Berlin, Techn. Univ., Diss., 2004. / Computerdatei im Fernzugriff.

Berlin, Techn. Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Berlin, Techn. Univ., Diss., 2003. / Computerdatei im Fernzugriff.

The multi-order response of the tuned secondary circuit of a Tesla transformer, following impulse excitation from its tuned primary circuit, is presented and analysed at the fundamental resonant frequency and at higher-order mode frequencies. A novel way of modifying the frequency response of the secondary coil is then investigated by utilising a technique normally applied to the design of a certain type of filter known as a helical filter. In general, these are used in radio and microwave frequency circuits in order to pass certain frequencies with little attenuation whilst significantly attenuating other frequencies. Design techniques, developed over several decades, modify and optimise the performance of such filters. The frequency response of the helical filter is modified by altering the geometry of the helical resonator component therein, which is typically in the form of an air-cored single-layer solenoid. A Tesla transformer whose secondary is constructed to be some form of single-layer solenoidal winding resonates at its designed frequency - its fundamental mode - but also at non-integer harmonics (higher-order anharmonic frequencies, also known as overtones). Those multi-order oscillatory voltages and currents energised in the secondary circuit have been identified and measured and research has determined the fundamental and higher-order mode frequencies and amplitudes for various experimental secondary winding configurations derived from helical filter design techniques. Applied to the Tesla transformer secondary winding, such techniques lead to a new design with a performance that is improved by the suppression of higher- order anharmonic frequencies whilst imparting little change to the fundamental response. It is anticipated that this feature will lead to Tesla transformers which exhibit enhanced spectral purity and which will be better suited to use in certain pulsed power applications than conventionally wound designs.

The plasma opening switch (POS) is used in pulsed power systems where a very fast opening and high current switch is required. Plasma is injected into the switch, which carries a large conduction current, before it opens in a process that lasts for a few nanosecond and transfers the current to a parallel-connected load at a much increased voltage and with a much shorter rise time. The conduction and opening times of the switch are dependent on plasma parameters such as the distribution, speed and species, all of which are determined by the plasma source. Most of the earlier reported work involves large dimension POSs and a correspondingly high input current (more than 100 kA) and uses carbon plasma. One main objective of the present research was to achieve a low input current (20 kA) and miniaturised POS by using hydrogen plasma rather than carbon plasma on account of its lower mass. A cable gun was selected for producing the plasma, since although this produces both hydrogen and carbon plasma these arise different times during its operation. For the present application a Tesla transformer was used in preference to a Marx generator to produce an initial high voltage pulse for the system, on the basis of its simpler design and cost effectiveness. This transformer together with an associated water PFL (pulse forming line) and pressurised switch was capable of producing a load current in excess of 20 kA with a rise time of 53 ns, which was fed through the POS to the final load. Special diagnostics arrangements were necessary to measure the fast high current and voltage pulse a in nonintrusive way. Faraday cups and a high speed camera were used to measure the plasma parameters. The overall system built (i.e. including the POS) is capable of producing a 22 kA current with a rise time of 5 ns, and of generating a power of more than 10 GW. Much of the work detailed in the thesis has already been presented in peer reviewed journals and at prestigious international conferences.

A Tesla-Blumlein PFL-Bipolar pulsed power generator, has been successfully designed, manufactured and demonstrated. The compact Tesla transformer that it employs has successfully charged capacitive loads to peak voltages up to 0.6 MV with an overall energy efficiency in excess of 90%. The Tesla driven Blumlein PFL generator is capable of producing a voltage impulse approaching 0.6 MV with a rise time close to 2 ns, generating a peak electrical power of up to 10 GW for 5 ns when connected to a 30 Ω resistive load. Potentially for medical application, a bipolar former has been designed and successfully implemented as an extension to the system and to enable the generation of a sinusoid-like voltage impulse with a peak-to-peak value reaching 650 kV and having a frequency bandwidth beyond 1 GHz. This thesis describes the application of various numerical techniques used to design a successful generator, such as filamentary modelling, electrostatic and transient (PSpice) circuit analysis, and Computer Simulation Technology (CST) simulation. All the major parameters of both the Tesla transformer, the Blumlein pulse forming line and the bipolar former were determined, enabling accurate modelling of the overall unit to be performed. The wide bandwidth and ultrafast embedded sensors used to monitor the dynamic characteristics of the overall system are also presented. Experimental results obtained during this major experimental programme are compared with theoretical predictions and the way ahead towards connecting to an antenna for medical application is considered.

