Coupling In Arrays Research Articles

Spontaneous PT -symmetry breaking in non-Hermitian coupled-cavity array

We study the effects of the position of the passive and active cavities on the spontaneous parity-time (PT) symmetry breaking behavior in non-Hermitian coupled cavities array model. We analyze and discuss the energy eigenvalue spectrums and PT symmetry in the topologically trivial and nontrivial regimes under three different cases in detail, i.e., the passive and active cavities are located at, respectively, the two end positions, the second and penultimate positions, and each position in coupled cavities array. The odevity of the number of cavities is further considered to check the effects of the non-Hermitian terms applied on the PT symmetric and asymmetric systems. We find that the position of the passive and active cavities has remarkable impacts on the spontaneous PT symmetry breaking behavior, and in each case the system exhibits distinguishable and novel spontaneous PT symmetry breaking characteristic, respectively. The effects of the non-Hermitian terms on the $\mathcal{PT}$ symmetric and asymmetric systems due to the odevity are comparatively different in the first case while qualitatively same in the second case.

A Biologically Inspired Coupled Microphone Array for Sound Source Bearing Estimation

The Ormia ochracea, a species of parasitic fly, has a remarkable localization ability despite the tiny interaural distance compared with the incoming wavelength. The mechanical coupling between its ears enhances the differences of the two received signals, the main cues to locate the source. Inspired by the coupling mechanism, we present a miniature coupled two-microphone array for estimating sound source horizontal bearing. The coupled array consists of a standard two-microphone array and a two-input, two-output filter which implements the coupling. The relationship between filter parameters and time delay magnification is investigated to provide theoretical support for array design. With appropriate parameters, the time delay of received signals can be linearly magnified. Based on the linear magnification, we present a method for estimating source direction using the coupled array. The influence of time delay magnification on time delay estimation accuracy is explored through the general cross-correlation (GCC) method. Experiments are conducted to verify the coupled array and demonstrate its advantages on improving the resolution of estimation of time delay and accuracy of bearing estimation compared with the standard array with the same element spacing.

Novel Decoupling Concept for Strongly Coupled Frequency-Dependent Antenna Arrays

This paper presents a novel wideband decoupling network for strongly frequency-dependent antenna couplings. The network consists of directional couplers, a transmission line, and a parallel resonant circuit. It cancels mutual coupling by the superposition of a designed coupling with the same magnitude as the original coupling but the opposite phase. Further, the proposed approach accommodates variations in the coupling magnitude and large group delays in the coupling phase. Therefore, it is easy to apply the approach to wideband applications. The design formulas are also derived. With these formulas, the computational results show that the resultant coupling with the proposed technique is 26.4 dB smaller than that of the original coupling at 12.2% bandwidth with a large group delay. Moreover, this paper also describes a technique for practical implementation using short stubs. The resultant coupling with the fabricated multiantenna is 12.6 dB smaller than the original, over the entire 12.2% frequency range. The degradation of radiation efficiency by the proposed circuit is sufficiently small and the enhancement of signal-to-noise ratio is demonstrated.

Birdcage Coil with Inductively Coupled RF Coil Array for Improving |B₁|-Field Sensitivity In 7-T MRI

A birdcage coil integrated with a 16-channel, inductively coupled, radio-frequency (RF) array was designed to improve the magnetic-flux distribution for human brain magnetic resonance imaging at 7-T. A numerical calculation was performed using the finite-difference time-domain method for the birdcage coil with an inductively coupled array. The electromagnetic calculation results for the birdcage coil with the inductively coupled array were compared to those for the birdcage coil without an inductively coupled array in terms of their magnetic- flux, electric-field, and specific-absorption-rate distributions in a cylindrical phantom and human model. The proposed birdcage coil with an inductively coupled array offers a superior magnetic-flux sensitivity without sacrificing the RF power deposition at 7-T. The modifications of the coil geometry accompanying the inductively coupled RF array could be applied to the generally used transmit/receive volume coils and extended to parallel RF transmission array in ultra-high-field magnetic resonance imaging.

