Electronic Dissipation Research Articles

A Passive and Remote Heat Transfer Solution for Avionics Thermal Management

A heat pipe utilizes liquid–vapor phase change mechanism to efficiently transfer heat. Among different heat pipes, loop heat pipe (LHP) and pulsating heat pipe (PHP) are known to be capable of high heat flux/high load heat transfer. In this article, LHP and PHP heat transfer systems are combined to achieve passive, reliable, and remote/long-distance heat transfer for thermal management of modern avionics systems. Aiming at this goal, a 2 m long LHP is developed to transport heat from the avionics chassis to the remote heat rejection site. To reduce inner saturation pressure and ensure structural safety at high operating temperature, water is used as the operating fluid in LHP. Within the avionics chassis, conduction heat transfer is enhanced by sandwiching a PHP with two printed circuit boards (PCBs) and solder-bonding them. Each PHP/PCB assembly is 20 cm long and 12.5 cm wide, with electrical heaters mounted on both sides to mimic electronic heat dissipation. Heat transfer demonstration of the LHP and PHP combo system is conducted in a lab environment with input power varying from 100 to 400 W. For all the three PHP/PCB assemblies set in the avionic chassis, heat source temperature is maintained below the required 150 °C even when heat dissipation is twice as high as the state-of-the-art (and coolant temperature is 50 °C). This combo heat transfer system reduces power consumption and increases reliability, enabling the avionic system operation in harsh environments.

Synergistic effects of nuclear and electronic energy loss in KTaO3 under ion irradiation

We use the inelastic thermal spike model for insulators and molecular dynamic simulations to investigate the effects of pre-existing damage on the energy dissipation and structural alterations in KTaO3 under irradiation with 21 MeV Ni ions. Our results reveal a synergy between the pre-existing defects and the electronic energy loss, indicating that the defects play an important role on the energy deposition in the system. Our findings highlight the need for better understanding on the role of defects in electronic energy dissipation and the coupling of the electronic and atomic subsystems.

Thin low frequency sound absorbers based on shunted loudspeakers

There are two main reasons for using shunted loudspeakers as sound absorbers. One is that the absorbers can be made very thin for the low frequency sound with electronic energy dissipation mechanism and the other is that their absorption performance can be adjusted with the shunt circuit. A shunted loudspeaker typically has high absorption coefficients around its resonance frequencies which are determined by the loudspeaker unit and the shunt circuit together. To extend the effective frequency range of the shunted loudspeaker, one method is constructing more resonant sub-systems in the absorber to have absorption at more resonance frequencies. In this research, two designs based on shunted loudspeakers will be introduced. One is the composite absorber with a micro-perforated panel in front of a shunted loudspeaker, which combines two resonance subsystems to provide broadband absorption. The other is a shunted loudspeaker with a specifically designed shunt circuit for the absorption of three tonal componen...

Relaxation of a Classical Spin Coupled to a Strongly Correlated Electron System.

A classical spin which is antiferromagnetically coupled to a system of strongly correlated conduction electrons is shown to exhibit unconventional real-time dynamics which cannot be described by Gilbert damping. Depending on the strength of the local Coulomb interaction U, the two main electronic dissipation channels, namely transport of excitations via correlated hopping and via excitations of correlation-induced magnetic moments, become active on largely different time scales. We demonstrate that correlations can lead to a strongly suppressed relaxation which so far has been observed in purely electronic systems only and which is governed here by proximity to the divergent magnetic time scale in the infinite-U limit.

Measurement of electronic heat dissipation in highly disordered graphene

We have measured the electronic heat dissipation of hot electrons in highly disordered millimeter scale graphene at temperatures $T=0.3\text{--}3$ K. Disorder was introduced by hydrogenation of graphene, bringing low-temperature electron conduction below the Ioffe-Regel criterion for metallic conduction. Resistive thermometry was employed to determine the dependence of electron temperature on applied electrical power. The relation between heat flow and electron temperature was found to be well described by a power law with an exponent $\ensuremath{\beta}\ensuremath{\sim}3.7\text{--}3.9$ and a coupling coefficient $\mathrm{\ensuremath{\Sigma}}\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{mW}/{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{\beta}}$. Our observations are similar to electronic heat dissipation of a two-dimensional electron gas in the hydrodynamic limit of electron-phonon coupling, corresponding to acoustic phonon emission into the substrate.

