Publications
217 results found
Gower MC, Davies E, Holmes A, 2012, Optical Modeling of Laser Ablated Microstructures, LPM 2012
Dou G, Holmes AS, 2012, Thermosonic flip-chip assembly on flex substrates, 2012 13th International Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2012
Thermosonic (TS) flip-chip assembly on rigid substrates has been successfully demonstrated previously. In this paper we extend the TS bonding technique to the application of flip-chip assembly on flexible substrates. A custom TS bonder was constructed for this purpose that can heat the assembly rapidly without causing thermal damage to the flexible substrate. The reliability of the assemblies produced was investigated by the Temperature and Humidity reliability test. It was found that the interconnections of the TS flip-chip assemblies were more reliable than those of anisotropic adhesive assemblies prepared on the same bonder. The results indicate that TS bonding may have the potential to improve the reliability of chip-on-flex assemblies. © 2012 IEEE.
Howey DA, Childs PRN, Holmes AS, 2012, Air-gap convection in rotating electrical machines, IEEE Transactions on Industrial Electronics, Vol: 58
This paper reviews convective heat transfer within the air-gap of both cylindrical and disc geometry rotating electrical machines, including worked examples relevant to fractional horsepower electrical machines. Thermal analysis of electrical machines is important because torque density is limited by maximum temperature. Knowledge of surface convective heat transfer coefficients is necessary for accurate thermal modelling for example using lumped parameter models. There exists a wide body of relevant literature, but much of it has traditionally been in other application areas, dominated by mechanical engineers, such as gas turbine design. Particular attention is therefore given to the explanation of the relevant non-dimensional parameters, and to the presentation of measured convective heat transfer correlations for a wide variety of situations from laminar to turbulent flow at small and large gap sizes for both radial flux and axial flux electrical machines.
Episkopou E, Papantonis S, Holmes AS, et al., 2012, Optically-controlled plasma switch for integrated terahertz applications, 39th IEEE International Conference on Plasma Science (ICOPS2012)
Dou G, Holmes AS, 2012, Thermosonic-Adhesive Flip-chip Assembly, 4th Electronic System-Integration Technology Conference (ESTC), Publisher: IEEE
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- Citations: 1
Pillatsch P, Yeatman EM, Holmes AS, 2012, Piezoelectric Rotational Energy Harvester For Body Sensors Using An Oscillating Mass, BSN
Pillatsch P, Yeatman EM, Holmes AS, 2012, A Scalable Piezoelectric Impulse-Excited Generator For Random Low Frequency Excitation, IEEE MEMS
Ku ISY, Reddyhoff T, Wayte R, et al., 2012, Lubrication of microelectromechanical devices using liquids of different viscosities, Journal of Tribology, Vol: 134, ISSN: 0742-4787
Lubrication of contacting and sliding surfaces in MEMS (microelectromechanical systems) is particularly challenging because of the predominance of surface forces at the microscale. The current paper explores the possibility of using liquid lubrication in this application. Measurements of friction and lubricant film thickness have been made for liquid lubricants of different viscosities, including low viscosity silicone oil, hexadecane, squalane, and water. Testing was carried out using a newly developed MEMS tribometer in which a rotating silicon disk is loaded against a stationary silicon disk. Two different test setups were used: one where both disks are flat, and the other where the stationary disk is structured as in a thrust pad bearing. In all tests the disks were fully submerged in the lubricant. With the flat-on-patterned disk combination, the variation of friction with rotation speed was found to follow classical Stribeck curves for all the lubricants tested. The friction at high speeds also decreased with increasing normal load, in accordance with hydrodynamic lubrication theory. For the least viscous lubricants, it was found that the hydrodynamic friction coefficients remained relatively low even at higher speeds. In particular, for water the friction coefficient for water was around 0.1 at 10,000 rpm. However, boundary friction was found to be unacceptably high at low speeds where there was insufficient lubricant entrainment. The experimental results have been compared with a finite difference solution of Reynolds equation and reasonable agreement is seen between theory and experiment. The results indicate that liquid lubrication is potentially an effective means of lubricating MEMS components with high levels of sliding. 2012 American Society of Mechanical Engineers.
