Transmission Line Oscillator Research Articles

On the two-dimensional Brillouin flow

The Brillouin flow is a rectilinear, sheared electron fluid flow in a crossed electric field (E) and magnetic field (B), in the E × B direction with zero flow velocity and zero electric field at the surface with which the flow is in contact. It is broadly considered as the equilibrium electron flow in high power crossed-field devices including the magnetron and magnetically insulated transmission line oscillator. This paper provides an examination of Brillouin flow in two dimensions, in a cylindrical geometry where the anode radius changes abruptly at a single axial location, while the cathode surface has a constant radius. Our simulation confirms the proof that there is no equilibrium Brillouin flow solution for such a geometry. It further reveals that this change in the anode radius introduces novel bunching of the electrons within the Brillouin hub. This bunching occurs at low frequencies and is very pronounced if the Brillouin flow is from the small gap region to the large gap region, but is minimal if the Brillouin flow is from the large gap region to the small gap region. New insights are provided into the physical processes that initiate and sustain the bunching processes that are unique for a crossed-field diode, as compared with a non-magnetized diode. We argue that this enhanced bunching, and its concomitant formation of strong vortices, is not restricted to an abrupt change in the anode–cathode gap spacing.

Implementation of NATO standards to improve the electromagnetic immunity and compatibility of equipment of the critical infrastructure objects

Ensuring that domestic technical equipment meets modern safety and reliability requirements in accordance with NATO standards is a pressing problem in Ukraine. Without metrological support for testing the electromagnetic compatibility and immunity to powerful electromagnetic fields of natural and artificial origin, it is impossible to ensure reliable and safe use of modern electronic, electroenergetics and electric equipment in critical infrastructure facilities.
 The paper presents the metrological traceability paths of the state measurement standards in the field of electromagnetic measurements, established at the NSC “Institute of Metrology”, to the SI units. The results of the research on the measurement standard of the electromagnetic field strength unit in the frequency range from 0.01 MHz to 43 GHz (NDETU EM-05-2021), established at the NSC “Institute of Metrology”, are described. The connection of the NDETU EM-05-2021 measurement standard with the measurement standards of the power unit of electromagnetic oscillations in coaxial and waveguide transmission lines and the standard of AC electric voltage is demonstrated.
 The lists of tests in accordance with the AESTR-500 standard, which are supported by the measurement standards of the NSC “Institute of Metrology”, and the equipment that can be calibrated by the national measurement standards are given. The examples of tests for electromagnetic compatibility carried out in the testing centre of the State Enterprise “Kharkivstandartmetrologiya” are provided.
 Based on the results of the developed statistical models at the Research and Design Institute “Molniya” for predicting the vulnerability to electromagnetic effects of atmospheric phenomena on critical infrastructure facilities, the examples of the distribution of lines of the equal potential (in kilovolts) on the ground surface in the short circuit mode and the distributions of probability density of lightning strikes are presented. The distributions of the equal potential lines on the ground surface in the short-circuit mode of high-voltage substations are modelled based on calculations.

Experimental Study on the Frequency Tunability of a Magnetically Insulated Transmission Line Oscillator

In the present study, the frequency tunability of a magnetically insulated transmission line oscillator (MILO) is investigated by simulation in conjunction with an experiment. In the simulation, the tunable MILO reaches a maximum output power of approximately 5.0 GW with an applied voltage of 590 kV and an input power of 29 GW. The corresponding power efficiency is 17.2%, and the frequency is 1.575 GHz. In addition, by adjusting the outer radius of the vane from 77 to 150 mm, the 3-dB tunable frequency of the tunable MILO ranges from 0.85 to 2.12 GHz, and the tuning bandwidth is 85.5%. The experimental results show that when the voltage and current are 405 kV and 42 kA, respectively, the peak microwave power of the tunable MILO is approximately 2.3 GW with a microwave frequency of approximately 1.900 GHz. The difference in the two frequencies at the peak microwave power is significant because of the tuning mechanism. When the outer radius of the vane varies in the range of 76.6–93.0 mm, the 3-dB tunable frequency range is between 1.552 and 2.168 GHz, corresponding to a 3-dB tuning bandwidth of 33.1%. The experimental measurements verify the simulation results.

