192 results found
Shi M, Holmes A, Yeatman E, 2020, Piezoelectric wind velocity sensor based on the variation of galloping frequency with drag force, Applied Physics Letters, Vol: 116, ISSN: 0003-6951
In this paper, we demonstrate a miniature energy harvesting wind velocity sensor of simple, low-cost construction, based on a single-degree-of-freedom galloping structure. The sensor consists of a prismatic bluff body with a triangular cross section attached to the free end of acantilever incorporating a commercial polyvinylidene fluoride piezoelectric film. In the wind, the bluff body causes vibration of the cantileverbased on galloping, and the piezoelectric film converts the vibration energy into an electrical signal. We have observed a negative correlationbetween the wind velocity and the vibration frequency, and we demonstrate that this relationship can be used to detect wind velocity directlywith useful accuracy. A simple theoretical model indicates that the frequency shift can be accounted for by the effect of the axial loading dueto form drag. The model shows close agreement with the experimental results. In wind tunnel tests, a prototype wind velocity sensor basedon this principle could measure wind velocities from 4.45 to 10 m/s, with the measured velocity typically being within 4% of the referencevalue obtained using a Pitot tube.
Dou G, Holmes AS, 2020, System integration for plastic electronics using room temperature ultrasonic welding, Advanced Engineering Materials, Vol: 22, Pages: 1-6, ISSN: 1438-1656
Plastic electronics is attracting increasing attention for both high‐end applications such as flexible OLED displays in mobile phones and low‐cost items such as plastic RFID tags for product labelling and tracking. However, there are numerous technological challenges, not the least of which is to develop robust and reliable packaging methods. Unfortunately, most of the established packaging technologies used in conventional silicon electronics are not transferable to plastic electronics due to the high process temperatures involved. We have explored the use of room temperature ultrasonic welding for the realization of multilayer plastic electronic circuits, identifying two distinct modes of ultrasonic welding that can form combined electrical and mechanical connections between adjacent low‐temperature polymer films with either aluminum or printed silver metallisation. We have fabricated fully functional multilayer wireless charging coils and RFID tags to demonstrate the potential of this new system integration approach.
Shi M, Yeatman EM, Holmes AS, 2019, Energy Harvesting Piezoelectric Wind Speed Sensor, 18th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Blad TWA, Machekposhti DF, Herder JL, et al., 2018, Vibration Energy Harvesting from Multi-Directional Motion Sources, International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), Publisher: IEEE
Shi M, Yeatman E, Holmes AS, 2018, MINIATURE WIND ENERGY HARVESTER BASED ON FLOW-INDUCED VIBRATION
This work demonstrates an experimental study of wideband wind energy harvesting by self-sustained flow induced vibration. We fabricated a novel folded structure using PET film as a bluffbody, which was directly mountedon a piezoelectric film to generate vibration in wind flow. The lock-in of the flow-induced vibration of the flutter was observed in our work. The vibration frequency of this device was locked at 10.8 Hz, which was its natural frequency, across a wide wind speed range from 5.8 m/s to 12.2 m/s. The continuous resonance gives this device stable output in this wide range of wind speed. Just using a small piezoelectric PVDF film of 3 cm2, the peak power output of our device can achieve 3.16 μW and keep at a high level once the self-sustained flow induced vibration occurs.
Dou G, Holmes AS, Cobb B, et al., 2018, Thermosonic-Adhesive (TS-A) Integration of Flexible Integrated Circuits on Flexible Plastic Substrates, 7th Electronic System-Integration Technology Conference (ESTC), Publisher: IEEE
Wang P, Zhang J, Spikes HA, et al., 2016, Development of hydrodynamic micro-bearings, 16th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2016), Publisher: IOP Publishing, ISSN: 1742-6588
This paper describes the modelling and testing of mm-scale hydrodynamic bearings which are being developed to improve the efficiency of a cm-scale turbine energy harvester, whose efficiency was previously limited by poorly lubricated commercial jewel-bearings. The bearings were fabricated using DRIE and their performance was assessed using a custom built MEMS tribometer. Results demonstrate that acceptably low friction is achieved when low viscosity liquid lubricants are used in combination with an appropriate choice of friction modifier additive. Further reduction in friction is demonstrated when the step height of bearing is adjusted in accordance with hydrodynamic theory. In parallel with the experiments, hydrodynamic lubricant modelling has been carried out to predict and further optimize film thickness and friction performance. Modelling results are presented and validated against experimental friction data.
Pu SH, Darbyshire DA, Wright RV, et al., 2016, RF MEMS Zipping Varactor With High Quality Factor and Very Large Tuning Range, IEEE ELECTRON DEVICE LETTERS, Vol: 37, Pages: 1340-1343, ISSN: 0741-3106
Pillatsch P, Yeatman EM, Holmes AS, et al., 2016, Wireless power transfer system for a human motion energy harvester, Sensors and Actuators A: Physical, Vol: 244, Pages: 77-85, ISSN: 1873-3069
Human motion energy harvesting as an alternative to battery powering in body worn and implanted devices is challenging during prolonged periods of inactivity. Even a buffer energy storage system will run out of power eventually if there is no external acceleration to the harvester. This paper presents a method to actuate the rotor inside a previously presented rotational piezoelectric energy harvester wirelessly via a magnetic reluctance coupling to an external driving rotor with one or more permanent magnet stacks attached. This makes it possible to recharge a battery or super-capacitor even if a patient is not moving. The use of a permanent magnet coupling has potential advantages compared to traditional inductive or ultrasonic methods, e.g. in terms of tissue damage and transmission depth. Simulation results show the achievable coupling torque for different configurations of magnet geometries and relative positions between the driving magnet stack(s) and the harvester. It is shown that using a single magnet stack yields better results than using two diametrically opposite stacks. Measurements are performed with different magnets, driving frequencies and orientations of the harvester. The results are discussed and successful energy transfer was achieved regardless of the orientation of the device with respect to gravity, which is desirable for real world applications. Lateral misalignment between the harvester and the driving magnet can also be overcome. The largest distance of power transfer reached was 32 mm with the largest magnets tested, and the optimal power output into a resistive load was over 100 μW at a frequency of 25 Hz. The functional volume of the harvester is 1.85 cm3 – similar to the size of a wristwatch.
Otter W, Hu F, Hanham S, et al., 2016, Terahertz metamaterial devices, International Conference on Semiconductor Mid-IR and THz Materials and Optics (SMMO2016)
Dou G, Gower MC, Holmes AS, 2016, Micro-welding using laser-generated ultrasound, 6th Electronic System-Integration Technology Conference (ESTC), Publisher: IEEE
Leong JY, Zhang J, Reddyhoff T, et al., 2016, Confining of liquids under induced motion, Pages: 555-558
Leong J, Zhang J, Reddyhoff T, et al., 2016, Prevention of spreading of lubricant on silicon surfaces, Pages: 533-536
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
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
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, Magnetic plucking of piezoelectric beams for frequency up-converting energy harvesters, SMART MATERIALS AND STRUCTURES, Vol: 23, ISSN: 0964-1726
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.
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
Otter WJ, Hanham SM, Ridler N, et al., 2014, MM-wave photonic crystal technology, IET Colloquium on Millimetre-wave and Terahertz Engineering & Technology
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
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
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
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
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
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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