1,720,988 research outputs found
An FPGA-based adaptive tuning control for a cochlea-mimicking filter channel
No full textThis paper presents the design and experimental results of an FPGA-based cochlea filter tuning control block that emulates the active nonlinear behaviour of outer hair cells (OHC) in the cochlea. The tuning block uses data measured from physiological experiments which are mapped into adaptive voltage bias of a CMOS cochlea-mimicking filter channel to tune it. It extracts signal level from inputs to the cochlea channel and feedforwards the corresponding voltage bias to the tuning stage of the filter channel. A level-dependent control of the filter gain and quality factor was observed in the measurement results. The tuning control block nonlinearly compressed wide range of audio input distinctively into about 20 dB, which is the active gain inherent in the sample cochlea channel used. Based on this work, we will be able to build an intelligent audio front-end for future machine hearing systems that is able to adaptively process sound and cope with wide dynamic sound input like the cochlea does
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Design of a silicon cochlea system with biologically faithful response
Full text linkThis paper presents the design and simulation results of a silicon cochlea system that has closely similar behavior as the real cochlea. A cochlea filter-bank based on the improved three-stage filter cascade structure is used to model the frequency decomposition function of the basilar membrane; a filter tuning block is designed to model the adaptive response of the cochlea; besides, an asynchronous event-triggered spike codec is employed as the system interface with bank-end spiking neural networks. As shown in the simulation results, the system has biologically faithful frequency response, impulse response, and active adaptation behavior; also the system outputs multiple
band-pass channels of spikes from which the original sound input can be recovered. The proposed silicon cochlea is feasible for analog VLSI implementation so that it not only emulates the way that sounds are preprocessed in human ears but also is able match the compact physical size of a real cochlea
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Crowd sourced self beacon mapping with isolated signal aware bluetooth low energy positioning
Full text linkIn the past few decades, there has been an increase in the demand for positioning and
navigation systems in various fields. Location-based service (LBS) usage covers a range of
different variations from advertising and navigation to social media. Positioning based on a
global navigation satellite system (GNSS) is the commonly used technology for positioning
nowadays. However, the GNSS has a limitation of needing the satellites to be in line-of-sight
(LOS) to provide an accurate position. Given this limitation, several different approaches are
employed for indoor positioning needs.
Bluetooth low energy (BLE) is one of the wireless technologies used for indoor positioning.
However, BLE is well-known for having unstable signals, which will affect an estimated
distance. Moreover, unlike Wi-Fi, BLE is not commonly and widely used, and BLE beacons
must thus be placed to enable a venue with BLE positioning. The need to deploy the beacons
results in a lengthy process to place and record the position of each placed beacon.
This thesis proposes several solutions to solve these problems. A filter based on a Fourier
transform is proposed to stabilise a BLE signal to obtain a more reliable reading. This allows
the BLE signals to be less affected by internal variation than unfiltered signal. An obstruction-aware
algorithm is also proposed using a statistical approach, which allows for the detection
of non-line-of-sight (NLOS). These proposed solutions allow for a more stable BLE signal,
which will result in a more reliable estimation of distance using the signal. The proposed
solutions will enable accurate distance estimation, which will translate into improved
positioning accuracy. An improvement in 88% of the test points is demonstrated by
implementing the proposed solutions. Furthermore, to reduce the calibration needed when deploying the BLE beacons, a
beacon-mapping algorithm is proposed that can be used to determine the position of BLE
beacons. The proposed algorithm is based on trilateration with added information about
direction. It uses the received signal strength (RSS) and the estimated distance to determine
the error range, and a direction line is drawn based on the estimated error range.
Finally, to further reduce the calibration needed, a crowdsource approach is proposed.
This approach is proposed alongside a complete system to map the location of unknown
beacons. The proposed system uses three phases to determine the user location, determine
the beacons’ position, and recalculate BLE scans that have insufficient number of known BLE
beacons. Each beacon and user’s position determined is assigned a weight to represent the
reliability of that position. This is important to ensure that the position generated from a
more reliable source will be emphasised. The proposed system demonstrates that the
beacon-mapping system can map beacons with a root mean squared error (RMSE) of 4.64 m
and a mean of absolute error (MAE) of 4.28 m
Efficient runtime placement management for high performance and reliability in COTS FPGAs
Full text linkDesigning high-performance, fault-tolerant multisensory electronic systems for
hostile environments such as nuclear plants and outer space within the constraints of
cost, power and flexibility is challenging. Issues such as ionizing radiation, extreme
temperature and ageing can lead to faults in the electronics of these systems. In
addition, the remote nature of these environments demands a level of flexibility and
autonomy in their operations. The standard practice of using specially hardened
electronic devices for such systems is not only very expensive but also has limited
flexibility.
