bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study on Reliability of High-Temperature Joint in Packaging Structure
Authors: Ishikawa Takayuki , Oshidari Toshikazu , Sugihara Hiromi , Yu Qiang
Published: February 2012

In recent years, the research and development of hybrid cars and electrical vehicles become one of the top targets. High electric power is necessary for those cars to run in motor drive, and power devices such as inverter are employed for the control. Since operative temperature of Si power device is from −40 to 150°C level, a big cooling system is needed to control the temperature lower than 150°C. Recently the SiC chip had been developed to downsize the cooling system and reduce the loss of energy, because the operative temperature of SiC chip can be increased to over 300°C. However mounting method that can be used at high temperature environment is not established yet. The author’s group has proposed a new mounting method using Ag-Nano material to mount the SiC chip on a metal board. In existing mounting method, stress was relieved by transformation of comparatively soft solder region. Thus, in the new method, the junction Ag-Nano is too hard to relax the stress. So stress relaxation facility is given to the pure aluminum substrate side. In addition, jointing Ag-Nano on aluminum board is not possible, enabled by Ag and Ni plating on substrate. And these films prevent aluminum board from oxidizing. This mounting method achieves low temperature mounting and high reliability in thermal cycle. In this study, reliability of Ni plating was investigated because it was brought out that Ni plating becomes as a new weak point during high temperature cycle test ranged from −40 to 300°C. Mechanical properties of Ni plating were investigated first. Test specimens with plating and without plating for four point bending test were prepared to compare the difference. And stress-strain relation of plating was evaluated. In addition, fatigue strength was investigated by cyclic bending test. With these material properties, fatigue life of Ni plating in packaging structure was evaluated by finite-element-analysis. And optimum dimension of the structure was studied.
A Data-Centric Approach for Integrated Data Center Management
Authors: Hoover Christopher
Published: February 2012

In this paper, we present the Daffy data model and messaging framework for data centers. The model is a hybrid model, combining physical, structural, geometrical, and logical modeling techniques. The messaging scheme has excellent performance and allows for the loose coupling of the various framework components. The framework bridges the gap between facilities and IT domains and enables the holistic, cross-domain management of data centers. The framework supports rich visualization, cross-domain queries and sophisticated cross-domain autonomic control systems.
Advances in Fan Modeling: Using Multiple Reference Frame (MRF) Approach on Blowers
Authors: Shankaran Gokul , Dogruoz M. Baris
Published: February 2012

Forced convection air-cooled electronic systems utilize fans to sustain air flow through the enclosure. These fans are typically axial flow fans, radial impellers, and centrifugal blowers. When computing flow fields in electronic enclosures, axial fans have traditionally been abstracted as lumped fan models which may or may not be able to capture the necessary details. Under certain conditions, such lumped models may also capture some flow characteristics in the case of impellers and centrifugal blowers. These lumped models comprise a significantly simplified fan geometry, i.e. usually a planar (2-D) rectangular or circular surface with/without an inner (hub) concentric no-flow region for an axial fan or a rectangular prism/cylinder with a planar inlet for blowers/impellers, and a “pressure head-flow rate” (P-Q) curve, which may be supplied by the fan vendor or experimentally derived by the thermal designer. Irrespective of the source, the P-Q curve is obtained from laboratory experiments that conform to the test codes published by societies such as ASME and AMCA. Convenience and accuracy of lumped fan models are dependent on the specific application, cooling method and also the acceptable error margin. The acceptable error margin of the thermal design has shrunk significantly in the last decade. This has caused an interest in more accurate and robust fan modeling techniques such as Multiple Reference Frame (MRF) model which has already been commonly and successfully used in many different industries for a while. In this paper, an attempt was made to provide a validation of the MRF fan modeling applied to different types of fans. The computational fluid dynamics (CFD) model of an AMCA standard wind tunnel was used for each of the fans investigated. The P-Q curve obtained from the MRF model is benchmarked against the corresponding experimentally derived P-Q curve. Benefits and limitations of the MRF model are also discussed.
High Performance Micro-Grooved Evaporative Heat Transfer Surface for Low Grade Waste Heat Recovery Applications
Authors: Jha Vibhash , Dessiatoun Serguei , Ohadi Michael , Shooshtari Amir , Al-Hajri Ebrahim
Published: February 2012

