Array Edges Research Articles

A violation of Fitts' Law occurs when a target range is presented before and during movement.

According to Fitts' Law, the time to reach a target (movement time, MT) increases with distance. A violation of Fitts' Law occurs when target positions are outlined before and during movement, as MTs are not different when reaching to the farthest and penultimate targets. One hypothesis posits that performers cognitively process the edges of a target array before the center, allowing for corrective movements to be completed more quickly when moving to edge targets compared to middle targets. The objective of this study was to test this hypothesis by displaying a target range rather than outlines of individual targets in an effort to identify the effects of array edges. Using a touch-screen laptop, participants (N = 24) were asked to reach to one of three targets which would appear within a presented range. Separately, targets were also presented without a range to determine if the display protocol could evoke Fitts' Law. Movements were assessed with the touch screen and optical position measurement. A main effect was found for relative position within a range (touch: F2,44 = 15.4, p < 0.001, η2p = 0.412; position: F2,40 = 15.6, p < 0.001, η2p = 0.439). As hypothesised, MT to the farthest target in a range was not significantly different than MT to the middle target (touch: p = 0.638, position: p = 0.449). No violation was found when a target range was not presented (touch: p = 0.003, position: p = 0.001). Thus, a target range reproduces the Fitts' Law violation previously documented with individually outlined targets, which supports and extends the discussed hypothesis.

Radiation-free and non-Hermitian topology inertial defect states of on-chip magnons

Radiative damping is a strong dissipation source for the quantum emitters hybridized with propagating photons, electrons, or phonons, which is not easily avoidable for on-chip magnonic emitters as well that can radiate via the surface acoustic waves of the substrate. Here we demonstrate in an array of on-chip nanomagnets coupled in a long range via exchanging the surface acoustic waves that a point defect in the array, which can be introduced by the local magnon frequency shift by a local biased magnetic field or the absence of a magnetic wire, strongly localizes the magnons, in contrast to the well spreading Bloch-like collective magnon modes in such an array setting. The radiation of the magnon defect states is exponentially suppressed by the distance of the defect to the array edges. Moreover, this defect state is strikingly inertial to the non-Hermitian topology that localizes all the extended states at one boundary. Such configuration robust magnon defect states towards radiation-free limit may be suitable for high-fidelity magnon quantum information storage in the future on-chip magnonic devices.

Advection-enhanced diffusion in biased convection arrays.

We numerically investigated the transport of a passive colloidal particle in a one-dimensional periodic array of planar counter-rotating convection rolls at high Péclet numbers. We show that advection-enhanced diffusion is drastically suppressed by an external transverse bias but strongly reinforced by a longitudinal drive of appropriate intensity. Both effects are magnified by imposing free-slip flows at the array's edges. The dependence of the diffusion constant on an external forcing is interpreted as a measure of the fluid-mechanical robustness of the flow boundary layer mechanism governing diffusion in convection rolls.

Synchronization properties and reservoir computing capability of hexagonal spintronic oscillator arrays

The influence of array geometry on synchronization properties of a 2-D oscillator array is investigated based on a comparison between a rectangular and a hexagonal grid. The Kuramoto model is solved for a nearest-neighbor case with periodic boundary conditions and for a small-scale, realistic coupling case with 1/r3 decay characteristic of spintronic oscillators. In both cases, it is found that the hexagonal grid choice leads to lower synchronization threshold and higher emission power than its rectangular counterpart, which results from increased connectivity, as well as, in the realistic-coupling case, from decreased contributions of the array edges. Additionally, a more general spin-torque oscillator model including both amplitude and phase as degrees of freedom is employed for reservoir computing simulations, showing that by using hexagonal grid one can increase the short-term memory capacity but not the parity-check capacity of the system.