This thesis proposes novel techniques that promote the use of Commercial Off-The-
Shelf (COTS) reconfigurable devices to meet the challenges of high-performance
systems for hostile environments. Reconfigurable hardware such as Field
Programmable Gate Arrays (FPGA) have a unique combination of flexibility and
high performance. The flexibility offered through features such as dynamic partial
reconfiguration (DPR) can be harnessed not only to achieve cost-effective designs as
a smaller area can be used to execute multiple tasks, but also to improve the
reliability of a system as a circuit on one portion of the device can be physically
relocated to another portion in the case of fault occurrence. However, to harness
these potentials for high performance and reliability in a cost-effective manner, novel
runtime management tools are required. Most runtime support tools for
reconfigurable devices are based on ideal models which do not adequately consider
the limitations of realistic FPGAs, in particular modern FPGAs which are
increasingly heterogeneous. Specifically, these tools lack efficient mechanisms for
ensuring a high utilization of FPGA resources, including the FPGA area and the
configuration port and clocking resources, in a reliable manner.
To ensure high utilization of reconfigurable device area, placement management is a
key aspect of these tools. This thesis presents novel techniques for the management
of hardware task placement on COTS reconfigurable devices for high performance
and reliability. To this end, it addresses design-time issues that affect efficient
hardware task placement, with a focus on reliability. It also presents techniques to
maximize the utilization of the FPGA area in runtime, including techniques to
minimize fragmentation. Fragmentation leads to the creation of unusable areas due to
dynamic placement of tasks and the heterogeneity of the resources on the chip.
Moreover, this thesis also presents an efficient task reuse mechanism to improve the
availability of the internal configuration infrastructure of the FPGA for critical
responsibilities like error mitigation. The task reuse scheme, unlike previous
approaches, also improves the utilization of the chip area by offering
defragmentation.
Task relocation, which involves changing the physical location of circuits is a
technique for error mitigation and high performance. Hence, this thesis also provides
a functionality-based relocation mechanism for improving the number of locations to
which tasks can be relocated on heterogeneous FPGAs. As tasks are relocated, clock
networks need to be routed to them. As such, a reliability-aware technique of clock
network routing to tasks after placement is also proposed.
Finally, this thesis offers a prototype implementation and characterization of a
placement management system (PMS) which is an integration of the aforementioned
techniques. The performance of most of the proposed techniques are tested using
data processing tasks of a NASA JPL spectrometer application. The results show that
the proposed techniques have potentials to improve the reliability and performance of
applications in hostile environment compared to state-of-the-art techniques. The task
optimization technique presented leads to better capacity to circumvent permanent
faults on COTS FPGAs compared to state-of-the-art approaches (48.6% more errors
were circumvented for the JPL spectrometer application). The proposed task reuse
scheme leads to approximately 29% saving in the amount of configuration time. This
frees up the internal configuration interface for more error mitigation operations. In
addition, the proposed PMS has a worst-case latency of less than 50% of that of state-of-
the-art runtime placement systems, while maintaining the same level of placement
quality and resource overhead
Antenna and rectifier designs for miniaturized radio frequency energy scavenging systems
Full text linkWith ample radio transmitters scattered throughout urban landscape, RF
energy scavenging emerges as a promising approach to extract energy from
propagating radio waves in the ambient environment to continuously charge low
power electronics. With the ability of generating power from RF energy, the need for
batteries could be eliminated. The effective distance of a RF energy scavenging
system is highly dependent on its conversion efficiency. This results in significant
limitations on the mobility and space requirement of conventional RF energy
scavenging systems as they operate only in presence of physically large antennas and
conversion circuits to achieve acceptable efficiency. This thesis presents a number of
novel design strategies in the antenna and rectifier designs for miniaturized RF energy
scavenging system.
In the first stage, different energy scavenging systems including solar energy
scavenging system, thermoelectric energy scavenging system, wind energy
scavenging system, kinetic energy scavenging system, radio frequency energy
scavenging system and hybrid energy scavenging system are investigated with
regard to their principle and performance. Compared with the other systems, RF
energy scavenging system has its advantages on system size and power density with
relatively stable energy source. For a typical RF energy scavenging system, antenna
and rectifier (AC-DC convertor) are the two essential components to extract RF
energy and convert to usable electricity.
As the antenna occupies most of the area in the RF energy scavenging system,
reduction in antenna size is necessary in order to design a miniaturized system.
Several antennas with different characteristics are proposed in the second stage.
