36 results found
Kkelis G, Yates DC, Mitcheson PD, 2017, Class-E half-wave zero dv/dt rectifiers for inductive power transfer, IEEE Transactions on Power Electronics, Vol: 32, Pages: 8322-8337, ISSN: 0885-8993
This paper analyses and compares candidate zero dv/dt half-wave Class-E rectifier topologies for integration into multi-MHz inductive power transfer (IPT) systems. Furthermore, a hybrid Class-E topology comprising advantageous properties from all existing Class-E half-wave zero dv/dt rectifiers is analysed for the first time. From the analysis, it is shown that the hybrid Class-E rectifier provides an extra degree of design freedom which enables optimal IPT operation over a wider range of operating conditions. Furthermore, it is shown that by designing both the hybrid and the current driven rectifiers to operate below resonance provides a low deviation input reactance and inherent output voltage regulation with duty cycle allowing efficient IPT operation over wider dc load range than would otherwise be achieved. A set of case studies demonstrated the following performances: 1) For a constant dc load resistance, a receiving end efficiency of 95% was achieved when utilising the hybrid rectifier, with a tolerance in required input resistance of 2.4% over the tested output power range (50W to 200W). 2) For a variable dc load in the range of 100% to 10%, the hybrid and current driven rectifiers presented an input reactance deviation less than 2% of the impedance of the magnetising inductance of the inductive link respectively and receiving end efficiencies greater than 90%. 3) For a constant current in the receiving coil, both the hybrid and the current driven rectifier achieve inherent output voltage regulation in the order of 3% and 8% of the nominal value respectively, for a variable dc load range from 100% to 10%.
Aldhaher S, Mitcheson PD, Yates DC, 2016, Load-independent Class EF inverters for inductive wireless power transfer, 2016 IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE
This paper will present the modelling, analysis and design of a load-independent Class EF inverter. This inverter is able to maintain zero-voltage switching (ZVS) operation and produce a constant output current for any load value without the need for tuning or replacement of components. The load-independent feature of this inverter is beneficial when used as the primary coil driver in multi megahertz high power inductive wireless power transfer (WPT) applications where the distance between the coils and the load are variable. The work here begins with the traditional load-dependent Class EF topology for inversion and then specifies the criteria that are required to be met in order achieve load-independence. The design and development of a 240W load-independent Class EF inverter to drive the primary coil of a 6.78MHz WPT system will be discussed and experimental results will be presented to show the load-independence feature when the distance between the coils of the WPT system changes.
Goverdovsky V, Yates DC, Willerton M, et al., 2016, Modular Software-Defined Radio Testbed for Rapid Prototyping of Localization Algorithms, IEEE Transactions on Instrumentation and Measurement, Vol: 65, Pages: 1577-1584, ISSN: 1557-9662
A fully synchronized modular multichannel software-defined radio (SDR) testbed has been developed for the rapid prototyping and evaluation of array processing algorithms. Based on multiple universal software radio peripherals, this testbed is low cost, wideband, and highly reconfigurable. The testbed can be used to develop new techniques and algorithms in a variety of areas including, but not limited to, direction finding, source triangulation, and wireless sensor networks. A combination of hardware and software techniques is presented, which is shown to successfully remove the inherent phase and frequency uncertainties that exist between the individual SDR peripherals. The adequacy of the developed techniques is demonstrated through the application of the testbed to super-resolution direction finding algorithms, which rely on accurate phase synchronization.