The continued demand for high performance electronic products and the simultaneous trend of miniaturization has raised the dissipated power and power densities to new unprecedented levels in electronic systems. Thermal management is becoming increasingly critical to the electronics industry to satisfy the increasing market demand for faster, smaller, lighter and more cost effective products. Utilization of waste heat for the purpose of cooling chip is a promising area for enhancing the thermal management and net energy efficiency of the system. This paper focuses on the development of a tubular microgrooved evaporator and its performance characterization based on heat transfer coefficients and pressure drop measurements. Channel with aspect ratio of 3:1 (channel width – 100 μm, channel height – 300 μm) microgrooved structure was used in the evaporator. The system has been tested with R134a as refrigerant for refrigerant flow rate range of 0.005–0.02 kg/s and water flow rate range of 0.25–0.65 kg/s. Very promising results has been obtained in preliminary investigation. Heat transfer coefficient as high as 13,500 W/m2k has been obtained which is almost five times higher than comparative state of art technologies. The associated pressure drop is quite modest and much less than state of the art conventional evaporators.
Characterization of Hysteresis Loop Evolution in Aged Lead Free Solders
Authors: Mustafa Muhannad , Cai Zijie , Suhling Jeffrey C. , Lall Pradeep
Published: February 2012

Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials leads to the solder joints being subjected to cyclic (positive/negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior. In this investigation, we have examined the effects of aging on the cyclic stress-strain behavior of lead free solders. Uniaxial SAC lead free solder specimens were subjected to cyclic (tension/compression) mechanical loading. Samples were cyclically loaded under both strain control (constant positive and negative strain limits) and stress control (constant positive and negative stress limits). The hysteresis loop size (area) was calculated from the measured cyclic stress-strain curves for a given solder alloy and temperature. This area represents the strain energy density dissipated per cycle, which can be typically correlated to the damage accumulation in the joint. The tests in this investigation were performed with SAC105 solder alloy. Prior to cyclic loading, the specimens in this study were aged (preconditioned) at 125 °C for various aging times (0–6 months). From the recorded cyclic stress-strain curves, we have been able to characterize and empirically model the evolution of the solder hysteresis loops with aging. Similar to solder stress-strain and creep behaviors, there is a strong effect of aging on the hysteresis loop size (and thus the rate of damage accumulation) in the solder specimens. The observed degradations in the fatigue/cyclic behavior of the lead free solders are highly accelerated for lower silver content alloys (e.g., SAC105), and for aging and testing at higher temperatures. In our current work, we are also subjecting aged solder samples to cyclic loading until failure occurs. Our ultimate goal is to understand the effects of aging on the thermomechanical fatigue life.
Experimental and Simulation Study of the Effect of Power Package Configuration on its Thermal Performance
Authors: Yue Cong , Lu Jun , Zhang Xiaotian , Ho Yueh-Se
Published: February 2012

RthJA (Junction-to-Ambient Thermal Resistance) for power device packages was measured and modeled in order to correlate the results from our experiments and simulations. The packages studied, including TO (Transistor Outline), DFN (Dual Flat Non-Leaded), SOP (Small Outline Package) and DPAK with sizes from 3×3mm to 15×10mm, were tested under natural convection environment. An important observation from our testing is the significant influence of the external wires connecting the test coupon to the power supply on the thermal resistance value derived from the test data. The increase in the RthJA based on the test is more than 50% for TO packages and 19% for smaller packages once the external wires changed from gauge 18 to 30. A simple yet effective simulation approach was then introduced to predict RthJA incorporating the critical influence from the external wire size variation. With the validated finite element model, the effects of package factors such as package outline, die size, die attach, encapsulation and interconnection on the thermal resistances of the power semiconductor packages were studied by simulation to provide further insights and guides for new package developments.
Exergy Analysis and Entropy Generation Minimization of Thermoelectric Waste Heat Recovery for Electronics
Authors: Yazawa Kazuaki , Shakouri Ali
Published: February 2012

Energy recovery from waste heat is attracting more and more attention. All electronic systems consume electricity but only a fraction of it is used for information processing and for human interfaces, such as displays. Lots of energy is dissipated as heat. There are some discussions on waste heat recovery from the electronic systems such as laptop computers. However the efficiency of energy conversion for such utilization is not very attractive due to the maximum allowable temperature of the heat source devices. This leads to very low limits of Carnot efficiency. In contrast to thermodynamic heat engines, Brayton cycle, free piston Stirling engines, etc., authors previously reported that thermoelectric (TE) can be a cost-effective device if the TE and the heat sink are co-optimized, and if some parasitic effects could be reduced. Since the heat already exists and it is free, the additional cost and energy payback time are the key measures to evaluate the value of the energy recovery system. In this report, we will start with the optimum model of the TE power generation system. Then, theoretical maximum output, cost impact and energy payback are evaluated in the examples of electronics system. Entropy Generation Minimization (EGM) is a method already familiar in thermal management of electronics. The optimum thermoelectric waste heat recovery design is compared with the EGM approach. Exergy analysis evaluates the useful energy flow in the optimum TE system. This comprehensive analysis is used to predict the potential future impact of the TE material development, as the dimensionless figure-of-merit (ZT) is improved.
A Statistical Approach to Thermal Zone Mapping
Authors: Li Hongfei , Hamann Hendrik F.
Published: February 2012