5.3 μm-Emitting Diffraction-Limited Leaky-Wave-Coupled Quantum Cascade Laser Phase-Locked Array

A three-element phase-locked array of ∼5.3 μm-emitting quantum cascade lasers fabricated by a two-step MOCVD process is demonstrated which operates in a diffraction-limited beam to 5.3 W peak pulsed power. To compensate for overetching at the array edges, the fabrication process was modified such that it resulted in array elements of equal width. Then the array operates in a pure in-phase array mode, in agreement with simulations based on the actual device dimensions, which indicate that resonant leaky-wave coupling occurs for this device's geometry. Measured uniform near-field intensity profiles confirm resonant coupling. Simulations indicate that chirping of the element widths would allow for modification of the near-field intensity profile to mitigate the effects of thermal lensing in continuous-wave operation.

Metastable inhomogeneous vortex configuration with non-uniform filling fraction inside a blind hole array patterned in a BSCCO single crystal and concentrating magnetic flux inside it

Using magneto-optical imaging, we map the local magnetic field distribution inside a hexagonally ordered array of blind holes patterned in BSCCO single crystals. The nature of the spatial distribution of local magnetic field and shielding currents across the array reveals the presence of a non-uniform vortex configuration partially matched with the blind holes at sub-matching fields. We observe that the filling fraction is different in two different regions of the array. The mean vortex configuration within the array is described as a patchy vortex configuration with the patches having different mean filling fraction. The patchy nature of the vortex configuration is more pronounced at partial filling of the array at low fields while the configuration becomes more uniform with a unique filling fraction at higher fields. The metastable nature of this patchy vortex configuration is revealed by the application of magnetic field pulses of fixed height or individual pulses of varying height to the array. The metastability of the vortex configuration allows a relatively easy way of producing flux reorganization and flux focusing effects within the blind hole array. The effect of the magnetic field pulses modifies the vortex configuration within the array and produces a uniform enhancement in the shielding current around the patterned array edges. The enhanced shielding current concentrates magnetic flux within the array by driving vortices away from the edges and towards the center of the array. The enhanced shielding current also prevents the uninhibited entry of vortices into the array. We propose that the metastable patchy vortex configuration within the blind hole array is due to a non-uniform pinning landscape leading to non-uniform filling of individual blind holes.

Self-induced topological transitions and edge states supported by nonlinear staggered potentials

The canonical Su-Schrieffer-Heeger (SSH) model is one of the basic geometries that have spurred significant interest in topologically nontrivial bandgap modes with robust properties. Here, we show that the inclusion of suitable third-order Kerr nonlinearities in SSH arrays opens rich new physics in topological insulators, including the possibility of supporting self-induced topological transitions based on the applied intensity. We highlight the emergence of a new class of topological solutions in nonlinear SSH arrays, localized at the array edges. As opposed to their linear counterparts, these nonlinear states decay to a plateau with non-zero amplitude inside the array, highlighting the local nature of topologically nontrivial bandgaps in nonlinear systems. We derive the conditions under which these unusual responses can be achieved, and their dynamics as a function of applied intensity. Our work paves the way to new directions in the physics of topologically non-trivial edge states with robust propagation properties based on nonlinear interactions in suitably designed periodic arrays.

Ultrasonic Vibration Assisted Grinding of Microstructures on Binderless Tungsten Carbide (WC)

Microstructured optical elements made of glass are generally replicated by hot pressing with super-hard materials, such as binderless tungsten carbide (WC) and precision ceramic. However, in grinding of microstructures, problems frequently occur in terms of rough ground surface, chipping and rounding of micro-structures edges when compared to conventional grinding. In order to overcome these technological constraints, a promising precision grinding method for microstructured surfaces that applies ultrasonic vibration to improve the surface quality, and protect the edges and tips of microstructured surfaces is presented. The experimental investigation of ultrasonic vibration assisted grinding of microstructures on binderless WC is researched. The effects of ultrasonic vibration on surface roughness, form accuracy and edge radius were analyzed. The morphology of surface and array edges was examined with a scanning electron microscope (SEM), while the surface roughness was measured by a laser interferometer. And a contact probe profilometer was used to assess the form of array and radius of microstructured edges. Experimental results showed that the application of ultrasonic vibration leads to significant improvements of the surface roughness and edges of microstructures compared with traditional precision grinding processes. A micro cylinder lens array of binderless WC with surface roughness of 78nm and edge radius of less than 1μm was obtained. The novel grinding method is feasible and applicable in machining higher form accuracy microstructures.

