Longitudinal Section Electric Modes Research Articles

New insights on Titan's plasma-driven Schumann resonance inferred from Huygens and Cassini data

After a preliminary analysis of the low-frequency data collected with the electric antenna of the Permittivity, Wave and Altimetry (PWA) experiment onboard the Huygens Probe that landed on Titan on 14 January, 2005, it was anticipated in a previous article [Béghin et al., 2007. A Schumann-like resonance on Titan driven by Saturn's magnetosphere possibly revealed by the Huygens Probe. Icarus, 191, 251–266] that the Extremely Low-Frequency (ELF) signal at around 36 Hz observed throughout the descent, might have been generated in the upper ionosphere of Titan, driven by a plasma instability mechanism associated with the co-rotating Kronian plasma flow. The involved process was proposed as the most likely source of a Schumann resonance in the moon's atmospheric cavity, the second eigenmode of which is actually found by models to occur at around 36 Hz. In this paper, we present a thorough analysis of this signal based upon the Huygens Probe attitude data deduced from the Descent Imager Spectral Radiometer (DISR), and relevant measurements obtained from the Radio Plasma Wave Science (RPWS) experiment and from the magnetometer (MAG) onboard Cassini orbiter during flybys of Titan. We have derived several coherent characteristics of the signal which confirm the validity of the mechanism initially proposed and provide new and significant insights about such a unique type of Schumann resonance in the solar system. Indeed, the 36 Hz signal contains all the characteristics of a polarized wave, with the measured electric field horizontal component modulated by the antenna rotation, and an altitude profile in agreement with a Longitudinal Section Electric (LSE) eigenmode of the atmospheric cavity. In contrast to Earth's conditions where the conventional Transverse Magnetic mode is considered, the LSE mode appears to be the only one complying with the observations and the unexpected peculiar conditions on Titan. These conditions are essentially the lack of any lightning activity that can be ascertained from Cassini observations, the presence of an ionized layer centered around 62 km altitude that was discovered by the PWA instrumentation, and the existence of a subsurface conducting boundary which is mandatory for trapping ELF waves. A simple theoretical model derived from our analysis places tentatively consequential constraints on the conductivity profile in the lower ionosphere. It is also consistent with the presence of a conductive water ocean below an icy crust some tens of kilometers thick.

Fundamental modal properties of SRR metamaterials and metamaterial based waveguiding structures

A rigorous full wave analysis of bianisotropic split ring resonator (SRR) metamaterials is presented for different electromagnetic field polarization and propagation directions. An alternative physical explanation is gained by revealing the fact that imaginary wave number leads to the SRR resonance. Metamaterial based parallel plate waveguide and rectangular waveguide are then examined to explore the resonance response to transverse magnetic and transverse electric waves. It is shown that different dispersion properties, such as non-cutoff frequency mode propagation and enhanced bandwidth of single mode operation, become into existence under certain circumstances. In addition, salient dispersion properties are imparted to non-radiative dielectric waveguides and H waveguides by uniaxial bianisotropic SRR metamaterials. Both longitudinal-section magnetic and longitudinal-section electric modes are capable of propagating very slowly due to metamaterial bianisotropic effects. Particularly, the abnormal falling behavior of some higher-order modes, eventually leading to the leakage, may appear when metamaterials are double negative. Fortunately, for other modes, leakage can be reduced due to the magnetoelectric coupling. When the metamaterials are of single negative parameters, leakage elimination can be achieved.

Slow wave propagation in nonradiative dielectric waveguides with bianisotropic split ring resonator metamaterials

Different dispersion properties are imparted to nonradiative dielectric (NRD) waveguides by split ring resonator metamaterials. Both longitudinal section magnetic and longitudinal section electric modes are capable of propagating very slowly due to the metamaterial bianisotropic effects, and can even approach zero velocity under certain condition. Enhanced energy flow in the considered structure is also demonstrated. Finally, miniaturization of NRD waveguide based on these unusual properties is proposed.

Slow wave propagation in metamaterial based nonradiative dielectric waveguides and its application

Different dispersion properties are imparted to nonradiative dielectric (NRD) waveguides by split ring resonator metamaterials. Both longitudinal-section magnetic and longitudinal-section electric modes are capable of propagating very slowly due to the metamaterial bianisotropic effects, and can even approach zero velocity. Enhanced energy flow in the considered structure is also demonstrated under certain conditions. Finally, miniaturization of NRD waveguide based on these unusual properties is proposed.

Hamiltonian symplectic semi-analytical method and its application in inhomogeneous electromagnetic waveguides

Dual vectors are applied in Hamilton system of applied mechanics. Electric and magnetic field vectors are the dual vectors in electromagnetic field. The Hamilton system method is introduced into the analysis of electromagnetism waveguide with inhomogeneous materials. The transverse electric and magnetic fields are regarded as the dual. The basic equations are solved in Hamilton system and symplectic geometry. With the Hamilton variational principle, the symplectic semi-analytical equations are derived and preserve their symplectic structures. The given numerical example demonstrates the solution of LSE (Longitudinal Section Electric) mode in a dielectric waveguide.

Dipole-mode wakefields in dielectric-loaded rectangular waveguide accelerating structures.

By applying different symmetric boundary conditions, we found that the transverse wakefields generated by an electron bunch traveling through a partially loaded rectangular dielectric structure at an off center position can be decomposed into corresponding orthogonal longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes for guided waves as in the case of longitudinal wakefields treated previously. The wakefields are characterized using the normalized shunt impedance R/Q, a function of the geometry of the accelerating structure, for both LSE and LSM modes. A numerical example is given for an X-band waveguide structure and detailed results are given for the several leading transverse wakefield terms. The analytic results obtained are in agreement with the results from the time domain simulation tool MAFIA.

Complete characterization of transmission losses in generalized nonradiative dielectric (NRD) waveguide

In this paper, transmission losses of the generalized nonradiative dielectric (NRD) waveguide are modeled and presented by our closed-form equations for the design of hybrid and monolithic millimeter-wave integrated circuits. This generalized structure includes our recently proposed channelized NRD-guide. Parametric effects are studied with respect to complex propagation constant and characteristic impedance, and some useful guidelines are generated for practical design considerations. Calculated results are discussed separately for the conductor and dielectric losses for the two fundamental longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes. It is found that the LSE mode may have losses, in some cases, comparable or even smaller than those of its LSM counterpart, contradicting what has usually been perceived for the conventional NRD-guide design.

CAD-oriented, generalised admittance matrix approach for arbitrarily corrugated E-plane sectoral horns

The paper presents an efficient algorithm for the analysis and computer aided design of arbitrarily corrugated E-plane sectoral horn. This algorithm is based on the generalised admittance matrix method, which allows an efficient evaluatiom of the modal scattering matrix of cascaded discontinuities and junctions. The use of longitudinal section electric modes and of analytical or semianalytical expressions for calculating the modal reaction integrals for both the internal and the external regions, results in extreme speed-up of the overall procedure. Furthermore, an efficient connection scheme is implemented to save dynamic memory and inversion matrix CPU time. The results and the simplified assumption in the modal expression are successfully validated through comparisons with other numerical methods and experimental data. An example on dual-band corrugated horns is presented.