Although in most buildings the spatial allocation of cooling resources can be managed using multiple air handling units and an air ducting system, it can be challenging for an operator to leverage this capability, partially because of the complex interdependencies between the different control options. This is in particular important for data centers, where cooling is a major cost while the sufficient allocation of cooling resources has to ensure the reliable operation of mission-critical information processing equipment. It has been shown that thermal zones can provide valuable decision support for optimizing cooling. Such Thermal zones are generally defined as the region of influence of a particular cooling unit or cooling “source” (such as an air condition unit (ACU)). In this paper we show results using a statistical approach, where we leverage real-time sensor data to obtain thermal zones in realtime. Specifically, we model the correlations between temperatures observed from sensors located at the discharge of an ACU and the other sensors located in the room. Outputs from the statistical solution can be used to optimize the placement of equipment in a data center, investigate failure scenarios, and make sure that a proper cooling solution has been achieved.
Thin Film Residual Stress Assessment of MEMS Microphone Using Process Modeling Technology
Authors: Wang Han-Jung , Deng Hung-An , Chiang Shih-Ying , Chiang Kuo-Ning
Published: February 2012

The characteristic of MEMS component is affected by different process procedures such as depositing and etching thin films on substrate. These processes might induce residual stresses or deformations in MEMS component, which will reduce its efficiency and quality, and it is very unfavorable in MEMS development. This study develops a methodology that uses Finite Element Analysis (FEA) along with process modeling technology to analyze the residual stress in a MEMS microphone structure. The residual stress of thin film is composed of thermal and intrinsic stress. The thermal stress can be obtained directly in FEA but not for the intrinsic stress, which is a process-dependent material property. The intrinsic stress in multilayered structure is obtained from Stoney’s experiment which measures the curvature on blanket wafer after each process. A comparison of the experimental and simulated results showed that dislocation induced intrinsic stress in aluminum can be rearrangement after first annealing. The lattice mismatch induced intrinsic stress, however, will influence the residual stress of the aluminum film when its thickness is under 1μm. The residual stresses and the deformations in two electrode plates are presented for the process simulation in the MEMS microphone. The polysilicon would buckle and warp downward if it is subjected to compressive stress. However, the polysilicon diaphragm would be flat in the positive intrinsic stress.
An Innovative Way to Measure Temperature by Using the Faraday Effect
Authors: Limaye Pranav , Rehman Anisur
Published: February 2012

An innovative temperature sensor has been presented based on “Faraday Effect”. The Faraday Effect or the Faraday rotation is a magneto-optical phenomenon; that is, an interaction between electromagnetic wave and a magnetic field in a medium. Optical sensors based on the Faraday Effect have the advantages of simplicity, high electrical insulation and immunity to electromagnetic interference. We will be making use of an optical fiber and a permanent magnet as our sensing elements. The magnet will be the sensing element for change in temperature and the fiber optic cable will sense the change in magnetic field intensity corresponding to the change in temperature.
Experimental Characterization of Server Rack Energy Use at Elevated Ambient Temperatures
Authors: Iyengar Madhusudan , Schmidt Roger , Kamath Vinod , Kochuparambil Bejoy
Published: February 2012

It is now common for data center managers to question the impact on server energy usage of two recent impact factors: (1) the rise in the data center inlet air temperature to servers per 2008 ASHRAE guidelines, and (2) the fan speed increase from the use of rack level heat exchangers such as Rear Door Heat Exchangers. To help acquire a deeper understanding of the relevant issues, a system floor thermal test was built on the IBM New York data center benchmark floor which consisted of a standard 19″ rack filled with 39 3.0 GHz 1U servers that dissipated between 10–17 kW depending on extent of server utilization. Fan speed, chip temperature metrics, and server power data was collected using product debug codes and server level programs. A simulated air heat load was installed right in front of this server rack to allow the manipulation of air inlet temperature into the servers from 20 °C to 32 °C. Two different rack level configurations were considered for the experiments: (i) a perforated front door and no door at the rear, and (ii) a perforated front door and a Rear Door Heat Exchanger at the rear. An exerciser program was used to vary the CPU utilization from Idle to 70% which represented a typical data center work load. Data was collected for 19 servers of the 39 servers (remaining were in use by Benchmark Lab) for the two rack configurations, for 4 inlet server air temperatures, and for two chip exerciser settings, i.e. 16 experiments. For the 70% exerciser setting (typical operation) and the base line rack configuration without rack level heat exchangers, the rise in server power for an increase in inlet air temperature was 5.2% for the 20 °C to 27 °C change and was 17% for the 20 °C to 31 °C change. For the 70% exerciser setting (typical), the increase in server power from the use of rack level heat exchangers (Rear Door Heat Exchanger) was less than 1.3% for all the conditions. Given the broad range of fan speed algorithms and cooling hardware in server products on the market and their change over each generation, significant further study will be required to characterize each category of systems for these conditions. However, the present study provides a template for quantifying server energy usage in a context that data center managers can understand and use.
Experimental Characterization and Viscoplastic Modeling of the Temperature Dependent Material Behavior of Underfill Encapsulants
Authors: Chhanda Nusrat J. , Suhling Jeffrey C. , Lall Pradeep
Published: February 2012

