Distribution Of Power Dissipation Research Articles

Hot deformation behavior analysis of CNT/2009Al composite with bimodal heterostructure via constructing a new processing map

Bimodal heterostructure consisted of reinforcement-rich and reinforcement-free micro-regions could significantly enhance the strength-ductility of metal matrix composites. However, it could also induce difficult controlling of the heterostructure during hot deformation processing. In this work, an innovative coordination coefficient map based on processing map was proposed to qualitatively evaluate the deformation coordination of two micro-regions within bimodal heterostructure CNT/2009Al composite under different hot compression parameters and analyze its influencing factors. The results showed that the deformation coordination of the two micro-regions was influenced by microstructure evolution as well as the stress-strain distribution between the CNT-rich and CNT-free micro-regions. At medium temperature with medium strain rate (400 °C-0.1 s−1) rather than other parameters, the deformation coordination between the CNT-rich and CNT-free micro-regions was well, and the power dissipation distribution within heterostructure conformed to the rule of mixtures. While the additional microstructure evolution at high temperature would lead to the opposite deviation trend of the calculated coordination coefficient. The abnormal grain growth at low strain rate (450 °C-0.001 s−1) and the distortion energy between the different micro-regions interfaces at high strain rate (500 °C-1 s−1) were the reasons for this phenomenon. The establishment of the new coordination coefficient map provided guidance for the analysis of the hot deformation behavior of the bimodal heterostructure CNT/2009Al composite.

Effect of focus ring with external circuit on cathode edge sheath dynamics in a capacitively coupled plasma

Capacitively coupled plasmas are widely used in semiconductor processes. The control of plasma to obtain uniform deposition and etching is an open problem, particularly within a few millimeters of the substrate edge. Complex material stacks commonly referred to as focus rings are placed at the wafer edge to provide uniform processes across the entire substrate but have limitations with regard to process window and eventual material erosion. One approach is to combine a focus ring with a tunable external circuit ground path termination to extend the plasma uniformity to the wafer edge over a wider process space. The external circuit coupling focus ring to the ground influences the ion energy profile and the ion angular profile by changing the impedance between the focus ring and the ground and allows wafer edge tuning over a wide range of operating parameters. In this work, it is found that the adjustable external circuit can control the partitioning of bias and RF voltages between the RF powered and passively coupled plasma facing surfaces. The focus ring with an external circuit assembly can also control the spatial distribution of plasma density and, therefore, improve the sheath edge profile. These results point to possible source designs for engineering the distribution of power dissipation and the electric field of the wafer edge in industrial plasma reactors.

Single-switch boost converter with extremely high step-up voltage gain

This paper presents a single-switch high-voltage gain DC–DC converter with a coupled-inductor. The proposed converter overcomes the drawbacks of traditional DC–DC converters such as insufficient boost capability and high stress on the devices. Its advantages include having a small number of switch devices, low voltage stress on the switch, and a high voltage gain. This paper analyzes the operating modes of the proposed converter in detail and derives the voltage/current stresses on the components. The efficiency of the converter and the power dissipation distribution are quantitatively studied. To verify the efficiency and feasibility of the proposed converter, a 200 W prototype was built in the laboratory. Experimental results obtained from the prototype match well with the theoretical analysis. The highest efficiency is equal to 95.82%, which can be obtained at half of the rated output power.

Gallium nitride high electron mobility transistor with an effective graphene-based heat removal system

The self-heating effect is a major problem for gallium nitride electronic, optoelectronic and photonic devices. Average temperature increase and non-uniform distribution of dissipated power in the gallium nitride high electron mobility transistor lead to the forming of a hot spot in the vicinity of the conducting channel and to degradation of the drain current, output power and gain, as well as poor reliability. The purpose of this work is to develop the design using numerical simulation and to study the thermal phenomena that occur in the gallium nitride high-electron mobility transistor with a graphene-based heat removal system. The objects of the research are the structures fabricated on sapphire, silicon and silicon carbide substrates. The subject of the research is the electrical, frequency and thermal characteristics of the gallium nitride high-electron mobility transistor with a graphene-based heat removal system. The calculation results show that the integration of a graphene-based heat removal element into the design of the high electron mobility transistor can effectively mitigate the self-heating effect and thus improve the device performance. The advantage of the proposed concept is that the graphene-based heat removal element is structurally connected with a heat sink and aims at removing heat immediately from the maximum temperature region, providing an additional heat escape channel. The obtained results can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics.

