Skip to main content Accessibility help

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.

Close cookie message
×
  1. Home
  2. Browse subjects
  3. Engineering
  4. Electronic, optoelectronic devices, and nanotechnology
  5. Content listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

4948 results in Electronic, optoelectronic devices, and nanotechnology

Page 64 of 248

  • 8 - Electron Flow in Crossed Fields

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 287-316

  • Summary

    The electron velocity in a linear, cylindrical (pencil), electron beam is determined by the potential difference between the cathode and the beam tunnel, taking space-charge potential depression into account. The effect of space-charge forces is to cause the beam radius to expand and static electric and magnetic fields can act as electron lenses. Beam spreading can be opposed by a uniform axial magnetic (solenoid) field if the beam is rotating. The conditions for stable flow are established using Busch’s theorem. The beam radius varies periodically (scalloping) if the initial conditions are incorrect. Increasing the current density increases the equilibrium beam radius to an extent controlled by the fraction of the magnetic flux linking the cathode (the beam stiffness). A pencil beam can also be collimated by a periodic array of converging magnetic lenses in periodic permanent magnet (PPM) focusing. Its properties are similar to those of a solenoid-focused beam with the addition of a periodic ripple in the radius. The design of practical focusing systems is described and the effects of imperfections including thermal velocities and trapped ions are discussed. Brief consideration is given to periodic electrostatic focusing and to the control of annular and sheet electron beams.

  • 16 - Crossed-Field Amplifiers

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 629-658

  • Summary

    In a magnetron oscillator electrons emitted from a cylindrical cathode interact with the π-mode resonance of a cylindrical, re-entrant, slow-wave structure on the anode. The electrons move under the influence of a radial static electric field and an axial magnetic field. Rotating spokes of charge synchronous with the wave on the anode are formed on the surface of a space-charge hub. As the electrons drift outwards along the spokes the change in potential energy is converted to r.f. energy with high efficiency. Because a magnetron is an oscillator its steady-state operation is always non-linear. Care must be taken in the design of the anode and in the operation of the tube to avoid excitation of modes other than the π-mode. The design of the anode is considered in detail. The performance of magnetrons is reviewed including the effects of the external match on frequency, power output and efficiency. Useful understanding of the properties of a magnetron can be gained from a model which assumes a fixed hub, determined by the theory of the cut-off magnetron diode, and rigid spokes. This model reproduces all the main features of the performance of a magnetron.

  • 11 - Beam-Wave Interaction

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 375-432

  • Summary

    The spent electron beam in an electron tube carries power which must be dissipated safely as heat. In gridded tubes, magnetrons and most CFAs the power is dissipated on the anode. In linear-beam tubes and gyrotrons the beam is allowed to expand to give a reduced power density on a separate collector electrode. In every case the surface temperature must be low enough to avoid physical damage or out-gassing of the collector surface. The collecting electrode may be cooled by conduction, air or liquid flow or liquid boiling. The power dissipated in the collector of a linear-beam tube can be reduced by using a multi-element depressed collector in which the collecting electrodes are held at negative potentials with respect to the body of the tube. In these collectors it is necessary to ensure that the performance is not reduced by the emission of secondary electrons. The design of collectors is discussed including the effect of the distribution of velocities in the spent electron beam.

  • 6 - Triodes and Tetrodes

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 224-249

  • Summary

    The basis of nearly all types of vacuum tube is the diode in which the electrons emitted by thermionic emission from a cathode are attracted to a positively charged anode. The current through the diode increases as the emitted current increases until it is limited by the negative space-charge of the electrons. The properties of planar, cylindrical and spherical space-charge limited diodes are discussed including the effects of relativity and of the initial thermal velocities of the electrons. When the voltage applied to the anode varies rapidly with time a static solution is no longer valid and transit-time effects must be considered. The properties of diodes in which the electrons are injected with a finite velocity and those in which the electron flow is two-dimensional are reviewed.

Microwave and RF Vacuum Electronic Power Sources
  • Richard G. Carter
  • Published online:
    27 April 2018
    Print publication:
    12 April 2018
  • Do you design and build vacuum electron devices, or work with the systems that use them? Quickly develop a solid understanding of how these devices work with this authoritative guide, written by an author with over fifty years of experience in the field. Rigorous in its approach, it focuses on the theory and design of commercially significant types of gridded, linear-beam, crossed-field and fast-wave tubes. Essential components such as waveguides, resonators, slow-wave structures, electron guns, beams, magnets and collectors are also covered, as well as the integration and reliable operation of devices in microwave and RF systems. Complex mathematical analysis is kept to a minimum, and Mathcad worksheets supporting the book online aid understanding of key concepts and connect the theory with practice. Including coverage of primary sources and current research trends, this is essential reading for researchers, practitioners and graduate students working on vacuum electron devices.