In this work, the viscoplastic mechanical response of a typical underfill encapsulant has been characterized via rate dependent stress-strain testing over a wide temperature range, and creep testing for a large range of applied stress levels and temperatures. A specimen preparation procedure has been developed to manufacture 80 × 5 mm uniaxial tension test samples with a specified thickness of .5 mm. The test specimens are dispensed and cured with production equipment using the same conditions as those used in actual flip chip assembly, and no release agent is required to extract them from the mold. Using the manufactured test specimens, a microscale tension-torsion testing machine has been used to evaluate stress-strain and creep behavior of the underfill material as a function of temperature. Stress-strain curves have been measured at 5 temperatures (25, 50, 75, 100 and 125 C), and strain rates spanning over 5 orders of magnitude. In addition, creep curves have been evaluated for the same 5 temperatures and several stress levels. With the obtained mechanical property data, several viscoelastic and viscoplastic material models have been fit to the data, and optimum constitutive models for subsequent use in finite element simulations have been determined.
High Strain Rate Fracture Behavior of Sn-Ag-Cu Solder Joints on Cu Substrates
Authors: Huang Z. , Kumar P. , Dutta I. , Pang J. H. L. , Sidhu R. , Renavikar M. , Mahajan R.
Published: February 2012

During service, micro-cracks form inside solder joints, making a microelectronic package prone to failure particularly during a drop. Hence, the understanding of the fracture behavior of solder joints under drop conditions, synonymously at high strain rates and in mixed mode, is critically important. This study reports: (i) the effects of processing conditions (reflow parameters and aging) on the microstructure and fracture behavior of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates, and (ii) the effects of the loading conditions (strain rate and loading angle) on the fracture toughness of these joints, especially at high strain rates. A methodology for calculating critical energy release rate, GC, was employed to quantify the fracture toughness of the joints. Two parameters, (i) effective thickness of the interfacial intermetallic compounds (IMC) layer, which is proportional to the product of the thickness and the roughness of the IMC layer, and (ii) yield strength of the solder, which depends on the solder microstructure and the loading rate, were identified as the dominant quantities affecting the fracture behavior of the solder joints. The fracture toughness of the solder joint decreased with an increase in the effective thickness of the IMC layer and the yield strength of the solder. A 2-dimensional fracture mechanism map with the effective thickness of the IMC layer and the yield strength of the solder as two axes and the fracture toughness as well as the fraction of different fracture paths as contour-lines was prepared. Trends in the fracture toughness of the solder joints and their correlation with the fracture modes are explained using the fracture mechanism map.
Advanced Liquid Cooling Technology Evaluation for High Power CPUs and GPUs
Authors: Sahan Ridvan A. , Mohammed Rahima K. , Xia Amy , Pang Ying-Feng
Published: February 2012

Increasing thermal design power (TDP) trends with shrinking form factor requirements creates the need for advanced cooling technology development. This investigation proposes multiple innovative water cooler technologies to achieve higher thermal performance liquid-cooling (LC) solutions addressing the limitations of air-cooling (AC). High performance water cooler design options will also meet the miniaturization trends of computing market by providing scalable solution to address smaller board real-estate. This investigation serves multi-fold advantages: 1) introduces four water cooler technologies employing different fin base plate designs, diamond fins, micro-fins, skived micro-fins, and twisted diamond fins, along with an optimized flow distribution path design accompanying each cooler, 2) provides scalable thermal solutions, 3) addresses particle clogging via fin base plate as well as flow distribution path optimization, 4) addresses galvanic corrosion by eliminating the use of two dissimilar metals and introducing acrylic housing, 5) introduces acrylic housing for weight management. Results show that twisted diamond fin, micro-fin and skived micro-fin coolers provide up to 5°C performance improvement resulting in lower pressure drop across water cooler compared to diamond fin cooler and about 37°C improvement compared to air-cooled active heatsink solution.
Employing Thermal Zones for Energy Optimization in Data Centers
Authors: Yarlanki Srinivas , Das Rajarshi , Hamann Hendrik , Lopez Vanessa , Stepanchuk Andrew
Published: February 2012

