Avram Bar-Cohen

Bio: Avram Bar-Cohen is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Heat transfer & Heat sink. The author has an hindex of 50, co-authored 329 publications receiving 8329 citations. Previous affiliations of Avram Bar-Cohen include Auburn University & DARPA.

Thermal management of portable electronic equipment using thermoelectric energy conversion

Abstract: It has been well established that thermal management of electronic equipment is critical for the continued success of the microelectronics industry. Portable electronic devices, such as notebook computers and cellular telephones, require that the thermal solution be small, light, and energy efficient. Small-scale thermoelectric (TE) technology used to generate electricity from the waste heat of the microprocessor provides an opportunity to de-couple the thermal solution of electronic equipment from battery power. Suski proposed the concept of using a TE module to generate electricity from the waste heat of a microprocessor in a patent. The configuration shown in the patent, referred to here as the 'direct attach' configuration, does not lend itself to higher power microprocessors, as the thermal resistance for state-of-the-art TE modules is on the order of 15 K/W. This paper proposes an alternate configuration, referred to as the 'shunt attach' configuration, as a viable solution for using TE generation in the thermal management of portable electronic equipment. The new concept uses an alternate heat path to shunt excess heat away from the TE module. By managing the heat flow paths, sufficient electricity can be generated by using today's off-the-shelf TE technology to drive a cooling fan.

Thermal management of systems having localized regions of elevated heat flux

Abstract: A thermal management system ( 300 ) includes a first heat transfer body ( 330 ) for providing a opposing heat flux to at least one localized region of elevated heat flux residing in adjacency to a region of lesser flux, such as on a surface ( 315 a ) of a circuit die ( 315 ) due to a integrated circuit hot-spot ( 310 ). A contact ( 320, 321 962 a, 962 b, 970 a, 970 b or 950 ) defines a thermal conduction path for the opposing flux. A second heat transfer body ( 350 ) is in a heat transport relationship with the first heat transfer boy ( 330 ) and a second heat transport relationship with the region of lesser heat flux. In such arrangement, each region of heat flux is provided a thermal solution commensurate with the level of heat flux in the region. For example, the opposing heat flux of an active first heat transfer body ( 330 ), such as a thermoelectric cooler, may be provided at the hot-spot ( 310 ), while at the same time the lesser heat flux is absorbed by a passive second heat transfer body ( 350 ), such as a heat spreader.

Design for manufacturability of SISE parallel plate forced convection heat sinks

Abstract: The development of cost/effective heat sinks for microelectronic applications involves the achievement of a subtle balance between the thermal design, for maximum heat rejection, and "design for manufacturability," for lowest material and manufacturing costs. The study reported herein extends a previously reported methodology to forced convection cooled rectangular plate heat sinks. Using a well validated analytical model, the thermofluid performance of the side-inlet-side-exit (SISE) heat sink has been characterized, parametric optimization carried out, and the maximum heat transfer capabilities for a range of operating points has been determined. A least-material optimization has been performed to achieve optimal material use. The analysis indicates the least-material design to provide significant mass savings for a moderate penalty in thermal performance. Empirical criteria for manufacturability obtained from several heat sink manufacturers lead to qualitative guidelines.

Energy Efficiency of Low Form Factor Cooling Devices

Abstract: With increasing attention to the energy efficiency of consumer and commercial products, thermal engineering and science community is devoting greater effort and attention to the design and implementation of energy-efficient cooling solutions. This study focuses on the cooling potential and Coefficient of Performance, (COP), achievable with three distinct meso-scale cooling technologies, applicable to a wide range of electronics cooling challenges. The thermo-fluid and thermodynamic characteristics of synthetic jets, piezo-driven vibrating blades, and compact muffin fans will be addressed. We are dedicating this paper to Prof. Kakac for his contributions to heat transfer science and technology, developing young scientists, writing highly valuable heat transfer textbooks, and most importantly for his kindness and friendship.Copyright © 2007 by ASME

Light-emitting diodes

Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

A review of Ga2O3 materials, processing, and devices

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Low loss dielectric materials for LTCC applications: a review

Abstract: Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...