1,721,027 research outputs found
Novel Pendulum Vibration Energy Harvesters for Unmanned Surface Vehicles
Get PDFUnmanned Surface Vehicles (USVs) are typically used for data gathering operations
such as remote exploration and surveillance, though their practicality for
these applications is limited by the finite capacity of existing energy storage mechanisms.
Through the design, simulation, fabrication and testing of four novel energy
harvester concepts, this work delivers solutions that improve the viability of
energy harvesting technologies for USV applications, thereby providing the potential
to increase the operational time of these vessels. By critically analysing existing
vibration energy harvester designs, key areas for improvement were identified
in the literature review to allow for the further development of these technologies.
To address the need for greater efficiency and power output capabilities of electromagnetic
vibration energy harvesters, a pendulum-based transducer with an
original mechanical rotation rectifier (MRR) has been presented. This demonstrated
a higher average normalised power density than existing works with a
value of 12.32 W/g2/kg, and an efficiency of 43.5% at a 1Hz resonance. This design
was also shown to be highly scalable, and the use of offset spur gears and
sprag clutches in the MRR assembly allows the device to handle large amounts of
torque. Taking this a step further, a counterweight system was proposed, which
was proven to be capable of tuning the resonant frequency of a pendulum energy
harvester without increasing its arm length. This allowed the device to operate
at ultra-low frequencies in the 0.5-1.0 Hz range, thus increasing the power output
at 0.75 Hz by a factor of 5.95x compared to the same device without the counterweight.
The third device presented herein provides an improved mechanical
energy storage regulator, which was shown to produce the same voltage smoothing
effects as a flywheel while simultaneously improving start-up performance
and reducing the torque which critical components were subjected to. Finally,
a simplified mechanical rectifier was proposed, which was shown to be capable
of converting bidirectional input rotation to unidirectional rotation of a DC motor
while using just a single clutch and no gearing, thus providing a method for reducing
the complexity of electromagnetic vibration energy harvesters of this kind.
Overall, each of these four transducers addresses fundamental challenges with
existing vibration energy harvesters, providing mechanisms through which the
viability of this technology for USV applications is significantly improved.Engineering and Physical Sciences Research Council (EPSRC)Engineering and Physical Sciences Research Council (EPSRC)Engineering and Physical Sciences Research Council (EPSRC
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi-level and multidisciplinary optimisation of microelectromechanical systems
Get PDFA comparative investigation into the role multi-level and multidisciplinary design
optimisation can play in the automated design synthesis of microelectromechanical
systems (MEMS) is presented. Microelectromechanical systems are a field grown out of
the integrated circuit industry, with the goal of developing smart micro devices which
can interact with the environment in some form. They promise to revolutionise our
present day lifestyles as much as the integrated circuit has done in recent decades.
The complexity in fabrication, the delicacy in size that each device encompasses and the
multidisciplinary nature means design synthesis is a highly complicated process. Current
challenges stemming from their design include the high levels of computational cost
required in their modeling and analysis, and the often increasing complexity of design
through the coupling of multiple components and devices into a functioning system.
The development of automated design synthesis tools and methodologies to aid MEMS
design is therefore important to overcome these challenges in order to accommodate
the growing field of MEMS as it expands into more and more areas and continues
opening up to more and more applications.
An update of the current state of the art in automated MEMS design synthesis and
optimisation is first presented, utilizing state of the art multi-objective evolutionary
algorithms over five separate MEMS design optimisation case studies. The field of multilevel
and multidisciplinary optimisation is critically reviewed and discussed with respect
to their application to MEMS design synthesis and optimisation. The outcome is twofold,
with the construction of both a novel multidisciplinary optimisation algorithm tailored
towards MEMS design and a set of multi-level design optimisation strategies.
This thesis next outlines and develops a novel modular soft computing framework to
house the multi-objective, multi-level and multidisciplinary design optimisation
strategies. In order to evaluate both the current state of the art in automated MEMS
design synthesis and the multi-level and multidisciplinary optimisation strategies
outlined a hierarchical MEMS bandpass filter case study has been constructed.
Incorporating a novel state of the art electrical equivalent modelling and design
synthesis approach, six novel design problems structured around the MEMS bandpass
filter were developed and formed the basis for the comparative study to follow.
Finally both the current state of the art in automated MEMS design synthesis, multiobjective
evolutionary algorithms, and the outlined and developed multi-level and
multidisciplinary optimisation strategies are applied to the six design problems
developed. Comparative analysis and discussion is then given, showing a marked
improvement in MEMS design synthesis for the multi-level and multidisciplinary
optimisation strategies over the current state of the art methodology
Enhanced piezoelectric energy harvesting powered wireless sensor nodes using passive interfaces and power management approach
Get PDFLow-frequency vibrations typically occur in many practical structures and
systems when in use, for example, in aerospaces and industrial machines.