Energy consumption has become a critical issue for data centers, triggered by the rise in energy costs, volatility in the supply and demand of energy and the wide spread proliferation of power-hungry information technology (IT) equipment. Since nearly half the energy consumed in a data center (DC) goes towards cooling, much of the efforts in minimizing energy consumption in DCs have focused on improving the efficiency of cooling strategies by optimally provisioning the cooling power to match the heat dissipation in the entire DC. However, at a more granular level within the DC, the large range of heat densities of today’s IT equipment makes this task of provisioning cooling power at the level of individual computer room air conditioning (CRAC) units much more challenging. In this work, we employ utility functions to present a principled and flexible method for determining the optimal settings of CRACs for joint management of power and temperature objectives at a more granular level within a DC. Such provisioning of cooling power to match the heat generated at a local level requires the knowledge of thermal zones — the region of DC space cooled by a specific CRAC. We show how thermal zones can be constructed for arbitrary settings of CRACs using the potential flow theory. As a case study, we apply our methodology in a 10,000 sq. ft commercial DC using actual measured conditions and evaluate the usefulness of the method by quantifying possible energy savings in this DC.
IR Based Inverse Calculation of Two-Phase Heat Transfer Coefficients in Microgap Channels
Authors: Sheehan Jessica , Bar-Cohen Avram
Published: February 2012

IR thermography of the heated wall for the two-phase flow of FC-72 in microgap channels provides explicit evidence of the quality-driven M-shaped variations in the two-phase microgap heat transfer coefficients. Data obtained from a 210μ microgap channel, operated with an FC-72 mass flux of 195 and 780 kg/m2-s and asymmetric heat fluxes of 28 W/cm2 to 35 W/cm2 are presented and discussed.
Effect of Heat Generation on Fatigue-Crack Propagation of Solder in Power Devices
Authors: Hiramitsu Shinji , Shintani Hiroshi , Satake Takahiro , Tanie Hisashi
Published: February 2012

Power devices are used in inverters in a variety of electrical equipment, for instance, hybrid-power cars, electric vehicles, and generators. These types of equipment are used to decrease the negative impact on the environment, and thus, the power devices need to function effectively as electric power converters for the long-term stability of the equipment. In short, the long-term reliability, i.e., the life, of the power device is important, and a high level of reliability is required. In the development process of power devices, it is necessary to conduct thermal fatigue tests to evaluate the reliability. However, such tests are extended over a long period of time, which makes it difficult to shorten the development period. Therefore, a simulation technique needs to be developed to forecast the life of a thermal fatigue test in order to reduce the development period. During the thermal fatigue test, thermal stress is caused by differences in the line expansion coefficient between solder joint materials. Thermal stress causes crack generation and propagation in solder. The thermal resistance of a device increases steadily as the cracks grow. This raises the temperature of the device and increases thermal stress. As a result, crack propagation is accelerated. However, conventional crack propagation analysis does not take this phenomenon into account. We developed a method of crack propagation analysis that takes into account the changes in thermal and electrical boundary conditions resulting from the crack propagation. The method is a combination of electrical conduction analysis, heat transfer analysis, and crack propagation analysis. The boundary condition of the heat transfer analysis is determined from the results of the electrical conduction analysis. The boundary condition of the crack propagation analysis is determined from the results of the heat transfer analysis. The crack propagation behavior in solder is calculated by repeating these analyses. This method reproduces the drastic increase in thermal resistance in the latter part of the thermal fatigue test, and the results agree well with the experimental results. We confirmed that the temperature distribution of the device changes as the crack propagates and that thermal and electrical coupled analysis has a major effect on the prediction of fatigue life of power device products. We also revealed that the thermal fatigue life is affected by the position of the heat source and cracks.
Estimation of the Parameters Determining Strength and Fatigue Behaviors of Arbitrarily-Shaped Polysilicon Thin Films
Authors: Huy Vu Le , Gaspar Joao , Paul Oliver , Kamiya Shoji
Published: February 2012

The fracture and fatigue behaviors of polysilicon thin film structures with arbitrary shapes were formulated by taking the stress distribution into account. The parameters appearing in both Weibull distribution and Paris’ law that describe the static strength and fatigue behaviors, respectively, are estimated using the maximum likelihood method on the basis of the results of tensile static fracture and fatigue tests performed on two types of polysilicon thin film specimens with different shapes fabricated using the same conditions. The difference between the fatigue lifetime distributions between the two types was well explained by applying the formula with a unique set of parameters. These results suggest that the fracture and fatigue behaviors of polysilicon thin films have a unique characteristics regardless of stress distributions.
Microprocessor Package Embedded Thin Film Capacitor for Power Delivery Improvement
Authors: Hill Michael J. , Aygun Kemal , Radhakrishnan Kaladhar
Published: February 2012

