Interchannel Coupling Effects Research Articles

A practical approach for calibration of MMW MIMO near-field imaging

Near-field millimeter-wave (MMW) imaging techniques typically employ multiple-input-multiple-output (MIMO) arrays to obtain high-resolution images. However, the image quality can be seriously affected by array miscalibration. In this paper, a simple and efficient calibration method for MMW MIMO arrays is proposed and validated with real data. The approach makes use of a metal plate as a reference target to collect data in the presence and absence of the reference target. By processing the two sets of received data, we can reduce the effects of inter-channel coupling and environmental interference. The method calculates the reflected position and transmission distance of the electromagnetic wave based on the transmission model of the electromagnetic wave by the metal plate. And the transmission distance difference of all transceiver pairs is eliminated. Then, the delay error and phase error between the channels are successively calculated. Numerical simulations and real measured data are processed to validate the proposed calibration method. The results demonstrate that it is an effective tool for calibrating MMW MIMO arrays.

Interchannel Coupling Effects on Atomic Photoionization: Correlation in the Continuum

Correlation in the form of interchannel coupling of continuum states is explained in the context of atomic photoionization. A number of examples are presented illustrating some of the qualitative and quantitative effects of this coupling.

Capturing Correlation Effects on Photoionization Dynamics.

A highly correlated combination of the equation-of-motion coupled cluster (EOM-CC) Dyson orbital and the multicentric B-spline time-dependent density functional theory (TDDFT)-based approach is proposed and implemented within the single-channel approximation to describe molecular photoionization processes. The twofold objective of the approach is to capture interchannel coupling effects, missing in the B-spline DFT treatment, and to explore the response of Dyson orbitals to strong correlation effects and its influence on the photoionization observables. We validate our scheme by computing partial cross sections, branching ratios, asymmetry parameters, and molecular frame photoelectron angular distributions of simple molecules. Finally, the method has been applied to the study of photoelectron spectra of the Ni(C3H5)2 molecule, where giant correlation effects completely destroy the Koopmans picture.

Photoionization of C60: Effects of Correlation on Cross Sections and Angular Distributions of Valence Subshells.

Calculations of the photoionization cross section and asymmetry parameter, β, are performed at the density functional theory (DFT) and time-dependent density functional theory (TDDFT) levels for all 32 valence levels of C60. Accurate numerical results are obtained for the isolated molecule in icosahedral symmetry. A detailed analysis based on the comparison between the DFT and TDDFT results allows the identification of four types of resonances: the well-known confinement resonances of mainly geometrical origin, shape resonances native to the ionization channel, induced shape resonances, and autoionization resonances brought about by interchannel coupling, as well as their different prominence in cross section or asymmetry parameter. Generally, cross sections are enhanced at the TDDFT level, which includes contribution from the bound-state excitations from closed channels, neglected at the DFT level, and the effect persists even well above the highest ionization threshold. This effect is best seen in the total cross section, although not as dramatic as found from simpler models, probably due to the stiffer electronic structure inherent in the full molecular description. The effects of interchannel coupling on individual native resonances are rather less predictable, leading to both enhancement and decreases and often altering the details of the structure significantly. A comparison with the previous accurate total cross-sectional calculations, as well as with the available experimental data, is very good for cross sections but slightly inferior for β's. The results reported can serve as a reference to compare the effects of different environments on C60, as well as chemical substitution, notably endohedral fullerenes.

A Single Layer 3-D Touch Sensing System for Mobile Devices Application

Touch sensing has been widely implemented as a main methodology to bridge human and machine interactions. The traditional touch sensing range is 2-D and therefore limits the user experience. To overcome these limitations, we propose a novel 3-D contactless touch sensing called Airtouch system, which improves user experience by remotely detecting single/multi-finger position. A single layer touch panel with triangle-shaped electrodes is proposed to achieve multitouch detection capability as well as manufacturing cost reduction. Moreover, an oscillator-based-capacitive touch sensing circuit is implemented as the sensing hardware with the bootstrapping technique to eliminate the interchannel coupling effects. To further improve the system accuracy, a grouping algorithm is proposed to group the useful channels’ data and filter out hardware noise impact. Finally, improved algorithms are proposed to eliminate the fringing capacitance effect and achieve accurate finger position estimation. EM simulation proved that the proposed algorithm reduced the maximum systematic error by 11 dB in the horizontal position detection. The proposed system consumes 2.3 mW and is fully compatible with existing mobile device environments. A prototype is built to demonstrate that the system can successfully detect finger movement in a vertical direction up to 6 cm and achieve a horizontal resolution up to 0.6 cm at 1 cm finger-height. As a new interface for human and machine interactions, this system offers great potential in finger movement detection and gesture recognition for small-sized electronics and advanced human interactive games for mobile device.

Time-dependent configuration-interaction-singles calculation of the 5p -subshell two-photon ionization cross section in xenon

The $5p$ two-photon ionization cross section of xenon in the photon-energy range below the one-photon ionization threshold is calculated within the time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS calculations are compared to random-phase-approximation (RPA) calculations [Wendin \textit{et al.}, J. Opt. Soc. Am. B \textbf{4}, 833 (1987)] and are found to reproduce the energy positions of the intermediate Rydberg states reasonably well. The effect of interchannel coupling is also investigated and found to change the cross section of the $5p$ shell only slightly compared to the intrachannel case.