Piezoelectric materials feature compactness, lightweight, high integration
potential, and permit to transduce mechanical energy from vibrations into
electrical energy. Because of their properties, piezoelectric materials have been
receiving growing interest during the last decades as potential vibration-
harvested energy generators for the proliferating number of embeddable
wireless sensor systems in applications such as structural health monitoring
(SHM). The basic idea behind piezoelectric energy harvesting (PEH) powered
architectures, or energy harvesting (EH) more in general, is to develop truly “fit
and forget” solutions that allow reducing physical installations and burdens to
maintenance over battery-powered systems. However, due to the low
mechanical energy available under low-frequency conditions and the relatively
high power consumption of wireless sensor nodes, PEH from low-frequency
vibrations is a challenge that needs to be addressed for the majority of the
practical cases. Simply saying, the energy harvested from low-frequency
vibrations is not high enough to power wireless sensor nodes or the power
consumption of the wireless sensor nodes is higher than the harvested energy.
This represents a main barrier to the widespread use of PEH technology at the
current state of the development, despite the advantages it may offer.
The main contribution of this research work concerns the proposal of a novel
EH circuitry, which is based on a whole-system approach, in order to develop
enhanced PEH powered wireless sensor nodes, hence to compensate the
existing mismatch between harvested and demanded energy. By whole-system
approach, it is meant that this work develops an integrated system-of-systems
rather than a single EH unit, thus getting closer to the industrial need of a ready-
to-use energy-autonomous solution for wireless sensor applications such as
SHM. To achieve so, this work introduces:
Novel passive interfaces in connection with the piezoelectric harvester
that permit to extract more energy from it (i.e., a complex conjugate
impedance matching (CCIM) interface, which uses a PC permalloy
toroidal coil to achieve a large inductive reactance with a centimetre-
scaled size at low frequency; and interfaces for resonant PEH
applications, which exploit the harvester‟s displacement to achieve a
mechanical amplification of the input force, a magnetic and a mechanical
activation of a synchronised switching harvesting on inductor (SSHI)
mechanism).
A novel power management approach, which permits to minimise the
power consumption for conditioning the transduced signal and optimises
the flow of the harvested energy towards a custom-developed wireless
sensor communication node (WSCN) through a dedicated energy-aware
interface (EAI); where the EAI is based on a voltage sensing device
across a capacitive energy storage.
Theoretical and experimental analyses of the developed systems are carried
in connection with resistive loads and the WSCN under excitations of low
frequency and strain/acceleration levels typical of two potential energy-
autonomous applications, that are: 1) wireless condition monitoring of
commercial aircraft wings through non-resonant PEH based on Macro-Fibre
Composite (MFC) material bonded to aluminium and composite substrates; and
wireless condition monitoring of large industrial machinery through resonant
PEH based on a cantilever structure.
shown that under similar testing conditions the developed systems feature a
performance in comparison with other architectures reported in the
literature or currently available on the market. Power levels up to 12.16 mW and
116.6 µW were respectively measured across an optimal resistive load of 66
277 kΩ for an implemented non-resonant MFC energy harvester on
aluminium substrate and a resonant cantilever-based structure when no
interfaces were added into the circuits. When the WSCN was connected to the
harvesters in place of the resistive loads, data transmissions as fast as 0.4 and
s were also respectively measured. By use of the implemented passive
interfaces, a maximum power enhancement of around 95% and 452% was
achieved in the two tested cases and faster data transmissions obtained with a
maximum percentage improvement around 36% and 73%, respectively. By the
use of the EAI in connection with the WSCN, results have also shown that the
overall system‟s power consumption is as low as a few microwatts during non-
active modes of operation (i.e., before the WSCN starts data acquisition and
transmission to a base station).
Through the introduction of the developed interfaces, this research work takes a
whole-system approach and brings about the capability to continuously power
wireless sensor nodes entirely from vibration-harvested energy in time intervals
of a few seconds or fractions of a second once they have been firstly activated.
Therefore, such an approach has potential to be used for real-world energy-
autonomous applications of SHM
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Design analysis and fabrication of a mobile energy harvesting device to scavenge bio-kinetic energy.