It's the little things: On the complexity of planar electrode heating in MRI

Neurological disorders are increasingly analysed and treated with implantable electrodes, and patients with such electrodes are studied with MRI despite the risk of radio-frequency (RF) induced heating during the MRI exam. Recent clinical research suggests that electrodes with smaller diameters of the electrical interface between implant and tissue are beneficial; however, the influence of this electrode contact diameter on RF-induced heating has not been investigated. In this work, electrode contact diameters between 0.3 and 4 mm of implantable electrodes appropriate for stimulation and electrocorticography were evaluated in a 1.5 T MRI system. In situ temperature measurements adapted from the ASTM standard test method were performed and complemented by simulations of the specific absorption rate (SAR) to assess local SAR values, temperature increase and the distribution of dissipated power. Measurements showed temperature changes between 0.8 K and 53 K for different electrode contact diameters, which is well above the legal limit of 1 K. Systematic errors in the temperature measurements are to be expected, as the temperature sensors may disturb the heating pattern near small electrodes. Compared to large electrodes, simulations suggest that small electrodes are subject to less dissipated power, but more localized power density. Thus, smaller electrodes might be classified as safe in current certification procedures but may be more likely to burn adjacent tissue. To assess these local heating phenomena, smaller temperature sensors or new non-invasive temperature sensing methods are needed.

Asymmetric dynamics in a horizontally stirred mill using DEM

Discrete Element Method simulations were performed on a horizontally run annular shear cell in order to extract relevant dimensionless quantities necessary for a description of the granular rheology. The change from the usual upright orientation greatly increases the complexity of the equations governing the granular flow dynamics. Volume fraction and velocity distributions were extracted from the simulation outputs, to ultimately be used to calculate shear stress, pressure and power dissipation distributions within the horizontal shear cell. The volume fractions were found to follow a power law distribution within the band of sheared material, while the velocity followed an exponential in the sheared region. Additionally, a clear anisotropy in the velocity distributions exists, dependent on friction between particles and the applied shear rate. Analysis of this anisotropic behaviour resulted in the boundary condition of the velocity distribution at the shearing wall, along with a description of the behaviour of the shear band under differing applied shear rate and particle friction conditions. This simulation work can be used to control the wear patterns in horizontally stirred mills by tuning the shear rate and the material friction.

A variational homogenization approach applied to the multiscale analysis of the viscoelastic behavior of tendon fascicles

This work presents a variational homogenization approach based on representative volume elements (RVE) in order to investigate the macro- and microviscoelastic behavior of tendon fascicles. A three-dimensional hexagonal–helicoidal finite element RVE is proposed to properly account for the morphology of tendon fascicles observed in serial block-face scanning electron microscopy. Two material phases (collagen fibers and cells) comprising three finite strain variational viscoelastic models (fibrils, matrix of fibers and cells) compose the proposed multiscale model. The material parameters of the micromechanical models were identified with the aid of atomic force microscopy experiments extracted from the literature. A set of multiscale simulations of tensile tests under physiological strain amplitudes were performed, providing the following results. Firstly, numerical predictions corroborate experimental findings: collagen fibrils are the main load-bearing structures of tendons; the cellular matrix contributes neither to the stiffness nor to the energy dissipation of tendons. Secondly, the model brings insights about microscale mechanics of tendon fascicles not completely understood: prediction of uncoiling of fibers during axial loads which may explain the large apparent Poisson ratios and fluid loss, and significant strain localization in cells, which may lead to important mechanotransduction mechanisms. Moreover, the distribution of dissipated power became available, pointing out the fibrils as the main source of dissipation of fascicles under high macroscopic strain rates and during the unloading phase in cyclic regimes.