Evaluation of Explosive Emission Carbon Fiber Cathodes for High-Power Microwave Devices

Most high-power microwave (HPM) sources, such as the magnetically insulated transmission line oscillator (MILO) being developed at Texas Tech, utilize cold cathodes that generate electrons via explosive emission. Highly emissive cathodes such as the presented can generate current densities and currents greater than 1 kA/cm 2 and 10 kA, respectively, which are required for devices that can output radio frequency (RF) power greater than 100 MW. Typically, these cathodes are made of materials such as metal, silk or synthetic velvet, carbon fiber, and cesium iodine (CsI)-coated carbon fiber. In order to optimize the MILO performance, we fabricated carbon fiber velvet cathodes and compare their performance with other commercially available carbon fiber cathodes. Fabrication was done on a manual, mechanical loom using commercially available carbon fiber thread. Four carbon fiber cathodes were tested: in-house fabricated monomodal carbon fiber velvet, in-house fabricated bimodal carbon fiber velvet, in-house fabricated carbon fiber plain weave cloth, and bimodal carbon fiber velvet manufactured by ESLI Inc. Testing was performed in a vacuum chamber with variable AK gap in the high vacuum range (10−7 torr). High-speed optical imaging was performed in order to determine the uniformity of the generated plasma as well as the e-beam. Voltage and current measurements were performed to determine diode impedance and perveance.

Electromagnetic Analysis of an Axially Periodic Disk-Loaded Slow-Wave Structure With Low-Loss Dielectric Filling Between Disks for a Magnetically Insulated Line Oscillator

The partially dielectrically filled periodic disk-loaded co-axial structure as a slow wave interaction structure for magnetically insulated transmission line oscillator (MILO) has been electromagnetically analyzed using field matching technique. The slow wave structure (SWS) includes a periodic disk-loaded coaxial structure in which the low-loss dielectric material is partially filled between successive disks. In the analysis, the dispersion relationship and interaction impedance have been calculated taking into account all the harmonics generated inside the structure. The effect of the dielectric constant of the material on the dispersion characteristics and phase velocity has been investigated. Also, the effect of different structural parameters on the dispersion characteristics and the interaction impedance has been obtained. To validate the performed theoretical analysis, the analytically obtained dispersion results have been compared with previously known dispersion results and then also confirmed by the commercial code “Computer Simulation Tool (CST) Studio Suite.” The agreement between theoretical analysis and simulation with respect to the dispersion characteristics is within 5%.

A Repetitive Low Impedance High Power Microwave Driver

A low impedance high power microwave (HPM) driver is designed, which can be used in studying multi-gigawatt HPM devices such as the magnetically insulated transmission line oscillator (MILO), based on a helical pulse forming line (PFL) and the Tesla pulse transformer technology. The co-axial PFL is insulated by ethanol–water mixture, whose dielectric constant can be adjusted; and the helical line increases the output pulse width as well as the impedance to make a better match with the load. By the optimal combination of PFL charging voltage and output switch working voltage, the reliability of the PFL can be improved. The Tesla transformer has partial magnetic cores to increase the coupling coefficient and is connected like an autotransformer to increase the voltage step-up ratio. The primary capacitor of the transformer is charged by a high voltage constant current power supply and discharged by a triggered switch. A transmission line is installed between the PFL and the HPM load, to further increase the load voltage. A ceramic disk vacuum interface is used for improving the vacuum of the HPM tube. The experiments show that the driver can operate at 30 GW peak power, 75 ns pulse width and 5 Hz repetition rate.