Kaphengst NF, Toh TT, Mitcheson PD, et al., 2012, Adaptive Load Synthesis for Autonomous Resonant Frequency Tuning of Electromagnetic Energy Harvesters, PowerMEMS 2012
Wong KH, Toh TT, Mitcheson PD, et al., 2011, Tuning the Resonant Frequency and Damping of an Energy Harvester Using Power Electronics, IEEE Transactions on Circuits and Systems II
Mitcheson PD, Toh TT, Wong KH, et al., 2011, Tuning the Resonant Frequency and Damping of an Electromagnetic Energy Harvester Using Power Electronics, IEEE Transactions on Circuits and Systems. Part 2: Express Briefs, Vol: 58, Pages: 792-796
Pillatsch P, Yeatman EM, Holmes AS, 2011, Piezoelectric Impulse-Excited Generator for Low Frequency Non-Harmonic Vibrations, PowerMEMS 2011, Pages: 245-248
Malcolm A, Wright S, Syms RRA, et al., 2011, A miniature mass spectrometer for liquid chromatography applications, RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Vol: 25, Pages: 3281-3288, ISSN: 0951-4198
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- Citations: 41
Toh TT, Mitcheson PD, Dussud L, et al., 2011, Electronic Resonant Frequency Tuning of a Marine Energy Harvester, PowerMEMS 2011, Pages: 383-386
Ku ISY, Reddyhoff T, Holmes AS, et al., 2011, Wear of silicon surfaces in MEMS, Wear, Vol: 271, Pages: 1050-8, ISSN: 0043-1648
High levels of friction and wear are problems which currently limit the development of sliding micro-electro-mechanical systems (MEMS) - devices which would otherwise offer significant technological advancement. The current paper focuses on the wear of MEMS silicon surfaces, and specifically looks at the effect of environment and surface preparation on wear behaviour. Included in the study is the assessment of two self-replenishing lubrication mechanisms; namely liquid and vapour phase lubrication. All tests were carried out using a tribometer which operated and measured friction and wear under conditions representative of MEMS.It is shown that friction and wear behaviour depend strongly on subtle changes of the silicon surfaces prior to testing. Greatest wear was measured when the surfaces were tested immediately after plasma-cleaning, while subsequent exposure to ambient air for 15h reduced wear to negligible levels. Exposure of plasma-cleaned surfaces to water-saturated argon prior to testing prevented wear to a limited extent. Based on this, and TOF-SIMS analysis, it is suggested that the observed wear reduction after exposure to air is caused by tiny amounts of lubricious long chain hydrocarbon contaminants present in ambient air.Tests carried out with the specimens submerged in a liquid bath show that the presence of liquid water reduces friction and wear, but only if specimens have been plasma-cleaned beforehand. This behaviour is tentatively attributed to the hydrophilic nature of plasma treated silicon, reducing the corrosive action of water. When hexadecane or 1-pentanol was used as a liquid lubricant, friction was minimal, and wear was undetectable under all sliding conditions. This was the case even though the contact operated in the mixed lubrication regime, suggesting a boundary film is formed on the silicon surfaces by both of these organic liquids.Results of tests carried out with the lubricant being supplied in the form of pentanol vapour also showe
Howey DA, Holmes AS, Pullen KR, 2011, Measurement and CFD Prediction of Heat Transfer in Air-Cooled Disc-Type Electrical Machines, IEEE T IND APPL, Vol: 47, Pages: 1716-1723, ISSN: 0093-9994
Howey DA, Bansal A, Holmes AS, 2011, Design and performance of a cm-scale shrouded wind turbine for energy harvesting, Smart Materials and Structures, Vol: 20, Pages: 1-12
Dou G, Holmes AS, Yeatman EM, et al., 2011, Transfer of functional ceramic thin films using a thermal release process., Adv Mater, Vol: 23, Pages: 1252-1256, ISSN: 1521-4095
Pranonsatit S, Holmes AS, Lucyszyn S, 2011, Microwave modelling of radio frequency microelectromechanical rotary switches, IET Microwaves, Antennas & Propagation, Vol: 5, Pages: 255-261
In this study, both full 3D electromagnetic and equivalent circuit modelling of a radio frequencymicroelectromechanical systems (RF MEMS) single-pole eight-throw rotary switch are reported for the first time. Excellentagreement has been achieved between measurements and modelled performance for frequencies up to 12 GHz. In order tovalidate the effectiveness of the modelling, a 2-bit true time delay phase shifter having a centre frequency of 2 GHz has beendemonstrated. The traditional topology of the switched delay line was adopted with two rotary switches employed for signalrouting. This phase shifter represents the first ever application of any RF MEMS rotary switch. It is shown that the switchmodel can accurately predict the measured performance of the phase shifter, without the need for adding new circuit elementsor tweaking of model parameters. The low measured root mean square deviations of insertion phase from the predictedresponses increase as 1.3o, 1.9o, 2.5o and 3.4o when the phase states are stepped through 0o, 90o, 180o and 270o, respectively.