Aldhaher S, Mitcheson PD, Yates DC, 2016, Design and Development of a Class EF<sub>2</sub> Inverter and Rectifier for Multi-megahertz Wireless Power Transfer Systems, IEEE Transactions on Power Electronics, Vol: 31, Pages: 8138-8150, ISSN: 1941-0107
This paper presents the design and implementation of a Class EF2 inverter and Class EF2 rectifier for two -W wireless power transfer (WPT) systems, one operating at 6.78 MHz and the other at 27.12 MHz. It will be shown that the Class EF2 circuits can be designed to have beneficial features for WPT applications such as reduced second-harmonic component and lower total harmonic distortion, higher power-output capability, reduction in magnetic core requirements and operation at higher frequencies in rectification compared to other circuit topologies. A model will first be presented to analyze the circuits and to derive values of its components to achieve optimum switching operation. Additional analysis regarding harmonic content, magnetic core requirements and open-circuit protection will also be performed. The design and implementation process of the two Class-EF2-based WPT systems will be discussed and compared to an equivalent Class-E-based WPT system. Experimental results will be provided to confirm validity of the analysis. A dc-dc efficiency of 75% was achieved with Class-EF2-based systems.
Aldhaher S, yates D, Mitcheson P, 2015, Modelling and Analysis of Class EF and Class E/F Inverters with series-tuned resonant networks, IEEE Transactions on Power Electronics, Vol: 31, Pages: 3415-3430, ISSN: 0885-8993
Class EF and Class E/F inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their efficiency, output power and power output capability can be higher in some cases than the Class E inverter. Little is known about these inverters and no attempt has been made to provide an in depth analysis on their performance. The design equations that have been previously derived are limited and are only applicable under certain assumptions. This paper is the first to provide a comprehensive set of analytical analysis of Class EF and Class E/F inverters. The Class EF2 inverter is then studied in further detail and three special operation cases are defined that allow it to either operate at maximum power-output capability, maximum switching frequency or maximum output power. Final design equations are provided to allow for rapid design and development. Experimental results are provided to confirm the accuracy of the performed analysis based on a 23W Class EF2 inverter at 6.78MHz and 8.60MHz switching frequencies. The results also show that the Class EF2 inverter achieved an efficiency of 91% compared to a 88% efficiency when operated as a Class E inverter.
Kwan CH, Kkelis G, Aldhaher S, et al., 2015, Link efficiency-led design of mid-range inductive power transfer systems, Pages: 1-7
Aldhaher S, Kkelis G, Yates DC, et al., 2015, Class EF2 inverters for wireless power transfer applications, Pages: 1-4
Lawson J, Mitcheson PD, Yates DC, 2015, Efficient artificial magnetic conductor shield for wireless power, Wireless Power Transfer Conference (WPTC), 2015 IEEE
Artificial magnetic conductors (AMC) offer a solu-tion to increasing link efficiency in inductive power transfer (IPT)while reducing magnetic fields outside the air gap. A practicaldesign for an artificial magnetic conductor, suitable for use asa shield for inductive power transfer, is presented. The AMCmakes use of a ferrite substrate and lumped capacitor loading. Amodel of the plane wave behaviour of the structure is comparedto simulation and the performance of the AMC compared toother shielding solutions, in an IPT scenario. The plane wavebehaviour is found not to provide a good prediction of the AMCbehaviour in the IPT scenario. The AMC shield is found to offerthe greatest link efficiency, in the IPT scenario.
Kkelis G, Yates DC, Mitcheson PD, 2015, Comparison of Current Driven Class-D and Class-E Half-Wave Rectifiers for 6.78 MHz High Power IPT Applications, 3rd IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE
Jiang H, Kiziroglou ME, Yates DC, et al., 2015, A NON-HARMONIC MOTION-POWERED PIEZOELECTRIC FM WIRELESS SENSING SYSTEM, 18th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), Publisher: IEEE, Pages: 710-713
Carvalho NB, Georgiadis A, Costanzo A, et al., 2014, Wireless Power Transmission: R&D Activities Within Europe, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol: 62, Pages: 1031-1045, ISSN: 0018-9480
We report upon a recently developed long range inductive power transfer system (IPT) designed to power remote sensors with mW level power consumption at distances up to 7 m. In this paper an inductive link is established between a large planar (1 × 1 m) transmit coil (Tx) and a small planer (170 × 170 mm) receiver coil (Rx), demonstrating the viability of highly asymmetrical coil configurations that real-world applications such as sensor networks impose. High Q factor Tx and Rx coils required for viable power transfer efficiencies over such distances are measured using a resonant method. The applicability of the Class-E amplifier in very low magnetic coupling scenarios and at the high frequencies of operation required for high Q operation is demonstrated by its usage as the Tx coil driver.