Analysis of efficiency of different antennas for microwave ablation using simulation and experimental methods

The objective of this study is to analyze the efficiency of different antennas proposed for microwave ablation therapy using numerical simulation and experimental approach. The simulation was done with COMSOL MULTIPHYSICS® software to design antenna prototypes and evaluate its reflection coefficient, power dissipation distribution, power dissipation density, specific absorption rate and temperature distribution in tissue. Antennas were fabricated from a 50 Ω RG405/U semi-rigid coaxial cable to match the geometric prototypes generated during simulation. Ex vivo bovine livers were ablated with the fabricated antennas using 50 W for 5 and 10 min. Ablation diameters, ablation lengths and aspect ratios were determined. Sleeved antenna produced lowest reflection coefficient, high power dissipation, low power dissipation density, high SAR and high temperature in the simulation. Sleeved antenna provides excellent localization, large ablative diameter, low backward heating and high aspect ratio than single slot, dual slot and monopole antennas.

Radio emission in Mercury magnetosphere

Context: Active stars possess magnetized wind that has a direct impact on planets that can lead to radio emission. Mercury is a good test case to study the effect of the solar wind and interplanetary magnetic field on radio emission driven in the planet magnetosphere. Such studies could be used as proxies to characterize the magnetic field topology and intensity of exoplanets. Aims: The aim of this study is to quantify the radio emission in the Hermean magnetosphere. Methods: We use the MHD code PLUTO in spherical coordinates with an axisymmetric multipolar expansion for the Hermean magnetic field, to analyze the effect of the interplanetary magnetic field (IMF) orientation and intensity, as well as the hydrodynamic parameters of the solar wind (velocity, density and temperature), on the net power dissipated on the Hermean day and night side. We apply the formalism derived by Zarka [2001, 2007] to infer the radio emission level from the net dissipated power. We perform a set of simulations with different hydrodynamic parameters of the solar wind, IMF orientations and intensities, that allow us to calculate the dissipated power distribution and infer the existence of radio emission hot spots on the planet day side, and to calculate the integrated radio emission of the Hermean magnetosphere. Results: The obtained radio emission distribution of dissipated power is determined by the IMF orientation (associated with the reconnection regions in the magnetosphere), although the radio emission strength is dependent on the IMF intensity and solar wind hydro parameters. The calculated total radio emission level is in agreement with the one estimated in [Zarka, 2001], between $5 \times 10^{5}$ and $2 \times 10^{6}$ W.

Effect of spatial distribution of dissipated power on modeling of SMR BAW resonators at high power levels.

The modeling of bulk acoustic wave resonators at elevated power levels has been improved by taking the spatial distribution of the dominating loss mechanisms into account. The spatial distribution of the dissipated power enables more accurate modeling of the temperature increase caused by the applied power. Thus, it is also possible to more accurately model the frequency shifts of the resonators' impedance curves resulting from the temperature increase caused by the applied power. Simulation and measurement results for the temperatures and impedances of the resonators with different layerstacks at high power loads are presented. The simulation and measurement results are in good agreement, confirming the presented modeling approach. Furthermore, the de-embedding procedure used to obtain vectorial scattering parameters of the resonators during high power loads, the according measurement setup, and the procedure for measuring absolute temperatures by infrared thermography are discussed.

Optimal Design and Thermal Analysis of Undepressed Collectors for 35-GHz Gyro-TWTs

A new curved-profile undepressed collector designed for a planned 35-GHz gyrotron traveling-wave tube (gyro-TWT) is proposed in this paper. This gyro-TWT, which is driven by a 70-kV, 10-A electron beam, is working at the fundamental TE01 mode with an efficiency of 20% and gain of 45 dB. Studies including theoretical analysis, numerical calculation, and computational simulation have been done. Key issues concerning electronic collecting density, dissipated power distribution, transmission performance, secondary electrons, and thermal property are considered. Simulation results show that curved-profile structure collector has a better heat-handling capacity than the conventional line structure collector.