Microwave generation modes of ferrite nonlinear transmission lines up to 20 GHz

The generation modes of high-voltage microwave oscillations of nonlinear coaxial transmission lines filled with NiZn ferrite rings with an ordinary (smoothed) hysteresis loop and MgMn ferrite rings with a rectangular hysteresis loop are presented for comparison. Results across a wide frequency range (∼5.5–12.7 GHz) demonstrated that the anisotropic magnetic properties of ferrite with a rectangular loop provide a much more stable and effective generation of powerful microwave oscillations with peak amplitudes up to −350 kV and deep modulation in a wide biasing field (∼4–85 kA/m), as well as the possibility of a generation mode without an external biasing field. New experimental data enable the observed processes in nonlinear ferrite lines to be related to the theoretical positions of the ferrite anisotropic properties and the spin waves of magnetization precession under high-power microwave radiation. Results were also considered in relation to the theory of ferrite. The possibility of achieving an effective frequency of oscillations of 18.5 (up to 20) GHz using solid-state nonlinear transmission lines was also shown.

Common Questions When Using Soil Moisture Sensors for Citrus and Other Fruit Trees

This guide is for Extension personnel who may encounter questions from growers about the functioning and accuracy of soil moisture sensors (SMSs) for fruit tree production. The 4-page publication focuses on two types of handheld sensors currently used in Florida for irrigation management of citrus and other trees: the transmission line oscillator (TLO) and time-domain transmissometer (TDT). Written by Eric Herrera, Sandra M. Guzmán, and Eduart Murcia, and published by the UF/IFAS Department of Agricultural and Biological Engineering, February 2021.

Experimental Demonstration of a Ridged Magnetically Insulated Transmission Line Oscillator

In this study, we investigate the effect of including ridged disk vanes on the operation of a magnetically insulated transmission line oscillator (MILO) in an experiment using a comparison of a ridged MILO (RMILO) with a conventional MILO (CMILO). The only technical difference between the two models is the presence of ridges in the RMILO. The experimental results show that when the voltage is 486 kV and the current is 51 kA, the RMILO’s peak microwave power is approximately 2.9 GW with a pulse duration of more than 35 ns and a microwave frequency of approximately 1.48 GHz. In contrast, the CMILO has the highest power microwave with a peak power of 2.1 GW corresponding to a pulse duration of more than 40 ns and a microwave frequency of approximately 1.53 GHz. The RMILO’s power efficiency increases to 11.7%, a 25% increase compared to that of the CMILO under the same conditions. The experimental measurements exactly coincide with the simulation results. Thus, including ridged disk vanes produces a superior performance.

Analysis of Electromagnetic Pulse Effects Under High-Power Microwave Sources

High-power microwave sources applied to a directed-energy weapon can lead to permanent damage by radiating concentrated energy in a specific direction to disturb or overload electronic equipment. The effect analysis on the target, such as electronics exposed to electromagnetic pulse, should be considered as an important factor in determining the performance of high-power microwave sources and conducting experimental evaluations. In this study, a magnetically insulated transmission line oscillator, one of the representative high-power microwave sources based on vacuum electronics device, was constructed and experimental analysis with respect to electromagnetic pulse effects was performed. The specification of the magnetically insulated transmission line oscillator used in this study corresponded to 3 GW of high-power electromagnetic wave pulses operating at L-band. The power efficiency was approximately 10 – 15%. For effective targeting, a Vlasov antenna that converts TM01 mode to TE11 mode was designed and fabricated. The radiation pattern was confirmed via fluorescent lamps, and to confirm the effect of the directed-energy weapon on the target, an effect analysis was performed using a portable electronic device as a sample. Furthermore, the electric field was measured with a D-dot probe and quantified and compared. This study presents a future blueprint of the value of the directed-energy weapon by predicting the radiant output power of the weapon in the far-field region after it is mounted on a movable ground vehicle or unmanned aerial vehicle.