Kkelis G, Lawson J, Yates DC, et al., 2014, Integration of a Class-E Low dv/dt Rectifer in a Wireless Power Transfer System, IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE, Pages: 68-71
Kwan CH, Lawson J, Yates DC, et al., 2014, Position-insensitive long range inductive power transfer, 14th International Conference on Micro- and Nano-Technology for Power Generation and Energy Conversion Applications (PowerMEMS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Jiang H, Kiziroglou ME, Yates DC, et al., 2014, A Piezoelectric Pulse Generator and FM Transmission Circuit for Self-Powered BSN Nodes, Wearable and Implantable Body Sensor Networks (BSN), 2014 11th International Conference on, Publisher: IEEE, Pages: 1-5
Jiang H, Kiziroglou ME, D C Yates, et al., 2014, A Motion-Powered Piezoelectric Pulse Generator for Wireless Sensing via FM Transmission, IEEE Internet of Things Journal, Vol: Under Review
Pinuela M, Yates DC, Lucyszyn S, et al., 2013, Maximizing DC-to-Load Efficiency for Inductive Power Transfer, IEEE Transactions on Power Electronics, Vol: 28, Pages: 2437-2447, ISSN: 0885-8993
Inductive Power Transfer (IPT) systems for transmitting tens to hundreds of watts have been reported for almost a decade. Most of the work has concentrated on the optimization of the link efficiency and have not taken into account the efficiency of the driver. Class-E amplifiers have been identified as ideal drivers for IPT applications, but their power handling capabilityat tens of MHz has been a crucial limiting factor, since the load and inductor characteristics are set by the requirements of the resonant inductive system. The frequency limitation of the driver restricts the unloaded Q factor of the coils and thus the link efficiency. With a suitable driver, copper coilunloaded Q factors of over 1,000 can be achieved in the low MHz region, enabling a cost-effective high Q coil assembly. The system presented in this paper alleviates the use of heavy andexpensive field-shaping techniques by presenting an efficient IPT system capable of transmitting energy with a dc-to-load efficiency above 77% at 6 MHz across a distance of 30 cm. To the authorsknowledge this is the highest dc-to-load efficiency achieved for an IPT system without introducing restrictive coupling factor enhancement techniques.
Pinuela M, Yates DC, Mitcheson PD, et al., 2013, London RF Survey for Radiative Ambient RF Energy Harvesters and Efficient DC-load Inductive Power Transfer, 7th EurAAP European Conference on Antennas and Propagation (EUCAP 2013), Pages: 2839-2843
Pinuela M, Yates DC, Mitcheson PD, et al., 2012, Current State of Research at Imperial College London in RF Harvesting and Inductive Power Transfer, 2nd International Workshop on Wireless Energy Transport and Harvesting, Pages: 1-4
This paper presents simulation and experimental results for ambient RF energy harvesting and Inductive Power Transfer systems. End-to-end and dc-load efficiency measurements and calculations were performed to demonstrate the capabilities of both systems, respectively. An RF spectral survey was conducted across all the 270 underground stations in London. DTV, GSM900, GSM1800 and 3G were selected as the highest contributors and single banded rectennas were fabricated for all frequencies. Ground level measurements demonstrate that more than 50 stations have suitable channel power levels per band to allow ambient RF energy harvesting. Efficiencies of up to 40% were achieved with a single banded rectenna operating at GSM 900, and efficiencies higher than 20% were achieved for TV and 3G. Furthermore a high frequency, semi-resonant Class-E driver was used to transfer 60 W of power across a 30 cm distance with a dc-load efficiency of 66%.
