Search results for "lämmön johtuminen"
showing 10 items of 16 documents
Lämpösähköisen materiaalin lämmönjohtavuuden määrittäminen matalissa lämpötiloissa käyttäen 3ω-menetelmää
2014
Työssä tutkittiin mittausmenetelmää lämmönjohtavuuden määrittämiseen mata- lissa lämpötiloissa. Mittaukset perustuivat 3ω menetelmään, joka on alunperin ohut- kalvoille kehitetty menetelmä lämmönjohtavuuden mittaukseen. Menetelmässä läm- mitinlangan läpi kulkeva vaihtovirta synnyttää kolminkertaisella taajudella olevan jännitteen, jonka avulla saadaan tietoa kappaleen termisistä ominaisuuksista. Mit- tauksissa kultainen lämmitinlanka höyrystettiin Kapton kalvon päälle ja tämän päälle hyvin ohut alumiinioksidikerros. Mittaukset suoritettiin pulssituubijäähdyttimeen ra- kennetussa näytteenpitimessä. Laitteiston toiminta varmistettiin huoneenlämpötilas- sa borosilikaatti- ja Kapton näytteillä.…
Energy-efficient quantum computing
2016
In the near future, a major challenge in quantum computing is to scale up robust qubit prototypes to practical problem sizes and to implement comprehensive error correction for computational precision. Due to inevitable quantum uncertainties in resonant control pulses, increasing the precision of quantum gates comes with the expense of increased energy consumption. Consequently, the power dissipated in the vicinity of the processor in a well-working large-scale quantum computer seems unacceptably large in typical systems requiring low operation temperatures. Here, we introduce a method for qubit driving and show that it serves to decrease the single-qubit gate error without increasing the a…
Controlling thermal conductance using three-dimensional phononic crystals
2021
Controlling thermal transport at the nanoscale is vital for many applications. Previously, it has been shown that this control can be achieved with periodically nanostructured two-dimensional phononic crystals for the case of suspended devices. Here, we show that thermal conductance can also be controlled with three-dimensional phononic crystals, allowing the engineering of the thermal contact of more varied devices without the need for suspension in the future. We show the experimental results obtained at sub-Kelvin temperatures for two different period three-dimensional crystals and for a bulk control structure. The results show that the conductance can be enhanced with the phononic cryst…
Reliable estimates in the anisotropic heat conduction problems
2014
Abstract The heat conduction problems for anisotropic bodies are studied taking into account the uncertainties in the material orientation. The best estimations of the upper and lower bounds of the considered energy dissipation functional are based on developing new approach consisting in solution of some optimization problems and finding the extremal internal material structures, which realize minimal and maximal dissipation. The motivation of this study comes from paper making processes, and more precisely, drying process, which consumes about 50% of the energy fed into the paper machine. The understanding of the effect of uncertainties in the process arises from structural properties of …
In-plane conductive heat tansfer in solid and porous planar structures
2011
Methods for determining the in-plane thermal diffusivity in a planar sample geometry were developed. These methods were tested and verified by measuring planar metal samples with known thermal properties. The techniques used were based on heating the sample at one edge and recording the evolution of the temperature field in the sample by a thermographic camera. The temperature fields at different times were processed and then fitted by a solution to a heat equation describing the experimental setup, thermal diffusivity as one of the fitting parameters. In the first experimental setup the sample was placed in a weak constant flow of air, and the situation was improved in the second setup by …
Cellulose-inorganic hybrids of strongly reduced thermal conductivity
2022
Abstract The employment of atomic layer deposition and spin coating techniques for preparing inorganic-organic hybrid multilayer structures of alternating ZnO-CNC layers was explored in this study. Helium ion microscopy and X-ray reflectivity showed the superlattice formation for the nanolaminate structures and atomic force microscopy established the efficient control of the CNCs surface coverage on the Al-doped ΖnO by manipulating the concentration of the spin coating solution. Thickness characterization of the hybrid structures was performed via both ellipsometry and X-ray reflectivity and the thermal conductivity was examined by time domain thermoreflectance technique. It appears that ev…
Minimizing coherent thermal conductance by controlling the periodicity of two-dimensional phononic crystals
2019
Periodic hole array phononic crystals (PnC) can strongly modify the phonon dispersion relations, and have been shown to influence thermal conductance coherently, especially at low temperatures where scattering is suppressed. One very important parameter influencing this effect is the period of the structure. Here, we measured the sub-Kelvin thermal conductance of nanofabricated PnCs with identical hole filling factors, but three different periodicities, 4, 8, and 16 $\mu$m, using superconducting tunnel junction thermometry. We found that all the measured samples can suppress thermal conductance by an order of magnitude, and have a lower thermal conductance than the previously measured small…
Uncertainties in the heat conduction problems and reliable estimates
2013
The heat conduction problems for anisotropic bodies are studied taking into account the uncertainties in the material orientation. The best estimations of the upper and lower bounds of the considered energy dissipation functional are based on the developing new approach consisting in solution of some optimization problems and finding the extremal internal material structures, which realize minimal and maximal dissipation.
Computational and theoretical studies on lattice thermal conductivity and thermal properties of silicon clathrates
2016
The lattice thermal conductivity is usually an intrinsic property in the study of thermoelectricity. In particular, relatively low lattice thermal conductivity is usually a desired feature when higher thermoelectric efficiency is pursued. The mechanisms which lower the lattice thermal conductivity are not known in sufficient detail and deeper understanding about the phenomena is needed and if such understanding is achieved it can be used to design more efficient thermoelectric materials. In this thesis, the lattice thermal conductivity and other thermal properties of several silicon clathrates, which are known to be promising candidates for the thermoelectric applications, are studied by theoreti…
A Composite Phononic Crystal Design for Quasiparticle Lifetime Enhancement in Kinetic Inductance Detectors
2020
A nanoscale phononic crystal filter (reflector) is designed for a kinetic inductance detector where the reflection band is matched to the quasiparticle recombination phonons with the aim to increase quasiparticle lifetime in the superconducting resonator. The inductor is enclosed by a 1-μm-wide phononic crystal membrane section with two simple hole patterns that each contain a partial spectral gap for various high-frequency phonon modes. The phononic crystal is narrow enough for low-frequency thermal phonons to propagate unimpeded. With 3D phonon scattering simulation over a 40 dB attenuation in transmitted power is found for the crystal, which is estimated to give a lifetime enhancement of…