Electronic phase coherence vs. dissipation in solid-state quantum devices: Two approximations are better than one

In the microscopic modeling of new-generation electronic quantum nanodevices a variety of simulation strategies have been proposed and employed. The aim of this letter is to point out virtues vs. intrinsic limitations of non-Markovian density-matrix approaches; we shall show that the usual mean-field treatment may lead to highly unphysical results, like negative distribution probabilities and non-dissipative behaviours, which are particularly severe in zero-dimensional electronic systems coupled to dispersionless phonon modes. This is in striking contrast with Markovian treatments, where a proper combination of adiabatic limit and mean-field schemes guarantees a physically acceptable solution; as a result, the unusual conclusion is that two approximations are better than one.

Multi-Threshold Voltage CMOS Design for Low-Power Half Adder Circuit

The new era of portable electronic devices demands lesser power dissipation for longer battery life and design compactability. Leakage current and leakage power are dominating factors which greatly affect the power consumption in low voltage and low power applications. For many numerical representations of binary numbers, combinational circuits like adder, encoder, multiplexer, etc. are useful circuits for arithmetic operation. A novel high speed and low power half adder cell is introduced here which consists of AND gate and OR gate. This cell shows high speed, lower power consumption than conventional half adder. In CMOS technology, transistors used have small area and low power consumption. It is used in various applications like adder, subtract or, multiplexer, ALU and microprocessors digital VLSI systems. As the scaling technology reduces, the leakage power increases. In this paper, multi threshold complementary metal oxide semiconductor (MTCMOS) technique is proposed to reduce the leakage current and leakage power. MTCMOS is an effective circuit level technique that increases the performance of a cell by using both low- and high-threshold voltage transistors. Leakage current is reduced by 85.37% and leakage power is reduced by 87.45% using MTCMOS technique as compared to standard CMOS technique. The half adder design simulation work was performed by cadence simulation tool at 45-nm technology.

Electronic Friction-Based Vibrational Lifetimes of Molecular Adsorbates: Beyond the Independent-Atom Approximation.

We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.

Experimental investigation on the sintered wick of the anti-gravity loop-shaped heat pipe

The Anti-Gravity Loop-Shaped Heat Pipe (AGLSHP), designed with a special sintered wick structure, is a novel device used in electronic heat dissipation under the anti-gravity condition. Two kinds of wick structures, single-powder (SP) and continuous step-graded (CSG) structures were evaluated for design optimization. The copper powder utilized in the experiment were divided into six particle sizes (<25, 25–50, 50–75, 75–100, 100–125, and >125μm) to investigate their influence. The results show that the heat transfer performance of the sintered wick samples changes significantly with the variation of the copper powder size. SP75–100 is the optimal particle size for single-powder sintered wick heat transfer, while CSG25–50 is the optimal particle size for the continuous step-graded sintered wick. Furthermore, the CSG sintered wick possesses better overall performance than the SP sintered wick, obtaining higher maximum operating power and lower start-up temperature.

Quasiparticle dynamics in high-temperature superconductors far from equilibrium: An indication of pairing amplitude without phase coherence

We perform time-resolved photoelectron spectroscopy measurements of optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212) and Bi2Sr2−xLaxCuO6+δ (Bi-2201). The electron dynamics shows that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop in electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude. The latter vanishes near to the critical temperature and has no evident link to the pseudogap observed by angle-resolved photoelectron spectroscopy.

Band excitation Kelvin probe force microscopy utilizing photothermal excitation

A multifrequency open loop Kelvin probe force microscopy (KPFM) approach utilizing photothermal as opposed to electrical excitation is developed. Photothermal band excitation (PthBE)-KPFM is implemented here in a grid mode on a model test sample comprising a metal-insulator junction with local charge-patterned regions. Unlike the previously described open loop BE-KPFM, which relies on capacitive actuation of the cantilever, photothermal actuation is shown to be highly sensitive to the electrostatic force gradient even at biases close to the contact potential difference (CPD). PthBE-KPFM is further shown to provide a more localized measurement of true CPD in comparison to the gold standard ambient KPFM approach, amplitude modulated KPFM. Finally, PthBE-KPFM data contain information relating to local dielectric properties and electronic dissipation between tip and sample unattainable using conventional single frequency KPFM approaches.

Synergy of elastic and inelastic energy loss on ion track formation in SrTiO₃.

