Publications
217 results found
Dou G, Gower MC, Holmes AS, 2016, Micro-welding using laser-generated ultrasound, 6th Electronic System-Integration Technology Conference (ESTC), Publisher: IEEE
Pusch TP, D'Auria M, Tolou N, et al., 2015, LASER MICROMACHINING OF THIN BEAMS FOR SILICON MEMS: OPTIMIZATION OF CUTTING PARAMETERS USING THE TAGUCHI METHOD, ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Publisher: AMER SOC MECHANICAL ENGINEERS
While thin beams are widely used structural elements inMicro-Electro-Mechanical-Systems (MEMS) there are very fewstudies investigating the laser machining of clean high aspectratio silicon beams. This work presents a systematic study ofselected influencing cutting parameters with the goal of machininghigh aspect ratio beams with low side wall surface roughness(Ra) and high cross section verticality, i.e. low taper angle.The Taguchi method was used to find the optimal settingfor each of the selected parameters (pulse frequency, laser diodecurrent, pulse overlap, number of patterns to be marked, gapsize between patterns) utilizing orthogonal arrays and signalto-noise(S/N) ratio analysis. Double-sided clamped beams of100µm width and 10mm length were machined in silicon wafersof 525µm thickness using a nanosecond solid-state UV laser system(355nm wavelength). Our experimental results show thatbeams with an aspect ratio as high as 17.5 can be manufactured.Furthermore, a surface roughness of Ra = 0.37µm and taper angleof α = 2.52 degrees can be achieved. This will make the fastfabrication of MEMS devices with aspect ratios as high as thosefrom deep reactive ion etching possible.
Leong JY, Zhang J, Sinha SK, et al., 2015, Confining Liquids on Silicon Surfaces to Lubricate MEMS, Tribology Letters, Vol: 59, ISSN: 1573-2711
Liquid lubrication may provide a solution tothe problem of high friction and wear in micro-electromechanicalsystems. Although the effectiveness of thisapproach has been demonstrated in laboratory-based frictiontests, practical constraints prevent it from being appliedin commercial devices. The main problem is how toposition the lubricant on a silicon surface in order to limitspreading and evaporation. This paper describes twotechniques to address this issue. First, low concentrationsof additives are used to promote autophobic behaviour.Tests’ results show that certain concentrations of bothmultiply alkylated cyclopentane and amine additives areeffective in halting the spread of hexadecane on silicon,and, in the latter case, cause the hexadecane drop to subsequentlyretract. The second approach involves applying amicro-contact printing technique previously used on goldsurfaces. Here, silicon surfaces are coated with octadecyltrichlorosilanemono-layers that are then selectively removed,using oxygen plasma, to leave regions ofcontrasting surface energy. Results from spin tests showthat surfaces treated in this way can anchor 1 ll drops ofhexadecane and water when forces of up to 22 and 230 lN,respectively, are applied.
Otter WJ, Hanham SM, Ridler NM, et al., 2015, Terahertz photonic crystal technology, Workshop on THz
Holmes AS, 2015, Energy Harvesting from Fluid Flows, MICRO ENERGY HARVESTING, Editors: Briand, Yeatman, Roundy, Publisher: WILEY-V C H VERLAG GMBH, Pages: 297-319, ISBN: 978-3-527-31902-2
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- Citations: 3
Pillatsch P, Wright PK, Yeatman EM, et al., 2015, A Wireless Charging Mechanism For A Rotational Human Motion Energy Harvester, IEEE 12th International Conference on Wearable and Implantable Body Sensor Networks (BSN), Publisher: IEEE
Davies E, George DS, Gower MC, et al., 2014, MEMS Fabry-Perot optical accelerometer employing mechanical amplification via a V-beam structure, SENSORS AND ACTUATORS A-PHYSICAL, Vol: 215, Pages: 22-29, ISSN: 0924-4247
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- Citations: 31
Davies E, George DS, Holmes AS, 2014, Remote photothermal actuation for calibration of in-phase and quadrature readout in a mechanically amplified Fabry-Pérot accelerometer, IEEE Photonics Journal, Vol: 6, Pages: 1-1, ISSN: 1943-0647
A mechanically amplified Fabry-Pérot optical accelerometer is reported in which photothermal actuation is used to calibrate the in-phase and quadrature (I&Q) readout. The Fabry-Pérot interferometer (FPI) is formed between a gold-coated silicon mirror, situated in the middle of a V-beam amplifier, and the end surface of a cleaved optical fiber. On the opposite side of the silicon mirror, a further cleaved optical fiber transmits near-infrared laser light (λ = 785 nm), which is absorbed by the uncoated silicon causing heating. The thermal expansion of the V-beam is translated into an amplified change in cavity length of the FPI, large enough for the 2π-phase variation necessary for I&Q calibration. A simple 1D thermal analysis of the structure has been developed to predict the relationship between laser power and change in cavity length. A device having a V-beam of length 1.8 mm, width 20 μm, and angle 2 ° was found to undergo a cavity length change of 785 nm at 30 mW input power. The device response was approximately linear for input accelerations from 0.01 to 15 g. The noise was measured to be ~ 60 μg/√Hz from 100 Hz to 3.0 kHz, whereas the limit of detection was 47.7 mg from dc to 3.0 kHz.
