Graphene travelling wave amplifier for integrated millimeter-wave/terahertz systems

Terahertz (THz) technology offers exciting possibilities for various applications, including high resolution biomedical imaging, long-wavelength spectroscopy, security monitoring, communications, quality control, and process monitoring. However, the lack of efficient high power easy-to-integrate sources and highly sensitive detectors has created a bottleneck in developing THz technology. In an attempt to address this issue, this dissertation proposes a new type of graphene-based solid state travelling wave amplifier (TWA). Inspired by the unique properties of electrons in graphene two-dimensional (2D) fluid, the author proposes a new type of TWA in which graphene acts as the sheet electron beam. These properties include higher mobility and drift velocity at room temperature, zero effective mass, relativistic behavior, and a truly 2D configuration. Since the plasma properties of 2D electron fluid become more pronounced as the effective mass of electrons decreases and electron mobility increases, THz devices based on graphene with massless quasiparticles significantly outperform those made of relatively standard semiconductor heterostructures. Another significant advantage of graphene over semiconductors is that while the high drift velocity and electron mobility of semiconductors 2D electron gas (2DEG) are achieved only at very low temperatures, graphene has high mobility and drift velocity at room temperature. This thesis describes the theoretical and practical methods developed for the analysis, design, and fabrication of a graphene-based THz TWA. It investigates the interaction between the electromagnetic wave and the drifting plasma wave in graphene by two methods. In the first approach, electrons in graphene are modelled as a 2D Fermi liquid, and the hydrodynamic model derived from a relativistic fluid approach is used to find the conductivity. In the second approach, the travelling wave interaction is analyzed using a quantum mechanical model. The drifting Fermi distribution function is applied to the linear conductivity response function of graphene obtained from random phase approximation. The conductivity of graphene is obtained as a function of frequency, wave number, chemical potential, and drift velocity. The result is consistent with the hydrodynamic approach. Both methods show that negative conductivity, and thus gain, is obtained when the drift velocity is slightly greater than the phase velocity. It is shown that the two methods produce comparable results. In the next step, a slow-wave grating structure is designed and an estimate of the actual gain is obtained for the proposed graphene TWA structures. The Floquet mode analysis of top grated slab and rectangular silicon waveguides is presented. Here, a new theoretical method is developed to accurately estimate the field distribution of the first order space harmonic of a hybrid mode inside a periodic top-grated rectangular dielectric waveguide. This method gives explicit expressions for the interaction impedance of the slow wave grating structures that are then used to design the waveguide and the grating. To verify the proposed approximation method, the results obtained with this approach are compared with the simulation results. Finally, a prototype structure is fabricated. The recipes developed for different parts of the structure are presented. These parts include: a nanometer size grating, a sub-millimeter dielectric waveguide, and biasing contacts on top of the graphene layer. The developed recipes ensure reliable fabrication processes for large-area graphene devices. In addition, two different methods used to fabricate long uniform gratings are compared. This work ends by showing the measurement results obtained for the fabricated devices

Millimeter-Wave Band Pass Distributed Amplifier for Low-Cost Active Multi-Beam Antennas