The need for better high frequency performance, improved I/O power decoupling, and introduction of multi-chip processors are just some of the drivers for developing embedded capacitor technologies. One new technology, the Thin Film Embedded Package Capacitor (TFC) can target an improvement in the high frequency performance of the microprocessor power delivery network. Using this technology prototype packages for an Intel Microprocessor were fabricated and the impedance of the power delivery network (PDN) measured. The packages with the embedded TFCs demonstrated a reduction by more than a factor of 2 in the high frequency power delivery network impedance, and correspondingly improved voltage droop.
Laminar Convective Heat Transfer of Alumina-Polyalphaolefin Nanofluids Containing Spherical and Non-Spherical Nanoparticles
Authors: Yu Leyuan , Liu Dong , Botz Frank
Published: February 2012

As a promising candidate for advanced heat transfer fluids, nanofluids have been studied extensively during the past decade. In contrast to the early reports of dramatic heat transfer enhancement even at extremely low particle concentrations, the most recent studies suggest the laminar convective heat transfer of nanofluids is only mildly augmented and can be predicted by the conventional Navier-Stokes equations. The majority of the past studies were limited to water-based nanofluids synthesized from spherical nanoparticles. No systematic information is yet available for the convective heat transfer of nanofluids containing non-spherical particles, especially those formulated with the base fluid other than water. An experimental study was conducted in this work to investigate the thermophysical properties and convective heat transfer characteristics of Al2O3-Polyalphaolefin (PAO) nanofluids containing both spherical and rod-like nanoparticles. The effective viscosity and thermal conductivity were measured and compared to predictions from the effective medium theory. The friction factor and local Nusselt number were also measured for the laminar flow regime. It was found that established theoretical correlations can satisfactorily predict the experimental data for nanofluids containing spherical nanoparticles; however, they are less successful for nanofluids with nanorods. The possible reasons may be attributed to the shear-induced alignment of non-spherical nanoparticles and its subsequent influence on the development of the thermal boundary layer. The results suggest that the hydrodynamic interactions between the non-spherical nanoparticles and the surrounding fluid medium have a significant impact on the thermophysical properties as well as on the thermal transport characteristics of nanofluids.
A First-Principle Guided Circuit Simulator of Linear Complexity and its Linear Speedup for Die-Package Co-Design
Authors: He Qing , Chen Duo , Jiao Dan
Published: February 2012

In this work, guided by electromagnetics-based first principles, we develop a circuit simulator that allows for the simulation of a circuit including both nonlinear devices and the linear network in linear complexity. Moreover, it permits an almost embarrassingly parallel implementation on a many-core computing platform, and hence achieving linear speedup. The proposed circuit simulator rigorously captures the coupling between nonlinear circuits and the linear network. In addition, it bypasses the step of extraction, producing an RLC (resistor-inductor-capacitor) representation of the linear network without any numerical computation. Application to die-package co-simulation as well as simulation of very large-scale on-chip circuits involving over 800,000 CMOS transistors and interconnects having hundreds of millions of unknowns has demonstrated the superior performance of the proposed first-principle-guided circuit simulator.
Do You Know Your Onboard Temperature Sensing IC?
Authors: Chu Herman
Published: February 2012

It is a common practice in electronic packaging to deploy onboard temperature sensing ICs for thermal health monitoring and control. The IT equipment industry has seen exponential increase in power and power density growth on devices and PCBs. In turn, more and more IC temperature sensors are used in highly complex algorithms and are expected to be highly accurate in predicting the local thermal conditions. In many cases they are even used to correlate to air temperature. However, care must be taken in understanding the different factors that influence the temperature readings of these devices. Some of the factors that have direct impact on the quality of the temperature reading include parasitic heating due to adjacent components and placement location, airflow condition, circuit design in connecting these devices to the board, accuracy and tolerance of these devices. In addition, because of the increase in component power density, the temperature difference between the device temperature, for example junction temperature, and board sensor temperature can be very different and the range can vary a lot as well. In this paper, thermal numerical modeling, as well as empirical work at the system and board levels, was performed to understand the implications of the temperature readings from these devices. Several of the commercially available onboard temperature sensing ICs are compared as well. It is the intention of this work to point out these areas in order for thermal and system design practitioners to intelligently use these devices appropriately. Also, a high-level environmental monitoring and control system (EMCS) policy is illustrated for highly configurable multi-board equipment.
A Practical Approach for Low-Cost Hermetic Lid Sealing
Authors: Palmer Jeremy , Chu Dahwey
Published: February 2012

