Thermal decoupling

Microhotplates, however, are not only used for metal-oxide-based gas sensor applications. In all cases, in which elevated temperatures are required, or thermal decoupling from the bulk substrate is necessary, microhotplate-like structures can be used with various materials and detector configurations [25]. Examples include polymer-based capacitive sensors [26], pellistors [27-29], GasFETs [30,31], sensors based on changes in thermal conductivity [32], or devices that rely on metal films [33,34]. Only microhotplates for chemoresistive metal-oxide materials will be further detailed here. The relevant design considerations will be addressed. 

As a consequence, the temperature slope in the metal-line part of path 2 between the contact and the bulk chip is lower, which indicates a reduced heat flow through the metal line. This is equivalent to a better thermal decoupling of the metal power supply lines from the heated area, so that the presented microhotplate design is well suited to achieve operating temperatures up to 500 °C. 

The last and most advanced system presented in this book includes an array of three MOS-transistor-heated microhotplates (Sect. 6.3). The system relies almost exclusively on digital electronics, which entailed a significant reduction of the overall power consumption. The integrated C interface reduces the number of required wire bond connections to only ten, which allows to realize a low-prize and reliable packaging solution. The temperature controllers that were operated in the pulse-density mode showed a temperature resolution of 1 °C. An excellent thermal decoupling of each of the microhotplates from the rest of the array was demonstrated, and individual temperature modulation on the microhotplates was performed. The three microhotplates were coated with three different metal-oxide materials and characterized upon exposure to various concentrations of CO and CH4. 

Figure 5,35 Structure of tremolite projected on (001) plane. Dashed lines on [T40n] tetrahedral chains displacement (highly exaggerated for illustrative purposes) due to thermal decoupling. From Sueno et al. (1973). Reprinted with permission of The Mineralogi-cal Society of America.

Nearly complete thermal decoupling is enabled by the use of a special backbone element used for insulation (see Figure 4.39). This element is made of fiber-reinforced PTFE (Teflon ), which is chemically fairly inert and possesses an extremely small heat conductivity coefficient of 0.25 W mK4 compared with the standard backbone materials steel (16 W mK 1 and aluminum (204 W mKT1). 

The technique of microwave-recovery provides crucial information about the substates involved in the ODMR transitions. For this experiment, Pd(2-thpy)2 is optically excited by a c. w. source. This leads to specific populations of the three triplet substates. At low temperature, they are thermally decoupled and thus emit according to their specific populations and their individual decay constants (e. g. see Sect. 3.1.3 and Table 2). In the microwave recovery experiment, the steady state conditions are perturbed by a microwave pulse being in resonance with the zero-field transition at 2886 MHz. Due to the microwave pulse, the populations of the two states involved are changed. Subsequently, one monitors the recovery of the emission intensity in time until the steady state situation is reached again. The microwave pulses have, for example, a duration of 20 ps and are applied repeatedly to enable a detection with signal averaging [61]. 

A variable-temperature C n.m.r. study of the series Co3(CO)9CY (Y = H, Me, CgHj, CF3, CODMe, F, Cl, Br, or I) shows thermal decoupling of C from Co and scrambling of the carbonyls with apical carbon resonances observed in the low field region (310—230 p.p.m.). An i.r. spectroscopic study of Co2(CO)g in solution at various temperatures and CO pressures indicates that the previously proposed carbonyl-bridged species [Co2(CO)4] does not exist even above 150°C and CO pressures in excess of 150 atm. ... 

The thickness of the adhesive layers can be adjusted over a wide range from 5 to 15 mm. Any tolerance problems inherent in the assembling of large-scale metallic and composite components can be easily compensated. Due to the excellent insulation behavior of the PU adhesives, heat flow between the adher-ends can be minimized (i.e., by thermal decoupling). Additionally, elastic adhesives provide outstanding mechanical damping characteristics and help to reduce local vibrations. 

Thermally decoupled sample containers (Calvet principle)... 

Thermal decoupling has been observed to occur between quadrupolar nuclei ( B s) in BsHg, in a study of the H-decoupled B (32.1 MHz) n.m.r. spectrum. ... 

The air space beneath the bridges thermally decouples the heater and detectors from the silicon to a large extent. Consequently, large heater temperatnre differences in the 100 to 200°C range relative to the silicon can be sustained by small power inpnts. The thermal efficiency is typically 15°C per milliwatt of input power under no-flow conditions. The thin ceramic film permits the detector resistors to be placed closely adjacent to the heater so that they can operate at about 60 percent of the heater temperature elevation, and can develop large temperature differentials under small gaseous flow conditions. 

The TBS utilises both a passive radiator cooling system and a semi-active system comprising heaters and thermal sensors that are controlled and managed by the Thermal Control Unit (TCU). MLI is used to thermally decouple the experiment from deep space and solar effects. Thermal screens consisting of Kapton foil (X-Ray transparent) are interposed in the telescopes field of... 

Parapet the arched girders are not thermally decoupled in the parapet region. 

Desktop Chemical Factory, Fig. 5 United microreactor system. Example of a modular backbone 1 heat exchanger, 2 mixer, 3 valve, 4 safety valve, 5 pump, 6 heated residence time module, 7 mixer-settler extractor, 8 heated mixer tube reactor, 9 thermal decoupler [12]... 

Also at temperatures above 700 K thermal decoupling of the sample and the permanent magnet inside the (hot) reaction vessel is mandatory. Convection flows initiated by temperature gradients have to be suppressed or at least reduced by appropriate flow guide tubes. 

Fig. 7.2 (a) SEM view of thermally decoupled membrane array. [Reprinted with permission from Splinter et al. (2001). Copyright 2004 Elsevier], (b) SEM view of a free-standing sensor platform fabricated using a sacrificial layer of porous silicon [Reprinted with permission from Furjes et al. (2004). Copyright 2004 Elsevier], (c) Optical microscope photograph of a three-section heater sensor array. [Reprinted with permission from Frandoso et al. (2008). Copyright 2008 Elsevier], (d) Suspended porous silicon micro-hotplate with a Pt heater. The thickness of the membrane is 4 pm. The depth of the cavity under the membrane is more that 60 pm [Reprinted with permission from Tsamis et al. (2003). Copyright 2003 Elsevier]... 

Width at half-height at lowest temperature (thermally decoupled). ... 

This area is reviewed in more detail elsewhere, but important points merit brief mention here. Some aspects of coupling constant behavior are in Section 3.3.4 above. B decoupling and other multiple resonance experiments are of considerable use in this area (for example Refs. 29-32, 89, 109, 145, 151, 152, 156, 166, etc.), as is the phenomenon of thermal decoupling. ... 

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