Firstly, ultra-wideband microstrip antennas printed on a thin substrate with a
thickness of 0.2 mm are designed for both half-wave and full-wave wideband RF
energy scavenging. Ambient RF power is distributed over a wide range of frequency
bands. A wideband RF energy scavenging system can extract power from different
frequencies to maximize the input power, hence, generating sufficient output power
for charging devices. Wideband operation with 4 GHz bandwidth is obtained by the
proposed microstrip antenna. Secondly, multi-band planar inverted-F antennas with
low profile are proposed for frequency bands of GSM 900, DCS 1800 and Wi-Fi 2.4
GHz, which are the three most promising frequency bands for RF energy scavenging.
Compared with previous designs, the triple band antenna has smaller dimensions
with higher antenna gain. Thirdly, a novel miniature inverted-F antenna without
empty space covering Wi-Fi 2.4 GHz frequency band is presented dedicated for
indoor RF energy scavenging. The antenna has dimensions of only 10 × 5 × 3.5
mm3 with appreciable efficiency across the operating frequency range.
In the final stage, a passive CMOS charge pump rectifier in 0.35 μm CMOS
technology is proposed for AC to DC conversion. Bootstrapping capacitors are
employed to reduce the effective threshold voltage drop of the selected MOS
transistors. Transistor sizes are optimized to be 200/0.5 μm. The proposed rectifier
achieves improvements in both power conversion efficiency and voltage conversion
efficiency compared with conventional designs.
The design strategies proposed in this thesis contribute towards the realization of
miniaturized RF energy scavenging systems
Development of pyroelectric sensor integrated with two-dimensional transistor
Full text linkProgress in the complementary metal-oxide semiconductors (CMOS) integrated circuit technology and the acceptance of silicon based microelectronics have revolutionised the electronics world. Advancement in human endeavour relies on the improvement of our processes and the discovery of new materials with beneficial properties. The advent of two dimensional (2D) materials has created exciting new possibilities. Possibilities that not only include the replacement of silicon in microelectronics but also for application in other areas such as photonics. Also, the quest to move beyond silicon and its oxide has seen increased interest in potential high dielectric and/or pyroelectric materials.
The primary motivation for this work is to improve the output of Pyreos’s lead zirconium titanate (PZT) based pyroelectric sensor by integrating the device with a 2D tungsten diselenide (WSe2) field effect transistor (FET). A systematic approach has been taken to realise this goal by first exploring the material properties individually.
From varied literature, two dimensional (2D) materials have shown promise in both electrical and optical properties. In this work, studies have been conducted on the 2D material WSe2, which has been deposited via exfoliation and pulse laser deposition (PLD). Though PLD WSe2 offers good control during deposition, our findings show that the exfoliated WSe2 has better electrical and optical properties. The field effect mobility calculated for the exfoliated WSe2 and PLD-WSe2 FET is 12.06 cm2/Vs and 5.66 × 10-2 cm2/Vs respectively. A maskless lithography method has been employed for the fabrication of the devices and tests were carried out using a Keithley parameter analyser, Raman and photoluminescence (PL) spectroscopy. The PL spectra showed that the exfoliated WSe2 has a bandgap of 1.6 eV while the PLD WSe2 possessed no bandgap, thereby limiting its applications.
We studied the breakdown characteristics of a 20 nm anodic tantalum, a potential high dielectric gate oxide. At an electric field of 1.5 MV/cm, the leakage current extracted for the as-deposited, 200 °C and 400 °C annealed anodic tantalum are 10-5, 10-2 and 1 A/cm2 respectively while the breakdown field is 5.4, 5.1 and 3.3 MV/cm respectively. Upon integration of the anodic tantalum with a WSe2 FET, a field effect mobility of 0.9 cm2V-1s-1 has been realised.
Analysis has also been conducted on the PZT pyroelectric device to understand its surface profile using energy backscatter diffraction (EBSD) and a factorial design of experiment. From the EBSD analysis, the sputtered PZT possesses a grain size of about 100 nm and exists in tetragonal crystals having good correlation for an orientation along the [111] direction normal to the surface. Results and understanding from the factorial design of the experiment enabled the integration of PZT with a WSe2 FET. While the standalone PZT based sensor possesses a 1 nA/mm2 current density output, the integrated PZT based WSe2 FET has an output of 16 nA/mm2. This improvement in the overall current output is over ten orders of magnitude. Thus, we have succeeded in amplifying the output of the PZT pyroelectric based sensor.
The experimental outcomes of this thesis would help the research community in developing higher performing integrated sensors and possibly exposing other areas of interest on inexpensive and simple methods for producing materials with high dielectric constants
- …
