Cylindrical Cavity with Distributed Longitudinal Corrugations for Second-Harmonic Gyrotrons

Shcherbinin, Vitalii I.; Ткаченко, В. І.

doi:10.1007/s10762-017-0386-x

Cited by 27 publications

(18 citation statements)

References 55 publications

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“…(2), where Z ϕϕ = Z ⊥ cos 2 θ + Z sin 2 θ, Z zz = Z cos 2 θ + Z ⊥ sin 2 θ, Z ϕz = Z zϕ = (Z − Z ⊥ ) sin θ cos θ. Tensor (A6) describes the averaged surface impedance for a metallic cylinder with helical subwavelength corrugations. It takes the well-known diagonal form in the extreme cases of θ = 0 • and θ = 90 • , which correspond to the PEC cylinder with longitudinal [47,48,51,52] and transverse [22,24,47] rectangular corrugations, respectively.…”

Section: Appendix A: Subwavelength Corrugated Cylindermentioning

confidence: 99%

Superscattering from Subwavelength Corrugated Cylinders

et al. 2020

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Wave scattering from a cylinder with a tensor impedance surface is investigated based on the Lorentz-Mie theory. A practical example of such a cylinder is a subwavelength metallic rod with helical dielectric-filled corrugations. The investigation is performed with the aim to maximize scattering cross-section by tailoring the surface impedance of cylindrical scatterers. For the normally incident TEz and TMz waves the required surface impedance of a subwavelength cylinder can be produced by longitudinal (axial) and transverse (circumferential) corrugations, respectively. It is shown that such corrugations induce superscattering at multiple frequencies, which can be widely tuned with either or both the size and permittivity of dielectric-filled corrugations. In the microwave band, this effect is demonstrated to be robust to material losses and is validated against the fullwave simulations and experiment. For the TEz waves the enhanced scattering from the cylinder is found to have a broad frequency bandwidth, provided that the relative permittivity of corrugations is low or equal unity. In the latter case, the corrugated cylinder acts as an all-metal superscatterer. For such cylinders the near-field measurements are implemented and provide the first experimental evidence of the superscattering phenomenon for all-metal objects. In addition to multifrequency superscattering, the dielectric-filled corrugations are shown to provide multifrequency cloaking of the cylinder under the incidence of the TMz waves. Simultaneous superscattering and cloaking at multiple frequencies distinguishes corrugated cylinders from other known practicable scatterers for potential applications in antenna designing, sensing, and energy harvesting.Enhancement of wave scattering from small objects is a vital issue in present-day technologies [1-7], including miniaturized antennas, sensors and energy harvesting devices. This issue is directly related to the natural constraint inherent in most subwavelength scatterers [8]. This constraint is known as a single-channel limit [9], which represents an upper limit to scattering crosssection for such scatterers and is attained under resonance condition for one of the scattering modes (channels). The only way to overcome this constraint is to ensure resonant scattering of several modes at a single frequency. Such a resonance overlapping magnifies scattering from a given object and is known as superscattering [9,10]. The larger the number of resonant modes, the larger the superscattering cross-section. Therefore, theoretically, superscattering opens a way to arbitrary enhancement of wave scattering from subwavelength objects. In practice, however, this effect is often hindered by the lack of low-loss materials and appropriate design solutions.In the infrared and visible parts of spectrum, the superscattering can be realized in cylindrical structures formed by several plasmonic and dielectric layers. In the pioneering work [9], for such a structure the total scattering cross-section was optimized to excee...

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Section: Appendix A: Subwavelength Corrugated Cylindermentioning

confidence: 99%

Superscattering from Subwavelength Corrugated Cylinders

et al. 2020

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“…One way to weaken this unwanted phenomenon is to use longitudinal wall corrugations of cylindrical gyrotron cavity. As is shown in [2], with proper choice of corrugation parameters, including their longitudinal distribution, depth, width and number, it is possible to increase selectively the diffractive losses of the fundamental competing modes of the second-harmonic gyrotron.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, wall corrugations induce additional ohmic losses in the cavity and thereby may reduce the efficiency of sub-THz gyrotron [3]. These losses are frequency-dependent [2,4]. As a consequence, the corrugation parameters can be selected in such a way as to provide maximum ohmic losses for the first-harmonic modes, together with relatively low losses for the operating second-harmonic mode.…”

Section: Introductionmentioning

confidence: 99%

MODE SELECTION BY OHMIC LOSSES IN LONGITUDINALLY CORRUGATED CAVITIES OF SUB-THz SECOND-HARMONIC GYROTRONS

Tkachova¹,

Shcherbinin²,

Ткаченко³

2019

Problems of Atomic Science and Technology

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Ohmic wall losses are proposed as a means for improving the mode selection in a cylindrical gyrotron cavity with longitudinal wedge-shaped corrugations. Such losses depend on mode frequency and geometrical parameters of the corrugations. For cavity of the 0.4-THz second-harmonic gyrotron we find the corrugation depth, which corresponds to maximum ohmic losses of the competing modes excited at the first (fundamental) cyclotron resonance, as well as to reasonably low losses of the operating mode. For this depth, we determine the number of corrugations and their width, which ensure the maximum enhancement of the ohmic wall losses of the fundamental modes with respect to those of the operating second-harmonic mode, together with minimum conversion of the operating second-harmonic mode to higher Bloch harmonics. Parameters of the corrugations in hand are practicable.

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“…The cutoff manipulation can be also used for the open-ended cavity design in the gyrotron. Besides the conventional way of radius variation, some structures with anisotropic surface impedance, such as dielectric-lined [11] and corrugated surfaces [12], have been proposed. In addition, the distributed surface impedance of the waveguide wall also enhances the selective properties of the gyrotron cavity, which means it can preferably trap a certain mode instead of unwanted parasitic modes.…”

Section: Introductionmentioning

confidence: 99%

Cutoff manipulation of anisotropic reactance lining in circular waveguides

Luo

Cui

Feng

2018

Int. J. Microw. Wireless Technol.

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The control of cutoffs is of great interest in designs of circular waveguides. In this paper, this topic is investigated for pure transverse-electric (TE) and transverse-magnetic (TM) modes by taking advantage of anisotropic reactance lining loadings. It is found that the cutoffs of TE and TM modes are determined by the reactance in the azimuthal and axial directions, respectively. When the reactance values are positive, the cutoff frequencies are lower than those of a normal conducting waveguide with the same cross-section. However, in contrast to the claim made in the previous literature that the negative reactance values caused the same reducing effect on the cutoffs as the positive values did, the cutoffs are found to be increased by the negative reactances. The theoretical results are validated by the simulations using commercial software, where a delicate model with an approximate curved anisotropic impedance boundary is proposed for the first time. By lowering the TE cutoffs and raising the TM ones, some intriguing applications, such as single-mode bandwidth extension and degenerate mode avoidance, are predicted, which would pave a way for designs of novel waveguide devices.

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Cylindrical Cavity with Distributed Longitudinal Corrugations for Second-Harmonic Gyrotrons

Cited by 27 publications

References 55 publications

Superscattering from Subwavelength Corrugated Cylinders

Superscattering from Subwavelength Corrugated Cylinders

MODE SELECTION BY OHMIC LOSSES IN LONGITUDINALLY CORRUGATED CAVITIES OF SUB-THz SECOND-HARMONIC GYROTRONS

Cutoff manipulation of anisotropic reactance lining in circular waveguides

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