Study on Load-Side Optimization in Bifrequency MILO Source

In this article, we present an in-depth study of bifrequency magnetically insulated transmission line oscillator (MILO) generating RF output power in S-band with azimuthal partition. It is proposed to optimize the parameters across the load side, inserting gold plate in the collector and tuning the collector cavity depth. The proposal aims at enhancing the power conversion efficiency by employing the concept of a tapered extraction region and implementing four stubs. The stubs help to achieve proper impedance matching, subsequently improving the output power. Further, loss-free FR-4 dielectric is used in extractor vanes which helps to reduce the RF power distribution in other modes. The use of gold plate stimulates space charge near the surface and helps in deflecting the electrons toward the interaction cavities. The presence of FR-4 extractor vane helps to generate spoke current near the collector. The proposed system provides improvised RF coupling of the electron beam to the interaction cavities. The peak power efficiency of ~12.7% is achieved through the device. The beam–wave interaction process is illustrated using space charge instability mechanism. Taking into account the Lagrangian of electrons relationship between angular momentum and torque due to angular force is also derived. This in-depth study helps in the deep understanding of magnetic insulation process inside the device toward developing the proficient MILO source.

Improvement of vacuum maintenance capability and output pulse limit in a hard-tube MILO with a carbon fiber array cathode

This paper reports a great improvement of vacuum maintenance capability in a hard-tube magnetically insulated transmission line oscillator (MILO) by replacing traditional polymer velvet cathode with a low-outgassing carbon fiber array cathode. Based on this improvement, we tested and compared the output pulse limits of this hard-tube MILO with the two cathodes under the same conditions, without an external pumping system after base vacuum pressure was reached. Experimental results reveal that the acceptable pressure for MILO operation is about 1.7 Pa, which is about 100 times higher than the conventional vacuum level (~10−2 Pa). Moreover, the output pulse limit of this hard-tube MILO has been increased from 7 pluses with polymer velvet cathode to about 127 pulses with carbon fiber array cathode. This promotion in the output pulse limit will speed up the application process of MILO.

A High-Efficiency Ridged Magnetically Insulated Transmission Line Oscillator

In this study, we investigate the effect of the inclusion of ridged disk vanes on the operation of a magnetically insulated transmission line oscillator (MILO), using a combination of “cold” (without electron beam) and “hot” (with electron beam) simulations. Cold simulation shows that the inclusion of ridged-disks in a ridged MILO (RMILO) enhances its slow wave structure’s (SWS’s) coupling impedance, thus improving its power efficiency. Moreover, since the ridges’ effect on frequency is weak, the MILO’s inherent tunability is maintained. In hot simulation, the RMILO obtains a 3-dB tunable frequency range of 0.96–2.18 GHz with an applied voltage of 603 kV, in contrast to the 1.04–2.01-GHz range obtained with a conventional MILO (CMILO), owing to the former’s improved power efficiency. With this voltage, the device generates the high power microwave (HPM) with a maximum output power of 7.1 GW at a frequency of 1.40 GHz, corresponding to a power efficiency of 22.6%. The maximum power efficiency of 24.5%, corresponding to a 13.5-GW output, was obtained by increasing the applied voltage to 807 kV, an increase of 20.2% compared to the power efficiency obtained with a CMILO in the same condition.

A compact dual-band radiation system* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61671457 and 61871390).

Complex magnetically insulated transmission line oscillator (MILO), as an important development direction, can enhance the power efficiency and generate dual-band high power microwaves (HPMs). A complex MILO and a preliminary dual-band radiation system have been proposed in our previous studies. However, the axial length of the dual-band radiation system is too long to meet the compact requirements. In this paper, a compact dual-band radiation system is presented and investigated numerically. The compact dual-band radiation system comprises a dual-band cross-shaped mode converter and a dual-band coaxial conical horn antenna. It can convert two coaxial TEM mode microwaves (1.717 GHz and 4.167 GHz) generated by the complex MILO into the coaxial TE11 mode microwaves, and then radiate them into the air. At 1.717 GHz, the gain of the antenna is 17.9 dB, and the total return loss and diffraction loss are 1.50% and 0, respectively. At 4.167 GHz, the gain is 19.4 dB, and the total return loss and diffraction loss are 1.17% and 0.78%, respectively. The power handling capacity of the antenna is 5.1 GW at 1.717 GHz and 2.0 GW at 4.167 GHz. Comparing with the original structure, the length of the dual-band radiation system is reduced by 45.2%.