Recently, there have been a great interest in the millimeter-wave (mmW) and terahertz (THz) bands due to the unique features they provide for various applications. For example, the mmW is not significantly affected by the atmospheric constraints and it can penetrate through clothing and other dielectric materials. Therefore, it is suitable for a vast range of imaging applications such as vision, safety, health, environmental studies, security and non-destructive testing. Millimeter-wave imaging systems have been conventionally used for high end applications implementing sophisticated and expensive technologies. Recent advancements in the silicon integrated and low loss material passive technologies have created a great opportunity to study the feasibility of low cost mmW imaging systems. However, there are several challenges to be addressed first. Examples are modeling of active and passive devices and their low performance, highly attenuated channel and poor signal to noise ratio in the mmW. The main objective of this thesis is to investigate and develop new technologies enabling cost-effective implementation of mmW and sub-mmW imaging systems. To achieve this goal, an integrated active Rotman lens architecture is proposed as an ultimate solution to combine the unique properties of a Rotman lens with the superiority of CMOS technology for fabrication of cost effective integrated mmW systems. However, due to the limited sensitivity of on-chip detectors in the mmW, a large number of high gain, wide-band and miniaturized mmW Low Noise Amplifiers (LNA) are required to implement the proposed integrated Rotman lens architecture. A unique solution presented in this thesis is the novel Band Pass Distributed Amplifier (BPDA) topology. In this new topology, by short circuiting the line terminations in a Conventional Distributed Amplifier (CDA), standing waves are created in its artificial transmission lines. Conventionally, standing waves are strongly avoided by carefully matching these lines to 50 Ω in order to prevent instability of the amplifier. This causes that a large portion of the signal be absorbed in these resistive terminations. In this thesis, it is shown that due to presence of highly lossy parasitics of CMOS transistor at the mmW the amplifier stability is inherently achieved. Moreover, by eliminating these lossy and noise terminations in the CDA, the amplifier gain is boosted and its noise figure is reduced. In addition, a considerable decrease in the number of elements enables low power realization of many amplifiers in a small chip area. Using the lumped element model of the transistor, the transfer function of a single stage BPDAs is derived and compared to its conventional counter part. A methodology to design a single stage BPDA to achieve all the design goals is presented. Using the presented design guidelines, amplifiers for different mmW frequencies have been designed, fabricated and tested. Using only 4 transistors, a 60 GHz amplifier is fabricated on a very small chip area of 0.105 mm2 by a low-cost 130 nm CMOS technology. A peak gain of 14.7 dB and a noise figure of 6 dB are measured for this fabricated amplifier. oreover, it is shown that by further circuit optimization, high gain amplification can be realized at frequencies above the cut-off frequency of the transistor. Simulations show 32 and 28 dB gain can be obtained by implementing only 6 transistors using this CMOS technology at 60 and 77 GHz. A 4-stage 85 GHz amplifier is also designed and fabricated and a measured gain of 10 dB at 82 GHz is achieved with a 3 dB bandwidth of 11 GHz from 80 to 91 GHz. A good agreement between the simulated and measured results verifies the accuracy of the design procedure. In addition, a multi-stage wide-band BPDA has been designed to show the ability of the proposed topology for design of wide band mmW amplifiers using the CMOS technology. Simulated gain of 20.5 dB with a considerable 3 dB bandwidth of 38 GHz from 30 to 68 GHz is achieved while the noise figure is less than 6 dB in the whole bandwidth. An amplifier figure of merit is defined in terms of gain, noise figure, chip area, band width and power consumption. The results are compared to those of the state of the art to demonstrate the advantages of the proposed circuit topology and presented design techniques. Finally, a Rotman lens is designed and optimized by choosing a very small Focal Lens Ratio (FL), and a high measured efficiency of greater than 30% is achieved while the lens dimensions are less than 6 mm. The lens is designed and implemented using a low cost Alumina substrate and conventional microstrip lines to ease its integration with the active parts of the system.1 yea

High-Frequency Vacuum Electron Devices

Vacuum electron devices at frequencies of millimeter waves and terahertz play highly important roles in the modern high-data rate and broadband communication systems, high-resolution detection and imaging, medical diagnostics, magnetically confined nuclear fusion, etc. For the fast motion velocity of electrons in the vacuum medium, they have the advantages of high power and high efficiency, as well as compactness, compared with other present radiation sources, such as solid-state devices.We established the Special Issue of “High-Frequency Vacuum Electron Devices” with the aim of enhancing the exchange of research information on the theory, design, simulation, processes, and development of these devices to promote their applications, and to attract young researchers and engineers starting out in this important field, which is still vital on the basis of modern electronic science and information technology

Rotated Half-Mode Substrate Integrated Waveguide and other Planar Integrated Structures

High data rate communication channels are becoming more and more integrated into our increasingly technological society. Substrate Integrated Waveguides (SIW) are one planar solution available to the microwave engineer, offering a low-loss and low dispersion means of propagating these high speed, high bandwidth signals. In this thesis, a brief synopsis of SIW structures and components is presented covering the basic waveguide propagating modes and cut-off frequencies. The main analysis techniques associated with SIWs including full wave electromagnetic modelling methods are overviewed, and the associated loss mechanisms of conduction, dielectric and radiation defined, leading to the design rules and guidelines on how best to mitigate them. SIW antennas as both leaky-wave and radiating slots are discussed and an example of a single and dual resonating slot antenna design is presented, along with a detailed review of a novel switch beam antenna developed for use within the current WiFi bands. The Slot SIW (or SSIW), which has a small longitudinal gap in one of the main conducting surfaces, allows easy integration of lumped elements or active devices, enabling the waveguide to be loaded with impedances or to be shorted. When the slot is shorted, the waveguide reverts back to the full SIW mode, and when partially loaded an intermediate state results. This is discussed, and the SSIW analysed with the transverse resonance technique, leading to the development of a travelling wave attenuator with the SSIW being periodically loaded with pin diodes. The application of the pin diodes required the use of a capacitive overlay, a development of flexi circuit design to allow capacitive coupling of impedances to connect to the waveguide. The overlay concept is extended further, to form novel passive bandpass filters, with the introduction of virtual vias. A limitation of the SSIW is that the majority of the field resides within the dielectric; this allows only a limited interaction with the field at the slot. The rotated Half Mode SIW (rHMSIW), a new variant of the SIW family, places the maximum of the electric field directly on the top dielectric surface, allowing for direct interaction. The waveguide width a is now defined by the dielectric thickness, allowing for the waveguide height b to be adjustable, in normal SIWs this is the other way round; the dielectric thickness fixing the waveguide height and the waveguide width being adjustable. The rHMSIW is characterised with regard to the height and width ratios b/a and the dielectric exposed width (which is adjustable). These parameters effect the modal cut-off frequency, this is investigated and a new equation describing the fundamental mode cut-off frequency is empirically derived. Finally a test coupon which spans the Ku band is designed and measured, which required the development of a novel waveguide transition

