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Microwave technology as a viable sanitation technology option for sludge treatment
Published in Peter Matuku Mawioo, Novel Concepts, Systems and Technology for Sludge Management in Emergency and Slum Settings, 2020
A microwave heating system comprises four basic components: the power supply, the microwaves source, the transmission lines, and the applicator. The microwave source (vacuum tubes like magnetrons, traveling wave tubes (TWTs), and klystrons) generates the electromagnetic radiation, and the transmission lines (e.g. waveguides) transmit the electromagnetic radiation to the applicator (cavity) which holds the target material (Haque, 1999; Thostenson and Chou, 1999). Electromagnetic radiation results from acceleration of charge. High power and frequencies are required for microwave heating, and that is the reason why vacuum tubes are mostly used as microwave sources. Magnetron tubes, which are used in domestic microwave ovens, are efficient, reliable, and mass produced, and thus are the lowest cost microwaves source available. The magnetron tubes are only capable to generate a fixed frequency electromagnetic field since they use resonant structures for the generation. Conversely, a TWT is used for generating electromagnetic field in a variable frequency microwave since its design allows amplification of a broad band of microwave frequencies in the same tube.
Realization of Slow Wave Phenomena Using Coupled Transmission Lines and Their Application to Antennas and Vacuum Electronics
Published in Douglas H. Werner, Broadband Metamaterials in Electromagnetics, 2017
Md. R. Zuboraj, John L. Volakis
Since the CTLs are made of metallic conductors and can emulate dielectric behavior in their passband, they have the potential for high-power microwave applications. Interestingly, several SWSs, e.g., helix, double-helix, ring-bar structures [24], have been considered and termed as slow wave circuits in the literature. To improve coupling to microwave power delivery, Fig. 3.13 shows the curved ring-bar (CRB) structure [27]. CRB is an upgrade of the typical helical structures and can be modeled as a pair of CTLs as discussed earlier. Specifically, the top and bottom elliptically bent lines refer to the pair of transmission lines. These transmission lines are coupled through the inner rings. More bending of the elliptic feature (i.e., m > 1) of the transmission lines provides more coupling, implying a way to control the slow wave properties and interaction impedance of the TWT model (Figs. 3.1c and 3.13). In effect, the elliptic bent of the transmission line controls the effective permittivity of the propagating wave by reducing the phase velocity below c (Fig. 3.13). Indeed, the dispersion diagram in Fig. 3.13 (right) and Fig. 3.14 validates the second-order dispersion curve. The latter is, of course, the behavior caused by the inductively CTLs. The designed TWT, in this manner, can generate up to 1 MW of output power with a gain of around 30 dB, whereas typical pulsed helix TWTs can generate power up to several kilowatts [28]. This high-power enhancement is due to the slow wave phenomena and associated propagation constants caused by the CTLs.
Internet and Telecom
Published in Fred Huffman, Practical IP and Telecom for Broadcast Engineering and Operations, 2013
A key component of satellite technology, the traveling-wave tube (TWT) was invented in England and perfected at Bell Labs. It is used to generate the signal transmitted from the ground to the satellite and back from the satellite-to-ground station receivers. Achieving adequate power level for the signal to be received by the satellite and re-transmitted back to earth required very large (100-foot diameter) dish antennas in the early uplink transmission systems. Early TWT power output levels were only approximately 1W, but they have grown to more than 300W. Uplink antennas approaching one tenth the size of early versions now cost around 30,000. Receiving antennas that are the size of a large pizza now enable reception of several hundred TV programs and data links to millions of businesses requiring credit card authorizations and accurate inventory tracking.
Design of a Microfabricated Planar Slow Wave Structure for a 0.22-THz TWT for Communication, Imaging and Remote Sensing
Published in IETE Technical Review, 2019
Development activities addressed to 0.22 THz centre frequency is of significant importance for ultra-wideband communication, imaging and remote sensing because of the available atmospheric spectral window over wideband from 0.20 to 0.30 THz. Among various vacuum devices, TWT is preferred as a high power amplifier due to its wide bandwidth and high linearity. Compact microfabricated high power 0.22 THz planar TWT is being investigated for communication, imaging and remote sensing. Planar SDV-SWS is selected for the 0.22 THz TWT because of its wide bandwidth, high impedance, low loss, and ease in fabrication with high precision and surface finish. A simplified approach is presented for determining initial design parameters of the SDV-SWS. The initial design parameters of the SDV-SWS are used with suitable analytical expressions for determining dispersion and impedance characteristics. The structure was also simulated with the 3D e.m. field simulator (CST-MWS). In-house developed large signal analysis code (SUNRAY-p) is used to determine the RF performance of the planar TWT with sheet beam, and these results were compared with the CST-PS code. In the present design study of the SWS, the effects of changing dimensions with increasing body temperature during tube operation as well as alignment tolerances are not considered. These are the critical issues for a THz device, particularly when there is beam interception during tube operation. This study needs to be carried out separately.