While the interaction of energetic ions with solids is well known to result in inelastic energy loss to electrons and elastic energy loss to atomic nuclei in the solid, the coupled effects of these energy losses on defect production, nanostructure evolution and phase transformations in ionic and covalently bonded materials are complex and not well understood due to dependencies on electron-electron scattering processes, electron-phonon coupling, localized electronic excitations, diffusivity of charged defects, and solid-state radiolysis. Here we show that a colossal synergy occurs between inelastic energy loss and pre-existing atomic defects created by elastic energy loss in single crystal strontium titanate (SrTiO3), resulting in the formation of nanometer-sized amorphous tracks, but only in the narrow region with pre-existing defects. These defects locally decrease the electronic and atomic thermal conductivities and increase electron-phonon coupling, which locally increase the intensity of the thermal spike for each ion. This work identifies a major gap in understanding on the role of defects in electronic energy dissipation and electron-phonon coupling; it also provides insights for creating novel interfaces and nanostructures to functionalize thin film structures, including tunable electronic, ionic, magnetic and optical properties.

Predictive modeling of synergistic effects in nanoscale ion track formation.

Molecular dynamics techniques in combination with the inelastic thermal spike model are used to study the coupled effects of the inelastic energy loss due to 21 MeV Ni ion irradiation with pre-existing defects in SrTiO3. We determine the dependence on pre-existing defect concentration of nanoscale track formation occurring from the synergy between the inelastic energy loss and the pre-existing atomic defects. We show that the size of nanoscale ion tracks can be controlled by the concentration of pre-existing disorder. This work identifies a major gap in fundamental understanding on the role of defects in electronic energy dissipation and electron-lattice coupling.

Research of the Heat-transfer Performance on Methanol/Acetone Oscillating Heat Pipe

As a high efficient heat transfer element,the oscillating heat pipe(OHP) has unique advantages in solving the problem of electronic device heat dissipation with tiny space and high heat flux and its heat transfer performance is greatly affected by its working medium.The methanol/acetone binary mixture,as well as the pure methanol,acetone,have been selected as working mediums of OHP,then the heat transfer characteristics of methanol/acetone OHP has been researched by analysing the physical properties of the working mediums and its interaction characteristics on heat transfer performance of OHP under different ratios(7︰1,4︰1,1︰4,1︰7),filling ratios(45%,62%,70%)and heat inputs(10-100 W).The results show that all evaporator sections of OHP are dried out obviously with small filling ratios.Compared with pure working mediums,the thermal resistance of mixture working medium is smaller when dried out,namely when the heat input is 50 W,the pure methanol,acetone are 1.509 oC/W and 1.48 oC/W,the methanol/acetone 1︰7 thermal resistance is 0.88 oC/W,between them are the thermal resistances of the rest ratios.In addition,the effect is more obvious when little methanol is added into acetone as working medium(such as methanol/acetone 1︰7);With large filling ratios,the thermal resistances of mixture working mediums increased with little gradient and get close to each other as heat inputs increased gradually,the heat transfer performances are generally great.

High-speed reconfigurable card-to-card optical interconnects based on hybrid free-space and multi-mode fiber propagations

In this paper, a high-speed reconfigurable card-to-card optical interconnect architecture based on hybrid free-space and multi-mode fiber (MMF) propagation is proposed. The use of free-space signal transmission provides flexibility and reconfigurability and the MMF extends the achievable interconnection range. A printed-circuit-board (PCB) based integrated optical interconnect module is designed and developed and proof-of-concept demonstration experiments are carried out. Results show that 3 × 10 Gb/s reconfigurable optical interconnect is realized with ~12 cm free-space propagation and a 10 m MMF length. In addition, since air turbulence due to high temperature of electronic components and heat dissipation fans always exists in typical interconnect environments and it normally results in system performance degradation, its impact on the proposed reconfigurable optical interconnect scheme is also experimentally investigated. Results indicate that even with comparatively strong air turbulence, 3 × 10 Gb/s optical interconnects with flexibility can still be achieved and the power penalty is <0.7 dB.

