Tunable Sub-Nanosecond Ultra Wideband Narrow Pulse Generator For Microwave Imaging

In recent years, the Ultra Wideband (UWB) technology-based systems exhibited higher performance metrics over narrow band communication systems. The UWB microwave imaging is an emerging application in the biomedical, object detection, and ranging fields. The Narrowband Pulse Generator (NPG) is an essential element of any UWB imaging system and its characteristics partially determine the overall performance of the system. Numerous NPG designs have been developed for specific types of applications and most of them designed for CMOS technology integration. Additionally, they lack the flexibility of user pulse width tuning. In this research, the main contribution is the design of a low-cost sub-nanosecond NPG with many features like tunable pulse duration and to generate a pulse shape with ultrafast rise and fall times that could enhance the quality of UWB microwave images. The design aims to reduce the NPG cost with the use of off-the-shelf components. The very low pulse transition times led to higher BW values in the frequency spectrum and would presage to enhance the quality of images been reconstructed from UWB radar imaging systems. The shortest pulse provided by the proposed NPG is about 820 ps with a fall time of about 64 ps and a pulse level of 200 mV (single-ended). The aforementioned pulse data has been simulated in a locally developed image reconstruction algorithm (EDAS) to detect hypothetical objects and the resultant images show significant quality enhancement in comparison to a Gaussian pulse (or its derivative) with an equivalent duration. Image entropy values have been reduced from 248 to 51. This simulation validated the concept of trapezoidal pulse (or its derivative) influence on image resolution. For a further validation, an experimental UWB imaging system has been configured with a circular array of antennas to detect and locate different targets made of selected materials. The proposed NPG pulses have been applied, after amplification, to the above system. The reconstructed images compared to those obtained from other pulse sources like the VNA and PPG. The images generated from the proposed NPG show better quality in most cases. Compared to VNA images, image entropy values dropped from 63.66 to 43.23 for clay rod, and from 143.77 to 46.50 for an Aluminum rod. The promising results of the proposed NPG can hopefully be applied as a useful tool to obtain higher resolution images and better target detection accuracy in many industrial applications

Generadores de pulso del orden de nanosegundos para control de calidad y diagnosis de las cámaras de telescopios Cherenkov

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Aplicada III (Electricidad y Electrónica), leída el 30-11-2015Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Development of High Power Square Wave Electroporators

High power microsecond and submicrosecond electric pulse generation and the devices for pulse generation (electroporators) development and application problem is focused in the dissertation. The electric field technologies, pulse forming circuits and circuit transient process compensation methods are investigated. The introduction presents the investigated problem, objects of research, importance of the dissertation, describes research methodology, scientific novelty and the defended statements. In the first chapter the scientific publications in the area of the high power electric pulses generation and application for biological cell permeabilization are overviewed. The influence of the pulse parameters on the biological effects is analysed. The requirements for the electroporators are identified. In the second chapter the prototypes of the high power square wave 5 μs – 10 ms up to 4 kV, 100 A and 200 ns – 5 μs up to 8 kV, 100 A electroporators are developed. The models for investigation of the transient processes in the circuits and the solutions for compensation are overviewed. The adequacy of the proposed models to the experimental results is analysed. The interdigitated microelectrodes structure for planar electroporation is proposed. The resultant electric field distribution and the cell medium temperature rise due to the Joule heating are investigated. The third chapter is focused on the experimental application of the developed high power microsecond and submicrosecond electroporators prototypes in biological experiments. The experimental results with different cell types are presented and conclusions are formed. Research results on the dissertation subject are published in 5 scientific articles: 3 articles – Thomson Reuters ISI Web of Science database journals with impact factor, 2 – publications referenced and abstracted in other international databases, 4 presentations have been made in international conferences in Lithuania, Netherlands, Germany and Japan

New SOS diode pumping circuit based on an all-solid-state spiral generator for high-voltage nanosecond applications

Semiconductor opening switch (SOS) diodes are capable to switch currents with a density of more than 1 kA/cm 2 and withstand nanosecond pulses with an amplitude of up to 1 MV. SOS diodes, however, require a specific pumping circuit that must simultaneously provide forward and reverse pumping currents with a time of ∼ 500 and ∼ 100 ns, respectively. Such a pumping circuit with energies > 1 J typically requires a gas-discharge switch or a low-efficient solid-state solution. This study proposes a novel approach to pumping SOS diodes based on a spiral generator (SG) (also known as a vector inversion generator). Due to its wave characteristics, the SG produces a bipolar current discharge that meets the time duration and current amplitude required to pump an SOS diode. Moreover, the initial pulse from the spiral typically has a relatively low current amplitude compared to the opposite polarity secondary pulse, so the SOS diode can operate at very high efficiencies. This idea has been tested using an all-solid-state SG coupled with large-area SOS diodes (1 cm 2 ). With this combination, a voltage pulse of 62 kV having a rise time of only 11 ns was obtained on an open circuit load (3 pF, 1 M Ω ). The experiments were highly repeatable, with no damage to the components despite multiple tests. There is significant scope to further improve the results, with simple alterations to the SG