Pillatsch P, Yeatman EM, Holmes AS, 2014, A piezoelectric frequency up-converting energy harvester with rotating proof mass for human body applications, Sensors and Actuators A: Physical, Vol: 206, Pages: 178-185, ISSN: 0924-4247
Energy harvesting from human motion faces the challenges of low frequency and random excitation. One strategy that has been successful in the past is frequency up-conversion. This paper introduces an inertial device that combines this principle, in the form of piezoelectric beam plucking through magnetic coupling with a rotating proof mass. The advantages rotational systems can have for body movements are discussed. The prototype is described and tested in a real world environment during a running race and later on in a laboratory environment on a custom built linear excitation table. Throughout these tests it is confirmed that such a device can operate over a broad range of frequencies and under varying orientations, making it suitable for this intended application. Across frequencies between 0.5 and 4 Hz and accelerations between 1 and 20 m/s2 power outputs in the range of tens of microwatts were achieved, with a peak value of 43 μW at 2 Hz and 20 m/s2 when the rotor went into a continuous rotation.
Pillatsch P, Yeatman EM, Holmes AS, 2014, Magnetic plucking of piezoelectric beams for frequency up-converting energy harvesters, SMART MATERIALS AND STRUCTURES, Vol: 23, ISSN: 0964-1726
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- Citations: 63
Otter WJ, Hanham SM, Ridler N, et al., 2014, MM-wave photonic crystal technology, IET Colloquium on Millimetre-wave and Terahertz Engineering & Technology
Davies E, George DS, Holmes AS, 2014, Mechanically amplified MEMS optical accelerometer with FPI readout, Conference on MOEMS and Miniaturized Systems XIII, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
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- Citations: 2
Pillatsch P, Yeatman EM, Holmes AS, 2014, Experimental Validation of a Piezoelectric Frequency Up-Converting Rotational Harvester, 11th International Conference on Wearable and Implantable Body Sensor Networks, Publisher: IEEE, Pages: 6-10
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- Citations: 4
Otter WJ, Hanham SM, Klein N, et al., 2014, W-band Laser-controlled Photonic Crystal Variable Attenuator, IEEE MTT-S International Microwave Symposium (IMS), Publisher: IEEE, ISSN: 0149-645X
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- Citations: 2
Pillatsch P, Shashoua N, Holmes AS, et al., 2014, Degradation of Piezoelectric Materials for Energy Harvesting Applications, 14th International Conference on Micro- and Nano-Technology for Power Generation and Energy Conversion Applications (PowerMEMS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 11
Miller LM, Pillatsch P, Halvorsen E, et al., 2013, Experimental passive self-tuning behavior of a beam resonator with sliding proof mass, JOURNAL OF SOUND AND VIBRATION, Vol: 332, Pages: 7142-7152, ISSN: 0022-460X
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- Citations: 54
Pillatsch P, Yeatman EM, Holmes AS, 2013, A model for magnetic plucking of piezoelectric beams in energy harvesters, Pages: 1364-1367
This paper introduces a calculation model for piezoelectric energy harvesters based on the frequency up-conversion method. Magnetic coupling is used to pluck a beam without physical impact. The piezo bimorph itself is modeled with a fully distributed parameter approach and then combined with a simple inverse square assumption for the magnetic forces. The results are verified experimentally and it is shown that the model is capable of reproducing the effects of various parameters, such as magnet orientation, initial gap between magnets and magnetic force. © 2013 IEEE.