A Low Standing-Wave-Ratio Wideband Mode-Transducing Antenna for High-Power Microwaves

A novel $L$ -band wideband coaxial mode-transducing antenna, which converts the coaxial TEM mode into circular TM01 mode, is realized and tested in this article. The mode-transducing antenna is composed of a coaxial wideband multiple-reflection mode converter with the three groups of supporting rods and a compact coaxial conical horn with a dielectric lens. First, the schematic and operating principle of the mode-transducing antenna are analyzed theoretically. Then, the structure design and optimization with simulated results are performed for demonstration. Finally, a prototype of the mode-transducing antenna is fabricated, measured, and verified in terms of reflection characteristics, radiation patterns, and far-field waveforms. The measured results reveal that the mode-transducing antenna achieves the bandwidth wider than 31% with the transmission efficiency higher than 98.2%. The high-power test with the magnetically insulated transmission-line oscillator (MILO) show that the power handing capacity of the mode-transducing antenna is greater than 4.0 gigawatts (GW). The measured results are in good agreement with the simulated results. Therefore, the mode-transducing antenna has a good application prospect in the field of high-power microwave (HPM).

Optimum design of tuned mass damper via PSO algorithm for the passive control of forced oscillations in power transmission lines

Transmission lines are prone to external excitations due to their low density and internal damping coefficient. They are vulnerable to some natural events such as wind and rain which may disrupt power transmission. Forced vibration due to external disturbances is one of the most frequent causes of failures in these lines. In this study, effects of tuned-mass-dampers (TMDs) on reduction of forced vibrations are investigated. A mathematical model for the transmission line is proposed by using mode summation technique combined with the dynamics of the absorbers. Best values for the location, stiffness and mass of the absorbers are found by using Particle Swarm Optimization algorithm (damping coefficients are obtained as zero). The objective of the algorithm is to minimize the line deflection to postpone the failure and the replacement of the lines. Results show that the designed TMDs are efficient in reduction of forced vibrations. Finally, the same procedure is implemented under resonance condition. The designed TMDs lead to a high reduction factor in the line deflection. Similarly, the proposed optimization algorithm can be used in other industrial applications of the flexible cables; under various external excitations.

Design and Simulation of a Novel High-Efficiency Magnetically Insulated Transmission Line Oscillator

A novel high-efficiency magnetically insulated transmission line oscillator (MILO) is proposed and investigated in this article. It has three features. First of all, the widths of vanes are nonuniform while the width of resonant cavities in slow wave structure (SWS) remains unchanged. Second, the width of the first extract cavity shrinks and an extra extractor vane is added to enhance the power extraction. In addition, the emission surface of the cathode decreases, reducing the energy waste. The simulation results show that the novel high-efficiency MILO can generate high power microwave (HPM) with the output power of 6.3 GW and the frequency of 1.42 GHz when the applied voltage and current are 586 kV and 49 kA, respectively. The corresponding power efficiency is 22%. Given the same input, the conventional MILO generates the HPM with the same frequency but a lower power of 5.0 GW. The corresponding power efficiency is 17% smaller than that of our proposed MILO. Additionally, the maximum axial electric field in our proposed structure is 0.64 MV/cm after chamfering, which is lower than the breakdown threshold (1 MV/cm).

Frequency Tunability and Slow-Wave Characteristics of a High-Efficiency Ridged MILO

A high-efficiency ridged magnetically insulated transmission line oscillator (RMILO) is proposed and investigated theoretically and numerically in this paper. In the RMILO, ridge-disk vanes are introduced to enhance the power efficiency. Theoretical investigation shows that the ridge-disk can enhance the coupling impedance of the slow-wave structure (SWS), and so enhance the power efficiency. Moreover, the ridge has a weak influence on frequency, so, it influences little on the tunability of the MILO. In simulation, when the applied voltage is increased to 807 kV, the RMILO can get the 3 dB tunable frequency range with 7.6 - 13.9 GHz and the 3 dB tuning bandwidth with 58.6% which has an increase of 27.6% compared with the conventional MILO. So, the tuning performance of the RMILO is more superior. Besides, the RMILO gets the maximum output power of 7.1 GW, the corresponding power efficiency is 22.6% and the frequency is 1.400 GHz. Furthermore, when the applied voltage is increased to 807 kV, high-power microwave with a power of 13.5 GW, frequency of 1.400 GHz, and ef?ciency of 24.5% is generated, which has an increase of 20.2% compared with the conventional MILO. The simulation results con?rm the ones predicted by theoretical analysis.