Hermetic sealing of lids in ceramic microelectronic chip carriers is typically performed with eutectic solder in relatively large belt-style reflow furnaces. This process is characterized by 30 to 45-minute cycle times at temperatures above 350 C. An experimental study was undertaken with the goal of establishing a low-cost lid sealing method marked by a compact belt furnace with lower reflow temperature and lesser cycle time. This is particularly advantageous for GaAs devices which are limited to packaging process temperatures below 300 C. A series of instrumented test samples consisting of a representative die packaged in a HTCC leadless chip carrier (LCC) was prepared. Package lids were installed and sealed in a nitrogen environment with 80–20 Au-Sn lead-free solder under various cycle time and temperature conditions. Gross and fine leak testing confirmed hermeticity. Results indicate that practical sealing can be realized in the compact furnace apparatus with measurable reductions in temperature and cycle time. Seal performance is dependent upon package orientation, which suggests the process must be calibrated for unique package designs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Micro Accelerometer and Magnetoresistive (MR) Sensor Directly Fabricated on a Ceramic Substrate
Authors: Aoyagi Seiji , Suzuki Masato , Takahashi Tomokazu , Tajikawa Tsutomu , Saitoh Ken-ichi , Shingubara Shoso , Arai Yasuhiko , Tajiri Hiroyuki , Yoshikawa Yasuhiro
Published: February 2012

The concept of micro-electro-mechanical systems (MEMS) sensors directly fabricated on a ceramic substrate, which can be used for a package of end product, was proposed. As demonstrations of the sensors directly fabricated on a ceramic package, an accelerometer and a magnetoresistive (MR) sensor are focused on, and their fabrications on a ceramic substrate is investigated. The accelerometer utilizes a fringe capacitance formed in a ferroelectric material. For this sensor, in stead of a previously used bulk PZT plate, a screen-printed BaTiO3 (BTO) film on a ceramic alumina substrate was herein employed. An accelerometer using a BTO film was practically fabricated. The sensitivity of it was estimated as 0.1 pF/g, which is degraded a little compare with the previously developed accelerometer using a PZT plate; however, the order is the same. The magnetoresistive (MR) sensor can detect not only x- and y-axes magnetic field intensities but also z-axis one, where all fields are based on the sensor coordinate system. Namely, not only azimuth but also angle of elevation of the sensor can be detected from triaxis components of geomagnetic field. The principle is as follows: a permalloy (FeNi) plate is stood aside MR element. The plate distorts magnetic field and generates x- (or y-) component from originally z-directional field. So, the resistance of MR element changes in proportional to z-axis field intensity, provided that other axes intensities are kept constant.
Characterization of a Macrofiber Piezoelectric Composite
Authors: Miller David A.
Published: February 2012

Macrofiber piezoelectric composites are thin rectangular patches made of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate fibers and are commercially available. As a basis for this consideration, the useful life of the MFC is being characterized to determine the effect of loading condition on the performance of the material as it is fatigued by cyclical piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam using epoxy and is actuated at the first resonant frequency of the beam laminate by the cyclic application of 1000 volts. Strain and beam tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under varying beam thicknesses.
Horizontal coherence of low-frequency fixed-path sound in a continental shelf region with internal-wave activity
Authors: Duda Timothy F. , Collis Jon M. , Lin Ying-Tsong , Newhall Arthur E. , Lynch James F. , DeFerrari Harry A.
Published: February 2012

Sound at 85 to 450 Hz propagating in approximately 80-m depth water from fixed sources to a joint horizontal/vertical line array (HLA/VLA) is analyzed. The data are from a continental shelf area east of Delaware Bay (USA) populated with tidally generated long- and short-wavelength internal waves. Sound paths are 19 km in the along-shore (along internal-wave crest) direction and 30 km in the cross-shore direction. Spatial statistics of HLA arrivals are computed as functions of beam steering angle and time. These include array gain, horizontally lagged spatial correlation function, and coherent beam power. These quantities vary widely in magnitude, and vary over a broad range of time scales. For example, correlation scale can change rapidly from forty to five wavelengths, and correlation-scale behavior is anisotropic. In addition, the vertical array can be used to predict correlation expected for adiabatic propagation with cylindrical symmetry, forming a benchmark. Observed variations are in concert with internal-wave activity. Temporal variations of three coherence measures, horizontal correlation length, array gain, and ratio of actual correlation length to predicted adiabatic-mode correlation length, are very strong, varying by almost a factor of ten as internal waves pass.
Mid-frequency geoacoustic inversion using bottom loss data from the Shallow Water 2006 Experiment
Authors: Yang Jie , Jackson Darrell R. , Tang Dajun
Published: February 2012