Quantum Phase Transition of Polaritonic Excitations in a Multi-Excitation Coupled Array

We analyze the quantum phase transition-like behavior in the lowest energy state of a two-site coupled atom-cavity system, where each cavity contains one atom but the total excitation number is not limited to two. Under the large-detuning condition, we identify an interesting coexisting phase involving characteristics of both photonic superfluid and atomic insulator, which has not been previously revealed. For small hopping, we find that the signature of the photonic superfluid state becomes more pronounced with the increase in total excitation number, and that the boundaries of the various phases shift with respect to the case of two excitations. In the limit of small atom-field interaction, the polaritonic superfluid region becomes broader as the total excitation number increases. We use alternative order parameters to characterize the nonclassical property in the lowest-energy state, and find that the entanglement of photons in the photonic superfluid state has an approximately quadratic-like dependence on the total excitation number within the large-detuning limits. The second-order cross-correlation function is demonstrated to become inversely proportional to the total excitation number in the large detuning limits.

Increasing viability of nonlinear energy harvesters by adding an excited dynamic magnifier

Dynamic magnifiers and coupled harvester arrays are two strategies that have been developed over the past decade to improve the peak power and bandwidth of energy harvesters. However, both of these methods come with drawbacks. Dynamic magnifiers require retuning since they change the frequency of the peak response and some designs result in decreased power per unit mass. Coupled harvester arrays can increase the overall bandwidth, but also include central valleys between the peaks and a significant increase in the cost. This article describes an excited dynamic magnifier which borrows design characteristics from both traditional dynamic magnifiers and harvester arrays in order to overcome these drawbacks. A hardening-type nonlinear tuned energy harvester with excited dynamic magnifier can achieve higher peak power, greater power per unit mass, and wider bandwidth without the need for retuning and for a minimal added cost as compared to the uncoupled harvester. Most importantly, the addition of a dynamic energy harvester also significantly improves performance in the frequency range of coexisting solutions by expanding the basin of attraction for the larger amplitude solution.

Cavity Antiresonance Spectroscopy of Dipole Coupled Subradiant Arrays.

An array of N closely spaced dipole coupled quantum emitters exhibits super- and subradiance with characteristic tailorable spatial radiation patterns. Optimizing the emitter geometry and distance with respect to the spatial profile of a near resonant optical cavity mode allows us to increase the ratio between light scattering into the cavity mode and free space emission by several orders of magnitude. This leads to distinct scaling of the collective coherent emitter-field coupling vs the free space decay as a function of the emitter number. In particular, for subradiant states, the effective cooperativity increases much faster than the typical linear ∝N scaling for independent emitters. This extraordinary collective enhancement is manifested both in the amplitude and the phase profile of narrow collective antiresonances appearing at the cavity output port in transmission spectroscopy.

Design, transform and control of optical field in discrete optical system: an example

A discrete optical system can broaden the spatial distribution of the input light through optical coupling in array waveguides, just like diffraction in continuous media. Here, we theoretically demonstrate several kinds of control methods of optical field propagation in a discrete optical system, which is composed of an Airy fiber with two perpendicular arrayed cores. A brief transform mechanism between Gaussian and Airy beam propagation in such a fiber is presented. The wavefront of the output beam from the Airy fiber is actually dependent on the phased arrayed modulation of coupling array cores. Except the optical wavelength changing, we propose two new methods, including fiber length and bending-induced refractive-index changing, to accomplish that modulation. The calculation results show that these new methods are very effective for the Airy phase modulation. By combining these methods and controlling the corresponding parameters, the Gaussian beam, the one-dimension Airy beam, and the two-dimension Airy beam can be obtained by one same Airy fiber. These methods are also generally applicable to the other discrete optical system and can be extended to generate any other types of optical beams, such as Bessel beams and Mathieu beams.

Equivalent Transmission Line Models for the Analysis of Edge Effects in Finite Connected and Tightly Coupled Arrays

In this paper, we present an analysis of the edge effects in wideband connected arrays of slots and dipoles. Due to the strong mutual coupling between the elements, these arrays can support the propagation of guided waves along their surface. Such waves arise from the edges of the finite array and can be especially detrimental to the performance, since they can travel within the array without geometrical spreading. In this paper, we introduce Green’s function-based equivalent transmission line models to describe the propagation of the guided waves. The elements’ active impedances are represented as periodic loads on these transmission lines. The equivalent models can be used as a simple and convenient tool to control and minimize the edge effects. Finite array simulations of relevant array structures are discussed. The evidence is that the active impedance and the interelement capacitance can be tuned to attenuate and reflect the edge-born waves.