Effect of Sunlight Polarization on the Absorption Efficiency of V-shaped Organic Solar Cells

We numerically investigate the effect of sunlight polarization on the absorption efficiency of V-shaped organic solar cells (VOSCs) using the finite element method (FEM). The spectral distribution of absorbance and the spatial distribution of power dissipation are calculated as a function of the folding angle for s-and p-polarized light. The absorption enhancement caused by the light-trapping effect was more pronounced for s-polarized light at folding angles smaller than $20^{\circ}$ , where s-polarized light has a relatively larger reflectance than p-polarized light. On the other hand, the absorption efficiency for p-polarized light is relatively larger for folding angles larger than $20^{\circ}$ , where the smaller reflectance at the interface of the VOSC is more important in obtaining high absorption efficiency.

Efficiency Analysis of Near Field Optical Transducer Used in Heat-Assisted Magnetic Recording

For heat-assisted magnetic recording system, the efficiency of the optical energy delivery system is important for its application. It affects not only the requirement to laser source output power, but also the heat-assisted magnetic recording (HAMR) head performance and reliability. In this paper, the key factor caused the low efficiency of the near field optical transducer is studied. The results show that the main reason is the longitudinal polarization of the transducer radiation. Large permittivity difference between recording layer and air gap makes large electric field intensity difference within recording layer and air gap. Due to small electric field coupling from air to recording layer, large percentage of the incident power is reflected, absorbed or scattered by other components. The investigation results for power dissipation distributions show that the largest portion of power dissipation is reflection. Reusing the reflected power will be an effective way to improve whole optical system efficiency. Simulation results show that more than 30% increase of the efficiency can be obtained by reusing the reflected power.

Improved thermal management of low voltage power devices with optimized bond wire positions

This paper focuses on optimization of bond wire positions as a method to improve thermal management of power semiconductors. For this purpose, robustness of a new low-voltage MOSFET generation with an optimized multiple bond wire arrangement and device shape is compared to an older device design with lower number of bond wires. 2D electrical simulation is used to evaluate the lateral distribution of power dissipation due to the gate voltage de-biasing effect. 3D thermal finite element simulation and infrared thermography measurements are employed to analyze the corresponding surface temperature distribution. Finally, tests under extreme single pulse short-circuit conditions demonstrate the effectiveness of thermal management for improving robustness in automotive applications.

Full-Wave Design Considering Slot Admittance in 2-D Waveguide Slot Arrays with Perfect Input Matching

A novel design technique for two-dimensional (2-D) waveguide slot arrays is proposed in this paper that combines a full-wave method of moments (MoM) analysis and an equivalent circuit with the explicit restraint of input matching. The admittance and slot spacing are determined first in an equivalent circuit to realize the desired distribution of power dissipation and phase, with the explicit restraint of input matching. Secondly by applying a full-wave MoM analysis to the finite 2-D array, slot parameters are iteratively determined to realize the active admittance designed above where slot mutual coupling and wall thickness are fully taken into account. The admittance, treated as the key parameter in the equivalent circuit corresponds to the power dissipation of the slots but not to the slot voltage, which is directly synthesized from the radiation pattern. The initial value of the power dissipation is assumed to be proportional to the square of the amplitude of the desired slot voltage. This assumption leads to a feedback procedure, because the resultant slot voltage distribution generally differs from the desired ones due to the effect of non-uniformity in the characteristic impedance on slot apertures. This slot voltage error is used to renew the initial distribution of power dissipation in the equivalent circuit. Generally, only one feedback cycle is needed. Two 24×27-element arrays with uniform and Taylor distributions were designed and fabricated at 25.3GHz. The measured overall reflections for both antennas were suppressed below -18dB over the 24.3-26.3GHz frequency range. High aperture efficiencies of 86.8% and 55.1% were realized for the antennas with uniform and Taylor distributions, the latter of which has very low sidelobes below -33dB in both the E- and H-planes.

Application of time windowing to spatial maps of damping.