  • 20 - System Integration

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 765-788

  • Summary

    Magnetic fields having well-defined spatial distributions are essential to the operation of many types of vacuum tube. This chapter summarises the theory of magnetism and the properties of soft and hard ferro-magnetic materials. The use of magnetic circuit theory for the design of electro-magnets and permanent magnets is described. The magnets used in vacuum tubes can be divided into coil dominated magnets in which no iron is used to control the flux paths and iron dominated magnets in which the greater part of the flux passes through iron. The theory of coil-dominated magnets employing arrays of coils or solenoids is described with an emphasis on the production of a uniform magnetic field within a volume of space. In iron dominated magnets the shape of the pole-pieces has an important influence on the distribution of the flux in the intervening air gap. The design of iron-dominated magnets for magnetrons, CFAs and linear-beam tubes is discussed with a detailed discussion of the design of periodic permanent magnet (PPM) systems. The results are compared with the results of simulation using finite element methods.

  • Appendix: - Mathcad Worksheets

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 789-790

  • Summary

    Safe and reliable operation of vacuum tubes requires careful attention to be paid to their integration into the systems in which they are used. Particular attention must be paid to the electric power supplies especially those for high voltages where the stored energy and the risk of voltage breakdown may be high. The principles of operation of electric power converters and pulsed power supplies are described together with the means of protecting the tube under fault conditions. The operation of a tube also depends upon the correct operation of external radio-frequency, cooling and magnetic systems. The issues involved are discussed together with the protection systems and switch-on and switch-off procedures required. Under normal operation the end of life of a tube is determined by failure of emission from the cathode. Premature failure can be caused by failure of the tube vacuum or the focussing system or by mechanical damage. The symptoms of these causes of failure and the precautions required to avoid them are described. The operation of vacuum tubes also involves hazards from electric shock, radio-frequency and X-ray radiation, implosion and the presence of toxic materials. Their operation is safe if correct operating and handling procedures are employed.

  • 13 - Klystrons

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 466-506

  • Summary

    Gridded tubes use a control grid close to the cathode to modulate the electron current. In triodes and tetrodes the modulated current is collected by the anode and passes through the output resonant circuit. The amplification is class A if current flows at all times, class B is it flows for half the r.f. cycle and class C if less than half a cycle. The gain is reduced and the efficiency increases as the conduction time decreases. The design and construction of triodes and tetrodes and of amplifiers incorporating them is discussed. In an inductive output tube (IOT) a bunched electron beam is formed by a gridded electron gun. The bunched beam is passed through a gap in a cavity resonator which extracts r.f. power from the bunches. The design of IOTs and examples of their application are discussed.

  • 7 - Linear Electron Beams

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 250-286

  • Summary

    The flow of electrons between the cathode and the anode of a diode can be controlled by introducing permeable electrodes (grids). The properties of triodes can be understood using an electrostatic model in which space-charge is neglected. The influence of the anode voltage on the electric field at the cathode is described by the penetration factor. The effects of space-charge can be included using the concept of an equivalent diode whose properties are determined by considering limiting cases. Good agreement with experimental results is obtained in this way. When the control grid is close to the cathode the emission from the cathode becomes non-uniform (island formation) and the penetration factor varies with position. It is shown that the current in a triode generally obeys the 3/2 power law but varies from this near cut-off if there is island formation. The current intercepted by the grid can be estimated by calculating electron trajectories. Similar methods can be applied to the modelling of a tetrode by reducing it to an equivalent triode. The effects of space-charge in the region between the screen grid and the anode can be understood by regarding it as a diode with injected current.

  • 19 - Magnets

  • Richard G. Carter, Lancaster University
  • Book:
    Microwave and RF Vacuum Electronic Power Sources
    Published online:
    27 April 2018
    Print publication:
    12 April 2018, pp 735-764

  • Summary

    Electron and X-ray emission and voltage breakdown caused by static, pulsed, and radio-frequency electric fields are important for the operation of vacuum tubes and also set limits to their performance. The physical principles of thermionic, field enhance, field, photo-electric and secondary electron emission from solid surfaces and the generation of X-rays are reviewed. The construction and properties of the principal types of thermionic cathode are described together with a brief review of cold cathodes employing field emission. Voltage breakdown may occur in vacuum tubes both inside and outside the vacuum envelope and through insulators. The physics of each type of electrostatic breakdown are reviewed. The theory of r.f. vacuum breakdown (multipactor) is discussed in detail both with and without the presence of a static magnetic field revealing the conditions under which a discharge may occur.