Capacitively Coupled Arrays of Multiplexed Flexible Silicon Transistors for Long-Term Cardiac Electrophysiology.

Advanced capabilities in electrical recording are essential for the treatment of heart-rhythm diseases. The most advanced technologies use flexible integrated electronics; however, the penetration of biological fluids into the underlying electronics and any ensuing electrochemical reactions pose significant safety risks. Here, we show that an ultrathin, leakage-free, biocompatible dielectric layer can completely seal an underlying layer of flexible electronics while allowing for electrophysiological measurements through capacitive coupling between tissue and the electronics, and thus without the need for direct metal contact. The resulting current-leakage levels and operational lifetimes are, respectively, four orders of magnitude smaller and between two and three orders of magnitude longer than those of any other flexible-electronics technology. Systematic electrophysiological studies with normal, paced and arrhythmic conditions in Langendorff hearts highlight the capabilities of the capacitive-coupling approach. Our technology provides a realistic pathway towards the broad applicability of biocompatible, flexible electronic implants.

Parameter optimization for transitions between memory states in small arrays of Josephson junctions

Coupled arrays of Josephson junctions possess multiple stable zero voltage states. Such states can store information and consequently can be utilized for cryogenic memory applications. Basic memory operations can be implemented by sending a pulse to one of the junctions and studying transitions between the states. In order to be suitable for memory operations, such transitions between the states have to be fast and energy efficient. In this paper we employed simulated annealing, a stochastic optimization algorithm, to study parameter optimization of array parameters which minimizes times and energies of transitions between specifically chosen states that can be utilized for memory operations (Read, Write, and Reset). Simulation results show that such transitions occur with access times on the order of 10–100 ps and access energies on the order of 10−19–5×10−18 J. Numerical simulations are validated with approximate analytical results.

Single photon transport by a quantized cavity field driven cascade-type three-level atom in a dissipative coupled cavity array

In this paper, a new kind of quasi-boson method is used to eliminate the coordinates of the environment and redescribe the dissipative system by using an effective Hamiltonian; the localized mode and the interaction between cavities can be renormalized. Based on the quasi-boson approach, the single photon transport in one-dimensional coupled cavity array, with a driven cascade-type three-level atom embedded in one of the cavity, is investigated under the influence of the environment. The single-photon transmission and the reflection amplitudes are obtained analytically. And the additional effective potential induced by the interaction between the atom and the cavity is also derived. The effects of the controlling parameters on the reflection and transmission amplitudes are discussed with considering the dissipation. It is shown that the decay rates of the atoms and the cavity both reduce the reflection spectrum. But the dissipation of the atom has a significant influence on the reflection amplitude compared with the cavity decay under the same conditions. Due to the irreversible loss of energy, the photon number is non-conservative. Furthermore, the single-photon can be almost reflected by the three-level atom in the dissipative case when one adjusts the detuning and photon number of the quantized cavity field. The investigation will be of benefit to the realization of photon transport in a real experiment, which is also helpful for manipulating the photons in quantum information and quantum simulation.

Optimisation of Scanning Difference Pattern and Monopulse Feed

Certain radar applications may require maintaining the difference pattern slope and twin beam shape, while main null is scanning in the presence of mutual coupling. It is also desirable in monopulse radar applications to be able to generate acceptable sum and difference patterns using single simplified feed structure. This paper focuses on these problems and provides a solution based on Intelligent z-Plane Boundary Condition-Particle Swarm Optimiser (IzBC-PSO) to compensate for the difference pattern degradation while scanning a small coupled array (N=8). In second case, a simplified feed is proposed that only requires phase flip for 50% of elements to produce sum and difference patterns for the monopulse array, consisting of isotropic elements.