Competitions among modes in magnetically insulated transmission line oscillator

<sec>As a compact and high power microwave source, the competitions among various modes are prone to appear in the initial stage of the development of the radiated electromagnetic field in a magnetically insulated transmission line oscillator (MILO). If the mode competitions are not controlled effectively, the output characteristics of the MILO may decline in the end. </sec><sec>As is well known, the operating mode of MILO is generally designed on the π mode of the TM<sub>00</sub> mode and the coaxial disk-loaded waveguide is usually adopted as a slow-wave structure for beam-wave interaction in MILO. Therefore from the dispersion relations between the electron beam and the lower order electromagnetic modes(including TM<sub>00</sub>, TM<sub>01</sub> and HEM<sub>11</sub> modes) in the slow-wave structure, the characteristics and possible suppression methods of the three kinds of mode competitions are analyzed simply. The first kind mode competition is between the different axial modes of the fundamental TM<sub>00</sub> mode. In this case, the electromagnetic field of the competition mode is also axially symmetric and its frequency is slightly lower than that of the π mode. The second is the competition between the TM<sub>00</sub> and higher order TM<sub>01</sub> mode. In this case, the competition frequency is rather higher than that of the π mode (TM<sub>00</sub>). The third is the competitions between the TM<sub>00</sub> and low order asymmetric HEM<sub>11</sub> modes. In this case, the competition frequency is slightly higher than that of the main mode. Appropriately choosing the radii of the anode vanes, the number of the anode cavity and the load length of the cathode, the corresponding mode competition intensity can be weakened. </sec><sec>Based on the obtained results above and the existing model of the MILO, a compact high output power L-band MILO is proposed. Numerical studies of the mode competitions and output characteristics are carried by using the three dimensional particle-in-cell code. Cold-cavity test shows that in the low frequency range, the easily stimulated electromagnetic modes are the π mode of TM<sub>00</sub> and HEM<sub>11</sub> modes with frequencies of 1.61 GHz and 1.77 GHz, respectively. The numerical results of hot-cavity verify that the competition in the initial stage comes mainly from the asymmetric HEM<sub>11</sub> mode due to the fact that there exists the strut in the output region, the Cartesian coordinates are adopted during the simulation, and totally symmetry cannot be guaranteed. In addition, electron beam emission from the cathode is not ideally even. But stable and high output microwave power is obtained in the end in the L-band MILO by being optimized. The output power and efficiency are 8.1 GW and 18% respectively, and the mode purity reaches about 97%. </sec>

Resonant Tunneling Diode (RTD) Terahertz Active Transmission Line Oscillator with Graphene-Plasma Wave and Two Graphene Antennas

This study describes the design of a resonant tunneling diode (RTD) oscillator (RTD oscillator) with a RTD-gated-graphene-2DEF (two dimensional electron fluid) and demonstrates the functioning of this RTD oscillator through a transmission line simulation model. Impedance of the RTD oscillator changes periodically when physical dimension of the device is of considerable fraction of the electrical wavelength. As long as impedance matching is achieved, the oscillation frequency is not limited by the size of the device. An RTD oscillator with a graphene film and negative differential resistance (NDR) will produce power amplification. The positive electrode of the DC power supply is modified and designed as an antenna. So, the reflected power can also be radiated to increase RTD oscillator output power. The output analysis shows that through the optimization of the antenna structure, it is possible to increase the RTD oscillator output to 22 mW at 1.9 THz and 20 mW at 6.1 THz respectively. Furthermore, the RTD oscillator has the potential to oscillate at 50 THz with a matching antenna.