A w-band quasi-optical mode converter and gyro-BWO experiment

High power coherent microwave sources at shorter wavelengths (mm and sub-mm) are in great demand, especially in the fields of plasma physics, remote sensing and imaging and for electron spin resonance spectroscopy. Gyro-devices are by their nature particularly suited to this type of application due to the fast-wave cyclotron resonance maser instability, which is capable of producing high power radiation at frequencies that prove challenging for other sources. A W-band gyro-device based on a cusp electron beam source with a helically corrugated interaction region is currently under development to provide a continuously tuneable source over the range between 90 GHz to 100 GHz with a CW power output of ~10 kW. The work presented herein encompasses the design, construction and measurement of a prototype output launcher for this gyro-device. A corrugated mode converting horn was designed to act as a quasi-optical mode converter that converts the fundamental operating mode within the gyro-TWA (TE11) to a hybrid mode, which is closely coupled to the fundamental free space Gaussian mode (TEM00). This free space mode allows the possibility for the inclusion of an energy recovery system that can recover a percentage of the energy from the spent electron beam and is predicted to increase overall efficiency by up to 40%. For this scheme the electron beam must be decoupled from the radiation, which can pass through the collector system and vacuum window unperturbed while the electrons are collected at the energy recovery system. This type of corrugated mode converting horn was chosen due to the advantages of a greater bandwidth and the capability to provide a source that is continuously tuneable over this bandwidth. The results of the design and integration of this corrugated mode converting horn with the gyro-device are presented. The prototype operates over a continuously tuneable bandwidth of 90 to 100 GHz with a return loss better than -35 dB and a Gaussian coupling efficiency of 97.8%. The far field radiation pattern shows a highly symmetrical structure with 99.9% of the power radiated within a cone with a half angle of less than 19° and a cross-polar level less than -40 dB.High power coherent microwave sources at shorter wavelengths (mm and sub-mm) are in great demand, especially in the fields of plasma physics, remote sensing and imaging and for electron spin resonance spectroscopy. Gyro-devices are by their nature particularly suited to this type of application due to the fast-wave cyclotron resonance maser instability, which is capable of producing high power radiation at frequencies that prove challenging for other sources. A W-band gyro-device based on a cusp electron beam source with a helically corrugated interaction region is currently under development to provide a continuously tuneable source over the range between 90 GHz to 100 GHz with a CW power output of ~10 kW. The work presented herein encompasses the design, construction and measurement of a prototype output launcher for this gyro-device. A corrugated mode converting horn was designed to act as a quasi-optical mode converter that converts the fundamental operating mode within the gyro-TWA (TE11) to a hybrid mode, which is closely coupled to the fundamental free space Gaussian mode (TEM00). This free space mode allows the possibility for the inclusion of an energy recovery system that can recover a percentage of the energy from the spent electron beam and is predicted to increase overall efficiency by up to 40%. For this scheme the electron beam must be decoupled from the radiation, which can pass through the collector system and vacuum window unperturbed while the electrons are collected at the energy recovery system. This type of corrugated mode converting horn was chosen due to the advantages of a greater bandwidth and the capability to provide a source that is continuously tuneable over this bandwidth. The results of the design and integration of this corrugated mode converting horn with the gyro-device are presented. The prototype operates over a continuously tuneable bandwidth of 90 to 100 GHz with a return loss better than -35 dB and a Gaussian coupling efficiency of 97.8%. The far field radiation pattern shows a highly symmetrical structure with 99.9% of the power radiated within a cone with a half angle of less than 19° and a cross-polar level less than -40 dB

Mobile terrestrial LiDAR data-sets in a Spatial Database Framework

Mobile Mapping Systems (MMS) have become important and regularly used platforms for the collection of physical-environment data in commercial and governmental spheres. For example, a typical MMS may collect location, imagery, video, LiDAR and air quality data from which models of the built-environment can be generated. Numerous approaches to using these data to generate models can be envisaged which can help develop detailed knowledge in the monitoring, maintanence and development of our built-environment. In this context, the efficient storing of this raw spatial data is a significant problem such that bespoke and dynamic access is possible for the generation of modeling requirements. This fundamental requirement of managing these data, where upwards of 40 gigabytes per hour of spatial-information can be collected from an MMS survey, poses significant challanges in data management alone. Existing methodologies mantain bespoke, survey oriented approaches to data management and model generation where the original MMS spatial data is not generally used or available outside these requirements. Thus, there is a need for an MMS data management framework where effective storage and access solutions can hold this information for use and analysis in any modeling context. Towards this end we detail our storage solution and the experiments where the procedures for high volume navigation and LiDAR MMS-data loading are analysed and optimised for minimum upload times and maximum access efficiency. This solution is built upon a PostgreSQL Relational Database Management System (RDBMS) with the PostGIS spatial extension and pg bulkload data loading utility

LiDAR data management pipeline; from spatial database population to web-application visualization