Get PDFThe increasing prevalence of low power consumption electronics brings greater
potential to mobile energy harvesting devices as a possible power source. The main
contribution of this thesis is the study of a new piezoelectric energy harvesting device,
called the piezoelectric flex transducer (PFT), which is capable of working at non-
resonant and low frequencies to harvest bio-kinetic energy of a human walking. The
PFT consists of a piezoelectric element sandwiched between substrate layers and metal
endcaps, the endcaps are specifically designed to amplify the axial force load on the
piezoelectric element, instead of conventional designs of piezoelectric energy harvesters
that focus on utilising resonant frequency in order to increase power harvested. This
thesis presents the analyses, design, prototyping and characterisation of the PFT using a
coupled piezoelectric-circuit finite element model (CPC-FEM) to show the energy
harvesting capability of the proposed and developed novel device to harvest bio-kinetic
energy. Prior to the study of the new PFT, an initial focus was given to a traditional
Cymbal device to investigate its potential as a bio-kinetic energy harvesting device. To
gain an understanding, effects of geometrical parameters and material properties of the
device on its energy harvesting capability were studied and in doing so issues and
problems were identified with the traditional Cymbal device for use as a bio-kinetic
energy harvesting device. Its structural materials were not able to withstand higher than
a 50N applied load and it was proposed that a small adhesion area connection in a
fundamental part of the structure may have been at high risk of delamination. In order to
study these, the CPC-FEM model was developed using the commercial software of
ANSYS and validated by experimental methods. Later, based on a modelling and
experimental study, a novel PFT was proposed and implemented to overcome the issues
and problems of the traditional Cymbal device. For this initial study, the Cymbal was
analysed by studying how key dimensional parameters affect the energy harvesting
performance of the Cymbal. In addition to this, how piezoelectric material properties
affect the energy harvesting performance were studied using the developed CPC-FEM
model through comparisons of different piezoelectric materials and their electrical
performances to aid with selecting high power producing materials for the final PFT
design. It was found that (1) d₃₁ is a more dominant material property over other
material properties for higher power output, (2) Figure of Merit (FOM) was more linear
related to the power output than either the k₃₁ or the d₃₁, and (3) εᵀ r₃₃ had some role
when the materials have an identical d₃₁; a lower ε ᵀ₃₃ was preferred. A combined FOM
with d₃₁ parameters is recommended for selection of piezoelectric material for a higher
power outputs. The design of the new PFT is partly based on the traditional Cymbal
however, the new PFT has more potential for withstanding higher forces due to an
addition of substrate layers that reduced delamination risks. Using a similar approach to
designing the traditional Cymbal, the new PFT was designed and tested with force
frequencies of less than 5Hz and forces of up to 1kN. In the design process, the
validated CPC-FEM was used 1) to analyse then utilise correlations between geometric
parameters and power outputs, and 2) to ensure structural integrity by monitoring
mechanical stress in the PFT. The PFT was retrofitted into a shoe and the harvested
power was used to power an in-house developed wireless sensor module whilst the
subject with a body weight of 760N was wearing the shoe and ran at 3.1mph (equivalent
to 1.4Hz on the shoe), the PFT produced an average maximum power of 2.5mW over
2MΩ load and the power produced is able to power the wireless module approximately
every 10 seconds.Engineering and Physical Sciences (EPSRC)PhD in the School of Applied Science
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Design, modelling and testing of a novel energy harvesting device
Get PDFThis work is a feasibility study to develop a novel energy harvesting device.
Energy harvesting devices capture energy in various forms from the
surrounding and transform it into usable electrical energy. These devices
do not require any refuelling or recharging and are virtually a never ending
source of energy. The energy harvesting devices rely on di erent mechanisms
of energy conversion, depending on the energy source. This work focuses on
conversion of mechanical energy from vibrations into electric energy using
piezoelectric materials. Most of the existing devices are shaped like a cantilever
beam, thus limiting the tunability to a single resonance frequency.
It is believed that by modifying the geometry of the energy harvesting device
and applying a pre-load to the active material (piezoelectric), a variable
tunability can be achieved. Also, the application of an axial compressive
pre-load helps to further increase the power output of the device. Therefore,
in this present work, the performance of a simply supported beam shaped
energy harvesting device is investigated both numerically and experimentally.
For the numerical analyses nite element simulations are carried out using
ANSYS. An electro-mechanical model of the simply supported beam has been
developed through a series of approaching models with increasing complexity,
starting from an analytical solution. The nal three-dimensional model was
used as a base to create a model of the beam that has been used during
the experimental tests. Shape optimization studies were carried out on this
nite element model to analyse the power output of the device. It has been
observed, through pre-stressed modal analyses, that the axial pre-load decreases
the resonance frequency of the beam, thereby giving the beam the
ability to be tuned. Also,it has been observed that an optimisation of the
beam footprint shape can increase the power output by almost 40%.The experimental work focussed on the investigation of the harmonic behaviour
of the simply supported beam under di erent pre-load conditions.
It was observed that the experimental results were in disagreement with the
nite element simulations and also with the reference literature. The disagreement
was identi ed to be due to the hinge design that does not ensure
the alignment of the two tips of the beam and therefore the application of a
perfectly axial pre-load.
From the work presented here it emerges that the possibility to develop
a simply supported beam shaped energy harvesting device that rely on the
application of an axial pre-load to obtain tunability and an higher power
output is promising. The nite element simulations gave good results on the
beam behaviour and on the possibility to further increase its output by optimising
the shape of its footprint. The experimental work allowed to identify
the hinge design as a problem area to design a pro table device
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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