Aspects of magnetic pulse compression and pulse sharpening

Imperial Users onl

Theoretical and experimental studies on nonlinear lumped element transmission lines for RF generation

Ph.DDOCTOR OF PHILOSOPH

The manufacture and characterisation of microscale magnetic components.

Abstract unavailable please refer to PD

Investigation of the high-frequency effects in Mn-Zn ferrites for EMI filter applications

This thesis focuses on the analysis, identification, and experimental investigation of the high-frequency effects encountered within the magnetic core when used in high-frequency, high-power electromagnetic interference (EMI) filters. These applications require cost-optimized, high-performance, and high-power-density magnetic components. As the manufacturers’ material specifications usually do not provide sufficient information to optimize the design, this thesis develops new methods to determine the high-frequency properties of Mn-Zn ferrites up to 20 MHz. Complex permeability and permittivity, as well as specific power loss, are typically provided as one value by the manufacturer, regardless of the core shape and size. Therefore, various magnetic materials are characterized for their complex permeability and permittivity. These two parameters are of differentiated physical origins, and so two independent measurement fixtures are developed and built. The impacts of physical size, temperature and force on complex permeability and permittivity are also considered. The detailed analysis of magnetic flux is introduced based on a 1-D analytical model, a novel shell-based transmission-line model, and finally, based on the FEM and Maxwell 3D eddy-current field solver. These models are used to calculate the complex permeability characteristics for various core sizes made of two materials: 3E10 and 3F36. A complete experimental validation is presented for the calculated values. The analytical methods show a very good correlation with the experimental measurements. The novel shell-based transmission-line model has the best accuracy, and the calculation can be implemented into simulation of a higher-order system or into any other magnetic component design algorithm. Flux verification methods are developed which use precisely-bored cores to accurately predict flux distribution. The results of the flux propagation, starting from the simple three-hole model up to the advanced four-section model confirm that the magnetic flux distribution is affected by frequency-dependent dynamic effects. Flux distributions was experimentally measured for T50 and T80 cores made of 3E10 and 3F36 material. Results are consistent with the FEM simulations and help in the development of a more accurate analytical model. A novel laminated-core common mode choke (CMC) is developed and presented in this thesis. The presented CMC core structure divides the conduction path into sub-regions which allowing for the reduction of the high-frequency effects. Laminated cores, made of several Mn-Zn ferrite materials, were tested and special attention is paid to the effect of magnetic material selection, core size and lamination thickness on the core high-frequency performance. Common mode insertion loss characteristic for the novel CMC shows that laminated ferrite structure give rise to significant attenuation improvement

Design for Electromagnetic Compatibility--In a Nutshell

This open access book provides practicing electrical engineers and students a practical – and mathematically sound – introduction to the topic of electromagnetic compatibility (EMC). The author enables readers to understand better how to overcome commonly failed EMC tests for radiated emission, radiated immunity, and electrostatic discharge (ESD), while providing concrete EMC design guidelines. The book also presents an overview of EMC standards and regulations and how to test for a global market access

Linearization using Digital Predistortion of a High-Speed, Pulsed, Radio Frequency Power Amplifier for VHF Radar Depth-Sounder Systems

Depth-sounding radar systems provide the scientific data that are useful in modeling polar ice sheets and predicting sea-level rise. These radars are typically deployed on crewed aircraft; however, crewed missions over polar regions are difficult and dangerous. Thus, CReSIS is developing uninhabited aerial vehicles (UAVs) from which fine-resolution measurements can be made over vast areas. These fine-resolution measurements require highly linear power amplifiers (PAs) to create low range side-lobe levels. However, highly linear PAs are typically less efficient and require large and bulky heat sinks for heat dissipation, which increases the payload weight and decreases flight time. Furthermore, the linear FM chirp signal used for these radar systems creates Fresnel ripples and side-lobes will be generated when there are deviations from the ideal rectangular spectrum amplitude even with efficient windowing techniques, such as a Tukey window. Therefore, a 100 W, high-speed, pulsed, VHF power amplifier was developed and linearized using memoryless digital predistortion (DP) to obtain high linearity and high efficiency. The DP linearization decreased near-range side-lobe levels 11 dB from -46 dBc to -57 dBc, with a maximum reduction in the far-range side-lobe levels of 17 dB over the Tukey (transmit) and Blackmann2 (receive) windowing alone. The high-speed switching circuit reduced current consumption to 117 mA (or 3.28 W at +28 V) for a 10-us pulse at 1-kHz PRF

High Efficiency and High Sensitivity Wireless Power Transfer and Wireless Power Harvesting Systems.

In this dissertation, several approaches to improve the efficiency and sensitivity of wireless power transfer and wireless power harvesting systems, and to enhance their performance in fluctuant and unpredictable circumstances are described. Firstly, a nonlinear resonance circuit described by second-order differential equation with cubic-order nonlinearities (the Duffing equation) is developed. The Duffing nonlinear resonance circuit has significantly wider bandwidth as compared to conventional linear resonators, while achieving a similar level of amplitude. The Duffing resonator is successfully applied to the design of WPT systems to improve their tolerance to coupling factor variations stemming from changes of transmission distance and alignment of coupled coils. Subsequently, a high sensitivity wireless power harvester which collects RF energy from AM broadcast stations for powering the wireless sensors in structural health monitoring systems is introduced. The harvester demonstrates the capability of providing net RF power within 6 miles away from a local 50 kW AM station. The aforementioned Duffing resonator is also used in the design of WPH systems to improve their tolerance to frequency misalignment resulting from component aging, coupling to surrounding objects or variations of environmental conditions (temperature, humidity, etc.). At last, a rectifier array circuit with an adaptive power distribution method for wide dynamic range operation is developed. Adaptive power distribution is achieved through impedance transformation of the rectifiers’ nonlinear impedance with a passive network. The rectifier array achieves high RF-to-DC efficiency within a wide range of input power levels, and is useful in both WPT and WPH applications where levels of the RF power collected by the receiver are subject to unpredictable fluctuations.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133338/1/tinyfish_1.pd

Design for Electromagnetic Compatibility--In a Nutshell

This open access book provides practicing electrical engineers and students a practical – and mathematically sound – introduction to the topic of electromagnetic compatibility (EMC). The author enables readers to understand better how to overcome commonly failed EMC tests for radiated emission, radiated immunity, and electrostatic discharge (ESD), while providing concrete EMC design guidelines. The book also presents an overview of EMC standards and regulations and how to test for a global market access