Interplay between energy dissipation and reservoir-induced thermalization in nonequilibrium quantum nanodevices

A solid state electronic nanodevice is an intrinsically open quantum system, exchanging both energy with the host material and carriers with connected reservoirs. Its out-of-equilibrium behavior is determined by a non-trivial interplay between electronic dissipation and decoherence induced by inelastic processes within the device, and the coupling of the latter to metallic electrodes. We propose a unified description, based on the density matrix formalism, that accounts for both these aspects, enabling to predict various steady-state as well as ultrafast nonequilibrium phenomena, nowadays experimentally accessible. More specifically, we derive a generalized density-matrix equation, particularly suitable for the design and optimization of a wide class of electronic and optoelectronic quantum devices. The power and flexibility of this approach is demonstrated with the application to a photoexcited triple-barrier nanodevice.

Performance of High-Speed Reconfigurable Free-Space Card-to-Card Optical Interconnects Under Air Turbulence

Free-space based optical interconnects are promising candidates for the prevision of parallel, high-speed, densely integrated and reconfigurable card-to-card interconnectivities in data centers and for high-performance computing clusters. However, air turbulence due to high temperature of electronic components and heat dissipation fans typically results in degradation of system performance through effects such as signal scintillation, beam broadening and beam wander. In this paper, the impact of air turbulence on our recently proposed reconfigurable free-space card-to-card optical interconnect scheme is investigated. Experiments are carried out with lab-emulated moderate and comparatively strong turbulence and results show that the bit-error-rate (BER) performance of proposed interconnect scheme is degraded. A power penalty of ~ 0.5 dB is observed at BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> in emulated moderate turbulence, and in emulated comparatively strong turbulence the BER performance suffers power penalties of ~ 1.6 dB. It should be noted that a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> is not sufficient for typical card-to-card optical interconnects and FEC should be employed to improve the BER performance at the cost of some overhead. Nevertheless, experimental results show that our proposed 3×3 10 Gb/s reconfigurable optical interconnects with card-to-card spacing of up to 30 cm is still achieved even under considerably strong turbulence.

Thermal conductivities of electrospun PAN and PVP nanocomposite fibers incorporated with MWCNTs and NiZn ferrite nanoparticles

Polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) solutions incorporated with multi wall carbon nanotubes (MWCNTs) and NiZn ferrite (Ni0.6Zn0.4Fe2O4) nanoparticles were electrospun at various weight percentages, and then thermal conductivity values of these nanocomposite fibers were determined using a comparative method. During the electrospinning process, system and process parameters, such as concentrations, applied voltage, tip-to-collector distance, and pump speeds were optimized to receive the consistent nanocomposite fibers. Polymer composites with high thermal conductivities are required in many applications, such as electronic packaging, satellite devices, charging/discharging, energy dissipation, and low thermal expansions. The presence of conductive filler materials in polymers increased the thermal conductivity of MWCNTs-based fibers over 10 fold, which may be attributed to higher thermal conductivities of these filler materials. The electrospun fibers incorporated with NiZn ferrite did not show similar improvement.

Experimental investigation on isothermal performance of the micro-grooved heat pipe

The micro-grooved heat pipe (MGHP), which has grooves in the inner wall, is widely used in electronic heat dissipation at high heat flux. It was made via the technology of vacuuming and filling working fluid. The isothermal performance of MGHP was analyzed in the first vacuuming, filling rate of working fluid and second vacuuming. The experimental results show the following conclusions: firstly, the MGHP in low vacuum degree has more remarkable temperature drop than that in high vacuum degree. The maximum slope of temperature distribution curve of the MGHP in low vacuum degree moves to gas-gathering section with the increase of the heating temperature. Secondly, increasing the first vacuuming time does not always improve the isothermal performance remarkably. There exists optimal first vacuuming time, such as 30s in this study. Thirdly, at high working temperature, with increasing the filling rate of working fluid (ranges from 80% to 120%), the temperature difference between the evaporator and the end of condenser generally increases. Fourthly, second vacuuming has a remarkable influence on the isothermal performance of the MGHP. After second vacuuming, the MGHP has a small value of temperature difference that is nearly half of the initial value between the evaporator and the end of condenser. In this experiment, a second vacuuming time at 30s and a second vacuuming temperature at 100°C are preferred parameters.

Pulling the Levers of Photophysics: How Structure Controls the Rate of Energy Dissipation

Internal conversion: The energy difference between the Franck–Condon and equilibrium geometries and the vibrational frequency of one or a few modes determine the relative importance of adiabatic and nonadiabatic dynamics and thus the rate of electronic energy dissipation (see picture). In the cycloketones, variations in these quantities lead to a difference in the timescale for the S2→S1 transition. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.