He C, Kiziroglou ME, Yates DC, 2011, A MEMS Self-Powered Sensor and RF Transmission Platform for WSN Nodes, IEEE Sensors Journal, Vol: 11, Pages: 3437-3445
He C, Kiziroglou ME, Yates DC, et al., 2011, A MEMS self-powered sensor and RF transmission platform for WSN nodes, Sensors Journal, IEEE, Vol: 11, Pages: 3437-3445, ISSN: 1530-437X
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
He C, Kiziroglou ME, Yates DC, et al., 2010, MEMS energy harvester for wireless biosensors, Pages: 172-175
The electroencephalogram (EEG) is a classic noninvasive method for measuring a person's brainwaves and is used in a large number of fields: from epilepsy and sleep disorder diagnosis to brain–computer interfaces (BCIs). Electrodes are placed on the scalp to detect the microvolt-sized signals that result from synchronized neuronal activity within the brain. Current long-term EEG monitoring is generally either carried out as an inpatient in combination with video recording and long cables to an amplifier and recording unit or is ambulatory. In the latter, the EEG recorder is portable but bulky, and in principle, the subject can go about their normal daily life during the recording.
Yates DC, Holmes AS, 2009, Preferred Transmission Frequency for Size-Constrained Ultralow-Power Short-Range CMOS Oscillator Transmitters, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS, Vol: 56, Pages: 1173-1181, ISSN: 1549-8328
He C, Arora A, Kiziroglou ME, et al., 2009, MEMS Energy Harvesting Powered Wireless Biometric Sensor, Wearable and Implantable Body Sensor Networks, 2009. BSN 2009. Sixth International Workshop on, Pages: 207-212
One of the main challenges in developing wireless biometric sensors is the requirement for integration of various systems into a very compact device. Such systems include sensing units, conditioning electronics, transmitters and power supplies. In this work, a novel system integration architecture is presented. A unique feature of this new architecture is that the sub-systems are selected and designed for direct output-to-input connection. An array of active pH sensors is used to transform a pH level to an electrical potential in the range of 0 - 2 Volts. This signal is amplified by an electrostatic energy harvester suitable for human motion operation. The amplified signal drives a custom LC transmitter specially designed to suit the harvester output. A system of notable simplicity is achieved and may serve as a demonstrator for other wireless sensors.
Casson AJ, Yates DC, Patel S, et al., 2007, Algorithm for AEEG data selection leading to wireless and long term epilepsy monitoring, Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE, Pages: 2456-2459, ISSN: 1557-170X
Yates D C, Casson A, Rodriguez-Villegas E, 2007, Low Power Technology for Wearable Cognition Systems
Casson AJ, Yates DC, Patel S, et al., 2007, An analogue bandpass filter realisation of the Continuous Wavelet Transform, Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE, Publisher: IEEE, Pages: 1850-1854, ISSN: 1557-170X
Yates DC, Casson AJ, Rodriguez-Villegas E, 2007, Low power technology for wearable cognition systems, BERLIN, 3rd International Conference on Foundation of Augmented Cognition, Publisher: SPRINGER-VERLAG, Pages: 127-136, ISSN: 0302-9743
This paper analyses a key tradeoff behind miniature devices intended to monitor cognition-related parameters. These devices are supposed to be worn by people that would otherwise be carrying on a normal life and this factor imposes important constraints in the design. They have to be wireless, wearable, discrete, low maintenance and reliable. In order to reduce power intelligence will be built into the sensors aiming to reduce the data transmission to only that information that it is strictly necessary. This intelligence will be in the form of an algorithm which will be required to be implemented in electronic circuits as part of the system. The complexity of the algorithm affects the complexity of the electronics and hence the power consumption. This, in turn affects the size of the battery and the overall size of the device. For the sensor to be low maintenance the device must operate for extended periods from the battery, adding more constraints to the power consumption of the electronic circuits. The battery must be kept small so that the overall size of the device is small and lightweight enough to be worn on the body and the more discrete the device the higher consumer compliance. A tradeoff has to be met between the algorithm complexity, the power consumption of the electronics required to realize the latter, the power consumption required to transmit data and the battery size and lifetime.
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