Knowledge Driven Development
  • Bridging Waterfall and Agile Methodologies
  • Manoj Kumar Lal
  • Published online:
    20 October 2018
    Print publication:
    08 March 2018
  • This book presents a new methodology, known as Knowledge Driven Development, for managing project knowledge in an exhaustive and structured manner. The text highlights the importance of efficient project delivery methodology in the overall software development life cycle. Important topics such as requirement analysis, solution design, application design, and test design are discussed in depth. It establishes a connection between enterprise knowledge and project knowledge for continuous improvement and accelerated project delivery. Separate chapters on end-to-end project delivery, compliance and protocols and interface with existing methodologies makes it useful for the readers. Several case studies and examples are interspersed throughout the text for better understanding.

  • 14 - Suits Factory Model: Needs Cultural Change

  • Manoj Kumar Lal
  • Book:
    Knowledge Driven Development
    Published online:
    20 October 2018
    Print publication:
    08 March 2018, pp 233-240

  • Summary

    KDD can drive the digitisation of project knowledge that may lead to standardising the processes of the project delivery. This may take the IT industry away from being knowledge-based and nearer to being a process-based industry. The factory model is suited to process-based industries and we can now say that KDD may enable IT industry to follow the factory model. However, changing from the current knowledge-based approach to factory approach is not simple. It needs greater appreciation of the digitisation of the project knowledge and a change in mindset to inspire the project team to work in the factory model. This chapter discusses these two topics in detail: enablement of the factory model for IT industry and the cultural change required to make it happen.

    Bringing IT Project Delivery Closer to Process-Based Industry

    Traditional project knowledge is contained in the following set of project documents:

  • a. Business Requirement Specification (BRS)

  • b. Functional Specification Document (FSD)

  • c. High Level Design Document (HLD)

  • d. Test Cases

    • KDD has digitised the project knowledge from these four documents to 189 data points. These data points are integrated with each other and provide a framework to manage the project knowledge via PKM. This will revolutionise the treatment of project knowledge and, in fact, commoditise it. This has brought software development closer to being a process-based industry from being a knowledge-based industry.

    Let us understand the document production regime of project knowledge by an example. As a business analyst, I have to produce the BRS document. When I start the day in office, I will have limited idea on how long it will take; I only have an indicative estimate to refer to. With my skills, experience and networking with my colleagues I will try to complete the BRS within the given time. If I am highly skilled and experienced, I can complete the work in half the time allocated and if I am a novice business analyst, it might even take more than twice the effort and the quality of work may not be fit-for-purpose. This is a typical situation while working in a knowledge-based industry.

    Let us now understand what typically happens in a factory. At the start of the day, the worker in the factory will get a target of specific output for the day.

  • Foreword

  • Manoj Kumar Lal
  • Book:
    Knowledge Driven Development
    Published online:
    20 October 2018
    Print publication:
    08 March 2018, pp xv-xviii

  • Summary

    When we think of the challenges in software engineering, we focus on the various technical activities: requirements, architecture, design, implementation, verification etc. Various management dimensions also receive attention: processes, planning, change management, quality, teamwork, competency, domain understanding, customer interaction, value focus and so on. Clearly, each one of these is very important, even critical, to successful software engineering.

    However, there is another dimension that is central to software engineering: contextual knowledge and how it flows through the engineering process, into the final product. It is easy to see why this dimension is central if we examine the nature and role of software. Software is the agent of operations for systems. It implements/enables the concept of functioning of its target system, which could be a business function, embedded system and/or user task. The technical activity stream in software engineering as a whole is aimed at developing this contextual knowledge about the target system, and then ensuring that it is addressed accurately and consistently by the resulting software solution.

    This book introduces Knowledge Driven Development (KDD), a path-breaking software engineering technology (best practice) that manages and ensures the systematic flow of contextual knowledge into software solution. As the author Manoj Kumar Lal illustrates beautifully through the case studies in Chapter 1, even software projects that diligently follow modern best practices are extremely likely to face challenges associated with managing this flow. The problem is that contextual knowledge evolves continuously as the project progresses (In Agile, this means that knowledge relating to software generated by a particular Sprint continues to evolve even after the Sprint completes), and that consistent shared understanding of relevant contextual knowledge needs to be maintained across all team members (even in large distributed teams) to avoid quality problems. Readers will find that the typical problems described by him are familiar to them as commonplace in the projects that they execute, and that these problems lead to significant productivity losses and quality problems. Every project, large or small, will benefit substantially from a structured approach to managing the consistent flow of contextual knowledge into software solutions.

    The book goes on to introduce precisely such a structured approach. Contextual knowledge about the target system is captured through a Project Knowledge Model (PKM) classified into 18 ‘building block’ types, and a further n2matrix of 171 possible relationships among them.

Page 64 of 248