UWB Low-Profile Tightly Coupled Dipole Array With Integrated Balun and Edge Terminations

Tightly coupled phased arrays (TCPAs) provide UWB performance due to their strong inter-element coupling. However, in finite tightly coupled phased array realizations, mutual coupling is reduced near the array edges, causing the edge elements to become narrowband. To address this issue, a nonuniform array excitation scheme, referred to as “characteristic mode (CM) excitation,” was recently proposed. A more practical alternative for designing UWB tightly coupled phased arrays is proposed here. In this paper, we present a strategy that employs uniform excitation of the central array elements and short-circuits the periphery elements. We report that at least for medium size arrays, this approach provides up to 3 dB more gain and 50% higher efficiency than typical resistive termination. This concept is demonstrated using a 7 × 7 linearly polarized dipole array, 60.96 cm × 60.96 cm (2' × 2') in size, for operation from 200 MHz-600 MHz. Feeding of the active elements is challenging due to several constraints on the feed design, including balanced to unbalanced transitions, impedance transformations, common mode suppression, compact size, low cost, etc. To address these issues we propose a novel array feed using a compact, ultrawideband balun (with 10:1 bandwidth for VSWR ). Simulated and measured data are provided for broadside and 30 scan in the H-plane.

Development of a surgical approach for a wide-view suprachoroidal retinal prosthesis: evaluation of implantation trauma

Our research goal is to develop a safe, reproducible surgical approach for implantation of a wide-field retinal stimulating array. The aim of this study was to evaluate the pathological response to acute implantation of a functional prototype electrode array in the suprachoroidal space. The surgical techniques to implant a 72 platinum electrode array fabricated on 8 × 13 × 0.4mm polyimide and silicone substrate were developed in a pilot study in anesthetized cats. For the main study, nine eyes were implanted in vivo and unoperated eyes were used as controls. Surgery consisted of a temporal approach with a full-thickness scleral incision 5mm posterior to the limbus. A suprachoroidal "pocket" was created, the electrode array inserted to sit beneath the area centralis, and placement was confirmed visually. The eyes were collected subsequently for histopathology. The array was consistently inserted into the suprachoroidal space beneath the area centralis in nine eyes. There was a significant hemorrhage in two cases where implantation was complicated by choroidal congestion. Retinal folding occurred only when the array tip was within 2.6mm of the optic disc (p < 0.01). There was choroidal incarceration at the incision in six eyes and scleral distortion at the array edges in five. No cases were found where the implant breached the retina, choroid, or sclera. A large stimulation array can be reliably inserted into the suprachoroidal space without trauma to the neuroretina. These findings suggest that this is an appropriate surgical approach for the placement of an electrode array for use in retinal stimulation.

Surface modes and breathers in finite arrays of nonlinear waveguides

We present the complete set of symmetric and antisymmetric (edge and corner) surface modes in finite one- and two-dimensional arrays of waveguides. We provide classification of the modes based on the anti-continuum limit, study their stability and bifurcations, and discuss relation between surface and bulk modes. We put forward existence of surface breathers, which represent two-frequency modes localized about the array edges.