While the existence of very large and scalable Database Management Systems (DBMSs) is well recognized, it is the usage and extension of these technologies to managing spatial data that has seen increasing amounts of research work in recent years. A focused area of this research work involves the handling of very high resolution Light Detection and Ranging (LiDAR) data. While LiDAR has many real world applications, it is usually the purview of organizations interested in capturing and monitoring our environment where it has become pervasive. In many of these cases, it has now become the de facto minimum standard expected when a need to acquire very detailed 3D spatial data is required. However, significant challenges exist when working with these data sources, from data storage to feature extraction through to data segmentation all presenting challenges relating to the very large volumes of data that exist. In this paper, we present the complete LiDAR data pipeline as managed in our spatial database framework. This involves three distinct sections, populating the database, building a spatial hierarchy that describes the available data sources, and spatially segmenting data based on user requirements which generates a visualization of these data in a WebGL enabled web-application viewer. All work presented is in an experimental results context where we show how this approach is runtime efficient given the very large volumes of LiDAR data that are being managed

Wide-band HE11 mode terahertz wave windows for gyro-amplifiers

Broadband HE11 mode output windows, based on the multilayer concept, are studied for high power gyro-amplifiers operating in the low terahertz region. As the wave power in the hybrid HE11 mode is concentrated in the center of the circular waveguide, smaller reflection and better coupling to the fundamental free space Gaussian mode can be achieved for the windows. Two windows are designed for optimized performance through simulations for operation in two frequency ranges of 360– 400 GHz and 90–100 GHz. The simulated performance, practical constraints in realization and manufacturing methods of the 90–100 GHz window is discussed. This window was constructed and microwave properties measured showing a lower than -27 dB reflection. This result agrees with simulation data which validates the simulation methodology and effectiveness of the design

Measurement of a W-band output launcher system for a broadband gyro-TWA

An output system for a W-band (90-100 GHz) gyrotron-traveling wave amplifier is designed, simulated, measured and the results are presented. This is an updated system based on a previous design and the output shows more favorable properties for the amplifiers intended application, as a millimetre wave source in a cloud sensing radar. A greater than -30 dB reflection was measured over the frequency range and high Gaussian content obtained

Snake energy analysis and result validation for a mobile laser scanning data-based automated road edge extraction algorithm

© 2008-2012 IEEE. The negative impact of road accidents cannot be ignored in terms of the very sizeable social and economic loss. Road infrastructure has been identified as one of the main causes of the road accidents. They are required to be recorded, located, measured, and classified in order to schedule maintenance and identify the possible risk elements of the road. Toward this, an accurate knowledge of the road edges increases the reliability and precision of extracting other road features. We have developed an automated algorithm for extracting road edges from mobile laser scanning (MLS) data based on the parametric active contour or snake model. The algorithm involves several internal and external energy parameters that need to be analyzed in order to find their optimal values. In this paper, we present a detailed analysis of the snake energy parameters involved in our road edge extraction algorithm. Their optimal values enable us to automate the process of extracting edges from MLS data for tested road sections. We present a modified external energy in our algorithm and demonstrate its utility for extracting road edges from low and nonuniform point density datasets. A novel validation approach is presented, which provides a qualitative assessment of the extracted road edges based on direct comparisons with reference road edges. This approach provides an alternative to traditional road edge validation methodologies that are based on creating buffer zones around reference road edges and then computing quality measure values for the extracted edges. We tested our road edge extraction algorithm on datasets that were acquired using multiple MLS systems along various complex road sections. The successful extraction of road edges from these datasets validates the robustness of our algorithm for use in complex route corridor environments

A W-band corrugated output horn and window for gyro-devices

A W-band corrugated horn incorporating a broadband vacuum window for use in a gyro-device as a quasi-optical launcher has been designed, manufactured and experimentally measured. This horn, including a 3 disk vacuum window, converts a cylindrical TE11 mode into the free space TEM00 mode over the frequency band of 90-100 GHz with a reflection better than -30 dB and a coupling efficiency of ∼99.4%

Analytical and Numerical Simulation of Multipactor within a Helical Resonant Filter

Multipactor analysis of a helical resonant filter has been performed using CST Particle Studio and analytically using a 1-D particle tracking code, based on the Runge-Kutta-Nystrom method. A comparison of results is presented

Ultra-high field MRI: parallel-transmit arrays and RF pulse design

This paper reviews the field of multiple or parallel radiofrequency (RF) transmission for magnetic resonance imaging (MRI). Currently the use of ultra-high field (UHF) MRI at 7 tesla and above is gaining popularity, yet faces challenges with non-uniformity of the RF field and higher RF power deposition. Since its introduction in the early 2000s, parallel transmission (pTx) has been recognized as a powerful tool for accelerating spatially selective RF pulses and combating the challenges associated with RF inhomogeneity at UHF. We provide a survey of the types of dedicated RF coils used commonly for pTx and the important modeling of the coil behavior by electromagnetic (EM) field simulations. We also discuss the additional safety considerations involved with pTx such as the specific absorption rate (SAR) and how to manage them. We then describe the application of pTx with RF pulse design, including a practical guide to popular methods. Finally, we conclude with a description of the current and future prospects for pTx, particularly its potential for routine clinical use

Design and measurement of a broadband sidewall coupler for a W-band gyro-TWA

The input coupler is an important component for a microwave amplifier. In this paper, a sidewall single-hole input coupler for a W-band gyrotron traveling-wave amplifier that operates at the frequency range of 90–100 GHz was designed and measured. Instead of using a cutoff waveguide, a broadband Braggtype reflector with a small spread in phase was optimized for use as part of the input coupler. The minimum radius of the reflector was two times the size of a cutoff waveguide, which reduced the possibility for some of the beam electrons being collected in this section and lost to the amplifier interaction region