Various coupling configurations on the performance of two‐dimensional coupled oscillator arrays

Coupled oscillator arrays (COAs) can be used to control the phase distribution across the aperture of an array antenna in such a manner as to affect steering of the beam without the use of phase shifters. Given the various possible planar configurations of COAs, a systematic design approach is necessary. In this study, the authors present a comprehensive comparison of various configurations of planar COAs based on their sensitivity to random errors in their free running frequencies. The parameters considered are (a) the beam pointing error of the array, (b) the locking probability, (c) the side lobe level, and (d) the beam width of the radiation pattern. These results can serve as a design strategy for choosing optimal configurations of planar COAs based on the needs of each particular application.

Memory cell operation based on small Josephson junctions arrays

In this paper we analyze a cryogenic memory cell circuit based on a small coupled array of Josephson junctions. All the basic memory operations (e.g., write, read, and reset) are implemented on the same circuit and different junctions in the array can in principle be utilized for these operations. The presented memory operation paradigm is fundamentally different from conventional single quantum flux operation logics (SFQ). As an example, we demonstrate memory operation driven by a SFQ pulse employing an inductively coupled array of three Josephson junctions. We have chosen realistic Josephson junction parameters based on state-of-the-art fabrication capabilities and have calculated access times and access energies for basic memory cell operations. We also implemented an optimization procedure based on the simulated annealing algorithm to calculate the optimized and typical values of access times and access energies.

Acoustically Coupled Microphone Arrays

An analysis is presented of the performance benefits that can be achieved by introducing acoustic coupling between the diaphragms in an array of miniature microphones. The introduction of this coupling is analogous to the principles employed in the ears of small animals that are able to localize sound sources. Measured results are shown, which indicate a dramatic improvement in acoustic sensitivity, and noise performance can be achieved by packaging a pair of small microphones so that their diaphragms share a common back volume of air. This is also shown to reduce the adverse effects on directional response of mismatches in the mechanical properties of the microphones.

A Simple Technique to Readout and Characterize Coupled MEMS Resonators

Highly sensitive microelectromechanical system (MEMS) resonators have been used for extensive applications such as mass sensing. However, these arrays are prone to process variations and are difficult to characterize due to lack of connections with each resonator. Coupled array of such sensors can enhance functionality while reducing interconnections. This scheme allows a number of sensors to be read out using a single input/output channel. By perturbing the spring constant of one resonator, two sets of eigenvalues can be measured to reconstruct the system matrix of the coupled system. However, perturbation on MEMS devices can introduce non-linear or physical change. To prevent such undesired change, this paper proposes a technique to couple an electrical resonator to an array of MEMS resonators. Two sets of eigenvalues can therefore be measured by simply connecting/disconnecting the electrical resonator. Errors introduced by frequency noise, array size, coupling strength, and damping have been analyzed. The successful coupling between electrical and mechanical resonators brings huge promise for integrated MEMS devices that could be used for single input/output multi-sensor and monitoring variations in MEMS fabrication. [2015-0299]

Pfaffian states in coupled atom-cavity systems

Coupled atom-cavity arrays, such as those described by the Jaynes-Cummings Hubbard model, have the potential to emulate a wide range of condensed matter phenomena. In particular, the strongly correlated states of the fractional quantum Hall effect can be realised. At some filling fractions, the fraction quantum Hall effect has been shown to possess ground states with non-abelian excitations. The most well studied of these states is the Pfaffian state of Moore and Read, which is the groundstate of a Hall Liquid with a 3-body interaction. In this paper we show how an effective 3-body interaction can be generated within the Cavity QED framework, and that a Pfaffian-like groundstate of these systems exists.

Electrochemical Studies of Nickel/H2so4 Oscillating Systems and the Preparation and Testing of Copper Coupled Microelectrode Array Sensors