A hybrid spectral/spatial method to evaluate the active Green's function of large planar rectangular arrays: a combined asymptotic/numerical algorithm

The article illustrates a formulation to evaluate the array Green's function (AGF) of large finite planar phased array for observation points on the array plane, possibly close to the array contour. The procedure is based on the AGF representation in terms of a double spectral integral, whose integration paths are properly deformed to have an exponential attenuation of the integrand. The diffraction integral is evaluated numerically for point close to the array edges while an asymptotic treatment is proposed far from the edges. This latter comprises higher order contributions. Thanks to the convergence properties, the final algorithm is numerically accurate, stable and more efficient with respect to the individual element summation for large arrays. It also constitutes the basic step for the efficient evaluation of the AGF of a multilayer environment

How light emerges from an illuminated array of subwavelength holes

The extraordinary optical transmission through periodic arrays of subwavelength holes has been studied extensively since it was first reported in 1998, owing to both its fundamental implications and its technological potential. The picture of the underlying mechanism that emerges from most of the theoretical studies is a resonant process assisted by surface electromagnetic modes, such as surface plasmons. However, these studies consider an infinite array of holes. By combining experiment and theory, we have analysed the influence of the inherent finite size of the arrays and report here the unexpected spatial distribution of light as it emerges from the arrays. This distribution is strongly anisotropic and extremely sensitive to the angle of incidence of the impinging light. The behaviour can be explained by a model that takes into account the asymmetry induced by the array edges, and the effects this has on the emission pattern across the array.

Asymptotic high-frequency Green's function for a large rectangular planar periodic phased array of dipoles with weakly tapered excitation in two dimensions

This paper deals with the derivation and physical interpretation of a uniform high-frequency representation of the Green's function for a large planar rectangular phased array of dipoles with weakly varying excitation. Thereby, our earlier published results, valid for equiamplitude excitation, and those for tapered illumination in one dimension are extended to tapering along both dimensions, including dipole amplitudes tending to zero at the edges. As previously, the field obtained by direct summation over the contributions from the individual radiators is restructured into a double spectral integral whose high-frequency asymptotic reduction yields a series of propagating and evanescent Floquet waves (FWs) together with corresponding FW-modulated diffracted fields, which arise from FW scattering at the array edges and vertexes. To accommodate the weak amplitude tapering, new generalized periodicity-modulated edge and vertex slope transition functions are introduced, accompanied by a systematic procedure for their numerical evaluation. Special attention is given to the analysis and physical interpretation of the complex vertex diffracted ray fields. A sample calculation is included to demonstrate the accuracy of the asymptotic algorithm. The resulting array Green's function forms the basic building block for the full-wave analysis of planar weakly amplitude-tapered phased array antennas, and for the description of electromagnetic radiation and scattering from weakly amplitude-tapered rectangular periodic structures

Three-dimensional Green’s function for planar rectangular phased dipole arrays

This paper deals with the construction, physical interpretation and application of a uniform high-frequency representation of array Green’s functions (AGFs) for planar rectangular phased arrays of dipoles. An AGF is the basic constituent for the full-wave description of electromagnetic radiation from large periodic structures. For efficient treatment of high-frequency phenomena, the AGF obtained by direct summation over the contributions from the individual radiators is globally restructured via the Poisson sum formula into a series of propagating and evanescent Floquet waves (FWs) together with corresponding FW-modulated diffracted waves, which arise from FW scattering at the array edges and vertexes. These results are obtained by high-frequency uniform asymptotics applied to the wave integrals generated by Poisson summation in the spatial or spectral domains. The final algorithm is physically appealing, numerically accurate, and efficient, owing to the rapid convergence of both the FW series and the series of corresponding FW-modulated diffracted fields away from the array plane. The use of the asymptotic AGF in the full-wave analysis of large slot arrays is discussed, with the inclusion of numerical results.

Asymptotic high‐frequency Green's function for a planar phased sectoral array of dipoles

This paper deals with the derivation and physical interpretation of a uniform high‐frequency Green's function for a planar right‐angle sectoral phased array of dipoles. This high‐frequency Green's function represents the basic constituent for the full‐wave description of electromagnetic radiation from rectangular periodic arrays and scattering from rectangular periodic structures. The field obtained by direct summation over the contributions from the individual radiators is restructured into a double spectral integral whose high‐frequency asymptotic reduction yields a series of propagating and evanescent Floquet waves (FWs) together with corresponding FW‐modulated diffracted fields, which arise from FW scattering at the array edges and vertex. Emphasis is given to the analysis and physical interpretation of the vertex diffracted rays. The locally uniform asymptotics governing this phenomenology is physically appealing, numerically accurate, and efficient, owing to the rapid convergence of both the FW series and the series of corresponding FW‐modulated diffracted fields away from the array plane. A sample calculation is included to demonstrate the accuracy of the asymptotic algorithm.