NASA Tech Briefs, May 2008

Topics covered inclde: Deployable Wireless Camera Penetrators; Hand-Held Units for Short-Range Wireless Biotelemetry; Wearable Wireless Telemetry System for Implantable BioMEMS Sensors; Electronic Escape Trails for Firefighters; Architecture for a High-to-Medium-Voltage Power Converter; 24-Way Radial Power Combiner/Divider for 31 to 36 GHz; Three-Stage InP Submillimeter-Wave MMIC Amplifier; Fast Electromechanical Switches Based on Carbon Nanotubes; Solid-State High-Temperature Power Cells; Fast Offset Laser Phase-Locking System; Fabricating High-Resolution X-Ray Collimators; Embossed Teflon AF Laminate Membrane Microfluidic Diaphragm Valves; Flipperons for Improved Aerodynamic Performance; System Estimates Radius of Curvature of a Segmented Mirror; Refractory Ceramic Foams for Novel Applications; Self-Deploying Trusses Containing Shape-Memory Polymers; Fuel-Cell Electrolytes Based on Organosilica Hybrid Proton Conductors; Molecules for Fluorescence Detection of Specific Chemicals; Cell-Detection Technique for Automated Patch Clamping; Redesigned Human Metabolic Simulator; Compact, Highly Stable Ion Atomic Clock; LiGa(OTf)(sub 4) as an Electrolyte Salt for Li-Ion Cells; Compact Dielectric-Rod White-Light Delay Lines; Single-Mode WGM Resonators Fabricated by Diamond Turning; Mitigating Photon Jitter in Optical PPM Communication; MACOS Version 3.31; Fiber-Optic Determination of N2, O2, and Fuel Vapor in the Ullage of Liquid-Fuel Tanks; Spiking Neurons for Analysis of Patterns; Symmetric Phase-Only Filtering in Particle-Image Velocimetry; Efficient Coupler for a Bessel Beam Dispersive Element; and Attitude and Translation Control of a Solar Sail Vehicle

Piezoelectric Electromechanical Transducers for Underwater Sound, Part I

The book is the most comprehensive coverage of piezoelectric acoustic transducers and all the related aspects of practical transducer designing for underwater applications in the field. It uses a physics-based energy method for analyzing transducer problems. This gives great physical insight into the understanding of the electromechanical devices. The great benefit of the energy method is that the multidisciplinary subject of electro-mechano-acoustics can be presented in parts and the solutions to the problems (electrical, electro-piezo, mechanical, and radiation) are combined using equivalent electrical circuit network theory. The energy and equivalent electromechanical circuit method at first is illustrated with transducer examples that can be modeled as a single degree of freedom system (such as spheres, short cylinders and flexural beams and plates). Then transducers are modeled as multiple degrees of freedom devices and the results are presented using multi contour electromechanical circuits. Special focus is made on the effects of coupled vibrations on the transducer performance. The Book gives also extensive coverage of acoustic radiation including acoustic interaction between the transducers. It provides practical results that are directly useful for the transducers modeling. While there have been many studies of acoustic radiation of various shapes, non-previous presented the results in terms of such practical utility

Piezoelectric Electromechanical

The book is the most comprehensive coverage of piezoelectric acoustic transducers and all the related aspects of practical transducer designing for underwater applications in the field. It uses a physics-based energy method for analyzing transducer problems. This gives great physical insight into the understanding of the electromechanical devices. The great benefit of the energy method is that the multidisciplinary subject of electro-mechano-acoustics can be presented in parts and the solutions to the problems (electrical, electro-piezo, mechanical, and radiation) are combined using equivalent electrical circuit network theory. The energy and equivalent electromechanical circuit method at first is illustrated with transducer examples that can be modeled as a single degree of freedom system (such as spheres, short cylinders and flexural beams and plates). Then transducers are modeled as multiple degrees of freedom devices and the results are presented using multi contour electromechanical circuits. Special focus is made on the effects of coupled vibrations on the transducer performance. The Book gives also extensive coverage of acoustic radiation including acoustic interaction between the transducers. It provides practical results that are directly useful for the transducers modeling. While there have been many studies of acoustic radiation of various shapes, non-previous presented the results in terms of such practical utility

New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs

This work presents the development of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyro-TWTs. For the first time, it is shown that the operation of such passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. This could be of particular interest for some new time-domain DNP-NMR methods