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Cheng J.,University of North Texas | Chen C.-L.,Teledyne Scientific Company | Chen C.-L.,University of Missouri
Applied Physics Letters | Year: 2011

We report an electrowetting-controlled optofluidic system for adaptive beam tracking and agile steering. With two immiscible fluids in a transparent cell, we can actively control the contact angle along the fluid-fluid-solid tri-junction line and hence the orientation of the fluid-fluid interface via electrowetting. The naturally formed meniscus between the two liquids can function as an optical prism. We have fabricated a liquid prism module with an aperture size of 10 mm × 10mm. With 1 wt. %KCl and 1 wt.% Sodium Dodecyl Sulfate added into deionized water, the orientation of the water-silicone oil interface has been modulated between -26° and 26° that can deflect and steer beam within the incidence angle of 0°-15°. The wide-range beam tracking and steering enables the liquid prism work as an electrowetting solar cell. © 2011 American Institute of Physics.

Cai Q.,Teledyne Scientific Company | Bhunia A.,Teledyne Scientific Company
International Journal of Heat and Mass Transfer | Year: 2012

Carbon nanotube (CNT) forests are investigated as porous wick structures for chip-scale heat pipe cooling systems. An analytical model is developed to demonstrate the merits of phase change heat transfer on nanoscale porous structures, compared to that on microscale porous wick. Results indicate that nanoscale porous structures increase the thin-film evaporation surface area by one order of magnitude, which can significantly increase phase change heat transfer efficiency. The pertinent wick structure properties of the CNT forest are experimentally measured. Results show that the CNT forest is highly porous (∼95% porosity), and possesses large variations in effective thermal conductivity ranging from 0.8 to 180 W/m K. Effective pore size of the CNT wick structure varies between 50 and 180 nm, which can generate capillary pressure up to two orders of magnitude higher than the microscale wick structure. However, its low permeability, about three to four orders of magnitude lower than the traditional wicks, underscores the necessity of bi-porous CNT wick structures. The bi-porous CNT wick structures are composed of nanoscale porous CNT clusters, separated by microscale (∼50 μm wide) passages. Experimental results show a maximum heat flux of 770 W/cm 2 over a 2 mm × 2 mm heating area. With enhanced thin-film evaporation, heat transfer coefficients are improved by up to 100%, compared to the microscale wick. In contrast, the low CHF ∼140 W/cm 2 over a 10 × 10 mm 2 heating area is caused by vapor occupation of the microscale pores and the reduction of wick permeability. © 2012 Elsevier Ltd. All rights reserved.

Bale H.A.,University of California at Berkeley | Haboub A.,Lawrence Berkeley National Laboratory | Macdowell A.A.,Lawrence Berkeley National Laboratory | Nasiatka J.R.,Lawrence Berkeley National Laboratory | And 5 more authors.
Nature Materials | Year: 2013

Ceramic matrix composites are the emerging material of choice for structures that will see temperatures above ∼1,500°C in hostile environments, as for example in next-generation gas turbines and hypersonic-flight applications. The safe operation of applications depends on how small cracks forming inside the material are restrained by its microstructure. As with natural tissue such as bone and seashells, the tailored microstructural complexity of ceramic matrix composites imparts them with mechanical toughness, which is essential to avoiding failure. Yet gathering three-dimensional observations of damage evolution in extreme environments has been a challenge. Using synchrotron X-ray computed microtomography, we have fully resolved sequences of microcrack damage as cracks grow under load at temperatures up to 1,750°C. Our observations are key ingredients for the high-fidelity simulations used to compute failure risks under extreme operating conditions.

Cheng J.-T.,Teledyne Scientific Company | Chen C.-L.,Teledyne Scientific Company
Experiments in Fluids | Year: 2010

In response to the rapid advances in microelectronics, novel cooling technologies are needed to meet increasing cooling requirements. As a paradigm-shifting technique, electrowetting-on-dielectric (EWOD) uses electric potential to control the movement of a liquid droplet on a dielectric surface. In this work, we developed an EWOD-based microfluidic technique for active and adaptive thermal management of on-chip hot spots. A two-dimensional array of control electrodes was patterned on the chip surface for EWOD operations. By applying DC or AC voltages with appropriate sequence and timing to the electrode units, we were able to transport microdroplets of tens of μL along a programmable path. Without the need of external pumps and valves, the droplets were precisely delivered to cooling targets. With the driving voltage as low as 40 VAC, we demonstrate high heat flux (7.6 W/cm2) cooling on a hot spot. The EWOD-induced internal circulation within the droplets led to a time-averaged Nusselt number of ̃45. © 2010 Springer-Verlag.