Edge effects in a frustrated Josephson-junction array with modulated couplings

A square array of Josephson junctions with modulated strength in a magnetic field with half a flux quantum per plaquette is studied by analytic arguments and dynamical simulations. The modulation is such that alternate columns of junctions are of different strength to the rest. Previous work has shown that this system undergoes an XY followed by an Ising-like vortex lattice disordering transition at a lower temperature. We argue that resistance measurements are a possible probe of the vortex lattice disordering transition as the linear resistance $R_{L}(T)\sim A(T)/L$ with $ A(T) \propto (T-T_{cI})$ at intermediate temperatures $T_{cXY}>T>T_{cI}$ due to dissipation at the array edges for a particular geometry and vanishes for other geometries. Extensive dynamical simulations are performed which support the qualitative physical arguments.

Phase locking of a semiconductor diode array in an external cavity

Theoretical investigations are reported of the characteristics of high-power lasers with the active medium in the form of a semiconductor diode array. The selectivity of a Talbot cavity, of a cavity with an aspherical output mirror, and of a semiconfocal cavity is studied as a function of the array parameters. Estimates are obtained of the sensitivity of the laser radiation characteristics to fluctuations of the array parameters. It is shown that the dependence of the selectivity of an aspherical cavity on these parameters is nearly the same as that of a Talbot cavity, but the fundamental mode propagates without radiation losses between the diodes and beyond the array edges. A semiconfocal cavity is more selective than a Talbot or aspherical cavity. When the number of diodes in a linear array exceeds 20, the losses of the second mode in a semiconfocal cavity grow to more than 80%. The efficiency of a laser with a semiconfocal cavity, calculated ignoring the diode efficiency, can reach 80–90%.

Vortex reflection at boundaries of Josephson-junction arrays.

We study the propagation properties of a single vortex in square Josephson-junction arrays (JJA) with free boundaries and subject to an applied dc current. We model the dynamics of the JJA by the resistively and capacitively shunted junction (RCSJ) equations. For zero Stewart-McCumber parameter $\beta_c$ we find that the vortex always escapes from the array when it gets to the boundary. For $\beta_c\geq 2.5$ and for low currents we find that the vortex escapes, while for larger currents the vortex is reflected as an antivortex at one edge and the antivortex as a vortex at the other, leading to a stationary oscillatory state and to a non-zero time-averaged voltage. The escape and the reflection of a vortex at the array edges are qualitatively explained in terms of a coarse-grained model of a vortex interacting logarithmically with its image. We also discuss the case when the free boundaries are at $45$ degrees with respect to the direction of the vortex motion. Finally, we discuss the effect of self-induced magnetic fields by taking into account the full-range inductance matrix of the array, and find qualitatively equivalent results.

Statics and dynamics of single-electron solitons in two-dimensional arrays of ultrasmall tunnel junctions

We have analyzed the distribution and transfer of electric charge in a uniform two-dimensional array of ultrasmall tunnel junctions. The effects can be most adequately described in terms of topological solitons with charge ± e. Field distribution in the soliton, its intrinsic energy, and the energy of interaction between the solitons and array edges have been calculated and compared with those for the one-dimensional case studied earlier. Numerical simulations have shown that the solitons tend to form a two-dimensional Wigner crystal which can be driven along the array without melting, on certain conditions. Such a correlated transfer of charge induces narrow-band “SET” oscillations of frequency f s = I e , where I is the average current carried by the solitons. Conditions of experimental observation of this effect have been analyzed and compared with those for the one-dimensional arrays.