Some of the most challenging vibration control problems involve the selection and placement of frequency-dependent damping devices, such as multilayered viscoelastic materials. In complex structures involving the simultaneous use of several passive damping devices, it is difficult to determine the effectiveness of each device directly from measurements. This question motivates the present analysis, which seeks to quantify the power being dissipated by the structure at selected locations for a given force distribution. The analysis begins with an expression for power flow to the structure from a specified force distribution. This expression involves the real part of the admittance matrix looking into the structure at a set of measurement points. By expanding this matrix as a sum over damping elements that mechanically connect measurement points, one can spatially map the power flow into the structure. While thermodynamics requires that this power flow to the structure be equal to the power dissipated by the structure, it does not require equality of the spatial distributions. In order to understand the spatial distribution of power dissipation, time windowing of the impulse responses is introduced. Examples are developed to explore the effects of the time window. [Work supported by ONR under Grant No. N000140810531.]

On a Simplified Model for Numerical Simulation of Wear During Dry Rolling Contacts

We deal with rolling contact between quasi-identical bodies. As normal and tangential problems are uncoupled in that case, the simplified approach to determine contact area and normal loading distribution for rolling contact problems is presented in Sec. 2. In Sec. 3, the solution of the tangential problem is used to update the rolling profiles and enables to follow the wear evolution versus time. The method used to solve the normal problem is called semi-Hertzian approach with diffusion. It allows fast determination of the contact area for non-Hertzian cases. The method is based on the geometrical indentation of bodies in contact: The contact area is found with correct dimensions but affected by some irregularities coming from the curvature’s discontinuity that may arise during a wear process. Diffusion between independent stripes smoothes the contact area and the pressure distribution. The tangential problem is also solved on each stripe of the contact area using an extension of the simplified approach developed by Kalker and called FASTSIM. At the end, this approach gives the dissipated power distribution in the contact during rolling and this power is related to wear by Archard’s law. This enables the profiles of the bodies to be updated and the evolution of the geometry to be followed.

Power complexity of multiplexer-based optoelectronic crossbar switches

The integration of thousands of optical input/output (I/O) devices and large electronic crossbar switching elements onto a single optoelectronic integrated circuit (IC) can place stringent power demands on the CMOS substrates. Currently, there is no sufficiently general analytic methodology for power analysis and power reduction of large-scale crossbar switching systems. An analysis of the power complexity of single-chip optoelectronic switches is presented, assuming the classic broadcast-and-select crossbar architecture. The analysis yields the distribution of power dissipation and allows for design optimization. Both unpipelined and pipelined designs are analyzed, and a technique to reduce power dissipation significantly is proposed. The design of a 5.12 Tbit single-chip optoelectronic switch using 0.18-/spl mu/m CMOS technology is illustrated. The pipelined switch design occupies < 70 mm/sup 2/ of CMOS area, and consumes <80 W of power, which compares favorably to the power required in electrical crossbar switches of equivalent capacity.

Local Load Balancing for Globally Efficient Routing in Wireless Sensor Networks

One of the limitations of wireless sensor nodes is their inherent limited energy resource. Besides maximizing the lifetime of the sensor node, it is preferable to distribute the energy dissipated throughout the wireless sensor network in order to minimize maintenance and maximize overall system performance. Any communication protocol that involves synchronization of peer nodes incurs some overhead for setting up the communication. We introduce a new algorithm, e3D (energy-efficient Distributed Dynamic Diffusion routing algorithm), and compare it to two other algorithms, namely directed, and random clustering communication. We take into account the setup costs and analyze the energy-efficiency and the useful lifetime of the system. In order to better understand the characteristics of each algorithm and how well e3D really performs, we also compare e3D with its optimum counterpart and an optimum clustering algorithm. The benefit of introducing these ideal algorithms is to show the upper bound on performance at the cost of astronomical prohibitive synchronization costs. We compare the algorithms in terms of system lifetime, power dissipation distribution, cost of synchronization, and simplicity of the algorithm. Our simulation results show that e3D performs comparable to its optimal counterpart while having significantly less overhead.

Coaxial Antenna for Microwave Hyperthermia

We present in this paper a coaxial applicator in which the radiating source is a circular slot realised by exterior conductor interruption of a coaxial guide. The guide is immersed in a strong dissipated medium. A dielectric material girdle without losses or an air layer is inserted among the radiating slot and the load. In this paper, we study a single slot radiation and analyse the radiating field distributions in the load, the approaching field influences and the role of dielectric girdle on the dissipated power distribution in the load.