Organizational culture is a product of both internal and external factors. Leaders sometimes attempt to change culture using a variety of mechanisms, while the effects of external environment simultaneously exert influence. The external environment effects can be especially pronounced when comparing a traditional, Midwestern automotive firm (General Motors) with a Silicon Valley automotive startup (Tesla). A study was conducted to compare the social system of these two automakers and to identify some of the factors, both internal and external, shaping their culture. Data was collected on the employment history of engineers and managers using the social networking platform LinkedIn.com. Similarly, publicly-posted employee reviews were collected from the website Glassdoor.com and analyzed using a novel method for classifying and analyzing openorm written survey responses. Together, these records paint a picture of the employee perceptions of culture for both companies, the breadth of external experience represented in their workforces, and the tendency to fill management positions from internal candidates. The results suggest that external environment has broad effects on workforce experience, thereby creating certain cultural attributes such as loyalty or a drive to innovate. The results also suggest that promoting internal candidates more often does not necessarily lead to employee perception of better career opportunities. Taken together, the results reinforce but expand traditional views of organizational culture and call for further study on the matter across more industry groups.

Vehicular communication networking is a promising approach for facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. However, it is subject to various malicious abuses and security attacks which hinder it from practical implementation. In this study, we propose a novel security protocol called GSIS based on group signature and identity-based signature schemes to meet the unique requirements of vehicular communication networks. The proposed protocol not only guarantees security and anonymity, but also provides easy traceability when the identity of the sender of a message has to be revealed by the authority. However, the cryptographic operations introduced in GSIS as well as the existing public key based message authentication protocols incur some computation and communication overhead which affect the system performance. Simulation results show that the GSIS security protocol is only applicable under light traffic conditions in terms of the message end to end delay and message loss ratio. Both the GSIS protocol and the existing public key based security protocols have to sign and verify all the received messages with asymmetric algorithms. The PKI based approach also has to attach a public key certificate in each packet. Therefore, to enhance the system performance and mitigate the message overhead without compromising the security requirement, this study further proposes an enhanced TESLA based Secure Vehicular Communication (TSVC) protocol. In TSVC, the communication overhead can be significantly reduced due to the MAC tag attached in each packet and only a fast hash operation is required to verify each packet. Simulation results show that TSVC maintains acceptable message latency, using a much smaller packet size, and significantly reduces the message loss ratio as compared to GSIS and existing PKI based protocols, especially when the traffic is denser. We conclude that the proposed approach could serve as good candidate for future vehicular communication networks.

Vehicular communication networking is a promising approach for facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. However, it is subject to various malicious abuses and security attacks which hinder it from practical implementation. In this study, we propose a novel security protocol called GSIS based on group signature and identity-based signature schemes to meet the unique requirements of vehicular communication networks. The proposed protocol not only guarantees security and anonymity, but also provides easy traceability when the identity of the sender of a message has to be revealed by the authority. However, the cryptographic operations introduced in GSIS as well as the existing public key based message authentication protocols incur some computation and communication overhead which affect the system performance. Simulation results show that the GSIS security protocol is only applicable under light traffic conditions in terms of the message end to end delay and message loss ratio. Both the GSIS protocol and the existing public key based security protocols have to sign and verify all the received messages with asymmetric algorithms. The PKI based approach also has to attach a public key certificate in each packet. Therefore, to enhance the system performance and mitigate the message overhead without compromising the security requirement, this study further proposes an enhanced TESLA based Secure Vehicular Communication (TSVC) protocol. In TSVC, the communication overhead can be significantly reduced due to the MAC tag attached in each packet and only a fast hash operation is required to verify each packet. Simulation results show that TSVC maintains acceptable message latency, using a much smaller packet size, and significantly reduces the message loss ratio as compared to GSIS and existing PKI based protocols, especially when the traffic is denser. We conclude that the proposed approach could serve as good candidate for future vehicular communication networks.

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