Geoacoustic inversion work has typically been carried out at frequencies below 1 kHz, assuming flat, horizontally stratified bottom models. Despite the relevance to Navy sonar systems many of which operate at mid-frequencies (1–10 kHz), limited inversion work has been carried out in this frequency band. This paper is an effort to demonstrate the viability of geoacoustic inversion using bottom loss data between 2 and 5 kHz. The acoustic measurements were taken during the Shallow Water 2006 Experiment off the coast of New Jersey. A half-space bottom model, with three parameters density, compressional wave speed, and attenuation, was used for inversion by fitting the model to data in the least-square sense. Inverted sediment sound speed and attenuation were compared with direct measurements and with inversion results using different techniques carried out in SW06. Inverted results of the present work are consistent with other measurements, considering the known spatial variability in this area. The observations and modeling results demonstrate that forward scattering from topographical changes is important at mid-frequencies and should be taken into account in sound propagation predictions and geoacoustic inversion. To cope with fine-scale topographic variability, measurement technique such as averaging over tracks may be necessary.
Observations of sound-speed fluctuations on the New Jersey continental shelf in the summer of 2006
Authors: Colosi John A. , Duda Timothy F. , Lin Ying-Tsong , Lynch James F. , Newhall Arthur E. , Cornuelle Bruce D.
Published: February 2012

Environmental sensors moored on the New Jersey continental shelf tracked constant density surfaces (isopycnals) for 35 days in the summer of 2006. Sound-speed fluctuations from internal-wave vertical isopycnal displacements and from temperature/salinity variability along isopycnals (spiciness) are analyzed using frequency spectra and vertical covariance functions. Three varieties of internal waves are studied: Diffuse broadband internal waves (akin to waves fitting the deep water Garrett/Munk spectrum), internal tides, and, to a lesser extent, nonlinear internal waves. These internal-wave contributions are approximately distinct in the frequency domain. It is found that in the main thermocline spicy thermohaline structure dominates the root mean square sound-speed variability, with smaller contributions coming from (in order) nonlinear internal waves, diffuse internal waves, and internal tides. The frequency spectra of internal-wave displacements and of spiciness have similar form, likely due to the advection of variable-spiciness water masses by horizontal internal-wave currents, although there are technical limitations to the observations at high frequency. In the low-frequency, internal-wave band the internal-wave spectrum follows frequency to the −1.81 power, whereas the spice spectrum shows a −1.73 power. Mode spectra estimated via covariance methods show that the diffuse internal-wave spectrum has a smaller mode bandwidth than Garrett/Munk and that the internal tide has significant energy in modes one through three.
Long distance passive localization of vocalizing sei whales using an acoustic normal mode approach
Authors: Newhall Arthur E. , Lin Ying-Tsong , Lynch James F. , Baumgartner Mark F. , Gawarkiewicz Glen G.
Published: February 2012

During a 2 day period in mid-September 2006, more than 200, unconfirmed but identifiable, sei whale (Balaenoptera borealis) calls were collected as incidental data during a multidisciplinary oceanography and acoustics experiment on the shelf off New Jersey. Using a combined vertical and horizontal acoustic receiving array, sei whale movements were tracked over long distances (up to tens of kilometers) using a normal mode back propagation technique. This approach uses low-frequency, broadband passive sei whale call receptions from a single-station, two-dimensional hydrophone array to perform long distance localization and tracking by exploiting the dispersive nature of propagating normal modes in a shallow water environment. The back propagation approach is examined for accuracy and application to tracking the sei whale vocalizations identified in the vertical and horizontal array signals. This passive whale tracking, combined with the intensive oceanography measurements performed during the experiment, was also used to examine sei whale movements in relation to oceanographic features observed in this region.
Evidence of the enhancement effect in electrical stimulation via electrode matching (L)
Authors: Goupell Matthew J. , Mostardi Mitchell J.
Published: February 2012

The ability to match a pulsing electrode during multi-electrode stimulation through a research interface was measured in seven cochlear-implant (CI) users. Five listeners were relatively good at the task and two could not perform the task. Performance did not vary as a function of the number of electrodes or stimulation level. Performance on the matching task was not correlated to performance on an electrode-discrimination task. The listeners may have experienced the auditory enhancement effect, and this may have implications for speech recognition in noise for CI users.
On the role of glottis-interior sources in the production of voiced sound
Authors: Howe M. S. , McGowan R. S.
Published: February 2012

The voice source is dominated by aeroacoustic sources downstream of the glottis. In this paper an investigation is made of the contribution to voiced speech of secondary sources within the glottis. The acoustic waveform is ultimately determined by the volume velocity of air at the glottis, which is controlled by vocal fold vibration, pressure forcing from the lungs, and unsteady backreactions from the sound and from the supraglottal air jet. The theory of aerodynamic sound is applied to study the influence on the fine details of the acoustic waveform of “potential flow” added-mass-type glottal sources, glottis friction, and vorticity either in the glottis-wall boundary layer or in the portion of the free jet shear layer within the glottis. These sources govern predominantly the high frequency content of the sound when the glottis is near closure. A detailed analysis performed for a canonical, cylindrical glottis of rectangular cross section indicates that glottis-interior boundary/shear layer vortex sources and the surface frictional source are of comparable importance; the influence of the potential flow source is about an order of magnitude smaller.