non-inductive voltages generated under irradiation have to be reduced to well below 1 μV in order to support long pulse (3000 s) operation. In situ measurements of the differential voltage between the ends of two magnetic coils wound with mineral-insulated (MI) cable have been carried out at the JMTR fission reactor. The MI cables of the two magnetic coils had copper center conductor with diameter 0.5 and 0.8 mm, respectively, stainless steel outer sheath and MgO insulation. The measured differential voltage for the two MI cables increased with neutron fluence, reaching 4.5 and −0.7 μV in the two coils, at a fast neutron fluence of 1.26 × 10 23 n/m 2. The magnitude of the measured voltage can be explained by thermoelectric potentials, enabled mainly by non-uniform transmutation and displacement damages of the copper core of the cable.