Bansal A, Hergert R, Dou G, et al., 2011, Laser transfer of sol-gel ferroelectric thin films using an ITO release layer, MICROELECTRONIC ENGINEERING, Vol: 88, Pages: 145-149, ISSN: 0167-9317
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- Citations: 7
Reddyhoff T, Ku ISY, Holmes AS, et al., 2011, Friction Modifier Behaviour in Lubricated MEMS Devices, Tribology Letters, Vol: 41, Pages: 239-46, ISSN: 1023-8883
Low viscosity fluids could provide reliable lubrication for certain microelectromechanical system's (MEMS) applications where high-sliding speeds and/or high sliding distances occur. However, while the use of low viscosity fluids leads to reduced hydrodynamic friction, high boundary friction can be a significant issue at low entrainment speeds. This article describes a series of tests of low viscosity fluids, blended with a friction modifier additive so as to provide a combination of both low hydrodynamic and low boundary friction at MEMS scales. The low viscosity fluids tested were hexadecane, low viscosity silicone oil, toluene and water. With the exception of water, the addition of the organic friction modifier octadecylamine to all these lubricating fluids produced a significant reduction in boundary friction. For a MEMS contact lubricated with silicone oil for instance, boundary friction was reduced from 0.5 to close to 0.05. The presence of the amine dissolved in the toluene had the effect of reducing boundary friction from 0.75 to 0.55; this was further reduced to 0.25 after the specimens had been immersed in the toluene-additive blend for 48 h. A water-soluble additive, diethylamine, was added to de-ionized water, at 0.1% by weight concentration. Although an initial reduction in boundary friction was observed (0.45-0.25), under these conditions the rapid onset of severe wear negated these effects. It is suggested that corrosion of silicon by water, followed by abrasion, is the cause of this accelerated wear.
Holmes AS, Howey DA, Bansal A, et al., 2010, Self-powered wireless sensor for duct monitoring, PowerMEMS 2010, the 10th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications, Pages: 115-118
Lucyszyn S, Pranonsatit S, Choi J-Y, et al., 2010, Niche switch technologies, Advanced RF MEMS, Publisher: Cambridge University Press, Pages: 73-108, ISBN: 978-0-521-89771-6
Wright S, O'Prey S, Syms RRA, et al., 2010, Microfabricated Quadrupole Mass Spectrometer With a Brubaker Prefilter, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, Vol: 19, Pages: 325-337, ISSN: 1057-7157
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- Citations: 24
Pu SH, Holmes AS, Yeatman EM, et al., 2010, Stable zipping RF MEMS varactors, JOURNAL OF MICROMECHANICS AND MICROENGINEERING, Vol: 20, ISSN: 0960-1317
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- Citations: 13
Howey DA, Holmes AS, Pullen KR, 2010, Prediction and measurement of heat transfer in air-cooled disc-type electrical machines, 5th IET International Conference on Power Electronics, Machines and Drives (PEMD 2010), Publisher: IET
Accurate thermal analysis of axial flux permanent magnet (AFPM) machines is crucial in predicting maximum power output. Stator convective heat transfer is one of the most important and least investigated heat transfer mechanisms and is the focus of this paper. Experimental measurements were undertaken using a thin-film electrical heating method, providing radially resolved steady state heat transfer data from an experimental rotor-stator system designed as a geometric mockup of a through-flow ventilated AFPM machine. The measurements are compared with computational fluid dynamics (CFD) simulations using both 2D axisymmetric and 3D models. These were found to give a conservative estimate of heat transfer, with inaccuracies near the edge and in the transitional flow regime. Predicted stator heat transfer was found to be relatively insensitive to the choice of turbulence model and the SST model was used for most of the simulations.
Hergert R, Ku ISY, Reddyhoff T, et al., 2010, Micro rotary ball bearing with integrated ball cage: Fabrication and characterization, Hong Kong, China, 23rd IEEE International Conference on Micro Electro Mechanical Systems, MEMS 2010, January 24, 2010 - January 28, 2010, Publisher: Institute of Electrical and Electronics Engineers Inc., Pages: 687-690, ISSN: 1084-6999
This paper presents a rotary MEMS ball bearing with an integrated silicon ball cage. The device is a deep groove radial ball bearing consisting of steel balls encapsulated between two micromachined silicon wafers. The silicon ball cage is released from the bulk silicon substrate during fabrication. The objective was to show that a simple caged bearing design provides reliable motion at both high and low speeds. The running torque of two identical devices was measured for speeds ranging from 10 to 20,000 rpm. One of the devices was disassembled before failure to provide images of the wear experienced during testing. 2010 IEEE.
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