A 2.3-mW 11-cm Range Bootstrapped and Correlated-Double-Sampling Three-Dimensional Touch Sensing Circuit for Mobile Devices

This brief discusses an oscillator-based capacitive 3-D touch-sensing circuit for mobile devices. The proposed 3-D touch sensor uses correlated double sampling to achieve a high sensing resolution in the Z-direction and employs bootstrapping circuitry to reduce the mobile screen's interchannel-coupling effects. Additionally, to reduce chip area and assembly, the sensing oscillator is implemented with inverter-based active resonators instead of using either on- or off-chip inductors. The prototyped 3-D touch sensor is fabricated using 65-nm CMOS process technology and consumes an area of 2 mm2, with a 2.3-mW power consumption from a 1-V power supply. Measured together with a 3.4′′ HTC standard mobile screen, the sensor achieves an 11-cm Z-direction sensing range with a 1-cm resolution, demonstrating the potential implementation of 3-D finger position sensing in a mobile device.

Photoionization of endohedral atoms: Molecular and interchannel-coupling effects

Calculations of the photoionization cross section of the $2p$ and $3s$ subshells of free Ar and Ar@${\mathrm{C}}_{60}$ as examples have been performed using the molecular structure of the confined system and time-dependent density functional theory for the dynamical quantities. The results for $\mathrm{Ar}\phantom{\rule{0.28em}{0ex}}2p$ in the combined system exhibit significant confinement resonances with the lower-energy ones being quite sharp, in contrast to the results of jellium-model calculations. In addition, calculations done with and without interchannel coupling between the photoionization channels of the $2p$ subshell of the Ar atom and the $1s$ subshell of the ${\mathrm{C}}_{60}$ shell show that, in this case, the coupling is of negligible importance, even though the $\mathrm{C}\phantom{\rule{0.28em}{0ex}}1s$ cross section is more than an order of magnitude larger than that of $\mathrm{Ar}\phantom{\rule{0.28em}{0ex}}2p$ in the 300 eV range. The $\mathrm{Ar}\phantom{\rule{0.28em}{0ex}}3s$, which is not hybridized, also exhibits confinement resonances, but is very strongly affected by interchannel coupling with photoionization channels from the ${\mathrm{C}}_{60}$ shell. The phenomenology of both $2p$ and $3s$ subshells is explained in terms of the interchannel-coupling matrix elements. These results should be applicable to inner-shell ionization of essentially any endohedral fullerene system.

Interchannel coupling effects in the valence photoionization of SF6.

The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u (6)1t2g (6)3eg (4)(5t1u (6)+1t2u (6)) 1t1g (6) as the most likely ordering.

Valence photoionization of noble-gas atoms confined in the fullereneC60

A systematic study and comparison of the photoionization cross sections of the outer and inner shells of the noble-gas atoms He, Ne, Ar, Kr, and Xe confined endohedrally inside a ${\text{C}}_{60}$ molecule are calculated by employing a time-dependent local-density-approximation formulation. Confinement resonances are found to be a general feature of these cross sections and dramatic interchannel coupling effects, significantly increasing the atomic cross sections, are exhibited in all cases in the vicinity of the ${\text{C}}_{60}$ plasmons. Hybridization effects, the mixing of the atomic and cage bound-state wave functions, are also found, but no systematics of the hybridization present themselves.

Effect of confinement and interchannel coupling on high-Z atoms

Photoionization studies of outer shells of high-Z atoms like Radon (Z=86) and Radium (Z=88) have been studied using relativistic random phase approximation (RRPA) [1,2]. Multiple minima found in the pho-toionization cross section were attributed to many electron correlations resulting from interchannel coupling with photoionization channels from neighboring subshells. In the present work, we report the combined effect of confinement, correlation and relativistic interactions on the structure of these multiple minima in high-Z atoms by using the RRPA.

Pronounced effects of interchannel coupling in high-energy photoionization

The 3d core level photoemission of metallic Ag and In was measured over a wide energy range including the 2p ionization thresholds. The intensities (photoionization cross sections) of the 3d5/2 and 3d3/2 lines were observed to modulate significantly with photon energy, both absolute and relative, and this is most pronounced in the vicinity of the 2p thresholds, i.e., at photon energies about an order of magnitude above the 3d thresholds. Calculations based on the relativistic-random-phase approximation show that this effect is due to interchannel coupling of the 3d photoionization channels with the 2p channels affecting the cross section over a wide range of energies. It is argued that this is a general phenomenon in high-energy photoionization throughout the periodic table.

Effect of Interchannel Coupling and Confinement on the Photoionization of Kr

The effect of interchannel coupling and confinement on the photoionization of the Kr atom is examined. It is found that the position of the Cooper minimum is sensitive to interchannel coupling in both free and confined Kr. The strengths of the confinement oscillations are also sensitive to interchannel coupling.