Williams D.F.,U.S. National Institute of Standards and Technology | Young A.C.,Teledyne Scientific Company | Urteaga M.,Teledyne Scientific Company
IEEE Transactions on Terahertz Science and Technology | Year: 2013

In this paper, we present an approach for characterizing transistors embedded in microstrip lines formed on a thin bisbenzocyclobutene- based (BCB) monomers film at sub-millimeterwave wavelengths.We demonstrate the approach at frequencies up to 750 GHz and estimate the uncertainty of the procedure. © 2013 IEEE.

Teledyne Scientific Company | Date: 2013-07-02

A method and device for producing an aligned carbon nanotube array. The arrays of aligned carbon nanotubes (CNTs) may be formed by drying liquid dispersions of CNTs on a nanoporous substrate under an applied electrostatic field. The array may be used in a number of applications including electronics, optics, and filtration, including desalination.

Teledyne Scientific Company | Date: 2013-07-02

A method and device for producing an aligned carbon nanotube array. The arrays of aligned carbon nanotubes (CNTs) may be formed by drying liquid dispersions of CNTs on a nanoporous substrate under an applied electrostatic field. The array may be used in a number of applications including electronics, optics, and filtration, including desalination.

Kim D.-H.,Teledyne Scientific Company | Del Alamo J.A.,Massachusetts Institute of Technology
IEEE Transactions on Electron Devices | Year: 2010

We have experimentally studied the scaling behavior of sub-100-nm InAs high-electron mobility transistors (HEMTs) on InP substrate from the logic operation point of view. These devices have been designed for scalability and combine a thin InAlAs barrier and a thin channel containing a pure InAs subchannel. InAs HEMTs with gate length down to 40 nm exhibit excellent logic figures of merit, such as ION/IOFF= 9104, drain-induced-barrier lowering = 80 mV/V , S = 70\ mV/dec , and an estimated logic gate delay of 0.6 ps at VDS = 0.5V . In addition, we have obtained excellent high-frequency operation with Lg = 40nm , such as fT = 491GHz and fmax = 402GHz at VDS = 0.5V . In spite of the narrow bandgap of InAs subchannel, under the studied conditions, our devices are shown not to suffer from excessive band-to-band tunneling. When benchmarked against state-of-the-art Si devices, 40-nm InAs HEMTs exhibit ION0.6Am at ILeak = 200n μm . This is about two times higher ION than state-of-the-art high-performance 65-nm nMOSFET with comparable physical gate length and ILeak . © 2006 IEEE.

Kim D.-H.,Massachusetts Institute of Technology | Kim D.-H.,Teledyne Scientific Company | Del Alamo J.A.,Massachusetts Institute of Technology
IEEE Electron Device Letters | Year: 2010

We present 30-nm InAs pseudomorphic HEMTs (PHEMTs) on an InP substrate with record fT characteristics and well-balanced fT and f max values. This result was obtained by improving short-channel effects through widening of the side-recess spacing (Lside) to 150 nm, as well as reducing parasitic source and drain resistances. To compensate for an increase in Rs and Rd due to Lside widening, we optimized the ohmic contact process so as to decrease the specific ohmic contact resistance (Rc) to the InGaAs cap to 0.01 Ωmm. A 30-nm InAs PHEMT with tins4 exhibits excellent gmmax of 1.9 S/mm, fT of 644 GHz, and fmax of 681 GHz at V DS0.5V simultaneously. To the knowledge of the authors, the obtained fT in this work is the highest ever reported in any FET on any material system. This is also the first demonstration of simultaneous f T and fmax higher than 640 GHz in any transistor technology. © 2010 IEEE.

Yang Q.D.,University of Miami | Cox B.,Teledyne Scientific Company
Engineering Fracture Mechanics | Year: 2010

First introduced over a decade ago, the Binary Model has evolved into a computationally efficient tool for predicting the properties of textile composites. Key to the formulation is the question of what details of the textile composite and the distributions of stress, strain, temperature, etc., are necessary and sufficient to represent the physics of the problem adequately and to ensure useful engineering predictions. This paper is concerned specifically with the prediction of the ultimate strength in cases where failure follows a single substantial local damage event, such as the rupture or kinking of a tow or the creation of a shear band mediated by matrix damage, without further increase in the external load. The accuracy of predictions is assessed for some triaxially braided carbon/epoxy composites. A gauge length is introduced that is suggested by the micromechanics of the failure mechanisms. Predictions are made by reference to strains that are averaged over a volume whose sides are commensurate with this gauge, but nevertheless retain spatial variations associated with the textile architecture. Failure criteria for tow rupture and matrix shear failure are taken from a single un-notched tensile test; the calibrated model then successfully predicts the failure mechanism (matrix shear or fiber rupture) and ultimate strength in un-notched and open-hole tension tests for any orientation of the textile fabric relative to the load axis, as well as bending and simple shear tests. The successful predictions are made using strains calculated for an entirely elastic representation of the material, which is possible because of the brittle character of the stress-strain curves. Predictions are also attempted using strains computed under the assumption that the textile material is homogeneous. These predictions are significantly inferior. © 2010 Elsevier Ltd.

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