Pu SH, Holmes AS, Yeatman EM, 2013, Stress in electroplated gold on silicon substrates and its dependence on cathode agitation, MICROELECTRONIC ENGINEERING, Vol: 112, Pages: 21-26, ISSN: 0167-9317
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- Citations: 5
Hergert RJ, Hanrahan B, Ghodssi R, et al., 2013, Performance of integrated retainer rings in silicon micro-turbines with thrust style micro-ball bearings, JOURNAL OF MICROMECHANICS AND MICROENGINEERING, Vol: 23, ISSN: 0960-1317
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- Citations: 5
Otter WJ, Hanham SM, Ridler NM, et al., 2013, 100 GHz photonic crystal devices, ARMMS RF & Microwave Society Conference
Otter WJ, Hanham SM, Ridler N, et al., 2013, Sub-THz photonic crystal devices, International Conference on THz and Mid Infrared Radiation and Applications to Cancer Detection using Laser Imaging, Workgroup Meetings of COST ACTIONs MP1204 and BM1205
Leong JY, Reddyhoff T, Sinha SK, et al., 2013, Hydrodynamic friction reduction in a MAC-hexadecane lubricated MEMS contact, Tribology Letters, Vol: 49, Pages: 217-225, ISSN: 1023-8883
Recent research has shown that hydrodynamic lubrication is an effective means of reducing friction in high sliding micro-electromechanical systems (MEMS). At high speeds, however, such lubrication can lead to increased friction due to viscous drag. This article describes a series of hydrodynamic tests on a silicon MEMS contact lubricated with a blend of hexadecane and a multiplyalkylated cyclopentane (MAC). Results show that the presence of the MAC reduces hydrodynamic friction compared with neat hexadecane. Such behaviour is contrary to conventional hydrodynamic theory, since the viscosity of the MAC - a mixture of di and tri(2 octyldodecyl)cyclopentane - is significantly higher than that of neat hexadecane. This effect increases with MAC concentration up to an optimum value of 3 wt%, where the hydrodynamic friction coefficient at 15,000 rpm is reduced from 0.5 to 0.3. Above this concentration, friction begins to rise due to the overriding effect of increasing viscosity. The viscosity of the blended lubricant increased monotonically with MAC concentration, when measured using both a Stabinger and an ultrahigh shear viscometer. In addition to this, no reduction in friction was observed when a squalane-hexadecane blend of equal viscosity was tested. This suggests that some property of the MAC-hexadecane lubricant, other than its viscosity, is influencing hydrodynamic lubrication. A tentative explanation for this behaviour is that the MAC induces the liquid to slip, rather than shear, close to the silicon surfaces. This hypothesis is supported by the fact that the friction reducing ability of the MAC blend was inhibited by the inclusion of octade-cylamine - a substance known to form films on silicon surfaces. Furthermore, the MAC reduces friction in the mixed regime, in a manner suggesting that the formation of a viscous boundary layer. This unusual behaviour may have useful implications for reducing hydrodynamic friction in liquidlubricated MEMS devices. © Sprin
Leong JY, Reddyhoff T, Sinha SK, et al., 2013, Hydrodynamic Friction Reduction in a MAC-Hexadecane Lubricated MEMS Contact, TRIBOLOGY LETTERS, Vol: 49, Pages: 217-225, ISSN: 1023-8883
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- Citations: 24
Gower MC, Davies E, Holmes AS, 2013, Optical Modeling of Laser Ablation for Microstructure Fabrication, JOURNAL OF LASER MICRO NANOENGINEERING, Vol: 8, Pages: 56-64, ISSN: 1880-0688
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- Citations: 2
Otter WJ, Hanham SM, Episkopou E, et al., 2013, Photoconductive Photonic Crystal Switch, 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027
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- Citations: 2
Pillatsch P, Yeatman EM, Holmes AS, 2013, A Wearable Piezoelectric Rotational Energy Harvester, IEEE International Conference on Body Sensor Networks, Publisher: IEEE
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- Citations: 9
Pillatsch P, Miller LM, Halvorsen E, et al., 2013, Self-tuning behavior of a clamped-clamped beam with sliding proof mass for broadband energy harvesting, 13th International Conference on Micro and Nano Technology for Power Generation and Energy Conversion Applications (PowerMEMS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 24
Davies E, George DS, Gower MC, et al., 2013, OPTICAL ACCELEROMETER WITH MECHANICAL AMPLIFICATION VIA A V-BEAM MECHANISM, 26th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Publisher: IEEE, Pages: 609-612, ISSN: 1084-6999
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- Citations: 8
Pillatsch P, Yeatman EM, Holmes AS, 2013, Real World Testing Of A Piezoelectric Rotational Energy Harvester For Human Motion, 13th International Conference on Micro and Nano Technology for Power Generation and Energy Conversion Applications (PowerMEMS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 15
Pillatsch P, Yeatman EM, Holmes AS, 2012, A scalable piezoelectric impulse-excited energy harvester for human body excitation, SMART MATERIALS AND STRUCTURES, Vol: 21, ISSN: 0964-1726
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- Citations: 87
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