Dipole and Quadrupole Photoionization of Intermediate Subshells of Atomic Mercury

Dipole and quadrupole photoionization parameters for intermediate subshells of mercury have been studied using the relativistic-random-phase-approximation (RRPA). Multiple Cooper minima are observed in 5d quadrupole cross sections, even at the level of intrashell coupling. It has been found that the effect of interchannel coupling is much more significant for dipole photoionization parameters than for quadrupole parameters.

Photoionization of atomic krypton confined in the fullerene C60

The combined effects of interchannel coupling, relativistic interactions and endohedral confinement on the photoionization of atomic Kr are studied. The confinement of the Kr atom placed at the centre of the C60 cage is modelled by placing the atom inside an annular spherical potential. Cross sections for the photoionization and angular distribution of photoelectrons from the 4p, 4s, 3d and 3p subshells are reported within the framework of the relativistic-random-phase approximation.

Strong-field ionization and high-order-harmonic generation during polyatomic molecular dynamics of N2O4

We present state-of-the-art ab initio--type computations of strong-field ionization (SFI) and the single-molecule response contribution to high-order-harmonic generation (HHG) in the polyatomic molecule N${}_{2}$O${}_{4}$. The numerical method uses a mixed orbital- and grid-based approach to model the multielectron bound states and single-electron continuum. The effects of ionic-core attraction and Coulomb-mediated interchannel coupling are rigorously included. We show that full-dimensionality time-dependent multielectron computations of SFI and HHG in polyatomic molecules are now feasible. The computational results indicate that (a) SFI yields in N${}_{2}$O${}_{4}$ are dominated by a single ionic state (the ${A}_{g}$ state), and are strongly modulated by the N-N stretch coordinate; and (b) the HHG radiating dipole as a function of the N${}_{2}$O${}_{4}$ N-N stretch is dominated by the same, single state. The molecular-beam coincidence measurements presented here support the computational results. Due to the differences in the estimated vibrational amplitude, however, the computations are not in full agreement with previous HHG data.

Nondipole and interchannel-coupling effects in the photodetachment ofCl−

Nondipole photodetachment parameters for the $3p$ subshell of ${\text{Cl}}^{\ensuremath{-}}$ are calculated using relativistic random-phase approximation (RRPA). Interchannel-coupling effects on nondipole photodetachment parameters for the $3p$ subshell are studied with different degrees of truncation of the RRPA. It is inferred from the present investigations that the shape resonance in the photodetachment cross-section profile and the positions of the Cooper minima are sensitive to interchannel coupling. An analysis of the angular distribution of the photoelectrons reveals how the Cooper minima in the dipole and the quadrupole channels introduce a complex energy dependence, with peaks and zeroes, of the nondipole asymmetry parameter $\ensuremath{\zeta}$.

Spin-orbit-interaction activated interchannel coupling in dipole and quadrupole photoionization

The effect of spin-orbit interaction activated interchannel coupling in dipole and quadrupole photoionization of the $4p$ and $4d$ subshells of Xe and the $5p$ and $5d$ subshells of Rn using the relativistic random phase approximation (RRPA) is studied. Interference between channels arising from spin-orbit split components is found to influence the dipole cross sections of $\text{Xe}\text{ }4d$ and $\text{Rn}\text{ }5d$ subshells, and also the quadrupole cross sections of $\text{Xe}\text{ }4p$ and $\text{Rn}\text{ }5p$ subshells. The photoelectron angular distribution parameters are also affected, but to a lesser extent. Using the understanding gained, the conditions required for large spin-orbit interaction activated interchannel coupling effects are delineated.

Time dependent density functional study of the photoionization dynamics of SF6

The B-spline linear combination of atomic orbitals method has been employed to study the valence and core photoionization dynamics of SF6. The cross section and asymmetry parameter profiles calculated at the time dependent density functional theory level have been found to be in fairly nice agreement with the experimental data, with the quality of the exchange-correlation statistical average of orbital potential results superior to the Van Leeuwen-Baerends 94 (LB94) ones [Phys. Rev. A 49, 2421 (1994)]. The role of response effects has been identified by a comparison of the time dependent density functional theory results with the Kohn-Sham ones interchannel coupling effects and autoionization resonances play an important role at low kinetic energies. Prominent shape resonances features have been analyzed in terms of "dipole prepared" continuum orbitals and interpreted as due to a large angular momentum centrifugal barrier as well as anisotropic (nonspherical) molecular effective potential. Finally, the method has been proven numerically stable, robust, and efficient, thanks to a noniterative implementation of the time dependent density functional theory equations and suitability of the multicentric B-spline basis set to describe continuum states from outer valence to deep core states.

Interchannel coupling effects on non-dipole photoionization parameters

Interchannel coupling effects involving non-dipole matrix elements on photoelectron angular distribution have been recently found to be of significant importance even at energies not so high above ionization thresholds. Studies have been reported on the angular distribution of photoelectrons from some inert gas atoms: Ne, Ar, Kr and Xe. In the present work, we report further studies on atomic xenon, and also results on atomic mercury, using the relativistic random phase approximation. Also, we report the angular distribution asymmetry parameters with the inclusion of non-dipole terms for a confined atom; @ Ca is considered as a model system for this study.