Nickel is one of the most important passive metals used for electrodeposition processes in the world (1). Over 150 metric tons of Ni is consumed yearly for electroplating (2). Nickel is well known for its highly lustrous finish and corrosion resistant properties. Although Ni is very resistant to corrosion, it is not completely resistant. Nickel has been known to corrode in acidic medium such as sulfuric acid. The corrosion of Ni in Ni/H2SO4 produce periodic states of oscillations as a potential is applied or a current is passed through the system (3)-(5). Studies on these types of oscillatory states have been performed since 1950. Traditionally, Ni electrochemical studies on Ni/H2SO4 oscillating systems have been performed by applying external forcing techniques through variations of applied potential or current during the electrodissolution (corrosion) of Ni single wire electrodes in high concentrations of H2SO4 solutions (1 M, 3 M, and 4.5 M). External forcing is the process in which perturbations are applied to a system by an external source and have helped to provide a better understanding of Ni/H2SO4 oscillating systems. However, little attention has been given to performing electrochemical studies on Ni/H2SO4 oscillating systems in low concentrations of H2SO4 solutions (0.3 M - 0.9 M) and no attention has been given to the possibility for the external forcing of these unique systems via concentration change at the Ni electrode surface until now (for example, Figure (1)). Although electrochemical studies on Ni single wire electrodes provided a significant amount of information about self-organization and periodic oscillations, an in depth analysis of the Ni/H2SO4 oscillating system was not possible because of the lack of adequate technology (6). In order to overcome this issue, coupled microelectrode array sensors (CMAS) have been recently developed. CMAS are integrated devices with multiple electrodes that are connected externally in a circuit, and all of the electrodes on the CMAS have the same amount of potential applied or current passing through them during experiments. CMAS can be used for studying self-organization and periodic oscillations via external forcing (7)-(8). CMAS have also been used for real-time corrosion monitoring in cooling water systems, simulated seawater, and concrete (9). CMAS are useful devices because they are capable of simulating single wire electrodes of the same size (5)-(6), (9). During the last six decades, many electrochemical studies have been performed by using CMAS; however, there is little published detailed descriptions of CMAS fabrication. The work demonstrates control of periodic oscillations by changing the concentration of the proton concentration at the Ni electrode surface via external forcing. We present results collected from CV experiments performed on the modified CMAS. In addition, we outline the steps in which the CMAS were fabricated and how the CMAS was modified via electrodeposition of Ni. Figure 1. (a) changes in oscillations observed with external local forcing a) CVs at 10 mV/s on a 500 μm Ni electrode (WE) in 0.7 M H2SO4 with an 18.5 kΩ series resistor. During the sweeps 8 mA to 10 mA of anodic current is applied to a nearby 300 μm Pt wire, b) Plot of detrended data, (c)Top of the CMAS, (d) Top view of array assembly showing placement of the carbon auxiliary electrodes, (e) Assembled Cu CMAS. REFERENCES 1. Di Bari, G. A., Electrodeposition of Nickel. In Modern Electroplating, p.79, John Wiley & Sons, Boston (2010). 2. Nickel Institute, Nickel Plating Handbook, p. 80, Nickel Institute, North Carolina, (2013) 3. Zhou, C.; Kurths, J.; Kiss, I. Z.; Hudson, J. L.,. Phys. Rev. Lett., 89, 014101 (2002). 4. Wang, W.; Green, B. J.; Hudson, J. L., J. Phys. Chem. B, 105, 7366 (2001). 5. Kiss, I. Z.; Wang, W.; Hudson, J. L., J. Phys. Chem. B, 103, 11433 (1999). 6. Orlik, M., Self-Organization in Electrochemical Systems I General Principles of Self-Organization. Temporal Instabilities, p 473, Springer, Berlin (2012). 7. Fei, Z.; Kelly, R. G.; Hudson, J. L., J. of Phys. Chem., 100, 18986 (1996). 8. Wickramasinghe, M.; Kiss, I. Z., Physical Review E, 88, 062911 (2013). 9. Yang, L., Techniques for Corrosion Monitoring, p. 187, Woodhead Publishing Limited, Boston (2008). Figure 1

Bottom-Emitting Coherently Coupled Vertical Cavity Laser Arrays

Two-dimensional coherently coupled photonic crystal ion-implanted bottom emitting vertical cavity surface emitting laser arrays are demonstrated. Subthreshold luminescence shows uniform current injection below threshold, benefiting from the improved contact alignment compared with the top emitting arrays. In-phase operation has been achieved in $2\times 2$ and $3\times 3$ arrays at lasing threshold. A remaining challenge is achieving uniform current distribution above lasing threshold for larger arrays due to the variation of series resistance through each of the elements of the arrays.